initial commit of ebook 8144HEAD main

author: Roger Frank <rfrank@pglaf.org> 2025-10-15 05:31:01 -0700
committer: Roger Frank <rfrank@pglaf.org> 2025-10-15 05:31:01 -0700
commit: 29ea61f647bf83c6f5b7b5e8e69aa9940e65a477 (patch)
tree: eaadfc4e66cf2820ae6edfe9f150c3abbab89ffa /8144-h
125 files changed, 19383 insertions, 0 deletions
diff --git a/8144-h/8144-h.htm b/8144-h/8144-h.htm
new file mode 100644
index 0000000..6742867
--- /dev/null
+++ b/8144-h/8144-h.htm
@@ -0,0 +1,19383 @@
+<?xml version="1.0" encoding="iso-8859-1"?>
+
+<!DOCTYPE html
+   PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
+   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" >
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <title>
+      The Principles Of Its Generation And Use, by F. H. Leeds and W. J.
+      Atkinson Butterfield
+    </title>
+    <style type="text/css" xml:space="preserve">
+
+body {margin-left: 15%; margin-right: 15%; background-color: white}
+img {border: 0;}
+h1,h2,h3 {text-align: center;}
+.ind {margin-left: 10%; margin-right: 10%;}
+hr {text-align: center; width: 50%;}
+.ctr {text-align: center;}
+
+</style>
+  </head>
+  <body>
+
+
+<pre>
+
+The Project Gutenberg EBook of Acetylene, The Principles Of Its Generation
+And Use, by F. H. Leeds and W. J. Atkinson Butterfield
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Acetylene, The Principles Of Its Generation And Use
+
+Author: F. H. Leeds
+        W. J. Atkinson Butterfield
+
+
+Release Date: May, 2005  [EBook #8144]
+This file was first posted on June 19, 2003
+Last Updated: May 17, 2013
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ACETYLENE ***
+
+
+
+
+Produced by Richard Prairie, Tonya Allen, Juliet Sutherland,
+Charles Franks, and the Online Distributed Proofreading Team
+
+
+
+
+
+</pre>
+
+    <h1>
+      ACETYLENE
+    </h1>
+    <h2>
+      THE PRINCIPLES OF ITS GENERATION AND USE
+    </h2>
+    <h3>
+      A PRACTICAL HANDBOOK ON THE PRODUCTION, PURIFICATION, AND SUBSEQUENT
+      TREATMENT OF ACETYLENE FOR THE DEVELOPMENT OF LIGHT, HEAT, AND POWER
+    </h3>
+    <h3>
+      BY
+    </h3>
+    <h2>
+      F. H. LEEDS, F.I.C.
+    </h2>
+    <h3>
+      FOR SOME YEARS TECHNICAL EDITOR OF THE JOURNAL "ACETYLENE"
+    </h3>
+    <h3>
+      AND
+    </h3>
+    <h2>
+      W. J. ATKINSON BUTTERFIELD, M.A.
+    </h2>
+    <h3>
+      AUTHOR OF "THE CHEMISTRY OF GAS MANUFACTURE"
+    </h3>
+    <h3>
+      Second Edition
+    </h3>
+    <h3>
+      REVISED AND ENLARGED
+    </h3>
+    <p>
+      <br /> <br /> <br />
+    </p>
+    <h2>
+      PREFATORY NOTE TO THE FIRST EDITION
+    </h2>
+    <p>
+      In compiling this work on the uses and application of acetylene, the
+      special aim of the authors has been to explain the various physical and
+      chemical phenomena:
+    </p>
+    <p>
+      (1) Accompanying the generation of acetylene from calcium carbide and
+      water.
+    </p>
+    <p>
+      (2) Accompanying the combustion of the gas in luminous or incandescent
+      burners, and
+    </p>
+    <p>
+      (3) Its employment for any purpose--(a) neat, (b) compressed into
+      cylinders, (c) diluted, and (d) as an enriching material.
+    </p>
+    <p>
+      They have essayed a comparison between the value of acetylene and other
+      illuminants on the basis of "illuminating effect" instead of on the
+      misleading basis of pure "illuminating power," a distinction which they
+      hope and believe will do much to clear up the misconceptions existing on
+      the subject. Tables are included, for the first time (it is believed) in
+      English publications, of the proper sizes of mains and service-pipes for
+      delivering acetylene at different effective pressures, which, it is hoped,
+      will prove of use to those concerned in the installation of acetylene
+      lighting systems.
+    </p>
+    <p>
+      <i>June</i> 1903
+    </p>
+    <p>
+      <br /> <br />
+    </p>
+    <h2>
+      NOTE TO THE SECOND EDITION
+    </h2>
+    <p>
+      The revision of this work for a new edition was already far advanced when
+      it was interrupted by the sudden death on April 30, 1908, of Mr. F. H.
+      Leeds. The revision was thereafter continued single-handed, with the help
+      of very full notes which Mr. Leeds had prepared, by the undersigned. It
+      had been agreed prior to Mr. Leeds' death that it would add to the utility
+      of the work if descriptions of a number of representative acetylene
+      generators were given in an Appendix, such as that which now appears at
+      the conclusion of this volume. Thanks are due to the numerous firms and
+      individuals who have assisted by supplying information for use in this
+      Appendix.
+    </p>
+    <p>
+      W. J. ATKINSON BUTTERFIELD
+    </p>
+    <p>
+      WESTMINSTER
+    </p>
+    <p>
+      <i>August 1909</i>
+    </p>
+    <p>
+      <br /> <br /> <br />
+    </p>
+    <p>
+      <b>CONTENTS</b>
+    </p>
+    <p>
+      <a href="#linki">CHAPTER I</a>
+    </p>
+    <p>
+      INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING
+    </p>
+    <p>
+      Intrinsic advantages<br /> Hygienic advantages<br /> Acetylene and paraffin
+      oil<br /> Blackened ceilings<br /> Cost of acetylene lighting<br /> Cost of
+      acetylene and coal-gas<br /> Cost of acetylene and electric lighting<br />
+      Cost of acetylene and paraffin oil<br /> Cost of acetylene and air-gas<br />
+      Cost of acetylene and candles<br /> Tabular statement of costs (<i>to face</i>)<br />
+      Illuminating power and effect
+    </p>
+    <p>
+      <a href="#linkii">CHAPTER II</a>
+    </p>
+    <p>
+      THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER
+    </p>
+    <p>
+      Nature of calcium carbide<br /> Storage of calcium carbide<br /> Fire risks
+      of acetylene lighting<br /> Purchase of carbide<br /> Quality and sizes of
+      carbide<br /> Treated and scented carbide<br /> Reaction between carbide and
+      water<br /> --chemical nature<br /> --heat evolved<br /> --difference between
+      heat and temperature<br /> --amount of heat evolved<br /> --effect of heat
+      on process of generation<br /> Reaction:<br /> --effects of heat<br />
+      --effect of heat on the chemical reaction<br /> --effects of heat on the
+      acetylene<br /> --effects of heat on the carbide<br /> Colour of spent
+      carbide<br /> Maximum attainable temperatures<br /> Soft solder in
+      generators<br /> Reactions at low temperatures<br /> Reactions at high
+      temperatures<br /> Pressure in generators
+    </p>
+    <p>
+      <a href="#linkiii">CHAPTER III</a>
+    </p>
+    <p>
+      THE GENERAL PRINCIPLES OF ACETYLENE GENERATION ACETYLENE GENERATING
+      APPARATUS
+    </p>
+    <p>
+      Automatic and non-automatic generators<br /> Control of the chemical
+      reaction<br /> Non-automatic carbide-to-water generators<br /> Non-automatic
+      water-to-carbide generators<br /> Automatic devices<br /> Displacement
+      gasholders<br /> Action of water-to-carbide generators<br /> Action of
+      carbide-to-water generators<br /> Use of oil in generator<br /> Rising
+      gasholder<br /> Deterioration of acetylene on storage<br /> Freezing and its
+      avoidance<br /> Corrosion in apparatus<br /> Isolation of holder from
+      generator<br /> Water-seals<br /> Vent pipes and safety valve<br /> Frothing
+      in generator<br /> Dry process of generation<br /> Artificial lighting of
+      generator sheds
+    </p>
+    <p>
+      <a href="#linkiv">CHAPTER IV</a>
+    </p>
+    <p>
+      THE SELECTION OF AN ACETYLENE GENERATOR
+    </p>
+    <p>
+      Points to be observed<br /> Recommendations of Home Office Committee<br />
+      British and Foreign regulations for the construction and installation of
+      acetylene generating plant
+    </p>
+    <p>
+      <a href="#linkv">CHAPTER V</a>
+    </p>
+    <p>
+      THE TREATMENT OF ACETYLENE AFTER GENERATION
+    </p>
+    <p>
+      Impurities in calcium carbide<br /> Impurities of acetylene<br /> Removal of
+      moisture<br /> Generator impurities in acetylene<br /> Filters<br /> Carbide
+      impurities in acetylene<br /> Washers<br /> Reasons for purification<br />
+      Necessary extent of purification<br /> Quantity of impurities in acetylene<br />
+      Purifying materials<br /> Bleaching powder<br /> Heratol, frankoline,
+      acagine, and puratylene<br /> Efficiency of purifying material<br /> Minor
+      reagent<br /> Method of a gas purifier<br /> Methods of determining
+      exhaustion of purifying material<br /> Regulations for purification<br />
+      Drying<br /> Position of purifier<br /> Filtration<br /> General arrangement
+      of plans<br /> Generator residues<br /> Disposal of residue
+    </p>
+    <p>
+      <a href="#linkvi">CHAPTER VI</a>
+    </p>
+    <p>
+      THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE
+    </p>
+    <p>
+      Physical properties<br /> Leakage<br /> Heat of combustion<br /> Explosive
+      limits<br /> Range of explosibility<br /> Solubility in liquids<br />
+      Toxicity<br /> Endothermic nature<br /> Polymerisation<br /> Heats of
+      formation and combustion<br /> Colour of flame<br /> Radiant efficiency<br />
+      Chemical properties<br /> Reactions with copper
+    </p>
+    <p>
+      <a href="#linkvii">CHAPTER VII</a>
+    </p>
+    <p>
+      MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS
+    </p>
+    <p>
+      Meters<br /> Governors<br /> Gasholder pressure<br /> Pressure-gauges<br />
+      Dimensions of mains and pipes<br /> Velocity of flow in pipes<br />
+      Service-pipes and mains<br /> Leakage<br /> Pipes and fittings<br /> Laying
+      mains<br /> Expelling air from pipes<br /> Tables of pipes and mains
+    </p>
+    <p>
+      <a href="#linkviii">CHAPTER VIII</a>
+    </p>
+    <p>
+      COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION
+    </p>
+    <p>
+      Nature of luminous flames<br /> Illuminating power<br /> Early burners<br />
+      Injector and twin-flame burners<br /> Illuminating power of self-luminous
+      burners<br /> Glassware for burners
+    </p>
+    <p>
+      <a href="#linkix">CHAPTER IX</a>
+    </p>
+    <p>
+      INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING
+    </p>
+    <p>
+      Merits of incandescent lighting<br /> Conditions for incandescent lighting<br />
+      Illuminating power of incandescent burners<br /> Durability of mantles<br />
+      Typical incandescent burners<br /> Acetylene for heating and cooking<br />
+      Acetylene motors<br /> Blowpipes<br /> Autogenous soldering and welding
+    </p>
+    <p>
+      <a href="#linkx">CHAPTER X</a>
+    </p>
+    <p>
+      CARBURETTED ACETYLENE
+    </p>
+    <p>
+      Carburetted acetylene<br /> Illuminating power of carburetted acetylene<br />
+      Carburetted acetylene for "power"
+    </p>
+    <p>
+      <a href="#linkxi">CHAPTER XI</a>
+    </p>
+    <p>
+      COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES
+    </p>
+    <p>
+      Compression<br /> Dissolved acetylene<br /> Solution in acetone<br />
+      Liquefied acetylene<br /> Dilution with carbon dioxide<br /> Dilution with
+      air<br /> Mixed carbides<br /> Dilution with, methane and hydrogen<br />
+      Self-inflammable acetylene<br /> Enrichment with acetylene<br /> Partial
+      pressure<br /> Acetylene-oil-gas
+    </p>
+    <p>
+      <a href="#linkxii">CHAPTER XII</a>
+    </p>
+    <p>
+      SUNDRY USES
+    </p>
+    <p>
+      Destruction of noxious moths<br /> Destruction of phylloxera and mildew<br />
+      Manufacture of lampblack<br /> Production of tetrachlorethane<br />
+      Utilisation of residues<br /> Sundry uses for the gas
+    </p>
+    <p>
+      <a href="#linkxiii">CHAPTER XIII</a>
+    </p>
+    <p>
+      PORTABLE ACETYLENE LAMPS AND PLANT
+    </p>
+    <p>
+      Table and vehicular lamps<br /> Flare lamps<br /> Cartridges of carbide<br />
+      Cycle-lamp burners<br /> Railway lighting
+    </p>
+    <p>
+      <a href="#linkxiv">CHAPTER XIV</a>
+    </p>
+    <p>
+      VALUATION AND ANALYSIS OF CARBIDE
+    </p>
+    <p>
+      Regulations of British Acetylene Association<br /> Regulations o� German
+      Acetylene Association<br /> Regulations of Austrian Acetylene Association<br />
+      Sampling carbide<br /> Yield of gas from small carbide<br /> Correction of
+      volumes for temperature and pressure<br /> Estimation of impurities<br />
+      Tabular numbers
+    </p>
+    <p>
+      <a href="#linkappendix">APPENDIX</a>
+    </p>
+    <p>
+      DESCRIPTIONS OP GENERATORS
+    </p>
+    <p>
+      America: Canada<br /> America: United States<br /> Austria-Hungary<br />
+      Belgium<br /> France<br /> Germany<br /> Great Britain and Ireland
+    </p>
+    <p>
+      <a href="#linkindex">INDEX</a>
+    </p>
+    <p>
+      <a href="#linkindex2">INDEX TO APPENDIX</a> <br /> <br /> <br />
+    </p>
+    <p>
+      <br /> <br />
+    </p>
+    <h1>
+      ACETYLENE
+    </h1>
+    <p>
+      <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linki" id="i">CHAPTER I</a>
+    </h2>
+    <h3>
+      INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING
+    </h3>
+    <p>
+      Acetylene is a gas [Footnote: For this reason the expression, "acetylene
+      gas," which is frequently met with, would be objectionable on the ground
+      of tautology, even if it were not grammatically and technically incorrect.
+      "Acetylene-gas" is perhaps somewhat more permissible, but it is equally
+      redundant and unnecessary.] of which the most important application at the
+      present time is for illuminating purposes, for which its properties render
+      it specially well adapted. No other gas which can be produced on a
+      commercial scale is capable of giving, volume for volume, so great a yield
+      of light as acetylene. Hence, apart from the advantages accruing to it
+      from its mode of production and the nature of the raw material from which
+      it is produced, it possesses an inherent advantage over other illuminating
+      gases in the smaller storage accommodation and smaller mains and
+      service-pipes requisite for the maintenance of a given supply of
+      artificial light. For instance, if a gasholder is required to contain
+      sufficient gas for the lighting of an establishment or district for
+      twenty-four hours, its capacity need not be nearly so great if acetylene
+      is employed as if oil-gas, coal-gas, or other illuminating gas is used.
+      Consequently, for an acetylene supply the gasholder can be erected on a
+      smaller area and for considerably less outlay than for other gas supplies.
+      In this respect acetylene has an unquestionable economical advantage as a
+      competitor with other varieties of illuminating gas for supplies which
+      have generally been regarded as lying peculiarly within their preserves.
+      The extent of this advantage will be referred to later.
+    </p>
+    <p>
+      The advantages that accrue to acetylene from its mode of production, and
+      the nature of the raw material from which it is obtained, are in reality
+      of more importance. Acetylene is readily and quickly produced from a raw
+      material--calcium carbide--which, relatively to the yield of light of the
+      gaseous product, is less bulky than the raw materials of other gases. In
+      comparison also with oils and candles, calcium carbide is capable of
+      yielding, through the acetylene obtainable from it, more light per unit of
+      space occupied by it. This higher light-yielding capacity of calcium
+      carbide, ready to be developed through acetylene, gives the latter gas a
+      great advantage over all other illuminants in respect of compactness for
+      transport or storage. Hence, where facilities for transport or storage are
+      bad or costly, acetylene may be the most convenient or cheapest
+      illuminant, notwithstanding its relatively high cost in many other cases.
+      For example, in a district to which coal and oil must be brought great
+      distances, the freight on them may be so heavy that--regarding the
+      question as simply one of obtaining light in the cheapest manner--it may
+      be more economical to bring calcium carbide an equal or even greater
+      distance and generate acetylene from it on the spot, than to use oil or
+      make coal-gas for lighting purposes, notwithstanding that acetylene may
+      not be able to compete on equal terms with oil--or coal-gas at the place
+      from which the carbide is brought. Likewise where storage accommodation is
+      limited, as in vehicles or in ships or lighthouses, calcium carbide may be
+      preferable to oil or other illuminants as a source of light. Disregarding
+      for the moment intrinsic advantages which the light obtainable from
+      acetylene has over other lights, there are many cases where, owing to
+      saving in cost of carriage, acetylene is the most economical illuminant;
+      and many other cases where, owing to limited space for storage, acetylene
+      far surpasses other illuminants in convenience, and is practically
+      indispensable.
+    </p>
+    <p>
+      The light of the acetylene flame has, however, some intrinsic advantages
+      over the light of other artificial illuminants. In the first place, the
+      light more closely resembles sunlight in composition or "colour." It is
+      more nearly a pure "white" light than is any other flame or incandescent
+      body in general use for illuminating purposes. The nature or composition
+      of the light of the acetylene flame will be dealt with more exhaustively
+      later, and compared with that afforded by other illuminants; but, speaking
+      generally, it may be said that the self-luminous acetylene light is
+      superior in tint, to all other artificial lights, for which reason it is
+      invaluable for colour-judging and shade-matching. In the second place,
+      when the gas issues from a suitable self-luminous burner under proper
+      pressure, the acetylene flame is perfectly steady; and in this respect it
+      in preferable to most types of electric light, to all self- luminous
+      coal-gas flames and candles, and to many varieties of oil-lamp. In
+      steadiness and freedom from flicker it is fully equal to incandescent
+      coal-gas light, but it in distinctly superior to the latter by virtue of
+      its complete freedom from noise. The incandescent acetylene flame emits a
+      slight roaring, but usually not more than that coming from an atmospheric
+      coal-gas burner. With the exception of the electric arc, self-luminous
+      acetylene yields a flame of unsurpassed intensity, and yet its light is
+      agreeably soft. In the third place, where electricity is absent, a
+      brilliancy of illumination which can readily be obtained from
+      self-luminous acetylene can otherwise only be procured by the employment
+      of the incandescent system applied either to coal-gas or to oil; and there
+      are numerous situations, such as factories, workshops, and the like, where
+      the vibration of the machinery or the prevalence of dust renders the use
+      of mantles troublesome if not impossible. Anticipating what will be said
+      later, in cases like these, the cost of lighting by self-luminous
+      acetylene may fairly be compared with self-luminous coal- gas or oil only;
+      although in other positions the economy of the Welsbach mantle must be
+      borne in mind.
+    </p>
+    <p>
+      Acetylene lighting presents also certain important hygienic advantages
+      over other forms of flame lighting, in that it exhausts, vitiates, and
+      heats the air of a room to a less degree, for a given yield of light, than
+      do either coal-gas, oils, or candles. This point in favour of acetylene is
+      referred to here only in general terms; the evidence on which the
+      foregoing statement is based will be recorded in a tabular comparison of
+      the cost and qualities of different illuminants. Exhaustion of the air
+      means, in this connexion, depletion of the oxygen normally present in it.
+      One volume of acetylene requires 2-1/2 volumes of oxygen for its complete
+      combustion, and since 21 volumes of oxygen are associated in atmospheric
+      air with 79 volumes of inert gases--chiefly nitrogen--which do not
+      actively participate in combustion, it follows that about 11.90 volumes of
+      air are wholly exhausted, or deprived of oxygen, in the course of the
+      combustion of one volume of acetylene. If the light which may be developed
+      by the acetylene is brought into consideration, it will be found that,
+      relatively to other illuminants, acetylene causes less exhaustion of the
+      air than any other illuminating agent except electricity. For instance,
+      coal-gas exhausts only about 6- 1/2 times its volume of air when it is
+      burnt; but since, volume for volume, acetylene ordinarily yields from
+      three to fifteen times as much light as coal-gas, it follows that the same
+      illuminative value is obtainable from acetylene by considerably less
+      exhaustion of the air than from coal-gas. The exact ratio depends on the
+      degree of efficiency of the burners, or of the methods by which light is
+      obtained from the gases, as will be realised by reference to the table
+      which follows. Broadly speaking, however, no illuminant which evolves
+      light by combustion (oxidation), and which therefore requires a supply of
+      oxygen or air for its maintenance, affords light with so little exhaustion
+      of the air as acetylene. Hence in confined, ill-ventilated, or crowded
+      rooms, the air will suffer less exhaustion, and accordingly be better for
+      breathing, if acetylene is chosen rather than any other illuminant, except
+      electricity.
+    </p>
+    <p>
+      Next, in regard to vitiation of the air, by which is meant the alteration
+      in its composition resulting from the admixture of products of combustion
+      with it. Electric lighting is as superior to other modes of lighting in
+      respect of direct vitiation as of exhaustion of the air, because it does
+      not depend on combustion. Putting it aside, however, light is obtainable
+      by means of acetylene with less attendant vitiation of the air than by
+      means of any other gas or of oil or candles. The principal vitiating
+      factor in all cases is the carbonic acid produced by the combustion. Now
+      one volume of acetylene on combustion yields two volumes of carbonic acid,
+      whereas one volume of coal-gas yields about 0.6 volume of carbonic acid.
+      But even assuming that the incandescent system of lighting is applied in
+      the case of coal-gas and not of acetylene, the ratio of the consumption of
+      the two gases for the development of a given illuminative effect will be
+      such that no more carbonic acid will be produced by the acetylene; and if
+      the incandescent system is applied either in both cases or in neither, the
+      ratio will be greatly in favour of acetylene. The other factors which
+      determine the vitiation of the air of a room in which the gas is burning
+      are likewise under ordinary conditions more in favour of acetylene. They
+      are not, however, constant, since the so-called "impurities," which on
+      combustion cause vitiation of the air, vary greatly in amount according to
+      the extent to which the gases have been purified. London coal-gas, which
+      was formerly purified to the highest degree practically attainable, used
+      to contain on the average only 10 to 12 grains of sulphur per 100 cubic
+      feet, and virtually no other impurity. But now coal-gas, in London and
+      most provincial towns, contains 40 to 50 grains of sulphur per 100 cubic
+      foot. At least 5 grains of ammonia per 100 cubic foot in also present in
+      coal-gas in some towns. Crude acetylene also contains sulphur and ammonia,
+      that coming from good quality calcium carbide at the present day including
+      about 31 grains of the former and 25 grains of the latter per 100 cubic
+      feet. But crude acetylene is also accompanied by a third impurity, viz.,
+      phosphoretted hydrogen or phosphine, which in unknown in coal-gas, and
+      which is considerably more objectionable than either ammonia or sulphur.
+      The formation, behaviour, and removal of those various impurities will be
+      discussed in Chapter V.; but here it may be said that there is no reason
+      why, if calcium carbide of a fair degree of purity has been used, and if
+      the gas has been generated from it in a properly designed and smoothly
+      working apparatus-- this being quite as important as, or even more
+      important than, the purity of the original carbide--the gas should not be
+      freed from phosphorus, sulphur, and ammonia to the utmost necessary or
+      desirable extent, by processes which are neither complicated nor
+      expensive. And if this is done, as it always should be whenever the
+      acetylene is required for domestic lighting, the vitiation of the air of a
+      room due to the "impurities" in the gas will become much less in the case
+      of acetylene than in that of even well-purified coal-gas; taking equal
+      illuminating effect as the basis for comparison.
+    </p>
+    <p>
+      Acetylene is similarly superior, speaking generally, to petroleum in
+      respect of impurities, though the sulphur present in petroleum oils, such
+      as are sold in this country for household use, though very variable, is
+      often quite small in amount, and seldom is responsible for serious
+      vitiation of the atmosphere.
+    </p>
+    <p>
+      Regarding somewhat more closely the relative convenience and safety of
+      acetylene and paraffin for the illumination of country residences, it may
+      be remarked that an extraordinarily great amount of care must be bestowed
+      upon each separate lamp if the whole house is to be kept free from an
+      odour which is very offensive to the nostrils; and the time occupied in
+      this process, which of itself is a disagreeable one, reaches several hours
+      every day. Habit has taught the country dweller to accept as inevitable
+      this waste of time, and largely to ignore the odour of petroleum in his
+      abode; but the use of acetylene entirely does away with the daily cleaning
+      of lamps, and, if the pipe-fitting work has been done properly, yields
+      light absolutely unaccompanied by smell. Again, unless most carefully
+      managed, the lamp-room of a large house, with its store of combustible
+      oil, and its collection of greasy rags, must unavoidably prove a sensible
+      addition to the risk of fire. The analogue of the lamp- room when
+      acetylene is employed is the generator-house, and this is a separate
+      building at some distance from the residence proper. There need be no
+      appreciable odour in the generator-house, except during the times of
+      charging the apparatus; but if there is, it passes into the open air
+      instead of percolating into the occupied apartments.
+    </p>
+    <p>
+      The amount of heat developed by the combustion of acetylene also is less
+      for a given yield of light than that developed by most other illuminants.
+      The gas, indeed, is a powerful heating gas, but owing to the amount
+      consumed being so small in proportion to the light developed, the heat
+      arising from acetylene lighting in a room is less than that from most
+      other illuminating agents, if the latter are employed to the extent
+      required to afford equally good illumination. The ratio of the heat
+      developed in acetylene lighting to that developed in, <i>e.g.</i>,
+      lighting by ordinary coal-gas, varies considerably according to the degree
+      of efficiency of the burners, or, in other words, of the methods by which
+      light is obtained from the gases. Volume for volume, acetylene yields on
+      combustion about three and a half times as much heat as coal- gas, yet,
+      owing to its superior efficiency as an illuminant, any required light may
+      be obtained through it with no greater evolution of heat than the best
+      practicable (incandescent) burners for coal-gas produce. The heat evolved
+      by acetylene burners adequate to yield a certain light is very much less
+      than that evolved by ordinary flat-flame coal-gas burners or by oil-lamps
+      giving the same light, and is not more than about three times as much as
+      that from ordinary electric lamps used in numbers sufficient to give the
+      same light. More exact figures for the ratio between the heat developed in
+      acetylene lighting and that in other modes of lighting are given in the
+      table already referred to.
+    </p>
+    <p>
+      In connexion with the smaller amount of heat developed per unit of light
+      when acetylene is the illuminant, the frequently exaggerated claim that
+      acetylene does not blacken ceilings at all may be studied. Except it be a
+      carelessly manipulated petroleum-lamp, no form of artificial illuminant
+      employed nowadays ever emits black smoke, soot, or carbon, in spite of the
+      fact that all luminous flames commercially capable of utilisation do
+      contain free carbon in the elemental state. The black mark on a ceiling
+      over a source of light is caused by a rising current of hot air and
+      combustion products set up by the heat accompanying the light, which
+      current of hot gas carries with it the dust and dirt always present in the
+      atmosphere of an inhabited room. As this current of air and burnt gas
+      travels in a fairly concentrated vertical stream, and as the ceiling is
+      comparatively cool and exhibits a rough surface, that dust and dirt are
+      deposited on the ceiling above the flame, but the stain is seldom or never
+      composed of soot from the illuminant itself. Proof of this statement may
+      be found in the circumstance that a black mark is eventually produced over
+      an electric glow-lamp and above a pipe delivering hot water. Clearly,
+      therefore, the depth and extent of the mark will depend on the volume and
+      temperature of the hot gaseous current; and since per unit of light
+      acetylene emits a far smaller quantity of combustion products and a far
+      smaller amount of heat than any other flame illuminant except incandescent
+      coal-gas, the inevitable black mark over its flame takes very much longer
+      to appear. Quite roughly speaking, as may be deduced from what has already
+      been said on this subject, the luminous flame of acetylene "blackens" a
+      ceiling at about the same rate as a coal-gas burner of the best Welsbach
+      type.
+    </p>
+    <p>
+      There is one respect in which acetylene and other flame illuminants are
+      superior to electric lighting, viz., that they sterilise a larger volume
+      of air. All the air which is needed to support combustion, as well as the
+      excess of air which actually passes through the burner tube and flame in
+      incandescent burners, is obviously sterilised; but so also is the much
+      larger volume of air which, by virtue of the up-current due to the heat of
+      the flame, is brought into anything like close proximity with the light.
+      The electric glow-lamp, and the most popular and economical modern
+      enclosed electric arc-lamp, sterilise only the much smaller volume of air
+      which is brought into direct contact with their glass bulbs. Moreover,
+      when large numbers of persons are congregated in insufficiently ventilated
+      buildings--and many public rooms are insufficiently ventilated--the air
+      becomes nauseous to inspire and positively detrimental to the health of
+      delicate people, by reason of the human effluvia which arise from soiled
+      raiment and uncleansed or unhealthy bodies, long before the proportion of
+      carbonic acid by itself is high enough to be objectionable. Thus a certain
+      proportion of carbonic acid coming from human lungs and skin is more
+      harmful than the same proportion of carbonic acid derived from the
+      combustion of gas or oil. Hence acetylene and flame illuminants generally
+      have the valuable hygienic advantages over electric lighting, not only of
+      killing a far larger number of the micro-organisms that may be present in
+      the air, but, by virtue of their naked flames, of burning up and
+      destroying a considerable quantity of the aforesaid odoriferous matter,
+      thus relieving the nose and materially assisting in the prevention of that
+      lassitude and an�mia occasionally follow the constant inspiration of air
+      rendered foul by human exhalations.
+    </p>
+    <p>
+      The more important advantages of acetylene as an illuminant have now been
+      indicated, and it remains to discuss the cost of acetylene lighting in
+      comparison with other modes of procuring artificial light. At the outset
+      it may be stated that a very much greater reduction in the price of
+      calcium carbide--from which acetylene is produced--than is likely to ensue
+      under the present methods and conditions of manufacture will be required
+      to make acetylene lighting as cheap as ordinary gas lighting in towns in
+      this country, provided incandescent burners are used for the gas. On the
+      score of cheapness (and of convenience, unless the acetylene were
+      delivered to the premises from some central generating station) acetylene
+      cannot compete as an illuminant with coal-gas where the latter costs, say,
+      not more than 5s. per 1000 cubic feet, if only reasonable attention is
+      given to the gas-burners, and at least a quarter of them are on the
+      incandescent system. If, on the other hand, coal-gas is misused and wasted
+      through the employment only of interior or worn-out flat-flame burners,
+      while the best types of burner are used for acetylene, the latter gas may
+      prove as cheap for lighting as coal-gas at, say, 2s. 6d. per 1000 cubic
+      feet (and be far better hygienically); whereas, contrariwise, if coal-gas
+      is used only with good and properly maintained incandescent burners, it
+      may cost over 10s. per 1000 cubic feet, and be cheaper than acetylene
+      burned in good burners (and as good from the hygienic standpoint). More
+      precise figures on the relative costs of coal-gas lighting and acetylene
+      lighting are given in the tabular statement at the close of this chapter.
+    </p>
+    <p>
+      With regard to electric lighting it is somewhat difficult to lay down a
+      fair basis of comparison, owing to the wide variations in the cost of
+      current, and in the efficiency of lamps, and to the undoubted hygienic and
+      aesthetic claims of electric lighting to precedence. But in towns in this
+      country where there is a public electricity supply, electric lighting will
+      be used rather than acetylene for the same reasons that it is preferred to
+      coal-gas. Cost is only a secondary consideration in such cases, and where
+      coal-gas is reasonably cheap, and nevertheless gives place to electric
+      lighting, acetylene clearly cannot hope to supplant the latter. [Footnote:
+      Where, however, as is frequently the case with small public
+      electricity-supply works, the voltage of the supply varies greatly, the
+      fluctuations in the light of the lamps, and the frequent destruction of
+      fuses and lamps, are such manifest inconveniences that acetylene is in
+      fact now being generally preferred to electric lighting in such
+      circumstances.] But where current cannot be had from an electricity-supply
+      undertaking, and it is a question, in the event of electric lighting being
+      adopted, of generating current by driving a dynamo, either by means of a
+      gas-engine supplied from public gas-mains, by means of a special boiler
+      installation, or by means of an oil-engine or of a power gas-plant and
+      gas-engine, the claims of acetylene to preference are very strong. An
+      important factor in the estimation of the relative advantages of
+      electricity and acetylene in such cases is the cost of labour in looking
+      after the generating plant. Where a gas-engine supplied from public
+      gas-mains is used for driving the dynamo, electric lighting can be had at
+      a relatively small expenditure for attendance on the generating plant. But
+      the cost of the gas consumed will be high, and actually light could be
+      obtained directly from the gas by means of incandescent mantles at far
+      loss cost than by consuming the gas in a motor for the indirect production
+      of light by means of electric current. Therefore electric lighting, if
+      adopted under these conditions, must be preferred to gas lighting from
+      considerations which are deemed to outweigh those of a much higher cost,
+      and acetylene does not present so great advantages over coal-gas as to
+      affect the choice of electric lighting. But in the cases where there is no
+      public gas-supply, and current must be generated from coal or coke or oil
+      consumed on the spot, the cost of the skilled labour required to look
+      after either a boiler, steam-engine and dynamo, or a power gas-plant and
+      gas-engine or oil- engine and dynamo, will be so heavy that unless the
+      capacity of the installation is very great, acetylene will almost
+      certainly prove a cheaper and more convenient method of obtaining light.
+      The attention required by an acetylene installation, such as a country
+      house of upwards of thirty rooms would want, is limited to one or two
+      hours' labour per diem at any convenient time during daylight. Moreover,
+      the attendant need not be highly paid, as he will not have required an
+      engineman's training, as will the attendant on an electric lighting plant.
+      The latter, too, must be present throughout the hours when light is wanted
+      unless a heavy expenditure has been incurred on accumulators. Furthermore,
+      the capital outlay on generating plant will be very much less for
+      acetylene than for electric lighting. General considerations such as these
+      lead to the conclusion that in almost all country districts in this
+      country a house or institution could be lighted more cheaply by means of
+      acetylene than by electricity. In the tabular statement of comparative
+      costs of different modes of lighting, electric lighting has been included
+      only on the basis of a fixed cost per unit, as owing to the very varied
+      cost of generating current by small installations in different parts of
+      the country it would be futile to attempt to give the cost of electric
+      lighting on any other basis, such as the prime cost of coal or coke in a
+      particular district. Where current is supplied by a public electricity-
+      supply undertaking, the cost per unit is known, and the comparative costs
+      of electric light and acetylene can be arrived at with tolerable
+      precision. It has not been thought necessary to include in the tabular
+      statement electric arc-lamps, as they are only suitable for the lighting
+      of large spaces, where the steadiness and uniformity of the illumination
+      are of secondary importance. Under such conditions, it may be stated
+      parenthetically, the electric arc-light is much less costly than acetylene
+      lighting would be, but it is now in many places being superseded by
+      high-pressure gas or oil incandescent lights, which are steady and
+      generally more economical than the arc light.
+    </p>
+    <p>
+      The illuminant which acetylene is best fitted to supersede on the score of
+      convenience, cleanliness, and hygienic advantages is oil. By oil is meant,
+      in this connection, the ordinary burning petroleum, kerosene, or paraffin
+      oil, obtained by distilling and refining various natural oils and shales,
+      found in many countries, of which the United States (principally
+      Pennsylvania), Russia (the Caucasus chiefly), and Scotland are practically
+      the only ones which supply considerable quantities for use in Great
+      Britain. Attempts are often made to claim superiority for particular
+      grades of these oils, but it may be at once stated that so for as actual
+      yield of light is concerned, the same weight of any of the commercial oils
+      will give practically the same result. Hence in the comparative statement
+      of the cost of different methods of lighting, oil will be taken at the
+      cheapest rate at which it could ordinarily be obtained, including delivery
+      charges, at a country house, when bought by the barrel. This rate at the
+      present time is about ninepence per gallon. A higher price may be paid for
+      grades of mineral oil reputed to be safer or to give a "brighter" or
+      "clearer" light; but as the quantity of light depends mainly upon the care
+      and attention bestowed on the burner and glass fittings of the lamp, and
+      partly upon the employment of a suitable wick, while the safety of each
+      lamp depends at least as much upon the design of that lamp, and the
+      accuracy with which the wick fits the burner tube, as upon the temperature
+      at which the oil "flashes," the extra expense involved in burning
+      fancy-priced oils will not be considered here.
+    </p>
+    <p>
+      The efficiency (<i>i.e.</i>, the light yielded per pint or other unit
+      volume consumed) of oil-lamps varies greatly, and, speaking broadly,
+      increases with the power of the lamp. But as large or high-power lamps are
+      not needed throughout a house, it is fairer to assume that the light
+      obtainable from oil in ordinary household use is the mean of that afforded
+      by large and that afforded by small lamps. A large oil-lamp as commonly
+      used in country houses will give a light of about 20 candle- power, while
+      a convenient small lamp will give a light of not more than about 5
+      candle-power. The large lamp will burn about 55 hours for every gallon of
+      oil consumed, or give an illuminating duty of about 1100 candle-hours (<i>i.e.</i>,
+      the product of candle-power by burning-hours) per gallon. The small lamp,
+      on the other hand, will burn about 140 hours for every gallon of oil
+      consumed, or give an illuminating duty of about 700 candle-hours per
+      gallon. Actually large lamps would in most country houses be used only in
+      the entrance hall, living-rooms, and kitchen, while passages and minor
+      rooms on the lower floors would be lighted by small lamps. Hence, making
+      due allowance for the lower rate of consumption of the small lamps, it
+      will be seen that, given equal numbers of large and small lamps in use,
+      the mean illuminating duty of a gallon of oil as burnt in country houses
+      will be 987, or, in round figures, 990 candle-hours. Usually candles are
+      used in the bedrooms of country houses where the lower floors are lighted
+      by means of petroleum lamps; but when acetylene is installed in such a
+      house it will frequently be adopted in the principal bed- and
+      dressing-rooms as well as in the living-rooms, as, unless candles are
+      employed very lavishly, they are really totally inadequate to meet the
+      reasonable demands for light of, <i>e.g.</i>, a lady dressing for dinner.
+      Where acetylene displaces candles as well as lamps in a country house, it
+      is necessary, in comparing the cost of the new illuminant with that of the
+      candles and oil, to bear in mind the superior degree of illumination which
+      is secured in all rooms, at least where candles were formerly used.
+    </p>
+    <p>
+      In regard to exhaustion and vitiation of the air, and to heat evolved,
+      self-luminous petroleum lamps stand on much the same footing as coal-gas
+      when the latter is burned in flat-flame burners, if the comparison is
+      based on a given yield of light. A large lamp, owing to its higher
+      illuminating efficiency, is better in this respect than a small one--
+      light for light, it is more hygienic than ordinary flat-flame coal-gas
+      burners, while a small lamp is less hygienic. It will therefore be
+      understood at once, from what has already been said about the superiority
+      on hygienic grounds of acetylene to flat-flame coal-gas lighting, that
+      acetylene is in this respect far superior to petroleum lamps. The degree
+      of its superiority is indicated more precisely by the figures quoted in
+      the tabular statement which concludes this chapter.
+    </p>
+    <p>
+      Before giving the tabular statement, however, it is necessary to say a few
+      words in regard to one method of lighting which, may possibly develop into
+      a more serious competitor with acetylene for the lighting of the better
+      class of country house than any of the illuminating agents and modes of
+      lighting so far referred to. The method in question is lighting by
+      so-called air-gas used for raising mantles to incandescence in upturned or
+      inverted burners of the Welsbach-Kern type. "Air-gas" is ordinary
+      atmospheric air, more or less completely saturated with the vapour of some
+      highly volatile hydrocarbon. The hydrocarbons practically applied have so
+      far been only "petroleum spirit" or "carburine," and "benzol." "Petroleum
+      spirit" or "carburine" consists of the more highly volatile portion of
+      petroleum, which is removed by distillation before the kerosene or burning
+      oil is recovered from the crude oil. Several grades of this highly
+      volatile petroleum distillate are distinguished in commerce; they differ
+      in the temperature at which they begin to distil and the range of
+      temperature covered by their distillation, and, speaking more generally,
+      in their degree of volatility, uniformity, and density. If the petroleum
+      distillate is sufficiently volatile and fairly uniform in character, good
+      air-gas may be produced merely by allowing air to pass over an extended
+      surface of the liquid. The vapour of the petroleum spirit is of greater
+      density than air, and hence, if the course of the air-gas is downward from
+      the apparatus at which it is produced, the flow of air into the apparatus
+      and over the surface of the spirit will be automatically maintained by the
+      "pull" of the descending air-gas when once the flow has been started until
+      the outlet for the air-gas is stopped or the spirit in the apparatus is
+      exhausted. Hence, if the apparatus for saturating air with the vapour of
+      the light petroleum is placed well above all the points at which the
+      air-gas is to be burnt-- <i>e.g.</i>, on the roof of the house--the
+      production of the air-gas may by simple devices become automatic, and the
+      only attention the apparatus will require will be the replenishing of its
+      reservoir from time to time with light petroleum. But a number of
+      precautions are required to make this simple process operate without
+      interruption or difficulty. For instance, the evaporation of the spirit
+      must not be so rapid relatively to its total bulk as to lower its
+      temperature, and thereby that of the overflowing air, too much; the
+      reservoir must be protected from extreme cold and extreme heat; and the
+      risk of fire from the presence of a highly volatile and highly inflammable
+      liquid on or near the roof of the house must be met. This risk is one to
+      which fire insurance companies take exception.
+    </p>
+    <p>
+      More commonly, however, air-gas is made non-automatically, or more or less
+      automatically by the employment of some mechanical means. The light
+      petroleum, benzol, or other suitable volatile hydrocarbon is volatilised,
+      where necessary, by the application of gentle heat, while air is driven
+      over or through it by means of a small motor, which in some cases is a
+      hot-air engine operated by heat supplied by a flame of the air-gas
+      produced. These air-gas producers, or at least the reservoir of volatile
+      hydrocarbon, may be placed in an outbuilding, so that the risk of fire in
+      the house itself is minimised. They require, however, as much attention as
+      an acetylene generator, usually more. It is difficult to give reliable
+      data as to the cost of air-gas, inclusive of the expenses of production.
+      It varies considerably with the description of hydrocarbon employed, and
+      its market price. Air-gas is only slightly inferior hygienically to
+      acetylene, and the colour of its light is that of the incandescent light
+      as produced by coal-gas or acetylene. Air-gas of a certain grade may be
+      used for lighting by flat-flame burners, but it has been available thus
+      for very many years, and has failed to achieve even moderate success. But
+      the advent of the incandescent burner has completely changed its position
+      relatively to most other illuminants, and under certain conditions it
+      seems likely to be the most formidable competitor with acetylene. Since
+      air-gas, and the numerous chemically identical products offered under
+      different proprietary names, is simply atmospheric air more or less loaded
+      with the vapour of a volatile hydrocarbon which is normally liquid, it
+      possesses no definite chemical constitution, but varies in composition
+      according to the design of the generating plant, the atmospheric
+      temperature at the time of preparation, the original degree of volatility
+      of the hydrocarbon, the remaining degree of volatility after the more
+      volatile portions have been vaporised, and the speed at which the air is
+      passed through the carburettor. The illuminating power and the calorific
+      value of air-gas, unless the manufacture is very precisely controlled, are
+      apt to be variable, and the amount of light, emitted, either in
+      self-luminous or in incandescent burners, is somewhat indeterminate. The
+      generating plant must be so constructed that the air cannot at any time be
+      mixed with as much hydrocarbon vapour as constitutes an explosive mixture
+      with it, otherwise the pipes and apparatus will contain a gas which will
+      forthwith explode if it is ignited, <i>i.e.</i>, if an attempt is made to
+      consume it otherwise than in burners with specially small orifices. The
+      safely permissible mixtures are (1) air with less hydrocarbon vapour than
+      constitutes an explosive mixture, and (2) air with more hydrocarbon vapour
+      than constitutes an explosive mixture. The first of these two mixtures is
+      available for illuminating purposes only with incandescent mantles, and to
+      ensure a reasonable margin of safety the mixing apparatus must be so
+      devised that the proportion of hydrocarbon vapour in the air-gas can never
+      exceed 2 per cent. From Chapter VI. it will be evident that a little more
+      than 2 per cent. of benzene, pentane or benzoline vapour in air forms an
+      explosive mixture. What is the lowest proportion of such vapours in
+      admixture with air which will serve on combustion to maintain a mantle in
+      a state of incandescence, or even to afford a flame at all, does not
+      appear to have been precisely determined, but it cannot be much below 1-
+      1/2 per cent. Hence the apparatus for producing air-gas of this first
+      class must be provided with controlling or governing devices of such
+      nicety that the proportion of hydrocarbon vapour in the air-gas is
+      maintained between about 1-1/2 and 2 per cent. It is fair to say that in
+      normal working conditions a number of devices appear to fulfil this
+      requirement satisfactorily. The second of the two mixtures referred to
+      above, viz., air with more hydrocarbon vapour than constitutes an
+      explosive mixture, is primarily suitable for combustion in self-luminous
+      burners, but may also be consumed in properly designed incandescent
+      burners. But the generating apparatus for such air-gas must be equipped
+      with some governing or controlling device which will ensure the proportion
+      of hydrocarbon vapour in the mixture never falling below, say, 7 per cent.
+      On the other hand, if saturation of the air with the vapour is practically
+      attained, should the temperature of the gas fall before it arrives at the
+      point of combustion, part of the spirit will condense out, and the product
+      will thus lose part of its illuminating or calorific intensity, besides
+      partially filling the pipes with liquid products of condensation. The loss
+      of intensity in the gas during cold weather may or may not be inconvenient
+      according to circumstances; but the removal of part of the combustible
+      material brings the residual air-gas nearer to its limit of
+      explosibility--for it is simply a mixture of combustible vapour with air,
+      which, normally, is not explosive because the proportion of spirit is too
+      high--and thus, when led into an atmospheric burner, the extra amount of
+      air introduced at the injector jets may cause the mixture to be an
+      explosive mixture of air and spirit, so that it will take fire within the
+      burner tube instead of burning quietly at the proper orifice. This matter
+      will be made clearer on studying what is said about explosive limits in
+      Chapter VI., and what is stated about incandescent acetylene (carburetted
+      or not) in Chapters IX. and X. Clearly, however, high-grade air-gas is
+      only suitable for preparation at the immediate spot where it is to be
+      consumed; it cannot be supplied to a complete district unless it is
+      intentionally made of such lower intensity that the proportion of spirit
+      is too small ever to allow of partial deposition in the mains during the
+      winter.
+    </p>
+    <p>
+      It is perhaps necessary to refer to the more extended use of candles for
+      lighting in some few houses in which lamps are disliked on aesthetic, or,
+      in some cases, ostensibly on hygienic grounds. Candle lighting, speaking
+      broadly, is either very inadequate so far as ordinary living-rooms are
+      concerned, or, if adequate, is very costly. Tests specially carried out by
+      one of the authors to determine some of the figures required in the
+      ensuing table show that ordinary paraffin or "wax" candles usually emit
+      about 20 per cent. more light than that given by the standard spermaceti
+      candle, whose luminosity is the unit by which the intensity of other
+      lights is reckoned in Great Britain; and also that the light so emitted by
+      domestic candles is practically unaffected by the sizes--"sixes,"
+      "eights," or "twelves"--burnt. In the sizes examined the light evolved has
+      varied between 1.145 and 1.298 "candles," perhaps tending to increase
+      slightly with the diameter of the candle tested. Hence, to obtain
+      illumination in a room equal on the average to that afforded by 100
+      standard candles, or some other light or lights aggregating 100 candle-
+      power, would require the use of only 80 to 85 ordinary paraffin,
+      ozokerite, or wax candles. But actually the essential objects in a room
+      could be equally well illuminated by, say, 30 candles well distributed, as
+      by two or three incandescent gas-burners, or four or five large oil-
+      lamps. Lights of high intensity, such as powerful gas-burners or oil-
+      lamps, must give a higher degree of illumination in their immediate
+      vicinity than is really necessary, if they are to illuminate adequately
+      the more distant objects. The dissemination and diffusion of their light
+      can be greatly aided by suitable colouring of ceilings, walls and
+      drapings; but unless the illumination by means of lights of relatively
+      high intensity is made almost wholly indirect, candles or other lights of
+      low intensity, such as small electric glow-lamps, can, by proper
+      distribution, be made to give more uniform or more suitably apportioned
+      illumination. In this respect candles have an economical and, in some
+      measure, a material advantage over acetylene also. (But when the method of
+      lighting is by flames--candle or other--the multiplication of the number
+      of units which is involved when they are of low intensity, seriously
+      increases the risk of fire through accidental contact of inflammable
+      material with any one of the flames. This risk is much greater with naked
+      flames, such as candles, than with, say, inverted incandescent gas flames,
+      which are to all intents and purposes fully protected by a closed glass
+      globe.) Hence, in the tabular statement which follows of the comparative
+      cost, &amp;c., of different illuminants, it will be assumed that 30 good
+      candles would in practice be equally efficient in regard to the
+      illumination of a room as large oil-lamps, acetylene flames, or
+      incandescent gas-burners aggregating 100 candle-power.
+    </p>
+    <p>
+      For the same reason it will be assumed that electric glow-lamps of low
+      intensity (nominally of 8 candle-power or less), aggregating 70-80
+      candle-power, will practically serve, if suitably distributed, equally as
+      well as 100 candle-power obtained from more powerful sources of light.
+      Electric glow-lamps of a nominal intensity of 16 candles or thereabouts,
+      and good flat-flame gas-burners, aggregating 90-95 candle-power, will
+      similarly be taken as equivalent, if suitably distributed, to 100 candle-
+      power from more powerful sources of light. Of the latter it will be
+      assumed that each source has an intensity between 20 and 30 candle-power,
+      such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned,
+      or a "Bijou" inverted incandescent gas-burner, or a 0.70-cubic-foot-per-
+      hour acetylene burner. Either of these sources of light, when used in
+      sufficient numbers, so that with proper distribution they light a room
+      adequately, will be taken in the tabular statement which follows as
+      affording, per candle-power evolved, the standard illuminating effect
+      required in that room. The same illuminating effect will be regarded as
+      attainable by means of candles aggregating only 35 per cent., or small
+      electric glow-lamps aggregating 77 per cent., or large electric glow-
+      lamps and flat-flame gas-burners aggregating 90 to 95 per cent. of this
+      candle-power; while if sources of light of higher intensity are used, such
+      as Osram or Tantalum electric lamps, or the larger incandescent gas-
+      burners (the Welsbach "C" or "York," or the Nos. 3 or 4 Welsbach-Kern
+      upturned, or the No. 1 or larger size inverted burners) or incandescent
+      acetylene burners, it will be assumed that their aggregate candle-power
+      must be in excess by about 15 per cent., in order to compensate for the
+      impossibility of obtaining equally well distributed illumination. These
+      assumptions are based on general considerations and data as to the effect
+      of sources of light of different intensities in giving practically the
+      same degree of illumination in a room; it would occupy too much space here
+      to discuss more fully the grounds on which they have been made. It must
+      suffice to say that they have been adopted with the object of being
+      perfectly fair to each means of illumination.
+    </p>
+    <p>
+      COST PER HOUR AND HYGIENIC EFFECT OF LIGHTING BY DIFFERENT MEANS
+    </p>
+    <p>
+      The data (except in the column headed "cost per 100 candle-hours") refer
+      to the illumination afforded by medium-sized (0.5 to 0.7 cubic foot per
+      hour) acetylene burners yielding together a light of about 100 candle-
+      power, and to the approximately equivalent illumination as afforded by
+      other means of illumination, when the lighting-units or sources of light
+      are rationally distributed.
+    </p>
+    <p>
+      Interest and depreciation charges on the outlay on piping or wiring a
+      house, on brackets, fittings, lamps, candelabra, and storage accommodation
+      (for carbide and oil) have been taken as equivalent for all modes of
+      lighting, and omitted in computing the total cost. The cost of labour for
+      attendance on acetylene plant, oil lamps, and candles is an uncertain and
+      variable item--approximately equal for all these modes of lighting, but
+      saved in coal-gas and electric lighting from public supply mains.
+    </p>
+<pre xml:space="preserve">
+ ______________________________________________________________________
+|            |                    |        |         |         |       |
+|            |                    |Candle- | Number  |Aggregate| Cost  |
+|            |                    |Power of|   of    | Candle- | per   |
+|            |  Description of    |  each  |Lighting | Power   | 100   |
+|Illuminant. |  Burner or Lamp.   |Lighting|  Units  |Afforded.|Candle-|
+|            |                    |  Unit. |Required.|(About.) |Hours. |
+|            |                    |(About.)|         |         |Pence. |
+|____________|____________________|________|_________|_________|_______|
+|            |                    |        |         |         |       |
+|            |Self-luminous; 0.5  |        |         |         |       |
+|            | cubic foot per hour|  18    |    5    |    90   | 1.11  |
+|            |Self-luminous; 0.7  |        |         |         |       |
+| Acetylene  | cubic foot per hour|  27    |    4    |   108   | 1.02  |
+|            |Self-luminous; 1.0  |        |         |         |       |
+|            | cubic foot per hour|  45.5  |    3    |   136   | 0.85  |
+|            |Incandescent; 0.5   |        |         |         |       |
+|            | cubic foot per hour|  50    |    3    |   150   | 0.49  |
+|____________|____________________|________|_________|_________|_______|
+|            |                    |        |         |         |       |
+| Petroleum  | Large lamp . . . . |  20    |    5    |   100   | 0.84  |
+| (paraffin  |                    |        |         |         |       |
+|   oil)     | Small lamp . . . . |   5    |   14    |    70   | 1.31  |
+|____________|____________________|________|_________|_________|_______|
+|            |                    |        |         |         |       |
+|            |Flat flame (bad) 5  |        |         |         |       |
+|            | cubic feet per hour|   8    |   10    |    80   | 3.75  |
+|            |Flat flame (good) 6 |        |         |         |       |
+| Coal Gas   | cubic feet per hour|  16    |    6    |    96   | 2.25  |
+|            |Incandescent (No. 1 |        |         |         |       |
+|            | Kern or Bijou In-  |  25    |    4    |   100   | 0.38  |
+|            | verted); 1-1/2     |        |         |         |       |
+|            | cubic feet per hour|        |         |         |       |
+|____________|____________________|________|_________|_________|_______|
+|            |                    |        |         |         |       |
+| Candles    |"Wax" (so-called) . |   1.2  |   30    |    35   | 6.14  |
+|____________|____________________|________|_________|_________|_______|
+|            |                    |        |         |         |       |
+|            | Small glow . . . . |   7    |   11    |    77   | 2.81  |
+|            | Large glow . . . . |  13    |    7    |    91   | 2.90  |
+| Electricity|                    |        |         |         |       |
+|            | Tantalum . . . . . |  19    |    5    |    95   | 1.52  |
+|            | Osram  . . . . . . |  14    |    7    |    98   | 1.00  |
+|____________|____________________|________|_________|_________|_______|
+</pre>
+<pre xml:space="preserve">
+ ___________________________________________________________________
+|            |                    |                    |            |
+|            |                    |                    |            |
+|            |                    |                    | Equivalent |
+|            |  Description of    |   Assumed Cost     |  Illumin-  |
+|Illuminant. |  Burner or Lamp.   |  of Illuminant.    |   ation.   |
+|            |                    |                    |   Pence.   |
+|            |                    |                    |            |
+|____________|____________________|____________________|____________|
+|            |                    |                    |            |
+|            |Self-luminous; 0.5  | Calcium carbide    |            |
+|            | cubic foot per hour|  (yielding 5       |    1.00    |
+|            |Self-luminous; 0.7  |  cubic feet of     |            |
+| Acetylene  | cubic foot per hour|  acetylene per     |    1.10    |
+|            |Self-luminous; 1.0  |  lb.) at 15s.      |            |
+|            | cubic foot per hour|  per cwt., inclu-  |    1.16    |
+|            |Incandescent; 0.5   |  ding delivery     |            |
+|            | cubic foot per hour|  charges.          |    0.74    |
+|____________|____________________|____________________|____________|
+|            |                    |                    |            |
+| Petroleum  | Large lamp . . . . | Oil, 9d. per gal-  |    0.84    |
+| (paraffin  |                    |  lon, including    |            |
+|   oil)     | Small lamp . . . . |  delivery charges. |    0.92    |
+|____________|____________________|____________________|____________|
+|            |                    |                    |            |
+|            |Flat flame (bad) 5  |                    |            |
+|            | cubic feet per hour| Public supply      |    3.00    |
+|            |Flat flame (good) 6 |  from small        |            |
+| Coal Gas   | cubic feet per hour|  country works,    |    2.16    |
+|            |Incandescent (No. 1 |  at 5s. per 1000   |            |
+|            | Kern or Bijou In-  |  cubic feet.       |    0.38    |
+|            | verted); 1-1/2     |                    |            |
+|            | cubic feet per hour|                    |            |
+|____________|____________________|____________________|____________|
+|            |                    |                    |            |
+| Candles    |"Wax" (so-called) . | 5d. per lb.        |    2.60    |
+|____________|____________________|____________________|____________|
+|            |                    |                    |            |
+|            | Small glow . . . . | Public supply      |    2.16    |
+|            | Large glow . . . . |  from small        |    2.64    |
+| Electricity|                    |  town works        |            |
+|            | Tantalum . . . . . |  at 6d. per        |    1.45    |
+|            | Osram  . . . . . . |  B.O.T. unit.      |    0.98    |
+|____________|____________________|____________________|____________|
+</pre>
+<pre xml:space="preserve">
+ _______________________________________________________________________
+|            |                    |      |         |          |         |
+|            |                    |Inci- | Exhaus- |Vitiation |  Heat   |
+|            |                    | den- | tion of | of Air.  |Produced.|
+|            |  Description of    | tal  |Air.Cubic|Cubic Feet|Number of|
+|Illuminant. |  Burner or Lamp.   |Expen-|Feet Dep-| of Car-  |Units of |
+|            |                    | ces. |rived of |bonic Acid|  Heat.  |
+|            |                    |      | Oxygen. | Formed.  |Calories.|
+|____________|____________________|______|_________|__________|_________|
+|            |                    |      |         |          |         |
+|            |Self-luminous; 0.5  |      |         |          |         |
+|            | cubic foot per hour| [1]  |   29.8  |   5.0    |   900   |
+|            |Self-luminous; 0.7  |      |         |          |         |
+| Acetylene  | cubic foot per hour|      |   33.3  |   5.6    |  1010   |
+|            |Self-luminous; 1.0  |      |         |          |         |
+|            | cubic foot per hour|      |   35.7  |   6.0    |  1000   |
+|            |Incandescent; 0.5   |      |         |          |         |
+|            | cubic foot per hour| [2]  |   17.9  |   3.0    |   545   |
+|____________|____________________|______|_________|__________|_________|
+|            |                    |      |         |          |         |
+| Petroleum  | Large lamp . . . . |      |  140.0  |  19.6    |  3630   |
+| (paraffin  |                    | [3]  |         |          |         |
+|   oil)     | Small lamp . . . . |      |  154.0  |  21.6    |  4000   |
+|____________|____________________|______|_________|__________|_________|
+|            |                    |      |         |          |         |
+|            |Flat flame (bad) 5  |      |         |          |         |
+|            | cubic feet per hour| Nil  |  270.0  |  27.0    |  7750   |
+|            |Flat flame (good) 6 |      |         |          |         |
+| Coal Gas   | cubic feet per hour| Nil  |  195.0  |  19.5    |  5580   |
+|            |Incandescent (No. 1 |      |         |          |         |
+|            | Kern or Bijou In-  | [4]  |   27.0  |   2.7    |   775   |
+|            | verted); 1-1/2     |      |         |          |         |
+|            | cubic feet per hour|      |         |          |         |
+|____________|____________________|______|_________|__________|_________|
+|            |                    |      |         |          |         |
+| Candles    |"Wax" (so-called) . | Nil  |  100.5  |   13.7   |  2700   |
+|____________|____________________|______|_________|__________|_________|
+|            |                    |      |         |          |         |
+|            | Small glow . . . . |2s.6d.|   Nil   |    Nil   |   285   |
+|            | Large glow . . . . |2s.6d.|    "    |     "    |   360   |
+| Electricity|                    | [5]  |         |          |         |
+|            | Tantalum . . . . . |7s.6d.|    "    |     "    |   172   |
+|            | Osram  . . . . . . | 6s.  |    "    |     "    |    96   |
+|____________|____________________|______|_________|__________|_________|
+</pre>
+    <p>
+      [Footnote 1: Interest and depreciation charges on generating and purifying
+      plant = 0.15 penny. Purifying material and burner renewals = 0.05 penny.]
+    </p>
+    <p>
+      [Footnote 2: Mantle renewals as for coal-gas.]
+    </p>
+    <p>
+      [Footnote 3: Renewals of wicks and chimneys = 0.02 penny.]
+    </p>
+    <p>
+      [Footnote 4: Renewals and mantles (and chimneys) at contract rate of 3s.
+      per burner per annum.]
+    </p>
+    <p>
+      [Footnote 5: Renewals of lamps and fuses, at price indicated per lamp per
+      annum.]
+    </p>
+    <p>
+      The conventional method of making pecuniary comparisons between different
+      sources of artificial light consists in simply calculating the cost of
+      developing a certain number of candle-hours of light--<i>i.e.</i>, a
+      certain amount of standard candle-power for a given number of hours--on
+      the assumption that as many separate sources of light are employed as may
+      be required to bring the combined illuminating power up to the total
+      amount wanted. In view of the facts as to dissemination and diffusion, or
+      the difference between sheer illuminating power and useful illuminating
+      effect, which have just been elaborated, and in view of the different
+      intensities of the different unit sources of light (which range from the
+      single candle to a powerful large incandescent gas-burner or a metallic
+      filament electric lamp), such a method of calculation is wholly illusory.
+      The plan adopted in the following table may also appear unnecessarily
+      complicated; but it is not so to the reader if he remembers that the
+      apparently various amount of illumination is corrected by the different
+      numbers of illuminating units until the amount of simple candle-power
+      developed, whatever illuminant be employed, suffices to light a room
+      having an area of about 300 square feet (<i>i.e.</i>, a room, 17-1/2 feet
+      square, or one 20 feet long by 15 feet wide), so that ordinary print may
+      be read comfortably in any part of the room, and the titles of books,
+      engravings, &amp;c., in any position on the walls up to a height of 8 feet
+      from the ground may be distinguished with ease. The difference in cost,
+      &amp;c., of a greater or less degree of illumination, or of lighting a
+      larger or smaller room by acetylene or any other of the illuminants named,
+      will be almost directly proportional to the cost given for the stated
+      conditions. Nevertheless, it should be recollected that when the
+      conventional system is retained--useful illuminating effect being
+      sacrificed to absolute illuminating power--acetylene is made to appear
+      cheaper in comparison with all weaker unit sources of light, and dearer in
+      comparison with all stronger unit sources of light than the accompanying
+      table indicates it to be. In using the comparative figures given in the
+      table, it should be borne in mind that they refer to more general and more
+      brilliant illumination of a room than is commonly in vogue where the
+      lighting is by means of electric light, candles, or oil- lamps. The
+      standard of illumination adopted for the table is one which is only
+      gaining general recognition where incandescent gas or acetylene lighting
+      is available, though in exceptional cases it has doubtless been attained
+      by means of oil-lamps or flat-flame gas-burners, but very rarely if ever
+      by means of carbon-filament electric glow-lamps, or candles. It assumes
+      that the occupants of a room do not wish to be troubled to bring work or
+      book "to the light," but wish to be able to work or read wheresoever in
+      the room they will, without consideration of the whereabouts of the light
+      or lights.
+    </p>
+    <p>
+      It should, perhaps, be added that so high a price as 5s. per 1000 cubic
+      feet for coal-gas rarely prevails in Great Britain, except in small
+      outlying towns, whereas the price of 6d. per Board of Trade unit for
+      electricity is not uncommonly exceeded in the few similar country places
+      in which there is a public electricity supply. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkii" id="ii">CHAPTER II</a>
+    </h2>
+    <h3>
+      THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER
+    </h3>
+    <p>
+      THE NATURE OF CALCIUM CARBIDE.--The raw material from which, by
+      interaction with water, acetylene is obtained, is a solid body called
+      calcium carbide or carbide of calcium. Inasmuch as this substance can at
+      present only be made on a commercial scale in the electric furnace--and so
+      far as may be foreseen will never be made on a large scale except by means
+      of electricity--inasmuch as an electric furnace can only be worked
+      remuneratively in large factories supplied with cheap coal or water power;
+      and inasmuch as there is no possibility of the ordinary consumer of
+      acetylene ever being able to prepare his own carbide, all descriptions of
+      this latter substance, all methods of winning it, and all its properties
+      except those which concern the acetylene-generator builder or the gas
+      consumer have been omitted from the present book. Hitherto calcium carbide
+      has found but few applications beyond that of evolving acetylene on
+      treatment with water or some aqueous liquid, hygroscopic solid, or salt
+      containing water of crystallisation; but it has possibilities of further
+      employment, should its price become suitable, and a few words will be
+      devoted to this branch of the subject in Chapter XII. Setting these minor
+      uses aside, calcium carbide has no intrinsic value except as a producer of
+      acetylene, and therefore all its characteristics which interest the
+      consumer of acetylene are developed incidentally throughout this volume as
+      the necessity for dealing with them arises.
+    </p>
+    <p>
+      It is desirable, however, now to discuss one point connected with solid
+      carbide about which some misconception prevails. Calcium carbide is a body
+      which evolves an inflammable, or on occasion an explosive, gas when
+      treated with water; and therefore its presence in a building has been said
+      to cause a sensible increase in the fire risk because attempts to
+      extinguish a fire in the ordinary manner with water may cause evolution of
+      acetylene which should determine a further production of flame and heat.
+      In the absence of water, calcium carbide is absolutely inert as regards
+      fire; and on several occasions drums of it have been recovered uninjured
+      from the basement of a house which has been totally destroyed by fire.
+      With the exception of small 1-lb. tins of carbide, used only by cyclists,
+      &amp;c., the material is always put into drums of stout sheet-iron with
+      riveted or folded seams. Provided the original lid has not been removed,
+      the drums are air- and water-tight, so that the fireman's hose may be
+      directed upon them with impunity. When a drum has once been opened, and
+      not all of its contents have been put into the generator, ordinary
+      caution--not merely as regards fire, but as regards the deterioration of
+      carbide when exposed to the atmosphere--suggests either that the lid must
+      be made air-tight again (not by soldering it), [Footnote: Carbide drums
+      are not uncommonly fitted with self-sealing or lever-top lids, which are
+      readily replaced hermetically tight after opening and partial removal of
+      the contents of the drum.] or preferably that the rest of the carbide
+      shall be transferred to some convenient receptacle which can be perfectly
+      closed. [Footnote: It would be a refinement of caution, though hardly
+      necessary in practice, to fit such a receptacle with a safety-valve. If
+      then the vessel were subjected to sudden or severe heating, the expansion
+      of the air and acetylene in it could not possibly exert a disruptive
+      effect upon the walls of the receptacle, which, in the absence of the
+      safety-valve, is imaginable.] Now, assuming this done, the drums are not
+      dependent upon soft solder to keep them sound, and so they cannot open
+      with heat. Fire and water, accordingly, cannot affect them, and only two
+      risks remain: if stored in the basement of a tall building, falling
+      girders, beams or brickwork may burst them; or if stored on an upper
+      floor, they may fall into the basement and be burst with the shock--in
+      either event water then having free access to the contents. But drums of
+      carbide would never be stored in such positions: a single one would be
+      kept in the generator-house; several would be stored in a separate room
+      therein, or in some similar isolated shed. The generator-house or shed
+      would be of one story only; the drums could neither fall nor have heavy
+      weights fall on them during a fire; and therefore there is no reason why,
+      if a fire should occur, the firemen should not be permitted to use their
+      hose in the ordinary fashion. Very similar remarks apply to an active
+      acetylene generator. Well built, such plant will stand much heat and fire
+      without failure; if it is non-automatic, and of combustible materials
+      contains nothing but gas in the holder, the worst that could happen in
+      times of fire would be the unsealing of the bell or its fracture, and this
+      would be followed, not at all by any explosion, but by a fairly quiet
+      burning of the escaping gas, which would be over in a very short time, and
+      would not add to the severity of the conflagration unless the
+      generator-house were so close to the residence that the large flame of
+      burning gas could ignite part of the main building. Even if the heat were
+      so great near the holder that the gas dissociated, it is scarcely
+      conceivable that a dangerous explosion should arise. But it is well to
+      remember, that if the generator-house is properly isolated from the
+      residence, if it is constructed of non-inflammable materials, if the
+      attendant obeys instructions and refrains from taking a naked light into
+      the neighbourhood of the plant, and if the plant itself is properly
+      designed and constructed, a fire at or near an acetylene generator is
+      extremely unlikely to occur. At the same time, before the erection of
+      plant to supply any insured premises is undertaken, the policy or the
+      company should be consulted to ascertain whether the adoption of acetylene
+      lighting is possibly still regarded by the insurers as adding an extra
+      risk or even as vitiating the whole insurance.
+    </p>
+    <p>
+      REGULATIONS FOR THE STORAGE OF CARBIDE: BRITISH.--There are also certain
+      regulations imposed by many local authorities respecting the storage of
+      carbide, and usually a licence for storage has to be obtained if more than
+      5 lb. is kept at a time. The idea of the rule is perfectly justifiable,
+      and it is generally enforced in a sensible spirit. As the rules may vary
+      in different localities, the intending consumer of acetylene must make the
+      necessary inquiries, for failure to comply with the regulations may
+      obviously be followed by unpleasantness.
+    </p>
+    <p>
+      Having regard to the fact that, in virtue of an Order in Council dated
+      July 7, 1897, carbide may be stored without a licence only in separate
+      substantial hermetically closed metal vessels containing not more than 1
+      lb. apiece and in quantities not exceeding 5 lb. in the aggregate, and
+      having regard also to the fact that regulations are issued by local
+      authorities, the Fire Offices' Committee of the United Kingdom has not up
+      to the present deemed it necessary to issue special rules with reference
+      to the storage of carbide of calcium.
+    </p>
+    <p>
+      The following is a copy of the rules issued by the National Board of Fire
+      Underwriters of the UNITED STATES OF AMERICA for the storage of calcium
+      carbide on insured premises:
+    </p>
+    <p>
+      RULES FOR THE STORAGE OF CALCIUM CARBIDE.
+    </p>
+    <p>
+      (<i>a</i>) Calcium carbide in quantities not to exceed six hundred (600)
+      pounds may be stored, when contained in approved metal packages not to
+      exceed one hundred (100) pounds each, inside insured property, provided
+      that the place of storage be dry, waterproof and well ventilated, and also
+      provided that all but one of the packages in any one building shall be
+      sealed and the seals shall not be broken so long as there is carbide in
+      excess of one (1) pound in any other unsealed package in the building.
+    </p>
+    <p>
+      (<i>b</i>) Calcium carbide in quantities in excess of six hundred (600)
+      pounds must be stored above ground in detached buildings, used exclusively
+      for the storage of calcium carbide, in approved metal packages, and such
+      buildings shall be constructed to be dry, waterproof and well ventilated.
+    </p>
+    <p>
+      (<i>c</i>) Packages to be approved must be made of metal of sufficient
+      strength to insure handling the package without rupture, and be provided
+      with a screwed top or its equivalent.
+    </p>
+    <p>
+      They must be constructed so as to be water- and air-tight without the use
+      of solder, and conspicuously marked "CALCIUM CARBIDE--DANGEROUS IF NOT
+      KEPT DRY."
+    </p>
+    <p>
+      The following is a summary of the AUSTRIAN GOVERNMENT rules relating to
+      the storage and handling of carbide:
+    </p>
+    <p>
+      (1) It must be sold and stored only in closed water-tight vessels, which,
+      if the contents exceed 10 kilos., must be marked in plain letters "CALCIUM
+      CARBIDE--TO BE KEPT CLOSED AND DRY." They must not be of copper and if
+      soldered must be opened by mechanical means and not by unsoldering. They
+      must be stored out of the reach of water.
+    </p>
+    <p>
+      (2) Quantities not exceeding 300 kilos. may be stored in occupied houses,
+      provided the single drums do not exceed 100 kilos. nominal capacity. The
+      storage-place must be dry and not underground.
+    </p>
+    <p>
+      (3) The limits specified in Rule 2 apply also to generator-rooms, with the
+      proviso also that in general the amount stored shall not exceed five days'
+      consumption.
+    </p>
+    <p>
+      (4) Quantities ranging from 300 to 1000 kilos. must be stored in special
+      well-ventilated uninhabited non-basement rooms in which lights and smoking
+      are not allowed.
+    </p>
+    <p>
+      (5) Quantities exceeding 1000 kilos. must be stored in isolated fireproof
+      magazines with light water-tight roofs. The floors must be at least 8
+      inches above ground-level.
+    </p>
+    <p>
+      (6) Carbide in water-tight drums may be stored in the open in a fenced
+      enclosure at least 30 feet from buildings, adjoining property, or
+      inflammable materials. The drums must be protected from wet by a light
+      roof.
+    </p>
+    <p>
+      (7) The breaking of carbide must be done by men provided with respirators
+      and goggles, and care taken to avoid the formation of dust.
+    </p>
+    <p>
+      (8) Local or other authorities will issue from time to time special
+      regulations in regard to carbide trade premises.
+    </p>
+    <p>
+      The ITALIAN GOVERNMENT rules relating to the storage and transport of
+      carbide follow in the main those of the Austrian Government, but for
+      quantities between 300 and 2000 kilos sanction is required from the local
+      authorities, and for larger quantities from superior authorities. The
+      storage of quantities ranging from 300 to 2000 kilos is forbidden in
+      dwelling-houses and above the latter quantity the storage-place must be
+      isolated and specially selected. No special permit is required for the
+      storage of quantities not exceeding 300 kilos. Workmen exposed to carbide
+      dust arising from the breaking of carbide or otherwise must have their
+      eyes and respiratory organs suitably protected.
+    </p>
+    <p>
+      THE PURCHASE OF CARBIDE.--Since calcium carbide is only useful as a means
+      of preparing acetylene, it should be bought under a guarantee (1) that it
+      contains less impurities than suffice to render the crude gas dangerous in
+      respect of spontaneous inflammability, or objectionable in a manner to be
+      explained later on, when consumed; and (2) that it is capable of evolving
+      a fixed minimum quantity of acetylene when decomposed by water. Such
+      determination, however, cannot be carried out by the ordinary consumer for
+      himself. A generator which is perfectly satisfactory in general behaviour,
+      and which evolves a sufficient proportion of the possible total make of
+      gas to be economical, does not of necessity decompose the carbide
+      quantitatively; nor is it constructed in a fashion to render an exact
+      measurement of the gas liberated at standard temperature and pressure easy
+      to obtain. For obvious reasons the careful consumer of acetylene will keep
+      a record of the carbide decomposed and of the acetylene generated--the
+      latter perhaps only in terms of burner- hours, or the like; but in the
+      event of serious dispute as to the gas- making capacity of his raw
+      material, he must have a proper analysis made by a qualified chemist.
+    </p>
+    <p>
+      Calcium carbide is crushed by the makers into several different sizes, in
+      each of which all the lumps exceed a certain size and are smaller than
+      another size. It is necessary to find out by experiment, or from the
+      maker, what particular size suits the generator best, for different types
+      of apparatus require different sizes of carbide. Carbide cannot well be
+      crushed by the consumer of acetylene. It is a difficult operation, and
+      fraught with the production of dust which is harmful to the eyes and
+      throat, and if done in open vessels the carbide deteriorates in gas-
+      making power by its exposure to the moisture of the atmosphere. True dust
+      in carbide is objectionable, and practically useless for the generation of
+      acetylene in any form of apparatus, but carbide exceeding 1 inch in mesh
+      is usually sold to satisfy the suggestions of the British Acetylene
+      Association, which prescribes 5 per cent, of dust as the maximum. Some
+      grades of carbide are softer than others, and therefore tend to yield more
+      dust if exposed to a long journey with frequent unloadings.
+    </p>
+    <p>
+      There are certain varieties of ordinary carbide known as "treated
+      carbide," the value of which is more particularly discussed in Chapter
+      III. The treatment is of two kinds, or of a combination of both. In one
+      process the lumps are coated with a strong solution of glucose, with the
+      object of assisting in the removal of spent lime from their surface when
+      the carbide is immersed in water. Lime is comparatively much more soluble
+      in solutions of sugar (to which class of substances glucose belongs) than
+      in plain water; so that carbide treated with glucose is not so likely to
+      be covered with a closely adherent skin of spent lime when decomposed by
+      the addition of water to it. In the other process, the carbide is coated
+      with or immersed in some oil or grease to protect it from premature
+      decomposition. The latter idea, at least, fulfils its promises, and does
+      keep the carbide to a large extent unchanged if the lumps are exposed to
+      damp air, while solving certain troubles otherwise met with in some
+      generators (cf. Chapter III.); but both operations involve additional
+      expense, and since ordinary carbide can be used satisfactorily in a good
+      fixed generator, and can be preserved without serious deterioration by the
+      exercise of reasonable care, treated carbide is only to be recommended for
+      employment in holderless generators, of which table-lamps are the most
+      conspicuous forms. A third variant of plain carbide is occasionally heard
+      of, which is termed "scented" carbide. It is difficult to regard this
+      material seriously. In all probability calcium carbide is odourless, but
+      as it begins to evolve traces of gas immediately atmospheric moisture
+      reaches it, a lump of carbide has always the unpleasant smell of crude
+      acetylene. As the material is not to be stored in occupied rooms, and as
+      all odour is lost to the senses directly the carbide is put into the
+      generator, scented carbide may be said to be devoid of all utility.
+    </p>
+    <p>
+      THE REACTION BETWEEN CARBIDE AND WATER.--The reaction which occurs when
+      calcium carbide and water are brought into contact belongs to the class
+      that chemists usually term double decompositions. Calcium carbide is a
+      chemical compound of the metal calcium with carbon, containing one
+      chemical "part," or atomic weight, of the former united to two chemical
+      parts, or atomic weights, of the latter; its composition expressed in
+      symbols being CaC_2. Similarly, water is a compound of two chemical parts
+      of hydrogen with one of oxygen, its formula being H_2O. When those two
+      substances are mixed together the hydrogen of the water leaves its
+      original partner, oxygen, and the carbon of the calcium carbide leaves the
+      calcium, uniting together to form that particular compound of hydrogen and
+      carbon, or hydrocarbon, which is known as acetylene, whose formula is
+      C_2H_2; while the residual calcium and oxygen join together to produce
+      calcium oxide or lime, CaO. Put into the usual form of an equation, the
+      reaction proceeds thus--
+    </p>
+    <p>
+      (1) CaC_2 + H_2O = C_2H_2 + CaO.
+    </p>
+    <p>
+      This equation not only means that calcium carbide and water combine to
+      yield acetylene and lime, it also means that one chemical part of carbide
+      reacts with one chemical part of water to produce one chemical part of
+      acetylene and one of lime. But these four chemical parts, or molecules,
+      which are all equal chemically, are not equal in weight; although,
+      according to a common law of chemistry, they each bear a fixed proportion
+      to one another. Reference to the table of "Atomic Weights" contained in
+      any text-book of chemistry will show that while the symbol Ca is used, for
+      convenience, as a contraction or sign for the element calcium simply, it
+      bears a more important quantitative significance, for to it will be found
+      assigned the number 40. Against carbon will be seen the number 12; against
+      oxygen, 16; and against hydrogen, 1. These numbers indicate that if the
+      smallest weight of hydrogen ever found in a chemical compound is called 1
+      as a unit of comparison, the smallest weights of calcium, carbon, and
+      oxygen, similarly taking part in chemical reactions are 40, 12, and 16
+      respectively. Thus the symbol CaC_2, comes to convoy three separate ideas:
+      (<i>a</i>) that the substance referred to is a compound of calcium and
+      carbon only, and that it is therefore a carbide of calcium; (<i>b</i>)
+      that it is composed of one chemical part or atom of calcium and two atoms
+      of carbon; and (<i>c</i>) that it contains 40 parts by weight of calcium
+      combined with twice twelve, or 24, parts of carbon. It follows from (<i>c</i>)
+      that the weight of one chemical part, now termed a molecule as the
+      substance is a compound, of calcium carbide is (40 + 2 x 12) = 64. By
+      identical methods of calculation it will be found that the weight of one
+      molecule of water is 18; that of acetylene, 26; and that of lime, 56. The
+      general equation (1) given above, therefore, states in chemical shorthand
+      that 64 parts by weight of calcium carbide react with 18 parts of water to
+      give 26 parts by weight of acetylene and 56 parts of lime; and it is very
+      important to observe that just as there are the same number of chemical
+      parts, viz., 2, on each side, so there are the same number of parts by
+      weight, for 64 + 18 = 56 + 26 = 82. Put into other words equation (1)
+      shows that if 64 grammes, lb., or cwts. of calcium carbide are treated
+      with 18 grammes, lb., or cwts. of water, the whole mass will be converted
+      into acetylene and lime, and the residue will not contain any unaltered
+      calcium carbide or any water; whence it may be inferred, as is the fact,
+      that if the weights of carbide and water originally taken do not stand to
+      one another in the ratio 64 : 18, both substances cannot be entirely
+      decomposed, but a certain quantity of the one which was in excess will be
+      left unattacked, and that quantity will be in exact accordance with the
+      amount of the said excess--indifferently whether the superabundant
+      substance be carbide or water.
+    </p>
+    <p>
+      Hitherto, for the sake of simplicity, the by-product in the preparation of
+      acetylene has been described as calcium oxide or quicklime. It is,
+      however, one of the leading characteristics of this body to be
+      hygroscopic, or greedy of moisture; so that if it is brought into the
+      presence of water, either in the form of liquid or as vapour, it
+      immediately combines therewith to yield calcium hydroxide, or slaked lime,
+      whose chemical formula is Ca(OH)_2. Accordingly, in actual practice, when
+      calcium carbide is mixed with an excess of water, a secondary reaction
+      takes place over and above that indicated by equation (1), the quicklime
+      produced combining with one chemical part or molecule of water, thus--
+    </p>
+    <p>
+      CaO + H_2O = Ca(OH)_2.
+    </p>
+    <p>
+      As these two actions occur simultaneously, it is more usual, and more in
+      agreement with the phenomena of an acetylene generator, to represent the
+      decomposition of calcium carbide by the combined equation--
+    </p>
+    <p>
+      (2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2.
+    </p>
+    <p>
+      By the aid of calculations analogous to those employed in the preceding
+      paragraph, it will be noticed that equation (2) states that 1 molecule of
+      calcium carbide, or 64 parts by weight, combines with 2 molecules of
+      water, or 36 parts by weight, to yield 1 molecule, or 26 parts by weight
+      of acetylene, and 1 molecule, or 74 parts by weight of calcium hydroxide
+      (slaked lime). Here again, if more than 36 parts of water are taken for
+      every 64 parts of calcium carbide, the excess of water over those 36 parts
+      is left undecomposed; and in the same fashion, if less than 36 parts of
+      water are taken for every 64 parts of calcium carbide, some of the latter
+      must remain unattacked, whilst, obviously, the amount of acetylene
+      liberated cannot exceed that which corresponds with the quantity of
+      substance suffering complete decomposition. If, for example, the quantity
+      of water present in a generator is more than chemically sufficient to
+      attack all the carbide added, however largo or small that excess may be,
+      no more, and, theoretically speaking, no less, acetylene can ever be
+      evolved than 26 parts by weight of gas for every 64 parts by weight of
+      calcium carbide consumed. It is, however, not correct to invert the
+      proposition, and to say that if the carbide is in excess of the water
+      added, no more, and, theoretically speaking, no less, acetylene can ever
+      be evolved than 26 parts by weight of gas for every 36 parts of water
+      consumed, as might be gathered from equation (2); because equation (1)
+      shows that 26 parts of acetylene may, on occasion, be produced by the
+      decomposition of 18 parts by weight of water. From the purely chemical
+      point of view this apparent anomaly is explained by the circumstance that
+      of the 36 parts of water present on the left-hand aide of equation (2),
+      only one-half, <i>i.e.</i>, 18 parts by weight, are actually decomposed
+      into hydrogen and oxygen, the other 18 parts remaining unattacked, and
+      merely attaching themselves as "water of hydration" to the 56 parts of
+      calcium oxide in equation (1) so as to produce the 74 parts of calcium
+      hydroxide appearing on the right-hand side of equation (2). The matter is
+      perhaps rendered more intelligible by employing the old name for calcium
+      hydroxide or slaked lime, viz., hydrated oxide of calcium, and by writing
+      its formula in the corresponding form, when equation (2) becomes
+    </p>
+    <p>
+      CaC_2 + 2H_2O = C_2H_2 + CaO.H_2O.
+    </p>
+    <p>
+      It is, therefore, absolutely correct to state that if the amount of
+      calcium carbide present in an acetylene generator is more than chemically
+      sufficient to decompose all the water introduced, no more, and
+      theoretically speaking no less, acetylene can ever be liberated than 26
+      parts by weight of gas for every 18 parts by weight of water attacked.
+      This, it must be distinctly understood, is the condition of affairs
+      obtaining in the ideal acetylene generator only; since, for reasons which
+      will be immediately explained, when the output of gas is measured in terms
+      of the water decomposed, in no commercial apparatus, and indeed in no
+      generator which can be imagined fit for actual employment, does that
+      output of gas ever approach the quantitative amount; but the volume of
+      water used, if not actually disappearing, is always vastly in excess of
+      the requirements of equation (2). On the contrary, when the make of gas is
+      measured in terms of the calcium carbide consumed, the said make may, and
+      frequently does, reach 80, 90, or even 99 per cent. of what is
+      theoretically possible. Inasmuch as calcium carbide is the one costly
+      ingredient in the manufacture of acetylene, so long as it is not wasted--
+      so long, that is to say, as nearly the theoretical yield of gas is
+      obtained from it--an acetylene generator is satisfactory or efficient in
+      this particular; and except for the matter of solubility discussed in the
+      following chapter, the quantity of water consumed is of no importance
+      whatever.
+    </p>
+    <p>
+      HEAT EVOLVED IN THE REACTION.--The chemical reaction between calcium
+      carbide and water is accompanied by a large evolution of heat, which,
+      unless due precautions are taken to prevent it, raises the temperature of
+      the substances employed, and of the apparatus containing them, to a
+      serious and often inconvenient extent. This phenomenon is the most
+      important of all in connexion with acetylene manufacture; for upon a
+      proper recognition of it, and upon the character of the precautions taken
+      to avoid its numerous evil effects, depend the actual value and capacity
+      for smooth working of any acetylene generator. Just as, by an immutable
+      law of chemistry, a given weight of calcium carbide yields a given weight
+      of acetylene, and by no amount of ingenuity can be made to produce either
+      more or less; so, by an equally immutable law of physics, the
+      decomposition of a given weight of calcium carbide by water, or the
+      decomposition of a given weight of water by calcium carbide, yields a
+      perfectly definite quantity of heat--a quantity of heat which cannot be
+      reduced or increased by any artifice whatever. The result of a production
+      of heat is usually to raise the temperature of the material in which it is
+      produced; but this is not always the case, and indeed there is no
+      necessary connexion or ratio between the quantity of heat liberated in any
+      form of chemical reaction--of which ordinary combustion is the commonest
+      type--and the temperature attained by the substances concerned. This
+      matter has so weighty a bearing upon acetylene generation, and appears to
+      be so frequently misunderstood, that a couple of illustrations may with
+      advantage be studied. If a vessel full of cold water, and containing also
+      a thermometer, is placed over a lighted gas-burner, at first the
+      temperature of the liquid rises steadily, and there is clearly a ratio
+      between the size of the flame and the speed at which the mercury mounts up
+      the scale. Finally, however, the thermometer indicates a certain point,
+      viz., 100� C, and the water begins to boil; yet although the burner is
+      untouched, and consequently, although heat must be passing into the vessel
+      at the same rate as before, the mercury refuses to move as long as any
+      liquid water is left. By the use of a gas meter it might be shown that the
+      same volume of gas is always consumed (<i>a</i>) in raising the
+      temperature of a given quantity of cold water to the boiling- point, and
+      another equally constant volume of gas is always consumed (<i>b</i>) in
+      causing the boiling water to disappear as steam. Hence, as coal-gas is
+      assumed for the present purpose to possess invariably the same heating
+      power, it appears that the same quantity of heat is always needed to
+      convert a given amount of cold water at a certain temperature into steam;
+      but inasmuch as reference to the meter would show that about 5 times the
+      volume of gas is consumed in changing the boiling water into steam as is
+      used in heating the cold water to the boiling-point, it will be evident
+      that the temperature of the mass is raised as high by the heat evolved
+      during the combustion of one part of gas as it is by that liberated on the
+      combustion of 6 times that amount.
+    </p>
+    <p>
+      A further example of the difference between quantity of heat and sensible
+      temperature may be seen in the combustion of coal, for (say) one
+      hundredweight of that fuel might be consumed in a very few minutes in a
+      furnace fitted with a powerful blast of air, the operation might be spread
+      over a considerable number of hours in a domestic grate, or the coal might
+      be allowed to oxidise by exposure to warm air for a year or more. In the
+      last case the temperature might not attain that of boiling water, in the
+      second it would be about that of dull redness, and in the first it would
+      be that of dazzling whiteness; but in all three cases the total quantity
+      of heat produced by the time the coal was entirely consumed would be
+      absolutely identical. The former experiment with water and a gas-burner,
+      too, might easily be modified to throw light upon another problem in
+      acetylene generation, for it would be found that if almost any other
+      liquid than water were taken, less gas (<i>i.e.</i>, a smaller quantity of
+      heat) would be required to raise a given weight of it from a certain low
+      to a certain high temperature than in the case of water itself; while if
+      it were possible similarly to treat the same weight of iron (of which
+      acetylene generators are constructed), or of calcium carbide, the quantity
+      of heat used to raise it through a given number of thermometric degrees
+      would hardly exceed one-tenth or one- quarter of that needed by water
+      itself. In technical language this difference is due to the different
+      specific heats of the substances mentioned; the specific heat of a body
+      being the relative quantity of heat consumed in raising a certain weight
+      of it a certain number of degrees when the quantity of heat needed to
+      produce the same effect on the same weight of water is called unity. Thus,
+      the specific heat of water being termed 1.0, that of iron or steel is
+      0.1138, and that of calcium carbide 0.247, [Footnote: This is Carlson's
+      figure. Morel has taken the value 0.103 in certain calculations.] both
+      measured at temperatures where water is a liquid. Putting the foregoing
+      facts in another shape, for a given rise in temperature that substance
+      will absorb the most heat which has the highest specific heat, and
+      therefore, in this respect, 1 part by weight of water will do the work of
+      roughly 9 parts by weight of iron, and of about 4 parts by weight of
+      calcium carbide.
+    </p>
+    <p>
+      From the practical aspect what has been said amounts to this: During the
+      operation of an acetylene generator a large amount of heat is produced,
+      the quantity of which is beyond human control. It is desirable, for
+      various reasons, that the temperature shall be kept as low as possible.
+      There are three substances present to which the heat may be compelled to
+      transfer itself until it has opportunity to pass into the surrounding
+      atmosphere: the material of which the apparatus is constructed, the gas
+      which is in process of evolution, and whichever of the two bodies--
+      calcium carbide or water--is in excess in the generator. Of these, the
+      specific heat at constant pressure of acetylene has unfortunately not yet
+      been determined, but its relative capacity for absorbing heat is
+      undoubtedly small; moreover the gas could not be permitted to become
+      sufficiently hot to carry off the heat without grave disadvantages. The
+      specific heat of calcium carbide is also comparatively small, and there
+      are similar disadvantages in allowing it to become hot; moreover it is
+      deficient in heat-conducting power, so that heat communicated to one
+      portion of the mass does not extend rapidly throughout, but remains
+      concentrated in one spot, causing the temperature to rise objectionably.
+      Steel has a sufficient amount of heat-conducting power to prevent undue
+      concentration in one place; but, as has been stated, its specific heat is
+      only one-ninth that of water. Water is clearly, therefore, the proper
+      substance to employ for the dissipation of the heat generated, although it
+      is strictly speaking almost devoid of heat-conducting power; for not only
+      is the specific heat of water much greater than that of any other material
+      present, but it possesses in a high degree the faculty of absorbing heat
+      throughout its mass, by virtue of the action known as convection, provided
+      that heat is communicated to it at or near the bottom, and not too near
+      its upper surface. Moreover, water is a much more valuable substance for
+      dissipating heat than appears from the foregoing explanation; for
+      reference to the experiment with the gas- burner will show that six and a
+      quarter times as much heat can be absorbed by a given weight of water if
+      it is permitted to change into steam, as if it is merely raised to the
+      boiling-point; and since by no urging of the gas-burner can the
+      temperature be raised above 100� C. as long as any liquid water remains
+      unevaporated, if an excess of water is employed in an acetylene generator,
+      the temperature inside can never-- except quite locally--exceed 100� C.,
+      however fast the carbide be decomposed. An indefinitely large consumption
+      of water by evaporation in a generator matters nothing, for the liquid may
+      be considered of no pecuniary value, and it can all be recovered by
+      condensation in a subsequent portion of the plant.
+    </p>
+    <p>
+      It has been said that the quantity of heat liberated when a certain amount
+      of carbide suffers decomposition is fixed; it remains now to consider what
+      that quantity is. Quantities of heat are always measured in terms of the
+      amount needed to raise a certain weight of water a certain number of
+      degrees on the thermometric scale. There are several units in use, but the
+      one which will be employed throughout this book is the "Large Calorie"; a
+      large calorie being the amount of heat absorbed in raising 1 kilogramme of
+      water 1� C. Referring for a moment to what has been said about specific
+      heats, it will be apparent that if 1 large calorie is sufficient to heat 1
+      kilo, of water through 1� C. the same quantity will heat 1 kilo. of steel,
+      whose specific heat is roughly 0.11, through (10/011) = 9� C., or, which
+      comes to the same thing, will heat 9 kilos, of steel through 1� C.; and
+      similarly, 1 large calorie will raise 4 kilos. of calcium carbide 1� C. in
+      temperature, or 1 kilo. 4� C. The fact that a definite quantity of heat is
+      manifested when a known weight of calcium carbide is decomposed by water
+      is only typical; for in every chemical process some disturbance of heat,
+      though not necessarily of sensible (or thermometric) character, occurs,
+      heat being either absorbed or set free. Moreover, if when given weights of
+      two or more substances unite to form a given weight of another substance,
+      a certain quantity of heat is set free, precisely the same amount of heat
+      is absorbed, or disappears, when the latter substance is decomposed to
+      form the same quantities of the original substances; and, <i>per contra</i>,
+      if the combination is attended by a disappearance of heat, exactly the
+      same amount is liberated when the compound is broken up into its first
+      constituents. Compounds are therefore of two kinds: those which absorb
+      heat during their preparation, and consequently liberate heat when they
+      are decomposed--such being termed endothermic; and those which evolve heat
+      during their preparation, and consequently absorb heat when they are
+      decomposed--such being called exothermic. If a substance absorbs heat
+      during its formation, it cannot be produced unless that heat is supplied
+      to it; and since heat, being a form of motion, is equally a form of
+      energy, energy must be supplied, or work must be done, before that
+      substance can be obtained. Conversely, if a substance evolves heat during
+      its formation, its component parts evolve energy when the said substance
+      is being produced; and therefore the mere act of combination is
+      accompanied by a facility for doing work, which work may be applied in
+      assisting some other reaction that requires heat, or may be usefully
+      employed in any other fashion, or wasted if necessary. Seeing that there
+      is a tendency in nature for the steady dissipation of energy, it follows
+      that an exothermic substance is stable, for it tends to remain as it is
+      unless heat is supplied to it, or work is done upon it; whereas, according
+      to its degree of endothermicity, an endothermic substance is more or less
+      unstable, for it is always ready to emit heat, or to do work, as soon as
+      an opportunity is given to it to decompose. The theoretical and practical
+      results of this circumstance will be elaborated in Chapter VI., when the
+      endothermic nature of acetylene is more fully discussed.
+    </p>
+    <p>
+      A very simple experiment will show that a notable quantity of heat is set
+      free when calcium carbide is brought into contact with water, and by
+      arranging the details of the apparatus in a suitable manner, the quantity
+      of heat manifested may be measured with considerable accuracy. A lengthy
+      description of the method of performing this operation, however, scarcely
+      comes within the province of the present book, and it must be sufficient
+      to say that the heat is estimated by decomposing a known weight of carbide
+      by means of water in a small vessel surrounded on all sides by a carefully
+      jacketed receptacle full of water and provided with a sensitive
+      thermometer. The quantity of water contained in the outer vessel being
+      known, and its temperature having been noted before the reaction
+      commences, an observation of the thermometer after the decomposition is
+      finished, and when the mercury has reached its highest point, gives data
+      which show that the reaction between water and a known weight of calcium
+      carbide produces heat sufficient in amount to raise a known weight of
+      water through a known thermometric distance; and from these figures the
+      corresponding number of large calories may easily be calculated. A
+      determination of this quantity of heat has been made experimentally by
+      several investigators, including Lewes, who has found that the heat
+      evolved on decomposing 1 gramme of ordinary commercial carbide with water
+      is 0.406 large calorie. [Footnote: Lewes returns his result as 406
+      calories, because he employs the "small calorie." The small calorie is the
+      quantity of heat needed to raise 1 gramme of water 1� C.; but as there are
+      1000 grammes in 1 kilogramme, the large calorie is equal to 1000 small
+      calories. In many respects the former unit is to be preferred.] As the
+      material operated upon contained only 91.3 per cent. of true calcium
+      carbide, he estimates the heat corresponding with the decomposition of 1
+      gramme of pure carbide to be 0.4446 large calorie. As, however, it is
+      better, and more in accordance with modern practice, to quote such data in
+      terms of the atomic or molecular weight of the substance concerned, and as
+      the molecular weight of calcium carbide is 64, it is preferable to
+      multiply these figures by 64, stating that, according to Lewes'
+      researches, the heat of decomposition of "1 gramme- molecule" (<i>i.e.</i>,
+      64 grammes) of a calcium carbide having a purity of 91.3 per cent. is just
+      under 26 calories, or that of 1 gramme-molecule of pure carbide 28.454
+      calories. It is customary now to omit the phrase "one gramme-molecule" in
+      giving similar figures, physicists saying simply that the heat of
+      decomposition of calcium carbide by water when calcium hydroxide is the
+      by-product, is 28.454 large calories.
+    </p>
+    <p>
+      Assuming all the necessary data known, as happens to be the case in the
+      present instance, it is also possible to calculate theoretically the heat
+      which should be evolved on decomposing calcium carbide by means of water.
+      Equation (2), given on page 24, shows that of the substances taking part
+      in the reaction 1 molecular weight of calcium carbide is decomposed, and 1
+      molecular weight of acetylene is formed. Of the two molecules of water,
+      only one is decomposed, the other passing to the calcium hydroxide
+      unchanged; and the 1 molecule of calcium hydroxide is formed by the
+      combination of 1 atom of free calcium, 1 atom of free oxygen, and 1
+      molecule of water already existing as such. Calcium hydroxide and water
+      are both exothermic substances, absorbing heat when they are decomposed,
+      liberating it when they are formed. Acetylene is endothermic, liberating
+      heat when it is decomposed, absorbing it when it is produced.
+      Unfortunately there is still some doubt about the heat of formation of
+      calcium carbide, De Forcrand returning it as -0.65 calorie, and Gin as
+      +3.9 calories. De Forcrand's figure means, as before explained, that 64
+      grammes of carbide should absorb 0.65 large calorie when they are produced
+      by the combination of 40 grammes of calcium with 24 grammes of carbon; the
+      minus sign calling attention to the belief that calcium carbide is
+      endothermic, heat being liberated when it suffers decomposition. On the
+      contrary, Gin's figure expresses the idea that calcium carbide is
+      exothermic, liberating 3.9 calories when it is produced, and absorbing
+      them when it is decomposed. In the absence of corroborative evidence one
+      way or the other, Gin's determination will be accepted for the ensuing
+      calculation. In equation (2), therefore, calcium carbide is decomposed and
+      absorbs heat; water is decomposed and absorbs heat; acetylene is produced
+      and absorbs heat; and calcium hydroxide is produced liberating heat. On
+      consulting the tables of thermo-chemical data given in the various
+      text-books on physical chemistry, all the other constants needed for the
+      present purpose will be found; and it will appear that the heat of
+      formation of water is +69 calories, that of acetylene -58.1 calories, and
+      that of calcium hydroxide, when 1 atom of calcium, 1 atom of oxygen, and 1
+      molecule of water unite together, is +160.1 calories. [Footnote: When 1
+      atom of calcium, 2 atoms of oxygen, and 2 atoms of hydrogen unite to form
+      solid calcium hydroxide, the heat of formation of the latter is 229.1 (cf.
+      <i>infra</i>). This value is simply 160.1 + 69.0 = 229.1; 69.0 being the
+      heat of formation of water.] Collecting the results into the form of a
+      balance-sheet, the effect of decomposing calcium carbide with water is
+      this:
+    </p>
+<pre xml:space="preserve">
+_Heat liberated._              | _Heat absorbed._
+                               |
+Formation of Ca(OH)_2   16O.1  | Formation of acetylene    58.1
+| Decomposition of water    69.0
+                               | Decomposition of carbide   3.9
+                               |         Balance           29.1
+                        _____  |                           _____
+                               |
+         Total          160.1  |       Total              160.1
+</pre>
+    <p>
+      Therefore when 64 grammes of calcium carbide are decomposed by water, or
+      when 18 grammes of water are decomposed by calcium carbide (the by-
+      product in each case being calcium hydroxide or slaked lime, for the
+      formation of which a further 18 grammes of water must be present in the
+      second instance), 29.1 large calories are set free. It is not possible yet
+      to determine thermo-chemical data with extreme accuracy, especially on
+      such a material as calcium carbide, which is hardly to be procured in a
+      state of chemical purity; and so the value 28.454 calories experimentally
+      found by Lewes agrees very satisfactorily, considering all things, with
+      the calculated value 29.1 calories. It is to be noticed, however, that the
+      above calculated value has been deduced on the assumption that the calcium
+      hydroxide is obtained as a dry powder; but as slaked lime is somewhat
+      soluble in water, and as it evolves 3 calories in so dissolving, if
+      sufficient water is present to take up the calcium hydroxide entirely into
+      the liquid form (<i>i.e.</i>, that of a solution), the amount of heat set
+      free will be greater by those 3 calories, <i>i.e.</i>, 32.1 large calories
+      altogether.
+    </p>
+    <p>
+      THE PROCESS OF GENERATION.--Taking 28 as the number of large calories
+      developed when 64 grammes of ordinary commercial calcium carbide are
+      decomposed with sufficient water to leave dry solid calcium hydroxide as
+      the by-product in acetylene generation, this quantity of heat is capable
+      of exerting any of the following effects. It is sufficient (1) to raise
+      1000 grammes of water through 28� C., say from 10� C. (50� F., which is
+      roughly the temperature of ordinary cold water) to 38� C. It is sufficient
+      (2) to raise 64 grammes of water (a weight equal to that of the carbide
+      decomposed) through 438� C., if that were possible. It would raise (3) 311
+      grammes of water through 90� C., <i>i.e.</i>, from 10� C. to the
+      boiling-point. If, however, instead of remaining in the liquid state, the
+      water were converted into vapour, the same quantity of heat would suffice
+      (4) to change 44.7 grammes of water at 10� C. into steam at 100� C.; or
+      (5) to change 46.7 grammes of water at 10� C. into vapour at the same
+      temperature. It is an action of the last character which takes place in
+      acetylene generators of the most modern and usual pattern, some of the
+      surplus water being evaporated and carried away as vapour at a
+      comparatively low temperature with the escaping gas; for it must be
+      remembered that although steam, as such, condenses into liquid water
+      immediately the surrounding temperature falls below 100� C., the vapour of
+      water remains uncondensed, even at temperatures below the freezing- point,
+      when that vapour is distributed among some permanent gas--the precise
+      quantity of vapour so remaining being a function of the temperature and
+      barometric height. Thus it appears that if the heat evolved during the
+      decomposition of calcium carbide is not otherwise consumed, it is
+      sufficient in amount to vaporise almost exactly 3 parts by weight of water
+      for every 4 parts of carbide attacked; but if it were expended upon some
+      substance such as acetylene, calcium carbide, or steel, which, unlike
+      water, could not absorb an extra amount by changing its physical state
+      (from solid to liquid, or from liquid to gas), the heat generated during
+      the decomposition of a given weight of carbide would suffice to raise an
+      equal weight of the particular substance under consideration to a
+      temperature vastly exceeding 438� C. The temperature attained, indeed,
+      measured in Centigrade degrees, would be 438 multiplied by the quotient
+      obtained on dividing the specific heat of water by the specific heat of
+      the substance considered: which quotient, obviously, is the "reciprocal"
+      of the specific heat of the said substance.
+    </p>
+    <p>
+      The analogy to the combustion of coal mentioned on a previous page shows
+      that although the quantity of heat evolved during a certain chemical
+      reaction is strictly fixed, the temperature attained is dependent on the
+      time over which the reaction is spread, being higher as the process is
+      more rapid. This is due to the fact that throughout the whole period of
+      reaction heat is escaping from the mass, and passing into the atmosphere
+      at a fairly constant speed; so that, clearly, the more slowly heat is
+      produced, the better opportunity has it to pass away, and the less of it
+      is left to collect in the material under consideration. During the action
+      of an acetylene generator, there is a current of gas constantly travelling
+      away from the carbide, there is vapour of water constantly escaping with
+      the gas, there are the walls of the generator itself constantly exposed to
+      the cooling action of the atmosphere, and there is either a mass of
+      calcium carbide or of water within the generator. It is essential for good
+      working that the temperature of both the acetylene and the carbide shall
+      be prevented from rising to any noteworthy extent; while the amount of
+      heat capable of being dissipated into the air through the walls of the
+      apparatus in a given time is narrowly limited, depending upon the size and
+      shape of the generator, and the temperature of the surrounding air. If,
+      then, a small, suitably designed generator is working quite slowly, the
+      loss of heat through the external walls of the apparatus may easily be
+      rapid enough to prevent the internal temperature from rising objectionably
+      high; but the larger the generator, and the more rapidly it is evolving
+      gas, the less does this become possible. Since of the substances in or
+      about a generator water is the one which has by far the largest capacity
+      for absorbing heat, and since it is the only substance to which any
+      necessary quantity of heat can be safely or conveniently transmitted, it
+      follows that the larger in size an acetylene generator is, or the more
+      rapidly that generator is made to deliver gas, the more desirable is it to
+      use water as the means for dissipating the surplus heat, and the more
+      necessary is it to employ an apparatus in which water is in large chemical
+      excess at the actual place of decomposition.
+    </p>
+    <p>
+      The argument is sometimes advanced that an acetylene generator containing
+      carbide in excess will work satisfactorily without exhibiting an
+      undesirable rise in internal temperature, if the vessel holding the
+      carbide is merely surrounded by a large quantity of cold water. The idea
+      is that the heat evolved in that particular portion of the charge which is
+      suffering decomposition will be communicated with sufficient speed
+      throughout the whole mass of calcium carbide present, whence it will pass
+      through the walls of the containing vessel into the water all round.
+      Provided the generator is quite small, provided the carbide container is
+      so constructed as to possess the maximum of superficial area with the
+      minimum of cubical capacity (a geometrical form to which the sphere, and
+      in one direction the cylinder, are diametrically opposed), and provided
+      the walls of the container do not become coated internally or externally
+      with a coating of lime or water scale so as to diminish in heat-
+      transmitting power, an apparatus designed in the manner indicated is
+      undoubtedly free from grave objection; but immediately any of those
+      provisions is neglected, trouble is likely to ensue, for the heat will not
+      disappear from the place of actual reaction at the necessary speed.
+      Apparent proof that heat is not accumulating unduly in a water-jacketed
+      carbide container even when the generator is evolving gas at a fair speed
+      is easy to obtain; for if, as usually happens, the end of the container
+      through which the carbide is inserted is exposed to the air, the hand may
+      be placed upon it, and it will be found to be only slightly warm to the
+      touch. Such a test, however, is inconclusive, and frequently misleading,
+      because if more than a pound or two of carbide is present as an undivided
+      mass, and if water is allowed to attack one portion of it, that particular
+      portion may attain a high temperature while the rest is comparatively
+      cool: and if the bulk of the carbide is comparatively cool, naturally the
+      walls of the containing vessel themselves remain practically unheated.
+      Three causes work together to prevent this heat being dissipated through
+      the walls of the carbide vessel with sufficient rapidity. In the first
+      place, calcium carbide itself is a very bad conductor of heat. So
+      deficient in heat-conducting power is it that a lump a few inches in
+      diameter may be raised to redness in a gas flame at one spot, and kept hot
+      for some minutes, while the rest of the mass remains sufficiently cool to
+      be held comfortably in the fingers. In the second place, commercial
+      carbide exists in masses of highly irregular shape, so that when they are
+      packed into any vessel they only touch at their angles and edges; and
+      accordingly, even if the material were a fairly good heat conductor of
+      itself, the air or gas present between each lump would act as an
+      insulator, protecting the second piece from the heat generated in the
+      first. In the third place, the calcium hydroxide produced as the
+      by-product when calcium carbide is decomposed by water occupies
+      considerably more space than the original carbide--usually two or three
+      times as much space, the exact figures depending upon the conditions in
+      which it is formed--and therefore a carbide container cannot advisedly be
+      charged with more than one-third the quantity of solid which it is
+      apparently capable of holding. The remaining two-thirds of the space is
+      naturally full of air when the container is first put into the generator,
+      but the air is displaced by acetylene as soon as gas production begins.
+      Whether that space, however, is occupied by air, by acetylene, or by a
+      gradually growing loose mass of slaked lime, each separate lump of hot
+      carbide is isolated from its neighbours by a material which is also a very
+      bad heat conductor; and the heat has but little opportunity of
+      distributing itself evenly. Moreover, although iron or steel is a notably
+      better conductor of heat than any of the other substances present in the
+      carbide vessel, it is, as a metal, only a poor conductor, being
+      considerably inferior in this respect to copper. If heat dissipation were
+      the only point to be studied in the construction of an acetylene
+      apparatus, far better results might be obtained by the employment of
+      copper for the walls of the carbide container; and possibly in that case a
+      generator of considerable size, fitted with a water- jacketed decomposing
+      vessel, might be free from the trouble of overheating. Nevertheless it
+      will be seen in Chapter VI. that the use of copper is not permissible for
+      such purposes, its advantages as a good conductor of heat being
+      neutralised by its more important defects.
+    </p>
+    <p>
+      When suitable precautions are not taken to remove the heat liberated in an
+      acetylene apparatus, the temperature of the calcium carbide occasionally
+      rises to a remarkable degree. Investigating this point, Caro has studied
+      the phenomena of heat production in a "dipping" generator-- <i>i.e.</i>,
+      an apparatus in which a cage of carbide is alternately immersed in and
+      lifted out of a vessel containing water. Using a generator designed to
+      supply five burners, he has found a maximum recording thermometer placed
+      in the gas space of the apparatus to give readings generally between 60�
+      and 100� C.; but in two tests out of ten he obtained temperatures of about
+      160� C. To determine the actual temperature of the calcium carbide itself,
+      he scattered amongst the carbide charge fragments of different fusible
+      metallic alloys which were known to melt or soften at certain different
+      temperatures. In all his ten tests the alloys melting at 120� C. were
+      fused completely; in two tests other alloys melting at 216� and 240� C.
+      showed signs of fusion; and in one test an alloy melting at 280� C. began
+      to soften. Working with an experimental apparatus constructed on the
+      "dripping" principle-- <i>i.e.</i>, a generator in which water is allowed
+      to fall in single drops or as a fine stream upon a mass of carbide--with
+      the deliberate object of ascertaining the highest temperatures capable of
+      production when calcium carbide is decomposed in this particular fashion,
+      and employing for the measurement of the heat a Le Chatelier
+      thermo-couple, with its sensitive wires lying among the carbide lumps,
+      Lewes has observed a maximum temperature of 674� C. to be reached in 19
+      minutes when water was dripped upon 227 grammes of carbide at a speed of
+      about 8 grammes per minute. In other experiments he used a laboratory
+      apparatus designed upon the "dipping" principle, and found maximum
+      temperatures, in four different trials, of 703�, 734�, 754�, and 807� C.,
+      which were reached in periods of time ranging from 12 to 17 minutes. Even
+      allowing for the greater delicacy of the instrument adopted by Lewes for
+      measuring the temperature in comparison with the device employed by Caro,
+      there still remains an astonishing difference between Caro's maximum of
+      280� and Lewes' maximum of 807� C. The explanation of this discrepancy is
+      to be inferred from what has just been said. The generator used by Caro
+      was properly made of metal, was quite small in size, was properly designed
+      with some skill to prevent overheating as much as possible, and was worked
+      at the speed for which it was intended--in a word, it was as good an
+      apparatus as could be made of this particular type. Lewes' generator was
+      simply a piece of glass and metal, in which provisions to avoid
+      overheating were absent; and therefore the wide difference between the
+      temperatures noted does not suggest any inaccuracy of observation or
+      experiment, but shows what can be done to assist in the dissipation of
+      heat by careful arrangement of parts. The difference in temperature
+      between the acetylene and the carbide in Caro's test accentuates the
+      difficulty of gauging the heat in a carbide vessel by mere external touch,
+      and supplies experimental proof of the previous assertions as to the low
+      heat-conducting power of calcium carbide and of the gases of the
+      decomposing vessel. It must not be supposed that temperatures such as
+      Lewes has found ever occur in any commercial generator of reasonably good
+      design and careful construction; they must be regarded rather as
+      indications of what may happen in an acetylene apparatus when the
+      phenomena accompanying the evolution of gas are not understood by the
+      maker, and when all the precautions which can easily be taken to avoid
+      excessive heating have been omitted, either by building a generator with
+      carbide in excess too large in size, or by working it too rapidly, or more
+      generally by adopting a system of construction unsuited to the ends in
+      view. The fact, however, that Lewes has noted the production of a
+      temperature of 807� C. is important; because this figure is appreciably
+      above the point 780� C., at which acetylene decomposes into its elements
+      in the absence of air.
+    </p>
+    <p>
+      Nevertheless the production of a temperature somewhat exceeding 100� C.
+      among the lumps of carbide actually undergoing decomposition can hardly be
+      avoided in any practical generator. Based on a suggestion in the "Report
+      of the Committee on Acetylene Generators" which was issued by the British
+      Home Office in 1902, Fouch� has proposed that 130� C., as measured with
+      the aid of fusible metallic rods, [Footnote: An alloy made by melting
+      together 55 parts by weight of commercial bismuth and 45 parts of lead
+      fuses at 127� C., and should be useful in performing the tests.] should be
+      considered the maximum permissible temperature in any part of a generator
+      working at full speed for a prolonged period of time. Fouch� adopts this
+      figure on the ground that 130� C. sensibly corresponds with the
+      temperature at which a yellow substance is formed in a generator by a
+      process of polymerisation; and, referring to French conditions, states
+      that few actual apparatus permit the development of so high a temperature.
+      As a matter of fact, however, a fairly high temperature among the carbide
+      is less important than in the gas, and perhaps it would be better to say
+      that the temperature in any part of a generator occupied by acetylene
+      should not exceed 100� C. Fraenkel has carried out some experiments upon
+      the temperature of the acetylene immediately after evolution in a
+      water-to-carbide apparatus containing the carbide in a subdivided
+      receptacle, using an apparatus now frequently described as belonging to
+      the "drawer" system of construction. When a quantity of about 7 lb. of
+      carbide was distributed between 7 different cells of the receptacle, each
+      cell of which had a capacity of 25 fluid oz., and the apparatus was caused
+      to develop acetylene at the rate of 7 cubic feet per hour, maximum
+      thermometers placed immediately over the carbide in the different cells
+      gave readings of from 70� to 90� C., the average maximum temperature being
+      about 80� C. Hence the Austrian code of rules issued in 1905 governing the
+      construction of acetylene apparatus contains a clause to the effect that
+      the temperature in the gas space of a generator must never exceed 80� C.;
+      whereas the corresponding Italian code contains a similar stipulation, but
+      quotes the maximum temperature as 100� C. (<i>vide</i> Chapter IV.).
+    </p>
+    <p>
+      It is now necessary to see why the production of an excessively high
+      temperature in an acetylene generator has to be avoided. It must be
+      avoided, because whenever the temperature in the immediate neighbourhood
+      of a mass of calcium carbide which is evolving acetylene under the attack
+      of water rises materially above the boiling-point of water, one or more of
+      three several objectionable effects is produced--(<i>a</i>) upon the gas
+      generated, (<i>b</i>) upon the carbide decomposed, and (<i>c</i>) upon the
+      general chemical reaction taking place.
+    </p>
+    <p>
+      It has been stated above that in moat generators when the action between
+      the carbide and the water is proceeding smoothly, it occurs according to
+      equation (2)--
+    </p>
+    <p>
+      (2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2
+    </p>
+    <p>
+      rather than in accordance with equation (1)--
+    </p>
+    <p>
+      (1) CaC_2 + H_2O = C_2H_2 + CaO.
+    </p>
+    <p>
+      This is because calcium oxide, or quicklime, the by-product in (1), has
+      considerable affinity for water, evolving a noteworthy quantity of heat
+      when it combines with one molecule of water to form one molecule of
+      calcium hydroxide, or slaked lime, the by-product in (2). If, then, a
+      small amount of water is added to a large amount of calcium carbide, the
+      corresponding quantity of acetylene may be liberated on the lines of
+      equation (1), and there will remain behind a mixture of unaltered calcium
+      carbide, together with a certain amount of calcium oxide. Inasmuch as both
+      these substances possess an affinity for water (setting heat free when
+      they combine with it), when a further limited amount of water is
+      introduced into the mixture some of it will probably be attracted to the
+      oxide instead of to the carbide present. It is well known that at ordinary
+      temperatures quicklime absorbs moisture, or combines with water, to
+      produce slaked lime; but it is equally well known that in a furnace, at
+      about a red heat, slaked lime gives up water and changes into quicklime.
+      The reaction, in fact, between calcium oxide and water is reversible, and
+      whether those substances combine or dissociate is simply a question of
+      temperature. In other words, as the temperature rises, the heat of
+      hydration of calcium oxide diminishes, and calcium hydroxide becomes
+      constantly a less stable material. If now it should happen that the
+      affinity between calcium carbide and water should not diminish, or should
+      diminish in a lower ratio than the affinity between calcium oxide and
+      water as the temperature of the mass rises from one cause or other, it is
+      conceivable that at a certain temperature calcium carbide might be capable
+      of withdrawing the water of hydration from the molecule of slaked lime,
+      converting the latter into quicklime, and liberating one molecule of
+      acetylene, thus--
+    </p>
+    <p>
+      (3) CaC_2 + Ca_2(OH) = C_2H_2 + 2CaO.
+    </p>
+    <p>
+      It has been proved that a reaction of this character does occur, the
+      temperature necessary to determine it being given by Lewes as from 420� to
+      430� C., which is not much more than half that which he found in a
+      generator having carbide in excess, albeit one of extremely bad design.
+      Treating this reaction in the manner previously adopted, the thermo-
+      chemical phenomena of equation (3) are:
+    </p>
+<pre xml:space="preserve">
+_Heat liberated._              | _Heat liberated._
+                               |
+Formation of 2CaO       290.0  | Formation of acetylene         58.1
+                               | Decomposition of Ca(OH)_2 [1] 229.1
+                               | Decomposition of carbide        3.9
+        Balance           1.1  |
+                       ______  |                               _____
+                               |
+                        291.1  |                               291.1
+</pre>
+    <p>
+      [1 Footnote: Into its elements, Ca, O_2, and H_2; <i>cf.</i> footnote, p:
+      31.]
+    </p>
+    <p>
+      Or, since the calcium hydroxide is only dehydrated without being entirely
+      decomposed, and only one molecule of water is broken up, it may be
+      written:
+    </p>
+<pre xml:space="preserve">
+Formation of CaO         145.0 | Formation of acetylene         58.1
+                               | Decomposition of Ca(OH)_2      15.1
+                               | Decomposition of water         69.0
+        Balance            1.1 | Decomposition of carbide        3.9
+                         _____ |                               _____
+                               |
+                         146.1 |                               146.1
+</pre>
+    <p>
+      which comes to the same thing. Putting the matter in another shape, it may
+      be said that the reaction between calcium carbide and water is exothermic,
+      evolving either 14.0 or 29.1 calories according as the byproduct is
+      calcium oxide or solid calcium hydroxide; and therefore either reaction
+      proceeds without external assistance in the cold. The reaction between
+      carbide and slaked lime, however, is endothermic, absorbing 1.1 calories;
+      and therefore it requires external assistance (presence of an elevated
+      temperature) to start it, or continuous introduction of heat (as from the
+      reaction between the rest of the carbide present and the water) to cause
+      it to proceed. Of itself, and were it not for the disadvantages attending
+      the production of a temperature remotely approaching 400� C. in an
+      acetylene generator, which disadvantages will be explained in the
+      following paragraphs, there is no particular reason why reaction (3)
+      should not be permitted to occur, for it involves (theoretically) no loss
+      of acetylene, and no waste of calcium carbide. Only one specific feature
+      of the reaction has to be remembered, and due practical allowance made for
+      it. The reaction represented by equation (2) proceeds almost
+      instantaneously when the calcium carbide is of ordinarily good quality,
+      and the acetylene resulting therefrom is wholly generated within a very
+      few minutes. Equation (3), on the contrary, consumes much time for its
+      completion, and the gas corresponding with it is evolved at a gradually
+      diminishing speed which may cause the reaction to continue for hours--a
+      circumstance that may be highly inconvenient or quite immaterial according
+      to the design of the apparatus. When, however, it is desired to construct
+      an automatic acetylene generator, <i>i.e.</i>, an apparatus in which the
+      quantity of gas liberated has to be controlled to suit the requirements of
+      any indefinite number of burners in use on different occasions, equation
+      (3) becomes a very important factor in the case. To determine the normal
+      reaction (No. 2) of an acetylene generator, 64 parts by weight of calcium
+      carbide must react with 36 parts of water to yield 26 parts by weight of
+      acetylene, and apparently both carbide and water are entirely consumed;
+      but if opportunity is given for the occurrence of reaction (3), another 64
+      parts by weight of carbide may be attacked, without the addition of any
+      more water, producing, inevitably, another 26 parts of acetylene. If,
+      then, water is in chemical excess in the generator, all the calcium
+      carbide present will be decomposed according to equation (2), and the
+      action will take place without delay; after a few minutes' interval the
+      whole of the acetylene capable of liberation will have been evolved, and
+      nothing further can possibly happen until another charge of carbide is
+      inserted in the apparatus. If, on the other hand, calcium carbide is in
+      chemical excess in the generator, all the water run in will be consumed
+      according to equation (2), and this action will again take place without
+      delay; but unless the temperature of the residual carbide has been kept
+      well below 400� C., a further evolution of gas will occur which will not
+      cease for an indeterminate period of time, and which, by strict theory,
+      given the necessary conditions, might continue until a second volume of
+      acetylene equal to that liberated at first had been set free. In practice
+      this phenomenon of a secondary production of gas, which is known as
+      "after-generation," is regularly met with in all generators where the
+      carbide is in excess of the water added; but the amount of acetylene so
+      evolved rarely exceeds one-quarter or one-third of the main make. The
+      actual amount evolved and the rate of evolution depend, not merely upon
+      the quantity of undecomposed carbide still remaining in contact with the
+      damp lime, but also upon the rapidity with which carbide naturally
+      decomposes in presence of liquid water, and the size of the lumps. Where
+      "after-generation" is caused by the ascent of water vapour round lumps of
+      carbide, the volume of gas produced in a given interval of time is largely
+      governed by the temperature prevailing and the shape of the apparatus. It
+      is evident that even copious "after-generation" is a matter of no
+      consequence in any generator provided with a holder to store the gas,
+      assuming that by some trustworthy device the addition of water is stopped
+      by the time that the holder is two-thirds or three-quarters full. In the
+      absence of a holder, or if the holder fitted is too small to serve its
+      proper purpose, "aftergeneration" is extremely troublesome and sometimes
+      dangerous, but a full discussion of this subject must be postponed to the
+      next chapter.
+    </p>
+    <p>
+      EFFECT OF HEAT ON ACETYLENE.--The effect of excessive retention of heat in
+      an acetylene generator upon the gas itself is very marked, as acetylene
+      begins spontaneously to suffer change, and to be converted into other
+      compounds at elevated temperatures. Being a purely chemical phenomenon,
+      the behaviour of acetylene when exposed to heat will be fully discussed in
+      Chapter VI. when the properties of the gas are being systematically dealt
+      with. Here it will be sufficient to assume that the character of the
+      changes taking place is understood, and only the practical results of
+      those changes as affecting the various components of an acetylene
+      installation have to be studied. According to Lewes, acetylene commences
+      to "polymerise" at a temperature of about 600� C., when it is converted
+      into other hydrocarbons having the same percentage composition, but
+      containing more atoms of carbon and hydrogen in their molecules. The
+      formula of acetylene is C_2H_2 which means that 2 atoms of carbon and 2
+      atoms of hydrogen unite to form 1 molecule of acetylene, a body evidently
+      containing roughly 92.3 per cent. by weight of carbon and 7.7 per cent. by
+      weight of hydrogen. One of the most noteworthy substances produced by the
+      polymerisation of acetylene is benzene, the formula of which is C_6H_6,
+      and this is formed in the manner indicated by the equation--
+    </p>
+    <p>
+      (4) 3C_2H_2 = C_6H_6.
+    </p>
+    <p>
+      Now benzene also contains 92.3 per cent. of carbon and 7.7 per cent. by
+      weight of hydrogen in its composition, but its molecule contains 6 atoms
+      of each element. When the chemical formula representing a compound body
+      indicates a substance which is, or can be obtained as, a gas or vapour, it
+      convoys another idea over and above those mentioned on a previous page.
+      The formula "C_2H_2," for example, means 1 molecule, or 26 parts by weight
+      of acetylene, just as "H_2" means 1 molecule, or 2 parts by weight of
+      hydrogen; but both formul� also mean equal parts by volume of the
+      respective substances, and since H_2 must mean 2 volumes, being twice H,
+      which is manifestly 1, C_2H_2 must mean 2 volumes of acetylene as well.
+      Thus equation (4) states that 6 volumes of acetylene, or 3 x 26 parts by
+      weight, unite to form 2 volumes of benzene, or 78 parts by weight. If
+      these hydrocarbons are burnt in air, both are indifferently converted into
+      carbon dioxide (carbonic acid gas) and water vapour; and, neglecting for
+      the sake of simplicity the nitrogen of the atmosphere, the processes may
+      be shown thus:
+    </p>
+    <p>
+      (5) 2C_2H_2 + 5O_2 = 4CO_2 + 2H_2O.
+    </p>
+    <p>
+      (6) 2C_6H_6 + 15O_2 = 12CO_2 + 6H_2O.
+    </p>
+    <p>
+      Equation (5) shows that 4 volumes of acetylene combine with 10 volumes of
+      oxygen to produce 8 volumes of carbon dioxide and 4 of water vapour; while
+      equation (6) indicates that 4 volumes of benzene combine with 30 volumes
+      of oxygen to yield 24 volumes of carbon dioxide and 12 of water vapour.
+      Two parts by volume of acetylene therefore require 5 parts by volume of
+      oxygen for perfect combustion, whereas two parts by volume of benzene need
+      15--<i>i.e.</i>, exactly three times as much. In order to work
+      satisfactorily, and to develop the maximum of illuminating power from any
+      kind of gas consumed, a gas-burner has to be designed with considerable
+      skill so as to attract to the base of the flame precisely that volume of
+      air which contains the quantity of oxygen necessary to insure complete
+      combustion, for an excess of air in a flame is only less objectionable
+      than a deficiency thereof. If, then, an acetylene burner is properly
+      constructed, as most modern ones are, it draws into the flame air
+      corresponding with two and a half volumes of oxygen for every one volume
+      of acetylene passing from the jets; whereas if it were intended for the
+      combustion of benzene vapour it would have to attract three times that
+      quantity. Since any flame supplied with too little air tends to emit free
+      carbon or soot, it follows that any well-made acetylene burner delivering
+      a gas containing benzene vapour will yield a more or lens smoky flame
+      according to the proportion of benzene in the acetylene. Moreover, at
+      ordinary temperatures benzene is a liquid, for it boils at 81� C., and
+      although, as was explained above in the case of water, it is capable of
+      remaining in the state of vapour far below its boiling-point so long as it
+      is suspended in a sufficiency of some permanent gas like acetylene, if the
+      proportion of vapour in the gas at any given temperature exceeds a certain
+      amount the excess will be precipitated in the liquid form; while as the
+      temperature falls the proportion of vapour which can be retained in a
+      given volume of gas also diminishes to a noteworthy extent. Should any
+      liquid, be it water or benzene, or any other substance, separate from the
+      acetylene under the influence of cold while the gas is passing through
+      pipes, the liquid will run downwards to the lowest points in those pipes;
+      and unless due precautions are taken, by the insertion of draw-off cocks,
+      collecting wells, or the like, to withdraw the deposited water or other
+      liquid, it will accumulate in all bends, angles, and dips till the pipes
+      are partly or completely sealed against the passage of gas, and the lights
+      will either "jump" or be extinguished altogether. In the specific case of
+      an acetylene generator this trouble is very likely to arise, even when the
+      gas is not heated sufficiently during evolution for polymerisation to
+      occur and benzene or other liquid hydrocarbons to be formed, because any
+      excess of water present in the decomposing vessel is liable to be
+      vaporised by the heat of the reaction--as already stated it is desirable
+      that water shall be so vaporised--and will remain safely vaporised as long
+      as the pipes are kept warm inside or near the generator; but directly the
+      pipes pass away from the hot generator the cooling action of the air
+      begins, and some liquid water will be immediately produced. Like the
+      phenomenon of after- generation, this equally inevitable phenomenon of
+      water condensation will be either an inconvenience or source of positive
+      danger, or will be a matter of no consequence whatever, simply as the
+      whole acetylene installation, including the service-pipes, is ignorantly
+      or intelligently built.
+    </p>
+    <p>
+      As long as nothing but pure polymerisation happens to the acetylene, as
+      long, that is to say, as it is merely converted into other hydrocarbons
+      also having the general formula C_(2n)H_(2n), no harm will be done to the
+      gas as regards illuminating power, for benzene burns with a still more
+      luminous flame than acetylene itself; nor will any injury result to the
+      gas if it is required for combustion in heating or cooking stoves beyond
+      the fact that the burners, luminous or atmospheric, will be delivering a
+      material for the consumption of which they are not properly designed. But
+      if the temperature should rise much above the point at which benzene is
+      the most conspicuous product of polymerisation, other far more complicated
+      changes occur, and harmful effects may be produced in two separate ways.
+      Some of the new hydrocarbons formed may interact to yield a mixture of one
+      or more other hydrocarbons containing a higher proportion of carbon than
+      that which is present in acetylene and benzene, together with a
+      corresponding proportion of free hydrogen; the former will probably be
+      either liquids or solids, while the latter burns with a perfectly
+      non-luminous flame. Thus the quantity of gas evolved from the carbide and
+      passed into the holder is less than it should be, owing to the
+      condensation of its non-gaseous constituents. To quote an instance of
+      this, Haber has found 15 litres of acetylene to be reduced in volume to 10
+      litres when the gas was heated to 638� C. By other changes, some
+      "saturated hydrocarbons," <i>i.e.</i>, bodies having the general formula
+      C_nH_(2n+2), of which methane or marsh-gas, CH_4 is the best known, may be
+      produced; and those all possess lower illuminating powers than acetylene.
+      In two of those experiments already described, where Lewes observed
+      maximum temperatures ranging from 703� to 807� C., samples of the gas
+      which issued when the heat was greatest were submitted to chemical
+      analysis, and their illuminating powers were determined. The figures he
+      gives are as follows:
+    </p>
+<pre xml:space="preserve">
+                                     I.         II.
+                                  Per Cent.   Per Cent.
+       Acetylene                    70.0        69.7
+       Saturated hydrocarbons       11.3        11.4
+       Hydrogen                     18.7        18.9
+                                   _____       _____
+
+                                   100.0       100.0
+</pre>
+    <p>
+      The average illuminating power of these mixed gases is about 126 candles
+      per 5 cubic feet, whereas that of pure acetylene burnt under good
+      laboratory conditions is 240 candles per 5 cubic feet. The product, it
+      will be seen, had lost almost exactly 50 per cent. of its value as an
+      illuminant, owing to the excessive heating to which it had been, exposed.
+      Some of the liquid hydrocarbons formed at the same time are not limpid
+      fluids like benzene, which is less viscous than water, but are thick oily
+      substances, or even tars. They therefore tend to block the tubes of the
+      apparatus with great persistence, while the tar adheres to the calcium
+      carbide and causes its further attack by water to be very irregular, or
+      even altogether impossible. In some of the very badly designed generators
+      of a few years back this tarry matter was distinctly visible when the
+      apparatus was disconnected for recharging, for the spent carbide was
+      exceptionally yellow, brown, or blackish in colour, [Footnote: As will be
+      pointed out later, the colour of the spent lime cannot always be employed
+      as a means for judging whether overheating has occurred in a generator.]
+      and the odour of tar was as noticeable as that of crude acetylene.
+    </p>
+    <p>
+      There is another effect of heat upon acetylene, more calculated to be
+      dangerous than any of those just mentioned, which must not be lost sight
+      of. Being an endothermic substance, acetylene is prone to decompose into
+      its elements--
+    </p>
+    <p>
+      (7) C_2H_2 -> C_2 + H_2
+    </p>
+    <p>
+      whenever it has the opportunity; and the opportunity arrives if the
+      temperature of the gas risen to 780� C., or if the pressure under which
+      the gas is stored exceeds two atmospheres absolute (roughly 30 lb. per
+      square inch). It decomposes, be it carefully understood, in the complete
+      absence of air, directly the smallest spark of red-hot material or of
+      electricity, or directly a gentle shock, such as that of a fall or blow on
+      the vessel holding it, is applied to any volume of acetylene existing at a
+      temperature exceeding 780� or at a gross pressure of 30 lb. per square
+      inch; and however large that volume may be, unless it is contained in
+      tubes of very small diameter, as will appear hereafter, the decomposition
+      or dissociation into its elements will extend throughout the whole of the
+      gas. Equation (7) states that 2 volumes of acetylene yield 2 volumes of
+      hydrogen and a quantity of carbon which would measure 2 volumes were it
+      obtained in the state of gas, but which, being a solid, occupies a space
+      that may be neglected. Apparently, therefore, the dissociation of
+      acetylene involves no alteration in volume, and should not exhibit
+      explosive effects. This is erroneous, because 2 volumes of acetylene only
+      yield exactly 2 volumes of hydrogen when both gases are measured at the
+      same temperature, and all gases increase in volume as their temperature
+      rises. As acetylene is endothermic and evolves much heat on decomposition,
+      and as that heat must primarily be communicated to the hydrogen, it
+      follows that the latter must be much hotter than the original acetylene;
+      the hydrogen accordingly strives to fill a much larger space than that
+      occupied by the undecomposed gas, and if that gas is contained in a closed
+      vessel, considerable internal pressure will be set up, which may or may
+      not cause the vessel to burst.
+    </p>
+    <p>
+      What has been said in the preceding paragraph about the temperature at
+      which acetylene decomposes is only true when the gas is free from any
+      notable quantity of air. In presence of air, acetylene inflames at a much
+      lower temperature, viz., 480� C. In a manner precisely similar to that of
+      all other combustible gases, if a stream of acetylene issues into the
+      atmosphere, as from the orifices of a burner, the gas catches fire and
+      burns quietly directly any substance having a temperature of 480� C. or
+      upwards is brought near it; but if acetylene in bulk is mixed with the
+      necessary quantity of air to support combustion, and any object exceeding
+      480� C. in temperature comes in contact with it, the oxidation of the
+      hydrocarbon proceeds at such a high rate of speed as to be termed an
+      explosion. The proportion of air needed to support combustion varies with
+      every combustible material within known limits (<i>cf.</i> Chapter VI.),
+      and according to Eitner the smallest quantity of air required to make
+      acetylene burn or explode, as the case may be, is 25 per cent. If, by
+      ignorant design or by careless manipulation, the first batches of
+      acetylene evolved from a freshly charged generator should contain more
+      than 25 per cent. of air; or if in the inauguration of a new installation
+      the air should not be swept out of the pipes, and the first makes of gas
+      should become diluted with 25 to 50 per cent. of air, any glowing body
+      whose temperature exceeds 480� C. will fire the gas; and, as in the former
+      instance, the flame will extend all through the mass of acetylene with
+      disastrous violence and at enormous speed unless the gas is stored in
+      narrow pipes of extremely small diameter. Three practical lessons are to
+      be learnt from this circumstance: first, tobacco-smoking must never be
+      permitted in any building where an escape of raw acetylene is possible,
+      because the temperature of a lighted cigar, &amp;c., exceeds 480� C.;
+      secondly, a light must never be applied to a pipe delivering acetylene
+      until a proper acetylene burner has been screwed into the aperture;
+      thirdly, if any appreciable amount of acetylene is present in the air, no
+      operation should be performed upon any portion of an acetylene plant which
+      involves such processes as scraping or chipping with the aid of a steel
+      tool or shovel. If, for example, the iron or stoneware sludge-pipe is
+      choked, or the interior of the dismantled generator is blocked, and
+      attempts are made to remove the obstruction with a hard steel tool, a
+      spark is very likely to be formed which, granting the existence of
+      sufficient acetylene in the air, is perfectly able to fire the gas. For
+      all such purposes wooden implements only are best employed; but the remark
+      does not apply to the hand-charging of a carbide-to-water generator
+      through its proper shoot. Before passing to another subject, it may be
+      remarked that a quantity of air far less than that which causes acetylene
+      to become dangerous is objectionable, as its presence is apt to reduce the
+      illuminating power of the gas unduly.
+    </p>
+    <p>
+      EFFECT OF HEAT ON CARBIDE.--Chemically speaking, no amount of heat
+      possible of attainment in the worst acetylene generator can affect calcium
+      carbide in the slightest degree, because that substance may be raised to
+      almost any temperature short of those distinguishing the electric furnace,
+      without suffering any change or deterioration. In the absence of water,
+      calcium carbide is as inert a substance as can well be imagined: it cannot
+      be made to catch fire, for it is absolutely incombustible, and it can be
+      heated in any ordinary flame for reasonable periods of time, or thrown
+      into any non-electrical furnace without suffering in the least. But in
+      presence of water, or of any liquid containing water, matters are
+      different. If the temperature of an acetylene generator rises to such an
+      extent that part of the gas is polymerised into tar, that tar naturally
+      tends to coat the residual carbide lumps, and, being greasy in character,
+      more or less completely protects the interior from further attack. Action
+      of this nature not only means that the acetylene is diminished in quantity
+      and quality by partial decomposition, but it also means that the make is
+      smaller owing to imperfect decomposition of the carbide: while over and
+      above this is the liability to nuisance or danger when a mass of solid
+      residue containing some unaltered calcium carbide is removed from the
+      apparatus and thrown away. In fact, whenever the residue of a generator is
+      not so saturated with excess of water as to be of a creamy consistency, it
+      should be put into an uncovered vessel in the open air, and treated with
+      some ten times its volume of water before being run into any drain or
+      closed pipe where an accumulation of acetylene may occur. Even at
+      temperatures far below those needed to determine a production of tar or an
+      oily coating on the carbide, if water attacks an excess of calcium carbide
+      somewhat rapidly, there is a marked tendency for the carbide to be "baked"
+      by the heat produced; the slaked lime adhering to the lumps as a hard skin
+      which greatly retards the penetration of more water to the interior.
+    </p>
+    <p>
+      COLOUR OF SPENT CARBIDE.--In the early days of the industry, it was
+      frequently taken for granted that any degradation in the colour of the
+      spent lime left in an acetylene generator was proof that overheating had
+      taken place during the decomposition of the carbide. Since both calcium
+      oxide and hydroxide are white substances, it was thought that a brownish,
+      greyish, or blackish residue must necessarily point to incipient
+      polymerisation of the gas. This view would be correct if calcium carbide
+      were prepared in a state of chemical purity, for it also is a white body.
+      Commercial carbide, however, is not pure; it usually contains some foreign
+      matter which tints the residue remaining after gasification. When a
+      manufacturer strives to give his carbide the highest gas-making power
+      possible he frequently increases the proportion of carbon in the charge
+      submitted to electric smelting, until a small excess is reached, which
+      remains in the free state amongst the finished carbide. After
+      decomposition the fine particles of carbon stain the moist lime a bluish
+      grey tint, the depth of shade manifestly depending upon the amount
+      present. If such a sludge is copiously diluted with water, particles of
+      carbon having the appearance and gritty or flaky nature of coke often rise
+      to the surface or fall to the bottom of the liquid; whence they can easily
+      be picked out and identified as pure or impure carbon by simple tests.
+      Similarly the lime or carbon put into the electric furnace may contain
+      small quantities of compounds which are naturally coloured; and which,
+      reappearing in the sludge either in their original or in a different state
+      of combination, confer upon the sludge their characteristic tinge. Spent
+      lime of a yellowish brown colour is frequently to be met with in
+      circumstances that are clearly no reproach to the generator. Doubtless the
+      tint is due to the presence of some coloured metallic oxide or other
+      compound which has escaped reduction in the electric furnace. The colour
+      which the residual lime afterwards assumes may not be noticeable in the
+      dry carbide before decomposition, either because some change in the
+      colour-giving impurity takes place during the chemical reactions in the
+      generator or because the tint is simply masked by the greyish white of the
+      carbide and its free carbon. Hence it follows that a bad colour in the
+      waste lime removed from a generator only points to overheating and
+      polymerisation of the acetylene when corroborative evidence is
+      obtained--such as a distinct tarry smell, the actual discovery of oily or
+      tarry matters elsewhere, or a grave reduction in the illuminating power of
+      the gas.
+    </p>
+    <p>
+      MAXIMUM ATTAINABLE TEMPERATURES.--In order to discover the maximum
+      temperature which can be reached in or about an acetylene generator when
+      an apparatus belonging to one of the best types is fed at a proper rate
+      with calcium carbide in lumps of the most suitable size, the following
+      calculation may be made. In the first place, it will be assumed that no
+      loss of heat by radiation occurs from the walls of the generator;
+      secondly, the small quantity of heat taken up by the calcium hydroxide
+      produced will be ignored; and, thirdly, the specific heat of acetylene
+      will be assumed to be 0.25, which is about its most probable value. Now, a
+      hand-fed carbide-to-water generator will work with half a gallon of water
+      for every 1 lb. of carbide decomposed, quantities which correspond with
+      320 grammes of water per 64 grammes (1 molecular weight) of carbide. Of
+      those 320 grammes of water, 18 are chemically destroyed, leaving 302. The
+      decomposition of 64 grammes of commercial carbide evolves 28 large
+      calories of heat. Assuming all the heat to be absorbed by the water, 28
+      calories would raise 302 grammes through (28 X 1000 / 302) = 93� C., <i>i.e.</i>,
+      from 44.6� F. to the boiling-point. Assuming all the heat to be
+      communicated to the acetylene, those 28 calories would raise the 26
+      grammes of gas liberated through (28 X 1000 / 26 / 0.25) = 4308� C., if
+      that were possible. But if, as would actually be the case, the heat were
+      distributed uniformly amongst the 302 grammes of water and the 20 grammes
+      of acetylene, both gas and water would be raised through the same number
+      of degrees, viz., 90.8� C. [Footnote: Let x = the number of large calories
+      absorbed by the water; then 28 - x = those taken up by the gas. Then--
+    </p>
+    <p>
+      1000x / 302 = 1000 (28 - x) / (26 X 0.25)
+    </p>
+    <p>
+      whence x = 27.41; and 28 - x = 0.59.
+    </p>
+    <p>
+      Therefore, for water, the rise in temperature is--
+    </p>
+    <p>
+      27.41 X 1000 / 302 = 90.8� C.;
+    </p>
+    <p>
+      and for acetylene the rise is--
+    </p>
+    <p>
+      0.59 X 1000 / 26 / 0.25 = 90.8� C.]
+    </p>
+    <p>
+      If the generator were designed on lines to satisfy the United States Fire
+      Underwriters, it would contain 8.33 lb. of water to every 1 lb. of carbide
+      attacked; identical calculations then showing that the original
+      temperature of the water and gas would be raised through 53.7� C. Provided
+      the carbide is not charged into such an apparatus in lumps of too large a
+      size, nor at too high a rate, there will be no appreciable amount of local
+      overheating developed; and nowhere, therefore, will the rise in
+      temperature exceed 91� in the first instance, or 54� C. in the second.
+      Indeed it will be considerably smaller than this, because a large
+      proportion of the heat evolved will be lost by radiation through the
+      generator walls, while another portion will be converted from sensible
+      into latent heat by causing part of the water to pass off as vapour with
+      the acetylene.
+    </p>
+    <p>
+      EFFECT OF HIGH TEMPERATURES ON GENERATORS.--As the temperature amongst the
+      carbide in any generator in which water is not present in large excess may
+      easily reach 200� C. or upwards, no material ought to be employed in the
+      construction of such generators which is not competent to withstand a
+      considerable amount of heat in perfect safety. The ordinary varieties of
+      soft solder applied with the bitt in all kinds of light metal-work usually
+      melt, according to their composition, at about 180� C.; and therefore this
+      method of making joints is only suitable for objects that are never raised
+      appreciably in temperature above the boiling-point of water. No joint in
+      an acetylene generator, the partial or complete failure of which would
+      radically affect the behaviour of the apparatus, by permitting the charges
+      of carbide and of water to come into contact at an abnormal rate of speed,
+      by allowing the acetylene to escape directly through the crack into the
+      atmosphere, or by enabling the water to run out of the seal of any vessel
+      containing gas so as to set up a free communication between that vessel
+      and the air, ought ever to be made of soft solder--every joint of this
+      character should be constructed either by riveting, by bolting, or by
+      doubly folding the metal sheets. Apparently, a joint constantly immersed
+      in water on one side cannot rise in temperature above the boiling-point of
+      the liquid, even when its other side is heated strongly; but since, even
+      if a generator is not charged with naturally hard water, its fluid
+      contents soon become "hard" by dissolution of lime, there is always a
+      liability to the deposition of water scale over the joint. Such water
+      scale is a very bad heat conductor, as is seen in steam boilers, so that a
+      seam coated with an exceedingly thin layer of scale, and heated sharply on
+      one side, will rise above the boiling-point of water even if the liquid on
+      its opposite side is ice-cold. For a while the film of scale may be quite
+      water-tight, but after it has been heated by contact with the hot metal
+      several times it becomes brittle and cracks without warning. But there is
+      a more important reason for avoiding the use of plumbers' solder. It might
+      seem that as the natural hard, protective skin of the metal is liable to
+      be injured or removed by the bending or by the drilling or punching which
+      precedes the insertion of the rivets or studs, an application of soft
+      solder to such a joint should be advantageous. This is not true because of
+      the influence of galvanic action. As all soft solders consist largely of
+      lead, if a joint is soldered, a "galvanic couple" of lead and iron, or of
+      lead and zinc (when the apparatus is built of galvanised steel), is
+      exposed to the liquid bathing it; and since in both cases the lead is
+      highly electro-negative to the iron or zinc, it is the iron or zinc which
+      suffers attack, assuming the liquid to possess any corrosive properties
+      whatever. Galvanised iron which has been injured during the joint-making
+      presents a zinc-iron couple to the water, but the zinc protects the iron;
+      if a lead solder is present, the iron will begin to corrode immediately
+      the zinc has disappeared. In the absence of lead it is the less important
+      metal, but in the presence of lead it is the more important (the
+      foundation) metal which is the soluble element of the couple. Where
+      practicable, joints in an acetylene generator may safely be made by
+      welding or by autogenous soldering ("burning"), because no other metal is
+      introduced into the system; any other process, except that of riveting or
+      folding, only hastens destruction of the plant. The ideal method of making
+      joints about an acetylene generator is manifestly that of autogenous
+      soldering, because, as will appear in Chapter IX. of this book, the most
+      convenient and efficient apparatus for performing the operation is the
+      oxy-acetylene blow-pipe, which can be employed so as to convert two
+      separate pieces of similar metal into one homogeneous whole.
+    </p>
+    <p>
+      In less critical situations in an acetylene plant, such as the partitions
+      of a carbide container, &amp;c., where the collapse of the seam or joint
+      would not be followed by any of the effects previously suggested, there is
+      less cause for prohibiting the use of unfortified solder; but even here,
+      two or three rivets, just sufficient to hold the metal in position if the
+      solder should give way, are advisedly put into all apparatus. In other
+      portions of an acetylene installation where a merely soldered joint is
+      exposed to warm damp gas which is in process of cooling, instead of being
+      bathed in hard water, an equal, though totally dissimilar, danger is
+      courted. The main constituent of such solders that are capable of being
+      applied with the bitt is lead; lead is distinctly soluble in soft or pure
+      water; and the water which separates by condensation out of a warm damp
+      gas is absolutely soft, for it has been distilled. If condensation takes
+      place at or near a soldered joint in such a way that water trickles over
+      the solder, by slow degrees the metallic lead will be dissolved and
+      removed, and eventually a time will come when the joint is no longer tight
+      to gas. In fact, if an acetylene installation is of more than very small
+      dimensions, <i>e.g.</i>, when it is intended to supply any building as
+      large as, or larger than, the average country residence, if it is to give
+      satisfaction to both constructor and purchaser by being quite trustworthy
+      and, possessed of a due lease of life, say ten or fifteen years, it must
+      be built of stouter materials than the light sheets which alone are
+      suitable for manipulation with the soldering-iron or for bending in the
+      ordinary type of metal press. Sound cast-iron, heavy sheet-metal, or light
+      boiler-plate is the proper substance of which to construct all the
+      important parts of a generator, and the joints in wrought metal must be
+      riveted and caulked or soldered autogeneously as mentioned above. So
+      built, the installation becomes much more costly to lay down than an
+      apparatus composed of tinplate, zinc, or thin galvanised iron, but it will
+      prove more economical in the long run. It is not too much to say that if
+      ignorant and short-sighted makers in the earliest days of the acetylene
+      industry had not recommended and supplied to their customers lightly built
+      apparatus which has in many instances already begun to give trouble, to
+      need repairs, and to fail by thorough corrosion--apparatus which
+      frequently had nothing but cheapness in its favour--the use of the gas
+      would have spread more rapidly than it has done, and the public would not
+      now be hearing of partial or complete failures of acetylene installations.
+      Each of these failures, whether accompanied by explosions and injury to
+      persons or not, acts more powerfully to restrain a possible new customer
+      from adopting the acetylene light, than several wholly successful plants
+      urge him to take it up; for the average member of the public is not in a
+      position to distinguish properly between the collapse of a certain
+      generator owing to defective design or construction (which reflects no
+      discredit upon the gas itself), and the failure of acetylene to show in
+      practice those advantages that have been ascribed to it. One peculiar and
+      noteworthy feature of acetylene, often overlooked, is that the apparatus
+      is constructed by men who may have been accustomed to gas-making plant all
+      their lives, and who may understand by mere habit how to superintend a
+      chemical operation; but the same apparatus is used by persons who
+      generally have no special acquaintance with such subjects, and who, very
+      possibly, have not even burnt coal-gas at any period of their lives. Hence
+      it happens that when some thoughtless action on the part of the country
+      attendant of an acetylene apparatus is followed by an escape of gas from
+      the generator, and by an accumulation of that gas in the house where the
+      plant is situated, or when, in disregard of rules, he takes a naked light
+      into the house and an explosion follows, the builder dismisses the episode
+      as a piece of stupidity or wilful misbehaviour for which he can in nowise
+      be held morally responsible; whereas the builder himself is to blame for
+      designing an apparatus from which an escape of gas can be accompanied by
+      sensible risks to property or life. However unpalatable this assertion may
+      be, its truth cannot be controverted; because, short of criminal intention
+      or insanity on the part of the attendant, it is in the first place a mere
+      matter of knowledge and skill so to construct an acetylene plant that an
+      escape of gas is extremely unlikely, even when the apparatus is opened for
+      recharging, or when it is manipulated wrongly; and in the second place, it
+      is easy so to arrange the plant that any disturbance of its functions
+      which may occur shall be followed by an immediate removal of the surplus
+      gas into a place of complete safety outside and above the generator-house.
+    </p>
+    <p>
+      GENERATION AT LOW TEMPERATURES.--In all that has been said hitherto about
+      the reaction between calcium carbide and water being instantaneous, it has
+      been assumed that the two substances are brought together at or about the
+      usual temperature of an occupied room, <i>i.e.</i>, 15 degrees C. If,
+      however, the temperature is materially lower than this, the speed of the
+      reaction falls off, until at -5 degrees C., supposing the water still to
+      remain liquid, evolution of acetylene practically ceases. Even at the
+      freezing-point of pure water gas is produced but slowly; and if a lump of
+      carbide is thrown on to a block of ice, decomposition proceeds so gently
+      that the liberated acetylene may be ignited to form a kind of torch, while
+      heat is generated with insufficient rapidity to cause the carbide to sink
+      into the block. This fact has very important bearings upon the
+      manipulation of an acetylene generator in winter time. It is evident that
+      unless precautions are taken those portions of an apparatus which contain
+      water are liable to freeze on a cold night; because, even if the generator
+      has been at work producing gas (and consequently evolving heat) till late
+      in the evening, the surplus heat stored in the plant may escape into the
+      atmosphere long before more acetylene has to be made, and obviously while
+      frost is still reigning in the neighbourhood. If the water freezes in the
+      water store, in the pipes leading therefrom, in the holder seal, or in the
+      actual decomposing chamber, a fresh batch of gas is either totally
+      incapable of production, because the water cannot be brought into contact
+      with the calcium carbide in the apparatus, or it can only be generated
+      with excessive slowness because the carbide introduced falls on to solid
+      ice. Theoretically, too, there is a possibility that some portion of the
+      apparatus--a pipe in particular--may be burst by the freezing, owing to
+      the irresistible force with which water expands when it changes into the
+      solid condition. Probably this last contingency, clearly accompanied as it
+      would be by grave risk, is somewhat remote, all the plant being
+      constructed of elastic material; but in practice even a simple
+      interference with the functions of a generator by freezing, ideally of no
+      special moment, is highly dangerous, because of the great likelihood that
+      hurried and wholly improper attempts to thaw it will be made by the
+      attendant. As it has been well known for many years that the solidifying
+      point of water can be lowered to almost any degree below normal freezing
+      by dissolving in it certain salts in definite proportions, one of the
+      first methods suggested for preventing the formation of ice in an
+      acetylene generator was to employ such a salt, using, in fact, for the
+      decomposition of the carbide some saline solution which remains liquid
+      below the minimum night temperature of the winter season. Such a process,
+      however, has proved unsuitable for the purpose in view; and the
+      explanation of that fact is found in what has just been stated: the
+      "water" of the generator may admittedly be safely maintained in the fluid
+      state, but from so cold a liquid acetylene will not be generated smoothly,
+      if at all. Moreover, were it not so, a process of this character is
+      unnecessarily expensive, although suitable salts are very cheap, for the
+      water of the generator is constantly being consumed, [Footnote: It has
+      already been said that most generators "consume" a much larger volume of
+      water than the amount corresponding with the chemical reaction involved:
+      the excess of water passing into the sludge or by- product. Thus a
+      considerable quantity of any anti-freezing agent must be thrown aside each
+      time the apparatus is cleaned out or its fluid contents are run off.] and
+      as constantly needs renewal; which means that a fresh batch of salt would
+      be required every time the apparatus was recharged, so long as frost
+      existed or might be expected. A somewhat different condition obtains in
+      the holder of an acetylene installation. Here, whenever the holder is a
+      separate item in the plant, not constituting a portion of the generating
+      apparatus, the water which forms the seal of a rising holder, or which
+      fills half the space of a displacement holder, lasts indefinitely; and it
+      behaves equally well, whatever its temperature may be, so long as it
+      retains a fluid state. This matter will be discussed with greater detail
+      at the end of Chapter III. At present the point to be insisted on is that
+      the temperature in any constituent of an acetylene installation which
+      contains water must not be permitted to fall to the freezing-point; while
+      the water actually used for decomposition must be kept well above that
+      temperature.
+    </p>
+    <p>
+      GENERATION AT HIGH TEMPERATURES.--At temperatures largely exceeding those
+      of the atmosphere, the reaction between calcium carbide and water tends to
+      become irregular; while at a red heat steam acts very slowly upon carbide,
+      evolving a mixture of acetylene and hydrogen in place of pure acetylene.
+      But since at pressures which do not materially exceed that of the
+      atmosphere, water changes into vapour at 100� C., above that temperature
+      there can be no question of a reaction between carbide and liquid water.
+      Moreover, as has been pointed out, steam or water vapour will continue to
+      exist as such at temperatures even as low as the freezing-point so long as
+      the vapour is suspended among the particles of a permanent gas. Between
+      calcium carbide and water vapour a double decomposition occurs chemically
+      identical with that between carbide and liquid water; but the physical
+      effect of the reaction and its practical bearings are considerably
+      modified. The quantity of heat liberated when 30 parts by weight of steam
+      react with 64 parts of calcium carbide should be essentially unaltered
+      from that evolved when the reagent is in the liquid state; but the
+      temperature likely to be attained when the speed of reaction remains the
+      same as before will be considerably higher for two conspicuous reasons. In
+      the first place, the specific heat of steam in is only 0.48, while that of
+      liquid water is 1.0. Hence, the quantity of heat which is sufficient to
+      raise the temperature of a given weight of liquid water through <i>n</i>
+      thermometric degrees, will raise the temperature of the same weight of
+      water vapour through rather more than 2 <i>n</i> degrees. In the second
+      place, that relatively large quantity of heat which in the case of liquid
+      water merely changes the liquid into a vapour, becoming "latent" or
+      otherwise unrecognisable, and which, as already shown, forms roughly
+      five-sixths of the total heat needed to convert cold water into steam, has
+      no analogue if the water has previously been vaporised by other means; and
+      therefore the whole of the heat supplied to water vapour raises its
+      sensible temperature, as indicated by the thermometer. Thus it appears
+      that, except for the sufficient amount of cooling that can be applied to a
+      large vessel containing carbide by surrounding it with a water jacket,
+      there is no way of governing its temperature satisfactorily if water
+      vapour is allowed to act upon a mass of carbide--assuming, of course, that
+      the reaction proceeds at any moderate speed, <i>e.g.</i>, at a rate much
+      above that required to supply one or two burners with gas.
+    </p>
+    <p>
+      The decomposition which with perfect chemical accuracy has been stated to
+      occur quantitatively between 36 parts by weight, of water and 64 parts of
+      calcium carbide scarcely ever takes place in so simple a fashion in an
+      actual generator. Owing to the heat developed when carbide is in excess,
+      about half the water is converted into vapour; and so the reaction
+      proceeds in two stages: half the water added reacting with the carbide as
+      a liquid, the other half, in a state of vapour, afterwards reacting
+      similarly, [Footnote: This secondary reaction is manifestly only another
+      variety of the phenomenon known as "after-generation" (cf. <i>ante</i>).
+      After-generation is possible between calcium carbide and mechanically damp
+      slaked lime, between carbide and damp gas, or between carbide and calcium
+      hydroxide, as opportunity shall serve. In all cases the carbide must be in
+      excess.] or hardly reacting at all, as the case may be. Suppose a vessel,
+      A B, somewhat cylindrical in shape, is charged with carbide, and that
+      water is admitted at the end called A. Suppose now (1) that the exit for
+      gas is at the opposite end, B. As the lumps near A are attacked by half
+      the liquid introduced, while the other half is changed into steam, a
+      current, of acetylene and water vapour travels over the charge lying
+      between the decomposing spot and the end B. During its passage the second
+      half of the water, as vapour, reacts with the excess of carbide, the first
+      make of acetylene being dried, and more gas being produced. Thus a second
+      quantity of heat is developed, equal by theory to that previously evolved;
+      but a second elevation in temperature, far more serious, and far less
+      under control, than the former also occurs; and this is easily sufficient
+      to determine some of those undesirable effects already described.
+      Digressing for a moment, it may be admitted that the desiccation of the
+      acetylene produced in this manner is beneficial, even necessary; but the
+      advantages of drying the gas at this period of its treatment are
+      outweighed by the concomitant disadvantages and by the later inevitable
+      remoistening thereof. Suppose now (2) that both the water inlet and the
+      gas exit of the carbide cylinder are at the same end, A. Again half the
+      added water, as liquid, reacts with the carbide it first encounters, but
+      the hot stream of damp gas is not permitted to travel over the rest of the
+      lumps extending towards B: it is forced to return upon its steps, leaving
+      B practically untouched. The gas accordingly escapes from the cylinder at
+      A still loaded with water vapour, and for a given weight of water
+      introduced much less acetylene is evolved than in the former case. The
+      gas, too, needs drying somewhere else in the plant; but these defects are
+      preferable to the apparent superiority of the first process because
+      overheating is, or can be, more thoroughly guarded against.
+    </p>
+    <p>
+      PRESSURE IN GENERATORS.--Inasmuch as acetylene is prone to dissociate or
+      decompose into its elements spontaneously whenever its pressure reaches 2
+      atmospheres or 30 lb. per square inch, as well as when its temperature at
+      atmospheric pressure attains 780� C., no pressure approaching that of 2
+      atmospheres is permissible in the generator. A due observance of this
+      rule, however, unlike a proper maintenance of a low temperature in an
+      acetylene apparatus, is perfectly easy to arrange for. The only reason for
+      having an appreciable positive pressure in any form of generating plant is
+      that the gas may be compelled to travel through the pipes and to escape
+      from the burner orifices; and since the plant is only installed to serve
+      the burners, that pressure which best suits the burners must be thrown by
+      the generator or its holder. Therefore the highest pressure it is ever
+      requisite to employ in a generator is a pressure sufficient (<i>a</i>) to
+      lift the gasholder bell, or to raise the water in a displacement holder, (<i>b</i>)
+      to drive the gas through the various subsidiary items in the plant, such
+      as washers and purifiers, (<i>c</i>) to overcome the friction in the
+      service-pipes, [Footnote: This friction manifestly causes a loss of
+      pressure, <i>i.e.</i>, a fall in pressure, as a gas travels along a pipe;
+      and, as will be shown in Chapter VII., it is the fall in pressure in a
+      pipe rather than the initial pressure at which a gas enters a pipe that
+      governs the volume of gas passing through that pipe. The proper behaviour
+      and economic working of a burner (acetylene or other, luminous or
+      incandescent) naturally depend upon the pressure in the pipe to which the
+      burner is immediately attached being exactly suited to the design of that
+      burner, and have nothing to do with the fall in pressure occurring in the
+      delivery pipes. It is therefore necessary to keep entirely separate the
+      ideas of proper burner pressure and of maximum desirable fall in pressure
+      within the service due to friction.] and (d) to give at the points of
+      combustion a pressure which is required by the particular burners adopted.
+      In all except village or district installations, (<i>c</i>) may be
+      virtually neglected. When the holder has a rising bell, (<i>a</i>)
+      represents only an inch or so of water; but if a displacement holder is
+      employed the pressure needed to work it is entirely indeterminate, being
+      governed by the size and shape of the said holder. It will be argued in
+      Chapter III. that a rising holder is always preferable to one constructed
+      on the displacement principle. The pressure (d) at the burners may be
+      taken at 4 inches of water as a maximum, the precise figure being
+      dependent upon the kind of burners--luminous, incandescent, boiling, &amp;c.--attached
+      to the main. The pressure (<i>b</i>) also varies according to
+      circumstances, but averages 2 or 3 inches. Thus a pressure in the
+      generator exceeding that of the atmosphere by some 12 inches of water--<i>i.e.</i>,
+      by about 7 oz., or less than half a pound per square inch--is amply
+      sufficient for every kind of installation, the less meritorious generators
+      with displacement holders only excepted. This pressure, it should be
+      noted, is the net or effective pressure, the pressure with which the gas
+      raises the liquid in a water-gauge glass out of the level while the
+      opposite end of the water column is exposed to the atmosphere. The
+      absolute pressure in a vessel containing gas at an effective pressure of
+      12 inches of water is 7 oz. plus the normal, insensible pressure of the
+      atmosphere itself--say 15-1/4 lb. per square inch. The liquid in a
+      barometer which measures the pressure of the atmosphere stands at a height
+      of 30 inches only, because that liquid is mercury, 13.6 times as heavy as
+      water. Were it filled with water the barometer would stand at (30 X 13.6)
+      = 408 inches, or 34 feet, approximately. Gas pressures are always measured
+      in inches of water column, because expressed either as pounds per square
+      inch or as inches of mercury, the figures would be so small as to give
+      decimals of unwieldy length.
+    </p>
+    <p>
+      It would of course be perfectly safe so to arrange an acetylene plant that
+      the pressure in the generating chamber should reach the 100 inches of
+      water first laid down by the Home Office authorities as the maximum
+      allowable. There is, however, no appreciable advantage to be gained by so
+      doing, or by exceeding that pressure which feeds the burners best. Any
+      higher original pressure involves the use of a governor at the exit of the
+      plant, and a governor is a costly and somewhat troublesome piece of
+      apparatus that can be dispensed with in most single installations by a
+      proper employment of a well-balanced rising holder. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkiii" id="iii">CHAPTER III</a>
+    </h2>
+    <h3>
+      THE GENERAL PRINCIPLES OF ACETYLENE GENERATION--ACETYLENE GENERATING
+      APPARATUS
+    </h3>
+    <p>
+      Inasmuch as acetylene is produced by the mere interaction of calcium
+      carbide and water, that is to say, by simply bringing those two substances
+      in the cold into mutual contact within a suitable closed space, and
+      inasmuch as calcium carbide can always be purchased by the consumer in a
+      condition perfectly fit for immediate decomposition, the preparation of
+      the gas, at least from the theoretical aspect, is characterised by extreme
+      simplicity. A cylinder of glass or metal, closed at one end and open at
+      the other, filled with water, and inverted in a larger vessel containing
+      the same liquid, may be charged almost instantaneously with acetylene by
+      dropping into the basin a lump of carbide, which sinks to the bottom,
+      begins to decompose, and evolves a rapid current of gas, displacing the
+      water originally held in the inverted cylinder or "bell." If a very minute
+      hole is drilled in the top of the floating bell, acetylene at once escapes
+      in a steady stream, being driven out by the pressure of the cylinder, the
+      surplus weight of which causes it to descend into the water of the basin
+      as rapidly as gas issues from the orifice. As a laboratory experiment, and
+      provided the bell has been most carefully freed from atmospheric air in
+      the first instance, this escaping gas may be set light to with a match,
+      and will burn with a more or loss satisfactory flame of high illuminating
+      power. Such is an acetylene generator stripped of all desirable or
+      undesirable adjuncts, and reduced to its most elementary form; but it is
+      needless to say that so simple an apparatus would not in any way fulfil
+      the requirements of everyday practice.
+    </p>
+    <p>
+      Owing to the inequality of the seasons, and to the irregular nature of the
+      demand for artificial light and heat in all households, the capacity of
+      the plant installed for the service of any institution or district must be
+      amply sufficient to meet the consumption of the longest winter
+      evening--for, as will be shown in the proper place, attempts to make an
+      acetylene generator evolve gas more quickly than it is designed to do are
+      fraught with many objections--while the operation of the plant, must be
+      under such thorough control that not only can a sudden and unexpected
+      demand for gas be met without delay, but also that a sudden and unexpected
+      interruption or cessation of the demand shall not be followed by any
+      disturbance in the working of the apparatus. Since, on the one hand,
+      acetylene is produced in large volumes immediately calcium carbide is
+      wetted with water, so that the gas may be burnt within a minute or two of
+      its first evolution; and, on the other, that acetylene once prepared can
+      be stored without trouble or appreciable waste for reasonable periods of
+      time in a water-sealed gasholder closely resembling, in everything but
+      size, the holders employed on coal-gas works; it follows that there are
+      two ways of bringing the output of the plant into accord with the
+      consumption of the burners. It is possible to make the gas only as and
+      when it is required, or it is possible in the space of an hour or so,
+      during the most convenient part of the day, to prepare sufficient to last
+      an entire evening, storing it in a gasholder till the moment arrives for
+      its combustion. It is clear that an apparatus needing human attention
+      throughout the whole period of activity would be intolerable in the case
+      of small installations, and would only be permissible in the case of
+      larger ones if the district supplied with gas was populous enough to
+      justify the regular employment of two men at least in or about the
+      generating station. But with the conditions obtaining in such a country as
+      Great Britain, and in other lands where coal is equally cheap and
+      accessible, if a neighbourhood was as thickly populated as has been
+      suggested, it would be preferable on various grounds to lay down a coal-
+      gas or electricity works; for, as has been shown in the first chapter,
+      unless a very material fall in the price of calcium carbide should take
+      place--a fall which at present is not to be expected--acetylene can only
+      be considered a suitable and economical illuminant and heating agent for
+      such places as cannot be provided cheaply with coal-gas or electric
+      current. To meet this objection, acetylene generators have been invented
+      in which, broadly speaking, gas is only produced when it is required,
+      control of the chemical reaction devolving upon some mechanical
+      arrangement. There are, therefore, two radically different types of
+      acetylene apparatus to be met with, known respectively as "automatic" and
+      "non-automatic" generators. In a non-automatic generator the whole of the
+      calcium carbide put into the apparatus is more or less rapidly decomposed,
+      and the entire volume of gas evolved from it is collected in a holder,
+      there to await the moment of consumption. In an automatic apparatus, by
+      means of certain devices which will be discussed in their proper place,
+      the act of turning on a burner-tap causes some acetylene to be produced,
+      and the act of turning it off brings the reaction to an end, thus
+      obviating the necessity for storage. That, at any rate, is the logical
+      definition of the two fundamentally different kinds of generator: in
+      automatic apparatus the decomposition of the carbide is periodically
+      interrupted in such fashion as more or less accurately to synchronise with
+      the consumption of gas; in the non-automatic variety decomposition
+      proceeds without a break until the carbide vessels are empty.
+      Unfortunately a somewhat different interpretation of these two words has
+      found frequent acceptance, a generator being denominated non-automatic or
+      automatic according as the holder attached to it is or is not large enough
+      to store the whole of the acetylene which the charge of carbide is capable
+      of producing if it is decomposed all at once. Apart from the fact that a
+      holder, though desirable, is not an absolutely indispensable part of an
+      acetylene plant, the definition just quoted was sufficiently free from
+      objection in the earliest days of the industry; but now efficient
+      commercial generators are to be met with which become either automatic or
+      non-automatic according to the manner of working them, while some would be
+      termed non-automatic which comprise mechanism of a conspicuously self-
+      acting kind.
+    </p>
+    <p>
+      AUTOMATIC AND NON-AUTOMATIC GENERATORS.--Before proceeding to a detailed
+      description of the various devices which may be adopted to render an
+      acetylene generator automatic in action, the relative advantages of
+      automatic and non-automatic apparatus, irrespective of type, from the
+      consumer's point of view may be discussed. The fundamental idea underlying
+      the employment of a non-automatic generator is that the whole of the
+      calcium carbide put into the apparatus shall be decomposed into acetylene
+      as soon after the charge is inserted as is natural in the circumstances;
+      so that after a very brief interval of time the generating chambers shall
+      contain nothing but spent lime and water, and the holder be as full of gas
+      as is ever desirable. In an automatic apparatus, the fundamental idea is
+      that the generating chamber, or one at least of several generating
+      chambers, shall always contain a considerable quantity of undecomposed
+      carbide, and some receptacle always contain a store of water ready to
+      attack that carbide, so that whenever a demand for gas shall arise
+      everything may be ready to meet it. Inasmuch as acetylene is an
+      inflammable gas, it possesses all the properties characteristic of
+      inflammable gases in general; one of which is that it is always liable to
+      take fire in presence of a spark or naked light, and another of which is
+      that it is always liable to become highly explosive in presence of a naked
+      light or spark if, accidentally or otherwise, it becomes mixed with more
+      than a certain proportion of air. On the contrary, in the complete absence
+      of liquid or vaporised water, calcium carbide is almost as inert a body as
+      it is possible to imagine: for it will not take fire, and cannot in any
+      circumstances be made to explode. Hence it may be urged that a
+      non-automatic generator, with its holder always containing a large volume
+      of the actually inflammable and potentially explosive acetylene, must
+      invariably be more dangerous than an automatic apparatus which has less or
+      practically no ready-made gas in it, and which simply contains water in
+      one chamber and unaltered calcium carbide in another. But when the
+      generating vessels and the holder of a non-automatic apparatus are
+      properly designed and constructed, the gas in the latter is acetylene
+      practically free from air, and therefore while being, as acetylene
+      inevitably is, inflammable, is devoid of explosive properties, always
+      assuming, as must be the case in a water-sealed holder, that the
+      temperature of the gas is below 780� C.; and also assuming, as must always
+      be the case in good plant, that the pressure under which the gas is stored
+      remains less than two atmospheres absolute. It is perfectly true that
+      calcium carbide is non-inflammable and non-explosive, that it is
+      absolutely inert and incapable of change; but so comprehensive an
+      assertion only applies to carbide in its original drum, or in some
+      impervious vessel to which moisture and water have no access. Until it is
+      exhausted, an automatic acetylene generator contains carbide in one place
+      and water in another, dependence being put upon some mechanical
+      arrangement to prevent the two substances coming into contact prematurely.
+      Many of the devices adopted by builders of acetylene apparatus for keeping
+      the carbide and water separate, and for mixing them in the requisite
+      quantities when the proper time arrives, are as trustworthy, perhaps, as
+      it is possible for any automatic gear to be; but some are objectionably
+      complicated, and a few are positively inefficient. There are two
+      difficulties which the designer of automatic mechanism has to contend
+      with, and it is doubtful whether he always makes a sufficient allowance
+      for them. The first is that not only must calcium carbide and liquid water
+      be kept out of premature contact, but that moisture, or vapour of water,
+      must not be allowed to reach the carbide; or alternatively, that if water
+      vapour reaches the carbide too soon, the undesired reaction shall not
+      determine overheating, and the liberated gas be not wasted or permitted to
+      become a source of danger. The second difficulty encountered by the
+      designer of automata is so to construct his apparatus that it shall behave
+      well when attended to by completely unskilled labour, that it shall
+      withstand gross neglect and resist positive ill-treatment or
+      mismanagement. If the automatic principle is adopted in any part of an
+      acetylene apparatus it must be adopted throughout, so that as far as
+      possible--and with due knowledge and skill it is completely
+      possible--nothing shall be left dependent upon the memory and common sense
+      of the gasmaker. For instance, it must not be necessary to shut a certain
+      tap, or to manipulate several cocks before opening the carbide vessel to
+      recharge it; it must not be possible for gas to escape backwards out of
+      the holder; and either the carbide-feed gear or the water-supply mechanism
+      (as the case may be) must be automatically locked by the mere act of
+      taking the cover off the carbide store, or of opening the sludge-cock at
+      the bottom. It would be an advantage, even, if the purifiers and other
+      subsidiary items of the plant were treated similarly, arranging them in
+      such fashion that gas should be automatically prevented from escaping out
+      of the rest of the apparatus when any lid was removed. In fact, the
+      general notion of interlocking, which has proved so successful in railway
+      signal-cabins and in carburetted water gas-plant for the prevention of
+      accidents duo to carelessness or overnight, might be copied in principle
+      throughout an acetylene installation whenever the automatic system is
+      employed.
+    </p>
+    <p>
+      It is no part of the present argument, to allege that automatic generators
+      are, and must always be, inherently dangerous. Automatic devices of a
+      suitable kind may be found in plenty which are remarkably simple and
+      highly trustworthy; but it would be too bold a statement to say that any
+      such arrangement is incapable of failure, especially when put into the
+      hands of a person untrained in the superintendence of machinery. The more
+      reliable a piece of automatic mechanism proves itself to be, the more
+      likely is it to give trouble and inconvenience and utterly to destroy
+      confidence when it does break down; because the better it has behaved in
+      the past, and the longer it has lasted without requiring adjustment, the
+      less likely is it that the attendant will be at hand when failure occurs.
+      By suitable design and by an intelligent employment of safety-valves and
+      blow-off pipes (which will be discussed in their proper place) it is quite
+      easy to avoid the faintest possibility of danger arising from an increase
+      of pressure or an improper accumulation of gas inside the plant or inside
+      the building containing the plant; but every time such a safety-valve or
+      blow-off pipe comes into action a waste of gas occurs, which means a
+      sacrifice of economy, and shows that the generator is not working as it
+      should.
+    </p>
+    <p>
+      As glass is a fragile and brittle substance, and as it is not capable of
+      bearing large, rapid, and oft-repeated alterations of temperature in
+      perfect safety, it is not a suitable material for the construction of
+      acetylene apparatus or of portions thereof. Hence it follows that a
+      generator must be built of some non-transparent material which prevents
+      the interior being visible when the apparatus is at work. Although it is
+      comparatively easy, by the aid of a lamp placed outside the generator-
+      shed in such a position as to throw its beams of light through a window
+      upon the plant inside, to charge a generator after dark; and although it
+      is possible, without such assistance, by methodical habits and a
+      systematic arrangement of utensils inside the building to charge a
+      generator even in perfect darkness, such an operation is to be deprecated,
+      for it is apt to lead to mistakes, it prevents any slight derangement in
+      the installation from being instantly noticed, and it offers a temptation
+      to the attendant to break rules and to take a naked light with him. On all
+      those grounds, therefore, it is highly desirable that every manipulation
+      connected with a generator shall be effected during the daytime, and that
+      the apparatus-house shall be locked up before nightfall. But owing to the
+      irregular habits engendered by modern life it is often difficult to know,
+      during any given day, how much gas will be required in the ensuing
+      evening; and it therefore becomes necessary always to have, as ready-made
+      acetylene, or as carbide in a proper position for instant decomposition, a
+      patent or latent store of gas more than sufficient in quantity to meet all
+      possible requirements. Now, as already stated, a non-automatic apparatus
+      has its store of material in the form of gas in a holder; and since this
+      is preferably constructed on the rising or telescopic principle, a mere
+      inspection of the height of the bell--on which, if preferred, a scale
+      indicating its contents in cubic feet or in burner-hours may be
+      marked--suffices to show how near the plant is to the point of exhaustion.
+      In many types of automatic apparatus the amount of carbide remaining
+      undecomposed at any moment is quite unknown, or at best can only be
+      deduced by a tedious and inexact calculation; although in some generators,
+      where the store of carbide is subdivided into small quantities, or placed
+      in several different receptacles, an inspection of certain levers or
+      indicators gives an approximate idea as to the capacity of the apparatus
+      for further gas production. In any case the position of a rising holder is
+      the most obvious sign of the degree of exhaustion of a generator; and
+      therefore, to render absolutely impossible a failure of the light during
+      an evening, a non-automatic generator fitted with a rising holder is best.
+    </p>
+    <p>
+      Since calcium carbide is a solid body having a specific gravity of 2.2,
+      water being unity, and since 1 cubic foot of water weighs 62.4 lb., in
+      round numbers 137 lb. of <i>compact</i> carbide only occupy 1 cubic foot
+      of space. Again, since acetylene is a gas having a specific gravity of
+      0.91, air being unity, and since the specific gravity of air, water being
+      unity, is 0.0013, the specific gravity of acetylene, water being unity, is
+      roughly O.00116. Hence 1 cubic foot of acetylene weighs roughly 0.07 lb.
+      Furthermore, since 1 lb. of good carbide evolves 5 cubic feet of gas on
+      decomposition with water, acetylene stored at atmospheric pressure
+      occupies roundly 680 times as much space as the carbide from which it has
+      been evolved. This figure by no means represents the actual state of
+      affairs in a generator, because, as was explained in the previous chapter,
+      a carbide vessel cannot be filled completely with solid; and, indeed, were
+      it so "filled," in ordinary language, much of its space would be still
+      occupied with air. Nevertheless it is incontrovertible that an acetylene
+      plant calculated to supply so many burners for so long a period of time
+      must be very much larger if it is constructed on the non-automatic
+      principle, when the carbide is decomposed all at once, than if the
+      automatic system is adopted, when the solid remains unattacked until a
+      corresponding quantity of gas is required for combustion. Clearly it is
+      the storage part of a non-automatic plant alone which must be so much
+      larger; the actual decomposing chambers may be of the same size or even
+      smaller, according to the system of generation to which the apparatus
+      belongs. In practice this extra size of the non-automatic plant causes it
+      to exhibit two disadvantages in comparison with automatic apparatus,
+      disadvantages which are less serious than they appear, or than they may
+      easily be represented to be. In the first place, the non- automatic
+      generator requires more space for its erection. If acetylene were an
+      illuminating agent suitable for adoption by dwellers in city or suburb,
+      where the back premises and open-air part of the messuage are reduced to
+      minute proportions or are even non-existent, this objection might well be
+      fatal. But acetylene is for the inhabitant of a country village or the
+      occupier of an isolated country house; and he has usually plenty of space
+      behind his residence which he can readily spare. In the second place, the
+      extra size of the non-automatic apparatus makes it more expensive to
+      construct and more costly to instal. It is more cosily to construct and
+      purchase because of its holder, which must be well built on a firm
+      foundation and accurately balanced; it is more costly to instal because a
+      situation must be found for the erection of the holder, and the
+      apparatus-house may have to be made large enough to contain the holder as
+      well as the generator itself. As regards the last point, it may be said at
+      once that there is no necessity to place the holder under cover: it may
+      stand out of doors, as coal-gas holders do in England, for the seal of the
+      tank can easily be rendered frost-proof, and the gas itself is not
+      affected by changes of atmospheric temperature beyond altering somewhat in
+      volume. In respect of the other objections, it must be remembered that the
+      extra expense is one of capital outlay alone, and therefore only increases
+      the cost of the light by an inappreciable amount, representing interest
+      and depreciation charges on the additional capital expenditure. The
+      increased cost of a year's lighting due to these charges will amount to
+      only 10 or 15 per cent, on the additional capital sunk. The extra capital
+      sunk does not in any way increase the maintenance charges; and if, by
+      having a large holder, additional security and trustworthiness are
+      obtained, or if the holder leads to a definite, albeit illusive, sense of
+      extra security and trustworthiness, the additional expenditure may well be
+      permissible or even advantageous.
+    </p>
+    <p>
+      The argument is sometimes advanced that inasmuch as for the same, or a
+      smaller, capital outlay as is required to instal a non-automatic apparatus
+      large enough to supply at one charging the maximum amount of light and
+      heat that can ever be needed on the longest winter's night, an automatic
+      plant adequate to make gas for two or three evenings can be laid down, the
+      latter must be preferable, because the attendant, in the latter case, will
+      only need to enter the generator-house two or three times a week. Such an
+      argument is defective because it ignores the influence of habit upon the
+      human being. A watch which must be wound every day, or a clock which must
+      be wound every week, on a certain day of the week, is seldom permitted to
+      run down; but a watch requiring to be re-wound every other day, or a
+      fourteen-day clock (used as such), would rarely be kept going. Similarly,
+      an acetylene generator might be charged once a week or once a day without
+      likelihood of being forgotten; but the operation of charging at irregular
+      intervals would certainly prove a nuisance. With a non-automatic apparatus
+      containing all its gas in the holder, the attendant would note the
+      position of the bell each morning, and would introduce sufficient carbide
+      to fill the holder full, or partly full, as the case might be; with an
+      automatic apparatus he would be tempted to trust that the carbide holders
+      still contained sufficient material to last another night.
+    </p>
+    <p>
+      The automatic system of generating acetylene has undoubtedly one advantage
+      in those climates where frost tends to occur frequently, but only to
+      prevail for a short period. As the apparatus is in operation during the
+      evening hours, the heat evolved will, or can be made to, suffice to
+      protect the apparatus from freezing until the danger has passed; whereas
+      if the gas is generated of a morning in a non-automatic apparatus the
+      temperature of the plant may fall to that of the atmosphere before
+      evening, and some portion may freeze unless special precautions are taken
+      to protect it.
+    </p>
+    <p>
+      It was shown in Chapter II that overheating is one of the chief troubles
+      to be guarded against in acetylene generators, and that the temperature
+      attained is a function of the speed at which generation proceeds. Seeing
+      that in an automatic apparatus the rate of decomposition depends on the
+      rate at which gas is being burnt, while in a non-automatic generator it
+      is, or may be, under no control, the critic may urge that the reaction
+      must take place more slowly and regularly, and the maximum temperature
+      therefore be lower, when the plant works automatically. This may be true
+      if the non-automatic generator is unskilfully designed or improperly
+      manipulated; but it is quite feasible to arrange an apparatus, especially
+      one of the carbide-to-water or of the flooded-compartment type, in such
+      fashion that overheating to an objectionable extent is rendered wholly
+      impossible. In a non-automatic apparatus the holder is nothing but a
+      holder and may be placed wherever convenient, even at a distance from the
+      generating plant; in an automatic apparatus the holder, or a small
+      similarly constructed holder placed before the main storage vessel, has to
+      act as a water-supply governor, as the releasing gear for certain
+      carbide-food mechanism, or indeed as the motive power of such mechanism;
+      and accordingly it must be close to the water or carbide store, and more
+      or less intimately connected by means of levers, or the like, with the
+      receptacle in which decomposition occurs. Sometimes the holder surrounds,
+      or is otherwise an integral part of, the decomposing chamber, the whole
+      apparatus being made self-contained or a single structure with the object
+      of gaining compactness. But it is evident that such methods of
+      construction render additionally awkward, or even hazardous, any repair or
+      petty operation to the generating portion of the plant; while the more
+      completely the holder is isolated from the decomposing vessels the more
+      easily can they be cleaned, recharged, or mended, without blowing off the
+      stored gas and without interfering with the action of any burners that may
+      be alight at the time. Owing to the ingenuity of inventors, and the
+      experience they have acquired in the construction of automatic acetylene
+      apparatus during the years that the gas has been in actual employment, it
+      is going too far boldly to assert that non-automatic generators are
+      invariably to be preferred before their rivals. Still in view of the
+      nature of the labour which is likely to be bestowed on any domestic plant,
+      of the difficulty in having repairs or adjustments done quickly in
+      outlying country districts, and of the inconvenience, if not risk,
+      attending upon any failure of the apparatus, the greater capital outlay,
+      and the larger space required by non-automatic generators are in most
+      instances less important than the economy in space and prime cost
+      characteristic of automatic machines when the defects of each are weighed
+      fairly in the balance. Indeed, prolonged experience tends to show that a
+      selection between non-automatic and automatic apparatus may frequently be
+      made on the basis of capacity. A small plant is undoubtedly much more
+      convenient if automatic; a very large plant, such as that intended for a
+      public supply, is certainly better if non-automatic, but between these two
+      extremes choice may be exercised according to local conditions.
+    </p>
+    <p>
+      CONTROL OF THE CHEMICAL REACTION.--Coming now to study the principles
+      underlying the construction of an acetylene generator more closely it will
+      be seen that as acetylene is produced by bringing calcium carbide into
+      contact with water, the chemical reaction may be started either by adding
+      the carbide to the water, or by adding the water to the carbide.
+      Similarly, at least from the theoretical aspect, the reaction, may be
+      caused to stop by ceasing to add carbide to water, or by ceasing to add
+      water to carbide. Apparently if water is added by degrees to carbide,
+      until the carbide is exhausted, the carbide must always be in excess; and
+      manifestly, if carbide is added in small portions to water, the water must
+      always be in excess, which, as was argued in Chapter II., is emphatically
+      the more desirable position of affairs. But it in quite simple to have
+      carbide present in large excess of the water introduced when the whole
+      generator is contemplated, and yet to have the water always in chemical
+      excess in the desired manner; because to realise the advantages of having
+      water in excess, it is only necessary to subdivide the total charge of
+      carbide into a number of separate charges which are each so small that
+      more than sufficient water to decompose and flood one of them is permitted
+      to enter every time the feed mechanism comes into play, or (in a
+      non-automatic apparatus) every time the water-cock is opened; so arranging
+      the charges that each one is protected from the water till its
+      predecessor, or its predecessor, have been wholly decomposed. Thus it is
+      possible to regard either the carbide or the water as the substance which
+      has to be brought into contact with the other in specified quantity. It is
+      perhaps permissible to repeat that in the construction of an automatic
+      generator there is no advantage to be gained from regulating the supply of
+      both carbide and water, because just as the mutual decomposition will
+      begin immediately any quantity of the one meets any quantity of the other,
+      so the reaction will cease (except in one case owing to
+      "after-generation") directly the whole of that material which is not in
+      chemical excess has been consumed-quite independently of the amount of the
+      other material left unattacked. Being a liquid, and possessing as such no
+      definite shape or form of its own irrespective of the vessel in which it
+      is held, water is by far the more convenient of the two substances to move
+      about or to deliver in predetermined volume to the decomposing chamber. A
+      supply of water can be started instantaneously or cut oil as promptly by
+      the movement of a cock or valve of the usual description; or it may be
+      allowed to run down a depending pipe in obedience to the law of
+      gravitation, and stopped from running down such a pipe by opposing to its
+      passage a gas pressure superior to that gravitational force. In any one of
+      several obvious ways the supply of water to a mass of carbide may be
+      controlled with absolute certainty, and therefore it should apparently
+      follow that the make of acetylene should be under perfect control by
+      controlling the water current. On the other hand, unless made up into
+      balls or cartridges of some symmetrical form, calcium carbide exists in
+      angular masses of highly irregular shape and size. Its lumps alter in
+      shape and size directly liquid water or moisture reaches them; a loose
+      more or loss gritty powder, or a damp cohesive mud, being produced which
+      is well calculated to choke any narrow aperture or to jam any moving
+      valve. It is more difficult, therefore, by mechanical agency to add a
+      supply of carbide to a mass of water than to introduce a supply of water
+      to a stationary mass of carbide; and far more difficult still to bring the
+      supply of carbide under perfect control with the certainty that the
+      movement shall begin and stop immediately the proper time arrives.
+    </p>
+    <p>
+      But assuming the mechanical difficulties to be satisfactorily overcome,
+      the plan of adding carbide to a stationary mass of water has several
+      chemical advantages, first, because, however the generator be constructed,
+      water will be in excess throughout the whole time of gas production; and
+      secondly, because the evolution of acetylene will actually cease
+      completely at the moment when the supply of carbide is interrupted. There
+      is, however, one particular type of generator in which as a matter of fact
+      the carbide is the moving constituent, viz., the "dipping" apparatus (cf.
+      <i>infra</i>), to which these remarks do not apply; but this machine, as
+      will be seen directly, is, illogically perhaps, but for certain good
+      reasons, classed among the water-to-carbide apparatus. All the mechanical
+      advantages are in favour, as just indicated, of making water the moving
+      substance; and accordingly, when classified in the present manner, a great
+      majority of the generators now on the markets are termed water-to-carbide
+      apparatus. Their disadvantages are twofold, though these may be avoided or
+      circumvented: in all types save one the carbide is in excess at the
+      immediate place and time of decomposition; and in all types without
+      exception the carbide in the whole of the generator is in excess, so that
+      the phenomenon of "after- generation" occurs with more or less severity.
+      As explained in the last chapter, after-generation is the secondary
+      production of acetylene which takes place more or less slowly after the
+      primary reaction is finished, proceeding either between calcium hydroxide,
+      merely damp lime, or damp gas and calcium carbide, with an evolution of
+      more acetylene. As it is possible, and indeed usual, to fit a holder of
+      some capacity even to an automatic generator, the simple fact that more
+      acetylene is liberated after the main reaction is over does not matter,
+      for the gas can be safely stored without waste and entirely without
+      trouble or danger. The real objection to after-generation is the
+      difficulty of controlling the temperature and of dissipating the heat with
+      which the reaction is accompanied. It will be evident that the balance of
+      advantage, weighing mechanical simplicity against chemical superiority, is
+      somewhat even between carbide-to-water and water-to-carbide generators of
+      the proper type; but the balance inclines towards the former distinctly in
+      the ease of non-automatic apparatus, and points rather to the latter when
+      automatism is desired. In the early days of the industry it would have
+      been impossible to speak so favourably of automatic carbide-to-water
+      generators, for they were at first constructed with absurdly complicated
+      and unreliable mechanism; but now various carbide-feed gears have been
+      devised which seem to be trustworthy even when carbide not in cartridge
+      form is employed.
+    </p>
+    <p>
+      NON-AUTOMATIC CARBIDE-TO-WATER GENERATORS.--There is little to be said in
+      the present place about the principles underlying the construction of
+      non-automatic generators. Such apparatus may either be of the carbide-to-
+      water or the water-to-carbide type. In the former, lumps of carbide are
+      dropped by hand down a vertical or sloping pipe or shoot, which opens at
+      its lower end below the water-level of the generating chamber, and which
+      is fitted below its mouth with a deflector to prevent the carbide from
+      lodging immediately underneath that mouth. The carbide falls through the
+      water which stands in the shoot itself almost instantaneously, but during
+      its momentary descent a small quantity of gas is evolved, which produces
+      an unpleasant odour unless a ventilating hood is fixed above the upper end
+      of the tube. As the ratio of cubical contents to superficial area of a
+      lump is greater as the lump itself is larger, and as only the outer
+      surface of the lump can be attacked by the water in the shoot during its
+      descent, carbide for a hand-fed carbide-to-water generator should be in
+      fairly large masses--granulated material being wholly unsuitable--and this
+      quite apart from the fact that large carbide is superior to small in
+      gas-making capacity, inasmuch as it has not suffered the inevitable slight
+      deterioration while being crushed and graded to size. If carbide is
+      dropped too rapidly into such a generator which is not provided with a
+      false bottom or grid for the lumps to rest upon, the solid is apt to
+      descend among a mass of thick lime sludge produced at a former operation,
+      which lies at the bottom of the decomposing chamber; and here it may be
+      protected from the cooling action of fresh water to such an extent that
+      its surface is baked or coated with a hard layer of lime, while
+      overheating to a degree far exceeding the boiling-point of water may occur
+      locally. When, however, it falls upon a grid placed some distance above
+      the bottom of the water vessel, the various convection currents set up as
+      parts of the liquid become warm, and the mechanical agitations produced by
+      the upward current of gas rinse the spent lime from the carbide, and
+      entirely prevent overheating, unless the lumps are excessively large in
+      size. If the carbide charged into a hand-fed generator is in very large
+      lumps there is always a possibility that overheating may occur in the
+      centre of the masses, due to the baking of the exterior, even if the
+      generator is fitted with a reaction grid. Manifestly, when carbide in
+      lumps of reasonable size is dropped into excess of water which is not
+      merely a thick viscid cream of lime, the temperature cannot possibly
+      exceed the boiling-point--<i>i.e.</i>, 100� C.--provided always the
+      natural convection currents of the water are properly made use of.
+    </p>
+    <p>
+      The defect which is, or rather which may be, characteristic of a hand-fed
+      carbide-to-water generator is a deficiency of gas yield due to solubility.
+      At atmospheric temperatures and pressure 10 volumes of water dissolve 11
+      volumes of acetylene, and were the whole of the water in a large generator
+      run to waste often, a sensible loss of gas would ensue. If the carbide
+      falls nearly to the bottom of the water column, the rising gas is forced
+      to bubble through practically the whole of the liquid, so that every
+      opportunity is given it to dissolve in the manner indicated till the
+      liquid is completely saturated. The loss, however, is not nearly so
+      serious as is sometimes alleged, because (1) the water becomes heated and
+      so loses much of its solvent power; and (2) the generator is worked
+      intermittently, with sufficiently long intervals to allow the spent lime
+      to settle into a thick cream, and only that thick cream is run off, which
+      represents but a small proportion of the total water present. Moreover, a
+      hand-fed carbide-to-water generator will work satisfactorily with only
+      half a gallon [Footnote: The United States National Board of Fire
+      Underwriters stipulates for the presence of 1 (American) gallon of water
+      for every 1 lb. of carbide before such an apparatus is "permitted." This
+      quantity of liquid might retain nearly 4 per cent. of the total acetylene
+      evolved. Even this is an exaggeration; for neither her, nor in the
+      corresponding figure given in the text, is any allowance made for the
+      diminution in solvent power of the water as it becomes heated by the
+      reaction.] of liquid present for every 1 lb. of carbide decomposed, and
+      were all this water run off and a fresh quantity admitted before each
+      fresh introduction of carbide, the loss of acetylene by dissolution could
+      not exceed 2 per cent. of the total make, assuming the carbide to be
+      capable of yielding 5 cubic feet of gas per lb. Admitting, however, that
+      some loss of gas does occur in this manner, the defect is partly, if not
+      wholly, neutralised by the concomitant advantages of the system: (1)
+      granted that the generator is efficiently constructed, decomposition of
+      the carbide is absolutely complete, so that no loss of gas occurs in this
+      fashion; (2) the gas is evolved at a low temperature, so that it is
+      unaccompanied, by products of polymerisation, which may block the leading
+      pipes and must reduce the illuminating power; (3) the acetylene is not
+      mixed with air (as always happens at the first charging of a water-to-
+      carbide apparatus), which also lowers the illuminating power; and (4) the
+      gas is freed from two of its three chief impurities, viz., ammonia and
+      sulphuretted hydrogen, in the generating chamber itself. To prevent the
+      loss of acetylene by dissolution, carbide-to-water generators are
+      occasionally fitted with a reaction grid placed only just below the
+      water-level, so that the acetylene has no more than 1 inch or so of liquid
+      to bubble through. The principle is wrong, because hot water being lighter
+      than cold, the upper layers may be raised to the boiling-point, and even
+      converted into steam, while the bulk of the liquid still remains cold; and
+      if the water actually surrounding the carbide is changed into vapour,
+      nearly all control over the temperature attending the reaction is lost.
+    </p>
+    <p>
+      The hand-fed carbide-to-water generator is very simple and, as already
+      indicated, has proved itself perhaps the best type of all for the
+      construction of very large installations; but the very simplicity of the
+      generator has caused it more than once to be built in a manner that has
+      not given entire satisfaction. As shown at L in Fig. 6, p. 84, the
+      generator essentially consists of a closed cylindrical vessel
+      communicating at its top with a separate rising holder. At one side as
+      drawn, or disposed concentrically if so preferred, is an open-mouthed pipe
+      or shoot (American "shute") having its lower open extremity below the
+      water-level. Into this shoot are dropped by hand or shovel lumps of
+      carbide, which fall into the water and there suffer decomposition. As the
+      bottom of the shoot is covered with water, which, owing to the small
+      effective gas pressure in the generator given by the holder, stands a few
+      inches higher in the shoot than in the generator, gas cannot escape from
+      the shoot; because before it could do so the water in the generator would
+      have to fall below the level of the point <i>a</i>, being either driven
+      out through the shoot or otherwise. Since the point <i>b</i> of the shoot
+      extends further into the generator than <i>a</i>, the carbide drops
+      centrally, and as the bubbles of gas rise vertically, they have no
+      opportunity of ascending into the shoot. In practice, the generator is
+      fitted with a conical bottom for the collection of the lime sludge and
+      with a cock or other aperture at the apex of the cone for the removal of
+      the waste product. As it is not desirable that the carbide should be
+      allowed to fall directly from the shoot into the thicker portion of the
+      sludge within the conical part of the generator, one or more grids is
+      usually placed in the apparatus as shown by the dotted lines in the
+      sketch. It does not seem that there is any particular reason for the
+      employment of more than one grid, provided the size of the carbide
+      decomposed is suited to the generator, and provided the mesh of the grid
+      is suited to the size of the carbide. A great improvement, however, is
+      made if the grid is carried on a horizontal spindle in such a way that it
+      can be rocked periodically in order to assist in freeing the lumps of
+      carbide from the adhering particles of lime. As an alternative to the
+      movable grid, or even as an adjunct thereto, an agitator scraping the
+      conical sides of the generator may be fitted which also assists in
+      ensuring a reasonably complete absence of undecomposed carbide from the
+      sludge drawn off at intervals. A further point deserves attention. If
+      constructed in the ideal manner shown in Fig. 6 removal of some of the
+      sludge in the generator would cause the level of the liquid to descend
+      and, by carelessness, the level might fall below the point <i>a</i> at the
+      base of the shoot. In these circumstances, if gas were unable to return
+      from the holder, a pressure below that of the atmosphere would be
+      established in the gas space of the generator and air would be drawn in
+      through the shoot. This air might well prove a source of danger when
+      generation was started again. Any one of three plans may be adopted to
+      prevent the introduction of air. A free path may be left on the gas-main
+      passing from the generator to the holder so that gas may be free to return
+      and so to maintain the usual positive pressure in the decomposing vessel;
+      the sludge may be withdrawn into some vessel so small in capacity that the
+      shoot cannot accidentally become unsealed; or the waterspace of the
+      generator may be connected with a water-tank containing a ball-valve
+      attached to a constant service of water be that liquid runs in as quickly
+      as sludge is removed, and the level remains always at the same height. The
+      first plan is only a palliative and has two defects. In the first place,
+      the omission of any non-return valve between, the generator and the next
+      item in the train of apparatus is objectionable of itself; in the second
+      place, should a very careless attendant withdraw too much liquid, the
+      shoot might become unsealed and the whole contents of the holder be passed
+      into the air of the building containing the apparatus through the open
+      mouth of the shoot. The second plan is perfectly sound, but has the
+      practical defect of increasing the labour of cleaning the generator. The
+      third plan is obviously the best. It can indeed be adopted where no real
+      constant service of water is at hand by connecting the generator to a
+      water reservoir of relatively large size and by making the latter of
+      comparatively large transverse area, in proportion to its depth; so that
+      the escape of even a largo volume of water from the reservoir may not
+      involve a large reduction in the level at which it stands there.
+    </p>
+    <p>
+      The dust that always clings to lumps of carbide naturally decomposes with
+      extreme rapidity when the material is thrown into the shoot of a carbide-
+      to-water generator, and the sudden evolution of gas so produced has on
+      more than one occasion seriously alarmed the attendant on the plant.
+      Moreover, to a trifling extent the actual superficial layers of the
+      carbide suffer attack before the lumps reach the true interior of the
+      generator, and a small loss of gas thereby occurs through the open mouth
+      of the shoot. To remove these objections to the hand-fed generator it has
+      become a common practice in large installations to cause the lower end of
+      the shoot to dip under the level of some oil contained in an appropriate
+      receptacle, the carbide falling into a basket carried upon a horizontal
+      spindle. The basket and its support are so arranged that when a suitable
+      charge of carbide has been dropped into it, a partial rotation of an
+      external hand-wheel lifts the basket and carbide out of the oil into an
+      air-tight portion of the generator where the surplus oil can drain away
+      from the lumps. A further rotation of the hand-wheel then tips the basket
+      over a partition inside the apparatus, allowing the carbide to fall into
+      the actual decomposing chamber. This method of using oil has the advantage
+      of making the evolution of acetylene on a large scale appear to proceed
+      more quietly than usual, and also of removing the dust from the carbide
+      before it reaches the water of the generator. The oil itself obviously
+      does not enter the decomposing chamber to any appreciable extent and
+      therefore does not contaminate the final sludge. The whole process
+      accordingly lies to be favourably distinguished from those other methods
+      of employing oil in generators or in the treatment of carbide which are
+      referred to elsewhere in this book.
+    </p>
+    <p>
+      NON-AUTOMATIC WATER-TO-CARBIDE GENERATORS.--The only principle underlying
+      the satisfactory design of a non-automatic water-to-carbide generator is
+      to ensure the presence of water in excess at the spot where decomposition
+      is taking place. This may be effected by employing what is known as the
+      "flooded-compartment" system of construction, <i>i.e.</i>, by subdividing
+      the total carbide charge into numerous compartments arranged either
+      vertically or horizontally, and admitting the water in interrupted
+      quantities, each more than sufficient thoroughly to decompose and saturate
+      the contents of one compartment, rather than in a slow, steady stream. It
+      would be quite easy to manage this without adopting any mechanism of a
+      moving kind, for the water might be stored in a tank kept full by means of
+      a ball-valve, and admitted to an intermediate reservoir in a slow,
+      continuous current, the reservoir being fitted with an inverted syphon, on
+      the "Tantalus-cup" principle, so that it should first fill itself up, and
+      then suddenly empty into the pipe leading to the carbide container.
+      Without this refinement, however, a water-to-carbide generator, with
+      subdivided charge, behaves satisfactorily as long as each separate charge
+      of carbide is so small that the heat evolved on its decomposition can be
+      conducted away from the solid through the water- jacketed walls of the
+      vessel, or as the latent heat of steam, with sufficient rapidity. Still it
+      must be remembered that a water-to-carbide generator, with subdivided
+      charge, does not belong to the flooded- compartment type if the water runs
+      in slowly and continuously: it is then simply a "contact" apparatus, and
+      may or may not exhibit overheating, as well as the inevitable
+      after-generation. All generators of the water-to- carbide type, too, must
+      yield a gas containing some air in the earlier portions of their make,
+      because the carbide containers can only be filled one-third or one-half
+      full of solid. Although the proportion of air so passed into the holder
+      may be, and usually is, far too small in amount to render the gas
+      explosive or dangerous in the least degree, it may well be sufficient to
+      reduce the illuminating power appreciably until it is swept out of the
+      service by the purer gas subsequently generated. Moreover, all
+      water-to-carbide generators are liable, as just mentioned, to produce
+      sufficient overheating to lower the illuminating power of the gas whenever
+      they are wilfully driven too fast, or when they are reputed by their
+      makers to be of a higher productive capacity than they actually should be;
+      and all water-to-carbide generators, excepting those where the carbide is
+      thoroughly soaked in water at some period of their operation, are liable
+      to waste gas by imperfect decomposition.
+    </p>
+    <p>
+      DEVICES TO SECURE AUTOMATIC ACTION,--The devices which are commonly
+      employed to render a generator automatic in action, that is to say, to
+      control the supply of one of the two substances required in the
+      intermittent evolution of gas, may be divided into two broad classes: (A)
+      those dependent upon the position of a rising-holder bell, and (B) those
+      dependent upon the gas pressure inside the apparatus. As the bell of a
+      rising holder descends in proportion as its gaseous contents are
+      exhausted, it may (A^1) be fitted with some laterally projecting pin
+      which, arrived at a certain position, actuates a series of rods or levers,
+      and either opens a cock on the water-supply pipe or releases a mechanical
+      carbide-feed gear, the said cock being closed again or the feed-gear
+      thrown out of action when the pin, rising with the bell, once more passes
+      a certain position, this time in its upward path. Secondly (A^2), the bell
+      may be made to carry a perforated receptacle containing carbide, which is
+      dipped into the water of the holder tank each time the bell falls, and is
+      lifted out of the water when it rises again. Thirdly (A^3), by fitting
+      inside the upper part of the bell a false interior, conical in shape, the
+      descent of the bell may cause the level of the water in the holder tank to
+      rise until it is above some lateral aperture through which the liquid may
+      escape into a carbide container placed elsewhere. These three methods are
+      represented in the annexed diagram (Fig. 1). In Al the water-levels in the
+      tank and bell remain always at <i>l</i>, being higher in the tank than in
+      the bell by a distance corresponding with the pressure produced by the
+      bell itself. As the bell falls a pin <i>X</i> moves the lever attached to
+      the cock on the water- pipe, and starts, or shuts off, a current passing
+      from a store-tank or reservoir to a decomposing vessel full of carbide. It
+      is also possible to make <i>X</i> work some releasing gear which permits
+      carbide to fall into water--details of this arrangement are given later
+      on. In A^1 the water in the tank serves as a holder seal only, a separate
+      quantity being employed for the purposes of the chemical reaction. This
+      arrangement has the advantage that the holder water lasts indefinitely,
+      except for evaporation in hot weather, and therefore it may be prevented
+      from freezing by dissolving in it some suitable saline body, or by mixing
+      with it some suitable liquid which lowers its point of solidification. It
+      will be observed, too, that in A^1 the pin <i>X</i>, which derives its
+      motive power from the surplus weight of the falling bell, has always
+      precisely the same amount of work to do, viz., to overcome the friction of
+      the plug of the water-cock in its barrel. Hence at all times the pressure
+      obtaining in the service-pipe is uniform, except for a slight jerk
+      momentarily given each time the cock is opened or closed. When <i>X</i>
+      actuates a carbide-feed arrangement, the work it does may or may not vary
+      on different occasions, as will appear hereafter. In A^2 the bell itself
+      carries a perforated basket of carbide, which is submerged in the water
+      when the bell falls, and lifted out again when it rises. As the carbide is
+      thus wetted from below, the lower portion of the mass soon becomes a layer
+      of damp slaked lime, for although the basket is raised completely above
+      the water-level, much liquid adheres to the spent carbide by capillary
+      attraction. Hence, even when the basket is out of the water, acetylene is
+      being produced, and it is produced in circumstances which prevent any
+      control over the temperature attained. The water clinging to the lower
+      part of the basket is vaporised by the hot, half-spent carbide, and the
+      steam attacks the upper part, so that polymerisation of the gas and baking
+      of the carbide are inevitable. In the second place, the pressure in the
+      service-pipe attached to A^2 depends as before upon the net weight of the
+      holder bell; but here that net weight is made up of the weight of the bell
+      itself, that of the basket, and that of the carbide it contains. Since the
+      carbide is being gradually converted into damp slaked lime, it increases
+      in weight to an indeterminate extent as the generator in exhausted; but
+      since, on the other hand, some lime may be washed out of the basket each
+      time it is submerged, and some of the smaller fragments of carbide may
+      fall through the perforations, the basket tends to decrease in weight as
+      the generator is exhausted. Thus it happens in A^2 that the combined
+      weight of bell plus basket plus contents is wholly indefinite, and the
+      pressure in the service becomes so irregular that a separate governor must
+      be added to the installation before the burners can be expected to behave
+      properly. In the third place, the water in the tank serves both for
+      generation and for decomposition, and this involves the employment of some
+      arrangement to keep its level fairly constant lest the bell should become
+      unsealed, while protection from frost by saline or liquid additions is
+      impossible. A^2 is known popularly as a "dipping" generator, and it will
+      be seen to be defective mechanically and bad chemically. In both A^1 and
+      A^2 the bell is constructed of thin sheet- metal, and it is cylindrical in
+      shape; the mass of metal in it is therefore negligible in comparison with
+      the mass of water in the tank, and so the level of the liquid is sensibly
+      the same whether the bell be high or low. In A^3 the interior of the bell
+      is fitted with a circular plate which cuts off its upper corners and
+      leaves a circumferential space <i>S</i> triangular in vertical section.
+      This space is always full of air, or air and water, and has to be deducted
+      from the available storage capacity of the bell. Supposing the bell
+      transparent, and viewing it from above, its effective clear or internal
+      diameter will be observed to be smaller towards the top than near the
+      bottom; or since the space <i>S</i> is closed both against the water and
+      against the gas, the walls of the bell may be said to be thicker near its
+      top. Thus it happens that as the bell descends into the water past the
+      lower angle of <i>S</i>, it begins to require more space for itself in the
+      tank, and so it displaces the water until the levels rise. When high, as
+      shown in the sketch marked A^3(a), the water-level is at <i>l</i>, below
+      the mouth of a pipe <i>P</i>; but when low, as in A^3(b), the water is
+      raised to the point <i>l'</i>, which is above <i>P</i>. Water therefore
+      flows into <i>P</i>, whence it reaches the carbide in an attached
+      decomposing chamber. Here also the water in the tank is used for
+      decomposition as well as for sealing purposes, and its normal level must
+      be maintained exactly at <i>l</i>, lest the mouth of <i>P</i> should not
+      be covered whenever the bell falls.
+    </p>
+    <p class="ctr">
+      <a href="images/081.png"><img src="images/081th.png"
+      alt="FIG. 1.--TYPICAL METHODS OF AUTOMATIC GENERATION CONTROLLED BY BELL GASHOLDER" /></a>
+    </p>
+    <p>
+      The devices employed to render a generator automatic which depend upon
+      pressure (B) are of three main varieties: (B^1) the water-level in the
+      decomposing chamber may be depressed by the pressure therein until its
+      surface falls below a stationary mass of carbide; (B^2) the level in a
+      water-store tank may be depressed until it falls below the mouth of a pipe
+      leading to the carbide vessel; (B^3) the current of water passing down a
+      pipe to the decomposing chamber may be interrupted by the action of a
+      pressure superior to the force of gravitation. These arrangements are
+      indicated roughly in Fig. 2. In B^1, D is a hollow cylinder closed at all
+      points except at the cock G and the hole E, which are always below the
+      level of the water in the annulus F, the latter being open to the air at
+      its top. D is rigidly fastened to the outer vessel F so that it cannot
+      move vertically, and the carbide cage is rigidly fastened to D. Normally
+      the water-levels are at <i>l</i>, and the liquid has access to the carbide
+      through perforations in the basket. Acetylene is thus produced; but if G
+      is shut, the gas is unable to escape, and so it presses downwards upon the
+      water until the liquid falls in D to the dotted line <i>l"</i>, rising in
+      F to the dotted line <i>l'</i>. The carbide is then out of water, and
+      except for after-generation, evolution of gas ceases. On opening G more or
+      less fully, the water more or less quickly reaches its original position
+      at <i>l</i>, and acetylene is again produced. Manifestly this arrangement
+      is identical with that of A^2 as regards the periodical immersion of the
+      carbide holder in the liquid; but it is even worse than the former
+      mechanically because there is no rising holder in B^1, and the pressure in
+      the service is never constant. B^2 represents the water store of an
+      unshown generator which works by pressure. It consists of a vessel divided
+      vertically by means of a partition having a submerged hole N. One-half, H,
+      is cloned against the atmosphere, but communicates with the gas space of
+      the generator through L; the other half, K, is open to the air. M is a
+      pipe leading water to the carbide. When gas is being burnt as fast as, or
+      faster than, it is being evolved, the pressure in the generator is small,
+      the level of the water stands at <i>l</i>, and the mouth of M is below it.
+      When the pressure rises by cessation of consumption, that pressure acts
+      through L upon the water in H, driving it down in H and up in K till it
+      takes the positions <i>l"</i>, and <i>l'</i>, the mouth of M being then
+      above the surface. It should be observed that in the diagrams B^1 and B^3,
+      the amount of pressure, and the consequent alteration in level, is grossly
+      exaggerated to gain clearness; one inch or less in both cases may be
+      sufficient to start or retard evolution of acetylene. Fig. B^3 is somewhat
+      ideal, but indicates the principle of opposing gas pressure to a supply of
+      water depending upon gravitation; a method often adopted in the
+      construction of portable acetylene apparatus. The arrangement consists of
+      an upper tank containing water open to the air, and a lower vessel holding
+      carbide closed everywhere except at the pipe P, which leads to the
+      burners, and at the pipe S, which introduces water from the store-tank. If
+      the cock at T is closed, pressure begins to rise in the carbide holder
+      until it is sufficient to counterbalance the weight of the column of water
+      in the pipe S, when a further supply is prevented until the pressure sinks
+      again. This idea is simply an application of the displacement-holder
+      principle, and as such is defective (except for vehicular lamps) by reason
+      of lack of uniformity in pressure.
+    </p>
+    <p class="ctr">
+      <a href="images/084.png"><img src="images/084th.png"
+      alt="FIG. 2.--TYPICAL METHODS OF AUTOMATIC GENERATION CONTROLLED BY INTERNAL GAS PRESSURE" /></a>
+    </p>
+    <p>
+      DISPLACEMENT GASHOLDERS.--An excursion may here be made for the purpose of
+      studying the action of a displacement holder, which in its most elementary
+      form is shown at C. It consists of an upright vessel open at the top, and
+      divided horizontally into two equal portions by a partition, through which
+      a pipe descends to the bottom of the lower half. At the top of the closed
+      lower compartment a tube is fixed, by means of which gas can be introduced
+      below the partition. While the cock is open to the air, water is poured in
+      at the open top till the lower compartment is completely full, and the
+      level of the liquid is at <i>l</i>. If now, gas is driven in through the
+      side tube, the water is forced downwards in the lower half, up through the
+      depending pipe till it begins to fill the upper half of the holder, and
+      finally the upper half is full of water and the lower half of gas an shown
+      by the levels <i>l'</i> and <i>l"</i>. But the force necessary to
+      introduce gas into such an apparatus, which conversely is equal to the
+      force with which the apparatus strives to expel its gaseous contents,
+      measured in inches of water, is the distance at any moment between the
+      levels <i>l'</i> and <i>l"</i>; and as these are always varying, the
+      effective pressure needed to fill the apparatus, or the effective pressure
+      given by the apparatus, may range from zero to a few inches less than the
+      total height of the whole holder. A displacement holder, accordingly, may
+      be used either to store a varying quantity of gas, or to give a steady
+      pressure just above or just below a certain desired figure; but it will
+      not serve both purposes. If it is employed as a holder, it in useless as a
+      governor or pressure regulator; if it is used as a pressure regulator, it
+      can only hold a certain fixed volume of gas. The rising holder, which is
+      shown at A^1 in Fig. 1 (neglecting the pin X, &amp;c.) serves both
+      purposes simultaneously; whether nearly full or nearly empty, it gives a
+      constant pressure--a pressure solely dependent upon its effective weight,
+      which may be increased by loading its crown or decreased by supporting it
+      on counterpoises to any extent that may be required. As the bell of a
+      rising holder moves, it must be provided with suitable guides to keep its
+      path vertical; these guides being arranged symmetrically around its
+      circumference and carried by the tank walls. A fixed control rod attached
+      to the tank over which a tube fastened to the bell slides
+      telescope-fashion is sometimes adopted; but such an arrangement is in many
+      respects less admirable than the former.
+    </p>
+    <p>
+      Two other devices intended to give automatic working, which are scarcely
+      capable of classification among their peers, may be diagrammatically shown
+      in Fig. 3. The first of these (D) depends upon the movements of a flexible
+      diaphragm. A vessel (<i>a</i>) of any convenient size and shape is divided
+      into two portions by a thin sheet of metal, leather, caoutchouc, or the
+      like. At its centre the diaphragm is attached by some air-tight joint to
+      the rod <i>c</i>, which, held in position by suitable guides, is free to
+      move longitudinally in sympathy with the diaphragm, and is connected at
+      its lower extremity with a water-supply cock or a carbide-feed gear. The
+      tube <i>e</i> opens at its base into the gas space of the generator, so
+      that the pressure below the diaphragm in <i>a</i> is the same as that
+      elsewhere in the apparatus, while the pressure in <i>a</i> above the
+      diaphragm is that of the atmosphere. Being flexible and but slightly
+      stretched, the diaphragm is normally depressed by the weight of <i>c</i>
+      until it occupies the position <i>b</i>; but if the pressure in the
+      generator (<i>i.e.</i>, in <i>e</i>) rises, it lifts the diaphragm to
+      somewhat about the position <i>b'</i>--the extent of movement being, as
+      usual, exaggerated in the sketch. The movement of the diaphragm is
+      accompanied by a movement of the rod <i>c</i>, which can be employed in
+      any desirable way. In E the bell of a rising holder of the ordinary typo
+      is provided with a horizontal striker which, when the bell descends,
+      presses against the top of a bag <i>g</i> made of any flexible material,
+      such as india-rubber, and previously filled with water. Liquid is thus
+      ejected, and may be caused to act upon calcium carbide in some adjacent
+      vessel. The sketch is given because such a method of obtaining an
+      intermittent water-supply has at one time been seriously proposed; but it
+      is clearly one which cannot be recommended.
+    </p>
+    <p class="ctr">
+      <a href="images/086.png"><img src="images/086th.png"
+      alt="FIG. 3.--TYPICAL METHODS OF AUTOMATIC GENERATION CONTROLLED BY A FLEXIBLE DIAPHRAM OR BAG" /></a>
+    </p>
+    <p>
+      ACTION OF WATER-TO-CARBIDE GENERATORS.--Having by one or other of the
+      means described obtained a supply of water intermittent in character, it
+      remains to be considered how that supply may be made to approach the
+      carbide in the generator. Actual acetylene apparatus are so various in
+      kind, and merge from one type to another by such small differences, that
+      it is somewhat difficult to classify them in a simple and intelligible
+      fashion. However, it may be said that water-to-carbide generators, <i>i.e.</i>,
+      such as employ water as the moving material, may be divided into four
+      categories: (F^1) water is allowed to fall as single drops or as a fine
+      stream upon a mass of carbide--this being the "drip" generator; (F^2) a
+      mass of water is made to rise round and then recede from a stationary
+      vessel containing carbide--this being essentially identical in all
+      respects save the mechanical one with the "dip" or "dipping" generator
+      shown in A^2, Fig. 1; (F^3) a supply of water is permitted to rise round,
+      or to flow upon, a stationary mass of carbide without ever receding from
+      the position it has once assumed--this being the "contact" generator; and
+      (F^4) a supply of water is admitted to a subdivided charge of carbide in
+      such proportion that each quantity admitted is in chemical excess of the
+      carbide it attacks. With the exception of F^2, which has already been
+      illustrated as A^2 Fig. 1, or as B^1 in Fig. 2, these methods of
+      decomposing carbide are represented in Figs. 4 and 5. It will be observed
+      that whereas in both F^1 and F^3 the liberated acetylene passes off at the
+      top of the apparatus, or rather from the top of the non-subdivided charge
+      of carbide, in F^1 the water enters at the top, and in F^3 it enters at
+      the bottom. Thus it happens that the mixture of acetylene and steam, which
+      is produced at the spot where the primary chemical reaction is taking
+      place, has to travel through the entire mass of carbide present in a
+      generator belonging to type F^3, while in F^1 the damp gas flows directly
+      to the exit pipe without having to penetrate the lumps of solid. Both F^1
+      and F^3 exhibit after-generation caused by a reaction between the liquid
+      water mechanically clinging to the mass of spent lime and the excess of
+      carbide to an approximately equal extent; but for the reason just
+      mentioned, after-generation due to a reaction between the vaporised water
+      accompanying the acetylene first evolved and the excess of carbide is more
+      noticeable in F^3 than in F^1; and it is precisely this latter description
+      of after-generation which leads to overheating of the most ungovernable
+      kind. Naturally both F^1 and F^3 can be fitted with water jackets, as is
+      indicated by the dotted lines in the second sketch; but unless the
+      generating chamber in quite small and the evolution of gas quite slow, the
+      cooling action of the jacket will not prove sufficient. As the water in
+      F^1 and F^3 is not capable of backward motion, the decomposing chambers
+      cannot be employed as displacement holders, as is the case in the dipping
+      generator pictured at B^1, Fig. 2. They must be coupled, accordingly, to a
+      separate holder of the displacement or, preferably, of the rising type;
+      and, in order that the gas evolved by after-generation may not be wasted,
+      the automatic mechanism must cut off the supply of water to the generator
+      by the time that holder is two-thirds or three-quarters full.
+    </p>
+    <p class="ctr">
+      <a href="images/088.png"><img src="images/088th.png"
+      alt="FIG. 4.--TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TO CARBIDE)" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/089.png"><img src="images/089th.png"
+      alt="FIG. 5.--TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TO CARBIDE)" /></a>
+    </p>
+    <p>
+      The diagrams G, H, and K in Figs. 4 and 5 represent three different
+      methods of constructing a generator which belongs either to the contact
+      type (F^3) if the supply of water is essentially continuous, <i>i.e.</i>,
+      if less is admitted at each movement of the feeding mechanism than is
+      sufficient to submerge the carbide in each receptacle; or to the flooded-
+      compartment type (F') if the water enters in large quantities at a time.
+      In H the main carbide vessel is arranged horizontally, or nearly so, and
+      each partition dividing it into compartments is taller than its
+      predecessor, so that the whole of the solid in (1) must be decomposed, and
+      the compartment entirely filled with liquid before it can overflow into
+      (2), and so on. Since the carbide in all the later receptacles is exposed
+      to the water vapour produced in that one in which decomposition is
+      proceeding at any given moment, at least at its upper surface, some
+      after-generation between vapour and carbide occurs in H; but a partial
+      control over the temperature may be obtained by water-jacketing the
+      container. In G the water enters at the base and gas escapes at the top,
+      the carbide vessels being disposed vertically; hero, perhaps, more after-
+      generation of the same description occurs, as the moist gas streams round
+      and over the higher baskets. In K, the water enters at the top and must
+      completely fill basket (1) before it can run down the depending pipe into
+      (2); but since the gas also leaves the generator at the top, the later
+      carbide receptacles do not come in contact with water vapour, but are left
+      practically unattacked until their time arrives for decomposition by means
+      of liquid water. K, therefore, is the best arrangement of parts to avoid
+      after-generation, overheating, and polymerisation of the acetylene whether
+      the generator be worked as a contact or as a flooded-compartment
+      apparatus; but it may be freely admitted that the extent of the
+      overheating due to reaction between water vapour and carbide may be kept
+      almost negligible in either K, H, or G, provided the partitions in the
+      carbide container be sufficient in number--provided, that is to say, that
+      each compartment holds a sufficiently small quantity of carbide; and
+      provided that the quantity of water ultimately required to fill each
+      compartment is relatively so large that the temperature of the liquid
+      never approaches the boiling-point where vaporisation is rapid. The type
+      of generator indicated by K has not become very popular, but G is fairly
+      common, whilst H undoubtedly represents the apparatus which is most
+      generally adopted for use in domestic and other private installations in
+      the United Kingdom and the Continent of Europe. The actual generators made
+      according to the design shown by H usually have a carbide receptacle
+      designed in the form of a semi-cylindrical or rectangular vessel of steel
+      sliding fairly closely into an outside container, the latter being either
+      built within the main water space of the entire apparatus or placed within
+      a separate water-jacketed casing. Owing to its shape and the sliding
+      motion with which the carbide receptacle is put into the container these
+      generators are usually termed "drawer" generators. In comparison with type
+      G, the drawer generator H certainly exhibits a lower rise in temperature
+      when gas is evolved in it at a given speed and when the carbide
+      receptacles are constructed of similar dimensions. It is very desirable
+      that the whole receptacle should be subdivided into a sufficient number of
+      compartments and that it should be effectively water-cooled from outside.
+      It would also be advantageous if the water- supply were so arranged that
+      the generator should be a true flooded- compartment apparatus, but
+      experience has nevertheless shown that generators of type H do work very
+      well when the water admitted to the carbide receptacle, each time the feed
+      comes into action, is not enough to flood the carbide in one of the
+      compartments. Above a certain size drawer generators are usually
+      constructed with two or even more complete decomposing vessels,
+      arrangements being such that one drawer can be taken out for cleaning,
+      whilst the other is in operation. When this is the case a third carbide
+      receptacle should always be employed so that it may be dry, lit to receive
+      a charge of carbide, and ready to insert in the apparatus when one of the
+      others is withdrawn. The water-feed should always be so disposed that the
+      attendant can see at a glance which of the two (or more) carbide
+      receptacles is in action at any moment, and it should be also so designed
+      that the supply is automatically diverted to the second receptacle when
+      the first is wholly exhausted and back again to the first (unless there
+      are more than two) when the carbide in the second is entirely gasified. In
+      the sketches G, H, and K, the total space occupied by the various carbide
+      receptacles is represented as being considerably smaller than the capacity
+      of the decomposing chamber. Were this method of construction copied in
+      actual acetylene apparatus, the first makes of gas would be seriously
+      (perhaps dangerously) contaminated with air. In practice the receptacles
+      should fit so tightly into the outer vessel and into one another that when
+      loaded to the utmost extent permissible--space being left for the swelling
+      of the charge and for the passage of water and gas--but little room should
+      be left for the retention of air in the chamber.
+    </p>
+    <p>
+      ACTION OF CARBIDE-TO-WATER GENERATORS.--The methods which may be adopted
+      to render a generator automatic when carbide is employed as the moving
+      material are shown at M, N, and P, in Fig. 6; but the precise devices used
+      in many actual apparatus are so various that it is difficult to portray
+      them generically. Moreover it is desirable to subdivide automatic
+      carbide-to-water generators, according to the size of the carbide they are
+      constructed to take, into two or three classes, which are termed
+      respectively "large carbide-feed," "small carbide-feed," and "granulated
+      carbide-feed" apparatus. (The generator represented at L does not really
+      belong to the present class, being non-automatic and fed by hand; but the
+      sketch is given for completeness.) M is an automatic carbide-feed
+      generator having its store of carbide in a hopper carried by the rising-
+      holder bell. The hopper is narrowed at its mouth, where it is closed by a
+      conical or mushroom valve <i>d</i> supported on a rod held in suitable
+      guides. When the bell falls by consumption of gas, it carries the valve
+      and rod with it; but eventually the button at the base of <i>c</i> strikes
+      the bottom of the generator, or some fixed distributing plate, and the rod
+      can descend no further. Then, when the bell falls lower, the mushroom <i>d</i>
+      rises from its seat, and carbide drops from the hopper into the water.
+      This type of apparatus has the defect characteristic of A^2, Fig. 1; for
+      the pressure in the service steadily diminishes as the effective weight of
+      bell plus hopper decreases by consumption of carbide. But it has also two
+      other defects--(1) that ordinary carbide is too irregular in shape to fall
+      smoothly through the narrow annular space between the valve and its seat;
+      (2) that water vapour penetrates into the hopper, and liberates some gas
+      there, while it attacks the lumps of carbide at the orifice, producing
+      dust or causing them to stick together, and thus rendering the action of
+      the feed worse than ever. Most of these defects can be avoided by using
+      granulated carbide, which is more uniform in size and shape, or by
+      employing a granulated and "treated" carbide which has been dipped in some
+      non-aqueous liquid to make it less susceptible to the action of moisture.
+      Both these plans, however, are expensive to adopt; first, because of the
+      actual cost of granulating or "treating" the carbide; secondly, because
+      the carbide deteriorates in gas-making capacity by its inevitable exposure
+      to air during the granulating or "treating" process. The defects of
+      irregularity of pressure and possible waste of gas by evolution in the
+      hopper may be overcome by disposing the parts somewhat differently; making
+      the holder an annulus round the hopper, or making it cylindrical with the
+      hopper inside. In this case the hopper is supported by the main portion of
+      the apparatus, and does not move with the bell: the rod and valve being
+      given their motion in some fashion similar to that figured. Apparatus
+      designed in accordance with the sketch M, or with the modification just
+      described, are usually referred to under the name of "hopper" generators.
+      On several occasions trouble has arisen during their employment owing to
+      the jamming of the valve, a fragment of carbide rather larger than the
+      rest of the material lodging between the lips of the hopper and the edges
+      of the mushroom valve. This has been followed by a sudden descent of all
+      the carbide in the store into the water beneath, and the evolution of gas
+      has sometimes been too rapid to pass away at the necessary speed into the
+      holder. The trouble is rendered even more serious should the whole charge
+      of carbide fall at a time when, by neglect or otherwise, the body of the
+      generator contains much lime sludge, the decomposition then proceeding
+      under exceptionally bad circumstances, which lead to the production of an
+      excessively high temperature. Hopper generators are undoubtedly very
+      convenient for certain purposes, chiefly, perhaps, for the construction of
+      table-lamps and other small installations. Experience tends to show that
+      they may be employed, first, provided they are designed to take granulated
+      carbide--which in comparison with larger grades is much more uniform and
+      cylindrical in shape--and secondly, provided the quantity of carbide in
+      the hopper does not exceed a few pounds. The phenomenon of the sudden
+      unexpected descent of the carbide, popularly known as "dumping," can
+      hardly be avoided with carbide larger in size than the granulated variety;
+      and since the results of such an accident must increase in severity with
+      the size of the apparatus, a limit in their capacity is desirable.
+    </p>
+    <p class="ctr">
+      <a href="images/092.png"><img src="images/092th.png"
+      alt="FIG. 6.--TYPICAL METHODS OF DECOMPOSING CARBIDE (CARBIDE TO WATER)" /></a>
+    </p>
+    <p>
+      When it is required to construct a carbide-feed generator of large size or
+      one belonging to the large carbide-feed pattern, it is preferable to
+      arrange the store in a different manner. In N the carbide is held in a
+      considerable number of small receptacles, two only of which are shown in
+      the drawing, provided with detachable lids and hinged bottoms kept shut by
+      suitable catches. At proper intervals of time those catches in succession
+      are knocked on one side by a pin, and the contents of the vessel fall into
+      the water. There are several methods available for operating the pins. The
+      rising-holder bell may be made to actuate a train of wheels which
+      terminate in a disc revolving horizontally on a vertical axis somewhere
+      just below the catches; and this wheel may bear an eccentric pin which
+      hits each catch as it rotates. Alternatively the carbide boxes may be made
+      to revolve horizontally on a vertical axis by the movements of the bell
+      communicated through a clutch; and thus each box in succession may arrive
+      at a certain position where the catch is knocked aside by a fixed pin. The
+      boxes, again, may revolve vertically on a horizontal axis somewhat like a
+      water-wheel, each box having its bottom opened, or, by a different system
+      of construction, being bodily upset, when it arrives at the bottom of its
+      circular path. In no case, however, are the carbide receptacles carried by
+      the bell, which is a totally distinct part of the apparatus; and therefore
+      in comparison with M, the pressure given by the bell is much more uniform.
+      Nevertheless, if the system of carbide boxes moves at all, it becomes
+      easier to move by decrease in weight and consequent diminution in friction
+      as the total charge is exhausted; and accordingly the bell has less work
+      to do during the later stages of its operation. For this reason the plan
+      actually shown at N is preferable, since the work done by the moving pin,
+      <i>i.e.</i>, by the descending bell, is always the same. P represents a
+      carbide-feed effected by a spiral screw or conveyor, which, revolved
+      periodically by a moving bell, draws carbide out of a hopper of any
+      desired size and finally drops it into a shoot communicating with a
+      generating chamber such as that shown in L. Here the work done by the bell
+      is large, as the friction against the blades of the screw and the walls of
+      the horizontal tube is heavy; but that amount of work must always be
+      essentially identical. The carbide-feed may similarly be effected by means
+      of some other type of conveyor instead of the spiral screw, such as an
+      endless band, and the friction in these cases may be somewhat less than
+      with the screw, but the work to be done by the bell will always remain
+      large, whatever type of conveyor may be adopted. A further plan for
+      securing a carbide-feed consists in employing some extraneous driving
+      power to propel a charge of carbide out of a reservoir into the generator.
+      Sometimes the propulsive effort is obtained from a train of clockwork,
+      sometimes from a separate supply of water under high pressure. The
+      clockwork or the water power is used either to drive a piston travelling
+      through the vessel containing the carbide so that the proper quantity of
+      material is dropped over the open mouth of a shoot, or to upset one after
+      another a series of carbide receptacles, or to perform some analogous
+      operation. In these cases the pin or other device fitted to the acetylene
+      apparatus itself has nothing to do beyond releasing the mechanism in
+      question, and therefore the work required from the bell is but small. The
+      propriety of employing a generator belonging to these latter types must
+      depend upon local conditions, <i>e.g.</i>, whether the owner of the
+      installation has hydraulic power on a small scale (a constant supply of
+      water under sufficient pressure) at disposal, or whether he does not
+      object to the extra labour involved in the periodical winding up of a
+      train of clockwork.
+    </p>
+    <p>
+      It must be clear that all these carbide-feed arrangements have the defect
+      in a more or less serious degree of leaving the carbide in the main
+      storage vessel exposed to the attack of water vapour rising from the
+      decomposing chamber, for none of the valves or operating mechanism can be
+      made quite air-tight. Evolution of gas produced in this way does not
+      matter in the least, because it is easy to return the gas so liberated
+      into the generator or into the holder; while the extent of the action, and
+      the consequent production of overheating, will tend to be less than in
+      generators such as those shown in G and H of Figs. 4 and 5, inasmuch as
+      the large excess of water in the carbide-feed apparatus prevents the
+      liquid arriving at a temperature at which it volatilises rapidly. The main
+      objection to the evolution of gas in the carbide vessel of a
+      carbide-to-water generator depends on the danger that the smooth working
+      of the feed-gear may be interfered with by the formation of dust or by the
+      aggregation of the carbide lumps.
+    </p>
+    <p>
+      USE OF OIL IN GENERATORS.--Calcium carbide is a material which is only
+      capable of attack for the purpose of evolving acetylene by a liquid that
+      is essentially water, or by one that contains some water mixed with it.
+      Oils and the like, or even such non-aqueous liquids as absolute alcohol,
+      have no effect upon carbide, except that the former naturally make it
+      greasy and somewhat more difficult to moisten. This last property has been
+      found of service in acetylene generation, especially on the small scale;
+      for if carbide is soaked in, or given a coating of, some oil, fat, or
+      solid hydrocarbon like petroleum, cocoanut oil, or paraffin wax, the
+      substance becomes comparatively indifferent towards water vapour or the
+      moisture present in the air, while it still remains capable of complete,
+      albeit slow, decomposition by liquid water when completely immersed
+      therein. The fact that ordinary calcium carbide is attacked so quickly by
+      water is really a defect of the substance; for it is to this extreme
+      rapidity of reaction that the troubles of overheating are due. Now, if the
+      basket in the generator B^1 of Fig. 2, or, indeed, the carbide store in
+      any of the carbide-to-water apparatus, is filled with a carbide which has
+      been treated with oil or wax, as long as the water-level stands at <i>l'</i>
+      and <i>l"</i> or the carbide still remains in the hopper, it is
+      essentially unattacked by the vapour arising from the liquid; but directly
+      the basket is submerged, or the lumps fall into the water, acetylene is
+      produced, and produced more slowly and regularly than otherwise. Again,
+      oils do not mix with water, but usually float thereon, and a mass of water
+      covered by a thick film or layer of oil does not evaporate appreciably.
+      If, now, a certain quantity of oil, say lamp paraffin or mineral
+      lubricating oil, is poured on to the water in B^1, Fig. 2, it moves
+      upwards and downwards with the water. When the water takes the position <i>l</i>,
+      the oil is driven upwards away from the basket of carbide, and acetylene
+      is generated in the ordinary manner; but when the water falls to <i>l"</i>
+      the oil descends also, rinses off much of the adhering water from the
+      carbide lumps, covers them with a greasy film, and almost entirely stops
+      generation till it is in turn washed off by the next ascent of the water.
+      Similarly, if the carbide in generators F, G, and H (also K) has been
+      treated with a solid or semi-solid grease, it is practically unattacked by
+      the stream of warm damp gas, and is only decomposed when the liquid itself
+      arrives in the basket. For the same reason treated carbide can be kept for
+      fairly long periods of time, even in a drum with badly fitting lid,
+      without suffering much deterioration by the action of atmospheric
+      moisture. The problem of acetylene generation is accordingly simplified to
+      a considerable degree by the use of such treated carbide, and the
+      advantage becomes more marked as the plant decreases in size till a
+      portable apparatus is reached, because the smaller the installation the
+      more relatively expensive or inconvenient is a large holder for surplus
+      gas. The one defect of the method is the extra cost of such treated
+      carbide; and in English conditions ordinary calcium carbide is too
+      expensive to permit of any additional outlay upon the acetylene if it is
+      to compete with petroleum or the product of a tiny coal-gas works. The
+      extra cost of using treated carbide falls upon the revenue account, and is
+      much more noticeable than that of a large holder, which is capital
+      expenditure. When fluid oil is employed in a generator of type B^1,
+      evolution of gas becomes so regular that any holder beyond the
+      displacement one which the apparatus itself constitutes is actually
+      unnecessary, though still desirable; but B^1, with or without oil, still
+      remains a displacement apparatus, and as such gives no constant pressure.
+      It must be admitted that the presence of oil so far governs the evolution
+      of gas that the movement of the water, and the consequent variation of
+      pressure, is rendered very small; still a governor or a rising holder
+      would be required to give the best result at the burners. One point in
+      connexion with the use of liquid oil must not be overlooked, viz., the
+      extra trouble it may give in the disposal of the residues. This matter
+      will be dealt with more fully in Chapter V.; here it is sufficient to say
+      that as the oil does not mix with the water but floats on the surface,
+      care has to be taken that it is not permitted to enter any open stream.
+      The foregoing remarks about the use of oil manifestly only apply to those
+      cases where it is used in quantity and where it ultimately becomes mixed
+      with the sludge or floats on the water in the decomposing chamber. The
+      employment of a limpid oil, such as paraffin, as an intermediate liquid
+      into which carbide is introduced on its way to the water in the
+      decomposing vessel of a hand-fed generator in the manner described on page
+      70 is something quite different, because, except for trifling losses, one
+      charge of oil should last indefinitely.
+    </p>
+    <p>
+      RISING GASHOLDERS.--Whichever description of holder is employed in an
+      acetylene apparatus, the gas is always stored over, or in contact with, a
+      liquid that is essentially water. This introduces three subjects for
+      consideration: the heavy weight of a large body of liquid, the loss of gas
+      by dissolution in that liquid, and the protection of that liquid from
+      frost in the winter. The tanks of rising holders are constructed in two
+      different ways. In one the tank is a plain cylindrical vessel somewhat
+      larger in diameter than the bell which floats in it; and since there must
+      be nearly enough water in the tank to fill the interior of the bell when
+      the latter assumes its lowest position, the quantity of water is
+      considerable, its capacity for dissolving acetylene is large, and the
+      amount of any substance that may have to be added to it to lower its
+      freezing-point becomes so great as to be scarcely economical. All these
+      defects, including that of the necessity for very substantial foundations
+      under the holder to support its enormous weight, may be overcome by
+      adopting the second method of construction. It is clear that the water in
+      the centre of the tank is of no use,--all that is needed being a narrow
+      trough for the bell to work in. Large rising holders are therefore
+      advantageously built with a tank formed in the shape of an annulus, the
+      effective breadth of which is not more than 2 or 3 inches, the centre
+      portion being roofed over so as to prevent escape of gas. The same
+      principle may be retained with modified details by fitting inside a plain
+      cylindrical tank a "dummy" or smaller cylinder, closed by a flat or curved
+      top and fastened water- and air-tight to the bottom of the main vessel.
+      The construction of annular tanks or the insertion of a "dummy" may be
+      attended with difficulty if the tank is wholly or partly sunk below the
+      ground level, owing to the lifting force of water in the surrounding soil.
+      Where a steel tank is sunk, or a masonry tank is constructed, regard must
+      be paid, both in the design of the tank and in the manner of construction,
+      to the level of the underground water in the neighbourhood, as in certain
+      cases special precautions will be needed to avoid trouble from the
+      pressure of the water on the outside of the tank until it is balanced by
+      the pressure of the water with which the tank is filled. So far as mere
+      dissolution of gas is concerned, the loss may be reduced by having a
+      circular disc of wood, &amp;c., a little smaller in diameter than the
+      boll, floating on the water of a plain tank.
+    </p>
+    <p>
+      EFFECT OF STORAGE IN GASHOLDER ON ACETYLENE.--It is perfectly true, as has
+      been stated elsewhere, that the gas coming from an acetylene generator
+      loses some of its illuminating power if it is stored over water for any
+      great length of time; such loss being given by Nichols as 94 per cent, in
+      five months, and having been found by one of the authors as 0.63 per cent.
+      per day--figures which stand in fair agreement with one another. This
+      wastage is not due to any decomposition of the acetylene in contact with
+      water, but depends on the various solubilities of the different gases
+      which compose the product obtained from commercial calcium carbide.
+      Inasmuch as an acetylene evolved in the best generator contains some
+      foreign ingredients, and inasmuch as an inferior product contains more (<i>cf.</i>
+      Chapter V.), the contents of a holder are never pure; but as those
+      contents are principally made up of acetylene itself, that gas stands at a
+      higher partial pressure in the holder than the impurities. Since acetylene
+      is more soluble in water than any of its diluents or impurities,
+      sulphuretted hydrogen and ammonia excepted, and since the solubility of
+      all gases increases as the pressure at which they are stored rises, the
+      true acetylene in an acetylene holder dissolves in the water more rapidly
+      and comparatively more copiously than the impurities; and thus the
+      acetylene tends to disappear and the impurities to become concentrated
+      within the bell. Simultaneously at the outer part of the seal, air is
+      dissolved in the water; and by processes of diffusion the air so dissolved
+      passes through the liquid from the outside to the inside, where it escapes
+      into the bell, while the dissolved acetylene similarly passes from the
+      inside to the outside of the seal, and there mingles with the atmosphere.
+      Thus, the longer a certain volume of acetylene is stored over water, the
+      more does it become contaminated with the constituents of the atmosphere
+      and with the impurities originally present in it; while as the acetylene
+      is much more soluble than its impurities, more gas escapes from, than
+      enters, the holder by diffusion, and so the bulk of stored gas gradually
+      diminishes. However, the figures previously given show that this action is
+      too slow to be noticeable in practice, for the gas is never stored for
+      more than a few days at a time. The action cannot be accepted as a valid
+      argument against the employment of a holder in acetylene plant. Such
+      deterioration and wastage of gas may be reduced to some extent by the use
+      of a film of some cheap and indifferent oil floating on the water inside
+      an acetylene holder; the economy being caused by the lower solubility of
+      acetylene in oils than in aqueous liquids not saturated with some saline
+      material. Probably almost any oil would answer equally well, provided it
+      was not volatile at the temperature of the holder, and that it did not dry
+      or gum on standing, <i>e.g.</i>, olive oil or its substitutes; but mineral
+      lubricating oil is not so satisfactory. It is, however, not necessary to
+      adopt this method in practice, because the solvent power of the liquid in
+      the seal can be reduced by adding to it a saline body which simultaneously
+      lowers its freezing-point and makes the apparatus more trustworthy in
+      winter.
+    </p>
+    <p>
+      FREEZING OF GASHOLDER SEAL.--The danger attendant upon the congelation of
+      the seal in an acetylene holder is very real, not so much because of the
+      fear that the apparatus may be burst, which is hardly to be expected, as
+      because the bell will be firmly fixed in a certain position by the ice,
+      and the whole establishment lighted by the gas will be left in darkness.
+      In these circumstances, hurried and perhaps injudicious attempts may be
+      made to thaw the seal by putting red-hot bars into it or by lighting fires
+      under it, or the generator-house may be thoughtlessly entered with a naked
+      light at a time when the apparatus is possibly in disorder through the
+      loss of storage-room for the gas it is evolving. Should a seal ever
+      freeze, it must be thawed only by the application of boiling water; and
+      the plant-house must be entered, if daylight has passed, in perfect
+      darkness or with the assistance of an outside lamp whining through a
+      closed window. [Footnote: By "closed window" is to be understood one
+      incapable of being opened, fitted with one or two thicknesses of stout
+      glass well puttied in, and placed in a wall of the house as far as
+      possible from the door.] There are two ways of preventing the seal from
+      freezing. In all large installations the generator-house will be fitted
+      with a warm-water heating apparatus to protect the portion of the plant
+      where the carbide is decomposed, and if the holder is also inside the same
+      building it will naturally be safe. If it is outside, one of the
+      flow-pipes from the warming apparatus should be led into and round the
+      lowest part of the seal, care being taken to watch for, or to provide
+      automatic arrangements for making good, loss of water by evaporation. If
+      the holder is at a distance from the generator-house, or if for any other
+      reason it cannot easily be brought into the warming circuit, the seal can
+      be protected in another way; for unlike the water in the generator, the
+      water in the holder-seal will perform its functions equally well however
+      much it be reduced in temperature, always providing it is maintained in
+      the liquid condition. There are numerous substances which dissolve in, or
+      mix with, water, and yield solutions or liquids that do not solidify until
+      their temperature falls far below that of the natural freezing- point.
+      Assuming that those substances in solution do not attack the acetylene,
+      nor the metal of which the holder is built, and are not too expensive,
+      choice may be made between them at will. Strictly speaking the cost of
+      using them is small, because unless the tank is leaky they last
+      indefinitely, not evaporating with the water as it is vaporised into the
+      gas or into the air. The water-seal of a holder standing within the
+      generator-house may eventually become so offensive to the nostrils that
+      the liquid has to be renewed; but when this happens it is due to the
+      accumulation in the water of the water-soluble impurities of the crude
+      acetylene. If, as should be done, the gas is passed through a washer or
+      condenser containing much water before it enters the holder the
+      sulphuretted hydrogen and ammonia will be extracted, and the seal will not
+      acquire an obnoxious odour for a very long time.
+    </p>
+    <p>
+      Four principal substances have been proposed for lowering the freezing-
+      point of the water in an acetylene-holder seal; common salt (sodium
+      chloride), calcium chloride (not chloride of lime), alcohol (methylated
+      spirit), and glycerin. A 10 per cent. solution of common salt has a
+      specific gravity of 1.0734, and does not solidify above -6� C. or 21.2�
+      F.; a 15 per cent. solution has a density of 1.111, and freezes at -10� C.
+      or 14� F. Common salt, however, is not to be recommended, as its solutions
+      always corrode iron and steel vessels more or less quickly. Alcohol, in
+      its English denatured form of methylated spirit, is still somewhat
+      expensive to use, but it has the advantage of not increasing the viscosity
+      of the water; so that a frost-proof mixture of alcohol and water will flow
+      as readily through minute tubes choked with needle- valves, or through
+      felt and the like, or along wicks, as will plain water. For this reason,
+      and for the practically identical one that it is quite free from dirt or
+      insoluble matter, diluted spirit is specially suitable for the protection
+      of the water in cyclists' acetylene lamps, [Footnote: As will appear in
+      Chapter XIII., there is usually no holder in a vehicular acetylene lamp,
+      all the water being employed eventually for the purpose of decomposing the
+      carbide. This does not affect the present question. Dilute alcohol does
+      not attack calcium carbide so energetically as pure water, because it
+      stands midway between pure water and pure alcohol, which is inert. The
+      attack, however, of the carbide is as complete as that of pure water, and
+      the slower speed thereof is a manifest advantage in any holderless
+      apparatus.] where strict economy is less important than smooth working.
+      For domestic and larger installations it is not indicated. As between
+      calcium chloride and glycerin there is little to choose; the former will
+      be somewhat cheaper, but the latter will not be prohibitively expensive if
+      the high-grade pure glycerins of the pharmacist are avoided. The following
+      tables show the amount of each substance which must be dissolved in water
+      to obtain a liquid of definite solidifying point. The data relating to
+      alcohol were obtained by Pictet, and those for calcium chloride by
+      Pickering. The latter are materially different from figures given by other
+      investigators, and perhaps it would be safer to make due allowance for
+      this difference. In Germany the Acetylene Association advocates a 17 per
+      cent. solution of calcium chloride, to which Frank ascribes a specific
+      gravity of 1.134, and a freezing-point of -8� C. or 17.6� F.
+    </p>
+<pre xml:space="preserve">
+           <i>Freezing-Points of Dilute Alcohol.</i>
+ _________________________________________________________
+|               |                   |                     |
+| Percentage of | Specific Gravity. |   Freezing-point.   |
+|    Alcohol.   |                   |                     |
+|_______________|___________________|_____________________|
+|               |                   |          |          |
+|               |                   | Degs. C. | Degs. F. |
+|      4.8      |      0.9916       |   -2.0   |  +28.4   |
+|     11.3      |      0.9824       |    5.0   |   23.0   |
+|     16.4      |      0.9761       |    7.5   |   18.5   |
+|     18.8      |      0.9732       |    9.4   |   15.1   |
+|     20.3      |      0.9712       |   10.6   |   12.9   |
+|     22.1      |      0.9689       |   12.2   |   10.0   |
+|     24.2      |      0.9662       |   14.0   |    6.8   |
+|     26.7      |      0.9627       |   16.0   |    3.2   |
+|     29.9      |      0.9578       |   18.9   |   -2.0   |
+|_______________|___________________|__________|__________|
+</pre>
+<pre xml:space="preserve">
+           <i>Freezing-Points of Dilute Glycerin.</i>
+ _________________________________________________________
+|               |                   |                     |
+| Percentage of | Specific Gravity. |   Freezing-point.   |
+|    Glycerin.  |                   |                     |
+|_______________|___________________|_____________________|
+|               |                   |          |          |
+|               |                   | Degs. C. | Degs. F. |
+|      10       |       1.024       |   -1.0   |  +30.2   |
+|      20       |       1.051       |    2.5   |   27.5   |
+|      30       |       1.075       |    6.0   |   21.2   |
+|      40       |       1.105       |   17.5   |    0.5   |
+|      50       |       1.127       |   31.3   |  -24.3   |
+|_______________|___________________|__________|__________|
+</pre>
+<pre xml:space="preserve">
+      <i>Freezing-Points of Calcium Chloride Solutions.</i>
+ _________________________________________________________
+|               |                   |                     |
+| Percentage of | Specific Gravity. |   Freezing-point.   |
+|    CaCl_2.    |                   |                     |
+|_______________|___________________|_____________________|
+|               |                   |          |          |
+|               |                   | Degs. C. | Degs. F. |
+|       6       |       1.05        |   -3.0   |  +26.6   |
+|       8       |       1.067       |    4.3   |   24.3   |
+|      10       |       1.985       |    5.9   |   21.4   |
+|      12       |       1.103       |    7.7   |   18.1   |
+|      14       |       1.121       |    9.8   |   14.4   |
+|      16       |       1.140       |   12.2   |   10.0   |
+|      18       |       1.159       |   15.2   |    4.6   |
+|      20       |       1.170       |   18.6   |   -1.5   |
+|_______________|___________________|__________|__________|
+</pre>
+    <p>
+      Calcium chloride will probably be procured in the solid state, but it can
+      be purchased as a concentrated solution, being sold under the name of
+      "calcidum" [Footnote: This proprietary German article is a liquid which
+      begins to solidify at -42� C. (-43.6� F.), and is completely solid at -56�
+      C. (-69)� F.). Diluted with one-third its volume of water, it freezes
+      between -20� and -28� C. (-4� and-l8.4� F.). The makers recommend that it
+      should be mixed with an equal volume of water. Another material known as
+      "Gefrierschutzfl�ssigkeit" and made by the Fl�rsheim chemical works,
+      freezes at -35� C. (-3� F.). Diluted with one-quarter its volume of water,
+      it solidifies at -18� C. (-0.4� F.); with equal parts of water it freezes
+      at -12� C. (10.4� F.). A third product, called "calcidum oxychlorid," has
+      been found by Caro and Saulmann to be an impure 35 per cent. solution of
+      calcium chloride. Not one of these is suitable for addition to the water
+      used in the generating chamber of an acetylene apparatus, the reasons for
+      this having already been mentioned.] for the protection of gasholder
+      seals. Glycerin itself resembles a strong solution of calcium chloride in
+      being a viscid, oily-looking liquid; and both are so much heavier than
+      water that they will not mix with further quantities unless they are
+      thoroughly agitated therewith. Either may be poured through water, or have
+      water floated upon it, without any appreciable admixture taking place; and
+      therefore in first adding them to the seal great care must be taken that
+      they are uniformly distributed throughout the liquid. If the whole
+      contents of the seal cannot conveniently be run into an open vessel in
+      which the mixing can be performed, the sealing water must be drawn off a
+      little at a time and a corresponding quantity of the protective reagent
+      added to it. Care must be taken also that motives of economy do not lead
+      to excessive dilution of the reagent; the seal must be competent to remain
+      liquid under the prolonged influence of the most severe frost ever known
+      to occur in the neighbourhood where the plant is situated. If the holder
+      is placed out of doors in an exposed spot where heavy rains may fall on
+      the top of the bell, or where snow may collect there and melt, the water
+      is apt to run down into the seal, diluting the upper layers until they
+      lose the frost- resisting power they originally had. This danger may be
+      prevented by erecting a sloping roof over the bell crown, or by stirring
+      up the seal and adding more preservative whenever it has been diluted with
+      rain water. Quite small holders would probably always be placed inside the
+      generator-house, where their seals may be protected by the same means as
+      are applied to the generator itself. It need hardly be said that all
+      remarks about the dangers incidental to the freezing of holder seals and
+      the methods for obviating them refer equally to every item in the
+      acetylene plant which contains water or is fitted with a water-sealed
+      cover; only the water which is actually used for decomposing the calcium
+      carbide cannot be protected from frost by the addition of calcium chloride
+      or glycerin--that water must be kept from falling to its natural
+      freezing-point. From Mauricheau-Beaupr�'s experiments, referred to on page
+      106, it would appear that a further reason for avoiding an addition of
+      calcium chloride to the water used for decomposing carbide should lie in
+      the danger of causing a troublesome production of froth within the
+      generator.
+    </p>
+    <p>
+      It will be convenient to digress here for the purpose of considering how
+      the generators of an acetylene apparatus themselves should be protected
+      from frost; but it may be said at the outset that it is impossible to lay
+      down any fixed rules applicable to all cases, since local conditions, such
+      as climate, available resources, dimensions, and exposed or protected
+      position of the plant-house vary so largely in different situations. In
+      all important installations every item of the plant, except the holder,
+      will be collected in one or two rooms of a single building constructed of
+      brick or other incombustible material. Assuming that long-continued frost
+      reigns at times in the neighbourhood, the whole of such a building, with
+      the exception of one apartment used as a carbide store only, is
+      judiciously fitted with a heating arrangement like those employed in
+      conservatories or hothouses; a system of pipes in which warm water is kept
+      circulating being run round the walls of each chamber near the floor. The
+      boiler, heated with coke, paraffin, or even acetylene, must naturally be
+      placed in a separate room of the apparatus-house having no direct (indoor)
+      communication with the rooms containing the generators, purifiers, &amp;c.
+      Instead of coils of pipe, "radiators" of the usual commercial patterns may
+      be adopted; but the immediate source of heat should be steam, or
+      preferably hot water, and not hot air or combustion products from the
+      stove. In exposed situations, where the holder is out of doors, one branch
+      of the flow-pipe should enter and travel round the seal as previously
+      suggested. Most large country residences are already provided with
+      suitable heating apparatus for warming the greenhouses, and part of the
+      heat may be capable of diversion into the acetylene generator-shed if the
+      latter is erected in a convenient spot. In fact, if any existing hot-water
+      warming appliances are already at hand, and if they are powerful enough to
+      do a little more work, it may be well to put the generator-building in
+      such a position that it can be efficiently supplied with artificial warmth
+      from those boilers; for any extra length of main necessary to lead the gas
+      into the residence from a distant generator will cost less on the revenue
+      account than the fuel required to feed a special heating arrangement. In
+      smaller installations, especially such as are to be found in mild
+      climates, it may be possible to render the apparatus-house sufficiently
+      frost-proof without artificial heat by building it partly underground,
+      fitting it with a double skylight in place of a window for the entrance of
+      daylight, and banking up its walls all round with thick layers of earth.
+      The house must have a door, however, which must open outwards and easily,
+      so that no obstacle may prevent a hurried exit in emergencies. Such a door
+      can hardly be made very thick or double without rendering it heavy and
+      difficult to open; and the single door will be scarcely capable of
+      protecting the interior if the frost is severe and prolonged. Ventilators,
+      too, must be provided to allow of the escape of any gas that may
+      accidentally issue from the plant during recharging, &amp;c.; and some
+      aperture in the roof will be required for the passage of the vent pipe or
+      pipes, which, in certain types of apparatus, move upwards and downwards
+      with the bell of the holder. These openings manifestly afford facilities
+      for the entry of cold air, so that although this method of protecting
+      generator-houses has proved efficient in many places, it can only be
+      considered inferior to the plan of installing a proper heating
+      arrangement. Occasionally, where local regulations do not forbid, the
+      entire generator-house may be built as a "lean-to" against some brick wall
+      which happens to be kept constantly warm, say by having a furnace or a
+      large kitchen stove on its other side.
+    </p>
+    <p>
+      In less complicated installations, where there are only two distinct items
+      in the plant to be protected from frost--generator and holder--or where
+      generator and holder are combined into one piece of apparatus, other
+      methods of warming become possible. As the reaction between calcium
+      carbide and water evolves much heat, the most obvious way of preventing
+      the plant from freezing is to economise that heat, <i>i.e.</i>, to retain
+      as much of it as is necessary within the apparatus. Such a process,
+      clearly, is only available if the plant is suitable in external form, is
+      practically self-contained, and comprises no isolated vessels containing
+      an aqueous liquid. It is indicated, therefore, rather for carbide-to-
+      water generators, or for water-to-carbide apparatus in which the carbide
+      chambers are situated inside the main water reservoir--any apparatus, in
+      fact, where much water is present and where it is all together in one
+      receptacle. Moreover, the method of heat economy is suited for application
+      to automatic generators rather than to those belonging to the opposite
+      system, because automatic apparatus will be generating gas, and
+      consequently evolving heat, every evening till late at night--just at the
+      time when frost begins to be severe. A non-automatic generator will
+      usually be at work only in the mornings, and its store of heat will
+      accordingly be much more difficult to retain till nightfall. With the
+      object of storing up the heat evolved in the generator, it must be covered
+      with some material possessed of the lowest heat-conducting power possible;
+      and the proper positions for that material in order of decreasing
+      importance are the top, sides, and bottom of the plant. The generator may
+      either be covered with a thick layer of straw, carpet, flannel, or the
+      like, as is done in the protection of exposed water- pipes; or it may be
+      provided with a jacket filled with some liquid. In view of the
+      advisability of not having any organic or combustible material near the
+      generator, the solid substances just mentioned may preferably be replaced
+      by one of those partially inorganic compositions sold for "lagging"
+      steam-pipes and engine-cylinders, such as "Fossil meal." Indeed, the exact
+      nature of the lagging matters comparatively little, because the active
+      substance in retaining the heat in the acetylene generator or the
+      steam-pipe is the air entangled in the pores of the lagging; and therefore
+      the value of any particular material depends mainly on its exhibiting a
+      high degree of porosity. The idea of fitting a water jacket round an
+      acetylene generator is not altogether good, but it may be greatly improved
+      upon by putting into the jacket a strong solution of some cheap saline
+      body which has the property of separating from its aqueous solution in the
+      form of crystals containing water of crystallisation, and of evolving much
+      heat in so separating. This method of storing much heat in a small space
+      where a fire cannot be lighted is in common use on some railways, where
+      passengers' foot-warmers are filled with a strong solution of sodium
+      acetate. When sodium acetate is dissolved in water it manifestly exists in
+      the liquid state, and it is presumably present in its anhydrous condition
+      (i.e., not combined with water of crystallisation). The common crystals
+      are solid, and contain 3 molecules of water of crystallisation--also
+      clearly in the solid state. Now, the reaction
+    </p>
+    <p>
+      NaC_2H_3O_2 + 3H_2O = NaC_2H_3O_2.3H_2O
+    </p>
+    <p>
+      (anhydrous acetate)&nbsp;&nbsp;&nbsp;&nbsp;(crystals)
+    </p>
+    <p>
+      evolves 4.37 calories (Berthelot), or 1.46 calorie for each molecule of
+      water; and whereas 1 kilo. of water only evolves 1 large calorie of heat
+      as its temperature falls 1� C., 18 grammes of water (1 gramme-molecule)
+      evolve l.46 large calorie when they enter into combination with anhydrous
+      sodium acetate to assist in forming crystals--and this 1.46 calorie may
+      either be permitted to warm the mass of crystals, or made to do useful
+      work by raising the temperature of some adjacent substance. Sodium acetate
+      crystals dissolve in 3.9 parts by weight of water at 6� C. (43� F.) or in
+      2.4 parts at 37� C. (99� F.). If, then, a jacket round an acetylene
+      apparatus is filled with a warm solution of sodium acetate crystals in
+      (say) 3 parts by weight of water, the liquid will crystallise when it
+      reaches some temperature between 99� and 43� F.; but when the generator
+      comes into action, the heat liberated will change the mass of crystals
+      into a liquid without raising its sensible temperature to anything like
+      the extent that would happen were the jacket full of simple water. Not
+      being particularly warm to the touch, the liquefied product in the jacket
+      will not lose much heat by radiation, &amp;c., into the surrounding air;
+      but when the water in the generator falls again (after evolution of
+      acetylene ceases) the contents of the jacket will also cool, and finally
+      will begin to crystallise once more, passing a large amount of
+      low-temperature heat into the water of the generator, and safely
+      maintaining it for long periods of time at a temperature suitable for the
+      further evolution of gas. Like the liquid in the seal of an isolated
+      gasholder, the liquid in such a jacket will last indefinitely; and
+      therefore the cost of the sodium acetate in negligible.
+    </p>
+    <p>
+      Another method of keeping warm the water in any part of an acetylene
+      installation consists in piling round the apparatus a heap of fresh stable
+      manure, which, as is well known, emits much heat as it rots. Where horses
+      are kept, such a process may be said to cost nothing. It has the advantage
+      over methods of lagging or jacketing that the manure can be thrown over
+      any pipe, water-seal, washing apparatus, &amp;c., even if the plant is
+      constructed in several separate items. Unfortunately the ammonia and the
+      volatile organic compounds which are produced during the natural
+      decomposition of stable manure tend seriously to corrode iron and steel,
+      and therefore this method of protecting an apparatus from frost should
+      only be employed temporarily in times of emergency.
+    </p>
+    <p>
+      CORROSION IN APPARATUS.--All natural water is a solution of oxygen and may
+      be regarded also as a weak solution of the hypothetical carbonic acid. It
+      therefore causes iron to rust more or less quickly; and since no paint is
+      absolutely waterproof, especially if it has been applied to a surface
+      already coated locally with spots of rust, iron and steel cannot be
+      perfectly protected by its aid. More particularly at a few inches above
+      and below the normal level of the water in a holder, therefore, the metal
+      soon begins to exhibit symptoms of corrosion which may eventually proceed
+      until the iron is eaten away or becomes porous. One method of prolonging
+      the life of such apparatus is to give it fresh coats of paint
+      periodically; but unless the old layers are removed where they have
+      cracked or blistered, and the rust underneath is entirely scraped off
+      (which is practically impossible), the new paint films will not last very
+      long. Another more elegant process for preserving any metal like iron
+      which is constantly exposed to the attack of a corrosive liquid, and which
+      is readily applicable to acetylene holders and their tanks, depends on the
+      principle of galvanic action. When two metals in good electrical contact
+      are immersed in some liquid that is capable of attacking both, only that
+      metal will be attacked which is the more electro-positive, or which (the
+      same thing in other words) is the more readily attacked by the liquid,
+      evolving the more heat during its dissolution. As long as this action is
+      proceeding, as long, that is, as some of the more electro- positive
+      material is present, the less electro-positive material will not suffer.
+      All that has to be done, therefore, to protect the walls of an
+      acetylene-holder tank and the sides of its bell is to hang in the seal,
+      supported by a copper wire fastened to the tank walls by a trustworthy
+      electrical joint (soldering or riveting it), a plate or rod of some more
+      electro-positive metal, renewing that plate or rod before it is entirely
+      eaten away. [Footnote: Contact between the bell and the rod may be
+      established by means of a flexible metallic wire; or a separate rod might
+      be used for the bell itself.] If the iron is bare or coated with lead
+      (paint may be overlooked), the plate may be zinc; if the iron is
+      galvanised, <i>i.e.</i>, coated with zinc, the plate may be aluminium or
+      an alloy of aluminium and zinc. The joint between the copper wire and the
+      zinc or aluminium plate should naturally be above the water-level. The
+      foregoing remarks should be read in conjunction with what was said in
+      Chapter II., about the undesirability of employing a soft solder
+      containing lead in the construction of an acetylene generator. Here it is
+      proposed intentionally to set up a galvanic couple to prevent corrosion;
+      there, with the same object in view, the avoidances of galvanic action is
+      counselled. The reason for this difference is self-evident; here a foreign
+      metal is brought into electrical contact with the apparatus in order that
+      the latter may be made electro-negative; but when a joint is soldered with
+      lead, the metal of the generator is unintentionally made electro-positive.
+      Here the plant is protected by the preferential corrosion of a cheap and
+      renewable rod; in the former case the plant is encouraged to rust by the
+      unnecessary presence of an improperly selected metal.
+    </p>
+    <p>
+      OTHER ITEMS IN GENERATING PLANT.--It has been explained in Chapter II.
+      that the reaction between calcium carbide and water is very tumultuous in
+      character, and that it occurs with great rapidity. Clearly, therefore, the
+      gas comes away from the generator in rushes, passing into the next item of
+      the plant at great speed for a time, and then ceasing altogether. The
+      methods necessarily adopted for purifying the crude gas are treated of in
+      Chapter V.; but it is manifest now that no purifying material can prove
+      efficient unless the acetylene passes through it at a uniform rate, and at
+      one which is as slow as other conditions permit. For this reason the
+      proper position of the holder in an acetylene installation is before the
+      purifier, and immediately after the condenser or washer which adjoins the
+      generator. By this method of design the holder is filled up irregularly,
+      the gas passing into it sometimes at full speed, sometimes at an
+      imperceptible rate; but if the holder is well balanced and guided this is
+      a matter of no consequence. Out of the holder, on the other hand, the gas
+      issues at a rate which is dependent upon the number and capacity of the
+      burners in operation at any moment; and in ordinary conditions this rate
+      is so much more uniform during the whole of an evening than the rate at
+      which the gas is evolved from the carbide, that a purifier placed after
+      the holder is given a far better opportunity of extracting the impurities
+      from the acetylene than it would have were it situated before the holder,
+      as is invariably the case on coal-gas works.
+    </p>
+    <p>
+      For many reasons, such as capacity for isolation when being recharged or
+      repaired, it is highly desirable that each item in an acetylene plant
+      shall be separated, or capable of separation, from its neighbours; and
+      this observation applies with great force to the holder and the
+      decomposing vessel of the generator. In all large plants each vessel
+      should be fitted with a stopcock at its inlet and, if necessary, one at
+      its outlet, being provided also with a by-pass so that it can be thrown
+      out of action without interfering with the rest of the installation. In
+      the best practice the more important vessels, such as the purifiers, will
+      be in duplicate, so that unpurified gas need not be passed into the
+      service while a solitary purifier is being charged afresh. In smaller
+      plants, where less skilled labour will probably be bestowed on the
+      apparatus, and where hand-worked cocks are likely to be neglected or
+      misused, some more, automatic arrangement for isolating each item is
+      desirable. There are two automatic devices which may be employed for the
+      purposes in view, the non-return valve and the water-seal. The non-return
+      valve is simply a mushroom or ball valve without handle, lifted off its
+      seat by gas passing from underneath whenever the pressure of the gas
+      exceeds the weight of the valve, but falling back on to its seat and
+      closing the pipe when the pressure decreases or when pressure above is
+      greater than that below. The apparatus works perfectly with a clean gas or
+      liquid which is not corrosive; but having regard to the possible presence
+      of tarry products, lime dust, or sludge, condensed water loaded with
+      soluble impurities, &amp;c., in the acetylene, a non-return valve is not
+      the best device to adopt, for both it and the hand-worked cock or screw-
+      down valve are liable to stick and give trouble. The best arrangement in
+      all respects, especially between the generator and the holder, is a
+      water-seal. A water-seal in made by leading the mouth of a pipe delivering
+      gas under the level of water in a suitable receptacle, so that the issuing
+      gas has to bubble through the liquid. Gas cannot pass backwards through
+      the pipe until it has first driven so much liquid before it that the level
+      in the seal has fallen below the pipe's mouth; and if the end of the pipe
+      is vertical more pressure than can possibly be produced in the apparatus
+      is necessary to effect this. Omitting the side tube <i>b</i>, one variety
+      of water-seal is shown at D in Fig. 7 on page 103. The water being at the
+      level <i>l</i>, gas enters at <i>a</i> and bubbles through it, escaping
+      from the apparatus at <i>c</i>. It cannot return from <i>c</i> to <i>a</i>
+      without driving the water out of the vessel till its level falls from <i>f</i>
+      to <i>g</i>; and since the area of the vessel is much greater than that of
+      the pipe, so great a fall in the vessel would involve a far greater rise
+      in <i>a</i>. It is clear that such a device, besides acting as a
+      non-return valve, also fulfils two other useful functions: it serves to
+      collect and retain all the liquid matter that may be condensed in the pipe
+      <i>a</i> from the spot at which it was originally level or was given a
+      fall to the seal, as well as that condensing in <i>c</i> as far as the
+      spot where <i>c</i> dips again; and it equally acts as a washer to the
+      gas, especially if the orifice <i>g</i> of the gas-inlet pipe is not left
+      with a plain mouth as represented in the figure, but terminates in a large
+      number of small holes, the pipe being then preferably prolonged
+      horizontally, with minute holes in it so as to distribute the gas
+      throughout the entire vessel. Such an apparatus requires very little
+      attention. It may with advantage be provided with the automatic
+      arrangement for setting the water-level shown at <i>d</i> and <i>e</i>. <i>d</i>
+      is a tunnel tube extending almost to the bottom of the vessel, and <i>e</i>
+      is a curved run-off pipe of the form shown. The lower part of the upper
+      curve in <i>e</i> is above the level <i>f</i>, being higher than <i>f</i>
+      by a distance equal to that of the gas pressure in the pipes; and
+      therefore when water is poured into the funnel it fills the vessel till
+      the internal level reaches <i>f</i>, when the surplus overflows of itself.
+      The operation thus not only adjusts the quantity of water present to the
+      desired level so that <i>a</i> cannot become unsealed, but it also renews
+      the liquid when it has become foul and nearly saturated with dissolved and
+      condensed impurities from the acetylene. It would be a desirable
+      refinement to give the bottom of the vessel a slope to the mouth of <i>e</i>,
+      or to some other spot where a large-bore draw-off cock could be fitted for
+      the purpose of extracting any sludge of lime, &amp;c., that may collect.
+      By having such a water-seal, or one simpler in construction, between the
+      generator and the holder, the former may be safely opened at any time for
+      repairs, inspection, or the insertion of a fresh charge of carbide while
+      the holder is full of gas, and the delivery of acetylene to the burners at
+      a specified pressure will not be interrupted. If a cock worked by hand
+      were employed for the separation of the holder from the generator, and the
+      attendant were to forget to close it, part or all of the acetylene in the
+      holder would escape from the generator when it was opened or disconnected.
+    </p>
+    <p>
+      Especially when a combined washer and non-return valve follows immediately
+      after a generator belonging to the shoot type, and the mouth of the shoot
+      is open to the air in the plant-house, it is highly desirable that the
+      washer shall be fitted with some arrangement of an automatic kind for
+      preventing the water level rising much above its proper position. The
+      liquid in a closed washer tends to rise as the apparatus remains in use,
+      water vapour being condensed within it and liquid water, or froth of lime,
+      being mechanically carried forward by the stream of acetylene coming from
+      the decomposing chamber. In course of time, therefore, the vertical depth
+      to which the gas-inlet pipe in the washer is sealed by the liquid
+      increases; and it may well be that eventually the depth in question, plus
+      the pressure thrown by the holder bell, may become greater than the
+      pressure which can be set up inside the generator without danger of gas
+      slipping under the lower edge of the shoot. Should this state of things
+      arise, the acetylene can no longer force its way through the washer into
+      the holder bell, but will escape from the mouth of the shoot; filling the
+      apparatus-house with gas, and offering every opportunity for an explosion
+      if the attendant disobeys orders and takes a naked light with him to
+      inspect the plant.
+    </p>
+    <p>
+      It is indispensable that every acetylene apparatus shall be fitted with a
+      safety-valve, or more correctly speaking a vent-pipe. The generator must
+      have a vent-pipe in case the gas-main leading to the holder should become
+      blocked at any time, and the acetylene which continues to be evolved in
+      all water-to-carbide apparatus, even after the supply of water has been
+      cut off be unable to pass away. Theoretically a non-automatic apparatus
+      does not require a vent-pipe in its generator because all the gas enters
+      the holder immediately, and is, or should be, unable to return through the
+      intermediate water seal; practically such a safeguard is absolutely
+      necessary for the reason given. The holder must have a safety-valve in
+      case the cutting-off mechanism of the generator fails to act, and more gas
+      passes into it than it can store. Manifestly the pressure of the gas in a
+      water-sealed holder or in any generator fitted with a water-sealed lid
+      cannot rise above that corresponding with the depth of water in the seal;
+      for immediately the pressure, measured in inches of water, equals the
+      depth of the sealing liquid, the seal will be blown out, and the gas will
+      escape. Such an occurrence, however, as the blowing of a seal must never
+      be possible in any item of an acetylene plant, more especially in those
+      items that are under cover, for the danger that the issuing gas might be
+      fired or might produce suffocation would be extremely great. Typical
+      simple forms of vent-pipe suitable for acetylene apparatus are shown in
+      Fig. 7. In each case the pipe marked "vent" is the so-called safety-valve;
+      it is open at its base for the entry of gas, and open at its top for the
+      escape of the acetylene into the atmosphere, such top being in all
+      instances carried through the roof of the generator-house into the open
+      air, and to a spot distant from any windows of that house or of the
+      residence, where it can prove neither dangerous nor a nuisance by reason
+      of its odour. At A is represented the vent-pipe of a displacement vessel,
+      which may either be part of a displacement holder or of a generator
+      working on the displacement principle. The vent-pipe is rigidly fixed to
+      the apparatus. If gas is generated within the closed portion of the holder
+      or passes through it, and if the pressure so set up remains less than that
+      which is needed to move the water from the level <i>l</i> to the levels <i>l'</i>
+      and <i>l"</i>, the mouth of the pipe is under water, and acetylene cannot
+      enter it; but immediately such an amount of gas is collected, or such
+      pressure is produced that the interior level sinks below <i>l"</i>, which
+      is that of the mouth of the pipe, it becomes unsealed, and the surplus gas
+      freely escapes. There are two minor points in connexion with this form of
+      vent-pipe often overlooked. At the moment when the water arrives at <i>l"</i>
+      in the closed half of the apparatus, its level in the interior of the
+      vent-pipe stands at <i>l'</i>, identical with that in the open hall of the
+      apparatus (for the mouth of the vent-pipe and the water in the open hall
+      of the apparatus are alike exposed to the pressure of the atmosphere
+      only). When the water, then, descends just below <i>l"</i> there is an
+      amount of water inside the pipe equal in height to the distance between <i>l'</i>
+      and <i>l"</i>; and before the acetylene can escape, it must either force
+      this water as a compact mass out of the upper mouth of the vent-pipe
+      (which it is clearly not in a position to do), drive it out of the upper
+      mouth a little at a time, or bubble through it till the water is gradually
+      able to run downwards out of the pipe as its lower opening is more fully
+      unsealed. In practice the acetylene partly bubbles through this water and
+      partly drives it out of the mouth of the pipe; on some occasions
+      temporarily yielding irregular pressures at the burners which cause them
+      to jump, and always producing a gurgling noise in the vent- pipe which in
+      calculated to alarm the attendant. If the pipe is too small in diameter,
+      and especially if its lower orifice is cut off perfectly horizontal and
+      constricted slightly, the water may refuse to escape from the bottom
+      altogether, and the pipe will fail to perform its allotted task. It is
+      better therefore to employ a wide tube, and to cut off its mouth
+      obliquely, or to give its lower extremity the shape of an inverted funnel.
+      At the half of the central divided drawing marked B (Fig. 7) is shown a
+      precisely similar vent-pipe affixed to the bell of a rising holder, which
+      behaves in an identical fashion when by the rising of the bell its lower
+      end is lifted out of the water in the tank. The features described above
+      as attendant, upon the act of unsealing of the displacement-holder
+      vent-pipe occur here also, but to a less degree; for the water remaining
+      in the pipe at the moment of unsealing is only that which corresponds with
+      the vertical distance between <i>l'</i> and <i>l"</i>, and in a rising
+      holder this is only a height always equal to the pressure given by the
+      bell. Nevertheless this form of vent-pipe produces a gurgling noise, and
+      would be better for a trumpet-shaped mouth. A special feature of the pipe
+      in B is that unless it is placed symmetrically about the centre of the
+      bell its weight tends to throw the bell out of the vertical, and it may
+      have to be supported at its upper part; conversely, if the pipe is
+      arranged concentrically in the bell, it may be employed as part of the
+      guiding arrangement of the bell itself. Manifestly, as the pipe must be
+      long enough to extend through the roof of the generator-house, its weight
+      materially increases the weight of the bell, and consequently the gas
+      pressure in the service; this fact is not objectionable provided due
+      allowance is made for it. So tall a vent-pipe, however, seriously raises
+      the centre of gravity of the bell and may make it top-heavy. To work well
+      the centre of gravity of a holder bell should be as low as possible, any
+      necessary weighting being provided symmetrically about its circumference
+      and close to its bottom edge. The whole length of an ascending vent-pipe
+      need not be carried by the rising bell, because the lower portion, which
+      must be supported by the bell, can be arranged to slide inside a wider
+      length of pipe which is fixed to the roof of the generator-house at the
+      point where it passes into the open air.
+    </p>
+    <p class="ctr">
+      <a href="images/111.png"><img src="images/111th.png"
+      alt="FIG. 7.--TYPICAL FORMS OF VENT-PIPES OR SAFETY-VALVES" /></a>
+    </p>
+    <p>
+      A refinement upon this vent-pipe is represented at C, where it is rigidly
+      fastened to the tank of the holder, and has its internal aperture always
+      above the level of the water in the apparatus. Rigidly fixed to the crown
+      of the bell is a tube of wider diameter, <i>h</i>, which is closed at its
+      upper end. <i>h</i> is always full of gas, and its mouth is normally
+      beneath the level of the water in the seal; but when the bell rises to its
+      highest permissible position, the mouth of <i>h</i> comes above the water,
+      and communication is opened between the holder and the outer atmosphere.
+      No water enters the vent-pipe from the holder, and therefore no gurgling
+      or irregular pressure is produced. Another excellent arrangement of a
+      vent-pipe, suggested by Klinger of Gumpoldskirchen, is shown at D, a
+      drawing which has already been partly considered as a washer and
+      water-seal. For the present purpose the main vessel and its various pipes
+      are so dimensioned that the vertical height <i>g</i> to <i>f</i> is always
+      appreciably greater than the gas pressure in the service or in the
+      generator or gasholder to which it is connected. In these circumstances
+      the gas entering at <i>a</i> depresses the water in the pipe below the
+      level <i>f</i> to an extent equal to the pressure at which it enters that
+      pipe--an extent normally less than the distance <i>f</i> to <i>g</i>; and
+      therefore gas never passes into the body of the vessel, but travels away
+      by the side tube <i>b</i> (which in former references to this drawing was
+      supposed to be absent). If, however, the pressure at <i>a</i> exceeds that
+      of the vertical height <i>f</i> to <i>g</i>, gas escapes at <i>g</i>
+      through the water, and is then free to reach the atmosphere by means of
+      the vent <i>c</i>. As before, <i>d</i> serves to charge the apparatus with
+      water, and <i>e</i> to ensure a proper amount being added. Clearly no
+      liquid can enter the vent-pipe in this device. Safety-valves such as are
+      added to steam-boilers and the like, which consist of a weighted lever
+      holding a conical valve down against its seat, are not required in
+      acetylene apparatus, for the simpler hydraulic seals discussed above can
+      always be fitted wherever they may be needed. It should be noticed that
+      these vent-pipes only come into operation in emergencies, when they are
+      required to act promptly. No economy is to be effected by making them
+      small in diameter. For obvious reasons the vent-pipe of a holder should
+      have a diameter equal to that of the gas-inlet tube, and the vent-pipe of
+      a generator be equal in size to the gas-leading tube.
+    </p>
+    <p>
+      FROTHING IN GENERATORS.--A very annoying trouble which crops up every now
+      and then during the evolution of acetylene consists in the production of
+      large masses of froth within the generator. In the ordinary way,
+      decomposition of carbide is accompanied by a species of effervescence, but
+      the bubbles should break smartly and leave the surface of the liquid
+      reasonably free from foam. Sometimes, however, the bubbles do not break,
+      but a persistent "head" of considerable height is formed. Further
+      production of gas only increases the thickness of the froth until it rises
+      so high that it is carried forward through the gas-main into the next item
+      of the plant. The froth disappears gradually in the pipes, but leaves in
+      them a deposit of lime which sooner or later causes obstructions by
+      accumulating at the angles and dips; while during its presence in the main
+      the steady passage of gas to the holder is interrupted and the burners may
+      even be made to jump. Manifestly the defect is chiefly, if not always, to
+      be noticed in the working of carbide-to-water generators. The phenomenon
+      has been examined by Mauricheau-Beaupr�, who finds that frothing is not
+      characteristic of pure carbide and that it cannot be attributed to any of
+      the impurities normally present in commercial carbide. If, however, the
+      carbide contains calcium chloride, frothing is liable to occur. A 0.1 per
+      cent. solution of calcium chloride appears to yield some foam when carbide
+      is decomposed in it, and a 1 per cent. solution to foam in a pronounced
+      manner. In the absence of calcium chloride, the main cause of frothing
+      seems to be the presence in the generator of new paint or tar. If a
+      generator is taken into use before the paint in any part of it which
+      becomes moistened by warm lime-water has had opportunity of drying
+      thoroughly hard, frothing is certain to occur; and even if the carbide has
+      been stored for only a short time in a tin or drum which has been freshly
+      painted, a production of froth will follow when it is decomposed in water.
+      The products of the polymerisation of acetylene also tend to produce
+      frothing, but not to such an extent as the turpentine in paint and the
+      lighter constituents of coal-tar. Carbide stored even temporarily in a
+      newly painted tin froths on decomposition because it has absorbed among
+      its pores some of the volatile matter given off by the paint during the
+      process of desiccation.
+    </p>
+    <p>
+      THE "DRY" PROCESS OF GENERATION.--A process for generating acetylene,
+      totally different in principle from those hitherto considered, has been
+      introduced in this country. According to the original patents of G. J.
+      Atkins, the process consisted in bringing small or powdered carbide into
+      mechanical contact with some solid material containing water, the water
+      being either mixed with the solid reagent or attached to it as water of
+      crystallisation. Such reagents indeed were claimed as crude starch and the
+      like, the idea being to recover a by-product of pecuniary value. Now the
+      process seems to be known only in that particular form in which granulated
+      carbide is treated with crystallised sodium carbonate, <i>i.e.</i>, common
+      washing soda. Assuming the carbide employed to be chemically pure and the
+      reaction between it and the water of crystallisation contained in ordinary
+      soda crystals to proceed quantitatively, the production of acetylene by
+      the dry process should be represented by the following chemical equation:
+    </p>
+    <p>
+      5CaC_2 + Na_2CO_3.10H_2O = 5C_2H_2 + 5Ca(OH)_2 + Na_2CO_3.
+    </p>
+    <p>
+      On calculating out the molecular weights, it will be seen that 286 parts
+      of washing soda should suffice for the decomposition of 320 parts of pure
+      calcium carbide, or in round numbers 9 parts of soda should decompose 10
+      parts of carbide. In practice, however, it seems to be found that from 1
+      to 1.5 parts of soda are needed for every part of carbide.
+    </p>
+    <p>
+      The apparatus employed is a metal drum supported on a hollow horizontal
+      spindle, one end of which is closed and carries a winch handle, and the
+      other end of which serves to withdraw the gas generated in the plant. The
+      drum is divided into three compartments by means of two vertical
+      partitions so designed that when rotation proceeds in one particular
+      direction portions of the two reagents stored in one end compartment pass
+      into the centre compartment; whereas when rotation proceeds in the
+      opposite direction, the material in the centre compartment is merely mixed
+      together, partly by the revolution of the drum, partly with the assistance
+      of a stationary agitator slung loosely from the central spindle. The other
+      end compartment contains coke or sawdust or other dry material through
+      which the gas passes for the removal of lime or other dust carried in
+      suspension as it issues from the generating compartment. The gas then
+      passes through perforations into the central spindle, one end of which is
+      connected by a packed joint with a fixed pipe, which leads to a seal or
+      washer containing petroleum. Approached from a theoretical standpoint, it
+      will be seen that this method of generation entirely sacrifices the
+      advantages otherwise accruing from the use of liquid water as a means for
+      dissipating the heat of the chemical reaction, but on the other hand,
+      inasmuch as the substances are both solid, the reaction presumably occurs
+      more slowly than it would in the presence of liquid water; and moreover
+      the fact that the water employed to act upon the carbide is in the solid
+      state and also more or less combined with the rest of the sodium carbonate
+      molecule, means that, per unit of weight, the water decomposed must render
+      latent a larger amount of heat than it would were it liquid. Experiments
+      made by one of the authors of this book tend to show that the gas evolved
+      from carbide by the dry process contains rather less phosphorus than it
+      might in other conditions of generation, and as a fact gas made by the dry
+      process is ordinarily consumed without previous passage through any
+      chemical purifying agent. It is obvious, however, that the use of the
+      churn described above greatly increases the labour attached to the
+      production of the gas; while it is not clear that the yield per unit
+      weight of carbide decomposed should be as high as that obtained in wet
+      generation. The inventor has claimed that his by-product should be
+      valuable and saleable, apparently partly on the ground that it should
+      contain caustic soda. Evidence, however, that a reaction between the
+      calcium oxide or hydroxide and the sodium carbonate takes place in the
+      prevailing conditions is not yet forthcoming, and the probabilities are
+      that such decomposition would not occur unless the residue were largely
+      diluted with water. [Footnote: The oldest process employed for
+      manufacturing caustic soda consisted in mixing a solution of sodium
+      carbonate with quick or slaked lime, and it has been well established that
+      the causticisation of the soda will not proceed when the concentration of
+      the liquid is greater than that corresponding with a specific gravity of
+      about 1-10, <i>i.e.</i>, when the liquid contains more than some 8 to 10
+      per cent, of sodium hydroxide.] Conversely there are some grounds for
+      believing that the dry residue is less useful than an ordinary wet residue
+      for horticultural purposes, and also for the production of whitewash. From
+      a financial standpoint, the dry process suffers owing to the expense
+      involved in the purchase of a second raw material, for which but little
+      compensation can be discovered unless it is proved that the residue is
+      intrinsically more valuable than common acetylene-lime and can be sold or
+      used advantageously by the ordinary owner of an installation. The
+      discarding of the chemical purifier at the present day is a move of which
+      the advantage may well be overrated.
+    </p>
+    <p>
+      ARTIFICIAL LIGHTING OF GENERATOR SHEDS.--It has already been argued that
+      all normal or abnormal operations in connexion with an acetylene
+      generating plant should be carried out, if possible, by daylight; and it
+      has been shown that on no account must a naked light ever be taken inside
+      the house containing such a plant. It will occasionally happen, however,
+      that the installation must be recharged or inspected after nightfall. In
+      order to do this in safety, a double window, incapable of being opened,
+      should be fitted in one wall of the house, as far as possible from the
+      door, and in such a position that the light may fall on to all the
+      necessary places. Outside this window may be suspended an ordinary hand-
+      lantern burning oil or paraffin; or, preferably, round this window may be
+      built a closed lantern into which some source of artificial light may be
+      brought. If the acetylene plant has an isolated holder of considerable
+      size, there is no reason at all why a connexion should not be made with
+      the service-pipes, and an acetylene flame be used inside this lantern; but
+      with generators of the automatic variety, an acetylene light is not so
+      suitable, because of the fear that gas may not be available precisely at
+      the moment when it is necessary to have light in the shed. It would,
+      however, be a simple matter to erect an acetylene burner inside the
+      lantern in such a way that when needed an oil-lamp or candle could be used
+      instead. Artificial internal light of any kind is best avoided; the only
+      kind permissible being an electric glow-lamp. If this is employed, it
+      should be surrounded by a second bulb or gas-tight glass jacket, and
+      preferably by a wire cage as well; the wires leading to it must be
+      carefully insulated, and all switches or cut-outs (which may produce a
+      spark) must be out of doors. The well-known Davy safety or miner's lamp is
+      not a trustworthy instrument for use with acetylene because of (<i>a</i>)
+      the low igniting-point of acetylene; (<i>b</i>) the high temperature of
+      its flame; and (<i>c</i>) the enormous speed at which the explosive wave
+      travels through a mixture of acetylene and air. For these reasons the
+      metallic gauze of the Davy lamp is not so efficient a protector of the
+      flame as it is in cases of coal-gas, methane, &amp;c. Moreover, in
+      practice, the Davy lamp gives a poor light, and unless in constant use is
+      liable to be found out of order when required. It should, however, be
+      added that modern forms of the safety lamp, in which the light is
+      surrounded by a stout glass chimney and only sufficient gauze is used for
+      the admission of fresh air and for the escape of the combustion products,
+      appear quite satisfactory when employed in an atmosphere containing some
+      free acetylene. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkiv" id="iv">CHAPTER IV</a>
+    </h2>
+    <h3>
+      THE SELECTION OF AN ACETYLENE GENERATOR
+    </h3>
+    <p>
+      In Chapter II. an attempt has been made to explain the physical and
+      chemical phenomena which accompany the interaction of calcium carbide and
+      water, and to show what features in the reaction are useful and what
+      inconvenient in the evolution of acetylene on a domestic or larger scale.
+      Similarly in Chapter III. have been described the various typical devices
+      which may be employed in the construction of different portions of
+      acetylene plant, so that the gas may be generated and stored under the
+      best conditions, whether it is evolved by the automatic or by the non-
+      automatic system. This having been done, it seemed of doubtful utility to
+      include in the first edition of this work a long series of illustrations
+      of such generators as had been placed on the markets by British, French,
+      German, and American makers. It would have been difficult within
+      reasonable limits to have reproduced diagrams of all the generators that
+      had been offered for sale, and absolutely impossible within the limits of
+      a single hand-book to picture those which had been suggested or patented.
+      Moreover, some generating apparatus appeared on the market ephemerally;
+      some was constantly being modified in detail so as to alter parts which
+      experience or greater knowledge had shown the makers to be in need of
+      alteration, while other new apparatus was constantly being brought out. On
+      these and other grounds it did not appear that much good purpose would
+      have been served by describing the particular apparatus which at that time
+      would have been offered to prospective purchasers. It seemed best that the
+      latter should estimate the value and trustworthiness of apparatus by
+      studying a section of it in the light of the general principles of
+      construction of a satisfactory generator as enunciated in the book. While
+      the position thus taken by the authors in 1903 would still not be
+      incorrect, it has been represented to them that it would scarcely be
+      inconsistent with it to give brief descriptions of some of the generators
+      which are now being sold in Great Britain and a few other countries. Six
+      more years' experience in the design and manufacture of acetylene plant
+      has enabled the older firms of manufacturers to fix upon certain standard
+      patterns for their apparatus, and it may confidently be anticipated that
+      many of these will survive a longer period. Faulty devices and designs
+      have been weeded out, and there are lessons of the past as well as
+      theoretical considerations to guide the inventor of a new type of
+      generator. On those grounds, therefore, an attempt has now been made to
+      give brief descriptions, with sectional views, of a number of the
+      generators now on the market in Great Britain. Moreover, as the first
+      edition of this book found many readers in other countries, in several of
+      which there is greater scope for the use of acetylene, it has been decided
+      to describe also a few typical or widely used foreign generators. All the
+      generators described must stand or fall on their merits, which cannot be
+      affected by any opinion expressed by the authors. In the descriptions,
+      which in the first instance have generally been furnished by the
+      manufacturers of the apparatus, no attempt has therefore been made to
+      appraise the particular generators, and comparisons and eulogistic
+      comments have been excluded. The descriptions, however, would nevertheless
+      have been somewhat out of place in the body of this book; they have
+      therefore been relegated to a special Appendix. It has, of course, been
+      impossible to include the generators of all even of the English
+      manufacturers, and doubtless many trustworthy ones have remained
+      unnoticed. Many firms also make other types of generators in addition to
+      those described. It must not be assumed that because a particular make of
+      generator is not mentioned it is necessarily faulty. The apparatus
+      described may be regarded as typical or well known, and workable, but it
+      is not by reason of its inclusion vouched for in any other respect by the
+      authors. The Appendix is intended, not to bias or modify the judgment of
+      the would-be purchaser of a generator, but merely to assist him in
+      ascertaining what generators there are now on the market.
+    </p>
+    <p>
+      The observations on the selection of a generator which follow, as well as
+      any references in other chapters to the same matter, have been made
+      without regard to particular apparatus of which a description may (or may
+      not) appear in the Appendix. With this premise, it may be stated that the
+      intending purchaser should regard the mechanism of a generator as shown in
+      a sectional view or on inspection of the apparatus itself. If the
+      generator is simple in construction, he should be able to understand its
+      method of working at a glance, and by referring it to the type (<i>vide</i>
+      Chapter III.) to which it belongs, be able to appraise its utility from a
+      chemical and physical aspect from what has already been said. If the
+      generator is too complicated for ready understanding of its mode of
+      working, it is not unlikely to prove too complicated to behave well in
+      practice. Not less important than the mechanism of a generator is good
+      construction from the mechanical point of view, <i>i.e.</i>, whether stout
+      metal has been employed, whether the seams and joints are well finished,
+      and whether the whole apparatus has been built in the workman- like
+      fashion which alone can give satisfaction in any kind of plant. Bearing
+      these points in mind, the intending purchaser may find assistance in
+      estimating the mechanical value of an apparatus by perusing the remainder
+      of this chapter, which will be devoted to elaborating at length the
+      so-called scientific principles underlying the construction of a
+      satisfactory generator, and to giving information on the mechanical and
+      practical points involved.
+    </p>
+    <p>
+      It is perhaps desirable to remark that there is scarcely any feature in
+      the generation of acetylene from calcium carbide and water--certainly no
+      important feature--which introduces into practice principles not already
+      known to chemists and engineers. Once the gas is set free it ranks simply
+      as an inflammable, moisture-laden, somewhat impure, illuminating and
+      heat-giving gas, which has to be dried, purified, stored, and led to the
+      place of combustion; it is in this respect precisely analogous to coal-
+      gas. Even the actual generation is only an exothermic, or heat-producing,
+      reaction between a solid and a liquid, in which rise of temperature and
+      pressure must be prevented as far as possible. Accordingly there is no
+      fundamental or indispensable portion of an acetylene apparatus which lends
+      itself to the protection of the patent laws; and even the details (it may
+      be said truthfully, if somewhat cynically) stand in patentability in
+      inverse ratio to their simplicity and utility.
+    </p>
+    <p>
+      During the early part of 1901 a Committee appointed by the British Home
+      Office, "to advise as to the conditions of safety to which acetylene
+      generators should conform, and to carry out tests of generators in the
+      market in order to ascertain how far those conform with such conditions,"
+      issued a circular to the trade suggesting that apparatus should be sent
+      them for examination. In response, forty-six British generators were
+      submitted for trial, and were examined in a fashion which somewhat
+      exceeded the instructions given to the Committee, who finally reported to
+      the Explosives Department of the Home Office in a Blue Book, No. Cd. 952,
+      which can be purchased through any bookseller. This report comprises an
+      appendix in which most of the apparatus are illustrated, and it includes
+      the result of the particular test which the Committee decided to apply.
+      Qualitatively the test was useful, as it was identical in all instances,
+      and only lacks full utility inasmuch as the trustworthiness of the
+      automatic mechanism applied to such generators as were intended to work on
+      the automatic system was not estimated. Naturally, a complete valuation of
+      the efficiency of automatic mechanism cannot be obtained from one or even
+      several tests, it demands long-continued watching; but a general notion of
+      reliability might have been obtained. Quantitatively, however, the test
+      applied by the Committee is not so free from reproach, for, from the
+      information given, it would appear to have been less fair to some makers
+      of apparatus than to others. Nevertheless the report is valuable, and
+      indicates the general character of the most important apparatus which were
+      being offered for sale in the United Kingdom in 1900-1901.
+    </p>
+    <p>
+      It is not possible to give a direct answer to the question as to which is
+      the best type of acetylene generator. There are no generators made by
+      responsible firms at the present time which are not safe. Some may be
+      easier to charge and clean than others; some require more frequent
+      attention than others; some have moving parts less likely to fail, when
+      handled carelessly, than others; some have no moving mechanism to fail.
+      For the illumination of a large institution or district where one man can
+      be fully occupied in attending to the plant, cleaning, lighting, and
+      extinguishing the lamps, or where other work can be found for him so as to
+      leave him an hour or so every day to look after the apparatus, the
+      hand-fed carbide-to-water generator L (Fig. 6) has many advantages, and is
+      probably the best of all. In smaller installations choice must be made
+      first between the automatic and the non-automatic principle--the
+      advantages most frequently lying with the latter. If a non-automatic
+      generator is decided upon, the hand carbide-feed or the flooded-
+      compartment apparatus is almost equally good; and if automatism is
+      desired, either a flooded-compartment machine or one of the most
+      trustworthy types of carbide-feed apparatus may be taken. There are
+      contact apparatus on the markets which appear never to have given trouble,
+      and those are worthy of attention. Some builders advocate their own
+      apparatus because the residue is solid and not a cream. If there is any
+      advantage in this arising from greater ease in cleaning and recharging the
+      generator and in disposing of the waste, that advantage is usually
+      neutralised by the fear that the carbide may not have been wholly
+      decomposed within the apparatus; and whereas any danger arising from
+      imperfectly spent carbide being thrown into a closed drain may be
+      prevented by flooding the residue with plenty of water in an open vessel,
+      imperfect decomposition in the generator means a deficiency in the amount
+      of gas evolved from a unit weight of solid taken or purchased. In fact,
+      setting on one side apparatus which belong to a notoriously defective
+      system and such as are constructed in large sizes on a system that is only
+      free from overheating, &amp;c., in small sizes; setting aside all
+      generators which are provided with only one decomposing chamber when they
+      are of a capacity to require two or more smaller ones that can more
+      efficiently be cooled with water jackets; and setting aside any form of
+      plant which on examination is likely to exhibit any of the more serious
+      objections indicated in this and the previous chapters, there is
+      comparatively little to choose, from the chemical and physical points of
+      view, between the different types of generators now on the markets. A
+      selection may rather be made on mechanical grounds. The generator must be
+      well able to produce gas as rapidly as it will ever be required during the
+      longest or coldest evening; it must be so large that several more brackets
+      or burners can be added to the service after the installation is complete.
+      It must be so strong that it will bear careless handling and the frequent
+      rough manipulation of its parts. It must be built of stout enough material
+      not to rust out in a few years. Each and all of its parts must be
+      accessible and its exterior visible. Its pipes, both for gas and sludge,
+      must be of large bore (say 1 inch), and fitted at every dip with an
+      arrangement for withdrawing into some closed vessel the moisture, &amp;c.,
+      that may condense. The number of cocks, valves, and moving parts must be
+      reduced to a minimum; cocks which require to be shut by hand before
+      recharging must give way to water-seals. It must be simple in all its
+      parts, and its action intelligible at a glance. It must be easy to
+      charge--preferably even by the sense of touch in darkness. It must be easy
+      to clean. The waste lime must be easily removed. It must be so fitted with
+      vent-pipes that the pressure can never rise above that at which it is
+      supposed to work. Nevertheless, a generator in which these vent-pipes are
+      often brought into use is badly constructed and wasteful, and must be
+      avoided. The water of the holder seal should be distinct from that used
+      for decomposing the carbide; and those apparatus where the holder is
+      entirely separated from the generator are preferable to such as are built
+      all in one, even if water-seals are fitted to prevent return of gas.
+      Apparatus which is supposed to be automatic should be made perfectly
+      automatic, the water or the carbide-feed being locked automatically before
+      the carbide store, the decomposing chamber, or the sludge-cock can be
+      opened. The generating chamber must always be in communication with the
+      atmosphere through a water-sealed vent-pipe, the seal of which, if
+      necessary, the gas can blow at any time. All apparatus should be fitted
+      with rising holders, the larger the better. Duplicate copies of printed
+      instructions should be demanded of the maker, one copy being kept in the
+      generator-house, and the other elsewhere for reference in emergencies.
+      These instructions must give simple and precise information as to what
+      should be done in the event of a breakdown as well as in the normal
+      manipulation of the plant. Technical expressions and descriptions of parts
+      understood only by the maker must be absent from these rules.
+    </p>
+    <p>
+      ADDENDUM.
+    </p>
+    <p>
+      BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OF
+      ACETYLENE GENERATING PLANT
+    </p>
+    <p>
+      Dealing with the "conditions which a generator should fulfil before it can
+      be considered as being safe," the HOME OFFICE COMMITTEE of 1901 before
+      mentioned write as follows:
+    </p>
+    <p>
+      1. The temperature in any part of the generator, when run at the maximum
+      rate for which it is designed, for a prolonged period, should not exceed
+      130� C. This may be ascertained by placing short lengths of wire, drawn
+      from fusible metal, in those parts of the apparatus in which heat is
+      liable to be generated.
+    </p>
+    <p>
+      2. The generator should have an efficiency of not less than 90 per cent.,
+      which, with carbide yielding 5 cubic feet per pound, would imply a yield
+      of 4.5 cubic feet for each pound of carbide used.
+    </p>
+    <p>
+      3. The size of the pipes carrying the gas should be proportioned to the
+      maximum rate of generation, so that undue back pressure from throttling
+      may not occur.
+    </p>
+    <p>
+      4. The carbide should be completely decomposed in the apparatus, so that
+      lime sludge discharged from the generator shall not be capable of
+      generating more gas.
+    </p>
+    <p>
+      5. The pressure in any part of the apparatus, on the generator side of the
+      holder, should not exceed that of 20 inches of water, and on the service
+      side of same, or where no gasholder is provided, should not exceed that of
+      5 inches of water.
+    </p>
+    <p>
+      6. The apparatus should give no tarry or other heavy condensation products
+      from the decomposition of the carbide.
+    </p>
+    <p>
+      7. In the use of a generator regard should be had to the danger of
+      stoppage of passage of the gas and resulting increase of pressure which
+      may arise from the freezing of the water. Where freezing may be
+      anticipated, steps should be taken to prevent it.
+    </p>
+    <p>
+      8. The apparatus should be so constructed that no lime sludge can gain
+      access to any pipes intended for the passage of gas or circulation of
+      water.
+    </p>
+    <p>
+      9. The use of glass gauges should be avoided as far as possible, and,
+      where absolutely necessary, they should be effectively protected against
+      breakage.
+    </p>
+    <p>
+      10. The air space in a generator before charging should be as small as
+      possible.
+    </p>
+    <p>
+      11. The use of copper should be avoided in such parts of the apparatus as
+      are liable to come in contact with acetylene.
+    </p>
+    <p>
+      The BRITISH ACETYLENE ASSOCIATION has drawn up the following list of
+      regulations which, it suggests, shall govern the construction of
+      generators and the installation of piping and fittings:
+    </p>
+    <p>
+      1. Generators shall be so constructed that, when used in accordance with
+      printed instructions, it shall not be possible for any undecomposed
+      carbide to remain in the sludge removed therefrom.
+    </p>
+    <p>
+      2. The limit of pressure in any part of the generator shall not exceed
+      that of 20 inches of water, subject to the exception that if it be shown
+      to the satisfaction of the Executive of the Acetylene Association that
+      higher pressures up to 50 inches of water are necessary in certain
+      generators, and are without danger, the Executive may, with the approval
+      of the Home Office, grant exemption for such generators, with or without
+      conditions.
+    </p>
+    <p>
+      3. The limit of pressure in service-pipes, within the house, shall not
+      exceed 10 inches of water.
+    </p>
+    <p>
+      4. Except when used for special industrial purposes, such as oxy-
+      acetylene welding, factories, lighthouses, portable apparatus containing
+      not more than four pounds of carbide, and other special conditions as
+      approved by the Association, the acetylene plant, such as generators,
+      storage-holders, purifiers, scrubbers, and for washers, shall be in a
+      suitable and well-ventilated outhouse, in the open, or in a lean-to,
+      having no direct communication with a dwelling-house. A blow-off pipe or
+      safety outlet shall be arranged in such a manner as to carry off into the
+      open air any overmake of gas and to open automatically if pressure be
+      increased beyond 20 inches water column in the generating chamber or
+      beyond 10 inches in the gasholder, or beyond the depth of any fluid seal
+      on the apparatus.
+    </p>
+    <p>
+      5. Generators shall have sufficient storage capacity to make a serious
+      blow-off impossible.
+    </p>
+    <p>
+      6. Generators and apparatus shall be made of sufficiently strong material
+      and be of good workmanship, and shall not in any part be constructed of
+      unalloyed copper.
+    </p>
+    <p>
+      7. It shall not be possible under any conditions, even by wrong
+      manipulation of cocks, to seal the generating chamber hermetically.
+    </p>
+    <p>
+      8. It shall not be possible for the lime sludge to choke any of the gas-
+      pipes in the apparatus, nor water-pipes if such be alternately used as
+      safety-valves.
+    </p>
+    <p>
+      9. In the use of a generator, regard shall be had to the danger of
+      stoppage of passage of the gas, and resulting increase of pressure, which
+      may arise from the freezing of the water. Where freezing may be
+      anticipated, steps shall be taken to prevent it.
+    </p>
+    <p>
+      10. The use of glass gauges shall be avoided as far as possible, and where
+      absolutely necessary they shall be effectively protected against breakage.
+    </p>
+    <p>
+      11. The air space in the generator before charging shall be as small as
+      possible, <i>i.e.</i>, the gas in the generating chamber shall not contain
+      more than 8 per cent. of air half a minute after commencement of
+      generation. A sample of the contents, drawn from the holder any time after
+      generation has commenced, shall not contain an explosive mixture, <i>i.e.</i>,
+      more than 18 per cent, of air. This shall not apply to the initial charges
+      of the gasholder, when reasonable precautions are taken.
+    </p>
+    <p>
+      12. The apparatus shall produce no tarry or other heavy condensation
+      products from the decomposition of the carbide.
+    </p>
+    <p>
+      13. The temperature of the gas, immediately on leaving the charge, shall
+      not exceed 212� F. (100� C.)
+    </p>
+    <p>
+      14. No generator shall be sold without a card of instructions suitable for
+      hanging up in some convenient place. Such instructions shall be of the
+      most detailed nature, and shall not presuppose any expert knowledge
+      whatever on the part of the operator.
+    </p>
+    <p>
+      15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING
+      ALLOWED."
+    </p>
+    <p>
+      16. Every generator shall have marked clearly upon the outside a statement
+      of the maximum number of half cubic foot burners and the charge of carbide
+      for which it is designed.
+    </p>
+    <p>
+      17. The Association strongly advise the use of an efficient purifier with
+      generating plant for indoor lighting.
+    </p>
+    <p>
+      18. No composition piping shall be used in any part of a permanent
+      installation.
+    </p>
+    <p>
+      19. Before being covered in, all pipe-work (main and branches) shall be
+      tested in the following manner: A special acetylene generator, giving a
+      pressure of at least 10 inches water column in a gauge fixed on the
+      furthest point from the generator, shall be connected to the pipe-work.
+      All points shall be opened until gas reaches them, when they shall be
+      plugged and the main cock on the permanent generator turned off, but all
+      intermediate main cocks shall be open in order to test underground main
+      and all connexions. The gauge must not show a loss after generator has
+      been turned off for at least two hours.
+    </p>
+    <p>
+      20. After the fittings (pendants, brackets, &amp;c.) have been fixed and
+      all burners lighted, the gas shall be turned off at the burners and the
+      whole installation shall be re-tested, but a pressure of 5 inches shall be
+      deemed sufficient, which shall not drop lower than to 4-1/2 inches on the
+      gauge during one hour's test.
+    </p>
+    <p>
+      21. No repairs to, or alterations in, any part of a generator, purifier,
+      or other vessel which has contained acetylene shall be commenced, nor,
+      except for recharging, shall any such part or vessel be cleaned out until
+      it has been completely filled with water, so as to expel any acetylene or
+      mixture of acetylene and air which may remain in the vessel, and may cause
+      a risk of explosion.
+    </p>
+    <p>
+      <i>Recommendation</i>.--It being the general practice to store carbide in
+      the generator-house, the Association recommend that the carbide shall be
+      placed on a slightly raised platform above the floor level.
+    </p>
+    <p>
+      THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15,
+      1907, of its Rules and Regulations <i>re</i> artificial lighting on
+      insured premises, includes the following stipulations applicable to
+      acetylene:
+    </p>
+    <p>
+      Any apparatus, except as below, for generating, purifying, enriching,
+      compressing or storing gas, must be either in the open or in a building
+      used for such purposes only, not communicating directly with any building
+      otherwise occupied.
+    </p>
+    <p>
+      An acetylene portable apparatus is allowed, provided it holds a charge of
+      not more than 2 lb. of carbide.
+    </p>
+    <p>
+      A cylinder containing not more than 20 cubic feet of acetylene compressed
+      and (or) dissolved in accordance with an Order of Secretary of State under
+      the Explosives Act, 1875, is allowed.
+    </p>
+    <p>
+      The use of portable acetylene lamps containing charges of carbide
+      exceeding the limit of 2 lb. allowed under these Rules (the average charge
+      being about 18 lb.) is allowed in the open or in buildings in course of
+      erection.
+    </p>
+    <p>
+      Liquid acetylene must not be used or stored on the premises.
+    </p>
+    <p>
+      The pipe, whether flexible or not, connecting an incandescent gas lamp to
+      the gas-supply must be of metal with metal connexions.
+    </p>
+    <p>
+      (The reference in these Rules to the storage of carbide has been quoted in
+      Chapter II. (page 19).)
+    </p>
+    <p>
+      These rules are liable to revision from time to time.
+    </p>
+    <p>
+      The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following
+      code of rules for the construction, erection, and manipulation of
+      acetylene apparatus:
+    </p>
+    <p>
+      I. <i>Rules for Construction.</i>
+    </p>
+    <p>
+      1. All apparatus for the generation, purification, and storage of
+      acetylene must be constructed of sheet or cast iron. Holder tanks may be
+      built of brick.
+    </p>
+    <p>
+      2. When bare, galvanised, or lead-coated sheet-iron is used, the sides of
+      generators, purifiers, condensers, holder tanks, and (if present) washers
+      and driers must be built with the following gauges as minima:
+    </p>
+<pre xml:space="preserve">
+                             Holder bells.    All other apparatus.
+
+
+Up to 7 cubic feet capacity     0.75 mm.          1.00 mm.
+From 7 to 18         "          1.00              1.25
+From 18 to 53        "          1.25              1.50
+Above 53             "          1.50              2.00
+</pre>
+    <p>
+      When not constructed of cast-iron, the bottoms, covers, and "manhole" lids
+      must be 0.5 mm. thicker in each respective size.
+    </p>
+    <p>
+      In all circumstances, the thickness of the walls--especially in the case
+      of apparatus not circular in horizontal section--must be such that
+      alteration in shape appears impossible, unless deformation is guarded
+      against in other ways.
+    </p>
+    <p>
+      Generators must be so constructed that when they are being charged the
+      carbide cannot fall into the residue which has already been gasified; and
+      the residues must always be capable of easy, complete, and safe removal.
+    </p>
+    <p>
+      3. Generators, purifiers, and holders must be welded, riveted or folded at
+      the seams; soft solder is only permissible as a tightening material.
+    </p>
+    <p>
+      4. Pipes delivering acetylene, or uniting the apparatus, must be cast- or
+      wrought-iron. Unions, cocks, and valves must not be made of copper; but
+      the use of brass and bronze is permitted.
+    </p>
+    <p>
+      5. When cast-iron is employed, the rules of the German Gas and Water
+      Engineers are to be followed.
+    </p>
+    <p>
+      6. In generators where the whole amount of carbide introduced is not
+      gasified at one time, it must be possible to add fresh water or carbide in
+      safety, without interfering with the action of the apparatus. In such
+      generators the size of the gasholder space is to be calculated according
+      to the quantity of carbide which can be put into the generator. For every
+      1 kilogramme of carbide the available gasholder space must be: for the
+      first 50 kilos., 20 litres; for the next 50 kilos., 15 litres; for amounts
+      above 100 kilos., 10 litres per kilo. [One kilogramme may be taken as 2.2
+      lb., and 28 litres as 1 cubic foot.]
+    </p>
+    <p>
+      The generator must be large enough to supply the full number of normal
+      (10-litre) burners with gas for 5 hours; the yield of acetylene being
+      taken at 290 litres per kilo. [4.65 cubic feet per lb.]
+    </p>
+    <p>
+      The gasholder space of apparatus where carbide is not stored must be at
+      least 30 litres for every normal (10-litre) flame.
+    </p>
+    <p>
+      7. The gasholder must be fitted with an appliance for removing any gas
+      which may be generated (especially when the apparatus is first brought
+      into action) after the available space is full. This vent must have a
+      diameter at least equal to the inlet pipe of the holder.
+    </p>
+    <p>
+      8. Acetylene plant must be provided with purifying apparatus which
+      contains a proper purifying material in a suitable condition.
+    </p>
+    <p>
+      9. The dimensions of subsidiary apparatus, such as washers, purifiers,
+      condensers, pipes, and cocks must correspond with the capacity of the
+      plant.
+    </p>
+    <p>
+      10. Purifiers and washers must be constructed of materials capable of
+      resisting the attack of the substances in them.
+    </p>
+    <p>
+      11. Every generator must bear a plate giving the name of the maker, or the
+      seller, and the maximum number of l0-litre lights it is intended to
+      supply. If all the carbide put into the generator is not gasified at one
+      time, the plate must also state the maximum weight of carbide in the
+      charge. The gasholder must also bear a plate recording the maker's or
+      seller's name, as well as its storage capacity.
+    </p>
+    <p>
+      12. Rules 1 to 11 do not apply to portable apparatus serving up to two
+      lights, or to portable apparatus used only out of doors for the lighting
+      of vehicles or open spaces.
+    </p>
+    <p>
+      II. <i>Rules for Erection</i>
+    </p>
+    <p>
+      1. Acetylene apparatus must not be erected in or under rooms occupied or
+      frequented (passages, covered courts, &amp;c.) by human beings. Generators
+      and holders must only be erected in apartments covered with light roofs,
+      and separated from occupied rooms, barns, and stables by a fire-proof
+      wall, or by a distance of 15 feet. Any wall is to be considered fire-
+      proof which is built of solid brick, without openings, and one side of
+      which is "quite free." Apparatus may be erected in barns and stables,
+      provided the space required is partitioned off from the remainder by a
+      fire-proof wall.
+    </p>
+    <p>
+      2. The doors of apparatus sheds must open outwards, and must not
+      communicate directly with rooms where fires and artificial lights are
+      used.
+    </p>
+    <p>
+      3. Apparatus for the illumination of showmen's booths, "merry-go-rounds,"
+      shooting galleries, and the like must be erected outside the tents, and be
+      inaccessible to the public.
+    </p>
+    <p>
+      4. Permanent apparatus erected in the open air must be at least 15 feet
+      from an occupied building.
+    </p>
+    <p>
+      5. Apparatus sheds must be fitted at their highest points with outlet
+      ventilators of sufficient size; the ventilators leading straight through
+      the roof into the open air. They must be so arranged that the escaping
+      gases and vapours cannot enter rooms or chimneys.
+    </p>
+    <p>
+      6. The contacts of any electrical warning devices must be outside the
+      apparatus shed.
+    </p>
+    <p>
+      7. Acetylene plants must be prevented from freezing by erection in frost-
+      free rooms, or by the employment of a heating apparatus or other suitable
+      appliance. The heat must only be that of warm water or steam. Furnaces for
+      the heating appliance must be outside the rooms containing generators,
+      their subsidiary apparatus, or holders; and must be separated from such
+      rooms by fire-proof walls.
+    </p>
+    <p>
+      8. In one of the walls of the apparatus shed--if possible not that having
+      a door--a window must be fitted which cannot be opened; and outside that
+      window an artificial light is to be placed. In the usual way acetylene
+      lighting may be employed; but a lamp burning paraffin or oil, or a lantern
+      enclosing a candle, must always be kept ready for use in emergencies. In
+      all circumstances internal lighting is forbidden.
+    </p>
+    <p>
+      9. Every acetylene installation must be provided with a main cock, placed
+      in a conveniently accessible position so that the whole of the service may
+      be cut off from the plant.
+    </p>
+    <p>
+      10. The seller of an apparatus must provide his customer with a sectional
+      drawing, a description of the apparatus, and a set of rules for attending
+      to it. These are to be supplied in duplicate, and one set is to be kept
+      hanging up in the apparatus shed.
+    </p>
+    <p>
+      III. Rules for Working the Apparatus.
+    </p>
+    <p>
+      1. The apparatus must only be opened by daylight for addition of water. If
+      the generator is one of those in which the entire charge of carbide is not
+      gasified at once, addition of fresh carbide must only be made by daylight.
+    </p>
+    <p>
+      2. All work required by the plant, or by any portion of it, and all
+      ordinary attendance needed must be performed by daylight.
+    </p>
+    <p>
+      3. All water-seals must be carefully kept full.
+    </p>
+    <p>
+      4. When any part of an acetylene apparatus or a gas-meter freezes,
+      notwithstanding the precautions specified in II., 7, it must be thawed
+      only by pouring hot water into or over it; flames, burning fuel, or red-
+      hot iron bars must not be used.
+    </p>
+    <p>
+      5. Alterations to any part of an apparatus which involve the operations of
+      soldering or riveting, &amp;c., <i>i.e.</i>, in which a fire must be used,
+      or a spark may be produced by the impact of hammer on metal, must only be
+      carried out by daylight in the open air after the apparatus has been taken
+      to pieces. First of all the plant must be freed from gas. This is to be
+      done by filling every part with water till the liquid overflows, leaving
+      the water in it for at least five minutes before emptying it again.
+    </p>
+    <p>
+      6. The apparatus house must not be used for any other operation, nor
+      employed for the storage of combustible articles. It must be efficiently
+      ventilated, and always kept closed. A notice must be put upon the door
+      that unauthorised persons are not permitted to enter.
+    </p>
+    <p>
+      7. It in forbidden to enter the house with a burning lantern or lamp, to
+      strike matches, or to smoke therein.
+    </p>
+    <p>
+      8. A search for leaks in the pipes must not be made with the aid of a
+      light.
+    </p>
+    <p>
+      9. Alterations to the service must not be made while the pipes are under
+      pressure, but only after the main cock has been shut.
+    </p>
+    <p>
+      10. If portable apparatus, such as described in I., 12, are connected to
+      the burners with rubber tube, the tube must be fortified with an internal
+      or external spiral of wire. The tube must be fastened at both ends to the
+      cocks with thread, copper wire, or with ring clamps.
+    </p>
+    <p>
+      11. The preparation, storage, and use of compressed or liquefied acetylene
+      is forbidden. By compressed acetylene, however, is only to be understood
+      gas compressed to a pressure exceeding one effective atmosphere. Acetylene
+      compressed into porous matter, with or without acetone, is excepted from
+      this prohibition.
+    </p>
+    <p>
+      12. In the case of plants serving 50 lights or less, not more than 100
+      kilos. of carbide in closed vessels may be kept in the apparatus house
+      besides the drum actually in use.
+    </p>
+    <p>
+      A fresh drum is not to be opened before the previous one has been two-
+      thirds emptied. Opened drums must be closed with an iron watertight lid
+      covering the entire top of the vessel.
+    </p>
+    <p>
+      In the case of apparatus supplying over 500 lights, only one day's
+      consumption of carbide must be kept in the generator house. In other
+      respects the store of carbide for such installations is to be treated as a
+      regular carbide store.
+    </p>
+    <p>
+      13. Carbide drums must not be opened with the aid of a flame or a red-hot
+      iron instrument.
+    </p>
+    <p>
+      14. Acetylene apparatus must only be attended to by trustworthy and
+      responsible persons.
+    </p>
+    <p>
+      The rules issued by the AUSTRIAN GOVERNMENT in 1905 for the installation
+      of acetylene plant and the use of acetylene are divided into general
+      enactments relating to acetylene, and into special enactments in regard to
+      the apparatus and installation. The general enactments state that:
+    </p>
+    <p>
+      1. The preparation and use of liquid acetylene is forbidden.
+    </p>
+    <p>
+      2. Gaseous acetylene, alone, in admixture, or in solution, must not be
+      compressed above 2 atmospheres absolute except under special permission.
+    </p>
+    <p>
+      3. The storage of mixtures of acetylene with air or other gases containing
+      or evolving free oxygen is forbidden.
+    </p>
+    <p>
+      4. A description of every private plant about to be installed must be
+      submitted to the local authorities, who, according to its size and
+      character, may give permission for it to be installed and brought into use
+      either forthwith or after special inspection. Important alterations to
+      existing plant must be similarly notified.
+    </p>
+    <p>
+      5. The firms and fitters undertaking the installation of acetylene plant
+      must be licensed.
+    </p>
+    <p>
+      The special enactments fall under four headings, viz., (<i>a</i>)
+      apparatus; (<i>b</i>) plant houses; (<i>c</i>) pipes; (<i>d</i>) residues.
+    </p>
+    <p>
+      In regard to apparatus it is enacted that:
+    </p>
+    <p>
+      1. The type of apparatus to be employed must be one which has been
+      approved by one of certain public authorities in the country.
+    </p>
+    <p>
+      2. A drawing and description of the construction of the apparatus and a
+      short explanation of the method of working it must be fixed in a
+      conspicuous position under cover in the apparatus house. The notice must
+      also contain approved general information as to the properties of calcium
+      carbide and acetylene, precautions that must be observed to guard against
+      possible danger, and a statement of how often the purifier will require to
+      be recharged.
+    </p>
+    <p>
+      3. The apparatus must be marked with the name of the maker, the year of
+      its construction, the available capacity of the gasholder, and the maximum
+      generating capacity per hour.
+    </p>
+    <p>
+      4. Each constituent of the plant must be proportioned to the maximum
+      hourly output of gas and in particular the available capacity of the
+      holder must be 75 per cent. of the latter. The apparatus must not be
+      driven above its nominal productive capacity.
+    </p>
+    <p>
+      5. The productive capacity of generators in which the gasholder has to be
+      opened or the bell removed before recharging, or for the removal of
+      sludge, must not exceed 50 litres per hour, nor may the charge of carbide
+      exceed 1 kilo.
+    </p>
+    <p>
+      6. Generators exceeding 50 litres per hour productive capacity must be
+      arranged so that they can be freed from air before use.
+    </p>
+    <p>
+      7. Generators exceeding 1500 litres per hour capacity must be arranged so
+      that the acetylene, contained in the parts of the apparatus which have to
+      be opened for recharging or for the removal of sludge, can be removed
+      before they are opened.
+    </p>
+    <p>
+      8. Automatic generators of which the decomposing chambers are built inside
+      the gasholder must not exceed 300 litres per hour productive capacity.
+    </p>
+    <p>
+      9. Generators must be arranged so that after-generation cannot produce
+      objectionable results.
+    </p>
+    <p>
+      10. The holder of carbide-to-water generators must be large enough to take
+      all the gas which may be produced by the introduction of one charge of
+      carbide without undue pressure ensuing.
+    </p>
+    <p>
+      11. The maximum pressure permissible in any part of the apparatus is 1.1
+      atmosphere absolute.
+    </p>
+    <p>
+      12. The temperature in the gas space of a generator must never exceed 80�
+      C.
+    </p>
+    <p>
+      13. Generating apparatus, &amp;c., must be constructed in a workmanlike
+      manner of metal capable of resisting rust and distortion, and, where the
+      metal comes in contact with carbide or acetylene, it must not be one
+      (copper in particular) which forms an explosive compound with the gas.
+      Cocks and screw connexions, &amp;c., of brass, bronze, &amp;c., must
+      always be kept clean. Joints exposed to acetylene under pressure must be
+      made by riveting or welding except that in apparatus not exceeding 100
+      litres per hour productive capacity double bending may be used.
+    </p>
+    <p>
+      14. Every apparatus must be fitted with a safety-valve or vent-pipe
+      terminating in a safe place in the open, and of adequate size.
+    </p>
+    <p>
+      15. Every apparatus must be provided with an efficient purifier so fitted
+      that it may be isolated from the rest of the plant and with due
+      consideration of the possible action of the purifying material upon the
+      metal used.
+    </p>
+    <p>
+      16. Mercury pressure gauges are prohibited. Liquid gauges, if used must be
+      double the length normally needed, and with a cock which in automatic
+      apparatus must be kept shut while it is in action.
+    </p>
+    <p>
+      17. Proper steps must always be taken to prevent the apparatus freezing.
+      In the absence of other precautions water-seals and pressure-gauges must
+      be filled with liquid having a sufficiently low freezing-point and without
+      action on acetylene or the containing vessel.
+    </p>
+    <p>
+      18. Signal devices to show the position of the gasholder bell must not be
+      capable of producing sparks inside the apparatus house.
+    </p>
+    <p>
+      19. Leaks must not be sought for with an open flame and repairs requiring
+      the use of a blow-pipe, &amp;c., must only be carried out after the
+      apparatus has been taken to pieces or freed from gas by flooding.
+    </p>
+    <p>
+      20. Apparatus must only be attended to by trustworthy and responsible
+      adults.
+    </p>
+    <p>
+      21. Portable apparatus holding not more than 1 kilo. of carbide and of not
+      more than 50 litres per hour productive capacity, and apparatus fixed and
+      used out of doors are exempt from the foregoing regulations except Nos. 11
+      and 12, and the first part of 13.
+    </p>
+    <p>
+      In regard to (<i>b</i>), plant houses, it is enacted that:
+    </p>
+    <p>
+      1. Rooms containing acetylene apparatus must be of ample size, used for no
+      other purpose, have water-tight floors, be warmed without fireplaces or
+      chimneys, be lighted from outside through an air-tight window by an
+      independent artificial light, have doors opening outwards, efficient
+      ventilation and a store of sand or like material for fire extinction.
+      Strangers must be warned away.
+    </p>
+    <p>
+      2. Apparatus of not more than 300 litres per hour productive capacity may
+      be erected in basements or annexes of dwelling houses, but if of over 50
+      litres per hour capacity must not be placed under rooms regularly
+      frequented. Rooms regularly frequented and those under the same must not
+      be used.
+    </p>
+    <p>
+      3. Apparatus of more than 300 litres per hour productive capacity must be
+      erected in an independent building at least 15 feet distant from other
+      property, which building, unless it is at least 30 feet distant, must be
+      of fire-proof material externally.
+    </p>
+    <p>
+      4. Gasholders exceeding 280 cubic foot in capacity must be in a detached
+      room or in the open and inaccessible to strangers, and at least 30 feet
+      from other property and with lightning conductors.
+    </p>
+    <p>
+      5. In case of fire the main cock must not be shut until it is ascertained
+      that no one remains in the room served with the gas.
+    </p>
+    <p>
+      6. All acetylene installations must be known to the local fire brigade.
+    </p>
+    <p>
+      In regard to (<i>c</i>), pipes, it is enacted that:
+    </p>
+    <p>
+      1. Mains for acetylene must be separated from the generating apparatus by
+      a cock, and under a five-minute test for pressure must not show a fall of
+      over eight-tenths inch when the pressure is 13.8 inches, or three times
+      the working pressure, whichever is greater.
+    </p>
+    <p>
+      2. The pipes must as a rule be of iron, though lead may be used where they
+      are uncovered and not exposed to risk of injury. Rubber connexions may
+      only be used for portable apparatus, and attached to a terminal on the
+      metal pipes provided with a cock, and be fastened at both ends so that
+      they will not slip off the nozzles.
+    </p>
+    <p>
+      In regard to (<i>d</i>), residues, it is enacted that special open or
+      well-ventilated pits must be provided for their reception when the
+      apparatus exceeds 300 litres per hour productive capacity. With smaller
+      apparatus they may be discharged into cesspools if sufficiently diluted.
+      The ITALIAN GOVERNMENT regulations in regard to acetylene plant are
+      divided into eight sections. The first of these relates to the production
+      and use of liquid and compressed acetylene. The production and use of
+      liquid acetylene is prohibited except under the provisions of the laws
+      relating to explosives. Neat acetylene must not be compressed to more than
+      l-1/2 atmospheres except that an absolute pressure of 10 atmospheres is
+      allowed when the gas is dissolved in acetone or otherwise rendered free
+      from risk. Mixtures of acetylene with air or oxygen are forbidden,
+      irrespective of the pressure or proportions. Mixtures of acetylene with
+      hydrocarbons, carbonic oxide, hydrogen and inert gases are permitted
+      provided the proportion of acetylene does not exceed 50 per cent. nor the
+      absolute pressure 10 atmospheres.
+    </p>
+    <p>
+      The second section relates to acetylene installations, which are
+      classified in four groups, viz., (<i>a</i>) fixed or portable apparatus
+      supplying not more than thirty burners consuming 20 litres per hour; (<i>b</i>)
+      private installations supplying between 30 and 200 such burners; (<i>c</i>)
+      public or works installations supplying between 30 and 200 such burners; (<i>d</i>)
+      installations supplying more than 200 such burners.
+    </p>
+    <p>
+      The installations must comply with the following general conditions:
+    </p>
+    <p>
+      1. No part of the generator when working at its utmost capacity should
+      attain a temperature of more than 100� C.
+    </p>
+    <p>
+      2. The carbide must be completely decomposed in the apparatus so that no
+      acetylene can be evolved from the residue. The residues must be diluted
+      with water before being discharged into drains or cesspools, and sludge
+      storage-pits must be in the open.
+    </p>
+    <p>
+      3. The apparatus must preclude the escape of lime into the gas and water
+      connexions.
+    </p>
+    <p>
+      4. Glass parts must be adequately protected.
+    </p>
+    <p>
+      5. Rubber connexions between the generator, gasholder, and main are
+      absolutely prohibited with installations supplying more than 30 burners.
+    </p>
+    <p>
+      6. Cocks must be provided for cutting off the main and connexions from the
+      generator and gasholder.
+    </p>
+    <p>
+      7. Each burner must have an independent tap.
+    </p>
+    <p>
+      8. Generators of groups (<i>b</i>), (<i>c</i>), and (<i>d</i>) must be
+      constructed so that no after-generation of acetylene can take place
+      automatically and that any surplus gas would in any case be carried out of
+      the generator house by a vent-pipe.
+    </p>
+    <p>
+      The third section deals with generator houses, which must be well
+      ventilated and light; must not be used for any other purpose except to
+      store one day's consumption of carbide, not exceeding 300 kilos.; must be
+      fire-proof; must have doors opening outwards; and the vent-pipes must
+      terminate at a safe place in the open. Apparatus of group (<i>b</i>) must
+      not be placed in a dwelling-room and only in an adjoining room if the
+      gasholder is of less than 600 litres capacity. Apparatus of group (<i>c</i>)
+      must be in an independent building which must be at least 33 feet from
+      occupied premises if the capacity of the gasholder is 6000 litres and
+      upwards. Half this distance suffices for gasholders containing 600 to 6000
+      litres. These distances may be reduced at the discretion of the local
+      authorities provided a substantial partition wall at least 1 foot thick is
+      erected. Apparatus of group (<i>d</i>) must be at least 50 feet from
+      occupied premises and the gasholder and generator must not be in the same
+      building.
+    </p>
+    <p>
+      The fourth section deals with the question of authorisation for the
+      installation of acetylene plant. Apparatus of group (<i>a</i>) may be
+      installed without obtaining permission from any authorities. In regard to
+      apparatus of the other groups, permission for installation must be
+      obtained from local or other authorities.
+    </p>
+    <p>
+      The fifth section relates to the working of acetylene plant. It makes the
+      concessionaires and owners of the plant responsible for the manipulation
+      and supervision of the apparatus, and for the employment of suitable
+      operators, who must not be less than 18 years of age.
+    </p>
+    <p>
+      The sixth section relates to the inspection of acetylene plant from time
+      to time by inspectors appointed by the local or other authorities.
+      Apparatus of group (<i>a</i>) is not subject to these periodical
+      inspections.
+    </p>
+    <p>
+      The seventh section details the fees payable for the inspection of
+      installations and carbide stores, and fixes the penalties for non-
+      compliance with the regulations.
+    </p>
+    <p>
+      The eighth section refers to the notification of the position and
+      description of all carbide works, stores, and acetylene installations to
+      the local authorities.
+    </p>
+    <p>
+      The HUNGARIAN GOVERNMENT rules for the construction and examination of
+      acetylene plant forbid the use of copper and of its alloys; cocks,
+      however, may be made of a copper alloy. The temperature in the gas space
+      of a fixed generator must not exceed 50� C., in that of a portable
+      apparatus 80� C. The maximum effective pressure permissible is 0.15
+      atmosphere.
+    </p>
+    <p>
+      The CONSEIL D'HYGI�NE DE LA SEINE IN FRANCE allows a maximum pressure of
+      1.5 metres, i.e., 59 inches, of water column in generators used for the
+      ordinary purposes of illumination; but apparatus intended to supply gas to
+      the low-pressure oxy-acetylene blowpipe (see Chapter IX.) may develop up
+      to 2.5 metres, or 98.5 inches of water pressure, provided copper and its
+      alloys are entirely excluded from the plant and from the delivery- pipes.
+    </p>
+    <p>
+      The NATIONAL BOARD OF FIRE UNDERWRITERS OF THE UNITED STATES OF AMERICA
+      has issued a set of rules and requirements, of which those relating to
+      acetylene generators and plant are reproduced below. The underwriters
+      state that, "To secure the largest measure of safety to life and property,
+      these rules for the installation of acetylene gas machines must be
+      observed."
+    </p>
+    <p>
+      RULES FOR THE INSTALLATION AND USE OF ACETYLENE GAS GENERATORS. [Footnote:
+      The "gallon" of these rules is, of course, the American gallon, which is
+      equal to 0.83 English standard gallon.]
+    </p>
+    <p>
+      The use of liquid acetylene or gas generated therefrom is absolutely
+      prohibited.
+    </p>
+    <p>
+      Failure to observe these rules is as liable to endanger life as property.
+    </p>
+    <p>
+      To secure the largest measure of safety to life and property, the
+      following rules for the installation of acetylene gas machines must be
+      observed.
+    </p>
+    <p>
+      <i>Class A.--Stationary Automatic Apparatus.</i>
+    </p>
+    <p>
+      1. FOUNDATIONS.--(<i>a</i>) Must, where practicable, be of brick, stone,
+      concrete or iron. If necessarily of wood they shall be extra heavy,
+      located in a dry place and open to the circulation of air.
+    </p>
+    <p>
+      The ordinary board platform is not satisfactory. Wooden foundations shall
+      be of heavy planking, joists or timbers, arranged so that the air will
+      circulate around them so as to form a firm base.
+    </p>
+    <p>
+      (<i>b</i>) Must be so arranged that the machine will be level and unequal
+      strain will not be placed on the generator or connexions.
+    </p>
+    <p>
+      2. LOCATION.--(<i>a</i>) Generators, especially in closely built up
+      districts should preferably be placed outside of insured buildings in
+      generator houses constructed and located in compliance with Rule 9.
+    </p>
+    <p>
+      (<i>b</i>) Generators must be so placed that the operating mechanism will
+      have room for free and full play and can be adjusted without artificial
+      light. They must not be subject to interference by children or careless
+      persons, and if for this purpose further enclosure is necessary, it must
+      be furnished by means of slatted partitions permitting the free
+      circulation of air.
+    </p>
+    <p>
+      (<i>c</i>) Generators which from their construction are rendered
+      inoperative during the process of recharging must be so located that they
+      can be recharged without the aid of artificial light.
+    </p>
+    <p>
+      (<i>d</i>) Generators must be placed where water will not freeze.
+    </p>
+    <p>
+      3. ESCAPES OR RELIEF-PIPES.--Each generator must be provided with an
+      escape or relief-pipe of ample size; no such pipe to be less than 3/4-
+      inch internal diameter. This pipe shall be substantially installed,
+      without traps, and so that any condensation will drain back to the
+      generator. It must be carried to a suitable point outside the building,
+      and terminate in an approved hood located at least 12 feet above ground
+      and remote from windows.
+    </p>
+    <p>
+      The hood must be constructed in such a manner that it cannot be obstructed
+      by rain, snow, ice, insects or birds.
+    </p>
+    <p>
+      4. CAPACITY.--(<i>a</i>) Must be sufficient to furnish gas continuously
+      for the maximum lighting period to all lights installed. A lighting period
+      of at least 5 hours shall be provided for in every case.
+    </p>
+    <p>
+      (<i>b</i>) Generators for conditions of service requiring lighting period
+      of more than 5 hours must be of sufficient capacity to avoid recharging at
+      night. The following ratings will usually be found advisable.
+    </p>
+    <p>
+      (i) For dwellings, and where machines are always used intermittently, the
+      generator must have a rated capacity equal to the total number of burners
+      installed.
+    </p>
+    <p>
+      (ii) For stores, opera houses, theatres, day-run factories, and similar
+      service, the generator must have a rated capacity of from 30 to 50 per
+      cent, in excess of the total number of burners installed.
+    </p>
+    <p>
+      (iii) For saloons and all night or continued service, the generator must
+      have a rated capacity of from 100 to 200 per cent. in excess of the total
+      number of burners installed.
+    </p>
+    <p>
+      (<i>c</i>) A small generator must never be installed to supply a large
+      number of lights, even though it seems probable that only a few lights
+      will be used at a time. <i>An overworked generator adds to the cost of
+      producing acetylene gas</i>.
+    </p>
+    <p>
+      5. CARBIDE CHARGES.--Must be sufficient to furnish gas continuously for
+      the maximum lighting period to all burners installed. In determining
+      charges lump carbide must be estimated as capable of producing 4-1/2 cubic
+      foot of gas to the pound, commercial 1/4-inch carbide 4 cubic feet of gas
+      to the pound, and burners must be considered as requiring at least 25 per
+      cent. more than their rated consumption of gas.
+    </p>
+    <p>
+      6. BURNERS.--Burners consuming one-half of a cubic foot of gas per hour
+      are considered standard in rating generators. Those having a greater or
+      less capacity will decrease or increase the number of burners allowable in
+      proportion.
+    </p>
+    <p>
+      Burners usually consume from 25 to 100 per cent. more than their rated
+      consumption of gas, depending largely on the working pressure. The so-
+      called 1/2-foot burner when operated at pressures of from 20- to 25-
+      tenths inches water column (2 to 2-1/2 inches) is usually used with best
+      economy.
+    </p>
+    <p>
+      7. PIPING.--(<i>a</i>) Connexions from generators to service-pipes must be
+      made with right and left thread nipples or long thread nipples with lock
+      nuts. All forms of unions are prohibited.
+    </p>
+    <p>
+      (<i>b</i>) Piping must, as far as possible, be arranged so that any
+      moisture will drain back to the generator. If low points occur of
+      necessity in any piping, they must be drained through tees into drip cups
+      permanently closed with screw caps or plugs. No pet-cocks shall be used.
+    </p>
+    <p>
+      (<i>c</i>) A valve and by-pass connexion must be provided from the
+      service-pipe to the blow-off for removing the gas from the holder in case
+      it should be necessary to do so.
+    </p>
+    <p>
+      (<i>d</i>) The schedule of pipe sizes for piping from generators to
+      burners should conform to that commonly used for ordinary gas, but in no
+      case must the feeders be smaller than three-eighths inch.
+    </p>
+    <p>
+      The following schedule is advocated:
+    </p>
+<pre xml:space="preserve">
+    3/8 inch pipe,  26 feet, three burners.
+    1/2 inch pipe,  30 feet, six burners.
+    3/4 inch pipe,  50 feet, twenty burners.
+  1     inch pipe,  70 feet, thirty-five burners.
+  1-1/4 inch pipe, 100 feet, sixty burners.
+  1-1/2 inch pipe, 150 feet, one hundred burners.
+  2     inch pipe, 200 feet, two hundred burners.
+  2-1/2 inch pipe, 300 feet, three hundred burners.
+  3     inch pipe, 450 feet, four hundred and fifty burners,
+  3-1/2 inch pipe, 500 feet, six hundred burners.
+  4     inch pipe, 600 feet, seven hundred and fifty burners.
+</pre>
+    <p>
+      (<i>e</i>) Machines of the carbide-feed type must not be fitted with
+      continuous drain connexions leading to sewers, but must discharge into
+      suitable open receptacles which may have such connections.
+    </p>
+    <p>
+      (<i>f</i>) Piping must be thoroughly tested both before and after the
+      burners have been installed. It must not show loss in excess of 2 inches
+      within twelve hours when subjected to a pressure equal to that of 15
+      inches of mercury.
+    </p>
+    <p>
+      (<i>g</i>) Piping and connexions must be installed by persons experienced
+      in the installation of acetylene apparatus.
+    </p>
+    <p>
+      8. CARE AND ATTENDANCE.--In the care of generators designed for a lighting
+      period of more than five hours always clean and recharge the generating
+      chambers at regular stated intervals, regardless of the number of burners
+      actually used.
+    </p>
+    <p>
+      Where generators are not used throughout the entire year always remove all
+      water and gas and clean thoroughly at the end of the season during which
+      they are in service.
+    </p>
+    <p>
+      It is usually necessary to take the bell portion out and invert it so as
+      to allow all gas to escape. This should never be done in the presence of
+      artificial light or fire of any kind.
+    </p>
+    <p>
+      Always observe a regular time, during daylight hours only, for attending
+      to and charging the apparatus.
+    </p>
+    <p>
+      In charging the generating chambers of water-feed machines clean all
+      residuum carefully from the containers and remove it at once from the
+      building. Separate from the mass any unslacked carbide remaining and
+      return it to the containers, adding now carbide as required. Be careful
+      never to fill the containers over the specified mark, as it is important
+      to allow for the swelling of the carbide when it comes in contact with
+      water. The proper action and economy of the machine are dependent on the
+      arrangement and amount of carbide placed in the generator. Carefully guard
+      against the escape of gas.
+    </p>
+    <p>
+      Whenever recharging with carbide always replenish the water-supply.
+    </p>
+    <p>
+      Never deposit residuum or exhausted material from water-feed machines in
+      sewer-pipes or near inflammable material.
+    </p>
+    <p>
+      Always keep water-tanks and water-seals filled with clean water.
+    </p>
+    <p>
+      Never test the generator or piping for leaks with a flame, and never apply
+      flame to an outlet from which the burner has been removed.
+    </p>
+    <p>
+      Never use a lighted match, lamp, candle, lantern or any open light near
+      the machine.
+    </p>
+    <p>
+      Failure to observe the above cautions is as liable to endanger life as
+      property.
+    </p>
+    <p>
+      9. OUTSIDE GENERATOR HOUSES.--(<i>a</i>) Outside generator houses should
+      not be located within 5 feet of any opening into, nor shall they open
+      toward any adjacent building, and must be kept under lock and key.
+    </p>
+    <p>
+      (<i>b</i>) The dimensions must be no greater than the apparatus requires
+      to allow convenient room for recharging and inspection of parts. The floor
+      must be at least 12 inches above grade and the entire structure thoroughly
+      weather-proof.
+    </p>
+    <p>
+      (<i>c</i>) Generator houses must be thoroughly ventilated, and any
+      artificial heating necessary to prevent freezing shall be done by steam or
+      hot-water systems.
+    </p>
+    <p>
+      (<i>d</i>) Generator houses must not be used for the storage of calcium
+      carbide except in accordance with the rules relating to that subject (<i>vide</i>
+      Chapter II.).
+    </p>
+    <p>
+      <i>Class B.--Stationary Non-Automatic Apparatus</i>.
+    </p>
+    <p>
+      10. FOUNDATIONS.--(<i>a</i>) Must be of brick, stone or concrete.
+    </p>
+    <p>
+      (<i>b</i>) Must be so arranged that the machine will be level and so that
+      strain will not be brought upon the connexions.
+    </p>
+    <p>
+      11. GAS-HOUSES.--(<i>a</i>) Must be constructed entirely of non-
+      combustible material and must not be lighted by any system of illumination
+      involving open flames.
+    </p>
+    <p>
+      (<i>b</i>) Must be heated, where artificial heating is necessary to
+      prevent freezing, by steam or hot-water systems, the heater to be located
+      in a separate building, and no open flames to be permitted within
+      generator enclosures.
+    </p>
+    <p>
+      (<i>c</i>) Must be kept closed and locked excepting during daylight hours.
+    </p>
+    <p>
+      (<i>d</i>) Must be provided with a permanent and effective system of
+      ventilation which will be operative at all times, regardless of the
+      periods of operation of the plant.
+    </p>
+    <p>
+      12. ESCAPE-PIPES.--Each generator must be provided with a vent-pipe of
+      ample size, substantially installed, without traps. It must be carried to
+      a suitable point outside the building and terminate in an approved hood
+      located at least 12 feet above ground and remote from windows.
+    </p>
+    <p>
+      The hood must be constructed in such a manner that it cannot be obstructed
+      by rain, snow, ice, insects or birds.
+    </p>
+    <p>
+      13. CARE AND MAINTENANCE.--All charging and cleaning of apparatus,
+      generation of gas and execution of repairs must be done during daylight
+      hours only, and generators must not be manipulated or in any way tampered
+      with in the presence of artificial light.
+    </p>
+    <p>
+      This will require gasholders of a capacity sufficient to supply all lights
+      installed for the maximum lighting period, without the necessity of
+      generation of gas at night or by artificial light.
+    </p>
+    <p>
+      In the operation of generators of the carbide-feed type it is important
+      that only a limited amount of carbide be fed into a given body of water.
+      An allowance of at least one gallon of generating water per pound of
+      carbide must be made in every case, and when this limit has been reached
+      the generator should be drained and flushed, and clean water introduced.
+      These precautions are necessary to avoid over-heating during generation
+      and accumulation of hard deposits of residuum in the generating chamber.
+    </p>
+    <p>
+      (Rule 14, referring to the storage of carbide, has been quoted in Chapter
+      II. (page 19)).
+    </p>
+    <p>
+      RULES FOR THE CONSTRUCTION OF GENERATORS.
+    </p>
+    <p>
+      The following Rules are intended to provide only against the more
+      hazardous defects usually noted in apparatus of this kind. The Rules do
+      not cover all details of construction nor the proper proportioning of
+      parts, and devices which comply with these requirements alone are not
+      necessarily suitable for listing as permissible for use. These points are
+      often only developed in the examination required before permission is
+      given for installation.
+    </p>
+    <p>
+      <i>Class A.--Stationary Apparatus for Isolated Installations.</i>
+    </p>
+    <p>
+      15. GENERAL RULES. GENERATORS.--(<i>a</i>) Must be made of iron or steel,
+      and in a manner and of material to insure stability and durability.
+    </p>
+    <p>
+      (<i>b</i>) Must be automatically regulated and uniform in their action,
+      producing gas only as immediate consumption demands, and so designed that
+      gas is generated without producing sufficient heat to cause yellow
+      discoloration of residuum (which will occur at about 500� F.) or abnormal
+      pressure at any stage of the process when using carbide of any degree of
+      fineness.
+    </p>
+    <p>
+      The presence of excessive heat tends to change the chemical character of
+      the gas and may even cause its ignition, while in machines of the
+      carbide-feed type, finely divided carbide will produce excessive pressure
+      unless provision is made to guard against it.
+    </p>
+    <p>
+      (<i>c</i>) Must be so arranged that during recharging, back flow of gas
+      from the gasholder will be automatically prevented, or so arranged that it
+      will be impossible to charge the apparatus without first closing the
+      supply-pipe to the gasholder, and to the other generating chambers if
+      several are used.
+    </p>
+    <p>
+      This is intended to prevent the dangerous escape of gas.
+    </p>
+    <p>
+      (<i>d</i>) The water or carbide supply to the generating chamber must be
+      so arranged that gas will be generated long enough in advance of the
+      exhaustion of the supply already in the gasholder to allow the using of
+      all lights without exhausting such supply.
+    </p>
+    <p>
+      This provides for the continuous working of the apparatus under all
+      conditions of water-feed and carbide charge, and it obviates the
+      extinction of lights through intermittent action of the machine.
+    </p>
+    <p>
+      (<i>e</i>) No valves or pet-cocks opening into the room from the gas-
+      holding part or parts, the draining of which will allow an escape of gas,
+      are permitted, and condensation from all parts of the apparatus must be
+      automatically removed without the use of valves or mechanical working
+      parts.
+    </p>
+    <p>
+      Such valves and pet-cocks are not essential; their presence increases the
+      possibility of leakage. The automatic removal of condensation from the
+      apparatus is essential to the safe working of the machine.
+    </p>
+    <p>
+      U-traps opening into the room from the gas-holding parts must not be used
+      for removal of condensation. All sealed drip connexions must be so
+      arranged as to discharge gas to the blow-off when blown out, and the seals
+      must be self-restoring upon relief of abnormal pressure.
+    </p>
+    <p>
+      (<i>f</i>) The apparatus must be capable of withstanding fire from outside
+      causes.
+    </p>
+    <p>
+      Sheet-metal joints must be double-seamed or riveted and thoroughly sweated
+      with solder. Pipes must be attached to sheet-metal with lock-nuts or
+      riveted flanges.
+    </p>
+    <p>
+      This prohibits the use of wood or of joints relying entirely upon solder.
+    </p>
+    <p>
+      (<i>g</i>) Gauge glasses, the breakage of which would allow the escape of
+      gas, must not be used.
+    </p>
+    <p>
+      (<i>h</i>) The use of mercury seals is prohibited.
+    </p>
+    <p>
+      Mercury has been found unreliable as a seal in acetylene apparatus.(<i>i</i>)
+      Combustible oils must not be used in connexion with the apparatus.
+    </p>
+    <p>
+      (<i>j</i>) The construction must be such that liquid seals shall not
+      become thickened by the deposit of lime or other foreign matter.
+    </p>
+    <p>
+      (<i>k</i>) The apparatus must be constructed so that accidental siphoning
+      of water will be impossible.
+    </p>
+    <p>
+      (<i>l</i>) Flexible tubing, swing joints, unions, springs, mechanical
+      check-valves, chains, pulleys, stuffing-boxes and lead or fusible piping
+      must not be used on acetylene apparatus except where failure of such parts
+      will not vitally affect the working or safety of the machine.
+    </p>
+    <p>
+      Floats must not be used excepting in cases where failure will result only
+      in rendering the machine inoperative.
+    </p>
+    <p>
+      (<i>m</i>) Every machine must be plainly marked with the maximum number of
+      lights it is designed to supply, the amount of carbide necessary for a
+      single charge, the manufacturer's name and the name of the machine.
+    </p>
+    <p>
+      16. GENERATING CHAMBERS.--(<i>a</i>) Must be constructed of galvanised
+      iron or steel not less than No. 24 U.S. Standard gauge in thickness for
+      capacities up to and including 20 gallons, not less than No. 22 U.S.
+      Standard gauge for capacities between 20 and 75 gallons, and not less than
+      No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.
+    </p>
+    <p>
+      (<i>b</i>) Must each be connected with the gasholder in such a manner that
+      they will, at all times, give open connexion either to the gasholder or to
+      the blow-off pipe to the outer air.
+    </p>
+    <p>
+      This prevents dangerous pressure within or the escape of gas from the
+      generating chamber.
+    </p>
+    <p>
+      (<i>c</i>) Must be so constructed that not more than 5 pounds of carbide
+      can be acted upon at once, in machines which apply water in small
+      quantities to the carbide.
+    </p>
+    <p>
+      This tends to reduce the danger of overheating and excessive after-
+      generation by providing for division of the carbide charges in machines of
+      this type.
+    </p>
+    <p>
+      (<i>d</i>) Must be provided with covers having secure fastenings to hold
+      them properly in place and those relying on a water-seal must be submerged
+      in at least 12 inches of water. Water-seal chambers for covers depending
+      on a water-seal must be 1-1/2 inches wide and 15 inches deep, excepting
+      those depending upon the filling of the seal chambers for the generation
+      of gas, where 9 inches will be sufficient.
+    </p>
+    <p>
+      (<i>e</i>) Must be so designed that the residuum will not clog or affect
+      the working of the machine and can conveniently be handled and removed.
+    </p>
+    <p>
+      (<i>f</i>) Must be provided with suitable vent connexions to the blow-off
+      pipe so that residuum may be removed and the generating water replaced
+      without causing siphoning or introducing air to the gasholder upon
+      recharging.
+    </p>
+    <p>
+      This applies to machines of the carbide-feed type.
+    </p>
+    <p>
+      (<i>g</i>) Feed mechanism for machines of the carbide-feed type must be so
+      designed that the direct fall of carbide from the carbide holder into the
+      water of the generator is prevented at all positions of the feed
+      mechanisms; or, when actuated by the rise and fall of a gas-bell, must be
+      so arranged that the feed-valve will not remain open after the landing of
+      the bell, and so that the feed valve remains inoperative as long as the
+      filling opening on the carbide hopper remains open. Feed mechanisms must
+      always be far enough above the water-level to prevent clogging from the
+      accumulation of damp lime. For this purpose the distance should be not
+      less than 10 inches.
+    </p>
+    <p>
+      17. CARBIDE CHAMBERS.--(<i>a</i>) Must be constructed of galvanised iron
+      or steel not less than No. 24 U.S. Standard gauge in thickness for
+      capacities up to and including 50 pounds and not less than No. 22 U.S.
+      Standard gauge for capacities in excess of 50 pounds.
+    </p>
+    <p>
+      (<i>b</i>) Must have sufficient carbide capacity to supply the full number
+      of burners continuously and automatically during the maximum lighting
+      period.
+    </p>
+    <p>
+      This rule removes the necessity of recharging or attending to the machine
+      at improper hours. Burners almost invariably require more than their rated
+      consumption of gas, and carbide is not of staple purity, and there should
+      therefore be an assurance of sufficient quantity to last as long as light
+      is needed. Another important consideration is that in some establishments
+      burners are called upon for a much longer period of lighting than in
+      others, requiring a generator of greater gas-producing capacity. Machines
+      having several generating chambers must automatically begin generation in
+      each upon exhaustion of the preceding chamber.
+    </p>
+    <p>
+      (<i>c</i>) Must be arranged so that the carbide holders or charges may be
+      easily and entirely removed in case of necessity.
+    </p>
+    <p>
+      18. GASHOLDERS.--(<i>a</i>) Must be constructed of galvanised iron or
+      steel not less than No. 24 U.S. Standard gauge in thickness for capacities
+      up to and including 20 gallons, not less than No. 22 U.S. Standard gauge
+      for capacities between 20 and 75 gallons, and not less than No. 20 U.S.
+      Standard gauge for capacities in excess of 75 gallons.
+    </p>
+    <p>
+      Gas-bells, if used, may be two gauges lighter than holders.
+    </p>
+    <p>
+      Condensation chambers, if placed under holders, to be of same gauge as
+      holders.
+    </p>
+    <p>
+      (<i>b</i>) Must be of sufficient capacity to contain all gas generated
+      after all lights have been extinguished.
+    </p>
+    <p>
+      If the holder is too small and blows off frequently after the lights are
+      extinguished there is a waste of gas. This may suggest improper working of
+      the apparatus and encourage tampering.
+    </p>
+    <p>
+      (<i>c</i>) Must, when constructed on the gasometer principle, be so
+      arranged that when the gas-bell is filled to its maximum with gas at
+      normal pressure its lip or lower edge will extend at least 9 inches below
+      the inner water-level.
+    </p>
+    <p>
+      (<i>d</i>) Must, when constructed on the gasometer principle, have the
+      dimensions of the tank portion so related to those of the bell that a
+      pressure of at least 11 inches will be necessary before gas can be forced
+      from the holder.
+    </p>
+    <p>
+      (<i>e</i>) The bell portion of a gasholder constructed on the gasometer
+      principle must be provided with a substantial guide to its upward
+      movement, preferably in the centre of the holder, carrying a stop acting
+      to chock the bell 1 inch above the normal blow-off point.
+    </p>
+    <p>
+      This tends to insure the proper action of the bell and decreases the
+      liability of escaping gas.
+    </p>
+    <p>
+      (<i>f</i>) A space of at least three-quarters of an inch must be allowed
+      between the sides of the tank and the bell.
+    </p>
+    <p>
+      (<i>g</i>) All water-seals must be so arranged that the water-level may be
+      readily seen and maintained.
+    </p>
+    <p>
+      19. WATER-SUPPLY.--(<i>a</i>) The supply of water to the generator for
+      generating purposes must not be taken from the water-seal of any gasholder
+      constructed on the gasometer principle, unless the feed mechanism is so
+      arranged that the water-seals provided for in Rules 18, (<i>c</i>), (<i>d</i>),
+      and (<i>e</i>) may be retained under all conditions. This provides for the
+      proper level of water in the gasholder.
+    </p>
+    <p>
+      (<i>b</i>) In cases where machines of the carbide-feed type are supplied
+      with water from city water-mains or house-pipes, the pipe connexion must
+      discharge into the regularly provided filling trap on the generator and
+      not through a separate continuous connexion leading into the generating
+      chamber.
+    </p>
+    <p>
+      This is to prevent the expulsion of explosive mixtures through the filling
+      trap in refilling.
+    </p>
+    <p>
+      20. RELIEFS OR SAFETY BLOW-OFFS.--(<i>a</i>) Must in all cases be
+      provided, and must afford free vent to the outer air for any over-
+      production of gas, and also afford relief in case of abnormal pressure in
+      the machine.
+    </p>
+    <p>
+      Both the above-mentioned vents may be connected, with the same escape-
+      pipe.
+    </p>
+    <p>
+      (<i>b</i>) Must be of at least 3/4-inch internal diameter and be provided
+      with suitable means for connecting to the pipe loading outside of the
+      building.
+    </p>
+    <p>
+      (<i>c</i>) Must be constructed without valves or other mechanical working
+      parts.
+    </p>
+    <p>
+      (<i>d</i>) Apparatus requiring pressure regulators must be provided with
+      an additional approved safety blow-off attachment located between the
+      pressure regulator and the service-pipes and discharging to the outer air.
+    </p>
+    <p>
+      This is intended to prevent the possibility of undue pressure in the
+      service-pipes due to failure of the pressure regulator.
+    </p>
+    <p>
+      21. PRESSURES.--(<i>a</i>) The working pressure at the generator must not
+      vary more than ten-tenths (1) inch water column under all conditions of
+      carbide charge and feed, and between the limits of no load and 50 per
+      cent. overload.
+    </p>
+    <p>
+      (<i>b</i>) Apparatus not requiring pressure regulators must be so arranged
+      that the gas pressure cannot exceed sixty-tenths (6) inches water column.
+    </p>
+    <p>
+      This requires the use of the pressure relief provided for in Rule No. 20 (<i>a</i>).
+    </p>
+    <p>
+      (<i>c</i>) Apparatus requiring pressure regulators must be so arranged
+      that the gas pressure cannot exceed three pounds to the square inch.
+    </p>
+    <p>
+      The pressure limit of 3 pounds is taken since that is the pressure
+      corresponding to a water column about 6 feet high, which is about, the
+      limit in point of convenience for water-sealed reliefs.
+    </p>
+    <p>
+      22. AIR MIXTURES.--Generators must be so arranged as to contain the
+      minimum amount of air when first started or recharged, and no device or
+      attachment facilitating or permitting mixture of air with the gas prior to
+      consumption, except at the burners, shall be allowed.
+    </p>
+    <p>
+      Owing to the explosive properties of acetylene mixed with air, machines
+      must be so designed that such mixtures are impossible.
+    </p>
+    <p>
+      23. PURIFIERS.--(<i>a</i>) Must be constructed of galvanised iron or steel
+      not less than No. 24 U.S. Standard gauge in thickness.
+    </p>
+    <p>
+      (<i>b</i>) Where installed, purifiers must conform to the general rules
+      for the construction of other acetylene apparatus and allow the free
+      passage of gas.
+    </p>
+    <p>
+      (<i>c</i>) Purifiers must contain no carbide for drying purposes.
+    </p>
+    <p>
+      (<i>d</i>) Purifiers must be located inside of gasholders, or, where
+      necessarily outside, must have no hand-holes which can be opened without
+      first shutting off the gas-supply.
+    </p>
+    <p>
+      24. PRESSURE REGULATORS.--(<i>a</i>) Must conform to the rules for the
+      construction of other acetylene apparatus so far as they apply and must
+      not be subject to sticking or clogging.
+    </p>
+    <p>
+      (<i>b</i>) Must be capable of maintaining a uniform pressure, not varying
+      more than four-tenths inch water column, at any load within their rating.
+    </p>
+    <p>
+      (<i>c</i>) Must be installed between valves in such a manner as to
+      facilitate inspection and repairs.
+    </p>
+    <p>
+      <i>Class B.--Stationary Apparatus for Central Station Service.</i>
+    </p>
+    <p>
+      Generators of over 300 lights capacity for central station service are not
+      required to be automatic in operation. Generators of less than 300 lights
+      capacity must be automatic in operation and must comply in every respect
+      with the requirements of Class A.
+    </p>
+    <p>
+      25. GENERAL RULES. GENERATORS.--(<i>a</i>) Must be substantially
+      constructed of iron or steel and be protected against depreciation by an
+      effective and durable preventive of corrosion.
+    </p>
+    <p>
+      Galvanising is strongly recommended as a protection against oxidation, and
+      it may to advantage be reinforced by a thorough coating of asphaltum or
+      similar material.
+    </p>
+    <p>
+      (<i>b</i>) Must contain no copper or alloy of copper in contact with
+      acetylene, excepting in valves.
+    </p>
+    <p>
+      (<i>c</i>) Must be so arranged that generation will take place without
+      overheating; temperatures in excess of 500� F. to be considered excessive.
+    </p>
+    <p>
+      (<i>d</i>) Must be provided with means for automatic removal of
+      condensation from gas passages.
+    </p>
+    <p>
+      (<i>e</i>) Must be provided with suitable protection against freezing of
+      any water contained in the apparatus.
+    </p>
+    <p>
+      No salt or other corrosive chemical is permissible as a protection against
+      freezing.
+    </p>
+    <p>
+      (<i>f</i>) Must in general comply with the requirements governing the
+      construction of apparatus for isolated installations so far as they are
+      applicable.
+    </p>
+    <p>
+      (<i>g</i>) Must be so arranged as to insure correct procedure in
+      recharging and cleaning.
+    </p>
+    <p>
+      (<i>h</i>) Generators of the carbide-feed type must be provided with some
+      form of approved measuring device to enable the attendant to determine
+      when the maximum allowable quantity of carbide has been fed into the
+      generating chamber.
+    </p>
+    <p>
+      In the operation of generators of this type an allowance of at least 1
+      gallon of clean generating water per pound of carbide should be made, and
+      the generator should be cleaned after slaking of every full charge. Where
+      lump carbide is used the lumps may become embedded in the residuum, if the
+      latter is allowed to accumulate at the bottom of the generating chamber,
+      causing overheating from slow and restricted generation, and rendering the
+      mass more liable to form a hard deposit and bring severe stresses upon the
+      walls of the generator by slow expansion.
+    </p>
+    <p>
+      26. GENERATING CHAMBERS.--(<i>a</i>) Must each be connected with the
+      gasholder in such a manner that they will, at all times, give open
+      connexion either to the gasholder or to the blow-off pipe into the outer
+      air.
+    </p>
+    <p>
+      (<i>b</i>) Must be so arranged as to guard against appreciable escape of
+      gas to the room at any time during the introduction of the charges.
+    </p>
+    <p>
+      (<i>c</i>) Must be so designed that the residuum will not clog or affect
+      the operation of the machine and can conveniently be handled and removed.
+    </p>
+    <p>
+      (<i>d</i>) Must be so arranged that during the process of cleaning and
+      recharging the back-flow of gas from the gasholder or other generating
+      chambers will be automatically prevented.
+    </p>
+    <p>
+      27. GASHOLDERS.--(<i>a</i>) Must be of sufficient capacity to contain at
+      least 4 cubic feet of gas per 1/2-foot burner of the rating. This is to
+      provide for the requisite lighting period without the necessity of making
+      gas at night, allowance being made for the enlargement of burners caused
+      by the use of cleaners.
+    </p>
+    <p>
+      (<i>b</i>) Must be provided with suitable guides to direct the movement of
+      the bell throughout its entire travel.
+    </p>
+    <p>
+      28. PRESSURE RELIEFS.--Must in all cases be provided, and must be so
+      arranged as to prevent pressure in excess of 100-tenths (10) inches water
+      column in the mains.
+    </p>
+    <p>
+      29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of
+      approximately 25-tenths (2.5) inches water column in the mains. <br />
+      <br /> <br />
+    </p>
+    <h2>
+      <a name="linkv" id="v">CHAPTER V</a>
+    </h2>
+    <h3>
+      THE TREATMENT OF ACETYLENE AFTER GENERATION
+    </h3>
+    <p>
+      IMPURITIES IN CALCIUM CARBIDE.--The calcium carbide manufactured at the
+      present time, even when of the best quality commercially obtainable, is by
+      no means a chemically pure substance; it contains a large number of
+      foreign bodies, some of which evolve gas on treatment with water. To a
+      considerable extent this statement will probably always remain true in the
+      future; for in order to make absolutely pure carbide it would be necessary
+      for the manufacturer to obtain and employ perfectly pure lime, carbon, and
+      electrodes in an electric furnace which did not suffer attack during the
+      passage of a powerful current, or he would have to devise some process for
+      simultaneously or subsequently removing from his carbide those impurities
+      which were derived from his impure raw materials or from the walls of his
+      furnace--and either of these processes would increase the cost of the
+      finished article to a degree that could hardly be borne. Beside the
+      impurities thus inevitably arising from the calcium carbide decomposed,
+      however, other impurities may be added to acetylene by the action of a
+      badly designed generator or one working on a wrong system of construction;
+      and therefore it may be said at once that the crude gas coming from the
+      generating plant is seldom fit for immediate consumption, while if it be
+      required for the illumination of occupied rooms, it must invariably be
+      submitted to a rigorous method of chemical purification.
+    </p>
+    <p>
+      IMPURITIES OF ACETYLENE.--Combining together what may be termed the
+      carbide impurities and the generator impurities in crude acetylene, the
+      foreign bodies are partly gaseous, partly liquid, and partly solid. They
+      may render the gas dangerous from the point of view of possible
+      explosions; they, or the products derived from them on combustion, may be
+      harmful to health if inspired, injurious to the fittings and decorations
+      of rooms, objectionable at the burner orifices by determining, or
+      assisting in, the formation of solid growths which distort the flame and
+      so reduce its illuminating power; they may give trouble in the pipes by
+      condensing from the state of vapour in bends and dips, or by depositing,
+      if they are already solid, in angles, &amp;c., and so causing stoppages;
+      or they may be merely harmful economically by acting as diluents to the
+      acetylene and, by having little or no illuminating value of themselves,
+      causing the gas to emit less light than it should per unit of volume
+      consumed, more particularly, of course, when the acetylene is not burnt
+      under the mantle. Also, not being acetylene, or isomeric therewith, they
+      require, even if they are combustible, a different proportion of oxygen
+      for their perfect combustion; and a good acetylene jet is only calculated
+      to attract precisely that quantity of air to the flame which a gas having
+      the constitution C_2H_2 demands. It will be apparent without argument that
+      a proper system of purification is one that is competent to remove the
+      carbide impurities from acetylene, so far as that removal is desirable or
+      necessary; it should not be called upon to extract the generator
+      impurities, because the proper way of dealing with them is, to the utmost
+      possible extent, to prevent their formation. The sole exception to this
+      rule is that of water-vapour, which invariably accompanies the best
+      acetylene, and must be partially removed as soon as convenient. Vapour of
+      water almost always accompanies acetylene from the generator, even when
+      the apparatus does not belong to those systems of working where liquid
+      water is in excess, this being due to the fact that in a generator where
+      the carbide is in excess the temperature tends to rise until part of the
+      water is vapourised and carried out of the decomposing chamber before it
+      has an opportunity of reacting with the excess of carbide. The issuing gas
+      is therefore more or less hot, and it usually comes from the generating
+      chamber saturated with vapour, the quantity needed so to saturate it
+      rising as the temperature of the gas increases. Practically speaking,
+      there is little objection to the presence of water-vapour in acetylene
+      beyond the fear of deposition of liquid in the pipes, which may accumulate
+      till they are partially or completely choked, and may even freeze and
+      burst them in very severe weather. Where the chemical purifiers, too,
+      contain a solid material which accidentally or intentionally acts as a
+      drier by removing moisture from the acetylene, it is a waste of such
+      comparatively expensive material to allow gas to enter the purifier wetter
+      than need be.
+    </p>
+    <p>
+      EXTRACTION OF MOISTURE.--In all large plants the extraction of the
+      moisture may take place in two stages. Immediately after the generator,
+      and before the washer if the generator requires such an apparatus to
+      follow it, a condenser is placed. Here the gas is made to travel somewhat
+      slowly through one or more pipes surrounded with cold air or water, or is
+      made to travel through a space containing pipes in which cold water is
+      circulating, the precise method of constructing the condenser being
+      perfectly immaterial so long as the escaping gas has a temperature not
+      appreciably exceeding that of the atmosphere. So cooled, however, the gas
+      still contains much water-vapour, for it remains saturated therewith at
+      the temperature to which it is reduced, and by the inevitable law of
+      physics a further fall in temperature will be followed by a further
+      deposition of liquid water from the acetylene. Manifestly, if the
+      installation is so arranged that the gas can at no part of the service and
+      on no occasion fall to a lower temperature than that at which it issues
+      from the condenser, the removal of moisture as effected by such a
+      condenser will be sufficient for all practical purposes; but at least in
+      all large plants where a considerable length of main is exposed to the
+      air, a more complete moisture extractor must be added to the plant, or
+      water will be deposited in the pipes every cold night in the winter. It
+      is, however, useless to put a chemical drier, or one more searching in its
+      action than a water-cooled condenser, at so early a position in the
+      acetylene plant, because the gas will be subsequently stored in a water-
+      sealed holder, where it will most probably once again be saturated with
+      moisture from the seal. When such generators are adopted as require to
+      have a specific washer placed after them in order to remove the water-
+      soluble impurities, <i>e.g.</i>, those in which the gas does not actually
+      bubble through a considerable quantity of liquid in the generating chamber
+      itself, it is doubtful whether a separate condenser is altogether
+      necessary, because, as the water in the washer can easily be kept at the
+      atmospheric temperature (by means of water circulating in pipes or
+      otherwise), the gas will be brought to the atmospheric temperature in the
+      washer, and at that temperature it cannot carry with it more than a
+      certain fixed proportion of moisture. The notion of partially drying a gas
+      by causing it to pass through water may appear paradoxical, but a
+      comprehension of physical laws will show that it is possible, and will
+      prove efficient in practice, when due attention is given to the facts that
+      the gas entering the washer is hot, and that it is subsequently to be
+      stored over water in a holder.
+    </p>
+    <p>
+      GENERATOR IMPURITIES.--The generator impurities present in the crudest
+      acetylene consist of oxygen and nitrogen, <i>i.e.</i>, the main
+      constituents of air, the various gaseous, liquid, and semi-solid bodies
+      described in Chapter II., which are produced by the polymerising and
+      decomposing action of heat upon the carbide, water, and acetylene in the
+      apparatus, and, whenever the carbide is in excess in the generator, some
+      lime in the form of a very fine dust. In all types of water-to-carbide
+      plant, and in some automatic carbide-feed apparatus, the carbide chamber
+      must be disconnected and opened each time a fresh charge has to be
+      inserted; and since only about one-third of the space in the container can
+      be filled with carbide, the remaining two-thirds are left full of air. It
+      is easy to imagine that the carbide container of a small generator might
+      be so large, or loaded with so small a quantity of carbide, or that the
+      apparatus might in other respects be so badly designed, that the gas
+      evolved might contain a sufficient proportion of air to render it liable
+      to explode in presence of a naked light, or of a temperature superior to
+      its inflaming-point. Were a cock, however, which should have been shut, to
+      be carelessly left open, an escape of gas from, rather than an
+      introduction of air into, the apparatus would follow, because the pressure
+      in the generator is above that of the atmosphere. As is well known,
+      roughly four-fifths by volume of the air consist of nitrogen, which is
+      non-inflammable and accordingly devoid of danger- conferring properties;
+      but in all flames the presence of nitrogen is harmful by absorbing much of
+      the heat liberated, thus lowering the temperature of that flame, and
+      reducing its illuminating power far more seriously. On the other hand, a
+      certain quantity of air in acetylene helps to prevent burner troubles by
+      acting as a mere diluent (albeit an inferior one to methane or marsh-gas),
+      and therefore it has been proposed intentionally to add air to the gas
+      before consumption, such a process being in regular use on the large scale
+      in some places abroad. As Eitner has shown (Chapter VI.) that in a
+      3/4-inch pipe acetylene ceases to be explosive when mixed with less than
+      47.7 per cent. of air, an amount of, say, 40 per cent. or less may in
+      theory be safely added to acetylene; but in practice the amount of air
+      added, if any, would have to be much smaller, because the upper limit of
+      explosibility of acetylene-air mixtures is not rigidly fixed, varying from
+      about 50 per cent. of air when the mixture is in a small vessel, and fired
+      electrically to about 25 per cent. of air in a large vessel approached
+      with a flame. Moreover, safely to prepare such mixtures, after the
+      proportion of air had been decided upon, would require the employment of
+      some additional perfectly trustworthy automatic mechanism to the plant to
+      draw into the apparatus a quantity of air strictly in accordance with the
+      volume of acetylene made --a pair of meters geared together, one for the
+      gas, the other for the air--and this would introduce extra complexity and
+      extra expense. On the whole the idea cannot be recommended, and the action
+      of the British Home Office in prohibiting the use of all such mixtures
+      except those unavoidably produced in otherwise good generators, or in
+      burners of the ordinary injector type, is perfectly justifiable. The
+      derivation and effect of the other gaseous and liquid generator impurities
+      in acetylene were described in Chapter II. Besides these, very hot gas has
+      been found to contain notable amounts of hydrogen and carbon monoxide,
+      both of which burn with non-luminous flames. The most plausible
+      explanation of their origin has been given by Lewes, who suggests that
+      they may be formed by the action of water-vapour upon very hot carbide or
+      upon carbon separated therefrom as the result of previous dissociation
+      among the gases present; the steam and the carbon reacting together at a
+      temperature of 500� C. or thereabouts in a manner resembling that of the
+      production of water-gas. The last generator impurity is lime dust, which
+      is calcium oxide or hydroxide carried forward by the stream of gas in a
+      state of extremely fine subdivision, and is liable to be produced whenever
+      water acts rapidly upon an excess of calcium carbide. This lime
+      occasionally appears in the alternative form of a froth in the pipes
+      leading directly from the generating chamber; for some types of
+      carbide-to-water apparatus, decomposing certain kinds of carbide, foam
+      persistently when the liquid in them becomes saturated with lime, and this
+      foam or froth is remarkably difficult to break up.
+    </p>
+    <p>
+      FILTERS.--It has just been stated that the purifying system added to an
+      acetylene installation should not be called upon to remove these generator
+      impurities; because their appearance in quantity indicates a faulty
+      generator, which should be replaced by one of better action. On the
+      contrary, with the exception of the gases which are permanent at
+      atmospheric temperature--hydrogen, carbon monoxide, nitrogen, and oxygen--
+      and which, once produced, must remain in the acetylene (lowering its
+      illuminating value, but giving no further trouble), extraction of these
+      generator impurities is quite simple. The dust or froth of lime will be
+      removed in the washer where the acetylene bubbles through water--the dust
+      itself can be extracted by merely filtering the gas through cotton-wool,
+      felt, or the like. The least volatile liquid impurities will be removed
+      partly in the condenser, partly in the washer, and partly by the
+      mechanical dry-scrubbing action of the solid purifying material in the
+      chemical purifier. To some extent the more volatile liquid bodies will be
+      removed similarly; but a complete extraction of them demands the
+      employment of some special washing apparatus in which the crude acetylene
+      is compelled to bubble (in finely divided streams) through a layer of some
+      non-volatile oil, heavy mineral lubricating oil, &amp;c.; for though
+      soluble in such oil, the liquid impurities are not soluble in, nor do they
+      mix with, water; and since they are held in the acetylene as vapours, a
+      simple passage through water, or through water-cooled pipes, does not
+      suffice for their recovery. It will be seen that a sufficient removal of
+      these generator impurities need throw no appreciable extra labour upon the
+      consumer of acetylene, for he can readily select a type of generator in
+      which their production is reduced to a minimum; while a cotton-wool or
+      coke filter for the gas, a water washer, which is always useful in the
+      plant if only employed as a non-return valve between the generator and the
+      holder, and the indispensable chemical purifiers, will take out of the
+      acetylene all the remaining generator impurities which need, and can, be
+      extracted.
+    </p>
+    <p>
+      CARBIDE IMPURITIES.--Neglecting very minute amounts of carbon monoxide and
+      hydrogen (which may perhaps come from cavities in the calcium carbide
+      itself), as being utterly insignificant from the practical point of view,
+      the carbide impurities of the gas fall into four main categories: those
+      containing phosphorus, those containing sulphur, those containing silicon,
+      and those containing gaseous ammonia. The phosphorus in the gas comes from
+      calcium phosphide in the calcium carbide, which is attacked by water, and
+      yields phosphoretted hydrogen (or phosphine, as it will be termed
+      hereafter). The calcium phosphide, in its turn, is produced in the
+      electric furnace by the action of the coke upon the phosphorus in
+      phosphatic lime--all commercially procurable lime and some varieties of
+      coke (or charcoal) containing phosphates to a larger or smaller extent.
+      The sulphur in the gas comes from aluminium sulphide in the carbide, which
+      is produced in the electric furnace by the interaction of impurities
+      containing aluminium and sulphur (clay-like bodies, &amp;c.) present in
+      the lime and coke; this aluminium sulphide is attacked by water and yields
+      sulphuretted hydrogen. Even in the absence of aluminium compounds,
+      sulphuretted hydrogen may be found in the gases of an acetylene generator;
+      here it probably arises from calcium sulphide, for although the latter is
+      not decomposed by water, it gradually changes in water into calcium
+      sulphydrate, which appears to suffer decomposition. When it exists in the
+      gas the silicon is derived from certain silicides in the carbide; but this
+      impurity will be dealt with by itself in a later paragraph. The ammonia
+      arises from the action of the water upon magnesium, aluminium, or possibly
+      calcium nitride in the calcium carbide, which are bodies also produced in
+      the electric furnace or as the carbide is cooling. In the gas itself the
+      ammonia exists as such; the phosphorus exists mainly as phosphine, partly
+      as certain organic compounds containing phosphorus, the exact chemical
+      nature of which has not yet been fully ascertained; the sulphur exists
+      partly as sulphuretted hydrogen and partly as organic compounds analogous,
+      in all probability, to those of phosphorus, among which Caro has found oil
+      of mustard, and certain bodies that he regards as mercaptans. [Footnote:
+      It will be convenient to borrow the phrase used in the coal-gas industry,
+      calling the compounds of phosphorus other than phosphine "phosphorus
+      compounds," and the compounds of sulphur other than sulphuretted hydrogen
+      "sulphur compounds." The "sulphur compounds" of coal-gas, however, consist
+      mainly of carbon bisulphide, which is certainly not the chief "sulphur
+      compound" in acetylene, even if present to any appreciable extent.] The
+      precise way in which these organic bodies are formed from the phosphides
+      and sulphides of calcium carbide is not thoroughly understood; but the
+      system of generation employed, and the temperature obtaining in the
+      apparatus, have much to do with their production; for the proportion of
+      the total phosphorus and sulphur found in the crude gas which exists as
+      "compounds" tends to be greater as the generating plant yields a higher
+      temperature. It should be noted that ammonia and sulphuretted hydrogen
+      have one property in common which sharply distinguishes them from the
+      sulphur "compounds," and from all the phosphorus compounds, including
+      phosphine. Ammonia and sulphuretted hydrogen are both very soluble in
+      water, the latter more particularly in the lime-water of an active
+      acetylene generator; while all the other bodies referred to are completely
+      insoluble. It follows, therefore, that a proper washing of the crude gas
+      in water should suffice to remove all the ammonia and sulphuretted
+      hydrogen from the acetylene; and as a matter of fact those generators in
+      which the gas is evolved in presence of a large excess of water, and in
+      which it has to bubble through such water, yield an acetylene practically
+      free from ammonia, and containing nearly all the sulphur which it does
+      contain in the state of "compounds." It must also be remembered that
+      chemical processes which are perfectly suited to the extraction of
+      sulphuretted hydrogen and phosphine are not necessarily adapted for the
+      removal of the other phosphorus and sulphur compounds.
+    </p>
+    <p>
+      WASHERS.--In designing a washer for the extraction of ammonia and
+      sulphuretted hydrogen it is necessary to see that the gas is brought into
+      most intimate contact with the liquid, while yet no more pressure than can
+      possibly be avoided is lost. Subdivision of the gas stream may be effected
+      by fitting the mouth of the inlet-pipe with a rose having a large number
+      of very small holes some appreciable distance apart, or by bending the
+      pipe to a horizontal position and drilling it on its upper surface with
+      numbers of small holes. Another method is to force the gas to travel under
+      a series of partitions extending just below the water- level, forming the
+      lower edges of those partitions either perfectly horizontal or with small
+      notches like the teeth of a saw. One volume of pure water only absorbs
+      about three volumes of sulphuretted hydrogen at atmospheric temperatures,
+      but takes up some 600 volumes of gaseous ammonia; and as ammonia always
+      accompanies the sulphuretted hydrogen, the latter may be said to be
+      absorbed in the washer by a solution of ammonia, a liquid in which
+      sulphuretted hydrogen is much more soluble. Therefore, since water only
+      dissolves about an equal volume of acetylene, the liquid in the washer
+      will continue to extract ammonia and sulphuretted hydrogen long after it
+      is saturated with the hydrocarbon. For this reason, <i>i.e.</i>, to avoid
+      waste of acetylene by dissolution in the clean water of the washer, the
+      plan is sometimes adopted of introducing water to the generator through
+      the washer, so that practically the carbide is always attacked by a liquid
+      saturated with acetylene. Provided the liquid in the generator does not
+      become seriously heated, there is no objection to this arrangement; but if
+      the water is heated strongly in the generator it loses much or all of its
+      solvent properties, and the impurities may be driven back again into the
+      washer. Clearly if the waste lime of the generator occurs as a dry or damp
+      powder, the plan mentioned is not to be recommended; but when the waste
+      lime is a thin cream--water being in large excess--it may be adopted. If
+      the generator produces lime dust among the gas, and if the acetylene
+      enters the washer through minute holes, a mechanical filter to remove the
+      dust must be inserted between the generator and the washer, or the
+      orifices of the leading pipe will be choked. Whenever a water-cooled
+      condenser is employed after the generator, in which the gas does not come
+      in contact with the water, that liquid may always be used to charge the
+      generator. For compactness and simplicity of parts the water of the holder
+      seal is occasionally used as the washing liquid, but unless the liquid of
+      the seal is constantly renewed it will thus become offensive, especially
+      if the holder is under cover, and it will also act corrosively upon the
+      metal of the tank and bell. The water-soluble impurities in acetylene will
+      not be removed completely by merely standing over the holder seal for a
+      short time, and it is not good practice to pass unnecessarily impure gas
+      into a holder. [Footnote: This is not a contradiction of what has been
+      said in Chapter III. about the relative position of holder and chemical
+      purifiers, because reference is now being made to ammonia and sulphuretted
+      hydrogen only.]
+    </p>
+    <p>
+      HARMFULNESS OF IMPURITIES.--The reasons why the carbide impurities must be
+      removed from acetylene before it is burned have now to be explained. From
+      the strictly chemical point of view there are three compounds of
+      phosphorus, all termed phosphoretted hydrogen or phosphine: a gas, PH_3; a
+      liquid, P_2H_4; and a solid, P_4H_2. The liquid is spontaneously
+      inflammable in presence of air; that is to say, it catches fire of itself
+      without the assistance of spark or flame immediately it comes in contact
+      with atmospheric oxygen; being very volatile, it is easily carried as
+      vapour by any permanent gas. The gaseous phosphine is not actually
+      spontaneously inflammable at temperatures below 100� C.; but it oxidises
+      so rapidly in air, even when somewhat diluted, that the temperature may
+      quickly rise to the point of inflammation. In the earliest days of the
+      acetylene industry, directly it was recognised that phosphine always
+      accompanies crude acetylene from the generator, it was believed that
+      unless the proportion were strictly limited by decomposing only a carbide
+      practically free from phosphides, the crude acetylene might exhibit
+      spontaneously inflammable properties. Lewes, indeed, has found that a
+      sample of carbide containing 1 per cent of calcium phosphide gave
+      (probably by local decomposition--the bulk of the phosphide suffering
+      attack first) a spontaneously inflammable gas; but when examining
+      specimens of commercial carbide the highest amount of phosphine he
+      discovered in the acetylene was 2.3 per cent, and this gas was not capable
+      of self-inflammation. According to Bullier, however, acetylene must
+      contain 80 per cent of phosphine to render it spontaneously inflammable.
+      Berdenich has reported a case of a parcel of carbide which yielded on the
+      average 5.1 cubic foot of acetylene per lb., producing gas which contained
+      only 0.398 gramme of phosphorus in the form of phosphine per cubic metre
+      (or 0.028 per cent. of phosphine) and was spontaneously inflammable. But
+      on examination the carbide in question was found to be very irregular in
+      composition, and some lumps produced acetylene containing a very high
+      proportion of phosphorus and silicon compounds. No doubt the spontaneous
+      inflammability was due to the exceptional richness of these lumps in
+      phosphorus. As manufactured at the present day, calcium carbide ordinarily
+      never contains an amount of phosphide sufficient to render the gas
+      dangerous on the score of spontaneous inflammability; but should inferior
+      material ever be put on the markets, this danger might have to be guarded
+      against by submitting the gas evolved from it to chemical analysis.
+      Another risk has been suggested as attending the use of acetylene
+      contaminated with phosphine (and to a minor degree with sulphuretted
+      hydrogen), viz., that being highly toxic, as they undoubtedly are, the gas
+      containing them might be extremely dangerous to breathe if it escaped from
+      the service, or from a portable lamp, unconsumed. Anticipating what will
+      be said in a later paragraph, the worst kind of calcium carbide now
+      manufactured will not yield a gas containing more than 0.1 per cent. by
+      volume of sulphuretted hydrogen and 0.05 per cent. of phosphine. According
+      to Haldane, air containing 0.07 per cent. of sulphuretted hydrogen
+      produces fatal results on man if it is breathed for some hours, while an
+      amount of 0.2 per cent. is fatal in 1- 1/2 minutes. Similar figures for
+      phosphine cannot be given, because poisoning therewith is very rare or
+      quite unknown: the cases of "phossy- jaw" in match factories being caused
+      either by actual contact with yellow phosphorus or by inhalation of its
+      vapour in the elemental state. However, assuming phosphine to be twice as
+      toxic as sulphuretted hydrogen, its effect in crude acetylene of the
+      above-mentioned composition will be equal to that of the sulphuretted
+      hydrogen, so that in the present connexion the gas may be said to be
+      equally toxic with a sample of air containing 0.2 per cent. of
+      sulphuretted hydrogen, which kills in less than two minutes. But this
+      refers only to crude acetylene undiluted with air; and being a
+      hydrocarbon--being in fact neither oxygen nor common air--acetylene is
+      irrespirable of itself though largely devoid of specific toxic action.
+      Numerous investigations have been made of the amount of acetylene (apart
+      from its impurities) which can be breathed in safety; but although these
+      point to a probable recovery after a fairly long-continued respiration of
+      an atmosphere charged with 30 per cent. of acetylene, the figure is not
+      trustworthy, because toxicological experiments upon animals seldom agree
+      with similar tests upon man. If crude acetylene were diluted with a
+      sufficient proportion of air to remove its suffocating qualities, the
+      percentage of specifically toxic ingredients would be reduced to a point
+      where their action might be neglected; and short of such dilution the
+      acetylene itself would in all probability determine pathological effects
+      long before its impurities could set up symptoms of sulphur and phosphorus
+      poisoning.
+    </p>
+    <p>
+      Ammonia is objectionable in acetylene because it corrodes brass fittings
+      and pipes, and because it is partially converted (to what extent is
+      uncertain) into nitrous and nitric acids as it passes through the flame.
+      Sulphur is objectionable in acetylene because it is converted into
+      sulphurous and sulphuric anhydrides, or their respective acids, as it
+      passes through the flame. Phosphorus is objectionable because in similar
+      circumstances it produces phosphoric anhydride and phosphoric acid. Each
+      of these acids is harmful in an occupied room because they injure the
+      decorations, helping to rot book-bindings, [Footnote: It is only fair to
+      state that the destruction of leather bindings is commonly due to traces
+      of sulphuric acid remaining in the leather from the production employed in
+      preparing it, and is but seldom caused directly by the products of
+      combustion coming from gas or oil.] tarnishing "gold-leaf" ornaments, and
+      spoiling the colours of dyed fabrics. Each is harmful to the human system,
+      sulphuric and phosphoric anhydrides (SO_3, and P_4O_10) acting as specific
+      irritants to the lungs of persons predisposed to affections of the
+      bronchial organs. Phosphorus, however, has a further harmful action:
+      sulphuric anhydride is an invisible gas, but phosphoric anhydride is a
+      solid body, and is produced as an extremely fine, light, white voluminous
+      dust which causes a haze, more or less opaque, in the apartment.
+      [Footnote: Lewes suggests that ammonia in the gas burnt may assist in the
+      production of this haze, owing to the formation of solid ammonium salts in
+      the state of line dust.] Immediately it comes in contact with atmospheric
+      moisture phosphoric anhydride is converted into phosphoric acid, but this
+      also occurs at first as a solid substance. The solidity and visibility of
+      the phosphoric anhydride and acid are beneficial in preventing highly
+      impure acetylene being unwittingly burnt in a room; but, on the other
+      hand, being merely solids in suspension in the air, the combustion
+      products of phosphorus are not so easily carried away from the room by the
+      means provided for ventilation as are the products of the combustion of
+      sulphur. Phosphoric anhydride is also partly deposited in the solid state
+      at the burner orifices, perhaps actually corroding the steatite jets, and
+      always assisting in the deposition of carbon from any polymerised
+      hydrocarbons in the acetylene; thus helping the carbon to block up or
+      distort those orifices. Whenever the acetylene is to be burnt on the
+      incandescent system under a mantle of the Welsbach or other type,
+      phosphorus, and possibly sulphur, become additionally objectionable, and
+      rigorous extraction is necessary. As is well known, the mantle is composed
+      of the oxides of certain "rare earths" which owe their practical value to
+      the fact that they are non-volatile at the temperature of the gas-flame.
+      When a gas containing phosphorus is burnt beneath such a mantle, the
+      phosphoric anhydride attacks those oxides, partially converting them into
+      the respective phosphates, and these bodies are less refractory. A mantle
+      exposed to the combustion products of crude acetylene soon becomes brittle
+      and begins to fall to pieces, occasionally showing a yellowish colour when
+      cold. The actual advantage of burning acetylene on the incandescent system
+      is not yet thoroughly established-- in this country at all events; but it
+      is clear that the process will not exhibit any economy (rather the
+      reverse) unless the plant is provided with most capable chemical
+      purifiers. Phosphorus, sulphur, and ammonia are not objectionable in crude
+      acetylene because they confer upon the gas a nauseous odour. From a
+      well-constructed installation no acetylene escapes unconsumed: the gas
+      remains wholly within the pipes until it is burnt, and whatever odour it
+      may have fails to reach the human nostrils. A house properly piped for
+      acetylene will be no more conspicuous by its odour than a house properly
+      piped for coal-gas. On the contrary, the fact that the carbide impurities
+      of acetylene, which, in the absolutely pure state, is a gas of somewhat
+      faint, hardly disagreeable, odour, do confer upon that gas a persistent
+      and unpleasant smell, is distinctly advantageous; for, owing to that
+      odour, a leak in the pipes, an unclosed tap, or a fault in the generating
+      plant is instantly brought to the consumer's attention. A gas wholly
+      devoid of odour would be extremely dangerous in a house, and would have to
+      be scented, as is done in the case of non-carburetted water-gas when it is
+      required for domestic purposes.
+    </p>
+    <p>
+      AMOUNTS OF IMPURITIES AND SCOPE OF PURIFICATION.--Partly for the reason
+      which has just been given, and partly on the ground of expense, a complete
+      removal of the impurities from crude acetylene is not desirable. All that
+      need be done is to extract sufficient to deprive the gas of its injurious
+      effects upon lungs, decorations, and burners. As it stands, however, such
+      a statement is not sufficiently precise to be useful either to consumers
+      of acetylene or to manufacturers of plant, and some more or less arbitrary
+      standard must be set up in order to define the composition of
+      "commercially pure" acetylene, as well as to gauge the efficiency of any
+      process of purification. In all probability such limit may be reasonably
+      taken at 0.1 milligramme of either sulphur or phosphorus (calculated as
+      elementary bodies) per 1 litre of acetylene, <i>i.e.</i>, (0.0-1.1 grain
+      per cubic foot; a quantity which happens to correspond almost exactly with
+      a percentage by weight of 0.01. Owing to the atomic weights of these
+      substances, and the very small quantities being considered, the same limit
+      hardly differs from that of 0.01 per cent. by weight of sulphuretted
+      hydrogen or of phosphine--it being always recollected that the sulphur and
+      phosphorus do not necessarily exist in the gas as simple hydrides.
+      Keppeler, however, has suggested the higher figure of 0.15 milligramme of
+      either sulphur or phosphorus per litre of acetylene (=0.066 grain per
+      cubic foot) for the maximum amount of these impurities permissible in
+      purified acetylene. He adopts this standard on the basis of the results of
+      observations of the amounts of sulphur and phosphorus present in the gas
+      issuing from a purifier charged with heratol at the moment when the last
+      layer of the heratol is beginning to change colour. No limit has been
+      given for the removal of the ammonia, partly because that impurity can
+      more easily, and without concomitant disadvantage, be extracted entirely;
+      and partly because it is usually removed in the washer and not in the true
+      chemical purifier.
+    </p>
+    <p>
+      According to Lewes, the maximum amount of ammonia found in the acetylene
+      coming from a dripping generator is 0.95 gramme per litre, while in
+      carbide-to-water gas it is 0.16 gramme: 417 and 70.2 grains per cubic foot
+      respectively. Rossel and Landriset have found 4 milligrammes (1.756 grains
+      [Footnote: Milligrammes per litre; grains per cubic foot. It is convenient
+      to remember that since 1 cubic foot of water weighs 62.321 x 16 - 997.14
+      avoirdupois ounces, grammes per litre are approximately equal to oz. per
+      cubic foot; and grammes per cubic metre to oz. per 1000 cubic feet.]) to
+      be the maximum in water-to-carbide gas, and none to occur in
+      carbide-to-water acetylene. Rossel and Landriset return the minimum
+      proportion of sulphur, calculated as H_2S, found in the gaseous state in
+      acetylene when the carbide has not been completely flooded with water at
+      1.18 milligrammes per litre, or 0.52 grain per cubic foot; and the
+      corresponding maxima at 1.9 milligrammes, or 0.84 grain. In carbide-to-
+      water gas, the similar maxima are 0.23 milligramme or 0.1 grain. As
+      already stated, the highest proportion of phosphine yet found in acetylene
+      is 2.3 per cent. (Lewes), which is equal to 32.2 milligrammes of PH_3 per
+      litre or 14.13 grains per cubic foot (Polis); but this sample dated from
+      1897. Eitner and Keppeler record the minimum proportion of phosphorus,
+      calculated as PH_3, found in crude acetylene, as 0.45 milligramme per
+      litre, and the maximum as 0.89 milligramme per litre; in English terms
+      these figures are 0.2 and 0.4 grain per cubic foot. On an average,
+      however, British and Continental carbide of the present day may be said to
+      give a gas containing 0.61 milligramme of phosphorus calculated as PH_3
+      per litre and 0.75 milligramme of sulphur calculated as H_2S. In other
+      units these figures are equal to 0.27 grain of PH_3 and 0.33 grain of H_2S
+      per 1 cubic foot, or to 0.041 per cent. by volume of PH_3 and 0.052 per
+      cent. of H_2S. Yields of phosphorus and sulphur much higher than these
+      will be found in the journals and books, but such analytical data were
+      usually obtained in the years 1896-99, before the manufacture of calcium
+      carbide had reached its present degree of systematic control. A commercial
+      specimen of carbide was seen by one of the authors as late as 1900 which
+      gave an acetylene containing 1.12 milligramme of elementary sulphur per
+      litre, i.e., 0.096 per cent, by volume, or 0.102 per cent, by volume of
+      H_2S; but the phosphorus showed the low figure of 0.36 milligramme per
+      litre (0.031 per cent, of P or 0.034 per cent, of PH_3 by volume).
+    </p>
+    <p>
+      The British Acetylene Association's regulations relating to carbide of
+      calcium (<i>vide</i> Chap. XIV.) contain a clause to the effect that
+      "carbide which, when properly decomposed, yields acetylene containing from
+      all phosphorus compounds therein more than 0.05 per cent, by volume of
+      phosphoretted hydrogen, may be refused by the buyer." This limit is
+      equivalent to 0.74 milligramme of phosphorus calculated as PH_3 per litre.
+      A latitude of 0.01 per cent, is, however, allowed for the analysis, so
+      that the ultimate limit on which carbide could be rejected is: 0.06 volume
+      per cent. of PH_3, or 0.89 milligramme of phosphorus per litre.
+    </p>
+    <p>
+      The existence in appreciable quantity of combined silicon as a normal
+      impurity in acetylene seems still open to doubt. Calcium carbide
+      frequently contains notable quantities of iron and other silicides; but
+      although these bodies are decomposed by acids, yielding hydrogen silicide,
+      or siliciuretted hydrogen, they are not attacked by plain water.
+      Nevertheless Wolff and Gerard have found hydrogen silicide in crude
+      acetylene, and Lewes looks upon it as a common impurity in small amounts.
+      When it occurs, it is probably derived, as Vigouroux has suggested, from
+      "alloys" of silicon with calcium, magnesium, and aluminium in the carbide.
+      The metallic constituents of these substances would naturally be attacked
+      by water, evolving hydrogen; and the hydrogen, in its nascent state, would
+      probably unite with the liberated silicon to form hydrogen silicide. Many
+      authorities, including Keppeler, have virtually denied that silicon
+      compounds exist in crude acetylene, while the proportion 0.01 per cent.
+      has been given by other writers as the maximum. Caro, however, has stated
+      that the crude gas almost invariably contains silicon, sometimes in very
+      small quantities, but often up to the limit of 0.8 per cent.; the failure
+      of previous investigators to discover it being due to faulty analytical
+      methods. Caro has seen one specimen of (bad) carbide which gave a
+      spontaneously inflammable gas although it contained only traces of
+      phosphine; its inflammability being caused by 2.1 per cent. of hydrogen
+      silicide. Practically speaking, all the foregoing remarks made about
+      phosphine apply equally to hydrogen silicide: it burns to solid silicon
+      oxide (silica) at the burners, is insoluble in water, and is spontaneously
+      inflammable when alone or only slightly diluted, but never occurs in good
+      carbide in sufficient proportion to render the acetylene itself
+      inflammable. According to Caro the silicon may be present both as hydrogen
+      silicide and as silicon "compounds." A high temperature in the generator
+      will favour the production of the latter; an apparatus in which the gas is
+      washed well in lime-water will remove the bulk of the former. Fraenkel has
+      found that magnesium silicide is not decomposed by water or an alkaline
+      solution, but that dilute hydrochloric acid acts upon it and spontaneously
+      inflammable hydrogen silicide results. If it may be assumed that the other
+      silicides in commercial calcium carbide also behave in this manner it is
+      plain that hydrogen silicide cannot occur in crude acetylene unless the
+      gas is supposed to be hurried out of the generator before the alkaline
+      water therein has had time to decompose any traces of the hydrogen
+      silicide which is produced in the favouring conditions of high temperature
+      sometimes prevailing. Mauricheau-Beaupr� has failed to find silica in the
+      products of combustion of acetylene from carbide of varying degrees of
+      purity. He found, however, that a mixture of strong nitric and
+      hydrochloric acids (<i>aqua regia</i>), if contaminated with traces of
+      phosphoric acid, dissolved silica from the glass of laboratory vessels.
+      Consequently, since phosphoric acid results from the phosphine in crude
+      acetylene when the gas is passed through aqua regia, silica may be found
+      on subsequently evaporating the latter. But this, silica, he found, was
+      derived from the glass and not through the oxidation of silicon compounds
+      in the acetylene. It is possible that some of the earlier observers of the
+      occurrence of silicon compounds in crude acetylene may have been misled by
+      the solution of silica from the glass vessels used in their
+      investigations. The improbability of recognisable quantities of silicon
+      compounds occurring in acetylene in any ordinary conditions of generation
+      is demonstrated by a recent study by Fraenkel of the composition of the
+      deposit produced on reflectors exposed to the products of combustion of a
+      sample of acetylene which afforded a haze when burnt. The deposit
+      contained 51.07 per cent. of phosphoric acid, but no silica. The gas
+      itself contained from 0.0672 to 0.0837 per cent. by volume of phosphine.
+    </p>
+    <p>
+      PURIFYING MATERIALS.--When acetylene first began to be used as a domestic
+      illuminant, most generator builders denied that there was any need for the
+      removal of these carbide impurities from the gas, some going so far as to
+      assert that their apparatus yielded so much purer an acetylene than other
+      plant, where purification might be desirable, that an addition of a
+      special purifier was wholly unnecessary. Later on the more responsible
+      members of the trade took another view, but they attacked the problem of
+      purification in a perfectly empirical way, either employing some purely
+      mechanical scrubber filled with some moist or dry porous medium, or
+      perhaps with coke or the like wetted with dilute acid, or they simply
+      borrowed the processes adopted in the purification of coal-gas. At first
+      sight it might appear that the more simple methods of treating coal-gas
+      should be suitable for acetylene; since the former contains two of the
+      impurities--sulphuretted hydrogen and ammonia--characteristic of crude
+      acetylene. After removing the ammonia by washing with water, therefore, it
+      was proposed to extract the sulphur by passing the acetylene through that
+      variety of ferric hydroxide (hydrated oxide of iron) which is so
+      serviceable in the case of coal-gas. The idea, however, was quite unsound:
+      first, because it altogether ignores the phosphorus, which is the most
+      objectionable impurity in acetylene, but is not present in coal- gas;
+      secondly, because ferric hydroxide is used on gasworks to extract in a
+      marketable form the sulphur which occurs as sulphuretted hydrogen, and
+      true sulphuretted hydrogen need not exist in well-generated and well-
+      washed acetylene to any appreciable extent; thirdly, because ferric
+      hydroxide is not employed by gasmakers to remove sulphur compounds (this
+      is done with lime), being quite incapable of extracting them, or the
+      analogous sulphur compounds of crude acetylene.
+    </p>
+    <p>
+      About the same time three other processes based on somewhat better
+      chemical knowledge were put forward. Pictet proposed leading the gas
+      through a strong solution of calcium chloride and then through strong
+      sulphuric acid, both maintained at a temperature of -20� to -40� C.,
+      finally washing the gas in a solution of some lead salt. Proof that such
+      treatment would remove phosphorus to a sufficient degree is not altogether
+      satisfactory; but apart from this the necessity of maintaining such low
+      temperatures, far below that of the coldest winter's night, renders the
+      idea wholly inadmissible for all domestic installations. Willgerodt
+      suggested removing sulphuretted hydrogen by means of potassium hydroxide
+      (caustic potash), then absorbing the phosphine in bromine water. For many
+      reasons this process is only practicable in the laboratory. Berg� and
+      Reychler proposed extracting both sulphuretted hydrogen and phosphine in
+      an acid solution of mercuric chloride (corrosive sublimate). The
+      poisonousness of this latter salt, apart from all other objections, rules
+      such a method out.
+    </p>
+    <p>
+      BLEACHING POWDER.--The next idea, first patented by Smith of Aberdeen, but
+      fully elaborated by Lunge and Cedercreutz, was to employ bleaching- powder
+      [Footnote: Bleaching-powder is very usually called chloride of lime; but
+      owing to the confusion which is constantly arising in the minds of persons
+      imperfectly acquainted with chemistry between chloride of lime and
+      chloride of calcium--two perfectly distinct bodies--the less ambiguous
+      expression "bleaching-powder" will be adopted here.] either in the solid
+      state or as a liquid extract. The essential constituent of
+      bleaching-powder from the present aspect is calcium hypochlorite, which
+      readily oxidises sulphuretted hydrogen, and more particularly phosphine,
+      converting them into sulphuric and phosphoric acids, while the acetylene
+      is practically unattacked. In simple purifying action the material proved
+      satisfactory; but since high-grade commercial bleaching-powder contains
+      some free chlorine, or some is set free from it in the purifier under the
+      influence of the passing gas, the issuing acetylene was found to contain
+      chlorine, free or combined; and this, burning eventually to hydrochloric
+      acid, is hardly less harmful than the original sulphur compounds.
+      Moreover, a mixture of acetylene, chlorine, and air is liable to catch
+      fire of itself when exposed to bright sunlight; and therefore the use of a
+      bleaching-powder purifier, or rather the recharging thereof, was not
+      unattended by danger in the early days. To overcome these defects, the
+      very natural process was adopted of diluting the bleaching-powder, such
+      diluent also serving to increase the porosity of the material. A very
+      unsuitable substance, however, was selected for the purpose, viz.,
+      sawdust, which is hygroscopic organic, and combustible. Owing to the
+      exothermic chemical action between the impurities of the acetylene and the
+      bleaching-powder, the purifying mass became heated; and thus not only were
+      the phenomena found in a bad generator repeated in the purifying vessel,
+      but in presence of air and light (as in emptying the purifier), the
+      reaction proceeded so rapidly that the heat caused inflammation of the
+      sawdust and the gas, at least on one occasion an actual fire taking place
+      which created much alarm and did some little damage. For a time,
+      naturally, bleaching-powder was regarded as too dangerous a material to be
+      used for the purification of crude acetylene; but it was soon discovered
+      that danger could be avoided by employing the substance in a proper way.
+    </p>
+    <p>
+      HERATOL, FRANKOLINE, ACAGINE AND PURATYLENE.--Setting aside as unworthy of
+      attention certain compositions offered as acetylene purifying materials
+      whose constitution has not been divulged or whose action has not been
+      certified by respectable authority, there are now three principal chemical
+      reagents in regular use. Those are chromic acid, cuprous chloride (sub- or
+      proto-chloride of copper), and bleaching- powder. Chromic acid is employed
+      in the form of a solution acidified with acetic or hydrochloric acid,
+      which, in order to obtain the advantages (<i>see</i> below) attendant upon
+      the use of a solid purifying material, is absorbed in that highly porous
+      and inert description of silica known as infusorial earth or "kieselguhr."
+      This substance was first recommended by Ullmann, and is termed
+      commercially "heratol" As sold it contains somewhere about 136 grammes of
+      chromic acid per kilo. Cuprous chloride is used as a solution in strong
+      hydrochloric acid mixed with ferric chloride, and similarly absorbed in
+      kieselguhr. From the name of its proposer, this composition is called
+      "frankoline." It will be shown in Chapter VI. that the use of metallic
+      copper in the construction of acetylene apparatus is not permissible or
+      judicious, because the gas is liable to form therewith an explosive
+      compound known as copper acetylide; it might seem, therefore, that the
+      employment of a copper salt for purification courts accident. The
+      objection is not sound, because the acetylide is not likely to be produced
+      except in the presence of ammonia; and since frankoline is a highly acid
+      product, the ammonia is converted into its chloride before any copper
+      acetylide can be produced. As a special acetylene purifier,
+      bleaching-powder exists in at least two chief modifications. In one, known
+      as "acagine," it is mixed with 15 per cent. of lead chromate, and
+      sometimes with about the same quantity of barium sulphate; the function of
+      the latter being simply that of a diluent, while to the lead chromate is
+      ascribed by its inventor (Wolff) the power of retaining any chlorine that
+      may be set free from the bleaching-powder by the reduction of the chromic
+      acid. The utility of the lead chromate in this direction has always
+      appeared doubtful; and recently Keppeler has argued that it can have no
+      effect upon the chlorine, inasmuch as in the spent purifying material the
+      lead chromate may be found in its original condition unchanged. The second
+      modification of bleaching-powder is designated "puratylene," and contains
+      calcium chloride and quick or slaked lime. It is prepared by evaporating
+      to dryness under diminished pressure solutions of its three ingredients,
+      whereby the finished material is given a particularly porous nature.
+    </p>
+    <p>
+      It will be observed that both heratol and frankoline are powerfully acid,
+      whence it follows they are capable of extracting any ammonia that may
+      enter the purifier; but for the same reason they are liable to act
+      corrosively upon any metallic vessel in which they are placed, and they
+      therefore require to be held in earthenware or enamelled receivers. But
+      since they are not liquid, the casing of the purifier can be safely
+      constructed of steel or cast iron. Puratylene also removes ammonia by
+      virtue of the calcium chloride in it. Acagine would probably pass the
+      ammonia; but this is no real objection, as the latter can be extracted by
+      a preliminary washing in water. Heratol changes, somewhat obscurely, in
+      colour as it becomes spent, its original orange tint, due to the chromic
+      acid, altering to a dirty green, characteristic of the reduced salts of
+      chromium oxide. Frankoline has been asserted to be capable of regeneration
+      or revivification, <i>i.e.</i>, that when spent it may be rendered fit for
+      further service by being exposed to the air for a time, as is done with
+      gas oxide; this, however, may be true to some extent with the essential
+      constituents of frankoline, but the process is not available with the
+      commercial solid product. Of all these materials, heratol is the most
+      complete purifier of acetylene, removing phosphorus and sulphur most
+      rapidly and thoroughly, and not appreciably diminishing in speed or
+      efficiency until its chromic acid is practically quite used up. On the
+      other hand, heratol does act upon pure acetylene to some extent; so that
+      purifiers containing it should be small in size and frequently recharged.
+      In one of his experiments Keppeler found that 13 per cent. of the chromic
+      acid in heratol was wasted by reacting with acetylene. As this waste of
+      chromic acid involves also a corresponding loss of gas, small purifiers
+      are preferable, because at any moment they only contain a small quantity
+      of material capable of attacking the acetylene itself. Frankoline is very
+      efficacious as regards the phosphorus, but it does not wholly extract the
+      sulphur, leaving, according to Keppeler, from 0.13 to 0.20 gramme of the
+      latter in every cubic metre of the gas. It does not attack acetylene
+      itself; and if, owing to its free hydrochloric acid, it adds any acid
+      vapours to the purified gas, these vapours may be easily removed by a
+      subsequent passage through a vessel containing lime or a carbide drier.
+      Both being essentially bleaching-powder, acagine and puratylene are alike
+      in removing phosphorus to a satisfactory degree; but they leave some
+      sulphur behind. Acagine evidently attacks acetylene to a slight extent, as
+      Keppeler has found 0.2 gramme of chlorine per cubic metre in the issuing
+      gas.
+    </p>
+    <p>
+      Although some of these materials attack acetylene slightly, and some leave
+      sulphur in the purified gas, they may be all considered reasonably
+      efficient from the practical point of view; for the loss of true acetylene
+      is too small to be noticeable, and the quantity of sulphur not extracted
+      too trifling to be harmful or inconvenient. They may be valued,
+      accordingly, mainly by their price, proper allowance being made for the
+      quantity of gas purified per unit weight of substance taken. This quantity
+      of gas must naturally vary with the proportion of phosphorus and sulphur
+      in the crude acetylene; but on an average the composition of unpurified
+      gas is what has already been given above, and so the figures obtained by
+      Keppeler in his investigation of the subject may be accepted. In the
+      annexed table these are given in two forms: (1) the number of litres of
+      gas purified by 1 kilogramme of the substance, (2) the number of cubic
+      feet purified per lb. It should be noted that the volumes of gas refer to
+      a laboratory degree of purification; in practice they may all be increased
+      by 10 or possibly 20 per cent.
+    </p>
+<pre xml:space="preserve">
+ _________________________________________________
+|              |                   |              |
+|              |      Litres       | Cubic Feet   |
+|              |  per Kilogramme.  |   per Lb.    |
+|______________|___________________|______________|
+|              |                   |              |
+|  Heratol     |       5,000       |      80      |
+|  Frankoline  |       9,000       |     144      |
+|  Puratylene  |      10,000       |     160      |
+|  Acagine     |      13,000       |     208      |
+|______________|___________________|______________|
+</pre>
+    <p>
+      Another method of using dry bleaching-powder has been proposed by
+      Pfeiffer. He suggests incorporating it with a solution of some lead salt,
+      so that the latter may increase the capacity of the calcium hypochlorite
+      to remove sulphur. Analytical details as to the efficiency of this process
+      have not been given. During 1901 and 1902 Bullier and Maquenne patented a
+      substance made by mixing bleaching-powder with sodium sulphate, whereby a
+      double decomposition occurs, sodium hypochlorite, which is equally
+      efficient with calcium hypochlorite as a purifying material, being
+      produced together with calcium sulphate, which, being identical with
+      plaster of Paris, sets into a solid mass with the excess of water present,
+      and is claimed to render the whole more porous. This process seemed open
+      to objection, because Blagden had shown that a solution of sodium
+      hypochlorite was not a suitable purifying reagent in practice, since it
+      was much more liable to add chlorine to the gas than calcium hypochlorite.
+      The question how a solidified modification of sodium hypochlorite would
+      behave in this respect has been investigated by Keppeler, who found that
+      the Bullier and Maquenne material imparted more chlorine to the gas which
+      had traversed it than other hypochlorite purifying agents, and that the
+      partly foul material was liable to cause violent explosions. About the
+      same time Rossel and Landriset pointed out that purification might be
+      easily effected in all generators of the carbide-to-water pattern by
+      adding to the water of the generator itself a quantity of bleaching-powder
+      equivalent to 5 to 20 grammes for every 1 kilogramme of carbide
+      decomposed, claiming that owing to the large amount of liquid present,
+      which is usually some 4 litres per kilogramme of carbide (0.4 gallon per
+      lb.), no nitrogen chloride could be produced, and that owing to the
+      dissolved lime in the generator, chlorine could not be added to the gas.
+      The process is characterised by extreme simplicity, no separate purifier
+      being needed, but it has been found that an introduction of
+      bleaching-powder in the solid condition is liable to cause an explosive
+      combination of acetylene and chlorine, while the use of a solution is
+      attended by certain disadvantages. Granjon has proposed impregnating a
+      suitable variety of wood charcoal with chlorine, with or without an
+      addition of bleaching-powder; then grinding the product to powder, and
+      converting it into a solid porous mass by the aid of cement. The material
+      is claimed to last longer than ordinary hypochlorite mixtures, and not to
+      add chlorine to the acetylene.
+    </p>
+    <p>
+      SUBSIDIARY PURIFYING MATERIALS.--Among minor reagents suggested as
+      purifying substances for acetylene may be mentioned potassium
+      permanganate, barium peroxide, potassium bichromate, sodium plumbate and
+      arsenious oxide. According to Benz the first two do not remove the
+      sulphuretted hydrogen completely, and oxidise the acetylene to some
+      extent; while potassium bichromate leaves some sulphur and phosphorus
+      behind in the gas. Sodium plumbate has been suggested by Morel, but it is
+      a question whether its action on the impurities would not be too violent
+      and whether it would be free from action on the acetylene itself. The use
+      of arsenious oxide dissolved in a strong acid, and the solution absorbed
+      in pumice or kieselguhr has been protected by G. F. Jaubert. The phosphine
+      is said to combine with the arsenic to form an insoluble brownish
+      compound. In 1902 Javal patented a mixture of 1 part of potassium
+      permanganate, 5 of "sulphuric acid," and 1 of water absorbed in 4 parts of
+      infusorial earth. The acid constantly neutralised by the ammonia of the
+      crude gas is as constantly replaced by fresh acid formed by the oxidation
+      of the sulphuretted hydrogen; and this free acid, acting upon the
+      permanganate, liberates manganese peroxide, which is claimed to destroy
+      the phosphorus and sulphur compounds present in the crude acetylene.
+    </p>
+    <p>
+      �PUR�NE.--A purifying material to which the name of �pur�ne has been given
+      has been described, by Mauricheau-Beaupr�, as consisting of a mixture of
+      ferric chloride and ferric oxide in the proportion of 2 molecules, or 650
+      parts, of the former with one molecule, or 160 parts, of the latter,
+      together with a suitable quantity of infusorial earth. In the course of
+      preparation, however, 0.1 to 0.2 per cent. of mercuric chloride is
+      introduced into the material. This mercuric chloride is said to form an
+      additive compound with the phosphine of the crude acetylene, which
+      compound is decomposed by the ferric chloride, and the mercuric chloride
+      recovered. The latter therefore is supposed to act only as a carrier of
+      the phosphine to the ferric chloride and oxide, by which it is oxidised
+      according to the equation:
+    </p>
+    <p>
+      8Fe_2Cl_6 + 4Fe_2O_3 + 3PH_3 = 12Fe_2Cl_4 + 3H_3PO_4.
+    </p>
+    <p>
+      Thus the ultimate products are phosphoric acid and ferrous chloride, which
+      on exposure to air is oxidised to ferric chloride and oxide. It is said
+      that this revivification of the fouled or spent �pur�ne takes place in
+      from 20 to 48 hours when it is spread in the open in thin layers, or it
+      may be partially or wholly revivified <i>in situ</i> by adding a small
+      proportion of air to the crude acetylene as it enters the purifier. The
+      addition of 1 to 2 per cent. of air, according to Mauricheau-Beaupr�,
+      suffices to double the purifying capacity of one charge of the material,
+      while a larger proportion would achieve its continuous revivification.
+      �pur�ne is said to purify 10,000 to 11,000 litres of crude acetylene per
+      kilogramme, or, say, 160 to 176 cubic feet per pound, when the acetylene
+      contains on the average 0.05 per cent, by volume of phosphine.
+    </p>
+    <p>
+      For employment in all acetylene installations smaller than those which
+      serve complete villages, a solid purifying material is preferable to a
+      liquid one. This is partly due to the extreme difficulty of subdividing a
+      stream of gas so that it shall pass through a single mass of liquid in
+      small enough bubbles for the impurities to be removed by the time the gas
+      arrives at the surface. This time cannot be prolonged without increasing
+      the depth of liquid in the vessel, and the greater the depth of liquid,
+      the more pressure is consumed in forcing the gas through it. Perfect
+      purification by means of fluid reagents unattended by too great a
+      consumption of pressure is only to be effected by a mechanical scrubber
+      such as is used on coal-gas works, wherein, by the agency of external
+      power, the gas comes in contact with large numbers of solid surfaces kept
+      constantly wetted; or by the adoption of a tall tower filled with porous
+      matter or hollow balls over which a continuous or intermittent stream of
+      the liquid purifying reagent is made to trickle, and neither of these
+      devices is exactly suited to the requirements of a domestic acetylene
+      installation. When a solid material having a proper degree of porosity or
+      aggregation is selected, the stream of gas passing through it is broken up
+      most thoroughly, and by employing several separate layers of such
+      material, every portion of the gas is exposed equally to the action of the
+      chemical reagent by the time the gas emerges from the vessel. The amount
+      of pressure so consumed is less than that in a liquid purifier where much
+      fluid is present; but, on the other hand, the loss of pressure is
+      absolutely constant at all times in a liquid purifier, provided the head
+      of liquid is maintained at the same point. A badly chosen solid purifying
+      agent may exhibit excessive pressure absorption as it becomes partly
+      spent. A solid purifier, moreover, has the advantage that it may
+      simultaneously act as a drier for the gas; a liquid purifier, in which the
+      fluid is mainly water, obviously cannot behave in a similar fashion For
+      thorough purification it is necessary that the gas shall actually stream
+      through the solid material; a mere passage over its surface is neither
+      efficient nor economical of material.
+    </p>
+    <p>
+      DISPOSITION OF PURIFYING MATERIAL.--Although much has been written, and
+      some exaggerated claims made, about the maximum, volume of acetylene a
+      certain variety of purifying material will treat, little has been said
+      about the method in which such a material should be employed to obtain the
+      best results. If 1 lb. of a certain substance will purify 200 cubic feet
+      of normal crude acetylene, that weight is sufficient to treat the gas
+      evolved from 40 lb. of carbide; but it will only do so provided it is so
+      disposed in the purifier that the gas does not pass through it at too high
+      a speed, and that it is capable of complete exhaustion. In the coal- gas
+      industry it is usually assumed that four layers of purifying material,
+      each having a superficial area of 1 square foot, are the minimum necessary
+      for the treatment of 100 cubic feet of gas per hour, irrespective of the
+      nature of the purifying material and of the impurity it is intended to
+      extract. If there is any sound basis for this generalization, it should
+      apply equally to the purification of acetylene, because there is no
+      particular reason to imagine that the removal of phosphine by a proper
+      substance should occur at an appreciably different speed from the removal
+      of carbon dioxide, sulphuretted hydrogen, and carbon bisulphide by lime,
+      ferric oxide, and sulphided lime respectively, Using the coal gas figures,
+      then, for every 10 cubic feet of acetylene generated per hour, a
+      superficial area of (4 x 144 / 10) 57.6 square inches of purifying
+      material is required. In the course of Keppeler's research upon different
+      purifying materials it is shown that 400 grammes of heratol, 360 grammes
+      of frankoline, 250 grammes of acagine, and 230 grammes of puratylene each
+      occupy a space of 500 cubic centimetres when loosely loaded into a
+      purifying vessel, and from these data, the following table has been
+      calculated:
+    </p>
+<pre xml:space="preserve">
+ __________________________________________________________
+|             |            |                |              |
+|             |   Weight   |     Weight     | Cubic Inches |
+|             | per Gallon | per Cubic Foot |   Occupied   |
+|             |   in Lbs.  |     in Lbs.    |    per Lb.   |
+|_____________|____________|________________|______________|
+|             |            |                |              |
+|  Water      |    10.0    |     62.321     |     27.73    |
+|  Heratol    |     8.0    |     49.86      |     31.63    |
+|  Frankoline |     7.2    |     41.87      |     38.21    |
+|  Acagine    |     6.0    |     31.16      |     55.16    |
+|  Puratylene |     4.6    |     28.67      |     60.28    |
+|_____________|____________|________________|______________|
+</pre>
+    <p>
+      As regards the minimum weight of material required, data have been given
+      by Pfleger for use with puratylene. He states that 1 Kilogramme of that
+      substance should be present for every 100 litres of crude acetylene
+      evolved per hour, 4 kilogrammes being the smallest quantity put into the
+      purifier. In English units these figures are 1 lb. per 1.5 cubic feet per
+      hour, with 9 lb. as a minimum, which is competent to treat 1.1 cubic feet
+      of gas per hour. Thus it appears that for the purification of the gas
+      coming from any generator evolving up to 14 cubic feet of acetylene per
+      hour a weight of 9 lb of puratylene must be charged into the purifier,
+      which will occupy (60.28 / 9) 542 cubic inches of space; and it must be so
+      spread out as to present a total superficial area of (4 x 144 x 14 / 100)
+      80.6 square inches to the passing gas. It follows, therefore, that the
+      material should be piled to a depth of (542 / 80.6) 6.7 inches on a
+      support having an area of 80.6 square inches; but inasmuch as such a depth
+      is somewhat large for a small vessel, and as several layers are better
+      than one, it would be preferable to spread out these 540 cubic inches of
+      substance on several supports in such a fashion that a total surface of
+      80.6 square inches or upwards should be exhibited. These figures may
+      obviously be manipulated in a variety of ways for the design of a
+      purifying vessel; but, to give an example, if the ordinary cylindrical
+      shape be adopted with four circular grids, each having a clear diameter of
+      8 inches (<i>i.e.</i>, an area of 50.3 square inches), and if the material
+      is loaded to a depth of 3 inches on each, there would be a total volume of
+      (50.3 x 3 x 4) = 604 cubic inches of puratylene in the vessel, and it
+      would present a total area of (50.3 x 4) = 201 square inches to the
+      acetylene. At Keppeler's estimation such an amount of puratylene should
+      weigh roughly 10 lb., and should suffice for the purification of the gas
+      obtained from 320 lb. of ordinary carbide; while, applying the coal-gas
+      rule, the total area of 201 square inches should render such a vessel
+      equal to the purification of acetylene passing through it at a speed not
+      exceeding (201 / 5.76) = 35 cubic feet per hour. Remembering that it is
+      minimum area in square inches of purifying material that must govern the
+      speed at which acetylene may be passed through a purifier, irrespective
+      probably of the composition of the material; while it is the weight of
+      material which governs the ultimate capacity of the vessel in terms of
+      cubic feet of acetylene or pounds of carbide capable of purification,
+      these data, coupled with Keppeler's efficiency table, afford means for
+      calculating the dimensions of the purifying vessel to be affixed to an
+      installation of any desired number of burners. There is but little to say
+      about the design of the vessel from the mechanical aspect. A circular
+      horizontal section is more likely to make for thorough exhaustion of the
+      material. The grids should be capable of being lifted out for cleaning.
+      The lid may be made tight either by a clamp and rubber or leather washer,
+      or by a liquid seal. If the purifying material is not hygroscopic, water,
+      calcium chloride solution, or dilute glycerin may be used for sealing
+      purposes; but if the material, or any part of it, does absorb water, the
+      liquid in the seal should be some non-aqueous fluid like lubricating oil.
+      Clamped lids are more suitable for small purifiers, sealed lids for large
+      vessels. Care must be taken that condensation products cannot collect in
+      the purifying vessel. If a separate drying material is employed in the
+      same purifier the space it takes must be considered separately from that
+      needed by the active chemical reagent. When emptying a foul purifier it
+      should be recollected that the material may be corrosive, and being
+      saturated with acetylene is likely to catch fire in presence of a light.
+    </p>
+    <p>
+      Purifiers charged with heratol are stated, however, to admit of a more
+      rapid flow of the gas through them than that stated above for puratylene.
+      The ordinary allowance is 1 lb. of heratol for every cubic foot per hour
+      of acetylene passing, with a minimum charge of 7 lb. of the material. As
+      the quantity of material in the purifier is increased, however, the flow
+      of gas per hour may be proportionately increased, <i>e.g.</i>, a purifier
+      charged with 132 lb. of heratol should purify 144 cubic feet of acetylene
+      per hour.
+    </p>
+    <p>
+      In the systematic purification of acetylene, the practical question arises
+      as to how the attendant is to tell when his purifiers approach exhaustion
+      and need recharging; for if it is undesirable to pass crude gas into the
+      service, it is equally undesirable to waste so comparatively expensive a
+      material as a purifying reagent. In Chapter XIV. it will be shown that
+      there are chemical methods of testing for the presence, or determining the
+      proportion, of phosphorus and sulphur in acetylene; but these are not
+      suitable for employment by the ordinary gas-maker. Heil has stated that
+      the purity of the gas may be judged by an inspection of its atmospheric
+      flame as given by a Bunsen burner. Pure acetylene gives a perfectly
+      transparent moderately dark blue flame, which has an inner cone of a pale
+      yellowish green colour; while the impure gas yields a longer flame of an
+      opaque orange-red tint with a bluish red inner zone. It should be noted,
+      however, that particles of lime dust in the gas may cause the atmospheric
+      flame to be reddish or yellowish (by presence of calcium or sodium) quite
+      apart from ordinary impurities; and for various other reasons this
+      appearance of the non-luminous flame is scarcely to be relied upon. The
+      simplest means of ascertaining definitely whether a purifier is
+      sufficiently active consists in the use of the test-papers prepared by E.
+      Merck of Darmstadt according to G. Keppeler's prescription. These papers,
+      cut to a convenient size, are put up in small books from which they may be
+      torn one at a time. In order to test whether gas is sufficiently purified,
+      one of the papers is moistened with hydrochloric acid of 10 per cent.
+      strength, and the gas issuing from a pet-cock or burner orifice is allowed
+      to impinge on the moistened part. The original black or dark grey colour
+      of the paper is changed to white if the gas contains a notable amount of
+      impurity, but remains unchanged if the gas is adequately purified. The
+      paper consists of a specially prepared black porous paper which has been
+      dipped in a solution of mercuric chloride (corrosive sublimate) and dried.
+      Moistening the paper with hydrochloric acid provides in a convenient form
+      for application Berg�'s solution for the detection of phosphine (<i>vide</i>
+      Chapter XIV.). The Keppeler test-papers turn white when the gas contains
+      either ammonia, phosphine, siliciuretted hydrogen, sulphuretted hydrogen
+      or organic sulphur compounds, but with carbon disulphide the change is
+      slow. Thus the paper serves as a test for all the impurities likely to
+      occur in acetylene. The sensitiveness of the test is such that gas
+      containing about 0.15 milligramme of sulphur, and the same amount of
+      phosphorus, per litre (= 0.0655 grain per cubic foot) imparts in five
+      minutes a distinct white mark to the moistened part of the paper, while
+      gas containing 0.05 milligramme of sulphur per litre (= 0.022 grain per
+      cubic foot) gives in two minutes a dull white mark visible only by careful
+      inspection. If, therefore, a distinct white mark appears on moistened
+      Keppeler paper when it is exposed for five minutes to a jet of acetylene,
+      the latter is inadequately purified. If the gas has passed through a
+      purifier, this test indicates that the material is not efficient, and that
+      the purifier needs recharging. The moistening of the Keppeler paper with
+      hydrochloric acid before use is essential, because if not acidified the
+      paper is marked by acetylene itself. The books of Keppeler papers are put
+      up in a case which also contains a bottle of acid for moistening them as
+      required and are obtainable wholesale of E. Merek, 16 Jewry Street,
+      London, E.C., and retail of the usual dealers in chemicals. If Keppeler's
+      test-papers are not available, the purifier should be recharged as a
+      matter of routine as soon as a given quantity of carbide--proportioned to
+      the purifying capacity of the charge of purifying material--has been used
+      since the last recharging. Thus the purifier may conveniently contain
+      enough material to purify the gas evolved from two drums of carbide, in
+      which case it would need recharging when every second drum of carbide is
+      opened.
+    </p>
+    <p>
+      REGULATIONS AS TO PURIFICATION.--The British Acetylene Association has
+      issued the following set of regulations as to purifying material and
+      purifiers for acetylene:
+    </p>
+    <p>
+      Efficient purifying material and purifiers shall comply with the following
+      requirements:
+    </p>
+    <p>
+      (1) The purifying material shall remove phosphorus and sulphur compounds
+      to a commercially satisfactory degree; <i>i.e.</i>, not to a greater
+      degree than will allow easy detection of escaping gas through its odour.
+    </p>
+    <p>
+      (2) The purifying material shall not yield any products capable of
+      corroding the gas-mains or fittings.
+    </p>
+    <p>
+      (3) The purifying material shall, if possible, be efficient as a drying
+      agent, but the Association does not consider this an absolute necessity.
+    </p>
+    <p>
+      (4) The purifying material shall not, under working conditions, be capable
+      of forming explosive compounds or mixtures. It is understood, naturally,
+      that this condition does not apply to the unavoidable mixture of acetylene
+      and air formed when recharging the purifier.
+    </p>
+    <p>
+      (5) The apparatus containing the purifying material shall be simple in
+      construction, and capable of being recharged by an inexperienced person
+      without trouble. It shall be so designed as to bring the gas into proper
+      contact with the material.
+    </p>
+    <p>
+      (6) The containers in purifiers shall be made of such materials as are not
+      dangerously affected by the respective purifying materials used.
+    </p>
+    <p>
+      (7) No purifier shall be sold without a card of instructions suitable or
+      hanging up in some convenient place. Such instructions shall be of the
+      most detailed nature, and shall not presuppose any expert knowledge
+      whatever on the part of the operator.
+    </p>
+    <p>
+      Reference also to the abstracts of the official regulations as to
+      acetylene installations in foreign countries given in Chapter IV. will
+      show that they contain brief rules as to purifiers.
+    </p>
+    <p>
+      DRYING.--It has been stated in Chapter III. that the proper position for
+      the chemical purifiers of an acetylene plant is after the holder; and they
+      therefore form the last items in the installation unless a "station"
+      governor and meter are fitted. It is therefore possible to use them also
+      to remove the moisture in the gas, if a material hygroscopic in nature is
+      employed to charge them. This should be true more particularly with
+      puratylene, which contains a notable proportion of the very hygroscopic
+      body calcium chloride. If a separate drier is desirable, there are two
+      methods of charging it. It may be filled either with some hygroscopic
+      substance such as porous calcium chloride or quicklime in very coarse
+      powder, which retains the water by combining with it; or the gas may be
+      led through a vessel loaded with calcium carbide, which will manifestly
+      hold all the moisture, replacing it by an equivalent quantity of
+      (unpurified) acetylene. The objection is sometimes urged against this
+      latter method, that it restores to the gas the nauseous odour and the
+      otherwise harmful impurities it had more or less completely lost in the
+      purifiers; but as regards the first point, a nauseous odour is not, as has
+      previously been shown, objectionable in itself, and as regards the second,
+      the amount of impurities added by a carbide drier, being strictly limited
+      by the proportion of moisture in the damp gas, is too small to be
+      noticeable at the burners or elsewhere. As is the case with purification,
+      absolute removal of moisture is not called for; all that is needed is to
+      extract so much that the gas shall never reach its saturation-point in the
+      inaccessible parts of the service during the coldest winter's night. Any
+      accessible length of main specially exposed to cold may be safeguarded by
+      itself; being given a steady fall to a certain point (preferably in a
+      frost-free situation), and there provided with a collecting-box from which
+      the deposited liquid can be removed periodically with a pump or otherwise.
+    </p>
+    <p>
+      FILTRATION.--The gas issuing from the purifier or drier is very liable to
+      hold in suspension fine dust derived from the purifying or drying material
+      used. It is essential that thin dust should be abstracted before the gas
+      reaches the burners, otherwise it will choke the orifices and prevent them
+      functioning properly. Consequently the gas should pass through a
+      sufficient layer of filtering material after it has traversed the
+      purifying material (and drier if one is used). This filtering material may
+      be put either as a final layer in the purifier (or drier), or in a
+      separate vessel known as a filter. Among filtering materials in common use
+      may be named cotton-wool, fine canvas or gauze, felt and asbestos-wool.
+      The gas must be fairly well dried before it enters the filter, otherwise
+      the latter will become choked with deposited moisture, and obstruct the
+      passage of the gas.
+    </p>
+    <p>
+      Having now described the various items which go to form a well-designed
+      acetylene installation, it may be useful to recapitulate briefly, with the
+      object of showing the order in which they should be placed. From the
+      generator the gas passes into a condenser to cool it and to remove any
+      tarry products and large quantities of water. Next it enters a washing
+      apparatus filled with water to extract water-soluble impurities. If the
+      generator is of the carbide-to-water pattern, the condenser may be
+      omitted, and the washer is only required to retain any lime froth and to
+      act as a water-seal or non-return valve. If the generator does not wash
+      the gas, the washer must be large enough to act efficiently as such, and
+      between it and the condenser should be put a mechanical filter to extract
+      any dust. From the washer the acetylene travels to the holder. From the
+      holder it passes through one or two purifiers, and from there travels to
+      the drier and filter. If the holder does not throw a constant pressure, or
+      if the purifier and drier are liable to cause irregularities, a governor
+      or pressure regulator must be added after the drier. The acetylene is then
+      ready to enter the service; but a station meter (the last item in the
+      plant) is useful as giving a means of detecting any leak in the
+      delivery-pipes and in checking the make of gas from the amount of carbide
+      consumed. If the gas is required for the supply of a district, a station
+      meter becomes quite necessary, because the public lamps will be fed with
+      gas at a contract rate, and without the meter there would be no control
+      over the volume of acetylene they consume. Where the gas finally leaves
+      the generating-house, or where it enters the residence, a full-way
+      stopcock should be put on the main.
+    </p>
+    <p>
+      GENERATOR RESIDUES.--According to the type of generator employed the waste
+      product removed therefrom may vary from a dry or moist powder to a thin
+      cream or milk of lime. Any waste product which is quite liquid in its
+      consistency must be completely decomposed and free from particles of
+      calcium carbide of sensible magnitude; in the case of more solid residues,
+      the less fluid they are the greater is the improbability (or the less is
+      the evidence) that the carbide has been wholly spent within the apparatus.
+      Imperfect decomposition of the carbide inside the generator not only means
+      an obvious loss of economy, but its presence among the residues makes a
+      careful handling of them essential to avoid accident owing to a subsequent
+      liberation of acetylene in some unsuitable, and perhaps closed, situation.
+      A residue which is not conspicuously saturated with water must be taken
+      out of the generator- house into the open air and there flooded with
+      water, being left in some uncovered receptacle for a sufficient time to
+      ensure all the acetylene being given off. A residue which is liquid enough
+      to flow should be run directly from the draw-off cock of the generator
+      through a closed pipe to the outside; where, if it does not discharge into
+      an open conduit, the waste-pipe must be trapped, and a ventilating shaft
+      provided so that no gas can blow back into the generator-house.
+    </p>
+    <p>
+      DISPOSAL OF RESIDUES.--These residues have now to be disposed of. In some
+      circumstances they can be put to a useful purpose, as will be explained in
+      Chapter XII.; otherwise, and always perhaps on the small scale--certainly
+      always if the generator overheats the gas and yields tar among the spent
+      lime--they must be thrown into a convenient place. It should be remembered
+      that although methods of precipitating sewage by adding lime, or lime
+      water, to it have frequently been used, they have not proved satisfactory,
+      partly because the sludge so obtained is peculiarly objectionable in
+      odour, and partly because an excess of lime yields an effluent containing
+      dissolved lime, which among other disadvantages is harmful to fish. The
+      plan of running the liquid residues of acetylene manufacture into any
+      local sewerage system which may be found in the neighbourhood of the
+      consumer's premises, therefore, is very convenient to the consumer; but is
+      liable to produce complaints if the sewage is afterwards treated
+      chemically, or if its effluent is passed untreated into a highly preserved
+      river; and the same remark applies in a lesser degree if the residues are
+      run into a private cesspool the liquid contents of which automatically
+      flow away into a stream. If, however, the cesspool empties itself of
+      liquid matter by filtration or percolation through earth, there can be no
+      objection to using it to hold the lime sludge, except in so far as it will
+      require more frequent emptying. On the whole, perhaps the best method of
+      disposing of these residues is to run them into some open pit, allowing
+      the liquid to disappear by evaporation and percolation, finally burying
+      the solid in some spot where it will be out of the way. When a large
+      carbide-to-water generator is worked systematically so as to avoid more
+      loss of acetylene by solution in the excess of liquid than is absolutely
+      necessary, the liquid residues coming from it will be collected in some
+      ventilated closed tank where they can settle quietly. The clear lime-water
+      will then be pumped back into the generator for further use, and the
+      almost solid sludge will be ready to be carried to the pit where it is to
+      be buried. Special care must be taken in disposing of the residues from a
+      generator in which oil is used to control evolution of gas. Such oil
+      floats on the aqueous liquid; and a very few drops spread for an
+      incredible distance as an exceedingly thin film, causing those brilliant
+      rainbow-like colours which are sometimes imagined to be a sign of
+      decomposing organic matter. The liquid portions of these residues must be
+      led through a pit fitted with a depending partition projecting below the
+      level at which the water is constantly maintained; all the oil then
+      collects on the first side of the partition, only water passing
+      underneath, and the oil may be withdrawn and thrown away at intervals.
+      <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkvi" id="vi">CHAPTER VI</a>
+    </h2>
+    <h3>
+      THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE
+    </h3>
+    <p>
+      It will only be necessary for the purpose of this book to indicate the
+      more important chemical and physical properties of acetylene, and, in
+      particular, those which have any bearing on the application of acetylene
+      for lighting purposes. Moreover, it has been found convenient to discuss
+      fully in other chapters certain properties of acetylene, and in regard to
+      such properties the reader is referred to the chapters mentioned.
+    </p>
+    <p>
+      PHYSICAL PROPERTIES.--Acetylene is a gas at ordinary temperatures,
+      colourless, and, when pure, having a not unpleasant, so-called "ethereal"
+      odour. Its density, or specific gravity, referred to air as unity, has
+      been found experimentally by Leduc to be 0.9056. It is customary to adopt
+      the value 0.91 for calculations into which the density of the gas enters (<i>vide</i>
+      Chapter VII.). The density of a gas is important not only for the
+      determination of the size of mains needed to convey it at a given rate of
+      flow under a given pressure, as explained in Chapter VII., but also
+      because the volume of gas which will pass through small orifices in a
+      given time depends on its density. According to Graham's well-known law of
+      the effusion of gases, the velocity with which a gas effuses varies
+      directly as the square root of the difference of pressure on the two sides
+      of the opening, and inversely as the square root of the density of the
+      gas. Hence it follows that the volume of gas which escapes through a
+      porous pipe, an imperfect joint, or a burner orifice is, provided the
+      pressure in the gas-pipe is the same, a function of the square root of the
+      density of the gas. Hence this density has to be taken into consideration
+      in the construction of burners, i.e., a burner required to pass a gas of
+      high density must have a larger orifice than one for a gas of low density,
+      if the rate of flow of gas is to be the same under the same pressure.
+      This, however, is a question for the burner manufacturers, who already
+      make special burners for gases of different densities, and it need not
+      trouble the consumer of acetylene, who should always use burners devised
+      for the consumption of that gas. But the Law of effusion indicates that
+      the volume of acetylene which can escape from a leaky supply-pipe will be
+      less than the volume of a gas of lower density, <i>e.g.</i>, coal-gas, if
+      the pressure in the pipe is the same for both. This implies that on an
+      extensive distributing system, in which for practical reasons leakage is
+      not wholly avoidable, the loss of gas through leakage will be less for
+      acetylene than for coal-gas, given the same distributing pressure. If <i>v</i>
+      = the loss of acetylene from a distributing system and <i>v'</i> = the
+      loss of coal-gas from a similar system worked at the same pressure, both
+      losses being expressed in volumes (cubic feet) per hour, and the coal-gas
+      being assumed to have a density of 0.04, then
+    </p>
+    <p>
+      (1) (_v_/_v'_) = (0.40 / 0.91)^(1/2) = 0.663
+    </p>
+    <p>
+      or, _v_ = 0.663_v'_,
+    </p>
+    <p>
+      which signifies that the loss of acetylene by leakage under the same
+      conditions of pressure, &amp;c., will be only 0.663 times that of the loss
+      of coal-gas. In practice, however, the pressures at which the gases are
+      usually sent through mains are not identical, being greater in the case of
+      acetylene than in that of coal-gas. Formula (1) therefore requires
+      correction whenever the pressures are different, and calling the pressure
+      at which the acetylene exists in the main <i>p</i>, and the corresponding
+      pressure of the coal-gas <i>p'</i>, the relative losses by leakage are--
+    </p>
+    <p>
+      (2) (_v_/_v'_) = (0.40 / 0.91)^(1/2) x (_p_/_p'_)^(1/2)
+    </p>
+    <p>
+      _v_ = 0.663_v'_ x (_p_/_p'_)^(1/2)
+    </p>
+    <p>
+      It will be evident that whenever the value of the fraction
+      (_p_/_p'_)^(1/2), is less than 1.5, <i>i.e.</i>, whenever the pressure of
+      the acetylene does not exceed double that of the coal-gas present in pipes
+      of given porosity or unsoundness, the loss of acetylene will be less than
+      that of coal-gas. This is important, especially in the case of large
+      village acetylene installations, where after a time it would be impossible
+      to avoid some imperfect joints, fractured pipes, &amp;c., throughout the
+      extensive distributing mains. The same loss of gas by leakage would
+      represent a far higher pecuniary value with acetylene than with coal-gas,
+      because the former must always be more costly per unit of volume than the
+      latter. Hence it is important to recognise that the rate of leakage, <i>coeteris
+      paribus</i>, is less with acetylene, and it is also important to observe
+      the economical advantage, at least in terms of gas or calcium carbide, of
+      sending the acetylene into the mains at as low a pressure as is compatible
+      with the length of those mains and the character of the consumers'
+      burners. As follows from what will be said in Chapter VII., a high initial
+      pressure makes for economy in the prime cost of, and in the expense of
+      laying, the mains, by enabling the diameter of those mains to be
+      diminished; but the purchase and erection of the distributing system are
+      capital expenses, while a constant expenditure upon carbide to meet loss
+      by leakage falls upon revenue.
+    </p>
+    <p>
+      The critical temperature of acetylene, <i>i.e.</i>, the temperature below
+      which an abrupt change from the gaseous to the liquid state takes place if
+      the pressure is sufficiently high, is 37� C., and the critical pressure,
+      <i>i.e.</i>, the pressure under which that change takes place at that
+      temperature, is nearly 68 atmospheres. Below the critical temperature, a
+      lower pressure than this effects liquefaction of the gas, <i>i.e.</i>, at
+      13.5� C. a pressure of 32.77 atmospheres, at 0� C., 21.53 atmospheres
+      (Ansdell, <i>cf.</i> Chapter XI.). These data are of comparatively little
+      practical importance, owing to the fact that, as explained in Chapter XI.,
+      liquefied acetylene cannot be safely utilised.
+    </p>
+    <p>
+      The mean coefficient of expansion of gaseous acetylene between 0� C. and
+      100� C., is, under constant pressure, 0.003738; under constant volume,
+      0.003724. This means that, if the pressure is constant, 0.003738
+      represents the increase in volume of a given mass of gaseous acetylene
+      when its temperature is raised one degree (C.), divided by the volume of
+      the same mass at 0� C. The coefficients of expansion of air are: under
+      constant pressure, 0.003671; under constant volume, 0.003665; and those of
+      the simple gases (nitrogen, hydrogen, oxygen) are very nearly the same.
+      Strictly speaking the table given in Chapter XIV., for facilitating the
+      correction of the volume of gas measured over water, is not quite correct
+      for acetylene, owing to the difference in the coefficients of expansion of
+      acetylene and the simple gases for which the table was drawn up, but
+      practically no appreciable error can ensue from its use. It is, however,
+      for the correction of volumes of gases measured at different temperatures
+      to one (normal) temperature, and, broadly, for determining the change of
+      volume which a given mass of the gas will undergo with change of
+      temperature, that the coefficient of expansion of a gas becomes an
+      important factor industrially.
+    </p>
+    <p>
+      Ansdell has found the density of liquid acetylene to range from 0.460 at
+      -7� C. to 0.364 at +35.8� C., being 0.451 at 0� C. Taking the volume of
+      the liquid at -7� as unity, it becomes 1.264 at 35.8", and thence Ansdell
+      infers that the mean coefficient of expansion per degree is 0.00489� for
+      the total range of pressure." Assuming that the liquid was under the same
+      pressure at the two temperatures, the coefficient of expansion per degree
+      Centigrade would be 0.00605, which agrees more nearly with the figure
+      0.007 which is quoted, by Fouch� As mentioned before, data referring to
+      liquid (<i>i.e.</i>, liquefied) acetylene are of no practical importance,
+      because the substance is too dangerous to use. They are, however,
+      interesting in so far as they indicate the differences in properties
+      between acetylene converted into the liquid state by great pressure, and
+      acetylene dissolved in acetone under less pressure; which differences make
+      the solution fit for employment. It may be observed that as the solution
+      of acetylene in acetone is a liquid, the acetylene must exist therein as a
+      liquid; it is, in fact, liquid acetylene in a state of dilution, the
+      diluent being an exothermic and comparatively stable body. The specific
+      heat of acetylene is given by M. A. Morel at 0.310, though he has not
+      stated by whom the value was determined. For the purpose of a calculation
+      in Chapter III. the specific heat at constant pressure was assumed to be
+      0.25, which, in the absence of precise information, appears somewhat more
+      probable as an approximation to the truth. The ratio (<i>k</i> or C_p/C_v
+      ) of the specific heat at constant pressure to that at constant volume has
+      been found by Maneuvrier and Fournier to be 1.26; but they did not measure
+      the specific heat itself. [Footnote: The ratio 1.26 <i>k</i> or (C_p/C_v)
+      has been given in many text-books as the value of the specific heat of
+      acetylene, whereas this value should obviously be only about one-fourth or
+      one-fifth of 1.26.
+    </p>
+    <p>
+      By employing the ordinary gas laws it is possible approximately to
+      calculate the specific heat of acetylene from Maneuvrier and Fournier's
+      ratio. Taking the molecular weight of acetylene as 26, we have
+    </p>
+    <p>
+      26 C_p - 26 C_v = 2 cal.,
+    </p>
+    <p>
+      and
+    </p>
+    <p>
+      C_p = 1.26 C_v.
+    </p>
+    <p>
+      From this it follows that C_p, <i>i.e.</i>, the specific heat at constant
+      pressure of acetylene, should be 0.373.] It will be seen that this value
+      for <i>k</i> differs considerably from the corresponding ratio in the case
+      of air and many common gases, where it is usually 1.41; the figure
+      approaches more closely that given for nitrous oxide. For the specific
+      heat of calcium carbide Carlson quotes the following figures:
+    </p>
+<pre xml:space="preserve">
+  0�   1000�  1500�  2000�  2500�  3000�  3500�
+0.247  0.271  0.296  0.325  0.344  0.363  0.381
+</pre>
+    <p>
+      The molecular volume of acetylene is 0.8132 (oxygen = 1).
+    </p>
+    <p>
+      According to the international atomic weights adopted in 1908, the
+      molecular weight of acetylene is 26.016 if O = 16; in round numbers, as
+      ordinarily used, it is 26. Employing the latest data for the weight of 1
+      litre of dry hydrogen and of dry normal air containing 0.04 per cent. of
+      carbon dioxide at a temperature of 0� C. and a barometric pressure of 760
+      mm. in the latitude of London, viz., 0.089916 and 1.29395 grammes
+      respectively (Castell-Evans), it now becomes possible to give the weight
+      of a known volume of dry or moist acetylene as measured under stated
+      conditions with some degree of accuracy. Using 26.016 as the molecular
+      weight of the gas (O = 16), 1 litre of dry acetylene at 0� C. and 760 mm.
+      weighs 1.16963 grammes, or 1 gramme measures 0.854973 litre. From this it
+      follows that the theoretical specific gravity of the gas at 0�/0� C. is
+      0.9039 (air = 1), a figure which may be compared with Leduc's experimental
+      value of 0.9056. Taking as the coefficient of expansion at constant
+      pressure the figure already given, viz., 0.003738, the weights and
+      measures of dry and moist acetylene observed under British conditions (60�
+      F. and 30 inches of mercury) become approximately:
+    </p>
+<pre xml:space="preserve">
+                            Dry.             Saturated.
+     1 litre  .  .  .    1.108 grm.   .  .   1.102 grm.
+     1 gramme .  .  .    0.902 litre. .  .   0.907 litre.
+  1000 cubic feet   .   69.18 lb.  .  .  .  68.83  lb.
+</pre>
+    <p>
+      It should be remembered that unless the gas has been passed through a
+      chemical drier, it is always saturated with aqueous vapour, the amount of
+      water present being governed by the temperature and pressure. The 1 litre
+      of moist acetylene which weighs 1.102 gramme at 60� F. and 30 inches of
+      mercury, contains 0.013 gramme of water vapour; and therefore the weight
+      of dry acetylene in the 1 litre of moist gas is 1.089 gramme. Similarly,
+      the 68.83 pounds which constitute the weight of 1000 cubic feet of moist
+      acetylene, as measured under British standard conditions, are composed of
+      almost exactly 68 pounds of dry acetylene and 0.83 pound of water vapour.
+      The data required in calculating the mass of vapour in a known volume of a
+      saturated gas at any observed temperature and pressure, <i>i.e.</i>, in
+      reducing the figures to those which represent the dry gas at any other
+      (standard) temperature and pressure, will be found in the text-books of
+      physical chemistry. It is necessary to recollect that since coal-gas is
+      measured wet, the factors given in the table quoted in Chapter XIV. from
+      the "Notification of the Gas Referees" simply serve to convert the volume
+      of a wet gas observed under stated conditions to the equivalent volume of
+      the same wet gas at the standard conditions mentioned.
+    </p>
+    <p>
+      HEAT OF COMBUSTION, &amp;C--Based on Berthelot and Matignon's value for
+      the heat of combustion which is given on a subsequent page, viz., 315.7
+      large calories per molecular weight of 26.016 grammes, the calorific power
+      of acetylene under different conditions is shown in the following table:
+    </p>
+<pre xml:space="preserve">
+              Dry.              Dry.              Saturated.
+          0� C. &amp; 760 mm.   60� F &amp; 30 ins.   60� F. &amp; 30 ins.
+</pre>
+<pre xml:space="preserve">
+1 gramme     12.14 cals.      12.14 cals.        12.0  cals.
+1 litre      14.l9  "         13.45  "           13.22  "
+1 cubic foot 40.19  "        380.8   "          374.4   "
+</pre>
+    <p>
+      The figures in the last column refer to the dry acetylene in the gas, no
+      correction having been made for the heat absorbed by the water vapour
+      present. As will appear in Chapter X., the average of actual
+      determinations of the calorific value of ordinary acetylene is 363 large
+      calories or 1440 B.Th.U. per cubic foot. The temperature of ignition of
+      acetylene has been generally stated to be about 480� C. V. Meyer and M�nch
+      in 1893 found that a mixture of acetylene and oxygen ignited between 509�
+      and 515� C. Recent (1909) investigations by H. B. Dixon and H. F. Coward
+      show, however, that the ignition temperature in neat oxygen is between
+      416� and 440� (mean 428� C.) and in air between 406� and 440�, with a mean
+      of 429� C. The corresponding mean temperature of ignition found by the
+      same investigators for other gases are: hydrogen, 585�; carbon monoxide,
+      moist 664�, dry 692�; ethylene, in oxygen 510�, in air 543�; and methane,
+      in oxygen between 550� and 700�, and in air, between 650� and 750� C.
+    </p>
+    <p>
+      Numerous experiments have been performed to determine the temperature of
+      the acetylene flame. According to an exhaustive research by L. Nichols,
+      when the gas burns in air it attains a maximum temperature of 1900� C. �
+      20�, which is 120� higher than the temperature he found by a similar
+      method of observation for the coal-gas flame (fish-tail burner). Le
+      Chatelier had previously assigned to the acetylene flame a temperature
+      between 2100� and 2400�, while Lewes had found for the dark zone 459�, for
+      the luminous zone 1410�, and for the tip 1517� C, F�ry and Mahler have
+      also made measurements of the temperatures afforded by acetylene and other
+      fuels, some of their results being quoted below. F�ry employed his optical
+      method of estimating the temperature, Mahler a process devised by Mallard
+      and Le Chatelier. Mahler's figures all relate to flames supplied with air
+      at a temperature of 0� C. and a constant pressure of 760 mm.
+    </p>
+<pre xml:space="preserve">
+Hydrogen .   .   .   .   .   .   .   .   .   .   . 1900     1960
+Carbon monoxide  .   .   .   .   .   .   .   .   .  --      2100
+Methane  .   .   .   .   .   .   .   .   .   .   .  --   _  1850
+Coal-gas (luminous)  .   .   .   .   .   .   .   . 1712   |
+   " (atmospheric, with deficient supply of air) . 1812   | 1950
+   " (atmospheric, with full supply of air)  .   . 1871  _|
+Water-gas    .   .   .   .   .   .   .   .   .   .  --      2000
+Oxy-coal-gas blowpipe    .   .   .   .   .   .   . 2200      --
+Oxy-hydrogen blowpipe    .   .   .   .   .   .   . 2420      --
+Acetylene    .   .   .   .   .   .   .   .   .   . 2548     2350
+Alcohol  .   .   .   .   .   .   .   .   .   .   . 1705     1700
+Alcohol (in Denayrouze Bunsen)   .   .   .   .   . 1862      --
+Alcohol and petrol in equal parts    .   .   .   . 2053      --
+Crude petroleum (American)   .   .   .   .   .   .  --      2000
+Petroleum spirit    "    .   .   .   .   .   .   .  --      1920
+Petroleum oil       "    .   .   .   .   .   .   .  --      1660
+</pre>
+    <p>
+      Catani has published the following determinations of the temperature
+      yielded by acetylene when burnt with cold and hot air and also with
+      oxygen:
+    </p>
+<pre xml:space="preserve">
+Acetylene and cold air .   .   .   .   .   . 2568� C.
+   "          air at 500� C    .   .   .   . 2780� C.
+   "          air at 1000� C   .   .   .   . 3000� C.
+   "          oxygen   .   .   .   .   .   . 4160� C.
+</pre>
+    <p>
+      EXPLOSIVE LIMITS.--The range of explosibility of mixtures of acetylene and
+      air has been determined by various observers. Eitner's figures for the
+      lower and upper explosive limits, when the mixture, at 62.6� F., is in a
+      tube 19 mm. in diameter, and contains 1.9 per cent. of aqueous vapour, are
+      3.35 and 52.3 per cent. of acetylene (<i>cf.</i> Chapter X.). In this case
+      the mixture was fired by electric spark. In wider vessels, the upper
+      explosive limit, when the mixture was fired by a Bunsen flame, was found
+      to be as high as 75 per cent. of acetylene. Eitner also found that when 13
+      of the 21 volumes of oxygen in air are displaced by carbon dioxide, a
+      mixture of such "carbon dioxide air" with acetylene is inexplosive in all
+      proportions. Also that when carbon dioxide is added to a mixture of
+      acetylene and air, an explosion no longer occurs when the carbon dioxide
+      amounts to 46 volumes or more to every 54 volumes of air, whatever may be
+      the proportion of acetylene in the mixture. [Footnote: According to Caro,
+      if acetylene is added to a mixture composed of 55 per cent. by volume of
+      air and 45 per cent. of carbon dioxide, the whole is only explosive when
+      the proportion of acetylene lies between 5.0 and 5.8 per cent. Caro has
+      also quoted the effect of various inflammable vapours upon the explosive
+      limits of acetylene, his results being referred to in Chapter X.] These
+      figures are valuable in connexion with the prevention of the formation of
+      explosive mixtures of air and acetylene when new mains or plant are being
+      brought into operation (<i>cf.</i> Chapter VII.). Eitner has also shown,
+      by direct investigation on mixtures of other combustible gases and air,
+      that the range of explosibility is greatly reduced by increase in the
+      proportion of aqueous vapour present. As the proportion of aqueous vapour
+      in gas standing over water increases with the temperature the range of
+      explosibility of mixtures of a combustible gas and air is naturally and
+      automatically reduced when the temperature rises, provided the mixture is
+      in contact with water. Thus at 17.0� C., mixtures of hydrogen, air, and
+      aqueous vapour containing from 9.3 to 65.0 per cent, of hydrogen are
+      explosive, whereas at 78.1� C., provided the mixture is saturated with
+      aqueous vapour, explosion occurs only when the percentage of hydrogen in
+      the mixture is between 11.2 and 21.9. The range of explosibility of
+      mixtures of acetylene and air is similarly reduced by the addition of
+      aqueous vapour (though the exact figures have not been experimentally
+      ascertained); and hence it follows that when the temperature in an
+      acetylene generator in which water is in excess, or in a gasholder, rises,
+      the risk of explosion, if air is mixed with the gas, is automatically
+      reduced with the rise in temperature by reason of the higher proportion of
+      aqueous vapour which the gas will retain at the higher temperature. This
+      fact is alluded to in Chapter II. Acetone vapour also acts similarly in
+      lowering the upper explosive limit of acetylene (<i>cf.</i> Chapter XI.).
+    </p>
+    <p>
+      It may perhaps be well to indicate briefly the practical significance of
+      the range of explosibility of a mixture of air and a combustible gas, such
+      as acetylene. The lower explosive limit is the lowest percentage of
+      combustible gas in the mixture of it and air at which explosion will occur
+      in the mixture if a light or spark is applied to it. If the combustible
+      gas is present in the mixture with air in less than that percentage
+      explosion is impossible. The upper explosive limit is the highest
+      percentage of combustible gas in the mixture of it and air at which
+      explosion will occur in the mixture if a light or spark is applied to it.
+      If the combustible gas is present in the mixture with air in more than
+      that percentage explosion is impossible. Mixtures, however, in which the
+      percentage of combustible gas lies between these two limits will explode
+      when a light or spark is applied to them; and the comprehensive term
+      "range of explosibility" is used to cover all lying between the two
+      explosive limits. If, then, a naked light is applied to a vessel
+      containing a mixture of a combustible gas and air, in which mixture the
+      proportion of combustible gas is below the lower limit of explosibility,
+      the gas will not take fire, but the light will continue to burn, deriving
+      its necessary oxygen from the excess of air present. On the other hand, if
+      a light is applied to a vessel containing a mixture of a combustible gas
+      and air, in which mixture the proportion of combustible gas is above the
+      upper limit of explosibility, the light will be extinguished, and within
+      the vessel the gaseous mixture will not burn; but it may burn at the open
+      mouth of the vessel as it comes in contact with the surrounding air, until
+      by diffusion, &amp;c., sufficient air has entered the vessel to form, with
+      the remaining gas, a mixture lying within the explosive limits, when an
+      explosion will occur. Again, if a gaseous mixture containing less of its
+      combustible constituent than is necessary to attain the lower explosive
+      limit escapes from an open-ended pipe and a light is applied to it, the
+      mixture will not burn as a useful compact flame (if, indeed, it fires at
+      all); if the mixture contains more of its combustible constituent than is
+      required to attain the upper explosive limit, that mixture will burn
+      quietly at the mouth of the pipe and will be free from any tendency to
+      fire back into the pipe--assuming, of course, that the gaseous mixture
+      within the pipe is constantly travelling towards the open end. If,
+      however, a gaseous mixture containing a proportion of its combustible
+      constituent which lies between the lower and the upper explosive limit of
+      that constituent escapes from an open- ended pipe and a light is applied,
+      the mixture will fire and the flame will pass back into the pipe, there to
+      produce an explosion, unless the orifice of the said pipe is so small as
+      to prevent the explosive wave passing (as is the case with a proper
+      acetylene burner), or unless the pipe itself is so narrow as appreciably
+      to alter the range of explosibility by lowering the upper explosive limit
+      from its normal value.
+    </p>
+    <p>
+      By far the most potent factor in altering the range of explosibility of
+      any gas when mixed with air is the diameter of the vessel containing or
+      delivering such mixture. Le Chatelier has investigated this point in the
+      case of acetylene, and his values are reproduced overleaf; they are
+      comparable among themselves, although it will be observed that his
+      absolute results differ somewhat from those obtained by Eitner which are
+      quoted later:
+    </p>
+    <p>
+      <i>Explosive Limits of Acetylene mixed with Air.</i>--(Le Chatelier.)
+    </p>
+<pre xml:space="preserve">
+ ___________________________________________________________
+|                  |                       |                |
+|                  |    Explosive Limits.  |                |
+| Diameter of Tube |_______________________|    Range of    |
+| in Millimetres.  |           |           | Explosibility. |
+|                  |   Lower.  |   Upper.  |                |
+|__________________|___________|___________|________________|
+|                  |           |           |                |
+|                  | Per Cent. | Per Cent. |   Per Cent.    |
+|       40         |    2.9    |    64     |     61.1       |
+|       30         |    3.1    |    62     |     58.9       |
+|       20         |    3.5    |    55     |     51.5       |
+|        6         |    4.0    |    40     |     36.0       |
+|        4         |    4.5    |    25     |     20.5       |
+|        2         |    5.0    |    15     |     10.0       |
+|        0.8       |    7.7    |    10     |      2.3       |
+|        0.5       |    ...    |    ...    |      ...       |
+|__________________|___________|___________|________________|
+</pre>
+    <p>
+      Thus it appears that past an orifice or constriction 0.5 mm. in diameter
+      no explosion of acetylene can proceed, whatever may be the proportions
+      between the gas and the air in the mixture present.
+    </p>
+    <p>
+      With every gas the explosive limits and the range of explosibility are
+      also influenced by various circumstances, such as the manner of ignition,
+      the pressure, and other minor conditions; but the following figures for
+      mixtures of air and different combustible gases were obtained by Eitner
+      under similar conditions, and are therefore strictly comparable one with
+      another. The conditions were that the mixture was contained in a tube 19
+      mm. (3/4-inch) wide, was at about 60� to 65� F., was saturated with
+      aqueous vapour, and was fired by electric spark.
+    </p>
+    <p>
+      <i>Table giving the Percentage by volume of Combustible Gas in a Mixture
+      of that Gas and Air corresponding with the Explosive Limits of such a
+      Mixture.</i>--(Eitner.)
+    </p>
+<pre xml:space="preserve">
+ ____________________________________________________________________
+|                  |           |           |                         |
+| Description of   |   Lower   |   Upper   | Difference between the  |
+| Combustible Gas. | Explosive | Explosive | Lower and Upper Limits, |
+|                  |   Limit.  |  Limit.   |    showing the range    |
+|                  |           |           |     covered by the      |
+|                  |           |           |   Explosive Mixtures.   |
+|__________________|___________|___________|_________________________|
+|                  |           |           |                         |
+|                  | Per Cent. | Per Cent. |        Per Cent.        |
+| Carbon monoxide  |  16.50    |  74.95    |         58.45           |
+| Hydrogen         |   9.45    |  66.40    |         57.95           |
+| Water-gas        |           |           |                         |
+|  (uncarburetted) |  12.40    |  66.75    |         54.35           |
+| ACETYLENE        |   3.35    |  52.30    |         48.95           |
+| Coal-gas         |   7.90    |  19.10    |         11.20           |
+| Ethylene         |   4.10    |  14.60    |         10.50           |
+| Methane          |   6.10    |  12.80    |          6.70           |
+| Benzene (vapour) |   2.65    |   6.50    |          3.85           |
+| Pentane   "      |   2.40    |   4.90    |          2.50           |
+| Benzoline "      |   2.40    |   4.90    |          2.50           |
+|__________________|___________|___________|_________________________|
+</pre>
+    <p>
+      These figures are of great practical significance. They indicate that a
+      mixture of acetylene and air becomes explosive (<i>i.e.</i>, will explode
+      if a light is applied to it) when only 3.35 per cent. of the mixture is
+      acetylene, while a similar mixture of coal-gas and air is not explosive
+      until the coal-gas reaches 7.9 per cent. of the mixture. And again, air
+      may be added to coal-gas, and it does not become explosive until the
+      coal-gas is reduced to 19.1 per cent. of the mixture, while, on the
+      contrary, if air is added to acetylene, the mixture becomes explosive as
+      soon as the acetylene has fallen to 52.3 per cent. Hence the immense
+      importance of taking precautions to avoid, on the one hand, the escape of
+      acetylene into the air of a room, and, on the other hand, the admixture of
+      air with the acetylene in any vessel containing it or any pipe through
+      which it passes. These precautions are far more essential with acetylene
+      than with coal-gas. The table shows further how great is the danger of
+      explosion if benzene, benzoline, or other similar highly volatile
+      hydrocarbons [Footnote: The nomenclature of the different volatile spirits
+      is apt to be very confusing. "Benzene" is the proper name for the most
+      volatile hydrocarbon derived from coal-tar, whose formula is C_6H_6.
+      Commercially, benzene is often known as "benzol" or "benzole"; but it
+      would be generally advantageous if those latter words were only used to
+      mean imperfectly rectified benzene, <i>i.e.</i>, mixtures of benzene with
+      toluene, &amp;c., such as are more explicitly understood by the terms
+      "90.s benzol" and "50.s benzol." "Gasoline," "carburine," "petroleum
+      ether," "benzine," "benzoline," "petrol," and "petroleum spirit" all refer
+      to more or less volatile (the most volatile being mentioned first) and
+      more or less thoroughly rectified products obtained from petroleum. They
+      are mixtures of different hydrocarbons, the greater part of them having
+      the general chemical formula C_nH_2n+2 where n = 5 or more. None of them
+      is a definite chemical compound as is benzene; when n = 5 only the product
+      is pentane. These hydrocarbons are known to chemists as "paraffins,"
+      "naphthenes" being occasionally met with; while a certain proportion of
+      unsaturated hydrocarbons is also present in most petroleum spirits. The
+      hydrocarbons of coal-tar are "aromatic hydrocarbons," their generic
+      formula being C_nH_2^n-6, where n is never less than 6.] are allowed to
+      vaporise in a room in which a light may be introduced. Less of the vapour
+      of these hydrocarbons than of acetylene in the air of a room brings the
+      mixture to the lower explosive limit, and therewith subjects it to the
+      risk of explosion. This tact militates strongly against the use of such
+      hydrocarbons within a house, or against the use of air-gas, which, as
+      explained in Chapter I., is air more or less saturated with the vapour of
+      volatile hydrocarbons. Conversely, a combustible gas, such as acetylene,
+      may be safely "carburetted" by these hydrocarbons in a properly
+      constructed apparatus set up outside the dwelling-house, as explained in
+      Chapter X., because there would be no air (as in air-gas) in the pipes,
+      &amp;c., and a relatively large escape of carburetted acetylene would be
+      required to produce an explosive atmosphere in a room. Moreover, the odour
+      of the acetylene itself would render the detection of a leak far easier
+      with carburetted acetylene than with air-gas.
+    </p>
+    <p>
+      N. Teclu has investigated the explosive limits of mixtures of air with
+      certain combustible gases somewhat in the same manner as Eitner, viz.: by
+      firing the mixture in an eudiometer tube by means of an electric spark. He
+      worked, however, with the mixture dry instead of saturated with aqueous
+      vapour, which doubtless helps to account for the difference between his
+      and Eitner's results.
+    </p>
+    <p>
+      <i>Table giving the Percentages by volume of Combustible Gas in a
+      Dehydrated Mixture of that Gas and Air between which the Explosive Limits
+      of such a Mixture lie.</i>--(Teclu).
+    </p>
+<pre xml:space="preserve">
+ ____________________________________________________________________
+|                  |                        |                        |
+|                  | Lower Explosive Limit. | Upper Explosive Limit. |
+| Description of   |________________________|________________________|
+| Combustible Gas. |                        |                        |
+|                  |    Per Cent. of Gas.   |   Per Cent. of Gas.    |
+|__________________|________________________|________________________|
+|                  |                        |                        |
+| ACETYLENE        |       1.53-1.77        |      57.95-58.65       |
+| Hydrogen         |       9.73-9.96        |      62.75-63.58       |
+| Coal-gas         |       4.36-4.82        |      23.35-23.63       |
+| Methane          |       3.20-3.67        |       7.46- 7.88       |
+|__________________|________________________|________________________|
+</pre>
+    <p>
+      Experiments have been made at Lechbruch in Bavaria to ascertain directly
+      the smallest proportion of acetylene which renders the air of a room
+      explosive. Ignition was effected by the flame resulting when a pad of
+      cotton-wool impregnated with benzoline or potassium chlorate was fired by
+      an electrically heated wire. The room in which most of the tests were made
+      was 8 ft. 10 in. long, 6 ft. 7 in. wide, and 6 ft. 8 in. high, and had two
+      windows. When acetylene was generated in this room in normal conditions of
+      natural ventilation through the walls, the volume generated could amount
+      to 3 per cent. of the air-space of the room without explosion ensuing on
+      ignition of the wool, provided time elapsed for equable diffusion, which,
+      moreover, was rapidly attained. Further, it was found that when the whole
+      of the acetylene which 2 kilogrammes or 4.4 lb. of carbide (the maximum
+      permissible charge in many countries for a portable lamp for indoor use)
+      will yield was liberated in a room, a destructive explosion could not
+      ensue on ignition provided the air-space exceeded 40 cubic metres or 1410
+      cubic feet, or, if the evolved gas were uniformly diffused, 24 cubic
+      metres or 850 cubic feet. When the walls of the room were rendered
+      impervious to air and gas, and acetylene was liberated, and allowed time
+      for diffusion, in the air of the room, an explosion was observed with a
+      proportion of only 2-1/2 per cent. of acetylene in the air.
+    </p>
+    <p>
+      <i>Solubility of Acetylene in Various Liquids.</i>
+    </p>
+<pre xml:space="preserve">
+ _____________________________________________________________________
+|                           |         |            |                  |
+|                           |         | Volumes of |                  |
+|                           |  Tem-   | Acetylene  |                  |
+|       Solvent.            |perature.|dissolved by|   Authority.     |
+|                           |         |  100 Vols. |                  |
+|                           |         | of Solvent.|                  |
+|___________________________|_________|____________|__________________|
+|                           |         |            |                  |
+|                           | Degs. C |            |                  |
+| Acetone  .    .    .    . |   15    |   2500     | Claude and Hess  |
+|    "     .    .    .    . |   50    |   1250     |    "             |
+| Acetic acid; alcohol    . |   18    |    600     | Berthelot        |
+| Benzoline; chloroform   . |   18    |    400     |    "             |
+| Paraffin oil  .    .    . |    0    |    103.3   | E. Muller        |
+|    "          .    .    . |   18    |    150     | Berthelot        |
+| Olive oil .   .    .    . |   --    |     48     | Fuchs and Schiff |
+| Carbon bisulphide  .    . |   18    |    100     | Berthelot        |
+|    "   tetrachloride    . |    0    |     25     | Nieuwland        |
+| Water (at 4 65 atmospheres|         |            |                  |
+|         pressure)  .    . |    0    |    160     | Villard          |
+|    " (at 755 mm. pressure)|   12    |    118     | Berthelot        |
+|    " (760 mm. pressure) . |   12    |    106.6   | E. M�ller        |
+|    "         "          . |   15    |    110     | Lewes            |
+|    "         "          . |   18    |    100     | Berthelot        |
+|    "         "          . |   --    |    100     | E. Davy (in 1836)|
+|    "         "          . |   19.5  |     97.5   | E. M�ller        |
+| Milk of lime: about 10    |         |            |                  |
+|   grammes of calcium hy-  |    5    |    112     | Hammerschmidt    |
+|   droxide per 100 c.c.  . |         |            |  and Sandmann    |
+|   "        "        "     |   10    |     95     |        "         |
+|   "        "        "     |   20    |     75     |        "         |
+|   "        "        "     |   50    |     38     |        "         |
+|   "        "        "     |   70    |     20     |        "         |
+|   "        "        "     |   90    |      6     |        "         |
+| Solution of common salt,5%|   19    |     67.9   |        "         |
+|   (sodium chloride)     " |   25    |     47.7   |        "         |
+|       "                20%|   19    |     29.6   |        "         |
+|       "                 " |   25    |     12.6   |        "         |
+|       "(nearly saturated, |         |            |                  |
+|            26%)    .    . |   15    |     20.6   |        "         |
+|       "(saturated, sp. gr.|         |            |                  |
+|           1-21)    .    . |    0    |     22.0   | E. M�ller        |
+|       "       "        "  |   12    |     21.0   |    "             |
+|       "       "        "  |   18    |     20.4   |    "             |
+| Solution of calcium       |         |            | Hammerschmidt    |
+| chloride (saturated)    . |   15    |      6.0   |  and Sandmann    |
+| Berg� and Reychler's re-  |         |            |                  |
+|   agent   .   .    .    . |   --    |     95     | Nieuwland        |
+|___________________________|_________|____________|__________________|
+</pre>
+    <p>
+      SOLUBILITY.--Acetylene is readily soluble in many liquids. It is
+      desirable, on the one hand, as indicated in Chapter III., that the liquid
+      in the seals of gasholders, &amp;c., should be one in which acetylene is
+      soluble to the smallest degree practically attainable; while, on the other
+      hand, liquids in which acetylene is soluble in a very high degree are
+      valuable agents for its storage in the liquid state. Hence it is important
+      to know the extent of the solubility of acetylene in a number of liquids.
+      The tabular statement (p. 179) gives the most trustworthy information in
+      regard to the solubilities under the normal atmospheric pressure of 760
+      mm. or thereabouts.
+    </p>
+    <p>
+      The strength of milk of lime quoted in the above table was obtained by
+      carefully allowing 50 grammes of carbide to interact with 550 c.c. of
+      water at 5� C. A higher degree of concentration of the milk of lime was
+      found by Hammerschmidt and Sandmann to cause a slight decrease in the
+      amount of acetylene held in solution by it. Hammerschmidt and Sandmann's
+      figures, however, do not agree well with others obtained by Caro, who has
+      also determined the solubility of acetylene in lime-water, using first, a
+      clear saturated lime-water prepared at 20� C. and secondly, a milk of lime
+      obtained by slaking 10 grammes of quicklime in 100 c.c. of water. As
+      before, the figures relate to the volumes of acetylene dissolved at
+      atmospheric pressure by 100 volumes of the stated liquid.
+    </p>
+<pre xml:space="preserve">
+ _________________________________________________
+|               |               |                 |
+|  Temperature. |  Lime-water.  |  Milk of Lime.  |
+|_______________|_______________|_________________|
+|               |               |                 |
+|    Degs C.    |               |                 |
+|       0       |    146.2      |     152.6       |
+|       5       |    138.5      |       --        |
+|      15       |    122.8      |     134.8       |
+|      50       |     43.9      |      62.6       |
+|      90       |      6.2      |       9.2       |
+|_______________|_______________|_________________|
+</pre>
+    <p>
+      Figures showing the solubility of acetylene in plain water at different
+      temperatures have been published in Landolt-B�rnstein's Physico- Chemical
+      Tables. These are reproduced below. The "Coefficient of Absorption" is the
+      volume of the gas, measured at 0� C. and a barometric height of 760 mm.
+      taken up by one volume of water, at the stated temperature, when the gas
+      pressure on the surface, apart from the vapour pressure of the water
+      itself, is 760 mm. The "Solubility" is the weight of acetylene in grammes
+      taken up by 100 grammes of water at the stated temperature, when the total
+      pressure on the surface, including that of the vapour pressure of the
+      water, is 760 mm.
+    </p>
+<pre xml:space="preserve">
+ _____________________________________________
+|              |                |             |
+| Temperature. | Coefficient of | Solubility. |
+|              |   Absorption.  |             |
+|______________|________________|_____________|
+|              |                |             |
+|   Degs. C.   |                |             |
+|      0       |      1.73      |    0.20     |
+|      1       |      1.68      |    0.19     |
+|      2       |      1.63      |    0.19     |
+|      3       |      1.58      |    0.18     |
+|      4       |      1.53      |    0.18     |
+|      5       |      1.49      |    0.17     |
+|      6       |      1.45      |    0.17     |
+|      7       |      1.41      |    0.16     |
+|      8       |      1.37      |    0.16     |
+|      9       |      1.34      |    0.15     |
+|     10       |      1.31      |    0.15     |
+|     11       |      1.27      |    0.15     |
+|     12       |      1.24      |    0.14     |
+|     13       |      1.21      |    0.14     |
+|     14       |      1.18      |    0.14     |
+|     15       |      1.15      |    0.13     |
+|     16       |      1.13      |    0.13     |
+|     17       |      1.10      |    0.13     |
+|     18       |      1.08      |    0.12     |
+|     19       |      1.05      |    0.12     |
+|     20       |      1.03      |    0.12     |
+|     21       |      1.01      |    0.12     |
+|     22       |      0.99      |    0.11     |
+|     23       |      0.97      |    0.11     |
+|     24       |      0.95      |    0.11     |
+|     25       |      0.93      |    0.11     |
+|     26       |      0.91      |    0.10     |
+|     27       |      0.89      |    0.10     |
+|     28       |      0.87      |    0.10     |
+|     29       |      0.85      |    0.10     |
+|     30       |      0.84      |    0.09     |
+|______________|________________|_____________|
+</pre>
+    <p>
+      Advantage is taken, as explained in Chapter XI., of the high degree of
+      solubility of acetylene in acetone, to employ a solution of the gas in
+      that liquid when acetylene is wanted in a portable condition. The
+      solubility increases very rapidly with the pressure, so that under a
+      pressure of twelve atmospheres acetone dissolves about 300 times its
+      original volume of the gas, while the solubility also increases greatly
+      with a reduction in the temperature, until at -80� C. acetone takes up
+      2000 times its volume of acetylene under the ordinary atmospheric
+      pressure. Further details of the valuable qualities of acetone as a
+      solvent of acetylene are given in Chapter XI., but it may here be remarked
+      that the successful utilisation of the solvent power of acetone depends to
+      a very large extent on the absolute freedom from moisture of both the
+      acetylene and the acetone, so that acetone of 99 per cent. strength is now
+      used as the solvent.
+    </p>
+    <p>
+      Turning to the other end of the scale of solubility, the most valuable
+      liquids for serving as seals of gasholders, &amp;c., are readily
+      discernible. Far superior to all others is a saturated solution of calcium
+      chloride, and this should be selected as the confining liquid whenever it
+      is important to avoid dissolution of acetylene in the liquid as far as may
+      be. Brine comes next in order of merit for this purpose, but it is
+      objectionable on account of its corrosive action on metals. Olive oil
+      should, according to Fuchs and Schiff, be of service where a saline liquid
+      is undesirable; mineral oil seems useless. Were they concordant, the
+      figures for milk of lime would be particularly useful, because this
+      material is naturally the confining liquid in the generating chambers of
+      carbide-to-water apparatus, and because the temperature of the liquid
+      rises through the heat evolved during the generation of the gas (<i>vide</i>
+      Chapters II. and III.). It will be seen that these figures would afford a
+      means of calculating the maximum possible loss of gas by dissolution when
+      a known volume of sludge is run off from a carbide-to- water generator at
+      about any possible temperature.
+    </p>
+    <p>
+      According to Garelli and Falciola, the depression in the freezing-point of
+      water caused by the saturation of that liquid with acetylene is 0.08� C.,
+      the corresponding figure for benzene in place of water being 1.40� C.
+      These figures indicate that 100 parts by weight of water should dissolve
+      0.1118 part by weight of acetylene at 0� C., and that 100 parts of benzene
+      should dissolve about 0.687 part of acetylene at 5� C. In other words, 100
+      volumes of water at the freezing-point should dissolve 95 volumes of
+      acetylene, and 100 volumes of benzene dissolve some 653 volumes of the
+      gas. The figure calculated for water in this way is lower than that which
+      might be expected from the direct determinations at other temperatures
+      already referred to; that for benzene may be compared with Berthelot's
+      value of 400 volumes at 18� C. Other measurements of the solubility of
+      acetylene in water at 0� C. have given the figure 0.1162 per cent. by
+      weight.
+    </p>
+    <p>
+      TOXICITY.--Many experiments have been made to determine to what extent
+      acetylene exercises a toxic action on animals breathing air containing a
+      large proportion of it; but they have given somewhat inconclusive results,
+      owing probably to varying proportions of impurities in the samples of
+      acetylene used. The sulphuretted hydrogen and phosphine which are found in
+      acetylene as ordinarily prepared are such powerful toxic agents that they
+      would always, in cases of "acetylene" poisoning, be largely instrumental
+      in bringing about the effects observed. Acetylene <i>per se</i> would
+      appear to have but a small toxic action; for the principal toxic
+      ingredient in coal-gas is carbon monoxide, which does not occur in
+      sensible quantity in acetylene as obtained from calcium carbide. The
+      colour of blood is changed by inhalation of acetylene to a bright
+      cherry-red, just as in cases of poisoning by carbon monoxide; but this is
+      due to a more dissolution of the gas in the haemoglobin of the blood, so
+      that there is much more hope of recovery for a subject of acetylene
+      poisoning than for one of coal-gas poisoning. Practically the risk of
+      poisoning by acetylene, after it has been purified by one of the ordinary
+      means, is <i>nil</i>. The toxic action of the impurities of crude
+      acetylene is discussed in Chapter V.
+    </p>
+    <p>
+      Acetylene is an "endothermic" compound, as has been mentioned in Chapter
+      II., where the meaning of the expression endothermic is explained. It has
+      there been indicated that by reason of its endothermic nature it is unsafe
+      to have acetylene at either a temperature of 780� C. and upwards, or at a
+      pressure of two atmospheres absolute, or higher. If that temperature or
+      that pressure is exceeded, dissociation (<i>i.e.</i>, decomposition into
+      its elements), if initiated at any spot, will extend through the whole
+      mass of acetylene. In this sense, acetylene at or above 780� C., or at two
+      or more atmospheres pressure, is explosive in the absence of air or
+      oxygen, and it is thereby distinguished from the majority of other
+      combustible gases, such as the components of coal-gas. But if, by dilution
+      with another gas, the partial pressure of the acetylene is reduced, then
+      the mixture may be subjected to a higher pressure than that of two
+      atmospheres without acquiring explosiveness, as is fully shown in Chapter
+      XI. Thus it becomes possible safely to compress mixtures of acetylene and
+      oil-gas or coal-gas, whereas unadmixed acetylene cannot be safely kept
+      under a pressure of two atmospheres absolute or more. In a series of
+      experiments carried out by Dupr� on behalf of the British Home Office, and
+      described in the Report on Explosives for 1897, samples of moist
+      acetylene, free from air, but apparently not purified by any chemical
+      process, were exposed to the influence of a bright red-hot wire. When the
+      gas was held in the containing vessel at the atmospheric pressure then
+      obtaining, viz., 30.34 inches (771 mm.) of mercury, no explosion occurred.
+      When the pressure was raised to 45.34 inches (1150 mm.), no explosion
+      occurred; but when the pressure was further raised to 59.34 inches (1505
+      mm., or very nearly two atmospheres absolute) the acetylene exploded, or
+      dissociated into its elements.
+    </p>
+    <p>
+      Acetylene readily polymerises when heated, as has been stated in Chapter
+      II., where the meaning of the term "polymerisation" has been explained.
+      The effects of the products of the polymerisation of acetylene on the
+      flame produced when the gas is burnt at the ordinary acetylene burners
+      have been stated in Chapter VIII., where the reasons therefor have been
+      indicated. The chief primary product of the polymerisation of acetylene by
+      heat appears to be benzene. But there are also produced, in some cases by
+      secondary changes, ethylene, methane, naphthalene, styrolene, anthracene,
+      and homologues of several of these hydrocarbons, while carbon and hydrogen
+      are separated. The production of these bodies by the action of heat on
+      acetylene is attended by a reduction of the illuminative value of the gas,
+      while owing to the change in the proportion of air required for combustion
+      (<i>see</i> Chapter VIII.), the burners devised for the consumption of
+      acetylene fail to consume properly the mixture of gases formed by
+      polymerisation from the acetylene. It is difficult to compare the
+      illuminative value of the several bodies, as they cannot all be consumed
+      economically without admixture, but the following table indicates
+      approximately the <i>maximum</i> illuminative value obtainable from them
+      either by combustion alone or in admixture with some non- illuminating or
+      feebly-illuminating gas:
+    </p>
+<pre xml:space="preserve">
+ ________________________________________________
+|              |                   |             |
+|              |                   | Candles per |
+|              |                   | Cubic Foot  |
+|______________|___________________|_____________|
+|              |                   |             |
+|              |                   |    (say)    |
+| Acetylene    |  C_2H_2           |      50     |
+| Hydrogen     |  H_2              |       0     |
+| Methane      |  CH_4             |       1     |
+| Ethane       |  C_2H_6           |       7     |
+| Propane      |  C_3H_8           |      11     |
+| Pentane      |  C_5H_12 (vapour) |      35     |
+| Hexane       |  C_6H_14     "    |      45     |
+| Ethylene     |  C_2H_4           |      20     |
+| Propylene    |  C_3H_6           |      25     |
+| Benzene      |  C_6H_6  (vapour) |     200     |
+| Toluene      |  C_7H_8      "    |     250     |
+| Naphthalene  |  C_10H_8     "    |     400     |
+|______________|___________________|_____________|
+</pre>
+    <p>
+      It appears from this table that, with the exception of the three
+      hydrocarbons last named, no substance likely to be formed by the action of
+      heat on acetylene has nearly so high an illuminative value--volume for
+      volume--as acetylene itself. The richly illuminating vapours of benzene
+      and naphthalene (and homologues) cannot practically add to the
+      illuminative value of acetylene, because of the difficulty of consuming
+      them without smoke, unless they are diluted with a large proportion of
+      feebly- or non-illuminating gas, such as methane or hydrogen. The
+      practical effect of carburetting acetylene with hydrocarbon vapours will
+      be shown in Chapter X. to be disastrous so far as the illuminating
+      efficiency of the gas is concerned. Hence it appears that no conceivable
+      products of the polymerisation of acetylene by heat can result in its
+      illuminative value being improved--even presupposing that the burners
+      could consume the polymers properly--while practically a considerable
+      deterioration of its value must ensue.
+    </p>
+    <p>
+      The heat of combustion of acetylene was found by J. Thomson to be 310.57
+      large calories per gramme-molecule, and by Berthelot to be 321.00
+      calories. The latest determination, however, made by Berthelot and
+      Matignon shows it to be 315.7 calories at constant pressure. Taking the
+      heat of formation of carbon dioxide from diamond carbon at constant
+      pressure as 94.3 calories (Berthelot and Matignon), which is equal to 97.3
+      calories from amorphous carbon, and the heat of formation of liquid water
+      as 69 calories; this value for the heat of combustion of acetylene makes
+      its heat of formation to be 94.3 x 2 + 69 - 315.7 = -58.1 large calories
+      per gramme-molecule (26 grammes) from diamond carbon, or -52.1 from
+      amorphous carbon. It will be noticed that the heat of combustion of
+      acetylene is greater than the combined heats of combustion of its
+      constituents; which proves that heat has been absorbed in the union of the
+      hydrogen and carbon in the molecule, or that acetylene is endothermic, as
+      elsewhere explained. These calculations, and others given in Chapter IX.,
+      will perhaps be rendered more intelligible by the following table of
+      thermochemical phenomena:
+    </p>
+<pre xml:space="preserve">
+ _______________________________________________________________
+|                                |         |           |        |
+|           Reaction.            | Diamond | Amorphous |        |
+|                                | Carbon. |  Carbon.  |        |
+|________________________________|_________|___________|________|
+|                                |         |           |        |
+| (1) C (solid) + O    .   .   . |  26.1   |   29.1    |   ...  |
+| (2) C (solid) + O_2  .   .   . |  94.3   |   97.3    |   ...  |
+| (3) CO + O (2 - 1)   .   .   . |   ...   |    ...    |  68.2  |
+| (4) Conversion of solid carbon |         |           |        |
+|     into gas (3 - 1) .   .   . |  42.1   |   39.1    |   ...  |
+| (5) C (gas) + O (1 + 4)  .   . |   ...   |    ...    |  68.2  |
+| (6) Conversion of amorphous    |         |           |        |
+|     carbon to diamond    .   . |   ...   |    ...    |   3.0  |
+| (7) C_2 + H_2    .   .   .   . | -58.1   |  -52.1    |   ...  |
+| (8) C_2H_2 + 2-1/2O_2    .   . |   ...   |    ...    | 315.7  |
+|________________________________|_________|___________|________|
+</pre>
+    <p>
+      W. G. Mixter has determined the heat of combustion of acetylene to be
+      312.9 calories at constant volume, and 313.8 at constant pressure. Using
+      Berthelot and Matignon's data given above for amorphous carbon, this
+      represents the heat of formation to be -50.2 (Mixter himself calculates it
+      as -51.4) calories. By causing compressed acetylene to dissociate under
+      the influence of an electric spark, Mixter measured its heat of formation
+      as -53.3 calories. His corresponding heats of combustion of ethylene are
+      344.6 calories (constant volume) and 345.8 (constant pressure); for its
+      heat of formation he deduces a value -7.8, and experimentally found one of
+      about -10.6 (constant pressure).
+    </p>
+    <p>
+      THE ACETYLENE FLAME.--It has been stated in Chapter I. that acetylene
+      burnt in self-luminous burners gives a whiter light than that afforded by
+      any other artificial illuminant, because the proportion of the various
+      spectrum colours in the light most nearly resembles the corresponding
+      proportion found in the direct rays of the sun. Calling the amount of
+      monochromatic light belonging to each of the five main spectrum colours
+      present in the sun's rays unity in succession, and comparing the amount
+      with that present in the light obtained from electricity, coal-gas, and
+      acetylene, M�nsterberg has given the following table for the composition
+      of the several lights mentioned:
+    </p>
+<pre xml:space="preserve">
+ ______________________________________________________________________
+|          |                |                  |               |       |
+|          |  Electricity   |    Coal-Gas      |    Acetylene  |       |
+|          |________________|__________________|_______________|_______|
+|  Colour  |      |         |        |         |       |       |       |
+|   in     |      |         |        |         |       | With  |       |
+| Spectrum.| Arc. | Incan-  | Lumin- | Incan-  | Alone.| 3 per | Sun-  |
+|          |      | descent.|  ous.  | descent.|       | Cent. | light.|
+|          |      |         |        |         |       | Air.  |       |
+|__________|______|_________|________|_________|_______|_______|_______|
+|          |      |         |        |         |       |       |       |
+| Red      | 2.09 |  1.48   |  4.07  |  0.37   | 1.83  | 1.03  |   1   |
+| Yellow   | 1.00 |  1.00   |  1.00  |  0.90   | 1.02  | 1.02  |   1   |
+| Green    | 0.99 |  0.62   |  0.47  |  4.30   | 0.76  | 0.71  |   1   |
+| Blue     | 0.87 |  0.91   |  1.27  |  0.74   | 1.94  | 1.46  |   1   |
+| Violet   | 1.08 |  0.17   |  0.15  |  0.83   | 1.07  | 1.07  |   1   |
+| Ultra-   |      |         |        |         |       |       |       |
+|   Violet | 1.21 |   ...   |   ...  |   ...   |  ...  |  ...  |   1   |
+|__________|______|_________|________|_________|_______|_______|_______|
+</pre>
+    <p>
+      These figures lack something in explicitness; but they indicate the
+      greater uniformity of the acetylene light in its proportion of rays of
+      different wave-lengths. It does not possess the high proportion of green
+      of the Welsbach flame, or the high proportion of red of the luminous gas-
+      flame. It is interesting to note the large amount of blue and violet light
+      in the acetylene flame, for these are the colours which are chiefly
+      concerned in photography; and it is to their prominence that acetylene has
+      been found to be so very actinic. It is also interesting to note that an
+      addition of air to acetylene tends to make the light even more like that
+      of the sun by reducing the proportion of red and blue rays to nearer the
+      normal figure.
+    </p>
+    <p>
+      H. Erdmann has made somewhat similar calculation, comparing the light of
+      acetylene with that of the Hefner (amyl acetate) lamp, and with coal-gas
+      consumed in an Argand and an incandescent burner. Consecutively taking the
+      radiation of the acetylene flame as unity for each of the spectrum
+      colours, his results are:
+    </p>
+<pre xml:space="preserve">
+ __________________________________________________________________
+|           |               |              |                       |
+|           |               |              |    Coal-Gas           |
+| Colour in | Wave-Lengths, |              |_______________________|
+| Spectrum  |      uu       | Hefner Light |        |              |
+|           |               |              | Argand | Incandescent |
+|___________|_______________|______________|________|______________|
+|           |               |              |        |              |
+| Red       |      650      |     1.45     |  1.34  |     1.03     |
+| Orange    |      610      |     1.22     |  1.13  |     1.00     |
+| Yellow    |      590      |     1.00     |  1.00  |     1.00     |
+| Green     |      550      |     0.87     |  0.93  |     0.86     |
+| Blue      |      490      |     0.72     |  1.27  |     0.92     |
+| Violet    |      470      |     0.77     |  1.35  |     1.73     |
+|___________|_______________|______________|________|______________|
+</pre>
+    <p>
+      B. Heise has investigated the light of different flames, including
+      acetylene, by a heterochromatic photometric method; but his results varied
+      greatly according to the pressure at which the acetylene was supplied to
+      the burner and the type of burner used. Petroleum affords light closely
+      resembling in colour the Argand coal-gas flame; and electric glow-lamps,
+      unless overrun and thereby quickly worn out, give very similar light,
+      though with a somewhat greater preponderance of radiation in the red and
+      yellow.
+    </p>
+<pre xml:space="preserve">
+ ____________________________________________________________________
+|                            |                   |                   |
+|                            | Percent of Total  |                   |
+|          Light.            | Energy manifested |     Observer.     |
+|                            |     as Light.     |                   |
+|____________________________|___________________|___________________|
+|                            |                   |                   |
+| Candle, spermaceti   .   . |       2.1         | Thomsen           |
+|   "     paraffin .   .   . |       1.53        | Rogers            |
+| Moderator lamp   .   .   . |       2.6         | Thomsen           |
+| Coal-gas .   .   .   .   . |       1.97        | Thomsen           |
+|    "     .   .   .   .   . |       2.40        | Langley           |
+|    "   batswing  .   .   . |       1.28        | Rogers            |
+|    "   Argand    .   .   . |       1.61        | Rogers            |
+|    "   incandesce    .   . |      2 to 7       | Stebbins          |
+| Electric glow-lamp   .   . |     about 6       | Merritt           |
+|    "        "        .   . |       5.5         | Abney and Festing |
+| Lime light (new) .   .   . |      14           | Orehore           |
+|    "       (old) .   .   . |       8.4         | Orehore           |
+| Electric arc .   .   .   . |      10.4         | Tyndall; Nakano   |
+|    "         .   .   .   . |     8 to 13       | Marks             |
+| Magnesium light  .   .   . |      12.5         | Rogers            |
+| Acetylene    .   .   .   . |      10.5         | Stewart and Hoxie |
+|    "    (No. 0 slit burner |      11.35        | Neuberg           |
+|    "    (No. 00000   .   . |                   |                   |
+|            Bray fishtail)  |      13.8         | Neuberg           |
+|    "    (No. 3 duplex)   . |      14.7         | Neuberg           |
+| Geissler tube    .   .   . |      32.0         | Staub             |
+|____________________________|___________________|___________________|
+</pre>
+    <p>
+      Violle and F�ry, also Erdmann, have proposed the use of acetylene as a
+      standard of light. As a standard burner F�ry employed a piece of
+      thermometer tube, cut off smoothly at the end and having a diameter of 0.5
+      millimetre, a variation in the diameter up to 10 per cent. being of no
+      consequence. When the height of the flame ranged from 10 to 25 millimetres
+      the burner passed from 2.02 to 4.28 litres per hour, and the illuminating
+      power of the light remained sensibly proportional to the height of the
+      jet, with maximum variations from the calculated value of �0.008. It is
+      clear that for such a purpose as this the acetylene must be prepared from
+      very pure carbide and at the lowest possible temperature in the generator.
+      Further investigations in this direction should be welcome, because it is
+      now fairly easy to obtain a carbide of standard quality and to purify the
+      gas until it is essentially pure acetylene from a chemical point of view.
+    </p>
+    <p>
+      L. W. Hartmann has studied the flame of a mixture of acetylene with
+      hydrogen. He finds that the flame of the mixture is richer in light of
+      short wave-lengths than that of pure acetylene, but that the colour of the
+      light does not appear to vary with the proportion of hydrogen present.
+    </p>
+    <p>
+      Numerous investigators have studied the optical or radiant efficiency of
+      artificial lights, <i>i.e.</i>, the proportion of the total heat plus
+      light energy emitted by the flame which is produced in the form of visible
+      light. Some results are shown in the table on the previous page.
+    </p>
+    <p>
+      Figures showing the ratio of the visible light emitted by various
+      illuminants to the amount of energy expended in producing the light and
+      also the energy equivalent of each spherical Hefner unit evolved have been
+      published by H. Lux, whose results follow:
+    </p>
+<pre xml:space="preserve">
+ _______________________________________________________________________
+|                    |            |            |            |           |
+|                    |  Ratio of  |  Ratio of  |   Mean     |  Energy   |
+|                    |   Light    |   Light    | Spherical  |  Equiva-  |
+|       Light.       | emitted to | emitted to | Illuminat- | lent to 1 |
+|                    |    Total   |   Energy   | ing Power. | Spherical |
+|                    | Radiation. | Impressed. |  Hefners.  | Hefner in |
+|                    |            |            |            |   Watts.  |
+|____________________|____________|____________|____________|___________|
+|                    |            |            |            |           |
+|                    |  Per Cent. |  Per Cent. |            |           |
+| Hefner lamp        |    0.89    |    0.103   |     0.825  |   0.108   |
+| Paraffin lamp, 14" |    1.23    |    0.25    |    12.0    |   0.105   |
+| ACETYLENE, 7.2     |            |            |            |           |
+|     litre burner   |    6.36    |    0.65    |     6.04   |   0.103   |
+| Coal-gas incandes- |            |            |            |           |
+|     cent, upturned | 2.26-2.92  |    0.46    |    89.6    |   0.037   |
+|  "       incandes- |            |            |            |           |
+|     cent, inverted | 2.03-2.97  |    0.51    |    82.3    |   0.035   |
+| Carbon filament    |            |            |            |           |
+|     glow-lamp      |  3.2-2.7   |    2.07    |    24.5    |   0.085   |
+| Nernst lamp        |    5.7     | 4.21-3.85  |    91.9    |   0.073   |
+| Tantalum lamp      |    8.5     |    4.87    |    26.7    |   0.080   |
+| Osram lamp         |    9.1     |    5.36    |    27.4    |   0.075   |
+| Direct-current arc |    8.1     |    5.60    |   524      |   0.047   |
+|   "    "  enclosed |    2.0     |    1.16    |   295      |   0.021   |
+| Flame arc, yellow  |   15.7     |   13.20    |  1145      |   0.041   |
+|   "    "   white   |    7.6     |    6.66    |   760      |   0.031   |
+| Alternating-       |            |            |            |           |
+|     current arc    |    3.7     |    1.90    |    89      |   0.038   |
+| Uviol mercury      |            |            |            |           |
+|     vapour lamp    |    5.8     |    2.24    |   344      |   0.015   |
+| Quartz lamp        |   17.6     |    6.00    |  2960      |   0.014   |
+|____________________|____________|____________|____________|___________|
+</pre>
+    <p>
+      CHEMICAL PROPERTIES.--It is unnecessary for the purpose of this work to
+      give an exhaustive account of the general chemical reactions of acetylene
+      with other bodies, but a few of the more important must be referred to.
+      Since the gases are liable to unite spontaneously when brought into
+      contact, the reactions between, acetylene and chlorine require attention,
+      first, because of the accidents that have occurred when using bleaching-
+      powder (<i>see</i> Chapter V.) as a purifying material for the crude gas;
+      secondly, because it has been proposed to manufacture one of the products
+      of the combination, viz., acetylene tetrachloride, on a large scale, and
+      to employ it as a detergent in place of carbon tetrachloride or carbon
+      disulphide. Acetylene forms two addition products with chlorine,
+      C_2H_2Cl_2, and C_2H_2Cl_4. These are known as acetylene dichloride and
+      tetrachloride respectively, or more systematically as dichlorethylene and
+      tetrachlorethane. One or both of the chlorides is apt to be produced when
+      acetylene comes into contact with free chlorine, and the reaction
+      sometimes proceeds with explosive violence. The earliest writers, such as
+      E. Davy, W�hler, and Berthelot, stated that an addition of chlorine to
+      acetylene was invariably followed by an explosion, unless the mixture was
+      protected from light; whilst later investigators thought the two gases
+      could be safely mixed if they were both pure, or if air was absent. Owing
+      to the conflicting nature of the statements made, Nieuwland determined in
+      1905 to study the problem afresh; and the annexed account is chiefly based
+      on his experiments, which, however, still fail satisfactorily to elucidate
+      all the phenomena observed. According to Nieuwland's results, the
+      behaviour of mixtures of acetylene and chlorine appears capricious, for
+      sometimes the gases unite quietly, although sometimes they explode.
+      Acetylene and chlorine react quite quietly in the dark and at low
+      temperatures; and neither a moderate increase in temperature, nor the
+      admission of diffused daylight, nor the introduction of small volumes of
+      air, is necessarily followed by an explosion. Doubtless the presence of
+      either light, air, or warmth increases the probability of an explosive
+      reaction, while it becomes more probable still in their joint presence;
+      but in given conditions the reaction may suddenly change from a gentle
+      formation of addition products to a violent formation of substitution
+      products without any warning or manifest cause. When the gases merely
+      unite quietly, tetrachlorethane, or acetylene tetrachloride, is produced
+      thus:
+    </p>
+    <p>
+      C_2H_2 + 2Cl_2 = C_2H_2Cl_4;
+    </p>
+    <p>
+      but when the reaction is violent some hexachlorethane is formed,
+      presumably thus:
+    </p>
+    <p>
+      2C_2H_2 + 5Cl_2 = 4HCl + C_2 + C_2Cl_6.
+    </p>
+    <p>
+      The heat evolved by the decomposition of the acetylene by the formation of
+      the hydrochloric acid in the last equation is then propagated amongst the
+      rest of the gaseous mixture, accelerating the action, and causing the
+      acetylene to react with the chlorine to form more hydrochloric acid and
+      free carbon thus;
+    </p>
+    <p>
+      C_2H_2 + Cl_2 = 2HCl + C_2.
+    </p>
+    <p>
+      It is evident that these results do not altogether explain the mechanism
+      of the reactions involved. Possibly the formation of substitution products
+      and the consequent occurrence of an explosion is brought about by some
+      foreign substance which acts as a catalytic agent. Such substance may
+      conceivably be one of the impurities in crude acetylene, or the solid
+      matter of a bleaching-powder purifying material. The experiments at least
+      indicate the direction in which safety may be sought when bleaching-
+      powder is employed to purify the crude gas, viz., dilution of the powder
+      with an inert material, absence of air from the gas, and avoidance of
+      bright sunlight in the place where a spent purifier is being emptied.
+      Unfortunately Nieuwland did not investigate the action on acetylene of
+      hypochlorites, which are presumably the active ingredients in bleaching-
+      powder. As will appear in due course, processes have been devised and
+      patented to eliminate all danger from the reaction between acetylene and
+      chlorine for the purpose of making tetrachlorethane in quantity.
+    </p>
+    <p>
+      Acetylene combines with hydrogen in the presence of platinum black, and
+      ethylene and then ethane result. It was hoped at one time that this
+      reaction would lead to the manufacture of alcohol from acetylene being
+      achieved on a commercial basis; but it was found that it did not proceed
+      with sufficient smoothness for the process to succeed, and a number of
+      higher or condensation products were formed at the same time. It has been
+      shown by Erdmann that the cost of production of alcohol from acetylene
+      through this reaction must prove prohibitive, and he has indicated another
+      reaction which he considered more promising. This is the conversion of
+      acetylene by means of dilute sulphuric acid (3 volumes of concentrated
+      acid to 7 volumes of water), preferably in the presence of mercuric oxide,
+      to acetaldehyde. The yield, however, was not satisfactory, and the process
+      does not appear to have passed beyond the laboratory stage.
+    </p>
+    <p>
+      It has also been proposed to utilise the readiness with which acetylene
+      polymerises on heating to form benzene, for the production of benzene
+      commercially; but the relative prices of acetylene and benzene would have
+      to be greatly changed from those now obtaining to make such a scheme
+      successful. Acetylene also lends itself to the synthesis of phenol or
+      carbolic acid. If the dry gas is passed slowly into fuming sulphuric acid,
+      a sulpho-derivative results, of which the potash salt may be thrown down
+      by means of alcohol. This salt has the formula C_2H_4O_2,S_2O_6K_2, and on
+      heating it with caustic potash in an atmosphere of hydrogen, decomposing
+      with excess of sulphuric acid, and distilling, phenol results and may be
+      isolated. The product is, however, generally much contaminated with
+      carbon, and the process, which was devised by Berthelot, does not appear
+      to have been pursued commercially. Berthelot has also investigated the
+      action of ordinary concentrated sulphuric acid on acetylene, and obtained
+      various sulphonic derivatives. Schr�ter has made similar investigations on
+      the action of strongly fuming sulphuric acid on acetylene. These
+      investigations have not yet acquired any commercial significance.
+    </p>
+    <p>
+      If a mixture of acetylene with either of the oxides of carbon is led
+      through a red-hot tube, or if a similar mixture is submitted to the action
+      of electric sparks when confined within a closed vessel at some pressure,
+      a decomposition occurs, the whole of the carbon is liberated in the free
+      state, while the hydrogen and oxygen combine to form water. Analogous
+      reactions take place when either oxide of carbon is led over calcium
+      carbide heated to a temperature of 200� or 250� C., the second product in
+      this case being calcium oxide. The equations representing these actions
+      are:
+    </p>
+    <p>
+      C_2H_2 + CO = H_2O + 3C
+    </p>
+    <p>
+      2C_2H_2 + CO_2 = 2H_2O + 5C
+    </p>
+    <p>
+      CaC_2 + CO = CaO + 3C
+    </p>
+    <p>
+      2CaC_2 + CO_2 = 2CaO + 5C
+    </p>
+    <p>
+      By urging the temperature, or by increasing the pressure at which the
+      gases are led over the carbide, the free carbon appears in the graphitic
+      condition; at lower temperatures and pressures, it is separated in the
+      amorphous state. These reactions are utilised in Frank's process for
+      preparing a carbon pigment or an artificial graphite (<i>cf.</i> Chapter
+      XII.).
+    </p>
+    <p>
+      Parallel decompositions occur between carbon bisulphide and either
+      acetylene or calcium carbide, all the carbon of both substances being
+      eliminated, while the by-product is either sulphuretted hydrogen or
+      calcium (penta) sulphide. Other organic bodies containing sulphur are
+      decomposed in the same fashion, and it has been suggested by Ditz that if
+      carbide could be obtained at a suitable price, the process might be made
+      useful in removing sulphur (<i>i.e.</i>, carbon bisulphide and thiophen)
+      from crude benzol, in purifying the natural petroleum oil which contains
+      sulphur, and possibly in removing "sulphur compounds" from coal-gas.
+    </p>
+    <p>
+      COMPOUNDS WITH COPPER. By far the most important chemical reactions of
+      acetylene in connexion with its use as an illuminant or fuel are those
+      which it undergoes with certain metals, notably copper. It is known that
+      if acetylene comes in contact with copper or with one of its salts, in
+      certain conditions a compound is produced which, at least when dry, is
+      highly explosive, and will detonate either when warmed or when struck or
+      gently rubbed. The precise mechanism of the reaction, or reactions,
+      between acetylene and copper (or its compounds), and also the character of
+      the product, or products, obtained have been studied by numerous
+      investigators; but their results have been inconclusive and sometimes
+      rather contradictory, so that it can hardly be said that the conditions
+      which determine or preclude the formation of an explosive compound and the
+      composition of the explosive compound are yet known with certainty. Copper
+      is a metal which yields two series of compounds, cuprous and cupric salts,
+      the latter of which contain half the quantity of metal per unit of acid
+      constituent that is found in the former. It should follow, therefore, that
+      there are two compounds of copper with carbon, or copper carbides: cuprous
+      carbide, Cu_2C_2, and cupric carbide, CuC_2. Acetylene reacts at ordinary
+      temperatures with an ammoniacal solution of any cupric salt, forming a
+      black cupric compound of uncertain constitution which explodes between 50�
+      and 70� C. It is decomposed by dilute acids, yielding some polymerised
+      substances. At more elevated temperatures other cupric compounds are
+      produced which also give evidence of polymerisation. Cuprous carbide or
+      acetylide is the reddish brown amorphous precipitate which is the ultimate
+      product obtained when acetylene is led into an ammoniacal solution of
+      cuprous chloride. This body is decomposed by hydrochloric acid, yielding
+      acetylene; but of itself it is, in all probability, not explosive. Cuprous
+      carbide, however, is very unstable and prone to oxidation; so that, given
+      the opportunity, it combines with oxygen or hydrogen, or both, until it
+      produces the copper acetylide, or acetylene-copper, which is explosive--a
+      body to which Blochmann's formula C_2H_2Cu_2O is generally ascribed. Thus
+      it should happen that the exact nature of the copper acetylene compound
+      may vary according to the conditions in which it has been formed, from a
+      substance that is not explosive at all at first, to one that is violently
+      explosive; and the degree of explosiveness should depend on the greater
+      exposure of the compound to air and moisture, or the larger amount of
+      oxygen and moisture in the acetylene during its contact with the copper or
+      copper salt. For instance, Mai has found that freshly made copper
+      acetylide can be heated to 60� C. or higher without explosion; but that if
+      the compound is exposed to air for a few hours it explodes on warming,
+      while if warmed with oxygen it explodes on contact with acetylene. It is
+      said by Mai and by Caro to absorb acetylene when both substances are dry,
+      becoming so hot as to explode spontaneously. Freund and Mai have also
+      observed that when copper acetylide which has been dried in contact with
+      air for four or five hours at a temperature of 50� or 60� C. is allowed to
+      explode in the presence of a current of acetylene, an explosion
+      accompanied by light takes place; but it is always local and is not
+      communicated to the gas, whether the latter is crude or pure. In contact
+      with neutral or acid solutions of cuprous salts acetylene yields various
+      double compounds differing in colour and crystallising power; but
+      according to Chavastelon and to Caro they are all devoid of explosive
+      properties. Sometimes a yellowish red precipitate is produced in solutions
+      of copper salts containing free acid, but the deposit is not copper
+      acetylide, and is more likely to be, at least in part, a copper
+      phosphide--especially if the gas is crude. Hence acid solutions or
+      preparations of copper salts may safely be used for the purification of
+      acetylene, as is done in the case of frankoline, mentioned in Chapter V.
+      It is clear that the amount of free acid in such a material is much more
+      than sufficient to neutralise all the ammonia which may accompany the
+      crude acetylene into the purifier until the material is exhausted in other
+      respects; and moreover, in the best practice, the gas would have been
+      washed quite or nearly free from ammonia before entering the purifier.
+    </p>
+    <p>
+      From a practical aspect the possible interaction of acetylene and metallic
+      copper has been investigated by Gerdes and by Grittner, whose results,
+      again, are somewhat contradictory. Gerdes exposed neat acetylene and
+      mixtures of acetylene with oil-gas and coal-gas to a pressure of nine or
+      ten atmospheres for ten months at ordinary summer and winter temperatures
+      in vessels made of copper and various alloys. Those metals and alloys
+      which resisted oxidation in air resisted the attack of the gases, but the
+      more corrodible substances were attacked superficially; although in no
+      instance could an explosive body be detected, nor could an explosion be
+      produced by heating or hammering. In further experiments the acetylene
+      contained ammonia and moisture and Gerdes found that where corrosion took
+      place it was due exclusively to the ammonia, no explosive compounds being
+      produced even then. Grittner investigated the question by leading
+      acetylene for months through pipes containing copper gauze. His
+      conclusions are that a copper acetylide is always produced if impure
+      acetylene is allowed to pass through neutral or ammoniacal solutions of
+      copper; that dry acetylene containing all its natural impurities except
+      ammonia acts to an equal extent on copper and its alloys, yielding the
+      explosive compound; that pure and dry gas does not act upon copper or its
+      alloys, although it is possible that an explosive compound may be produced
+      after a great length of time. Grittner has asserted that an explosive
+      compound may be produced when acetylene is brought into contact with such
+      alloys of copper as ordinary brass containing 64.66 per cent. of copper,
+      or red brass containing 74.46 per cent. of copper, 20.67 per cent. of
+      zinc, and 4.64 per cent. of tin; whereas none is obtained when the metal
+      is either "alpaca" containing 64.44 per cent. of copper, 18.79 per cent.
+      of nickel, and 16.33 per cent. of zinc, or britannia metal composed of
+      91.7 per cent. of copper and 8.3 per cent. of tin. Caro has found that
+      when pure dry acetylene is led for nine months over sheets or filings of
+      copper, brass containing 63.2 per cent. of copper, red brass containing
+      73.8 per cent., so-called "alpaca-metal" containing 65.3 per cent., and
+      britannia metal containing 90.2 per cent. of copper, no action whatever
+      takes place at ordinary temperatures; if the gas is moist very small
+      quantities of copper acetylide are produced in six months, whatever metal
+      is tested, but the yield does not increase appreciably afterwards. At high
+      temperatures condensation occurs between acetylene and copper or its
+      alloys, but explosive bodies are not formed.
+    </p>
+    <p>
+      Grittner's statement that crude acetylene, with or without ammonia, acts
+      upon alloys of copper as well as upon copper itself, has thus been
+      corroborated by Caro; but experience renders it tolerably certain that
+      brass (and presumably gun-metal) is not appreciably attacked in practical
+      conditions. Gerdes' failure to obtain an explosive compound in any
+      circumstances may very possibly be explained by the entire absence of any
+      oxygen from his cylinders and gases, so that any copper carbide produced
+      remained unoxidised. Grittner's gas was derived, at least partially, from
+      a public acetylene supply, and is quite likely to have been contaminated
+      with air in sufficient quantity to oxidise the original copper compound,
+      and to convert it into the explosive modification.
+    </p>
+    <p>
+      For the foregoing reasons the use of unalloyed copper in the construction
+      of acetylene generators or in the subsidiary items of the plant, as well
+      as in burner fittings, is forbidden by statute or some quasi-legal
+      enactment in most countries, and in others the metal has been abandoned
+      for one of its alloys, or for iron or steel, as the case may be.
+      Grittner's experiments mentioned above, however, probably explain why even
+      alloys of copper are forbidden in Hungary. (<i>Cf.</i> Chapter IV., page
+      127.)
+    </p>
+    <p>
+      When acetylene is passed over finely divided copper or iron (obtained by
+      reduction of the oxide by hydrogen) heated to from 130� C. to 250� C., the
+      gas is more or less completely decomposed, and various products, among
+      which hydrogen predominates, result. Ethane and ethylene are undoubtedly
+      formed, and certain homologues of them and of acetylene, as well as
+      benzene and a high molecular hydrocarbon (C_7H_6)_n termed "cuprene," have
+      been found by different investigators. Nearly the same hydrocarbons, and
+      others constituting a mixture approximating in composition to some natural
+      petroleums, are produced when acetylene is passed over heated nickel (or
+      certain other metals) obtained by the reduction of the finely divided
+      oxide. These observations are at present of no technical importance, but
+      are interesting scientifically because they have led up to the
+      promulgation of a new theory of the origin of petroleum, which, however,
+      has not yet found universal acceptance. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkvii" id="vii">CHAPTER VII</a>
+    </h2>
+    <h3>
+      MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS
+    </h3>
+    <p>
+      The process by which acetylene is produced, and the methods employed for
+      purifying it and rendering it fit for consumption in dwelling-rooms,
+      having been dealt with in the preceding pages, the present chapter will be
+      devoted to a brief account of those items in the plant which lie between
+      the purifier outlet and the actual burner, including the meter, governor,
+      and pressure gauge; the proper sizes of pipe for acetylene; methods of
+      laying it, joint-making, quality of fittings, &amp;c.; while finally a few
+      words will be said about the precautions necessary when bringing a new
+      system of pipes into use for the first time.
+    </p>
+    <p>
+      THE METER.--A meter is required either to control the working of a
+      complete acetylene installation or to measure the volume of gas passing
+      through one particular pipe, as when a number of consumers are supplied
+      through separate services under agreement from a central supply plant. The
+      control which may be afforded by the inclusion of a meter in the equipment
+      of a domestic acetylene generating plant is valuable, but in practice will
+      seldom be exercised. The meter records check the yield of gas from the
+      carbide consumed in a simple and trustworthy manner, and also serve to
+      indicate when the material in the purifier is likely to be approaching
+      exhaustion. The meter may also be used experimentally to check the
+      soundness of the service-pipes or the consumption of a particular burner
+      or group of burners. Altogether it may be regarded as a useful adjunct to
+      a domestic lighting plant, provided full advantage is taken of it. If,
+      however, there is no intention to pay systematic attention to the records
+      of the meter, it is best to omit it from such an installation, and so save
+      its initial cost and the slight loss of pressure which its use involves on
+      the gas passing through it. A domestic acetylene lighting plant can be
+      managed quite satisfactorily without a meter, and as a multiplication of
+      parts is undesirable in an apparatus which will usually be tended by
+      someone not versed in technical operations, it is on the whole better to
+      omit the meter in such an installation. Where the plant is supervised by a
+      technical man, a meter may advisedly be included in the equipment. Its
+      proper position in the train of apparatus is immediately after the
+      purifier. A meter must not be used for unpurified or imperfectly purified
+      acetylene, because the impurities attack the internal metallic parts and
+      ultimately destroy them. The supply of acetylene to various consumers from
+      a central generating station entails the fixing of a meter on each
+      consumer's service-pipe, so that the quantity consumed by each may be
+      charged for accordingly, just as in the case of public coal-gas supplies.
+    </p>
+    <p>
+      There are two types of gas-meter in common use, either of which may,
+      without essential alteration, be employed for measuring the volume of
+      acetylene passing through a pipe. It is unnecessary to refer here at
+      length to their internal mechanism, because their manufacture by other
+      than firms of professed meter-makers is out of the question, and the user
+      will be justified in accepting the mechanism as trustworthy and durable.
+      Meters can always be had stamped with the seal of a local authority or
+      other body having duly appointed inspectors under the Sales of Gas Act,
+      and the presence of such a stamp on a meter implies that it has been
+      officially examined and found to register quantities accurately, or not
+      varying beyond 2 per cent. in favour of the seller, or 3 per cent, in
+      favour of the consumer. [Footnote: It may be remarked that when a meter--
+      wet or dry--begins to register incorrectly by reason of old age or want of
+      adjustment, its error is very often in the direction that benefits the
+      customer, <i>i.e.</i>, more gas passes through it than the dials record.]
+      Hence a "stamped" meter may be regarded for practical purposes as
+      affording a correct register of the quantities of gas passing through it.
+    </p>
+    <p>
+      Except that the use of unalloyed copper in any part of the meter where it
+      may come in contact with the gas must be wholly avoided, for the reason
+      that copper is inadmissible in acetylene apparatus (<i>see</i> Chapter
+      VI.), the meters ordinarily employed for coal-gas serve quite well for
+      acetylene. Obviously, however, since so very much less acetylene than
+      coal-gas is consumed per burner, comparatively small meters only will be
+      required even for large installations of acetylene lighting. This fact is
+      now recognised by meter-makers, and meters of all suitable sizes can be
+      obtained. It is desirable, if an ordinary coal-gas meter is being bought
+      for use with acetylene, to have it subjected to a somewhat more rigorous
+      test for soundness than is customary before "stamping" but the makers
+      would readily be able to carry out this additional test.
+    </p>
+    <p>
+      The two types of gas-meter are known as "wet" and "dry." The case of the
+      wet meter is about hall-filled with water or other liquid, the level of
+      which has to be maintained nearly constant. Several ingenious devices are
+      in use for securing this constancy of level over a more or less extended
+      period, but the necessity for occasional inspection and adjustment of the
+      water-level, coupled with the stoppage of the passage of gas in the event
+      of the water becoming frozen, are serious objections to the employment of
+      the wet meter in many situations. The trouble of freezing may be avoided
+      by substituting for the simple water an aqueous solution of glycerin, or
+      mixture of glycerin with water, suitable strengths for which may be
+      deduced from the table relating to the use of glycerin in holder seals
+      given at the close of Chapter III. The dry meter, on the other hand, is
+      very convenient, because it is not obstructed by the effects of frost, and
+      because it acts for years without requiring attention. It is not
+      susceptible of adjustment for measuring with so high a degree of accuracy
+      as a good wet meter, but its indications are sufficiently correct to fall
+      well within the legalised deviations already mentioned. Such errors,
+      perhaps, are somewhat large for so costly and powerful a gas as acetylene,
+      and they would be better reduced; but it is not so very often that a dry
+      meter reaches its limit of inaccuracy. Whether wet or dry, the meter
+      should be fixed in a place where the temperature is tolerably uniform,
+      otherwise the volumes registered at different times will not bear the same
+      ratio to the mass of gas (or volume at normal temperature), and the
+      registrations will be misleading unless troublesome corrections to
+      compensate for changes of temperature are applied.
+    </p>
+    <p>
+      THE GOVERNOR, which can be dispensed with in most ordinary domestic
+      acetylene lighting installations provided with a good gasholder of the
+      rising-bell type, is designed to deliver the acetylene to a service-pipe
+      at a uniform pressure, identical with that under which the burners develop
+      their maximum illuminating efficiency. It must therefore both cheek the
+      pressure anterior to it whenever that is above the determined limit to
+      which it is set, and deliver to the efferent service-pipe acetylene at a
+      constant pressure whether all or any number of the burners down to one
+      only are in use. Moreover, when the pressure anterior to the governor
+      falls to or below the determined limit, the governor should offer no
+      resistance--entailing a loss of pressure to the passage of the acetylene.
+      These conditions, which a perfect governor should fulfil, are not
+      absolutely met by any simple apparatus at present in use, but so far as
+      practical utility is concerned service governors which are readily
+      obtainable are sufficiently good. They are broadly of two types, viz.,
+      those having a bell floating in a mercury seal, and those having a
+      diaphragm of gas-tight leather or similar material, either the bell or the
+      diaphragm being raised by the pressure of the gas. The action is
+      essentially the same in both cases: the bell or the diaphragm is so
+      weighted that when the pressure of the gas exceeds the predetermined limit
+      the diaphragm or bell is lifted, and, through an attached rod and valve,
+      brings about a partial closure of the orifice by which the gas flows into
+      the bell or the diaphragm chamber. The valve of the governor, therefore,
+      automatically throttles the gas-way more or less according to the
+      difference in pressure before and after the apparatus, until at any moment
+      the gas-way is just sufficient in area to pass the quantity of gas which
+      any indefinite number of burners require at their fixed working pressure;
+      passing it always at that fixed working pressure irrespective of the
+      number of burners, and maintaining it constant irrespective of the amount
+      of pressure anterior to the governor, or of any variations in that
+      anterior pressure. In most patterns of service governor weights may be
+      added when it is desired to increase the pressure of the effluent gas. It
+      is necessary, in ordering a governor for an acetylene-supply, to state the
+      maximum number of cubic feet per hour it will be required to pass, and
+      approximately the pressure at which it will be required to deliver the gas
+      to the service-pipe. This will usually be between 3 and 5 inches (instead
+      of about 1 inch in the case of coal-gas), and if the anterior pressure is
+      likely to exceed 10 inches, this fact should be stated also. The
+      mercury-seal governors are usually the more trustworthy and durable, but
+      they are more costly than those with leather diaphragms. The seal should
+      have twice or thrice the depth it usually has for coal-gas. The governor
+      should be placed where it is readily accessible to the man in charge of
+      the installation, but where it will not be interfered with by
+      irresponsible persons. In large installations, where a number of separate
+      buildings receive service-pipes from one long main, each service-pipe
+      should be provided with a governor.
+    </p>
+    <p>
+      GASHOLDER PRESSURE.--In drawing up the specification or scheme of an
+      acetylene installation, it is frequently necessary either to estimate the
+      pressure which a bell gasholder of given diameter and weight will throw,
+      or to determine what should be the weight of the bell of a gasholder of
+      given diameter when the gas is required to be delivered from it at a
+      particular pressure. The gasholder of an acetylene installation serves not
+      only to store the gas, but also to give the necessary pressure for driving
+      it through the posterior apparatus and distributing mains and
+      service-pipes. In coal-gas works this office is generally given over
+      wholly or in part to a special machine, known as the exhauster, but this
+      machine could not be advantageously employed for pumping acetylene unless
+      the installation were of very great magnitude. Since, therefore, acetylene
+      is in practice always forced through mains and service-pipes in virtue of
+      the pressure imparted to it by the gasholder and since, for reasons
+      already given, only the rising-bell type of gasholder can be regarded as
+      satisfactory, it becomes important to know the relations which subsist
+      between the dimensions and weight of a gasholder bell and the pressure
+      which it "throws" or imparts to the contained gas.
+    </p>
+    <p>
+      The bell must obviously be a vessel of considerable weight if it is to
+      withstand reasonable wear and tear, and this weight will give a certain
+      hydrostatic pressure to the contained gas. If the weight of the bell is
+      known, the pressure which it will give can be calculated according to the
+      general law of hydrostatics, that the weight of the water displaced must
+      be equal to the weight of the floating body. Supposing for the moment that
+      there are no other elements which will have to enter into the calculation,
+      then if <i>d</i> is the diameter in inches of the (cylindrical) bell, the
+      surface of the water displaced will have an area of <i>d^2</i> x 0.7854.
+      If the level of the water is depressed <i>p</i> inches, then the water
+      displaced amounts to <i>p</i>(<i>d^2</i> x 0.7854) cubic inches, and its
+      weight will be (at 62� F.):
+    </p>
+    <p>
+      (0.7854<i>pd^2</i> x 0.03604) = 0.028302<i>pd^2</i> lb.
+    </p>
+    <p>
+      Consequently a bell which is <i>d</i> inches in diameter, and gives a
+      pressure of <i>p</i> inches of water, will weigh 0.028302<i>pd^2</i> lb.
+      Or, if W = the weight of the bell in lb., the pressure thrown by it will
+      be W/0.028302<i>d^2</i> or 35.333W/<i>d^2</i>. This is the fundamental
+      formula, which is sometimes given as <i>p</i> = 550W/<i>d^2</i>, in which
+      W = the weight of the bell in tons, and <i>d</i> the diameter in feet.
+      This value of <i>p</i>, however, is actually higher than the holder would
+      give in practice. Reductions have to be made for two influences, viz., the
+      lifting power of the contained gas, which is lighter than air, and the
+      diminution in the effective weight of so much of the bell as is immersed
+      in water. The effect of these influences was studied by Pole, who in 1839
+      drew up some rules for calculating the pressure thrown by a gasholder of
+      given dimensions and weight. These rules form the basis of the formula
+      which is commonly used in the coal-gas industry, and they may be applied,
+      <i>mutatis mutandis</i>, to acetylene holders. The corrections for both
+      the influences mentioned vary with the height at which the top of the
+      gasholder bell stands above the level of the water in the tank. Dealing
+      first with the correction for the lifting power of the gas, this,
+      according to Pole, is a deduction of <i>h</i>(1 - <i>d</i>)/828 where <i>d</i>
+      is the specific gravity of the gas and <i>h</i> the height (in inches) of
+      the top of the gasholder above the water level. This strictly applies only
+      to a flat-topped bell, and hence if the bell has a crown with a rise equal
+      to about 1/20 of the diameter of the bell, the value of <i>h</i> here must
+      be taken as equal to the height of the top of the sides above the
+      water-level (= <i>h'</i>), plus the height of a cylinder having the same
+      capacity as the crown, and the same diameter as the bell, that is to say,
+      <i>h</i>=<i>h'</i> + <i>d</i>/40 where <i>d</i> = the diameter of the
+      bell. The specific gravity of commercially made acetylene being constantly
+      very nearly 0.91, the deduction for the lifting power of the gas becomes,
+      for acetylene gasholders, 0.0001086<i>h</i> + 0.0000027<i>d</i>, where <i>h</i>
+      is the height in inches of the top of the sides of the bell above the
+      water- level, and <i>d</i> is the diameter of the bell. Obviously this is
+      a negligible quantity, and hence this correction may be disregarded for
+      all acetylene gasholders, whereas it is of some importance with coal-gas
+      and other gases of lower specific gravity. It is therefore wrong to apply
+      to acetylene gasholders formul� in which a correction for the lifting
+      power of the gas has been included when such correction is based on the
+      average specific gravity of coal-gas, as is the case with many abbreviated
+      gasholder pressure formul�.
+    </p>
+    <p>
+      The correction for the immersion of the sides of the bell is of greater
+      magnitude, and has an important practical significance. Let H be the total
+      height in inches of the side of the gasholder, <i>h</i> the height in
+      inches of the top of the sides of the gasholder above the water-level, and
+      <i>w</i> = the weight of the sides of the gasholder in lb.; then, for any
+      position of the bell, the proportion of the total height of the sides
+      immersed (H - <i>h</i>)/H, and the buoyancy is (H - <i>h</i>)/H x <i>w</i>/S
+      + pi/4<i>d^2</i>, in which S = the specific gravity of the material of
+      which the bell is made. Assuming the material to be mild steel or wrought
+      iron, having a specific gravity of 7.78, the buoyancy is (4<i>w</i>(H - <i>h</i>))
+      / (7.78Hpi<i>d^2</i>) lb. per square inch (<i>d</i> being inches and <i>w</i>
+      lb.), which is equivalent to (4<i>w</i>(H - <i>h</i>)) / (0.03604 x
+      7.78Hpi<i>d^2</i>) = (4.54<i>w</i>(H - <i>h</i>)) / (H<i>d^2</i>) inches
+      of water. Hence the complete formula for acetylene gasholders is:
+    </p>
+    <p>
+      <i>p</i> = 35.333W / <i>d^2</i> - 4.54<i>w</i>(H - <i>h</i>) / H<i>d^2</i>
+    </p>
+    <p>
+      It follows that <i>p</i> varies with the position of the bell, that is to
+      say, with the extent to which it is filled with gas. It will be well to
+      consider how great this variation is in the case of a typical acetylene
+      holder, as, if the variation should be considerable, provision must be
+      made, by the employment of a governor on the outlet main or otherwise, to
+      prevent its effects being felt at the burners.
+    </p>
+    <p>
+      Now, according to the rules of the "Acetylen-Verein" (<i>cf.</i> Chapter
+      IV.), the bells of holders above 53 cubic feet in capacity should have
+      sides 1.5 mm. thick, and crowns 0.5 mm. thicker. Hence for a holder from
+      150 to 160 cubic feet capacity, supposing it to be 4 feet in diameter and
+      about 12 feet high, the weight of the sides (say of steel No. 16 S.W.G. =
+      2.66 lb. per square foot) will be not less than 12 x 4pi x 2.66 = 401 lb.
+      The weight of the crown (say of steel No. 14 S.W.G. = 3.33 lb. per square
+      foot) will be not less than about 12.7 x 3.33 = about 42 lb. Hence the
+      total weight of holder = 401 + 42 = 443 lb. Then if the holder is full, <i>h</i>
+      is very nearly equal to H, and <i>p</i> = (35.333 x 443) / 48^2 = 6.79
+      inches. If the holder stands only 1 foot above the water-level, then <i>p</i>
+      = 6.79 - (4.54 x 401 (144 - 12)) / (144 x 48^2) = 6.79 - 0.72 = 6.07
+      inches. The same result can be arrived at without the direct use of the
+      second member of the formula:
+    </p>
+    <p>
+      For instance, the weight of the sides immersed is 11 x 4pi x 2.66 = 368
+      lb., and taking the specific gravity of mild steel at 7.78, the weight of
+      water displaced is 368 / 7.78 = 47.3 lb. Hence the total effective weight
+      of the bell is 443 - 47.3 = 395.7 lb., and <i>p</i> = (35.333 x 395.7) /
+      48^2 = 6.07 inches. [Footnote: If the sealing liquid in the gasholder tank
+      is other than simple water, the correction for the immersion of the sides
+      of the bell requires modification, because the weight of liquid displaced
+      will be <i>s'</i> times as great as when the liquid is water, if <i>s'</i>
+      is the specific gravity of the sealing liquid. For instance, in the
+      example given, if the sealing liquid were a 16 per cent. solution of
+      calcium chloride, specific gravity 1.14 (<i>vide</i> p. 93) instead of
+      water, the weight of liquid displaced would be 1.14 (368 / 7.78) = 53.9
+      lb., and the total effective weight of the bell = 443 - 53.9 = 389.1 lb.
+      Therefore <i>p</i> becomes = (35.333 x 389.1) / 48^2 = 5.97 inches,
+      instead of 6.07 inches.]
+    </p>
+    <p>
+      The value of <i>p</i> for any position of the bell can thus be arrived at,
+      and if the difference between its values for the highest and for the
+      lowest positions of the bell exceeds 0.25 inch, [Footnote: This figure is
+      given as an example merely. The maximum variation in pressure must be less
+      than one capable of sensibly affecting the silence, steadiness, and
+      economy of the burners and stoves, &amp;c., connected with the
+      installation.] a governor should be inserted in the main leading from the
+      holder to the burners, or one of the more or less complicated devices for
+      equalising the pressure thrown by a holder as it rises and falls should be
+      added to the holder. Several such devices were at one time used in
+      connexion with coal-gas holders, and it is unnecessary to describe them in
+      this work, especially as the governor is practically the better means of
+      securing uniform pressure at the burners.
+    </p>
+    <p>
+      It is frequently necessary to add weight to the bell of a small gasholder
+      in order to obtain a sufficiently high pressure for the distribution of
+      acetylene. It is best, having regard to the steadiness of the bell, that
+      any necessary weighting of it should be done near its bottom rim, which
+      moreover is usually stiffened by riveting to it a flange or curb of
+      heavier gauge metal. This flange may obviously be made sufficiently stout
+      to give the requisite additional weighting. As the flange is constantly
+      immersed, its weight must not be added to that of the sides in computing
+      the value of <i>w</i> for making the correction of pressure in respect of
+      the immersion of the bell. Its effective weight in giving pressure to the
+      contained gas is its actual weight less its actual weight divided by its
+      specific gravity (say 7.2 for cast iron, 7.78 for wrought iron or mild
+      steel, or 11.4 for lead). Thus if <i>x</i> lb. of steel is added to the
+      rim its weight in computing the value of W in the formula <i>p</i> =
+      35.333W / <i>d</i>^2 should be taken as x - x / 7.78. If the actual weight
+      is 7.78 lb., the weight taken for computing W is 7.78 - 1 = 6.78 lb.
+    </p>
+    <p>
+      THE PRESSURE GAUGE.--The measurement of gas pressure is effected by means
+      of a simple instrument known as a pressure gauge. It comprises a glass U-
+      tube filled to about half its height with water. The vacant upper half of
+      one limb is put in communication with the gas-supply of which the pressure
+      is to be determined, while the other limb remains open to the atmosphere.
+      The difference then observed, when the U-tube is held vertical, between
+      the levels of the water in the two limbs of the tube indicates the
+      difference between the pressure of the gas-supply and the atmospheric
+      pressure. It is this <i>difference</i> that is meant when the <i>pressure</i>
+      of a gas in a pipe or piece of apparatus is spoken of, and it must of
+      necessity in the case of a gas-supply have a positive value. That is to
+      say, the "pressure" of gas in a service-pipe expresses really by how much
+      the pressure in the pipe <i>exceeds</i> the atmospheric pressure.
+      (Pressures less than the atmospheric pressure will not occur in connexion
+      with an acetylene installation, unless the gasholder is intentionally
+      manipulated to that end.) Gas pressures are expressed in terms of inches
+      head or pressure of water, fractions of an inch being given in decimals or
+      "tenths" of an inch. The expression "tenths" is often used alone, thus a
+      pressure of "six-tenths" means a pressure equivalent to 0.6 inch head of
+      water.
+    </p>
+    <p>
+      The pressure gauge is for convenience provided with an attached scale on
+      which the pressures may be directly read, and with a connexion by which
+      the one limb is attached to the service-pipe or cock where the pressure is
+      to be observed. A portable gauge of this description is very useful, as it
+      can be attached by means of a short piece of flexible tubing to any tap or
+      burner. Several authorities, including the British Acetylene Association,
+      have recommended that pressure gauges should not be directly attached to
+      generators, because of the danger that the glass might be fractured by a
+      blow or by a sudden access of heat. Such breakage would be followed by an
+      escape of gas, and might lead to an accident. Fixed pressure gauges,
+      however, connected with every item of a plant are extremely useful, and
+      should be employed in all large installations, as they afford great aid in
+      observing and controlling the working, and in locating the exact position
+      of any block. All danger attending their use can be obviated by having a
+      stopcock between the gauge inlet and the portion of the plant to which it
+      is attached; the said stopcock being kept closed except when it is
+      momentarily opened to allow of a reading being taken. As an additional
+      precaution against its being left open, the stopcock may be provided with
+      a weight or spring which automatically closes the gas-way directly the
+      observer's hand is removed from the tap. In the best practice all the
+      gauges will be collected together on a board fastened in some convenient
+      spot on the wall of the generator-house, each gauge being connected with
+      its respective item of the plant by means of a permanent metallic tube.
+      The gauges must be filled with pure water, or with a liquid which does not
+      differ appreciably in specific gravity from pure water, or the readings
+      will be incorrect. Greater legibility will be obtained by staining the
+      water with a few drops of caramel solution, or of indigo sulphate (indigo
+      carmine); or, in the absence of these dyes, with a drop or two of common
+      blue-black writing ink. If they are not erected in perfectly frost-free
+      situations, the gauges may be filled with a mixture of glycerin and pure
+      alcohol (not methylated spirit), with or without a certain proportion of
+      water, which will not freeze at any winter temperature. The necessary
+      mixture, which must have a density of exactly 1.00, could be procured from
+      any pharmacist.
+    </p>
+    <p>
+      It is the pressure as indicated by the pressure gauge which is referred to
+      in this book in all cases where the term "pressure of the gas" or the like
+      is used. The quantity of acetylene which will flow in a given time from
+      the open end of a pipe is a function of this pressure, while the quantity
+      of acetylene escaping through a tiny hole or crack or a burner orifice
+      also depends on this total pressure, though the ratio in this instance is
+      not a simple one, owing to the varying influence of friction between the
+      issuing gas and the sides of the orifice. Where, however, acetylene or
+      other gas is flowing through pipes or apparatus there is a loss of energy,
+      indicated by a falling off in the pressure due to friction, or to the
+      performance of work, such as actuating a gas-meter. The extent of this
+      loss of energy in a given length of pipe or in a meter is measured by the
+      difference between the pressures of the gas at the two ends of the pipe or
+      at the inlet and outlet of the meter. This difference is the "loss" or
+      "fall" of pressure, due to friction or work performed, and is spoken of as
+      the "actuating" pressure in regard to the passage of gas through the
+      stretch of pipe or meter. It is a measure of the energy absorbed in
+      actuating the meter or in overcoming the friction. (Cf. footnote, Chapter
+      II., page 54.)
+    </p>
+    <p>
+      DIMENSIONS OF MAINS.--The diameter of the mains and service-pipes for an
+      acetylene installation must be such that the main or pipe will convey the
+      maximum quantity of the gas likely to be required to feed all the burners
+      properly which are connected to it, without an excessive actuating
+      pressure being called for to drive the gas through the main or pipe. The
+      flow of all gases through pipes is of course governed by the same general
+      principles; and it is only necessary in applying these principles to a
+      particular gas, such as acetylene, to know certain physical properties of
+      the gas and to make due allowance for their influence. The general
+      principles which govern the flow of a gas through pipes have been
+      exhaustively studied on account of their importance in relation to the
+      distribution of coal-gas and the supply of air for the ventilation of
+      places where natural circulation is absent or deficient. It will be
+      convenient to give a very brief reference to the way in which these
+      principles have been ascertained and applied, and then to proceed to the
+      particular case of the distribution of acetylene through mains and
+      service-pipes.
+    </p>
+    <p>
+      The subject of "The Motion of Fluids in Pipes" was treated in a lucid and
+      comprehensive manner in an Essay by W. Pole in the <i>Journal of Gas
+      Lighting</i> during 1852, and his conclusions have been generally adopted
+      by gas engineers ever since. He recapitulated the more important points of
+      this essay in the course of some lectures delivered in 1872, and one or
+      other of these two sources should be consulted for further information.
+      Briefly, W. Pole treated the question in the following manner:
+    </p>
+    <p>
+      The practical question in gas distribution is, what quantity of gas will a
+      given actuating pressure cause to flow along a pipe of given length and
+      given diameter? The solution of this question allows of the diameters of
+      pipes being arranged so that they will carry a required quantity of gas a
+      given distance under the actuating pressure that is most convenient or
+      appropriate. There are five quantities to be dealt with, viz.:
+    </p>
+    <p>
+      (1) The length of pipe = <i>l</i> feet.
+    </p>
+    <p>
+      (2) The internal diameter of the pipe = <i>d</i> inches.
+    </p>
+    <p>
+      (3) The actuating pressure = <i>h</i> inches of head of water. (4) The
+      specific gravity or density of the gas = <i>d</i> times that of air.
+    </p>
+    <p>
+      (5) The quantity of gas passing through the pipe--Q cubic feet per hour.
+      This quantity is the product of the mean velocity of the gas in the pipe
+      and the area of the pipe.
+    </p>
+    <p>
+      The only work done in maintaining the flow of gas along a pipe is that
+      required to overcome the friction of the gas on the walls of the pipe, or,
+      rather, the consequential friction of the gas on itself, and the laws
+      which regulate such friction have not been very exhaustively investigated.
+      Pole pointed out, however, that the existing knowledge on the point at the
+      time he wrote would serve for the purpose of determining the proper sizes
+      of gas-mains. He stated that the friction (1) is proportional to the area
+      of rubbing surface (viz., pi<i>ld</i>); (2) varies with the velocity, in
+      some ratio greater than the first power, but usually taken as the square;
+      and (3) is assumed to be proportional to the specific gravity of the fluid
+      (viz., <i>s</i>).
+    </p>
+    <p>
+      Thus the force (<i>f</i>) necessary to maintain the motion of the gas in
+      the pipe is seen to vary (1) as pi<i>ld</i>, of which pi is a constant;
+      (2) as <i>v^2</i>, where <i>v</i> = the velocity in feet per hour; and (3)
+      as <i>s</i>. Hence, combining these and deleting the constant pi, it
+      appears that
+    </p>
+    <p>
+      <i>f</i> varies as <i>ldsv^2</i>.
+    </p>
+    <p>
+      Now the actuating force is equal to <i>f</i>, and is represented by the
+      difference of pressure at the two ends of the pipe, <i>i.e.</i>, the
+      initial pressure, viz., that at the place whence gas is distributed or
+      issues from a larger pipe will be greater by the quantity <i>f</i> than
+      the terminal pressure, viz., that at the far end of the pipe where it
+      branches or narrows to a pipe or pipes of smaller size, or terminates in a
+      burner. The terminal pressure in the case of service-pipes must be
+      settled, as mentioned in Chapter II., broadly according to the pressure at
+      which the burners in use work best, and this is very different in the case
+      of flat-flame burners for coal-gas and burners for acetylene. The most
+      suitable pressure for acetylene burners will be referred to later, but may
+      be taken as equal to p_0 inches head of water. Then, calling the initial
+      pressure (<i>i.e.</i>, at the inlet head of service-pipe) p_1, it follows
+      that p_1 - p_0 = <i>f</i>. Now the cross-section of the pipe has an area
+      (pi/4)<i>d^2</i>, and if <i>h</i> represents the difference of pressure
+      between the two ends of the pipe per square inch of its area, it follows
+      that <i>f</i> = <i>h(pi/4)d^2</i>. But since <i>f</i> has been found above
+      to vary as <i>ldsv^2</i> , it is evident that
+    </p>
+    <p>
+      <i>h(pi/4)d^2</i> varies as <i>ldsv^2</i>.
+    </p>
+    <p>
+      Hence
+    </p>
+    <p>
+      <i>v^2</i> varies as <i>hd/ls</i>, and putting in some constant M, the
+      value of which must be determined by experiment, this becomes
+    </p>
+    <p>
+      <i>v^2</i> = M<i>hd/ls</i>.
+    </p>
+    <p>
+      The value of M deduced from experiments on the friction of coal-gas in
+      pipes was inserted in this equation, and then taking Q = pi/4<i>d^2v</i>,
+      it was found that for coal-gas Q = 780(<i>hd/sl</i>)^(1/2)
+    </p>
+    <p>
+      This formula, in its usual form, is
+    </p>
+    <p>
+      Q = 1350<i>d^2</i>(<i>hd/sl</i>)^(1/2)
+    </p>
+    <p>
+      in which <i>l</i> = the length of main in yards instead of in feet. This
+      is known as Pole's formula, and has been generally used for determining
+      the sizes of mains for the supply of coal-gas.
+    </p>
+    <p>
+      For the following reasons, among others, it becomes prudent to revise
+      Pole's formula before employing it for calculations relating to acetylene.
+      First, the friction of the two gases due to the sides of a pipe is very
+      different, the coefficient for coal-gas being 0.003, whereas that of
+      acetylene, according to Ortloff, is 0.0001319. Secondly, the mains and
+      service-pipes required for acetylene are smaller, <i>cateria paribus</i>,
+      than those needed for coal-gas. Thirdly, the observed specific gravity of
+      acetylene is 0.91, that of air being unity, whereas the density of
+      coal-gas is about 0.40; and therefore, in the absence of direct
+      information, it would be better to base calculations respecting acetylene
+      on data relating to the flow of air in pipes rather than upon such as are
+      applicable to coal-gas. Bernat has endeavoured to take these and similar
+      considerations into account, and has given the following formula for
+      determining the sizes of pipes required for the distribution of acetylene:
+    </p>
+    <p>
+      Q = 0.001253<i>d^2</i>(<i>hd/sl</i>)^(1/2)
+    </p>
+    <p>
+      in which the symbols refer to the same quantities as before, but the
+      constant is calculated on the basis of Q being stated in cubic metres, l
+      in metres, and d and h in millimetres. It will be seen that the equation
+      has precisely the same shape as Pole's formula for coal-gas, but that the
+      constant is different. The difference is not only due to one formula
+      referring to quantities stated on the metric and the other to the same
+      quantities stated on the English system of measures, but depends partly on
+      allowance having been made for the different physical properties of the
+      two gases. Thus Bernat's formula, when merely transposed from the metric
+      system of measures to the English (<i>i.e.</i>, Q being cubic feet per
+      hour, <i>l</i> feet, and <i>d</i> and <i>h</i> inches) becomes
+    </p>
+    <p>
+      Q = 1313.5<i>d^2</i>(<i>hd/sl</i>)^(1/2)
+    </p>
+    <p>
+      or, more simply,
+    </p>
+    <p>
+      Q = 1313.4(<i>hd^5/sl</i>)^(1/2)
+    </p>
+    <p>
+      But since the density of commercially-made acetylene is practically the
+      same in all cases, and not variable as is the density of coal-gas, its
+      value, viz., 0.91, may be brought into the constant, and the formula then
+      becomes
+    </p>
+    <p>
+      Q = 1376.9(<i>hd^5/l</i>)^(1/2)
+    </p>
+    <p>
+      Bernat's formula was for some time generally accepted as the most
+      trustworthy for pipes supplying acetylene, and the last equation gives it
+      in its simplest form, though a convenient transposition is
+    </p>
+    <p>
+      d = 0.05552(Q^2<i>l/h</i>)^(1/5)
+    </p>
+    <p>
+      Bernat's formula, however, has now been generally superseded by one given
+      by Morel, which has been found to be more in accordance with the actual
+      results observed in the practical distribution of acetylene. Morel's
+      formula is
+    </p>
+    <p>
+      D = 1.155(Q^2<i>l/h</i>)^(1/5)
+    </p>
+    <p>
+      in which D = the diameter of the pipe in centimetres, Q = the number of
+      cubic metres of gas passing per hour, <i>l</i> = the length of pipe in
+      metres, and <i>h</i> = the loss of pressure between the two ends of the
+      pipe in millimetres. On converting tins formula into terms of the English
+      system of measures (<i>i.e.</i>, <i>l</i> feet, Q cubic feet, and <i>h</i>
+      and <i>d</i> inches) it becomes
+    </p>
+    <p>
+      (i) d = 0.045122(Q^2<i>l/h</i>)^(1/5)
+    </p>
+    <p>
+      At first sight this formula does not appear to differ greatly from
+      Bernat's, the only change being that the constant is 0.045122 instead of
+      0.05552, but the effect of this change is very great--for instance, other
+      factors remaining unaltered, the value of Q by Morel's formula will be
+      1.68 times as much as by Bernat's formula. Transformations of Morel's
+      formula which may sometimes be more convenient to apply than (i) are:
+    </p>
+    <p>
+      (ii) Q = 2312.2(<i>hd^5/l</i>)^(1/2)
+    </p>
+    <p>
+      (iii) <i>h</i> = 0.000000187011(Q^2<i>l/d^5</i>)
+    </p>
+    <p>
+      and (iv) <i>l</i> = 5,346,340(<i>hd^5</i>/Q^2)
+    </p>
+    <p>
+      In order to avoid as far as possible expenditure of time and labour in
+      repeating calculations, tables have been drawn up by the authors from
+      Morel's formul� which will serve to give the requisite information as to
+      the proper sizes of pipes to be used in those cases which are likely to be
+      met with in ordinary practice. These tables are given at the end of this
+      chapter.
+    </p>
+    <p>
+      When dealing with coal-gas, it is highly important to bear in mind that
+      the ordinary distributing formul� apply directly only when the pipe or
+      main is horizontal, and that a rise in the pipe will be attended by an
+      increase of pressure at the upper end. But as the increase is greater the
+      lower the density of the gas, the disturbing influence of a moderate rise
+      in a pipe is comparatively small in the case of a gas of so high a density
+      as acetylene. Hence in most instances it will be unnecessary to make any
+      allowance for increase of pressure due to change of level. Where the
+      change is very great, however, allowance may advisedly be made on the
+      following basis: The pressure of acetylene in pipes increases by about
+      one-tenth of an inch (head of water) for every 75 feet rise in the pipe.
+      Hence where acetylene is supplied from a gasholder on the ground-level to
+      all floors of a house 75 feet high, a burner at the top of the house will
+      ordinarily receive its supply at a pressure greater by one-tenth of an
+      inch than a burner in the basement. Such a difference, with the relatively
+      high pressures used in acetylene supplies, is of no practical moment. In
+      the case of an acetylene-supply from a central station to different parts
+      of a mountainous district, the variations of pressure with level should be
+      remembered.
+    </p>
+    <p>
+      The distributing formul� also assume that the pipe is virtually straight;
+      bends and angles introduce disturbing influences. If the bend is sharp, or
+      if there is a right-angle, an allowance should be made if it is desired to
+      put in pipes of the smallest permissible dimensions. In the case of the
+      most usual sizes of pipes employed for acetylene mains or services, it
+      will suffice to reckon that each round or square elbow is equivalent in
+      the resistance it offers to the flow of gas to a length of 5 feet of pipe
+      of the same diameter. Hence if 5 feet is added to the actual length of
+      pipe to be laid for every bond or elbow which will occur in it, and the
+      figure so obtained is taken as the value of <i>l</i> in formul� (i), (ii),
+      or (iii), the values then found for Q, <i>d</i>, or <i>h</i> will be
+      trustworthy for all practical purposes.
+    </p>
+    <p>
+      It may now be useful to give an example of the manner of using the
+      foregoing formul� when the tables of sizes of pipes are not available. Let
+      it be supposed that an institution is being equipped for acetylene
+      lighting; that 50 burners consuming 0.70 cubic foot, and 50 consuming 1.00
+      cubic foot of acetylene per hour may be required in use simultaneously;
+      that a pressure of at least 2-1/2 inches is required at all the burners;
+      that for sufficient reasons it is considered undesirable to use a higher
+      distributing pressure than 4 inches at the gasholder, outlet of the
+      purifiers, or initial governor (whichever comes last in the train of
+      apparatus); that the gasholder is located 100 feet from the main building
+      of the institution, and that the trunk supply-pipe through the latter must
+      be 250 feet in length, and the supplies to the burners, either singly or
+      in groups, be taken from this trunk pipe through short lengths of tubing
+      of ample size. What should be the diameter of the trunk pipe, in which it
+      will be assumed that ten bonds or elbows are necessary?
+    </p>
+    <p>
+      In the first instance, it is convenient to suppose that the trunk pipe may
+      be of uniform diameter throughout. Then the value of <i>l</i> will be 100
+      (from gasholder to main building) + 250 (within the building) + 50
+      (equivalent of 10 elbows) = 400. The maximum value of Q will be (50 x 0.7)
+      + (50 x 1.0) = 85; and the value of <i>h</i> will be 1 - 2.5 - 1.5. Then
+      using formula (i), we have:
+    </p>
+    <p>
+      d = 0.045122((85^2 x 400)/1.5)^(1/5) = 0.045122(1,926,667)^(1/5)
+    </p>
+    <p>
+      = 0.045122 x 18.0713 = 0.8154.
+    </p>
+    <p>
+      The formula, therefore, shows that the pipe should have an internal
+      diameter of not less than 0.8154 inch, and consequently 1 inch (the next
+      size above 0.8154 inch) barrel should be used. If the initial pressure
+      (i.e., at outlet of purifiers) could be conveniently increased from 4 to
+      4.8 inches, 3/4 inch barrel could be employed for the service-pipe. But if
+      connexions for burners were made immediately the pipe entered the
+      building, these burners would then be supplied at a pressure of 4.2
+      inches, while those on the extremity of the pipe would, when all burners
+      were in use, be supplied at a pressure of only 2.5 inches. Such a great
+      difference of pressure is not permissible at the several burners, as no
+      type of burner retains its proper efficiency over more than a very limited
+      range of pressure. It is highly desirable in the case of the ordinary
+      Naphey type of burner that all the burners in a house should be supplied
+      at pressures which do not differ by more than half an inch; hence the
+      pipes should, wherever practicable, be of such a size that they will pass
+      the maximum quantity of gas required for all the burners which will ever
+      be in use simultaneously, when the pressure at the first burner connected
+      to the pipe after it enters the house is not more than half an inch above
+      the pressure at the burner furthermost removed from the first one, all the
+      burner-taps being turned on at the time the pressures are observed. If the
+      acetylene generating plant is not many yards from the building to be
+      supplied, it is a safe rule to calculate the size of pipes required on the
+      basis of a fall of pressure of only half an inch from the outlet of the
+      purifiers or initial governor to the farthermost burner. The extra cost of
+      the larger size of pipe which the application of this rule may entail will
+      be very slight in all ordinary house installations.
+    </p>
+    <p>
+      VELOCITY OF FLOW IN PIPES.--For various purposes, it is often desirable to
+      know the mean speed at which acetylene, or any other gas, is passing
+      through a pipe. If the diameter of the pipe is <i>d</i> inches, its
+      cross-sectional area is <i>d^2</i> x 0.7854 square inches; and since there
+      are 1728 cubic inches in 1 cubic foot, that quantity of gas will occupy in
+      a pipe whose diameter is <i>d</i> inches a length of
+    </p>
+    <p>
+      1728/(<i>d^2</i> x 0.7854) linear inches or 183/<i>d^2</i>^ linear feet.
+    </p>
+    <p>
+      If the gas is in motion, and the pipe is delivering Q cubic feet per hour,
+      since there are 3600 seconds of time in one hour, the mean speed of the
+      gas becomes
+    </p>
+    <p>
+      183/<i>d^2</i> x Q/3600 = Q/(19 x 7<i>d^2</i>) linear feet per second.
+    </p>
+    <p>
+      This value is interesting in several ways. For instance, taking a rough
+      average of Le Chatelier's results, the highest speed at which the
+      explosive wave proceeds in a mixture of acetylene and air is 7 metres or
+      22 feet per second. Now, even if a pipe is filled with an acetylene-air
+      mixture of utmost explosibility, an explosion cannot travel backwards from
+      B to A in that pipe, if the gas is moving from A to B at a speed of over
+      22 feet per second. Hence it may be said that no explosion can occur in a
+      pipe provided
+    </p>
+    <p>
+      Q/(19.7<i>d^2</i>) = 22 or more;
+    </p>
+    <p>
+      <i>i.e.</i>, Q/<i>d^2</i>=433.4
+    </p>
+    <p>
+      In plain language, if the number of cubic feet passing through the pipe
+      per hour divided by the square of the diameter of the pipe is at least
+      433.4, no explosion can take place within that pipe, even if the gas is
+      highly explosive and a light is applied to its exit.
+    </p>
+    <p>
+      In Chapter VI. are given the explosive limits of acetylene-air mixtures as
+      influenced by the diameter of the tube containing them. If we possessed a
+      similar table showing the speed of the explosive wave in mixtures of known
+      composition, the foregoing formul� would enable us to calculate the
+      minimum speed which would insure absence of explosibility in a supply-pipe
+      of any given diameter throughout its length, or at its narrowest part. It
+      would not, however, be possible simply by increasing the forward speed of
+      an explosive mixture of acetylene and air to a point exceeding that of its
+      explosion velocity to prevent all danger of firing back in an atmospheric
+      burner tube. A much higher pressure than is usually employed in
+      gas-burners, other than blowpipes, would be needed to confer a sufficient
+      degree of velocity upon the gas, a pressure which would probably fracture
+      any incandescent mantle placed in the flame.
+    </p>
+    <p>
+      SERVICE-PIPES AND MAINS.--The pipes used for the distribution of acetylene
+      must be sound in themselves, and their joints perfectly tight. Higher
+      pressures generally prevail in acetylene service-pipes within a house than
+      in coal-gas service-pipes, while slight leaks are more offensive and
+      entail a greater waste of resources. Therefore it is uneconomical, as well
+      as otherwise objectionable, to employ service-pipes or fittings for
+      acetylene which are in the least degree unsound. Unfortunately ordinary
+      gas-barrel is none too sound, nor well-threaded, and the taps and joints
+      of ordinary gas-fittings are commonly leaky. Hence something better should
+      invariably be used for acetylene. What is known as "water" barrel, which
+      is one gauge heavier than gas-barrel of the same size, may be adopted for
+      the service-pipes, but it is better to incur a slight extra initial
+      expense and to use "steam" barrel, which is of still heavier gauge and is
+      sounder than either gas or water-pipe. All elbows, tees, &amp;c., should
+      be of the same quality. The fitters' work in making the joints should be
+      done with the utmost care, and the sloppy work often passed in the case of
+      coal-gas services must on no account be allowed. It is no exaggeration to
+      say that the success of an acetylene installation, from the consumer's
+      point of view, will largely, if not principally, depend on the tightness
+      of the pipes in his house. The statement has been made that the "paint"
+      used by gas-fitters, <i>i.e.</i>, the mixture of red and white lead ground
+      in "linseed" oil, is not suitable for employment with acetylene, and it
+      has been proposed to adopt a similar material in which the vehicle is
+      castor-oil. No good reason has been given for the preference for
+      castor-oil, and the troubles which have arisen after using ordinary paint
+      may be explained partly on the very probable assumption that the oil was
+      not genuine linseed, and so did not dry, and partly on the fact that
+      almost entire reliance was placed on the paint for keeping the joint
+      sound. Joints for acetylene, like those for steam and high-pressure water,
+      must be made tight by using well-threaded fittings, so as to secure
+      metallic contact between pipe and socket, &amp;c.; the paint or spun-yarn
+      is only an additional safeguard. In making a faced joint, washers of (say,
+      7 lb) lead, or coils of lead-wire arc extremely convenient and quite
+      trustworthy; the packing can be used repeatedly.
+    </p>
+    <p>
+      LEAKAGE.--Broadly speaking, it may be said that the commercial success of
+      any village acetylene-supply--if not that of all large installations--
+      depends upon the leakage being kept within moderate limits. It follows
+      from what was stated in Chapter VI. about the diffusion of acetylene, that
+      from pipes of equal porosity acetylene and coal-gas will escape at equal
+      rates when the effective pressure in the pipe containing acetylene is
+      double that in the pipe containing coal-gas. The loss of coal-gas by
+      leakage is seldom less than 5 per cent. of the volume passed into the main
+      at the works; and provided a village main delivering acetylene is not
+      unduly long in proportion to the consumption of gas--or, in other words,
+      provided the district through which an acetylene distributing main passes
+      is not too sparsely populated--the loss of acetylene should not exceed the
+      same figure. Caro holds that the loss of gas by leakage from a village
+      installation should be quoted in absolute figures and not as a percentage
+      of the total make as indicated by the works meter, because that total make
+      varies so largely at different periods of the year, while the factors
+      which determine the magnitude of the leakage are always identical; and
+      therefore whereas the actual loss of gas remains the same, it is
+      represented to be more serious in the summer than in the winter. Such
+      argument is perfectly sound, but the method of returning leakage as a
+      percentage of the make has been employed in the coal-gas industry for many
+      years, and as it does not appear to have led to any misunderstanding or
+      inconvenience, there is no particular reason for departing from the usual
+      practice in the case of acetylene where the conditions as to uniform
+      leakage and irregular make are strictly analogous.
+    </p>
+    <p>
+      Caro has stated that a loss of 15 to 20 litres per kilometre per hour (<i>i.e.</i>,
+      of 0.85 to 1.14 cubic feet per mile per hour) from an acetylene
+      distributing main is good practice; but it should be noted that much lower
+      figures have been obtained when conditions are favourable and when due
+      attention has been devoted to the fitters' work. In one of the German
+      village acetylene installations where the matter has been carefully
+      investigated (D�se, near Cuxhaven), leakage originally occurred at the
+      rate of 7.3 litres per kilometre per hour in a main 8.5 kilometres, or 5.3
+      miles, long and 4 to 2 inches in diameter; but it was reduced to 5.2
+      litres, and then to 3.12 litres by tightening the plugs of the street
+      lantern and other gas cocks. In British units, these figures are 0.415,
+      0.295, and 0.177 cubic foot per mile per hour. By calculation, the volume
+      of acetylene generated in this village would appear to have been about
+      23,000 cubic feet per mile of main per year, and therefore it may be said
+      that the proportion of gas lost was reduced by attending to the cocks from
+      15.7 per cent, to 11.3 per cent, and then to 6.8 per cent. At another
+      village where the main was 2.5 kilometres long, tests extending over two
+      months, when the public lamps were not in use, showed the leakage to be
+      4.4 litres per kilometre per hour, <i>i.e.</i>, 1.25 cubic foot per mile
+      per hour, when the annual make was roughly 46,000 cubic feet per mile of
+      main. Here, the loss, calculated from the direct readings of the works
+      motor, was 4.65 per cent.
+    </p>
+    <p>
+      When all the fittings, burners excepted, have been connected, the whole
+      system of pipes must be tested by putting it under a gas (or air) pressure
+      of 9 or 12 inches of water, and observing on an attached pressure gauge
+      whether any fall in pressure occurs within fifteen minutes after the main
+      inlet tap has been shut. The pressure required for this purpose can be
+      obtained by temporarily weighting the holder, or by the employment of a
+      pump. If the gauge shows a fall of pressure of one quarter of an inch or
+      more in these circumstances, the pipes must be examined until the leak is
+      located. In the presence of a meter, the installation can conveniently be
+      tested for soundness by throwing into it, through the meter, a pressure of
+      12 inches or so of water from the weighted holder, then leaving the inlet
+      cock open, and observing whether the index hand on the lowest dial remains
+      perfectly stationary for a quarter of an hour--movement of the linger
+      again indicating a leak. The search for leaks must never be made with a
+      light; if the pipes are full of air this is useless, if full of gas,
+      criminal in its stupidity. While the whole installation is still under a
+      pressure of 12 inches thrown from the loaded holder, whether it contains
+      air or gas, first all the likely spots (joints, &amp;c.), then the entire
+      length of pipe is carefully brushed over with strong soapy water, which
+      will produce a conspicuous "soap- bubble" wherever the smallest flaw
+      occurs. The tightness of a system of pipes put under pressure from a
+      loaded holder cannot be ascertained safely by observing the height of the
+      bell, and noting if it falls on standing. Even if there is no issue of gas
+      from the holder, the position of the bell will alter with every variation
+      in temperature of the stored gas or surrounding air, and with every
+      movement of the barometer, rising as the temperature rises and as the
+      barometer falls, and <i>vice vers�</i>, while, unless the water in the
+      seal is saturated with whatever gas the holder contains, the bell will
+      steadily drop a little an part of its contents are lost by dissolution in
+      the liquid.
+    </p>
+    <p>
+      PIPES AND FITTINGS.--As a general rule it is unadvisable to use lead or
+      composition pipe for permanent acetylene connexions. If exposed, it is
+      liable to be damaged, and perhaps penetrated by a blow, and if set in the
+      wall and covered with paper or panel it is liable to be pierced if nails
+      or tacks should at any time be driven into the wall. There is also an
+      increased risk in case of fire, owing to its ready fusibility. If used at
+      all--and it has obvious advantages--lead or composition piping should be
+      laid on the surface of the walls, &amp;c., and protected from blows, &amp;c.,
+      by a light wooden casing, outwardly resembling the wooden coverings for
+      electric lighting wires. It has been a common practice, in laying the
+      underground mains required for supplying the villages which are lighted by
+      means of acetylene from a central works in different parts of France, to
+      employ lead pipes. The plan is economical, but in view of the danger that
+      the main might be flattened by the weight of heavy traction-engines
+      passing over the roads, or that it might settle into local dips from the
+      same cause or from the action of subterranean water, in which dips water
+      would be constantly condensing in cold weather, the use of lead for this
+      purpose cannot be recommended. Steam-barrel would be preferable to cast
+      pipe, because permanently sound joints are easier to make in the former,
+      and because it is not so brittle.
+    </p>
+    <p>
+      The fittings used for acetylene must have perfectly sound joints and taps,
+      for the same reasons that the service-pipes must be quite sound. Common
+      gas-fittings will not do, the joints, taps, ball-sockets, &amp;c., are not
+      accurately enough ground to prevent leakage. They may in many cases be
+      improved by regrinding, but often the plug and barrel are so shallow that
+      it is almost impossible to ensure soundness. It is therefore better to
+      procure fittings having good taps and joints in the first instance; the
+      barrels should be long, fairly wide, and there should be no sensible
+      "play" between plug and barrel when adjusted so that the plug turns easily
+      when lightly lubricated. Fittings are now being specially made for
+      acetylene, which is a step in the right direction, because, in addition to
+      superior taps and joints being essential, smaller bore piping and smaller
+      through-ways to the taps than are required for coal-gas serve for
+      acetylene. It is perhaps advisable to add that wherever a rigid bracket or
+      fitting will answer as well as a jointed one, the latter should on no
+      account be used; also water-slide pendants should never be employed, as
+      they are fruitful of accidents, and their apparent advantages are for the
+      most part illusory. Ball-sockets also should be avoided if possible; if it
+      is absolutely necessary to have a fitting with a ball-socket, the latter
+      should have a sleeve made of a short length of sound rubber-tubing of a
+      size to give a close fit, slipped over so as to join the ball portion to
+      the socket portion. This sleeve should be inspected once a quarter at
+      least, and renewed immediately it shows signs of cracking. Generally
+      speaking all the fittings used should be characterised by structural
+      simplicity; any ornamental or decorative effects desired may be secured by
+      proper design without sacrifice of the simplicity which should always mark
+      the essential and operative parts of the fitting. Flexible connexions
+      between the fixed service-pipe and a semi-portable or temporary burner may
+      at times be required. If the connexion is for permanent use, it must not
+      be of rubber, but of the metallic flexible tubing which is now commonly
+      employed for such connexions in the case of coal-gas. There should be a
+      tap between the service-pipe and the flexible connexion, and this tap
+      should be turned off whenever the burner is out of use, so that the
+      connexion is not at other times under the pressure which is maintained in
+      the service-pipes. Unless the connexion is very short--say 2 feet or
+      less--there should also be a tap at the burner. These flexible connexions,
+      though serviceable in the case of table-lamps, &amp;c., of which the
+      position may have to be altered, are undesirable, as they increase the
+      risk attendant on gas (whether acetylene or other illuminating gas)
+      lighting, and should, if possible, be avoided. Flexible connexions may
+      also be required for temporary use, such as for conveying acetylene to an
+      optical lantern, and if only occasionally called for, the cost of the
+      metallic flexible tubing will usually preclude its use. It will generally
+      be found, however, that the whole connexion in such a case can be of
+      composition or lead gas-piping, connected up at its two ends by a few
+      inches of flexible rubber tubing. It should be carried along the walls or
+      over the heads of people who may use the room, rather than across the
+      floor, or at a low level, and the acetylene should be turned on to it only
+      when actually required for use, and turned off at the fixed service-pipe
+      as soon as no longer required. Quite narrow composition tubing, say
+      1/4-inch, will carry all the acetylene required for two or three burners.
+      The cost of a composition temporary connexion will usually be less than
+      one of even common rubber tubing, and it will be safer. The composition
+      tubing must not, of course, be sharply bent, but carried by easy curves to
+      the desired point, and it should be carefully rolled in a roll of not less
+      than 18 inches diameter when removed. If these precautions are observed it
+      may be used very many times.
+    </p>
+    <p>
+      Acetylene service-pipes should, wherever possible, be laid with a fall,
+      which may be very slight, towards a small closed vessel adjoining the
+      gasholder or purifier, in order that any water deposited from the gas
+      owing to condensation of aqueous vapour may run out of the pipe into that
+      apparatus. Where it is impossible to secure an uninterrupted fall in that
+      direction, there should be inserted in the service-pipe, at the lowest
+      point of each dip it makes, a short length of pipe turned downwards and
+      terminating in a plug or sound tap. Water condensing in this section of
+      the service-pipe will then run down and collect in this drainage-pipe,
+      from which it can be withdrawn at intervals by opening the plug or tap for
+      a moment. The condensed water is thus removed from the service-pipe, and
+      does not obstruct its through-way. Similar drainage devices may be used at
+      the lowest points of all dips in mains, though there are special seal-pots
+      which take the place of the cock or plug used to seal the end of the
+      drainage-pipe. Such seal-pots or "syphons" are commonly used on ordinary
+      gas-distributing systems, and might be applied in the case of large
+      acetylene installations, as they offer facilities for removing the
+      condensed water from time to time in a convenient and expeditious manner.
+    </p>
+    <p>
+      EXPULSION OF AIR FROM MAINS.--After a service-pipe system has been proved
+      to be sound, it is necessary to expel the air from it before acetylene can
+      be admitted to it with a view to consumption. Unless the system is a very
+      large one, the expulsion of air is most conveniently effected by forcing
+      from the gasholder preliminary batches of acetylene through the pipes,
+      while lights are kept away from the vicinity. This precaution is necessary
+      because, while the acetylene is displacing the air in the pipes, they will
+      for some time contain a mixture of air and acetylene in proportions which
+      fall within the explosive limits of such a mixture. If the escaping
+      acetylene caught fire from any adjacent light under these conditions, a
+      most disastrous explosion would ensue and extend through all the
+      ramifications of the system of pipes. Therefore the first step when a new
+      system of pipes has to be cleared of air is to see that there are no
+      lights in or about the house--either fires, lamps, cigars or pipes,
+      candles or other flames. Obviously this work must be done in the daytime
+      and finished before nightfall. Burners are removed from two or more
+      brackets at the farthest points in the system from the gasholder, and
+      flexible connexions are temporarily attached to them, and led through a
+      window or door into the open air well clear of the house. One of the
+      brackets selected should as a rule be the lowest point supplied in the
+      house. The gasholder having been previously filled with acetylene, the tap
+      or taps on the pipe leading to the house are turned on, and the acetylene
+      is passed under slight pressure into the system of pipes, and escapes
+      through the aforesaid brackets, of which the taps have been turned on,
+      into the open. The taps of all other brackets are kept closed. The gas
+      should be allowed to flow thus through the pipes until about five times
+      the maximum quantity which all the burners on the system would consume in
+      an hour has escaped from the open brackets. The taps on these brackets are
+      then closed, and the burners replaced. Flexible tubing is then connected
+      in place of the burners to all the other brackets in the house, and
+      acetylene is similarly allowed to escape into the open air from each for a
+      quarter of an hour. All taps are then closed, and the burners replaced;
+      all windows in the house are left open wide for half an hour to allow of
+      the dissipation of any acetylene which may have accumulated in any part of
+      it, and then, while full pressure from the gasholder is maintained, a tap
+      is turned on and the gas lighted. If it burns with a good, fully luminous
+      flame it may be concluded that the system of pipes is virtually free from
+      air, and the installation may be used forthwith as required. If, however,
+      the flame is very feebly luminous, or if the escaping gas does not light,
+      lights must be extinguished, and the pipes again blown through with
+      acetylene into the open air. The burner must invariably be in position
+      when a light is applied, because, in the event of the pipes still
+      containing an explosive mixture, ignition would not be communicated
+      through the small orifices of the burner to the mixture in the pipes, and
+      the application of the light would not entail any danger of an explosion.
+    </p>
+    <p>
+      Gasfitters familiar with coal-gas should remember, when putting a system
+      of acetylene pipes into use for the first time, that the range over which
+      mixtures of acetylene and air are explosive is wider than that over which
+      mixtures of coal-gas and air are explosive, and that greater care is
+      therefore necessary in getting the pipes and rooms free from a dangerous
+      mixture.
+    </p>
+    <p>
+      The mains for very large installations of acetylene--<i>e.g.</i>, for
+      lighting a small town--may advisedly be freed from air by some other plan
+      than simple expulsion of the air by acetylene, both from the point of view
+      of economy and of safety. If the chimney gases from a neighbouring furnace
+      are found on examination to contain not more than about 8 per cent of
+      oxygen, they may be drawn into the gasholder and forced through the pipes
+      before acetylene is admitted to them. The high proportion of carbon
+      dioxide and the low proportion of oxygen in chimney gases makes a mixture
+      of acetylene and chimney gases non-explosive in any proportions, and hence
+      if the air is first wholly or to a large extent expelled from a pipe,
+      main, or apparatus, by means of chimney gases, acetylene may be admitted,
+      and a much shorter time allowed for the expulsion by it of the contents of
+      the pipe, before a light is applied at the burners, &amp;c. This plan,
+      however, will usually only be adopted in the case of very large pipes,
+      &amp;c.; but on a smaller scale the air may be swept out of a distributing
+      system by bringing it into connexion with a cylinder of compressed or
+      liquefied carbon dioxide, the pressure in which will drive the gas to any
+      spot where an outlet is provided. As these cylinders of "carbonic acid"
+      are in common employment for preparing aerated waters and for "lifting"
+      beer, &amp;c., they are easy to hire and use.
+    </p>
+    <p>
+      TABLE (B).
+    </p>
+    <p>
+      Giving the Sizes of Pipe which should be used in practice for Acetylene
+      when the fall of pressure in the Pipe is not to exceed 0.1 inch. (Based on
+      Morel's formula.)
+    </p>
+<pre xml:space="preserve">
+ _________________________________________________________
+|                |                                       |
+| Cubic Feet of  |  Diameters of Pipe to be used up to   |
+|   Acetylene    |        the lengths indicated.         |
+| which the Pipe |_______________________________________|
+| is required to |       |       |       |       |       |
+|    pass in     |  1/4  |  3/8  |  1/2  |  3/4  |   1   |
+|   One Hour.    | inch. | inch. | inch. | inch. | inch. |
+|________________|_______|_______|_______|_______|_______|
+|                |       |       |       |       |       |
+|                | Feet. | Feet. | Feet. | Feet. | Feet. |
+|  1             |  520  | 3960  | 16700 |  ...  |  ...  |
+|  2             |  130  |  990  |  4170 |  ...  |  ...  |
+|  3             |   58  |  440  |  1850 |  ...  |  ...  |
+|  4             |   32  |  240  |  1040 |  ...  |  ...  |
+|  5             |   21  |  150  |   660 | 5070  |  ...  |
+|  6             |   14  |  110  |   460 | 3520  |  ...  |
+|  7             |   10  |   80  |   340 | 2590  |  ...  |
+|  8             |  ...  |   62  |   260 | 1980  |  ...  |
+|  9             |  ...  |   49  |   200 | 1560  |  ...  |
+| 10             |  ...  |   39  |   160 | 1270  | 5340  |
+| 15             |  ...  |   17  |    74 |  560  | 2370  |
+| 20             |  ...  |   10  |    41 |  310  | 1330  |
+| 25             |  ...  |  ...  |    26 |  200  |  850  |
+| 30             |  ...  |  ...  |    18 |  140  |  590  |
+| 35             |  ...  |  ...  |    13 |  100  |  430  |
+| 40             |  ...  |  ...  |    10 |   79  |  330  |
+| 45             |  ...  |  ...  |   ... |   62  |  260  |
+| 50             |  ...  |  ...  |   ... |   50  |  210  |
+|________________|_______|_______|_______|_______|_______|
+</pre>
+    <p>
+      TABLE (A).
+    </p>
+    <p>
+      Showing the Quantities [Q] (in cubic feet) of Acetylene which will pass in
+      One Hour through Pipes of various diameters (in inches) under different
+      Falls of Pressure. (Based on Morel's formula.)
+    </p>
+<pre xml:space="preserve">
+ ____________________________________________________________________
+|          |    |    |    |     |     |     |    |    |    |    |    |
+| Diameter |    |    |    |     |     |     |    |    |    |    |    |
+| of Pipe  | 1/4| 3/8| 1/2| 3/4 |  1  |  1  |  1 |  1 |  2 |  2 |  3 |
+| [_d_] =  |    |    |    |     |     | 1/4 | 1/2| 3/4|    | 1/2|    |
+| inches   |    |    |    |     |     |     |    |    |    |    |    |
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |    Fall of Pressure in the Pipe [_h_] = 0.10 inch.      |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|    10    | 7.2|19.9|40.8|112  |230  |405  | 635| 935|1305|2285|3600|
+|    25    | 4.5|12.6|25.8| 71.2|146  |255  | 400| 590| 825|1445|2280|
+|    50    | 3.2| 8.9|18.3| 50.3|103  |180  | 285| 420| 585|1020|1610|
+|   100    | 2.3| 6.3|12.9| 35.6| 73.1|127  | 200| 295| 410| 720|1140|
+|   200    | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
+|   300    | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
+|   400    | 1.1| 3.1| 6.4| 17.8| 36.5| 63.8| 100| 148| 205| 360| 570|
+|   500    | 1.0| 2.8| 5.8| 15.9| 32.7| 57.1|  90| 132| 185| 320| 510|
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |    Fall of Pressure in the Pipe [_h_] = 0.25 inch.      |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|    25    | 7.2|19.9|40.8|112  |230  |405  | 635| 935|1305|2285|3600|
+|    50    | 5.1|14.1|28.9| 79.6|163  |285  | 450| 660| 925|1615|2550|
+|   100    | 3.6| 9.9|20.4| 56.3|115  |200  | 320| 470| 655|1140|1800|
+|   250    | 2.3| 6.3|12.9| 35.6| 73.1|127  | 200| 295| 410| 720|1140|
+|   500    | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
+|  1000    | 1.1| 3.1| 6.4| 17.8| 36.5| 63.8| 100| 148| 205| 360| 570|
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |    Fall of Pressure in the Pipe [_h_] = 0.50 inch.      |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|    25    |10.2|28.1|57.8|159  |325  |570  | 900|1325|1850|3230|5095|
+|    50    | 7.2|19.9|40.8|112  |230  |405  | 635| 935|1305|2285|3600|
+|   100    | 5.1|14.1|28.9| 79.6|163  |285  | 450| 660| 925|1615|2550|
+|   250    | 3.2| 8.9|18.3| 50.3|103  |180  | 285| 420| 585|1020|1610|
+|   500    | 2.3| 6.3|12.9| 35.6| 73.1|127  | 200| 295| 410| 720|1140|
+|  1000    | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |    Fall of Pressure in the Pipe [_h_] = 0.75 inch.      |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|    50    | 8.8|24.4|50.0|138  |280  |495  | 780|1145|1160|2800|4410|
+|   100    | 6.2|17.2|35.4| 97.5|200  |350  | 550| 810|1130|1980|3120|
+|   250    | 3.9|10.9|22.4| 61.7|126  |220  | 350| 510| 715|1250|1975|
+|   500    | 2.8| 7.7|15.8| 43.6| 89.5|156  | 245| 360| 505| 885|1395|
+|  1000    | 2.0| 5.4|11.2| 30.8| 63.3|110  | 174| 255| 360| 625| 985|
+|  2000    | 1.4| 3.8| 7.9| 21.8| 44.8| 78.2| 123| 181| 250| 440| 695|
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |    Fall of Pressure in the Pipe [_h_] = 1.0 inch.       |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|   100    | 7.2|19.9|40.8|112  |230  |405  | 635| 935|1305|2285|3600|
+|   250    | 4.5|12.6|25.8| 71.2|146  |255  | 400| 590| 825|1445|2280|
+|   500    | 3.2| 8.9|18.3| 50.3|103  |180  | 285| 420| 585|1020|1610|
+|  1000    | 2.3| 6.3|12.9| 35.6| 73.1|127  | 200| 295| 410| 720|1140|
+|  2000    | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
+|  3000    | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
+|__________|_________________________________________________________|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |    Fall of Pressure in the Pipe [_h_] = 1.5 inch.       |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|   250    | 5.6|15.4|31.6| 87.2|179  |310  | 495| 725|1010|1770|2790|
+|   500    | 3.9|10.9|22.4| 61.7|126  |220  | 350| 510| 715|1250|1975|
+|  1000    | 2.8| 7.7|15.8| 43.6| 89.5|156  | 245| 360| 505| 885|1395|
+|  2000    | 2.0| 5.4|11.2| 30.8| 63.3|110  | 174| 255| 360| 625| 985|
+|  3000    | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
+|  4000    | 1.4| 3.8| 7.9| 21.8| 44.8| 78.2| 123| 181| 250| 440| 695|
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+|          |                                                         |
+| Length   |                                                         |
+| of Pipe  |                                                         |
+| [_l_] =  |   Fall of Pressure in the Pipe [_h_] = 2.0 inches.      |
+| Feet     |                                                         |
+|__________|_________________________________________________________|
+|          |    |    |    |     |     |     |    |    |    |    |    |
+|   500    | 4.5|12.6|25.8| 71.2|146  |255  | 400| 590| 825|1445|2280|
+|  1000    | 3.2| 8.9|18.3| 50.3|103  |180  | 285| 420| 585|1020|1610|
+|  2000    | 2.3| 6.3|12.9| 35.6| 73.1|127  | 200| 295| 410| 720|1140|
+|  3000    | 1.8| 5.1|10.5| 29.1| 59.7|104  | 164| 240| 335| 590| 930|
+|  4000    | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
+|  5000    | 1.4| 4.0| 8.1| 22.5| 46.2| 80.8| 127| 187| 260| 455| 720|
+|  6000    | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
+|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
+</pre>
+    <p>
+      NOTE.--In order not to impart to the above table the appearance of the
+      quantities having been calculated to a degree of accuracy which has no
+      practical significance, quantities of less than 5 cubic feet have been
+      ignored when the total quantity exceeds 200 cubic feet, and fractions of a
+      cubic foot have been included only when the total quantity is less than
+      100 cubic feet.
+    </p>
+    <p>
+      TABLE (C).
+    </p>
+    <p>
+      Giving the Sizes of Pipe which should be used in practice for Acetylene
+      when the fall of pressure in the Pipe is not to exceed 0.25 inch. (Based
+      on Morel's formula.)
+    </p>
+<pre xml:space="preserve">
+ ____________________________________________________________________
+|            |                                                       |
+| Cubic feet |                                                       |
+|     of     |                                                       |
+| Acetylene  | Diameters of Pipe to be used up to the lengths stated.|
+| which the  |                                                       |
+|  Pipe is   |                                                       |
+|  required  |_______________________________________________________|
+|  to pass   |      |      |      |      |      |      |      |      |
+|  in One    |  1/4 |  1/2 |  3/4 |   1  | 1-1/4| 1-1/2| 1-3/4|   2  |
+|   Hour     | inch.| inch.| inch.| inch.| inch.| inch.| inch.| inch.|
+|____________|______|______|______|______|______|______|______|______|
+|            |      |      |      |      |      |      |      |      |
+|            | Feet.| Feet.| Feet.| Feet.| Feet.| Feet.| Feet.| Feet.|
+|    2-1/2   | 1580 | 6680 | 50750|  ... |  ... |  ... | ...  |  ... |
+|    5       |  390 | 1670 | 12690| 53160|  ... |  ... | ...  |  ... |
+|    7-1/2   |  175 |  710 |  5610| 23760|  ... |  ... | ...  |  ... |
+|   10       |   99 |  410 |  3170| 13360| 40790|  ... | ...  |  ... |
+|   15       |   41 |  185 |  1410|  5940| 18130| 45110| ...  |  ... |
+|   20       |   24 |  105 |   790|  3350| 10190| 25370| 54840|  ... |
+|   25       |   26 |   67 |   500|  2130|  6520| 16240| 35100|  ... |
+|   30       |   11 |   46 |   350|  1480|  4530| 11270| 24370| 47520|
+|   35       |  ... |   34 |   260|  1090|  3330|  8280| 17900| 34910|
+|   40       |  ... |   26 |   195|   830|  2550|  6340| 13710| 26730|
+|   45       |  ... |   20 |   155|   660|  2010|  5010| 10830| 21120|
+|   50       |  ... |   16 |   125|   530|  1630|  4060|  8770| 17110|
+|   60       |  ... |   11 |    88|   370|  1130|  2880|  6090| 11880|
+|   70       |  ... |  ... |    61|   270|   830|  2070|  4470|  8730|
+|   80       |  ... |  ... |    49|   210|   630|  1580|  3420|  6680|
+|   90       |  ... |  ... |    39|   165|   500|  1250|  2700|  5280|
+|  100       |  ... |  ... |    31|   130|   400|  1010|  2190|  4270|
+|  150       |  ... |  ... |    14|    59|   180|   450|   970|  1900|
+|  200       |  ... |  ... |  ... |    33|   100|   250|   540|  1070|
+|  250       |  ... |  ... |  ... |    21|    65|   160|   350|   680|
+|  500       |  ... |  ... |  ... |  ... |    16|    40|    87|   170|
+| 1000       |  ... |  ... |  ... |  ... |  ... |    10|    22|    42|
+|____________|______|______|______|______|______|______|______|______|
+</pre>
+    <p>
+      TABLE (D).
+    </p>
+    <p>
+      Giving the Sizes of Pipe which should be used in practice for Acetylene
+      Mains when the fall of pressure in the Main is not to exceed 0.5 inch,
+      (Based on Morel's formula.)
+    </p>
+<pre xml:space="preserve">
+ ____________________________________________________________________
+|            |                                                       |
+| Cubic feet |                                                       |
+|     of     |                                                       |
+| Acetylene  | Diameters of Pipe to be used up to the lengths stated.|
+| which the  |                                                       |
+|  Main is   |                                                       |
+|  required  |_______________________________________________________|
+|  to pass   |      |      |      |      |      |      |      |      |
+|  in One    | 3/4  |   1  | 1-1/4| 1-1/2| 1-3/4|   2  | 2-1/2|   3  |
+|   Hour     | inch.| inch.| inch.| inch.| inch.| inch.| inch.| inch.|
+|____________|______|______|______|______|______|______|______|______|
+|            |      |      |      |      |      |      |      |      |
+|            |Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|
+|     10     | 5.05 |  ... |  ... |  ... |  ... |  ... |  ... |  ... |
+|     25     | 0.80 | 2.45 | 6.15 |  ... |  ... |  ... |  ... |  ... |
+|     50     | 0.20 | 0.60 | 1.50 | 3.30 | 6.45 |  ... |  ... |  ... |
+|    100     | 0.05 | 0.15 | 0.35 | 0.80 | 1.60 | 4.95 |12.30 |  ... |
+|    200     |  ... | 0.04 | 0.09 | 0.20 | 0.40 | 1.20 | 3.05 |12.95 |
+|    300     |  ... |  ... | 0.04 | 0.09 | 0.18 | 0.55 | 1.35 | 5.75 |
+|    400     |  ... |  ... |  ... | 0.05 | 0.10 | 0.30 | 0.75 | 3.25 |
+|    500     |  ... |  ..  |  ... | 0.03 | 0.06 | 0.20 | 0.50 | 2.05 |
+|    750     |  ... |  ... |  ... |  ... | 0.03 | 0.08 | 0.20 | 0.80 |
+|   1100     |  ... |  ... |  ... |  ... |  ... | 0.05 | 0.12 | 0.50 |
+|   1500     |  ... |  ... |  ... |  ... |  ... | 0.02 | 0.05 | 0.23 |
+|   2000     |  ... |  ... |  ... |  ... |  ... |  ... | 0.03 | 0.13 |
+|   2500     |  ... |  ... |  ... |  ... |  ... |  ... | 0.02 | 0.08 |
+|   5000     |  ... |  ... |  ... |  ... |  ... |  ... |  ... | 0.03 |
+|____________|______|______|______|______|______|______|______|______|
+</pre>
+    <p>
+      TABLE (E).
+    </p>
+    <p>
+      Giving the Sizes of Pipe which should be used in practice for Acetylene
+      Mains when the fall of pressure in the Main is not to exceed 1.0 inch.
+      (Based on Morel's formula.)
+    </p>
+<pre xml:space="preserve">
+ __________________________________________________________________
+|            |                                                     |
+| Cubic feet |                                                     |
+|     of     |                                                     |
+| Acetylene  |Diameters of Pipe to be used up to the lengths stated|
+| which the  |                                                     |
+|  Main is   |                                                     |
+|  required  |_____________________________________________________|
+|  to pass   |     |     |     |     |     |     |     |     |     |
+|  in One    | 3/4 |  1  |1-1/4|1-1/2|1-3/4|  2  |2-1/2|  3  |  4  |
+|   Hour     |inch.|inch.|inch.|inch.|inch.|inch.|inch.|inch.|inch.|
+|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|
+|            |     |     |     |     |     |     |     |     |     |
+|            |Miles|Miles|Miles|Mile.|Miles|Miles|Miles|Miles|Miles|
+|     10     | 2.40|10.13|30.90| ... | ... | ... | ... | ... | ... |
+|     25     | 0.38| 1.62| 4.94|12.30| ... | ... | ... | ... | ... |
+|     50     | 0.09| 0.40| 1.23| 3.07| 6.65|12.96| ... | ... | ... |
+|    100     | 0.02| 0.10| 0.30| 0.77| 1.66| 3.24| 9.88| ... | ... |
+|    200     | ... | 0.02| 0.07| 0.19| 0.41| 0.81| 2.47| 6.15| ... |
+|    300     | ... | 0.01| 0.03| 0.08| 0.18| 0.36| 1.09| 2.73|11.52|
+|    400     | ... | ... | 0.0 | 0.05| 0.10| 0.20| 0.61| 1.53| 6.48|
+|    500     | ... | ... | 0.0 | 0.03| 0.06| 0.13| 0.39| 0.98| 4.14|
+|    750     | ... | ... | ... | 0.01| 0.03| 0.05| 0.17| 0.43| 1.84|
+|   1000     | ... | ... | ... | ... | 0.01| 0.03| 0.10| 0.24| 1.03|
+|   1500     | ... | ... | ... | ... | ... | 0.01| 0.01| 0.11| 0.46|
+|   2000     | ... | ... | ... | ... | ... | ... | 0.02| 0.06| 0.26|
+|   2500     | ... | ... | ... | ... | ... | ... | 0.01| 0.04| 0.16|
+|   5000     | ... | ... | ... | ... | ... | ... | ... | 0.01| 0.04|
+|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|
+</pre>
+    <p>
+      <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkviii" id="viii">CHAPTER VIII</a>
+    </h2>
+    <h3>
+      COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION
+    </h3>
+    <p>
+      NATURE OF LUMINOUS FLAMES.--When referring to methods of obtaining
+      artificial light by means of processes involving combustion or oxidation,
+      the term "incandescence" is usually limited to those forms of burner in
+      which some extraneous substance, such as a "mantle," is raised to a
+      brilliant white heat. Though convenient, the phrase is a mere convention,
+      for all artificial illuminants, even including the electric light, which
+      exhibit a useful degree of intensity depend on the same principle of
+      incandescence. Adopting the convention, however, an incandescent burner is
+      one in which the fuel burns with a non-luminous or atmospheric flame, the
+      light being produced by causing that flame to play upon some extraneous
+      refractory body having the property of emitting much light when it is
+      raised to a sufficiently high temperature; while a luminous burner is one
+      in which the fuel is allowed to combine with atmospheric oxygen in such a
+      way that one or more of the constituents in the gas evolves light as it
+      suffers combustion. From the strictly chemical point of view the
+      light-giving substance in the incandescent flame lasts indefinitely, for
+      it experiences no change except in temperature; whereas the light-giving
+      substance in a luminous flame lasts but for an instant, for it only
+      evolves light during the act of its combination with the oxygen of the
+      atmosphere. Any fluid combustible which burns with a flame can be made to
+      give light on the incandescent system, for all such materials either burn
+      naturally, or can be made to burn with a non- luminous flame, which can be
+      employed to raise the temperature of some mantle; but only those fuels can
+      be burnt on the self-luminous system which contain some ingredient that is
+      liberated in the elemental state in the flame, the said ingredient being
+      one which combines energetically with oxygen so as to liberate much local
+      heat. In practice, just as there are only two or three substances which
+      are suitable for the construction of an incandescent mantle, so there is
+      only one which renders a flame usefully self-luminous, viz., carbon; and
+      therefore only such fuels as contain carbon among their constituents can
+      be burnt so as to produce light without the assistance of the mantle. But
+      inasmuch as it is necessary for the evolution of light by the combustion
+      of carbon that that carbon shall be in the free state, only those
+      carbonaceous fuels yield light without the mantle in which the
+      carbonaceous ingredient is dissociated into its elements before it is
+      consumed. For instance, alcohol and carbon monoxide are both combustible,
+      and both contain carbon; but they yield non-luminous flames, for the
+      carbon burns to carbon dioxide in ordinary conditions without assuming the
+      solid form; ether, petroleum, acetylene, and some of the hydrocarbons of
+      coal-gas do emit light on combustion, for part of their carbon is so
+      liberated. The quantity of light emitted by the glowing substance
+      increases as the temperature of that substance rises: the gain in light
+      being equal to the fifth or higher power of the gain in heat; [Footnote:
+      Calculated from absolute zero.] therefore unnecessary dissipation of heat
+      from a flame is one of the most important matters to be guarded against if
+      that flame is to be an economical illuminant. But the amount of heat
+      liberated when a certain weight (or volume) of a particular fuel combines
+      with a sufficient quantity of oxygen to oxidise it wholly is absolutely
+      fixed, and is exactly the same whether that fuel is made to give a
+      luminous or a non-luminous flame. Nevertheless the atmospheric flame given
+      by a certain fuel may be appreciably hotter than its luminous flame,
+      because the former is usually smaller than the latter. Unless the luminous
+      flame of a rich fuel is made to expose a wide surface to the air, part of
+      its carbon may escape ultimate combustion; soot or smoke may be produced,
+      and some of the most valuable heat-giving substance will be wasted. But if
+      the flame is made to expose a large surface to the air, it becomes flat or
+      hollow in shape instead of being cylindrical and solid, and therefore in
+      proportion to its cubical capacity it presents to the cold air a larger
+      superficies, from which loss of heat by radiation, &amp;c., occurs. Being
+      larger, too, the heat produced is less concentrated.
+    </p>
+    <p>
+      It does not fall within the province of the present book to discuss the
+      relative merits of luminous and incandescent lighting; but it may be
+      remarked that acetylene ranks with petroleum against coal-gas, carburetted
+      or non-carburetted water-gas, and semi-water-gas, in showing a
+      comparatively small degree of increased efficiency when burnt under the
+      mantle. Any gas which is essentially composed of carbon monoxide or
+      hydrogen alone (or both together) burns with a non-luminous flame, and can
+      therefore only be used for illuminating purposes on the incandescent
+      system; but, broadly speaking, the higher is the latent illuminating power
+      of the gas itself when burnt in a non-atmospheric burner, the less marked
+      is the superiority, both from the economical and the hygienic aspect, of
+      its incandescent flame. It must be remembered also that only a gas yields
+      a flame when it is burnt; the flame of a paraffin lamp and of a candle is
+      due to the combustion of the vaporised fuel. Methods of burning acetylene
+      under the mantle are discussed in Chapter IX.; here only self-luminous
+      flames are being considered, but the theoretical question of heat economy
+      applies to both processes.
+    </p>
+    <p>
+      Heat may be lost from a flame in three several ways: by direct radiation
+      and conduction into the surrounding air, among the products of combustion,
+      and by conduction into the body of the burner. Loss of heat by radiation
+      and conduction to the air will be the greater as the flame exposes a
+      larger surface, and as a more rapid current of cold air is brought into
+      proximity with the flame. Loss of heat by conduction, into the burner will
+      be the greater as the material of which the burner is constructed is a
+      better conductor of heat, and as the mass of material in that burner is
+      larger. Loss of heat by passage into the combustion products will also be
+      greater as these products are more voluminous; but the volume of true
+      combustion products from any particular gas is a fixed quantity, and since
+      these products must leave the flame at the temperature of that
+      flame--where the highest temperature possible is requisite--it would seem
+      that no control can be had over the quantity of heat so lost. However,
+      although it is not possible in practice to supply a flame with too little
+      air, lest some of its carbon should escape consumption and prove a
+      nuisance, it is very easy without conspicuous inconvenience to supply it
+      with too much; and if the flame is supplied with too much, there is an
+      unnecessary volume of air passing through it to dilute the true combustion
+      products, which air absorbs its own proper proportion of heat. It is only
+      the oxygen of the air which a flame needs, and this oxygen is mixed with
+      approximately four times its volume of nitrogen; if, then, only a small
+      excess of oxygen (too little to be noticeable of itself) is admitted to a
+      flame, it is yet harmful, because it brings with it four times its volume
+      of nitrogen, which has to be raised to the same temperature as the oxygen.
+      Moreover, the nitrogen and the excess of oxygen occupy much space in the
+      flame, making it larger, and distributing that fixed quantity of heat
+      which it is capable of generating over an unnecessarily large area. It is
+      for this reason that any gas gives so much brighter a light when burnt in
+      pure oxygen than in air, (1) because the flame is smaller and its heat
+      more concentrated, and (2) because part of its heat is not being wasted in
+      raising the temperature of a large mass of inert nitrogen. Thus, if the
+      flame of a gas which naturally gives a luminous flame is supplied with an
+      excess of air, its illuminating value diminishes; and this is true whether
+      that excess is introduced at the base of the actual flame, or is added to
+      the gas prior to ignition. In fact the method of adding some air to a
+      naturally luminous gas before it arrives at its place of combustion is the
+      principle of the Bunsen burner, used for incandescent lighting and for
+      most forms of warming and cooking stoves. A well-made modern atmospheric
+      burner, however, does not add an excess of air to the flame, as might
+      appear from what has been said; such a burner only adds part of the air
+      before and the remainder of the necessary quantity after the point of
+      first ignition--the function of the primary supply being merely to insure
+      thorough admixture and to avoid the production of elemental carbon within
+      the flame.
+    </p>
+    <p>
+      ILLUMINATING POWER.--It is very necessary to observe that, as the combined
+      losses of heat from a flame must be smaller in proportion to the total
+      heat produced by the flame as the flame itself becomes larger, the more
+      powerful and intense any single unit of artificial light is, the more
+      economical does it become, because economy of heat spells economy of
+      light. Conversely, the more powerful and intense any single unit of light
+      is, the more is it liable to injure the eyesight, the deeper and, by
+      contrast, the more impenetrable are the shadows it yields, and the less
+      pleasant and artistic is its effect in an occupied room. For economical
+      reasons, therefore, one large central source of light is best in an
+      apartment, but for physiological and �sthetic reasons a considerable
+      number of correspondingly smaller units are preferable. Even in the street
+      the economical advantage of the single unit is outweighed by the
+      inconvenience of its shadows, and by the superiority of a number of evenly
+      distributed small sources to one central large source of light whenever
+      the natural transmission of light rays through the atmosphere is
+      interfered with by mist or fog. The illuminating power of acetylene is
+      commonly stated to be "240 candles" (though on the same basis Wolff has
+      found it to be about 280 candles). This statement means that when
+      acetylene is consumed in the most advantageous self-luminous burner at the
+      most advantageous rate, that rate (expressed in cubic feet per hour) is to
+      5 in the same ratio as the intensity of the light evolved (expressed in
+      standard candles) is to the said "illuminating power." Thus, Wolff found
+      that when acetylene was burnt in the "0000 Bray" fish- tail burner at the
+      rate of 1.377 cubic feet per hour, a light of 77 candle-power was
+      obtained. Hence, putting x to represent the illuminating power of the
+      acetylene in standard candles, we have:
+    </p>
+    <p>
+      1.377 / 5 = 77 / x hence x = 280.
+    </p>
+    <p>
+      Therefore acetylene is said to have, according to Wolff, an illuminating
+      power of about 280 candles, or according to other observers, whose results
+      have been commonly quoted, of 240 candles. The same method of calculating
+      the nominal illuminating power of a gas is applied within the United
+      Kingdom in the case of all gases which cannot be advantageously burnt at
+      the rate of 5 cubic feet per hour in the standard burner (usually an
+      Argand). The rate of 5 cubic feet per hour is specified in most Acts of
+      Parliament relating to gas-supply as that at which coal-gas is to be burnt
+      in testings of its illuminating power; and the illuminating power of the
+      gas is defined as the intensity, expressed in standard candles, of the
+      light afforded when the gas is burnt at that rate. In order to make the
+      values found for the light evolved at more advantageous rates of
+      consumption by other descriptions of gas--such as oil-gas or
+      acetylene--comparable with the "illuminating power" of coal- gas as
+      defined above, the values found are corrected in the ratio of the actual
+      rate of consumption to 5 cubic feet per hour.
+    </p>
+    <p>
+      In this way the illuminating power of 240 candles has been commonly
+      assigned to acetylene, though it would be clearer to those unfamiliar with
+      the definition of illuminating power in the Acts of Parliament which
+      regulate the testing of coal-gas, if the same fact were conveyed by
+      stating that acetylene affords a maximum illuminating power of 48 candles
+      (<i>i.e.</i>, 240 / 5) per cubic foot. Actually, by misunderstanding of
+      the accepted though arbitrary nomenclature of gas photometry, it has not
+      infrequently been assorted or implied that a cubic foot of acetylene
+      yields a light of 240 candle-power instead of 48 candle-power. It should,
+      moreover, be remembered that the ideal illuminating power of a gas is the
+      highest realisable in any Argand or flat-flame burner, while the said
+      burner may not be a practicable one for general use in house lighting.
+      Thus, the burners recommended for general use in lighting by acetylene do
+      not develop a light of 48 candles per cubic foot of gas consumed, but
+      considerably less, as will appear from the data given later in this
+      chapter.
+    </p>
+    <p>
+      It has been stated that in order to avoid loss of heat from a flame
+      through the burner, that burner should present only a small mass of
+      material (<i>i.e.</i>, be as light in weight as possible), and should be
+      constructed of a bad heat-conductor. But if a small mass of a material
+      very deficient in heat-conducting properties comes in contact with a
+      flame, its temperature rises seriously and may approach that of the base
+      of the flame itself. In the case of coal-gas this phenomenon is not
+      objectionable, is even advantageous, and it explains why a burner made of
+      steatite, which conducts heat badly, in always more economical (of heat
+      and therefore of light) than an iron one. In the case of acetylene the
+      same rule should, and undoubtedly does, apply also; but it is complicated,
+      and its effect sometimes neutralised, by a peculiarity of the gas itself.
+      It has been shown in Chapters II. and VI. that acetylene polymerises under
+      the influence of heat, being converted into other bodies of lower
+      illuminating power, together with some elemental carbon. If, now,
+      acetylene is fed into a burner which, being composed of some material like
+      steatite possessed of low heat-conducting and radiating powers, is very
+      hot, and if the burner comprises a tube of sensible length, the gas that
+      actually arrives at the orifice may no longer be pure acetylene, but
+      acetylene diluted with inferior illuminating agents, and accompanied by a
+      certain proportion of carbon. Neglecting the effect of this carbon, which
+      will be considered in the following paragraph, it is manifest that the
+      acetylene issuing from a hot burner--assuming its temperature to exceed
+      the minimum capable of determining polymerisation-- may emit less light
+      per unit of volume than the acetylene escaping from a cold burner. Proof
+      of this statement is to be found in some experiments described by Bullier,
+      who observed that when a small "Manchester" or fish-tail burner was
+      allowed to become naturally hot, the quantity of gas needed to give the
+      light of one candle (uncorrected) was 1.32 litres, but when the burner was
+      kept cool by providing it with a jacket in which water was constantly
+      circulating, only 1.13 litres of acetylene were necessary to obtain the
+      same illuminating value, this being an economy of 16 per cent.
+    </p>
+    <p>
+      EARLY BURNERS.--One of the chief difficulties encountered in the early
+      days of the acetylene industry was the design of a satisfactory burner
+      which should possess a life of reasonable length. The first burners tried
+      were ordinary oil-gas jets, which resemble the fish-tails used with coal-
+      gas, but made smaller in every part to allow for the higher illuminating
+      power of the oil-gas or acetylene per unit of volume. Although the flames
+      they gave were very brilliant, and indeed have never been surpassed, the
+      light quickly fell off in intensity owing to the distortion of their
+      orifices caused by the deposition of solid matter at the edges. Various
+      explanations have been offered to account for the precipitation of solid
+      matter at the jets. If the acetylene passes directly to the burner from a
+      generator having carbide in excess without being washed or filtered in any
+      way, the gas may carry with it particles of lime dust, which will collect
+      in the pipes mainly at the points where they are constricted; and as the
+      pipes will be of comparatively large bore until the actual burner is
+      readied, it will be chiefly at the orifices where the deposition occurs.
+      This cause, though trivial, is often overlooked. It will be obviated
+      whenever the plant is intelligently designed. As the phosphoric anhydride,
+      or pentoxide, which is produced when a gas containing phosphorus burns, is
+      a solid body, it may be deposited at the burner jets. This cause may be
+      removed, or at least minimised, by proper purification of the acetylene,
+      which means the removal of phosphorus compounds. Should the gas contain
+      hydrogen silicide siliciuretted hydrogen), solid silica will be produced
+      similarly, and will play its part in causing obstruction. According to
+      Lewes the main factor in the blocking of the burners is the presence of
+      liquid polymerised products in the acetylene, benzene in particular; for
+      he considers that these bodies will be absorbed by the porous steatite,
+      and will be decomposed under the influence of heat in that substance,
+      saturating the steatite with carbon which, by a "catalytic" action
+      presumably, assists in the deposition of further quantities of carbon in
+      the burner tube until distortion of the flame results. Some action of this
+      character possibly occurs; but were it the sole cause of blockage, the
+      trouble would disappear entirely if the gas were washed with some suitable
+      heavy oil before entering the burners, or if the latter were constructed
+      of a non-porous material. It is certainly true that the purer is the
+      acetylene burnt, both as regards freedom from phosphorus and absence of
+      products of polymerisation, the longer do the burners last; and it has
+      been claimed that a burner constructed at its jets of some non-porous
+      substance, e.g., "ruby," does not choke as quickly as do steatite ones.
+      Nevertheless, stoppages at the burners cannot be wholly avoided by these
+      refinements. Gaud has shown that when pure acetylene is burnt at the
+      normal rate in 1-foot Bray jets, growths of carbon soon appear, but do not
+      obstruct the orifices during 100 hours' use; if, however, the gas-supply
+      is checked till the flame becomes thick, the growths appear more quickly,
+      and become obstructive after some 60 hours' burning. On the assumption
+      that acetylene begins to polymerise at a temperature of 100� C., Gaud
+      calculates that polymerisation cannot cause blocking of the burners unless
+      the speed of the passing gas is so far reduced that the burner is only
+      delivering one- sixth of its proper volume. But during 1902 Javal
+      demonstrated that on heating in a gas-flame one arm of a twin,
+      non-injector burner which had been and still was behaving quite
+      satisfactorily with highly purified acetylene, growths were formed at the
+      jet of that arm almost instantaneously. There is thus little doubt that
+      the principal cause of this phenomenon is the partial dissociation of the
+      acetylene (i.e., decomposition into its elements) as it passes through the
+      burner itself; and the extent of such dissociation will depend, not at all
+      upon the purity of the gas, but upon the temperature of the burner, upon
+      the readiness with which the heat of the burner is communicated to the
+      gas, and upon the speed at which the acetylene travels through the burner.
+    </p>
+    <p>
+      Some experiments reported by R. Granjon and P. Mauricheau-Beaupr� in 1906
+      indicate, however, that phosphine in the gas is the primary cause of the
+      growths upon non-injector burners. According to these investigators the
+      combustion of the phosphine causes a deposit at the burner orifices of
+      phosphoric acid, which is raised by the flame to a temperature higher than
+      that of the burner. This hot deposit then decomposes some acetylene, and
+      the carbon deposited therefrom is rendered incombustible by the phosphoric
+      acid which continues to be produced from the combustion of the phosphine
+      in the gas. The incombustible deposit of carbon and phosphoric acid thus
+      produced ultimately chokes the burner.
+    </p>
+    <p>
+      It will appear in Chapter XI. that some of the first endeavours to avoid
+      burner troubles were based on the dilution of the acetylene with carbon
+      dioxide or air before the gas reached the place of combustion; while the
+      subsequent paragraphs will show that the same result is arrived at more
+      satisfactorily by diluting the acetylene with air during its actual
+      passage through the burner. It seems highly probable that the beneficial
+      effect of the earliest methods was due simply or primarily to the
+      dilution, the molecules of the acetylene being partially protected from
+      the heat of the burner by the molecules of a gas which was not injured by
+      the high temperature, and which attracted to itself part of the heat that
+      would otherwise have been communicated to the hydrocarbon. The modern
+      injector burner exhibits the same phenomenon of dilution, and is to the
+      same extent efficacious in preventing polymerisation; but inasmuch as it
+      permits a larger proportion of air to be introduced, and as the addition
+      is made roughly half-way along the burner passage, the cold air is more
+      effectual in keeping the former part of the tip cool, and in jacketing the
+      acetylene during its travel through the latter part, the bore of which is
+      larger than it otherwise would be.
+    </p>
+    <p>
+      INJECTOR AND TWIN-FLAME BURNERS.--In practice it is neither possible to
+      cool an acetylene burner systematically, nor is it desirable to construct
+      it of such a large mass of some good heat conductor that its temperature
+      always remains below the dissociation point of the gas. The earliest
+      direct attempts to keep the burner cool were directed to an avoidance of
+      contact between the flame of the burning acetylene and the body of the
+      jet, this being effected by causing the current of acetylene to inject a
+      small proportion of air through lateral apertures in the burner below the
+      point of ignition. Such air naturally carries along with it some of the
+      heat which, in spite of all precautions, still reaches the burner; but it
+      also apparently forms a temporary annular jacket round the stream of gas,
+      preventing it from catching fire until it has arrived at an appreciable
+      distance from the jet. Other attempts were made by placing two non-
+      injector jets in such mutual positions that the two streams of gas met at
+      an angle, there to spread fan-fashion into a flat flame. This is really
+      nothing but the old fish-tail coal-gas burner--which yields its flat flame
+      by identical impingement of two gas streams--modified in detail so that
+      the bulk of the flame should be at a considerable distance from the burner
+      instead of resting directly upon it. In the fish-tail the two orifices are
+      bored in the one piece of steatite, and virtually join at their external
+      ends; in the acetylene burner, two separate pieces of steatite,
+      three-quarters of an inch or more apart, carried by completely separate
+      supports, are each drilled with one hole, and the flame stands vertically
+      midway between them. The two streams of gas are in one vertical plane, to
+      which the vertical plane of the flame is at right angles. Neither of these
+      devices singly gave a solution of the difficulty; but by combining the
+      two--the injector and the twin-flame principle--the modern flat-flame
+      acetylene burner has been evolved, and is now met with in two slightly
+      different forms known as the Billwiller and the Naphey respectively. The
+      latter apparently ought to be called the Dolan.
+    </p>
+    <p class="ctr">
+      <a href="images/239.png"><img src="images/239th.png"
+      alt="FIG. 8.--TYPICAL ACETYLENE BURNERS" /></a>
+    </p>
+    <p>
+      The essential feature of the Naphey burner is the tip, which is shown in
+      longitudinal section at A in Fig. 8. It consists of a mushroom headed
+      cylinder of steatite, drilled centrally with a gas passage, which at its
+      point is of a diameter suited to pass half the quantity of acetylene that
+      the entire burner is intended to consume. The cap is provided with four
+      radial air passages, only two of which are represented in the drawing;
+      these unite in the centre of the head, where they enter into the
+      longitudinal channel, virtually a continuation of the gas-way, leading to
+      the point of combustion by a tube wide enough to pass the introduced air
+      as well as the gas. Being under some pressure, the acetylene issuing from
+      the jet at the end of the cylindrical portion of the tip injects air
+      through the four air passages, and the mixture is finally burnt at the top
+      orifice. As pointed out in Chapter VII., the injector jet is so small in
+      diameter that even if the service-pipes leading to the tip contain an
+      explosive mixture of acetylene and air, the explosion produced locally if
+      a light is applied to the burner cannot pass backwards through that jet,
+      and all danger is obviated. One tip only of this description evidently
+      produces a long, jet-like flame, or a "rat-tail," in which the latent
+      illuminating power of the acetylene is not developed economically. In
+      practice, therefore, two of these tips are employed in unison, one of the
+      commonest methods of holding them being shown at B. From each tip issues a
+      stream of acetylene mixed with air, and to some extent also surrounded by
+      a jacket of air; and at a certain point, which forms the apex of an
+      isosceles right-angled triangle having its other angles at the orifices of
+      the tips, the gas streams impinge, yielding a flat flame, at right-
+      angles, as mentioned before, to the plane of the triangle. If the two tips
+      are three-quarters of an inch apart, and if the angle of impingement is
+      exactly 90�, the distance of each tip from the base of the flame proper
+      will be a trifle over half an inch; and although each stream of gas does
+      take fire and burn somewhat before meeting its neighbour, comparatively
+      little heat is generated near the body of the steatite. Nevertheless,
+      sufficient heat is occasionally communicated to the metal stems of these
+      burners to cause warping, followed by a want of alignment in the gas
+      streams, and this produces distortion of the flame, and possibly smoking.
+      Three methods of overcoming this defect have been used: in one the arms
+      are constructed entirely of steatite, in another they are made of such
+      soft metal as easily to be bent back again into position with the fingers
+      or pliers, in the third each arm is in two portions, screwing the one into
+      the other. The second type is represented by the original Ph�s burner, in
+      which the curved arms of B are replaced by a pair of straight divergent
+      arms of thin, soft tubing, joined to a pair of convergent wider tubes
+      carrying the two tips. The third type is met with in the Drake burner,
+      where the divergent arms are wide and have an internal thread into which
+      screws an external thread cut upon lateral prolongations of the convergent
+      tubes. Thus both the Ph�s and the Drake burner exhibit a pair of exposed
+      elbows between the gas inlet and the two tips; and these elbows are
+      utilised to carry a screwed wire fastened to an external milled head by
+      means of which any deposit of carbon in the burner tubes can be pushed
+      out. The present pattern of the Ph�s burner is shown in Fig. 9, in which
+      <i>A</i> is the burner tip, <i>B</i> the wire or needle, and <i>C</i> the
+      milled head by which the wire is screwed in and out of the burner tube.
+    </p>
+    <p class="ctr">
+      <a href="images/241.png"><img src="images/241th.png"
+      alt="FIG. 9.--IMPROVED PH�S BURNER" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/241a.png"><img src="images/241ath.png"
+      alt="FIG. 10.--'WONDER' SINGLE AND TWO-FLAME BURNERS" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/242.png"><img src="images/242th.png"
+      alt="FIG. 11.--'SUPREMA' NO. 266651, TWO-FLAME BURNER" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/242a.png"><img src="images/242ath.png"
+      alt="FIG. 12.--BRAY'S MODIFIED NAPHEY INJECTOR BURNER TIP" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/243a.png"><img src="images/243ath.png"
+      alt="FIG. 13.--BRAY'S 'ELTA' BURNER" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/243b.png"><img src="images/243bth.png"
+      alt="FIG. 14.--BRAY'S 'LUTA' BURNER" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/243c.png"><img src="images/243cth.png"
+      alt="FIG. 15.--BRAY'S 'SANSAIR' BURNER" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/243d.png"><img src="images/243dth.png"
+      alt="FIG. 16.--ADJUSTABLE 'KONA' BURNER" /></a>
+    </p>
+    <p>
+      In the original Billwiller burner, the injector gas orifice was brought
+      centrally under a somewhat larger hole drilled in a separate sheet of
+      platinum, the metal being so carried as to permit entry of air. In order
+      to avoid the expense of the platinum, the same principle was afterwards
+      used in the design of an all-steatite head, which is represented at D in
+      Fig. 8. The two holes there visible are the orifices for the emission of
+      the mixture of acetylene with indrawn air, the proper acetylene jets lying
+      concentrically below these in the thicker portions of the heads. These two
+      types of burner have been modified in a large number of ways, some of
+      which are shown at C, E, and F; the air entering through saw- cuts,
+      lateral holes, or an annular channel. Burners resembling F in outward form
+      are made with a pair of injector jets and corresponding air orifices on
+      each head, so as to produce a pair of names lying in the same plane,
+      "end-on" to one another, and projecting at either side considerably beyond
+      the body of the burner; these have the advantage of yielding no shadow
+      directly underneath. A burner of this pattern, viz., the "Wonder," which
+      is sold in this country by Hannam's, Ltd., is shown in Fig. 10, alongside
+      the single-flame "Wonder" burner, which is largely used, especially in the
+      United States. Another two-flame burner, made of steatite, by J. von
+      Schwarz of Nuremberg, and sold by L. Wiener of London, is shown in Fig.
+      11. Burners of the Argand type have also been manufactured, but have been
+      unsuccessful. There are, of course, endless modifications of flat-flame
+      burners to be found on the markets, but only a few need be described. A
+      device, which should prove useful where it may be convenient to be able to
+      turn one or more burners up or down from the same common distant spot, has
+      been patented by Forbes. It consists of the usual twin-injector burner
+      fitted with a small central pinhole jet; and inside the casing is a
+      receptacle containing a little mercury, the level of which is moved by the
+      gas pressure by an adaptation of the displacement principle. When the main
+      is carrying full pressure, both of the jets proper are alight, and the
+      burner behaves normally, but if the pressure is reduced to a certain
+      point, the movement of the mercury seals the tubes leading to the main
+      jets, and opens that of the pilot flame, which alone remains alight till
+      the pressure is increased again. Bray has patented a modification of the
+      Naphey injector tip, which is shown in Fig. 12. It will be observed that
+      the four air inlets are at right-angles to the gas-way; but the essential
+      feature of the device is the conical orifice. By this arrangement it is
+      claimed that firing back never occurs, and that the burner can be turned
+      down and left to give a small flame for considerable periods of time
+      without fear of the apertures becoming choked or distorted. As a rule
+      burners of the ordinary type do not well bear being turned down; they
+      should either be run at full power or extinguished completely. The "Elta"
+      burner, made by Geo. Bray and Co., Ltd., which is shown in Fig. 13, is an
+      injector or atmospheric burner which may be turned low without any
+      deposition of carbon occurring on the tips. A burner of simple
+      construction but which cannot be turned low is the "Luta," made by the
+      same firm and shown in Fig. 14. Of the non- atmospheric type the
+      "Sansair," also made by Geo. Bray and Co., Ltd., is extensively used. It
+      is shown in Fig. 15. In order to avoid the warping, through the heat of
+      the flame, of the arms of burners which sometimes occurs when they are
+      made of metal, a number of burners are now made with the arms wholly of
+      steatite. One of the best-known of these, of the injector type, is the
+      "Kona," made by Falk, Stadelmann and Co., of London. It is shown in Fig.
+      16, fitted with a screw device for adjusting the flow of gas, so that when
+      this adjuster has been set to give a flame of the proper size, no further
+      adjustment by means of the gas-tap is necessary. This saves the trouble of
+      manipulating the tap after the gas is lighted. The same adjusting device
+      may also be had fitted to the Ph�s burner (Fig. 9) or to the "Orka" burner
+      (Fig. 17), which is a steatite- tip injector burner with metal arms made
+      by Falk, Stadelmann and Co., Ltd. A burner with steatite arms, made by J.
+      von Schwarz of Nuremberg, and sold in this country by L. Wiener of London,
+      is shown in Fig. 18.
+    </p>
+    <p class="ctr">
+      <a href="images/244a.png"><img src="images/244ath.png"
+      alt="FIG. 17.--'ORKA' BURNER" /></a>
+    </p>
+    <p class="ctr">
+      <a href="images/244b.png"><img src="images/244bth.png"
+      alt="FIG. 18.--'SUPREMA' NO. 216469 BURNER" /></a>
+    </p>
+    <p>
+      ILLUMINATING DUTY.--The illuminating value of ordinary self-luminous
+      acetylene burners in different sizes has been examined by various
+      photometrists. For burners of the Naphey type Lewes gives the following
+      table:
+    </p>
+<pre xml:space="preserve">
+ ___________________________________________________________
+|         |           |            |          |             |
+|         |           |    Gas     |          |  Candles    |
+| Burner. | Pressure, | Consumed,  | Light in |    per      |
+|         |  Inches   | Cubic Feet | Candles. | Cubic Foot. |
+|         |           | per Hour.  |          |             |
+|_________|___________|____________|__________|_____________|
+|         |           |            |          |             |
+| No. 6   |    2.0    |    0.155   |   0.794  |     5.3     |
+| "   8   |    2.0    |    0.27    |   3.2    |    11.6     |
+| "  15   |    2.0    |    0.40    |   8.0    |    20.0     |
+| "  25   |    2.0    |    0.65    |  17.0    |    26.6     |
+| "  30   |    2.0    |    0.70    |  23.0    |    32.85    |
+| "  42   |    2.0    |    1.00    |  34.0    |    34.0     |
+|_________|___________|____________|__________|_____________|
+</pre>
+    <p>
+      From burners of the Billwiller type Lewes obtained in 1899 the values:
+    </p>
+<pre xml:space="preserve">
+ ___________________________________________________________
+|         |           |            |          |             |
+|         |           |    Gas     |          |  Candles    |
+| Burner. | Pressure, | Consumed,  | Light in |    per      |
+|         |  Inches   | Cubic Feet | Candles. | Cubic Foot. |
+|         |           | per Hour.  |          |             |
+|_________|___________|____________|__________|_____________|
+|         |           |            |          |             |
+| No. 1   |    2.0    |    0.5     |    7.0   |    11.0     |
+| "   2   |    2.0    |    0.75    |   21.0   |    32.0     |
+| "   3   |    2.0    |    0.75    |   28.0   |    37.3     |
+| "   4   |    3.0    |    1.2     |   48.0   |    40.0     |
+| "   5   |    3.5    |    2.0     |   76.0   |    38.0     |
+|_________|___________|____________|__________|_____________|
+</pre>
+    <p>
+      Neuberg gives these figures for different burners (1900) as supplied by
+      Pintsch:
+    </p>
+<pre xml:space="preserve">
+ ______________________________________________________________________
+|                    |           |            |          |             |
+|                    |    Gas    |            |  Candles |             |
+|       Burner.      | Pressure, | Consumed,  | Light in |     per     |
+|                    |  Inches   | Cubic Feet | Candles. | Cubic Foot. |
+|                    |           | per Hour.  |          |             |
+|____________________|___________|____________|__________|_____________|
+|                    |           |            |          |             |
+| No. 0, slit burner |    3.9    |    1.59    |   59.2   |    37.3     |
+| "   00000 fishtail |    1.6    |    0.81    |   31.2   |    38.5     |
+| Twin burner No. 1  |    3.2    |    0.32    |   13.1   |    40.8     |
+|  "     "    "   2  |    3.2    |    0.53    |   21.9   |    41.3     |
+|  "     "    "   3  |    3.2    |    0.74    |   31.0   |    41.9     |
+|  "     "    "   4  |    3.2    |    0.95    |   39.8   |    41.9     |
+|____________________|___________|____________|__________|_____________|
+</pre>
+    <p>
+      The actual candle-power developed by each burner was not quoted by
+      Neuberg, and has accordingly been calculated from his efficiency values.
+      It is noteworthy, and in opposition to what has been found by other
+      investigators as well as to strict theory, that Neuberg represents the
+      efficiencies to be almost identical in all sizes of the same description
+      of burner, irrespective of the rate at which it consumes gas.
+    </p>
+    <p>
+      Writing in 1902, Capelle gave for Stadelmann's twin injector burners the
+      following figures; but as he examined each burner at several different
+      pressures, the values recorded in the second, third, and fourth columns
+      are maxima, showing the highest candle-power which could be procured from
+      each burner when the pressure was adjusted so as to cause consumption to
+      proceed at the most economical rate. The efficiency values in the fifth
+      column, however, are the mean values calculated so as to include all the
+      data referring to each burner. Capelle's results have been reproduced from
+      the original on the basis that 1 <i>bougie d�cimale</i> equals 0.98
+      standard English candle, which is the value he himself ascribes to it (1
+      <i>bougie d�cimale</i> equals 1.02 candles is the value now accepted).
+    </p>
+<pre xml:space="preserve">
+ _____________________________________________________________________
+|             |         |                     |          |            |
+|   Nominal   |   Best  | Actual Consumption  | Maximum  |   Average  |
+| Consumption,| Pressure| at Stated Pressure. | Light in | Candles per|
+|   Litres.   | Inches. | Cubic Feet per Hour.| Candles. | Cubic Foot.|
+|_____________|_________|_____________________|__________|____________|
+|             |         |                     |          |            |
+|     10      |   3.5   |         0.40        |    8.4   |    21.1    |
+|     15      |   2.8   |         0.46        |   16.6   |    33.3    |
+|     20      |   3.9   |         0.64        |   25.1   |    40.0    |
+|     25      |   3.5   |         0.84        |   37.8   |    46.1    |
+|     30      |   3.5   |         0.97        |   48.2   |    49.4    |
+|_____________|_________|_____________________|__________|____________|
+</pre>
+    <p>
+      Some testings of various self-luminous burners of which the results were
+      reported by R. Granjon in 1907, gave the following results for the duty of
+      each burner, when the pressure was regulated for each burner to that which
+      afforded the maximum illuminating duty. The duty in the original paper is
+      given in litres per Carcel-hour. The candle has been taken as equal to
+      0.102 Carcel for the conversion to candles per cubic foot.
+    </p>
+<pre xml:space="preserve">
+ ___________________________________________________________________
+|                       |             |           |                 |
+|                       |   Nominal   |   Best    | Duty. Candles   |
+|        Burner.        | Consumption.| Pressure. | per cubic foot. |
+|_______________________|_____________|__________ |_________________|
+|                       |             |           |                 |
+|                       |    Litres.  |  Inches.  |                 |
+| Twin  .   .   .   .   |      10     |    2.76   |       21.2      |
+|  "    .   .   .   .   |      20     |    2.76   |       23.5      |
+|  "    .   .   .   .   |      25     |    3.94   |       30.2      |
+|  "    .   .   .   .   |      30     | 3.94-4.33 |       44.8      |
+|  ", (pair of flames)  |      35     | 3.55-3.94 |       45.6      |
+| Bray's "Manchester"   |       6     |    1.97   |       18.8      |
+|          "            |      20     |    1.97   |       35.6      |
+|          "            |      40     |    2.36   |       42.1      |
+| Rat-tail  .   .   .   |       5     |    5.5    |       21.9      |
+|    "      .   .   .   |       8     |    4.73   |       25.0      |
+| Slit or batswing  .   |      30     | 1.97-2.36 |       37.0      |
+|_______________________|_____________|___________|_________________|
+</pre>
+    <p>
+      Granjon has concluded from his investigations that the Manchester or
+      fish-tail burners are economical when they consume 0.7 cubic foot per hour
+      and when the pressure is between 2 and 2.4 inches. When these burners are
+      used at the pressure most suitable for twin burners their consumption is
+      about one-third greater than that of the latter per candle-hour. The 25 to
+      35 litres-per-hour twin burners should be used at a pressure higher by
+      about 1 inch than the 10 to 20 litres-per-hour twin burners.
+    </p>
+    <p>
+      At the present time, when the average burner has a smaller hourly
+      consumption than 1 foot per hour, it is customary in Germany to quote the
+      mean illuminating value of acetylene in self-luminous burners as being 1
+      Hefner unit per 0.70 litre, which, taking
+    </p>
+    <p>
+      1 Hefner unit = 0.913 English candle
+    </p>
+    <p>
+      1 English candle = 1.095 Hefner units,
+    </p>
+    <p>
+      works out to an efficiency of 37 candles per foot in burners probably
+      consuming between 0.5 and 0.7 foot per hour.
+    </p>
+    <p>
+      Even when allowance is made for the difficulties in determining
+      illuminating power, especially when different photometers, different
+      standards of light, and different observers are concerned, it will be seen
+      that these results are too irregular to be altogether trustworthy, and
+      that much more work must be done on this subject before the economy of the
+      acetylene flame can be appraised with exactitude. However, as certain
+      fixed data are necessary, the authors have studied those and other
+      determinations, rejecting some extreme figures, and averaging the
+      remainder; whence it appears that on an average twin-injector burners of
+      different sizes should yield light somewhat as follows:
+    </p>
+<pre xml:space="preserve">
+ _______________________________________________________
+|                      |              |                 |
+| Size of Burner in    | Candle-power |    Candles      |
+| Cubic Feet per Hour. |  Developed.  | per Cubic Foot. |
+|______________________|______________|_________________|
+|                      |              |                 |
+|         0.5          |     18.0     |      35.9       |
+|         0.7          |     27.0     |      38.5       |
+|         1.0          |     45.6     |      45.6       |
+|______________________|______________|_________________|
+</pre>
+    <p>
+      In the tabular statement in Chapter I. the 0.7-foot burner was taken as
+      the standard, because, considering all things, it seems the best, to adopt
+      for domestic purposes. The 1-foot burner is more economical when in the
+      best condition, but requires a higher gas pressure, and is rather too
+      powerful a unit light for good illuminating effect; the 0.5 burner
+      naturally gives a better illuminating effect, but its economy is surpassed
+      by the 0.7-foot burner, which is not too powerful for the human eye.
+    </p>
+    <p>
+      For convenience of comparison, the illuminating powers and duties of the
+      0.5- and 0.7-foot acetylene burners may be given in different ways:
+    </p>
+    <p>
+      ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE.
+    </p>
+<pre xml:space="preserve">
+      _0.7-foot Burner._           |      _Half-foot Burner._
+                                   |
+1 litre      =  1.36 candles.      | 1 litre      =  1.27 candles.
+1 cubic foot = 38.5 candles.       | 1 cubic foot = 35.9 candles.
+1 candle     =  0.736 litre.       | 1 candle     =  0.79 litre.
+1 candle     =  0.026 cubic foot.  | 1 candle     =  0.028 cubic foot.
+</pre>
+    <p>
+      If the two streams of gas impinge at an angle of 90�, twin-injector
+      burners for acetylene appear to work best when the gas enters them at a
+      pressure of 2 to 2.5 inches; for a higher pressure the angle should be
+      made a little acute. Large burners require to have a wider distance
+      between the jets, to be supplied with acetylene at a higher pressure, and
+      to be constructed with a smaller angle of impingement. Every burner, of
+      whatever construction and size, must always be supplied with gas at its
+      proper pressure; a pressure varying from time to time is fatal.
+    </p>
+    <p>
+      It is worth observing that although injector burners are satisfactory in
+      practice, and are in fact almost the only jets yet found to give prolonged
+      satisfaction, the method of injecting air below the point of combustion in
+      a self-luminous burner is in some respects wrong in principle. If
+      acetylene can be consumed without polymerisation in burners of the simple
+      fish-tail or bat's-wing type, it should show a higher illuminating
+      efficiency. In 1902 Javal stated that it was possible to burn thoroughly
+      purified acetylene in twin non-injector burners, provided the two jets,
+      made of steatite as usual, were arranged horizontally instead of
+      obliquely, the two streams of gas then meeting at an angle of 180�, so as
+      to yield an almost circular flame. According to Javal, whereas
+      carbonaceous growths were always produced in non-injector acetylene
+      burners with either oblique or horizontal jets, in the former case the
+      growths eventually distorted the gas orifices, but in the latter the
+      carbon was deposited in the form of a tube, and fell off from the burner
+      by its own weight directly it had grown to a length of 1.2 or 1.5
+      millimetres, leaving the jets perfectly clear and smooth. Javal has had
+      such a burner running for 10 or 12 hours per day for a total of 2071
+      hours; it did not need cleaning out on any occasion, and its consumption
+      at the end of the period was the same as at first. He found that it was
+      necessary that the tips should be of steatite, and not of metal or glass;
+      that the orifices should be drilled in a flat surface rather than at the
+      apex of a cone, and that the acetylene should be purified to the utmost
+      possible extent. Subsequent experience has demonstrated the possibility of
+      constructing non-injector burners such as that shown in Fig. 13, which
+      behave satisfactorily even though the jets are oblique. But with such
+      burners trouble will inevitably ensue unless the gas is always purified to
+      a high degree and is tolerably dry and well filtered. Non-injector burners
+      should not be used unless special care is taken to insure that the
+      installation is consistently operated in an efficient manner in these
+      respects.
+    </p>
+    <p>
+      GLOBES, &amp;C.--It does not fall within the province of the present
+      volume to treat at length of chimneys, globes, or the various glassware
+      which may be placed round a source of light to modify its appearance. It
+      should be remarked, however, that obedience to two rules is necessary for
+      complete satisfaction in all forms of artificial illumination. First, no
+      light much stronger in intensity than a single candle ought ever to be
+      placed in such a position in an occupied room that its direct rays can
+      reach the eye, or the vision will be temporarily, and may be permanently,
+      injured. Secondly, unless economy is to be wholly ignored, no coloured or
+      tinted globe or shade should ever be put round a source of artificial
+      light. The best material for the construction of globes is that which
+      possesses the maximum of translucency coupled with non-transparency, <i>i.e.</i>,
+      a material which passes the highest proportion of the light falling upon
+      it, and yet disperses that light in such different directions that the
+      glowing body cannot be seen through the globe. Very roughly speaking,
+      plain white glass, such as that of which the chimneys of oil-lamps and
+      incandescent gas-burners are composed, is quite transparent, and therefore
+      affords no protection to the eyesight; a protective globe should be rather
+      of ground or opal glass, or of plain glass to which a dispersive effect
+      has been given by forming small prisms on its inner or outer surface, or
+      both. Such opal, ground, or dispersive shades waste much light in terms of
+      illuminating power, but waste comparatively little in illuminating effect
+      well designed, they may actually increase the illuminating effect in
+      certain positions; a tinted globe, even if quite plain in figure, wastes
+      both illuminating power and effect, and is only to be tolerated for
+      so-believed aesthetic reasons. Naturally no globe must be of such figure,
+      or so narrow at either orifice, as to distort the shape of the unshaded
+      acetylene flame--it is hardly necessary to say this now, but some years
+      ago coal-gas globes were constructed with an apparent total disregard of
+      this fundamental point. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkix" id="ix">CHAPTER IX</a>
+    </h2>
+    <h3>
+      INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING
+    </h3>
+    <p>
+      MERITS OF LIGHTING BY INCANDESCENT MANTLES.--It has already been shown
+      that acetylene bases its chief claim for adoption as an illuminant in
+      country districts upon the fact that, when consumed in simple self-
+      luminous burners, it gives a light comparable in all respects save that of
+      cost to the light of incandescent coal-gas. The employment of a mantle is
+      still accompanied by several objections which appear serious to the
+      average householder, who is not always disposed either to devote
+      sufficient attention to his burners to keep them in a high state of
+      efficiency or to contract for their maintenance by the gas company or
+      others. Coal-gas cannot be burnt satisfactorily on the incandescent system
+      unless the glass chimneys and shades are kept clean, unless the mantles
+      are renewed as soon as they show signs of deterioration, and, perhaps most
+      important of all, unless the burners are frequently cleared of the dust
+      which collects round the jets. For this reason luminous acetylene ranks
+      with luminous coal-gas in convenience and simplicity, while ranking with
+      incandescent coal-gas in hygienic value. Very similar remarks apply to
+      paraffin, and, in certain countries, to denatured alcohol. Since those
+      latter illuminants are also available in rural places where coal-gas is
+      not laid on, luminous acetylene is a less advantageous means of procuring
+      artificial light than paraffin (and on occasion than coal-gas and alcohol
+      when the latter fuels are burnt under the mantle), if the pecuniary aspect
+      of the question is the only one considered. Such a comparison, however, is
+      by no means fair; for if coal- gas, paraffin, and alcohol can be consumed
+      on the incandescent system, so can acetylene; and if acetylene is
+      hygienically equal to incandescent coal-gas, it is superior thereto when
+      also burnt under the mantle. Nevertheless there should be one minor but
+      perfectly irremediable defect in incandescent acetylene, viz., a sacrifice
+      of that characteristic property of the luminous gas to emit a light
+      closely resembling that of the sun in tint, which was mentioned in Chapter
+      1. Self-luminous acetylene gives the whitest light hitherto procurable
+      without special correction of the rays, because its light is derived from
+      glowing particles of carbon which happen to be heated (because of the high
+      flame temperature) to the best possible temperature for the emission of
+      pure white light. The light of any combustible consumed on the
+      "incandescent" system is derived from glowing particles of ceria, thoria,
+      or similar metallic oxides; and the character or shade of the light they
+      emit is a function, apart from the temperature to which they are raised,
+      of their specific chemical nature. Still, the light of incandescent
+      acetylene is sufficiently pleasant, and according to Caro is purer white
+      than that of incandescent coal-gas; but lengthy tests carried out by one
+      of the authors actually show it to be appreciably inferior to luminous
+      acetylene for colour-matching, in which the latter is known almost to
+      equal full daylight, and to excel every form of artificial light except
+      that of the electric arc specially corrected by means of glass tinted with
+      copper salts.
+    </p>
+    <p>
+      CONDITIONS FOR INCANDESCENT ACETYLENE LIGHTING.--For success in the
+      combustion of acetylene on the incandescent system, however, several
+      points have to be observed. First, the gas must be delivered at a strictly
+      constant pressure to the burner, and at one which exceeds a certain limit,
+      ranging with different types and different sizes of burner from 2 to 4 or
+      5 inches of water. (The authors examined, as long ago as 1903, an
+      incandescent burner of German construction claimed to work at a pressure
+      of 1.5 inches, which it was almost impossible to induce to fire back to
+      the jets however slowly the cock was manipulated, provided the pressure of
+      the gas was maintained well above the point specified. But ordinarily a
+      pressure of about 4 inches is used with incandescent acetylene burners.)
+      Secondly, it is necessary that the acetylene shall at all times be free
+      from appreciable admixture with air, even 0.5 per cent, being highly
+      objectionable according to Caro; so that generators introducing any
+      noteworthy amount of air into the holder each time their decomposing
+      chambers are opened for recharging are not suitable for employment when
+      incandescent burners are contemplated. The reason for this will be more
+      apparent later on, but it depends on the obvious fact that if the
+      acetylene already contains an appreciable proportion of air, when a
+      further quantity is admitted at the burner inlets, the gaseous mixture
+      contains a higher percentage of oxygen than is suited to the size and
+      design of the burner, so that flashing back to the injector jets is
+      imminent at any moment, and may be determined by the slightest fluctuation
+      in pressure--if, indeed, the flame will remain at the proper spot for
+      combustion at all. Thirdly, the fact that the acetylene which is to be
+      consumed under the mantle must be most rigorously purified from phosphorus
+      compounds has been mentioned in Chapter V. Impure acetylene will often
+      destroy a mantle in two or three hours; but with highly purified gas the
+      average life of a mantle may be taken, according to Giro, at 500 or 600
+      hours. It is safer, however, to assume a rather shorter average life, say
+      300 to 400 burning hours. Fourthly, owing to the higher pressure at which
+      acetylene must be delivered to an incandescent burner and to the higher
+      temperature of the acetylene flame in comparison with coal-gas, a mantle
+      good enough to give satisfactory results with the latter does not of
+      necessity answer with acetylene; in fact, the authors have found that
+      English Welsbach coal-gas mantles of the small sizes required by
+      incandescent acetylene burners are not competent to last for more than a
+      very few hours, although, in identical conditions, mantles prepared
+      specially for use with acetylene have proved durable. The atmospheric
+      acetylene flame, too, differs in shape from an atmospheric flame of
+      coal-gas, and it does not always happen that a coal- gas mantle contracts
+      to fit the former; although it usually emits a better light (because it
+      fits better) after some 20 hours use than at first. Caro has stated that
+      to derive the best results a mantle needs to contain a larger proportion
+      of ceria than the 1 per cent. present in mantles made according to the
+      Welsbach formula, that it should be somewhat coarser in mesh, and have a
+      large orifice at the head. Other authorities hold that mantles for
+      acetylene, should contain other rare earths besides the thoria and ceria
+      of which the coal-gas mantles almost wholly consist. It seems probable,
+      however, that the composition of the ordinary impregnating fluid need not
+      be varied for acetylene mantles provided it is of the proper strength and
+      the mantles are raised to a higher temperature in manufacture than
+      coal-gas mantles by the use of either coal-gas at very high pressure or an
+      acetylene flame. The thickness of the substance of the mantle cannot be
+      greatly increased with a view to attaining greater stability without
+      causing a reduction in the light afforded. But the shape should be such
+      that the mantle conforms as closely as possible to the acetylene Bunsen
+      flame, which differs slightly with different patterns of incandescent
+      burner heads. According to L. Cadenel, the acetylene mantle should be
+      cylindrical for the lower two- thirds of its length, and slightly conical
+      above, with an opening of moderate size at the top. The head of the mantle
+      should be of slighter construction than that of coal-gas mantles. Fifthly,
+      generators belonging to the automatic variety, which in most forms
+      inevitably add more or less air to the acetylene every time they are
+      cleaned or charged, appear to have achieved most popularity in Great
+      Britain; and these frequently do not yield a gas fit for use with the
+      mantle. This state of affairs, added to what has just been said, makes it
+      difficult to speak in very favourable terms of the incandescent acetylene
+      light for use in Great Britain. But as the advantages of an acetylene not
+      contaminated with air are becoming more generally recognised, and mantles
+      of several different makes are procurable more cheaply, incandescent
+      acetylene is now more practicable than hitherto. Carburetted acetylene or
+      "carburylene," which is discussed later, is especially suitable for use
+      with mantle burners.
+    </p>
+    <p>
+      ATMOSPHERIC ACETYLENE BURNERS.--The satisfactory employment of acetylene
+      in incandescent burners, for boiling, warming, and cooking purposes, and
+      also to some extent as a motive power in small engines, demands the
+      production of a good atmospheric or non-luminous flame, <i>i.e.</i>, the
+      construction of a trustworthy burner of the Bunsen type. This has been
+      exceedingly difficult to achieve for two reasons: first, the wide range
+      over which mixtures of acetylene and air are explosive; secondly, the high
+      speed at which the explosive wave travels through such a mixture. It has
+      been pointed out in Chapter VIII. that a Bunsen burner is one in which a
+      certain proportion of air is mixed with the gas before it arrives at the
+      actual point of ignition; and as that proportion must be such that the
+      mixture falls between the upper and lower limits of explosibility, there
+      is a gaseous mixture in the burner tube between the air inlets and the
+      outlet which, if the conditions are suitable, will burn with explosive
+      force: that is to say, will fire back to the air jets when a light is
+      applied to the proper place for combustion. Such an explosion, of course,
+      is far too small in extent to constitute any danger to person or property;
+      the objection to it is simply that the shock of the explosion is liable to
+      fracture the fragile incandescent mantle, while the gas, continuing to
+      burn within the burner tube (in the case of a warming or cooking stove),
+      blocks up that tube with carbon, and exhibits the other well-known
+      troubles of a coal-gas stove which has "fired back."
+    </p>
+    <p>
+      It has been shown, however, in Chapter VI. that the range over which
+      mixtures of acetylene and air are explosive depends on the size of the
+      vessel, or more particularly on the diameter of the tube, in which they
+      are stored; so that if the burner tube between the air inlets and the
+      point of ignition can be made small enough in diameter, a normally
+      explosive mixture will cease to exhibit explosive properties. Manifestly,
+      if a tube is made very small in diameter, it will only pass a small volume
+      of gas, and it may be useless for the supply of an atmospheric burner; but
+      Le Chatelier's researches have proved that a tube may be narrowed at one
+      spot only, in such fashion that the explosive wave refuses to pass the
+      constriction, while the virtual diameter of the tube, as far as passage of
+      gas is concerned, remains considerably larger than the size of the
+      constriction itself. Moreover, inasmuch as the speed of propagation of the
+      explosion is strictly fixed by the conditions prevailing, if the speed at
+      which the mixture, of acetylene and air travels from the air inlets to the
+      point of ignition is more rapid than the speed at which the explosion
+      tends to travel from the point of ignition to the air inlets, the said
+      mixture of acetylene and air will burn quietly at the orifice without
+      attempting to fire backwards into the tube. By combining together these
+      two devices: by delivering the acetylene to the injector jet at a pressure
+      sufficient to drive the mixture of gas and air forward rapidly enough, and
+      by narrowing the leading tube either wholly or at one spot to a diameter
+      small enough, it is easy to make an atmospheric burner for acetylene which
+      behaves perfectly as long as it is fairly alight, and the supply of gas is
+      not checked; but further difficulties still remain, because at the instant
+      of lighting and extinguishing, i.e., while the tap is being turned on or
+      off, the pressure of the gas is too small to determine a flow of acetylene
+      and air within the tube at a speed exceeding that of the explosive wave;
+      and therefore the act of lighting or extinguishing is very likely to be
+      accompanied by a smart explosion severe enough to split the mantle, or at
+      least to cause the burner to fire back. Nevertheless, after several early
+      attempts, which were comparative failures, atmospheric acetylene burners
+      have been constructed that work quite satisfactorily, so that the gas has
+      become readily available for use under the mantle, or in heating stoves.
+      Sometimes success has been obtained by the employment of more than one
+      small tube leading to a common place of ignition, sometimes by the use of
+      two or more fine wire- gauze screens in the tube, sometimes by the
+      addition of an enlarged head to the burner in which head alone thorough
+      mixing of the gas and air occurs, and sometimes by the employment of a
+      travelling sleeve which serves more or less completely to block the air
+      inlets.
+    </p>
+    <p>
+      DUTY OF INCANDESCENT ACETYLENE BURNERS.--Granting that the petty troubles
+      and expenses incidental to incandescent lighting are not considered
+      prohibitive--and in careful hands they are not really serious-- and that
+      mantles suitable for acetylene are employed, the gas may be rendered
+      considerably cheaper to use per unit of light evolved by consuming it in
+      incandescent burners. In Chapter VIII. it was shown that the modern
+      self-luminous, l/2-foot acetylene burner emits a light of about 1.27
+      standard English candles per litre-hour. A large number of incandescent
+      burners, of German and French construction, consuming from 7.0 to 22.2
+      litres per hour at pressures ranging between 60 and 120 millimetres have
+      been examined by Caro, who has found them to give lights of from 10.8 to
+      104.5 Hefner units, and efficiencies of from 2.40 to 5.50 units per
+      litre-hour. Averaging his results, it may be said that incandescent
+      burners consuming from 10 to 20 litres per hour at pressures of 80 or 100
+      millimetres yield a light of 4.0 Hefner units per litre- hour. Expressed
+      in English terms, incandescent acetylene burners consuming 0.5 cubic foot
+      per hour at a pressure of 3 or 4 inches give the duties shown in the
+      following table, which may advantageously be compared with that printed in
+      Chapter VIII., page 239, for the self-luminous gas:
+    </p>
+    <p>
+      ILLUMINATING POWER OF INCANDESCENT ACETYLENE. HALF-FOOT BURNERS.
+    </p>
+<pre xml:space="preserve">
+  1 litre      =   3.65 candles   |   1 candle = 0.274 litre.
+  1 cubic foot = 103.40 candles.  |   1 candle = 0.0097 cubic foot.
+</pre>
+    <p>
+      A number of tests of the G�ntner or Schimek incandescent burners of the 10
+      and 15 litres-per-hour sizes, made by one of the authors in 1906, gave the
+      following average results when tested at a pressure of 4 inches:
+    </p>
+<pre xml:space="preserve">
+ _________________________________________________________________
+|              |                         |          |             |
+| Nominal size | Rate of Consumption per | Light in |    Duty     |
+|  of Burner.  |          Hour           | Candles  | Candles per |
+|              |                         |          |  Cubic Foot |
+|______________|_________________________|__________|_____________|
+|              |            |            |          |             |
+| Litres.      | Cubic Foot |  Litres    |          |             |
+|   10         |    0.472   |   13.35    |   46.0   |    97.4     |
+|   15         |    0.663   |   18.80    |   70.0   |   105.5     |
+|______________|____________|____________|__________|_____________|
+</pre>
+    <p>
+      These figures indicate that the duty increases slightly with the size of
+      the burner. Other tests showed that the duty increased more considerably
+      with an increase of pressure, so that mantles used, or which had been
+      previously used, at a pressure of 5 inches gave duties of 115 to 125
+      candles per cubic foot.
+    </p>
+    <p>
+      It should be noted that the burners so far considered are small, being
+      intended for domestic purposes only; larger burners exhibit higher
+      efficiencies. For instance, a set of French incandescent acetylene burners
+      examined by Fouch� showed:
+    </p>
+<pre xml:space="preserve">
+ _________________________________________________________________
+|                |          |            |          |             |
+| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
+| in Litres.     |  Inches. |  per Hour. | Candles. | Cubic Feet. |
+|________________|__________|____________|__________|_____________|
+|                |          |            |          |             |
+|       20       |    5.9   |    0.71    |    70    |     98.6    |
+|       40       |    5.9   |    1.41    |   150    |    106.4    |
+|       70       |    5.9   |    2.47    |   280    |    113.4    |
+|      120       |    5.9   |    4.23    |   500    |    118.2    |
+|________________|__________|____________|__________|_____________|
+</pre>
+    <p>
+      By increasing the pressure at which acetylene is introduced into burners
+      of this type, still larger duties may be obtained from them:
+    </p>
+<pre xml:space="preserve">
+ _________________________________________________________________
+|                |          |            |          |             |
+| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
+| in Litres.     |  Inches. |  per Hour. | Candles. | Cubic Feet. |
+|________________|__________|____________|__________|_____________|
+|                |          |            |          |             |
+|       55       |   39.4   |    1.94    |   220    |    113.4    |
+|      100       |   39.4   |    3.53    |   430    |    121.8    |
+|      180       |   39.4   |    6.35    |   820    |    129.1    |
+|      260       |   27.6   |    9.18    |  1300    |    141.6    |
+|________________|__________|____________|__________|_____________|
+</pre>
+    <p>
+      High-power burners such as these are only fit for special purposes, such
+      as lighthouse illumination, or optical lantern work, &amp;c.; and they
+      naturally require mantles of considerably greater tenacity than those
+      intended for employment with coal-gas. Nevertheless, suitable mantles can
+      be, and are being, made, and by their aid the illuminating duty of
+      acetylene can be raised from the 30 odd candles per foot of the common
+      0.5-foot self-luminous jet to 140 candles or more per foot, which is a
+      gain in efficiency of 367 per cent., or, neglecting upkeep and sundries
+      and considering only the gas consumed, an economy of nearly 79 per cent.
+    </p>
+    <p>
+      In 1902, working apparently with acetylene dissolved under pressure in
+      acetone (<i>cf.</i> Chapter XI.), Lewes obtained the annexed results with
+      the incandescent gas:
+    </p>
+<pre xml:space="preserve">
+ ________________________________________________________
+|           |             |              |              |
+| Pressure. |  Cubic Feet | Candle Power |  Candles per |
+|  Inches.  |  per Hour.  |  Developed.  |  Cubic Foot. |
+|___________|_____________|______________|______________|
+|           |             |              |              |
+|     8     |    0.883    |      65      |      73.6    |
+|     9     |    0.94     |      72      |      76.0    |
+|    10     |    1.00     |     146      |     146.0    |
+|    12     |    1.06     |     150      |     141.2    |
+|    15     |    1.25     |     150      |     120.0    |
+|    20     |    1.33     |     166      |     124.8    |
+|    25     |    1.50     |     186      |     123.3    |
+|    40     |    2.12     |     257      |     121.2    |
+|___________|_____________|______________|______________|
+</pre>
+    <p>
+      It will be seen that although the total candle-power developed increases
+      with the pressure, the duty of the burner attained a maximum at a pressure
+      of 10 inches. This is presumably due to the fact either that the same
+      burner was used throughout the tests, and was only intended to work at a
+      pressure of 10 inches or thereabouts, or that the larger burners were not
+      so well constructed as the smaller ones. Other investigators have not
+      given this maximum of duty with a medium-sized or medium-driven burner;
+      but Lewes has observed a similar phenomenon in the case of 0.7 to 0.8
+      cubic foot self-luminous jets.
+    </p>
+    <p>
+      Figures, however, which seem to show that the duty of incandescent
+      acetylene does not always rise with the size of the burner or with the
+      pressure at which the gas is delivered to it, have been published in
+      connexion with the installation at the French lighthouse at Chassiron, the
+      northern point of the Island of Ol�ron. Here the acetylene is generated in
+      hand-fed carbide-to-water generators so constructed as to give any
+      pressure up to nearly 200 inches of water column; purified by means of
+      heratol, and finally delivered to a burner composed of thirty- seven small
+      tubes, which raises to incandescence a mantle 55 millimetres in diameter
+      at its base. At a pressure of 7.77 inches of water, the burner passes 3.9
+      cubic feet of acetylene per hour, and at a pressure of 49.2 inches (the
+      head actually used) it consumes 20.06 cubic feet per hour. As shown by the
+      following table, such increment of gas pressure raises the specific
+      intensity of the light, <i>i.e.</i>, the illuminating power per unit of
+      incandescent surface, but it does not appreciably raise the duty or
+      economy of the gas. Manifestly, in terms of duty alone, a pressure of 23.6
+      inches of water-column is as advantageous as the higher Chassiron figures;
+      but since intensity of light is an important matter in a lighthouse, it is
+      found better on the whole to work the generators at a pressure of 49.2
+      inches. In studying these figures referring to the French lighthouse, it
+      is interesting to bear in mind that when ordinary six-wick petroleum oil
+      burners wore used in the same place, the specific intensity of the light
+      developed was 75 candle-power per square inch, and when that plant was
+      abandoned in favour of an oil-gas apparatus, the incandescent burner
+      yielded 161 candle-power per square inch; substitution of incandescent
+      acetylene under pressure has doubled the brilliancy of the light.
+    </p>
+<pre xml:space="preserve">
+ ___________________________________________________________
+|                     |                  |                  |
+|                     |       Duty.      |    Intensity.    |
+| Pressure in Inches. | Candle-power per | Candle-power per |
+|                     |    Cubic Foot.   |   Square Inch.   |
+|_____________________|__________________|__________________|
+|                     |                  |                  |
+|        7.77         |      105.5       |      126.0       |
+|       23.60         |      106.0       |      226.0       |
+|       31.50         |      110.0       |      277.0       |
+|       39.40         |      110.0       |      301.0       |
+|       47.30         |      106.0       |      317.0       |
+|       49.20         |      104.0       |      324.9       |
+|      196.80         |      110.0       |      383.0       |
+|_____________________|__________________|__________________|
+</pre>
+    <p>
+      When tested in modern burners consuming between 12 and 18 litres per hour
+      at a pressure of 100 millimetres (4 inches), some special forms of
+      incandescent mantles constructed of ramie fibre, which in certain respects
+      appears to be better suited than cotton for use with acetylene, have shown
+      the following degree of loss in illuminating power after prolonged
+      employment (Caro):
+    </p>
+    <p>
+      _Luminosity in Hefner Units._
+    </p>
+<pre xml:space="preserve">
+ ________________________________________________________
+|         |       |            |            |            |
+| Mantle. | New.  |   After    |   After    |   After    |
+|         |       | 100 Hours. | 200 Hours. | 400 Hours. |
+|_________|_______|____________|____________|____________|
+|         |       |            |            |            |
+| No. 1.  | 53.2  |    51.8    |    50.6    |   49.8     |
+| No. 2.  | 76.3  |    75.8    |    73.4    |   72.2     |
+| No. 3.  | 73.1  |    72.5    |    70.1    |   68.6     |
+|_________|_______|____________|____________|____________|
+</pre>
+    <p>
+      It will be seen that the maximum loss of illuminating power in 400 hours
+      was 6.4 per cent., the average loss being 6.0 per cent.
+    </p>
+    <p>
+      TYPICAL INCANDESCENT BURNERS.--Of the many burners for lighting by the use
+      of incandescent mantles which have been devised, a few of the more widely
+      used types may be briefly referred to. There is no doubt that finality in
+      the design of these burners has not yet been reached, and that
+      improvements in the direction of simplification of construction and in
+      efficiency and durability will continue to be made.
+    </p>
+    <p>
+      Among the early incandescent burners, one made by the Allgemeine Carbid
+      und Acetylen Gesellschaft of Berlin in 1900 depended on the narrowness of
+      the mixing tube and the proportioning of the gas nipple and air inlets to
+      prevent lighting-back. There was a wider concentric tube round the upper
+      part of the mixing tube, and the lower part of the mantle fitted round
+      this. The mouth of the mixing tube of this 10-litres-per-hour burner was
+      0.11 inch in diameter, and the external diameter of the middle cylindrical
+      part of the mixing tube was 0.28 inch. There was no gauze diaphragm or
+      stuffing, and firing-back did not occur until the pressure was reduced to
+      about 1.5 inches. The same company later introduced a burner differing in
+      several important particulars from the one just described. The
+      comparatively narrow stem of the mixing tube and the proportions of the
+      gas nipple and air inlets were retained, but the mixing tube was
+      surmounted by a wide chamber or burner head, in which naturally there was
+      a considerable reduction in the rate of flow of the gas. Consequently it
+      was found necessary to introduce a gauze screen into the burner head to
+      prevent firing back. The alterations have resulted in the lighting duty of
+      the burner being considerably improved. Among other burners designed about
+      1900 may be mentioned the Ackermann, the head of which consisted of a
+      series of tubes from each of which a jet of flame was produced, the
+      Fouch�, the Weber, and the Trendel. Subsequently a tubular-headed burner
+      known as the Sirius has been produced for the consumption of acetylene at
+      high pressure (20 inches and upwards).
+    </p>
+    <p>
+      The more recent burners which have been somewhat extensively used include
+      the "Schimek," made by W. G�ntner of Vienna, which is shown in Fig. 19. It
+      consists of a tapering narrow injecting nozzle within a conical chamber C
+      which is open below, and is surmounted by the mixing tube over which
+      telescopes a tube which carries the enlarged burner head G, and the
+      chimney gallery D. There are two diaphragms of gauze in the burner head to
+      prevent firing back, and one in the nozzle portion of the burner. The
+      conical chamber has a perforated base-plate below which is a circular
+      plate B which rotates on a screw cut on the lower part of the nozzle
+      portion A of the burner. This plate serves as a damper to control the
+      amount of air admitted through the base of the conical chamber to the
+      mixing tube. There are six small notches in the lower edge of the conical
+      chamber to prevent the inflow of air being cut of entirely by the damper.
+      The mixing tube in both the 10-litre and the 15-litre burner is about 0.24
+      inch in internal diameter but the burner head is nearly 0.42 inch in the
+      10-litre and 0.48 inch in the 15-litre burner. The opening in the head of
+      the burner through which the mixture of gas and air escapes to the flame
+      is 0.15 and 0.17 inch in diameter in these two sizes respectively. The
+      results of some testings made with Schimek burners have been already
+      given.
+    </p>
+    <p class="ctr">
+      <a href="images/259.png"><img src="images/259th.png"
+      alt="FIG. 19.--'SCHIMEK' BURNER" /></a>
+    </p>
+    <p>
+      The "Knappich" burner, made by the firm of Keller and Knappich of
+      Augsburg, somewhat resembles the later pattern of the Allgemeine Carbid
+      und Acetylen Gesellschaft. It has a narrow mixing tube, viz., 0.2 inch in
+      internal diameter, and a wide burner head, viz., 0.63 inch in internal
+      diameter for the 25-litre size. The only gauze diaphragm is in the upper
+      part of the burner head. The opening in the cap of the burner head, at
+      which the gas burns, is 0.22 inch in diameter. The gas nipple extends into
+      a domed chamber at the base of the mixing tube, and the internal air is
+      supplied through four holes in the base-plate of that chamber. No means of
+      regulating the effective area of the air inlet holes are provided.
+    </p>
+    <p>
+      The "Zenith" burner, made by the firm of Gebr�der Jacob of Zwickau, more
+      closely resembles the Schimek, but the air inlets are in the side of the
+      lower widened portion of the mixing tube, and are more or less closed by
+      means of an outside loose collar which may be screwed up and down on a
+      thread on a collar fixed to the mixing tube. The mixing tube is 0.24 inch,
+      and the burner head 0.475 inch in internal diameter. The opening in the
+      cap of the burner is 0.16 inch in diameter. There is a diaphragm of double
+      gauze in the cap, and this is the only gauze used in the burner.
+    </p>
+    <p>
+      All the incandescent burners hitherto mentioned ordinarily have the gas
+      nipple made in brass or other metal, which is liable to corrosion, and the
+      orifice to distortion by heat or if it becomes necessary to remove any
+      obstruction from it. The orifice in the nipple is extremely small--
+      usually less than 0.015 inch--and any slight obstruction or distortion
+      would alter to a serious extent the rate of flow of gas through it, and so
+      affect the working of the burner. In order to overcome this defect,
+      inherent to metal nipples, burners are now constructed for acetylene in
+      which the nipple is of hard incorrodible material. One of these burners
+      has been made on behalf of the Office Central de l'Ac�tyl�ne of Paris, and
+      is commonly known as the "O.C.A." burner. In it the nipple is of steatite.
+      On the inner mixing tube of this burner is mounted an elongated cone of
+      wire wound spirally, which serves both to ensure proper admixture of the
+      gas and air, and to prevent firing-back. There is no gauze in this burner,
+      and the parts are readily detachable for cleaning when required. Another
+      burner, in which metal is abolished for the nipple, is made by Geo. Bray
+      and Co., Ltd., of Leeds, and is shown in Fig. 20. In this burner the
+      injecting nipple is of porcelain.
+    </p>
+    <p class="ctr">
+      <a href="images/260.png"><img src="images/260th.png"
+      alt="FIG. 20.--BRAY'S INCANDESCENT BURNER" /></a>
+    </p>
+    <p>
+      ACETYLENE FOR HEATING AND COOKING.--Since the problem of constructing a
+      trustworthy atmospheric burner has been solved, acetylene is not only
+      available for use in incandescent lighting, but it can also be employed
+      for heating or cooking purposes, because all boiling, most warming, and
+      some roasting stoves are simply arrangements for utilising the heat of a
+      non-luminous flame in one particular way. With suitable alterations in the
+      dimensions of the burners, apparatus for consuming coal-gas may be
+      imitated and made fit to burn acetylene; and as a matter of fact several
+      firms are now constructing such appliances, which leave little or nothing
+      to be desired. It may perhaps be well to insist upon the elementary point
+      which is so frequently ignored in practice, viz., that no stove, except
+      perhaps a small portable boiling ring, ought ever to be used in an
+      occupied room unless it is connected with a chimney, free from down-
+      draughts, for the products of combustion to escape into the outer air; and
+      also that no chimney, however tall, can cause an up-draught in all states
+      of the weather unless there is free admission of fresh air into the room
+      at the base of the chimney. Still, at the prices for coal, paraffin oil,
+      and calcium carbide which exist in Great Britain, acetylene is not an
+      economical means of providing artificial heat. If a 0.7 cubic foot
+      luminous acetylene burner gives a light of 27 candles, and if ordinary
+      country coal-gas gives light of 12 to 13 candles in a 5-foot burner, one
+      volume of acetylene is equally valuable with 15 or 16 volumes of coal-gas
+      when both are consumed in self-luminous jets; and if, with the mantle,
+      acetylene develops 99 candles per cubic foot, while coal-gas gives in
+      common practice 15 to 20 candles, one volume of acetylene is equally
+      valuable with 5 to 6-1/2 volumes of coal-gas when both are consumed on the
+      incandescent system; whereas, if the acetylene is burnt in a flat flame,
+      and the coal-gas under the mantle, 1 volume of the former is equally
+      efficient with 2 volumes of coal-gas as an artificial illuminant. This
+      last method of comparison being manifestly unfair, acetylene may be said
+      to be at least five times as efficient per unit of volume as coal-gas for
+      the production of light. But from the table given on a later page it
+      appears that as a source of artificial heat, acetylene is only equal to
+      about 2-3 times its volume of ordinary coal-gas. Nevertheless, the
+      domestic advantages of gas firing are very marked; and when a properly
+      constructed stove is properly installed, the hygienic advantages of
+      gas-firing are alone equally conspicuous--for the disfavor with which
+      gas-firing is regarded by many physicians is due to experience gained with
+      apparatus warming principally by convection [Footnote: Radiant heat is
+      high-temperature heat, like the heat emitted by a mass of red-hot coke;
+      convected heat is low-temperature heat, invisible to the eye. Radiant heat
+      heats objects first, and leaves them to warm the air; convected heat is
+      heat applied directly to air, and leaves the air to warm objects
+      afterwards. On all hygienic grounds radiant heat is better than convected
+      heat, but the latter is more economical. By an absurd and confusing
+      custom, that particular warming apparatus (gas, steam, or hot water) which
+      yields practically no radiant heat, and does all its work by convection,
+      is known to the trade as a "radiator."] instead of radiation; or to
+      acquaintance with intrinsically better stoves either not connected to any
+      flues or connected to one deficient in exhausting power. In these
+      circumstances, whenever an installation of acetylene has been laid down
+      for the illumination of a house or district, the merit of convenience may
+      outweigh the defect of extravagance, and the gas may be judiciously
+      employed in a boiling ring, or for warming a bedroom; while, if pecuniary
+      considerations are not paramount, the acetylene may be used for every
+      purpose to which the townsman would apply his cheaper coal-gas.
+    </p>
+    <p>
+      The difficulty of constructing atmospheric acetylene burners in which the
+      flame would not be likely to strike back to the nipple has already been
+      referred to in connexion with the construction atmospheric burners for
+      incandescent lighting. Owing, however, to the large proportions of the
+      atmospheric burners of boiling rings and stove and in particular to the
+      larger bore of their mixing tube, the risk of the flame striking back is
+      greater with them, than with incandescent lighting burners. The greatest
+      trouble is presented at lighting, and when the pressure of the gas-supply
+      is low. The risk of firing-back when the burner is lighted is avoided in
+      some forms of boiling rings, &amp;c., by providing a loose collar which
+      can be slipped over the air inlets of the Bunsen tube before applying a
+      light to the burner, and slipped clear of them as soon as the burner is
+      alight. Thus at the moment of lighting, the burner is converted
+      temporarily into one of the non-atmospheric type, and after the flame has
+      thus been established at the head or ring of the burner, the internal
+      air-supply is started by removing the loose collar from the air inlets,
+      and the flame is thus made atmospheric. In these conditions it does not
+      travel backwards to the nipple. In other heating burners it is generally
+      necessary to turn on the gas tap a few seconds before applying a light to
+      the burner or ring or stove; the gas streaming through the mixing tube
+      then fills it with acetylene and air mixed in the proper working
+      proportions, and when the light is applied, there is no explosion in the
+      mixing tube, or striking-back of the flame to the nipple.
+    </p>
+    <p>
+      Single or two-burner gas rings for boiling purposes, or for heating
+      cooking ovens, known as the "La Belle," made by Falk Stadelmann and Co.,
+      Ltd., of London, may be used at as low a gas pressure as 2 inches, though
+      they give better results at 3 inches, which is their normal working
+      pressure. The gas-inlet nozzle or nipple of the burner is set within a
+      spherical bulb in which are four air inlets. The mixing tube which is
+      placed at a proper distance in front of the nipple, is proportioned to the
+      rate of flow of the gas and air, and contains a mixing chamber with a
+      baffling pillar to further their admixture. A fine wire gauze insertion
+      serves to prevent striking-back of the flame. A "La Belle" boiling ring
+      consumes at 3 inches pressure about 48 litres or 1.7 cubic feet of
+      acetylene per hour.
+    </p>
+    <p>
+      ACETYLENE MOTORS.--The question as to the feasibility of developing
+      "power" from acetylene, <i>i.e.</i>, of running an engine by means of the
+      gas, may be answered in essentially identical terms. Specially designed
+      gas-engines of 1, 3, 6, or even 10 h.p. work perfectly with acetylene, and
+      such motors are in regular employment in numerous situations, more
+      particularly for pumping water to feed the generators of a large village
+      acetylene installation. Acetylene is not an economical source of power,
+      partly for the theoretical reason that it is a richer fuel even than
+      coal-gas, and gas-engines would appear usually to be more efficient as the
+      fuel they burn is poorer in calorific intensity, <i>i.e.</i>, in heating
+      power (which is explosive power) per unit of volume. The richer, or more
+      concentrated, any fuel in, the more rapidly does the explosion in a
+      mixture of that fuel with air proceed, because a rich fuel contains a
+      smaller proportion of non-inflammable gases which tend to retard explosion
+      than a poor one; and, in reason, a gas-engine works better the more slowly
+      the mixture of gas and air with which it is fed explodes. Still, by
+      properly designing the ports of a gas-engine cylinder, so that the normal
+      amount of compression of the charge and of expansion of the exploded
+      mixture which best suit coal-gas are modified to suit acetylene,
+      satisfactory engines can be constructed; and wherever an acetylene
+      installation for light exists, it becomes a mere question of expediency
+      whether the same fuel shall not be used to develop power, say, for pumping
+      up the water required in a large country house, instead of employing hand
+      labour, or the cheaper hot-air or petroleum motor. Taking the mean of the
+      results obtained by numerous investigators, it appears that 1 h.p.-hour
+      can be obtained for a consumption of 200 litres of acetylene; whence it
+      may be calculated that that amount of energy costs about 3d. for gas only,
+      neglecting upkeep, lubricating material (which would be relatively
+      expensive) and interest, &amp;c.
+    </p>
+    <p>
+      Acetylene Blowpipes--The design of a satisfactory blowpipe for use with
+      acetylene had at first proved a matter of some difficulty, since the jet,
+      like that of an ordinary self-luminous burner, usually exhibited a
+      tendency to become choked with carbonaceous growths. But when acetylene
+      had become available for various purposes at considerable pressure, after
+      compression into porous matter as described in Chapter XI, the troubles
+      were soon overcome; and a new form of blowpipe was constructed in which
+      acetylene was consumed under pressure in conjunction with oxygen. The
+      temperature given by this apparatus exceeds that of the familiar oxy-
+      hydrogen blowpipe, because the actual combustible material is carbon
+      instead of hydrogen. When 2 atoms of hydrogen unite with 1 of oxygen to
+      form 1 molecule of gaseous water, about 59 large calories are evolved, and
+      when 1 atom of solid amorphous carbon unites with 2 atoms of oxygen to
+      form 1 molecule of carbon dioxide, 97.3 calories are evolved. In both
+      cases, however, the heat attainable is limited by the fact that at certain
+      temperatures hydrogen and oxygen refuse to combine to form water, and
+      carbon and oxygen refuse to form carbon dioxide--in other words, water
+      vapour and carbon dioxide dissociate and absorb heat in the process at
+      certain moderately elevated temperatures. But when 1 atom of solid
+      amorphous carbon unites with 1 atom of oxygen to form carbon monoxide,
+      29.1 [Footnote: Cf. Chapter VI., page 185.] large calories are produced,
+      and carbon monoxide is capable of existence at much higher temperatures
+      than either carbon dioxide or water vapour. In any gaseous hydrocarbon,
+      again, the carbon exists in the gaseous state, and when 1 atom of the
+      hypothetical gaseous carbon combines with 1 atom of oxygen to produce 1
+      molecule of carbon monoxide, 68.2 large calories are evolved. Thus while
+      solid amorphous carbon emits more heat than a chemically equivalent
+      quantity of hydrogen provided it is enabled to combine with its higher
+      proportion of oxygen, it emits less if only carbon monoxide is formed; but
+      a higher temperature can be attained in the latter case, because the
+      carbon monoxide is more permanent or stable. Gaseous carbon, on the other
+      hand, emits more heat than an equivalent quantity of hydrogen, [Footnote:
+      In a blowpipe flame hydrogen can only burn to gaseous, not liquid, water.]
+      even when it is only converted into the monoxide. In other words, a
+      gaseous fuel which consists of hydrogen alone can only yield that
+      temperature as a maximum at which the speed of the dissociation of the
+      water vapour reaches that of the oxidation of the hydrogen; and were
+      carbon dioxide the only oxide of carbon, a similar state of affairs would
+      be ultimately reached in the flame of a carbonaceous gas. But since in the
+      latter case the carbon dioxide does not tend to dissociate completely, but
+      only to lose one atom of oxygen, above the limiting temperature for the
+      formation of carbon dioxide, carbon monoxide is still produced, because
+      there is less dissociating force opposed to its formation. Thus at
+      ordinary temperatures the heat of combustion of acetylene is 315.7
+      calories; but at temperatures where water vapour and carbon dioxide no
+      longer exist, there is lost to that quantity of 315.7 calories the heat of
+      combustion of hydrogen (69.0) and twice that of carbon monoxide (68.2 x 2
+      = 136.4); so that above those critical temperatures, the heat of
+      combustion of acetylene is only 315.7 - (69.0 + 136.4) = 110.3. [Footnote:
+      When the heat of combustion of acetylene is quoted as 315.7 calories, it
+      is understood that the water formed is condensed into the liquid state. If
+      the water remains gaseous, as it must do in a flame, the heat of formation
+      is reduced by about 10 calories. This does not affect the above
+      calculation, because the heat of combustion of hydrogen when the water
+      remains gaseous is similarly 10 calories less than 69, <i>i.e.</i>, 59, as
+      mentioned above in the text. Deleting the heat of liquefaction of water,
+      the calculation referred to becomes 305.7 - (59.0 + l36.4) = 110.3 as
+      before.] This value of 110.3 calories is clearly made up of the heat of
+      formation of acetylene itself, and twice the heat of conversion of carbon
+      into carbon monoxide, <i>i.e.</i>, for diamond carbon, 58.1 + 26.1 x 2 =
+      110.3; or for amorphous carbon, 52.1 + 29.1 x 2 = 110.3. From the
+      foregoing considerations, it may be inferred that the acetylene-oxygen
+      blowpipe can be regarded as a device for burning gaseous carbon in oxygen;
+      but were it possible to obtain carbon in the state of gas and so to lead
+      it into a blowpipe, the acetylene apparatus should still be more powerful,
+      because in it the temperature would be raised, not only by the heat of
+      formation of carbon monoxide, but also by the heat attendant upon the
+      dissociation of the acetylene which yields the carbon.
+    </p>
+    <p>
+      Acetylene requires 2.5 volumes of oxygen to burn it completely; but in the
+      construction of an acetylene-oxygen blowpipe the proportion of oxygen is
+      kept below this figure, viz., at 1.1 to 1.8 volumes, so that the
+      deficiency is left to be made up from the surrounding air. Thus at the jet
+      of the blowpipe the acetylene dissociates and its carbon is oxidised, at
+      first no doubt to carbon monoxide only, but afterwards to carbon dioxide;
+      and round the flame of the gaseous carbon is a comparatively cool, though
+      absolutely very hot jacket of hydrogen burning to water vapour in a
+      mixture of oxygen and air, which protects the inner zone from loss of
+      heat. As just explained, theoretical grounds support the conclusions at
+      which Fouch� has arrived, viz., that the temperature of the
+      acetylene-oxygen blowpipe flame is above that at which hydrogen will
+      combine with oxygen to form water, and that it can only be exceeded by
+      those found in a powerful electric furnace. As the hydrogen dissociated
+      from the acetylene remains temporarily in the free state, the flame of the
+      acetylene blowpipe, possesses strong reducing powers; and this, coupled
+      probably with an intensity of heat which is practically otherwise
+      unattainable, except by the aid of a high-tension electric current, should
+      make the acetylene-oxygen blowpipe a most useful piece of apparatus for a
+      large variety of metallurgical, chemical, and physical operations. In
+      Fouch�'s earliest attempts to design an acetylene blowpipe, the gas was
+      first saturated with a combustible vapour, such as that of petroleum
+      spirit or ether, and the mixture was consumed with a blast of oxygen in an
+      ordinary coal-gas blow-pipe. The apparatus worked fairly well, but gave a
+      flame of varying character; it was capable of fusing iron, raised a pencil
+      of lime to a more brilliant degree of incandescence than the eth-oxygen
+      burner, and did not deposit carbon at the jet. The matter, however, was
+      not pursued, as the blowpipe fed with undiluted acetylene took its place.
+      The second apparatus constructed by Fouch� was the high-pressure blowpipe,
+      the theoretical aspect of which has already been studied. In this,
+      acetylene passing through a water-seal from a cylinder where it is stored
+      as a solution in acetone (<i>cf.</i> Chapter XI.), and oxygen coming from
+      another cylinder, are each allowed to enter the blowpipe at a pressure of
+      118 to 157 inches of water column (<i>i.e.</i>, 8.7 to 11.6 inches of
+      mercury; 4.2 to 5.7 lb. per square inch, or 0.3 to 0.4 atmosphere). The
+      gases mix in a chamber tightly packed with porous matter such as that
+      which is employed in the original acetylene reservoir, and finally issue
+      from a jet having a diameter of 1 millimetre at the necessary speed of 100
+      to 150 metres per second. Finding, however, that the need for having the
+      acetylene under pressure somewhat limited the sphere of usefulness of his
+      apparatus, Fouch� finally designed a low-pressure blowpipe, in which only
+      the oxygen requires to be in a state of compression, while the acetylene
+      is drawn directly from any generator of the ordinary pattern that does not
+      yield a gas contaminated with air. The oxygen passes through a reducing
+      valve to lower the pressure under which it stands in the cylinder to that
+      of 1 or 1.5 effective atmosphere, this amount being necessary to inject
+      the acetylene and to give the previously mentioned speed of escape from
+      the blowpipe orifice. The acetylene is led through a system of long narrow
+      tubes to prevent it firing-back.
+    </p>
+    <p>
+      AUTOGENOUS SOLDERING AND WELDING.--The blowpipe is suitable for the
+      welding and for the autogenous soldering or "burning" of wrought or cast
+      iron, steel, or copper. An apparatus consuming from 600 to 1000 litres of
+      acetylene per hour yields a flame whose inner zone is 10 to 15 millimetres
+      long, and 3 to 4 millimetres in diameter; it is sufficiently powerful to
+      burn iron sheets 8 to 9 millimetres thick. By increasing the supply of
+      acetylene in proportion to that of the oxygen, the tip of the inner zone
+      becomes strongly luminous, and the flame then tends to carburise iron;
+      when the gases are so adjusted that this tip just disappears, the flame is
+      at its best for heating iron and steel. The consumption of acetylene is
+      about 75 litres per hour for each millimetre of thickness in the sheet
+      treated, and the normal consumption of oxygen is 1.7 times as much; a
+      joint 6 metres long can be burnt in 1 millimetre plate per hour, and one
+      of 1.5 metres in 10 millimetre plate. In certain cases it is found
+      economical to raise the metal to dull redness by other means, say with a
+      portable forge of the usual description, or with a blowpipe consuming
+      coal-gas and air. There are other forms of low- pressure blowpipe besides
+      the Fouch�, in some of which the oxygen also is supplied at low pressure.
+      Apart from the use of cylinders of dissolved acetylene, which are
+      extremely convenient and practically indispensable when the blowpipe has
+      to be applied in confined spaces (as in repairing propeller shafts on
+      ships <i>in situ</i>), acetylene generators are now made by several firms
+      in a convenient transportable form for providing the gas for use in
+      welding or autogenous soldering. It is generally supposed that the metal
+      used as solder in soldering iron or steel by this method must be iron
+      containing only a trifling proportion of carbon (such as Swedish iron),
+      because the carbon of the acetylene carburises the metal, which is heated
+      in the oxy-acetylene flame, and would thereby make ordinary steel too rich
+      in carbon. But the extent to which the metal used is carburised in the
+      flame depends, as has already been indicated, on the proper adjustment of
+      the proportion of oxygen to acetylene. Oxy-acetylene autogenous soldering
+      or welding is applicable to a great variety of work, among which may be
+      mentioned repairs to shafts, locomotive frames, cylinders, and to joints
+      in ships' frames, pipes, boilers, and rails. The use of the process is
+      rapidly extending in engineering works generally. Generators for acetylene
+      soldering or welding must be of ample size to meet the quickly fluctuating
+      demands on them and must be provided with water-seals, and a washer or
+      scrubber and filter capable of arresting all impurities held mechanically
+      in the crude gas, and with a safety vent- pipe terminating in the open at
+      a distance from the work in hand. The generator must be of a type which
+      affords as little after-generation as possible, and should not need
+      recharging while the blowpipe is in use. There should be a main tap on the
+      pipe between the generator and the blowpipe. It does not appear
+      conclusively established that the gas consumed should have been chemically
+      purified, but a purifier of ample size and charged with efficient material
+      is undoubtedly beneficial. The blowpipe must be designed so that it
+      remains sufficiently cool to prevent polymerisation of the acetylene and
+      deposition of the resultant particles of carbon or soot within it.
+    </p>
+    <p>
+      It is important to remember that if a diluent gas, such as nitrogen, is
+      present, the superior calorific power of acetylene over nearly all gases
+      should avail to keep the temperature of the flame more nearly up to the
+      temperature at which hydrogen and oxygen cease to combine. Hence a
+      blowpipe fed with air and acetylene would give a higher temperature than
+      any ordinary (atmospheric) coal-gas blowpipe, just as, as has been
+      explained in Chapter VI., an ordinary acetylene flame has a higher
+      temperature than a coal-gas flame. It is likely that a blowpipe fed with
+      "Lind�-air" (oxygen diluted with less nitrogen than in the atmosphere) and
+      acetylene would give as high a limelight effect as the oxy-hydrogen or
+      oxy-coal-gas blowpipe. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkx" id="x">CHAPTER X</a>
+    </h2>
+    <h3>
+      CARBURETTED ACETYLENE
+    </h3>
+    <p>
+      Now that atmospheric or Bunsen burners for the consumption of acetylene
+      for use in lighting by the incandescent system and in heating have been so
+      much improved that they seem to be within measurable reach of a state of
+      perfection, there appears to be but little use at the present time for a
+      modified or diluted acetylene which formerly seemed likely to be valuable
+      for heating and certain other purposes. Nevertheless, the facts relating
+      to this so-called carburetted acetylene are in no way traversed by its
+      failure to establish itself as an active competitor with simple acetylene
+      for heating purposes, and since it is conceivable that the advantages
+      which from the theoretical standpoint the carburetted gas undoubtedly
+      possesses in certain directions may ultimately lead to its practical
+      utilisation for special purposes, it has been deemed expedient to continue
+      to give in this work an account of the principles underlying the
+      production and application of carburetted acetylene.
+    </p>
+    <p>
+      It has already been explained that acetylene is comparatively a less
+      efficient heating agent than it is an illuminating material, because, per
+      unit of volume, its calorific power is not so much greater than that of
+      coal-gas as is its illuminating capacity. It has also been shown that the
+      high upper explosive limit of mixtures of acetylene and air--a limit so
+      much higher than the corresponding figure with coal-gas and other gaseous
+      fuels--renders its employment in atmospheric burners (either for lighting
+      or for heating) somewhat troublesome, or dependent upon considerable skill
+      in the design of the apparatus. If, therefore, either the upper explosive
+      limit of acetylene could be reduced, or its calorific value increased (or
+      both), by mixing with it some other gas or vapour which should not
+      seriously affect its price and convenience as a self-luminous illuminant,
+      acetylene would compare more favourably with coal-gas in its ready
+      applicability to the most various purposes. Such a method has been
+      suggested by Heil, and has been found successful on the Continent. It
+      consists in adding to the acetylene a certain proportion of the vapour of
+      a volatile hydrocarbon, so as to prepare what is called "carburetted
+      acetylene." In all respects the method of making carburetted acetylene is
+      identical with that of making "air-gas," which was outlined in Chapter I.,
+      viz., the acetylene coming from an ordinary generating plant is led over
+      or through a mass of petroleum spirit, or other similar product, in a
+      vessel which exposes the proper amount of superficial area to the passing
+      gas. In all respects save one the character of the product is similar to
+      that of air-gas, <i>i.e.</i>, it is a mixture of a permanent gas with a
+      vapour; the vapour may possibly condense in part within the mains if they
+      are exposed to a falling temperature, and if the product is to be led any
+      considerable distance, deposition of liquid may occur (conceivably
+      followed by blockage of the mains) unless the proportion of vapour added
+      to the gas is kept below a point governed by local climatic and similar
+      conditions. But in one most important respect carburetted acetylene is
+      totally different from air-gas: partial precipitation of spirit from
+      air-gas removes more or less of the solitary useful constituent of the
+      material, reducing its practical value, and causing the residue to
+      approach or overpass its lower explosive limit (<i>cf.</i> Chapter I.);
+      partial removal of spirit from carburetted acetylene only means a partial
+      reconversion of the material into ordinary acetylene, increasing its
+      natural illuminating power, lowering its calorific intensity somewhat, and
+      causing the residue to have almost its primary high upper explosive limit,
+      but essentially leaving its lower explosive limit unchanged. Thus while
+      air-gas may conceivably become inefficient for every purpose if supplied
+      from any distance in very cold weather, and may even pass into a dangerous
+      explosive within the mains; carburetted acetylene can never become
+      explosive, can only lose part of its special heating value, and will
+      actually increase in illuminating power.
+    </p>
+    <p>
+      It is manifest that, like air-gas, carburetted acetylene is of somewhat
+      indefinite composition, for the proportion of vapour, and the chemical
+      nature of that vapour, may vary. 100 litres of acetylene will take up 40
+      grammes of petroleum spirit to yield 110 litres of carburetted acetylene
+      evidently containing 9 per cent. of vapour, or 100 litres of acetylene may
+      be made to absorb as much as 250 grammes of spirit yielding 200 litres of
+      carburetted acetylene containing 50 per cent. of vapour; while the
+      petroleum spirit may be replaced, if prices are suitable, by benzol or
+      denatured alcohol.
+    </p>
+    <p>
+      The illuminating power of acetylene carburetted with petroleum spirit has
+      been examined by Caro, whose average figures, worked out in British units,
+      are:
+    </p>
+    <p>
+      ILLUMINATING POWER OF CARBURETTED ACETYLENE. HALF-FOOT BURNERS.
+    </p>
+<pre xml:space="preserve">
+   <i>Self-luminous.</i>           |          <i>Incandescent</i>
+1 litre      =  1.00 candle.       |   1 litre      =  3.04 candles.
+1 cubic foot = 28.4 candles.       |   1 cubic foot = 86.2 candles.
+1 candle     =  1.00 litre.        |   1 candle     =  0.33 litre.
+1 candle     =  0.035 cubic foot.  |   1 candle     =  0.012 cubic foot.
+</pre>
+    <p>
+      Those results may be compared with those referring to air-gas, which emits
+      in incandescent burners from 3.0 to 12.4 candles per cubic foot according
+      to the amount of spirit added to the air and the temperature to which the
+      gas is exposed.
+    </p>
+    <p>
+      The calorific values of carburetted acetylene (Caro), and those of other
+      gaseous fuels are:
+    </p>
+<pre xml:space="preserve">
+                                                    Large Calories per
+                                    _                  Cubic Foot.
+                                   | (Lewes)  .  320
+                                   | (Gand)   .  403
+    Ordinary acetylene     .    .  | (Heil)   .  365
+                                   |             ___
+                                   |_Mean          .    .    363
+
+
+                                   | Maximum  .  680
+    Carburetted acetylene  .    .  | Minimum  .  467
+     (petroleum spirit)            |             ___
+                                   |_Mean          .    .    573
+
+
+    Carburetted acetylene (50 per cent. benzol by volume)    685
+    Carburetted acetylene (50 per cent. alcohol by volume)   364
+    Coal-gas (common, unenriched)   .    .    .    .    .    150
+                                    _
+                                   | Maximum  .  178
+    Air-gas, self-luminous flame   | Minimum  .   57
+                                   |             ___
+                                   |_Mean     .    .    .    114
+                                    _
+                                   | Maximum  .   26
+    Air-gas, non-luminous flame    | Minimum  .   18
+                                   |             ___
+                                   |_Mean     .    .    .     22
+
+
+    Water-gas (Strache) from coke    .   .    .    .    .     71
+    Mond gas (from bituminous coal)  .   .    .    .    .     38
+    Semi-water-gas from coke or anthracite    .    .    .     36
+    Generator (producer) gas    .    .   .    .    .    .     29
+</pre>
+    <p>
+      Besides its relatively low upper explosive limit, carburetted acetylene
+      exhibits a higher temperature of ignition than ordinary acetylene, which
+      makes it appreciably safer in presence of a naked light. It also possesses
+      a somewhat lower flame temperature and a slower speed of propagation of
+      the explosive wave when mixed with air. These data are:
+    </p>
+<pre xml:space="preserve">
+ ______________________________________________________________________
+|                        |             |                  |            |
+|                        | Explosive   |   Temperature.   |            |
+|                        |  Limits.    |    Degrees C.    | Explosive  |
+|                        |19 mm. Tube. |                  | Explosive  |
+|                        |_____________|__________________|   Wave.    |
+|                        |      |      |        |         | Metres per |
+|                        |      |      |Of Igni-|         |  Second.   |
+|                        |Lower.|Upper.| tion.  |Of Flame.|            |
+|________________________|______|______|________|_________|____________|
+|                        |      |      |        |         |            |
+| Acetylene (theoretical)| ---  |  --- |  ---   |1850-2420|     ---    |
+|   "      (observed)    | 3.35 | 52.3 |  480   |1630-2020|  0.18-100  |
+| Carburetted \     from | 2.5  | 10.2 |  582   |   1620  |     3.2    |
+|  acetylene  /  .  . to | 5.4  | 30.0 |  720   |   1730  |     5.3    |
+| Carburetted acetylene\ | 3.4  | 22.0 |  ---   |   1820  |     1.3    |
+|  (benzol)   .  .  .  / |      |      |        |         |            |
+| Carburetted acetylene\ | 3.1  | 12.0 |  ---   |   1610  |     1.1    |
+|  (alcohol)  .  .  .  / |      |      |        |         |            |
+| Air-gas, self-luminous\|15.0  | 50.0 |  ---   |1510-1520|     ---    |
+|  flame   .  .  .  .   /|      |      |        |         |            |
+| Coal-gas    .  .  .    | 7.9  | 19.1 |  600   |   ---   |     ---    |
+|________________________|______|______|________|_________|____________|
+</pre>
+    <p>
+      In making carburetted acetylene, the pressure given by the ordinary
+      acetylene generator will be sufficient to drive the gas through the
+      carburettor, and therefore there will be no expense involved beyond the
+      cost of the spirit vaporised. Thus comparisons may fairly be made between
+      ordinary and carburetted acetylene on the basis of material only, the
+      expense of generating the original acetylene being also ignored. In Great
+      Britain the prices of calcium carbide, petroleum spirit, and 90s benzol
+      delivered in bulk in country places may be taken at 15� per ton, and 1s.
+      per gallon respectively, petroleum spirit having a specific gravity of
+      0.700 and benzol of 0.88. On this basis, a unit volume (100 cubic metres)
+      of plain acetylene costs 1135d., of "petrolised" acetylene containing 66
+      per cent. of acetylene costs 1277d., and of "benzolised" acetylene costs
+      1180d. In other words, 100 volumes of plain acetylene, 90 volumes of
+      petrolised acetylene, and 96 volumes of benzolised acetylene are of equal
+      pecuniary value. Employing the data given in previous tables, it appears
+      that 38.5 candles can be won from plain acetylene in a self-luminous
+      burner, and 103 candles therefrom in an incandescent burner at the same
+      price as 25.5-29.1 and 78-87 candles can be obtained from carburetted
+      acetylene; whence it follows that at English prices petrolised acetylene
+      is more expensive as an illuminant in either system of combustion than the
+      simple gas, while benzolised acetylene, burnt under the mantle only, is
+      more nearly equal to the simple gas from a pecuniary aspect. But
+      considering the calorific value, it appears that for a given sum of money
+      only 363 calories can be obtained from plain acetylene, while petrolised
+      acetylene yields 516, and benzolised acetylene 658; so that for all
+      heating or cooking purposes (and also for driving small motors)
+      carburetted acetylene exhibits a notable economy. Inasmuch as the partial
+      saturation of acetylene with any combustible vapour is an operation of
+      extreme simplicity, requiring no power or supervision beyond the
+      occasional recharging of the carburettor, it is manifest that the original
+      main coming from the generator supplying any large establishment where
+      much warming, cooking (or motor driving) might conveniently be done with
+      the gas could be divided within the plant-house, one branch supplying all,
+      or nearly all, the lighting burners with plain acetylene, and the other
+      branch communicating with a carburettor, so that all, or nearly all, the
+      warming and cooking stoves (and the motor) should be supplied with the
+      more economical carburetted acetylene. Since any water pump or similar
+      apparatus would be in an outhouse or basement, and the most important
+      heating stove (the cooker) be in the kitchen, such an arrangement would be
+      neither complicated nor involve a costly duplication of pipes.
+    </p>
+    <p>
+      It follows from the fact that even a trifling proportion of vapour reduces
+      the upper limit of explosibility of mixtures of acetylene with air, that
+      the gas may be so lightly carburetted as not appreciably to suffer in
+      illuminating power when consumed in self-luminous jets, and yet to burn
+      satisfactorily in incandescent burners, even if it has been generated in
+      an apparatus which introduces some air every time the operation of
+      recharging is performed. To carry out this idea, Caro has suggested that 5
+      kilos. of petroleum spirit should be added to the generator water for
+      every 50 cubic metres of gas evolved, <i>i.e.</i>, 1 lb. per 160 cubic
+      feet, or, say, 1 gallon per 1000 cubic feet, or per 200 lb. of carbide
+      decomposed. Caro proposed this addition in the case of central
+      installations supplying a district where the majority of the consumers
+      burnt the gas in self-luminous jets, but where a few preferred the
+      incandescent system; but it is clearly equally suitable for employment in
+      all private plants of sufficient magnitude.
+    </p>
+    <p>
+      A lowering of the upper limit of explosibility is also produced by the
+      presence of the acetone which remains in acetylene when obtained from a
+      cylinder holding the compressed gas (<i>cf.</i> Chapter XI.). According to
+      Wolff and Caro such gas usually carries with it from 30 to 60 grammes of
+      acetone vapour per cubic metre, <i>i.e.</i>, 1.27 grammes per cubic foot
+      on an average; and this amount reduces the upper limit of explosibility by
+      about 16 per cent., so that to this extent the gas behaves more smoothly
+      in an incandescent burner of imperfect design.
+    </p>
+    <p>
+      L�pinay has described some experiments on the comparative technical value
+      of ordinary acetylene, carburetted acetylene, denatured alcohol and
+      petroleum spirit as fuels for small explosion engines. One particular
+      motor of 3 (French) h.p. consumed 1150 grammes of petroleum spirit per
+      hour at full load; but when it was supplied with carburetted acetylene its
+      consumption fell to 150 litres of acetylene and 700 grammes of spirit
+      (specific gravity 0.680). A 1-1/4 h.p. engine running light required 48
+      grammes of 90 per cent. alcohol per horse-power-hour and 66 litres of
+      acetylene; at full load it took 220 grammes of alcohol and 110 litres of
+      acetylene. A 6 h.p. engine at full load required 62 litres of acetylene
+      carburetted with 197 grammes of petroleum spirit per horse-power-hour
+      (uncorrected); while a similar motor fed with low-grade Taylor fuel-gas
+      took 1260 litres per horse-power-hour, but on an average developed the
+      same amount of power from 73 litres when 10 per cent. of acetylene was
+      added to the gas. L�pinay found that with pure acetylene ignition of the
+      charge was apt to be premature; and that while the consumption of
+      carburetted acetylene in small motors still materially exceeded the
+      theoretical, further economics could be attained, which, coupled with the
+      smooth and regular running of an engine fed with the carburetted gas, made
+      carburetted acetylene distinctly the better power-gas of the two. <br />
+      <br /> <br />
+    </p>
+    <h2>
+      <a name="linkxi" id="xi">CHAPTER XI</a>
+    </h2>
+    <h3>
+      COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES
+    </h3>
+    <p>
+      In all that was said in Chapters II., III., IV., and V. respecting the
+      generation and employment of acetylene, it was assumed that the gas would
+      be produced by the interaction of calcium carbide and water, either by the
+      consumer himself, or in some central station delivering the acetylene
+      throughout a neighbourhood in mains. But there are other methods of using
+      the gas, which have now to be considered.
+    </p>
+    <p>
+      COMPRESSED ACETYLENE.--In the first place, like all other gases, acetylene
+      is capable of compression, or even of conversion into the liquid state;
+      for as a gas, the volume occupied by any given weight of it is not fixed,
+      but varies inversely with the pressure under which it is stored. A steel
+      cylinder, for instance, which is of such size as to hold a cubic foot of
+      water, also holds a cubic foot of acetylene at atmospheric pressure, but
+      holds 2 cubic feet if the gas is pumped into it to a pressure of 2
+      atmospheres, or 30 lb. per square inch; while by increasing the pressure
+      to 21.53 atmospheres at 0� C. (Ansdell, Willson and Suckert) the gas is
+      liquefied, and the vessel may then contain 1 cubic foot of liquid
+      acetylene, which is equal to some 400 cubic feet of gaseous acetylene at
+      normal pressure. It is clear that for many purposes acetylene so
+      compressed or liquefied would be convenient, for if the cylinders could be
+      procured ready charged, all troubles incidental to generation would be
+      avoided. The method, however, is not practically permissible; because, as
+      pointed out in Chapters II. and VI., acetylene does not safely bear
+      compression to a point exceeding 2 atmospheres; and the liability to
+      spontaneous dissociation or explosion in presence of spark or severe blow,
+      which is characteristic of compressed gaseous acetylene, is greatly
+      enhanced if compression has been pushed to the point of liquefaction.
+    </p>
+    <p>
+      However, two methods of retaining the portability and convenience of
+      compressed acetylene with complete safety have been discovered. In one,
+      due to the researches of Claude and Hess, the gas is pumped under pressure
+      into acetone, a combustible organic liquid of high solvent power, which
+      boils at 56� C. As the solvent capacity of most liquids for most gases
+      rises with the pressure, a bottle partly filled with acetone may be
+      charged with acetylene at considerable effective pressure until the vessel
+      contains much more than its normal quantity of gas; and when the valve is
+      opened the surplus escapes, ready for employment, leaving the acetone
+      practically unaltered in composition or quantity, and fit to receive a
+      fresh charge of gas. In comparison with liquefied acetylene, its solution
+      in acetone under pressure is much safer; but since the acetone expands
+      during absorption of gas, the bottle cannot be entirely filled with
+      liquid, and therefore either at first, or during consumption (or both),
+      above the level of the relatively safe solution, the cylinder contains a
+      certain quantity of gaseous acetylene, which is compressed above its limit
+      of safety. The other method consists in pumping acetylene under pressure
+      into a cylinder apparently quite full of some highly porous solid matter,
+      like charcoal, kieselguhr, unglazed brick, &amp;c. This has the practical
+      result that the gas is held under a high state of compression, or possibly
+      as a liquid, in the minute crevices of the material, which are almost of
+      insensible magnitude; or it may be regarded as stored in vessels whose
+      diameter is less than that in which an explosive wave can be propagated (<i>cf.</i>
+      Chapter VI.).
+    </p>
+    <p>
+      DISSOLVED ACETYLENE.--According to Fouch�, the simple solution of
+      acetylene in acetone has the same coefficient of expansion by heat as that
+      of pure acetone, viz., 0.0015; the corresponding coefficient of liquefied
+      acetylene is 0.007 (Fouch�), or 0.00489 (Ansdell) <i>i.e.</i>, three or
+      five times as much. The specific gravity of liquid acetylene is 0.420 at
+      16.4� C. (Ansdell), or 0.528 at 20.6� C. (Willson and Suckert); while the
+      density of acetylene dissolved in acetone is 0.71 at 15� C. (Claude). The
+      tension of liquefied acetylene is 21.53 atmospheres at 0� C., and 39.76
+      atmospheres at 20.15� C. (Ansdell); 21.53 at 0� C., and 39.76 at 19.5� C.
+      (Willson and Suckert); or 26.5 at 0� C., and 42.8 at 20.0� C. (Villard).
+      Averaging those results, it may be said that the tension rises from 23.2
+      atmospheres at 0� C. to 40.77 at 20� C., which is an increment of 1/26 or
+      0.88 atmosphere, per 1� Centigrade; while, of course, liquefied acetylene
+      cannot be kept at all at a temperature of 0� unless the pressure is 21
+      atmospheres or upwards. The solution of acetylene in acetone can be stored
+      at any pressure above or below that of the atmosphere, and the extent to
+      which the pressure will rise as the temperature increases depends on the
+      original pressure. Berthelot and Vieille have shown that when (<i>a</i>)
+      301 grammes of acetone are charged with 69 grammes of acetylene, a
+      pressure of 6.74 atmospheres at 14.0� C. rises to 10.55 atmospheres at
+      35.7� C.; (<i>b</i>) 315 grammes of acetone are charged with 118 grammes
+      of acetylene, a pressure of 12.25 atmospheres at 14.0� C. rises to 19.46
+      at 36.0� C.; (<i>c</i>) 315 grammes of acetone are charged with 203
+      grammes of acetylene, a pressure of 19.98 atmospheres at 13.0� C. rises to
+      30.49 at 36.0� C. Therefore in (<i>a</i>) the increase in pressure is 0.18
+      atmosphere, in (<i>b</i>) O.33 atmosphere, and in (<i>c</i>) 0.46
+      atmosphere per 1� Centigrade within the temperature limits quoted. Taking
+      case (<i>b</i>) as the normal, it follows that the increment in pressure
+      per 1� C. is 1/37 (usually quoted as 1/30); so that, measured as a
+      proportion of the existing pressure, the pressure in a closed vessel
+      containing a solution of acetylene in acetone increases nearly as much
+      (though distinctly less) for a given rise in temperature as does the
+      pressure in a similar vessel filled with liquefied acetylene, but the
+      absolute increase is roughly only one-third with the solution as with the
+      liquid, because the initial pressure under which the solution is stored is
+      only one-half, or less, that at which the liquefied gas must exist.
+    </p>
+    <p>
+      Supposing, now, that acetylene contained in a closed vessel, either as
+      compressed gas, as a solution in acetone, or as a liquid, were brought to
+      explosion by spark or shock, the effects capable of production have to be
+      considered. Berthelot and Vieille have shown that if gaseous acetylene is
+      stored at a pressure of 11.23 kilogrammes per square centimetre,
+      [Footnote: 1 kilo. per sq. cm. is almost identical with 1 atmosphere, or
+      15 lb. per sq. inch.] the pressure after explosion reaches 92.33
+      atmospheres on an average, which is an increase of 8.37 times the original
+      figure; if the gas is stored at 21.13 atmospheres, the mean pressure after
+      explosion is 213.15 atmospheres, or 10.13 times the original amount. If
+      liquid acetylene is tested similarly, the original pressure, which must
+      clearly be more than 21.53 atmospheres (Ansdell) at 0� C., may rise to
+      5564 kilos, per square centimetre, as Berthelot and Vieille observed when
+      a steel bomb having a capacity of 49 c.c. was charged with 18 grammes of
+      liquefied acetylene. In the case of the solution in acetone, the
+      magnitudes of the pressures set up are of two entirely different orders
+      according as the original pressure 20 atmospheres or somewhat less; but
+      apart from this, they vary considerably with the extent to which the
+      vessel is filled with the liquid, and they also depend on whether the
+      explosion is produced in the solution or in the gas space above. Taking
+      the lower original pressure first, viz., 10 atmospheres, when a vessel was
+      filled with solution to 33 per cent. of its capacity, the pressure after
+      explosion reached about 95 atmospheres if the spark was applied to the gas
+      space; but attained 117.4 atmospheres when the spark was applied to the
+      acetone. When the vessel was filled 56 per cent. full, the pressures after
+      explosion reached about 89, or 155 atmospheres, according as the gas or
+      the liquid was treated with the spark. But when the original pressure was
+      20 atmospheres, and the vessel was filled to 35 per cent. of its actual
+      capacity with solution, the final pressures ranged from 303 to 568
+      atmospheres when the gas was fired, and from 2000 to 5100 when the spark
+      was applied to the acetone. Examining these figures carefully, it will be
+      seen that the phenomena accompanying the explosion of a solution of
+      acetylene in acetone resemble those of the explosion of compressed gaseous
+      acetylene when the original pressure under which the solution is stored is
+      about 10 atmospheres; but resemble those of the explosion of liquefied
+      acetylene when the original pressure of the solution reaches 20
+      atmospheres, this being due to the fact that at an original pressure of 10
+      atmospheres the acetone itself does not explode, but, being exothermic,
+      rather tends to decrease the severity of the explosion; whereas at an
+      original pressure of 20 atmospheres the acetone does explode (or burn),
+      and adds its heat of combustion to the heat evolved by the acetylene. Thus
+      at 10 atmospheres the presence of the acetone is a source of safety; but
+      at 20 atmospheres it becomes an extra danger.
+    </p>
+    <p>
+      Since sound steel cylinders may easily be constructed to boar a pressure
+      of 250 atmospheres, but would be burst by a pressure considerably less
+      than 5000 atmospheres, it appears that liquefied acetylene and its
+      solution in acetone at a pressure of 20 atmospheres are quite unsafe; and
+      it might also seem that both the solution at a pressure of 10 atmospheres
+      and the simple gas compressed to the same limit should be safe. But there
+      is an important difference here, in degree if not in kind, because, given
+      a cylinder of known capacity containing (1) gaseous acetylene compressed
+      to 10 atmospheres, or (2) containing the solution at the same pressure, if
+      an explosion were to occur, in case (1) the whole contents would
+      participate in the decomposition, whereas in case (2), as mentioned
+      already, only the small quantity of gaseous acetylene above the solution
+      would be dissociated.
+    </p>
+    <p>
+      It is manifest that of the three varieties of compressed acetylene now
+      under consideration, the solution in acetone is the only one fit for
+      general employment; but it exhibits the grave defects (<i>a</i>) that the
+      pressure under which it is prepared must be so small that the pressure in
+      the cylinders can never approach 20 atmospheres in the hottest weather or
+      in the hottest situation to which they may be exposed, (<i>b</i>) that the
+      gas does not escape smoothly enough to be convenient from large vessels
+      unless those vessels are agitated, and (<i>c</i>) that the cylinders must
+      always be used in a certain position with the valve at the top, lest part
+      of the liquid should run out into the pipes. For these reasons the simple
+      solution of acetylene in acetone has not become of industrial importance;
+      but the processes of absorbing either the gas, or better still its
+      solution in acetone, in porous matter have already achieved considerable
+      success. Both methods have proved perfectly safe and trustworthy; but the
+      combination of the acetone process with the porous matter makes the
+      cylinders smaller per unit volume of acetylene they contain. Several
+      varieties of solid matter appear to work satisfactorily, the only
+      essential feature in their composition being that they shall possess a
+      proper amount of porosity and be perfectly free from action upon the
+      acetylene or the acetone (if present). Lime does attack acetone in time,
+      and therefore it is not a suitable ingredient of the solid substance
+      whenever acetylene is to be compressed in conjunction with the solvent; so
+      that at present either a light brick earth which has a specific gravity of
+      0.5 is employed, or a mixture of charcoal with certain inorganic salts
+      which has a density of 0.3, and can be introduced through a small aperture
+      into the cylinder in a semi-fluid condition. Both materials possess a
+      porosity of 80 per cent., that is to say, when a cylinder is apparently
+      filled quite full, only 20 per cent, of the space is really occupied by
+      the solid body, the remaining 80 per cent, being available for holding the
+      liquid or the compressed gas. If all comparisons as to degree of
+      explosibility and effects of explosion are omitted, an analogy may be
+      drawn between liquefied acetylene or its compressed solution in acetone
+      and nitroglycerin, while the gas or solution of the gas absorbed in porous
+      matter resembles dynamite. Nitroglycerin is almost too treacherous a
+      material to handle, but as an explosive (which in reason absorbed or
+      dissolved acetylene is not) dynamite is safe, and even requires special
+      arrangements to explode it.
+    </p>
+    <p>
+      In Paris, where the acetone process first found employment on a large
+      scale, the company supplying portable cylinders to consumers uses large
+      storage vessels filled, as above mentioned, apparently full of porous
+      solid matter, and also charged to about 43 per cent, of their capacity
+      with acetone, thus leaving about 37 per cent. of the apace for the
+      expansion which occurs as the liquid takes up the gas. Acetylene is
+      generated, purified, and thoroughly dried according to the usual methods;
+      and it is then run through a double-action pump which compresses it first
+      to a pressure of 3.5 kilos., next to a pressure of 3.5 x 3.5 = 12 kilos,
+      per square centimetre, and finally drives it into the storage vessels.
+      Compression is effected in two stages, because the process is accompanied
+      by an evolution of much heat, which might cause the gas to explode during
+      the operation; but since the pump is fitted with two cylinders, the
+      acetylene can be cooled after the first compression. The storage vessels
+      then contain 100 times their apparent volume of acetylene; for as the
+      solubility of acetylene in acetone at ordinary temperature and pressure is
+      about 25 volumes of gas in 1 of liquid, a vessel holding 100 volumes when
+      empty takes up 25 x 43 = 1000 volumes of acetylene roughly at atmospheric
+      pressure; which, as the pressure is approximately 10 atmospheres, becomes
+      1000 x 10 = 10,000 volumes per 100 normal capacity, or 100 times the
+      capacity of the vessel in terms of water. From these large vessels,
+      portable cylinders of various useful dimensions, similarly loaded with
+      porous matter and acetone, are charged simply by placing them in mutual
+      contact, thus allowing the pressure and the surplus gas to enter the small
+      one; a process which has the advantage of renewing the small quantity of
+      acetone vaporised from the consumers' cylinders as the acetylene is burnt
+      (for acetone is somewhat volatile, cf. Chapter X.), so that only the
+      storage vessels ever need to have fresh solvent introduced.
+    </p>
+    <p>
+      Where it is procurable, the use of acetylene compressed in this fashion is
+      simplicity itself; for the cylinders have only to be connected with the
+      house service-pipes through a reducing valve of ordinary construction, set
+      to give the pressure which the burners require. When exhausted, the bottle
+      is simply replaced by another. Manifestly, however, the cost of
+      compression, the interest on the value of the cylinders, and the carriage,
+      &amp;c., make the compressed gas more expensive per unit of volume (or
+      light) than acetylene locally generated from carbide and water; and indeed
+      the value of the process does not lie so much in the direction of domestic
+      illumination as in that of the lighting, and possibly driving, of vehicles
+      and motor-cars--more especially in the illumination of such vehicles as
+      travel constantly, or for business purposes, over rough road surfaces and
+      perform mostly out-and-home journeys. Nevertheless, absorbed acetylene may
+      claim close attention for one department of household illumination, viz.,
+      the portable table-lamp; for the base of such an apparatus might easily be
+      constructed to imitate the acetone cylinder, and it could be charged by
+      simple connexion with a larger one at intervals. In this way the size of
+      the lamp for a given number of candle-hours would be reduced below that of
+      any type of actual generator, and the troubles of after-generation, always
+      more or less experienced in holderless generators, would be entirely done
+      away with. Dissolved acetylene is also very useful for acetylene welding
+      or autogenous soldering.
+    </p>
+    <p>
+      The advantages of compressed and absorbed acetylene depend on the small
+      bulk and weight of the apparatus per unit of light, on the fact that no
+      amount of agitation can affect the evolution of gas (as may happen with an
+      ordinary acetylene generator), on the absence of any liquid which may
+      freeze in winter, and on there being no need for skilled attention except
+      when the cylinders are being changed. These vessels weigh between 2.5 and
+      3 kilos, per 1 litre capacity (normal) and since they are charged with 100
+      times their apparent volume of acetylene, they may be said to weigh 1
+      kilo, per 33 litres of available acetylene, or roughly 2 lb. per cubic
+      foot, or, again, if half-foot burners are used, 2 lb. per 36 candle-
+      hours. According to Fouch�, if electricity obtained from lead accumulators
+      is compared with acetylene on the basis of the weight of apparatus needed
+      to evolve a certain quantify of light, 1 kilo, of acetylene cylinder is
+      equal to 1.33 kilos, of lead accumulator with arc lamps, or to 4 kilos. of
+      accumulator with glow lamps; and moreover the acetylene cylinder can be
+      charged and discharged, broadly speaking, as quickly or as slowly as may
+      be desired; while, it may be added, the same cylinder will serve one or
+      more self-luminous jets, one or more incandescent burners, any number and
+      variety of heating apparatus, simultaneously or consecutively, at any
+      pressure which may be required. From the aspect of space occupied,
+      dissolved acetylene is not so concentrated a source of artificial light as
+      calcium carbide; for 1 volume of granulated carbide is capable of omitting
+      as much light as 4 volumes of compressed gas; although, in practice, to
+      the 1 volume of carbide must be added that of the apparatus in which it is
+      decomposed.
+    </p>
+    <p>
+      LIQUEFIED ACETYLENE.--In most civilised countries the importation,
+      manufacture, storage, and use of liquefied acetylene, or of the gas
+      compressed to more than a fraction of one effective atmosphere, is quite
+      properly prohibited by law. In Great Britain this has been done by an
+      Order in Council dated November 26, 1897, which specifies 100 inches of
+      water column as the maximum to which compression may be pushed. Power
+      being retained, however, to exempt from the order any method of
+      compressing acetylene that might be proved safe, the Home Secretary issued
+      a subsequent Order on March 28, 1898, permitting oil-gas containing not
+      more than 20 per cent, by volume of acetylene (see below) to be compressed
+      to a degree not exceeding 150 lb. per square inch, <i>i.e.</i>, to about
+      10 atmospheres, provided the gases are mixed together before compression;
+      while a third Order, dated April 10, 1901, allows the compression of
+      acetylene into cylinders filled as completely as possible with porous
+      matter, with or without the presence of acetone, to a pressure not
+      exceeding 150 lb. per square inch provided the cylinders themselves have
+      been tested by hydraulic pressure for at least ten minutes to a pressure
+      not less than double [Footnote: In France the cylinders are tested to six
+      times and in Russia to five times their working pressure.] that which it
+      is intended to use, provided the solid substance is similar in every
+      respect to the samples deposited at the Home Office, provided its porosity
+      does not exceed 80 per cent., provided air is excluded from every part of
+      the apparatus before the gas is compressed, provided the quantity of
+      acetone used (if used at all) is not sufficient to fill the porosity of
+      the solid, provided the temperature is not permitted to rise during
+      compression, and provided compression only takes place in premises
+      approved by H.M.'s Inspectors of Explosives.
+    </p>
+    <p>
+      DILUTED ACETYLENE.--Acetylene is naturally capable of admixture or
+      dilution with any other gas or vapour; and the operation may be regarded
+      in either of two ways; (1) as a, means of improving the burning qualities
+      of the acetylene itself, or (2) as a means of conferring upon some other
+      gas increased luminosity. In the early days of the acetylene industry,
+      generation was performed in so haphazard a fashion, purification so
+      generally omitted, and the burners were so inefficient, that it was
+      proposed to add to the gas a comparatively small proportion of some other
+      gaseous fluid which should be capable of making it burn without deposition
+      of carbon while not seriously impairing its latent illuminating power. One
+      of the first diluents suggested was carbon dioxide (carbonic acid gas),
+      because this gas is very easy and cheap to prepare; and because it was
+      stated that acetylene would bear an addition of 5 or even 8 per cent, of
+      carbon dioxide and yet develop its full degree of luminosity. This last
+      assertion requires substantiation; for it is at least a grave theoretical
+      error to add a non-inflammable gas to a combustible one, as is seen in the
+      lower efficiency of all flames when burning in common air in comparison
+      with that which they exhibit in oxygen; while from the practical aspect,
+      so harmful is carbon dioxide in an illuminating gas, that coal-gas and
+      carburetted water-gas are frequently most rigorously freed from it,
+      because a certain gain in illuminating power may often thus be achieved
+      more cheaply than by direct enrichment of the gas by addition of
+      hydrocarbons. Being prepared from chalk and any cheap mineral acid,
+      hydrochloric by preference, in the cold, carbon dioxide is so cheap that
+      its price in comparison with that of acetylene is almost <i>nil</i>; and
+      therefore, on the above assumption, 105 volumes of diluted acetylene might
+      be made essentially for the same price as 100 volumes of neat acetylene,
+      and according to supposition emit 5 per cent. more light per unit of
+      volume.
+    </p>
+    <p>
+      It is reported that several railway trains in Austria are regularly
+      lighted with acetylene containing 0.4 to 1.0 per cent. of carbon dioxide
+      in order to prevent deposition of carbon at the burners. The gas is
+      prepared according to a patent process which consists in adding a certain
+      proportion of a "carbonate" to the generator water. In the United Kingdom,
+      also, there are several installations supplying an acetylene diluted with
+      carbon dioxide, the gas being produced by putting into that portion of a
+      water-to-carbide generator which lies nearest to the water- supply some
+      solid carbonate like chalk, and using a dilute acid to attack the
+      material. Other inventors have proposed placing a solid acid, like oxalic,
+      in the former part of a generator and decomposing it with a carbonate
+      solution; or they have suggested putting into the generator a mixture of a
+      solid acid and a solid soluble carbonate, and decomposing it with plain
+      water.
+    </p>
+    <p>
+      Clearly, unless the apparatus in which such mixtures as these are intended
+      to be prepared is designed with considerable care, the amount of carbon
+      dioxide in the gas will be liable to vary, and may fall to zero. If any
+      quantity of carbide present has been decomposed in the ordinary way, there
+      will be free calcium hydroxide in the generator; and if the carbon dioxide
+      comes into contact with this, it will be absorbed, unless sufficient acid
+      is employed to convert the calcium carbonate (or hydroxide) into the
+      corresponding normal salt of calcium. Similarly, during purification, a
+      material containing any free lime would tend to remove the carbon dioxide,
+      as would any substance which became alkaline by retaining the ammonia of
+      the crude gas.
+    </p>
+    <p>
+      It cannot altogether be granted that the value of a process for diluting
+      acetylene with carbon dioxide has been established, except in so far as
+      the mere presence of the diluent may somewhat diminish the tendency of the
+      acetylene to polymerise as it passes through a hot burner (<i>cf.</i>
+      Chapter VIII.). Certainly as a fuel-gas the mixture would be less
+      efficient, and the extra amount of carbon dioxide produced by each flame
+      is not wholly to be ignored. Moreover, since properly generated and
+      purified acetylene can be consumed in proper burners without trouble, all
+      reason for introducing carbon dioxide has disappeared.
+    </p>
+    <p>
+      MIXTURES OF ACETYLENE AND AIR.--A further proposal for diluting acetylene
+      was the addition to it of air. Apart from questions of explosibility, this
+      method has the advantage over that of adding carbon dioxide that the air,
+      though not inflammable, is, in virtue of its contained oxygen, a supporter
+      of combustion, and is required in a flame; whereas carbon dioxide is not
+      only not a supporter of combustion, but is actually a product thereof, and
+      correspondingly more objectionable. According to some experiments carried
+      out by Dufour, neat acetylene burnt under certain conditions evolved
+      between 1.0 and 1.8 candle-power per litre- hour; a mixture of 1 volume of
+      acetylene with 1 volume of air evolved 1.4 candle-power; a mixture of 1
+      volume of acetylene with 1.2 volumes of air, 2.25 candle-power; and a
+      mixture of 1 volume of acetylene with 1.3 volumes of air, 2.70
+      candle-power per litre-hour of acetylene in the several mixtures.
+      Averaging the figures, and calculating into terms of acetylene (only)
+      burnt, Dufour found neat acetylene to develop 1.29 candle-power per
+      litre-hour, and acetylene diluted with air to develop 1.51 candle-power.
+      When, however, allowance is made for the cost and trouble of preparing
+      such mixtures the advantage of the process disappears; and moreover it is
+      accompanied by too grave risks, unless conducted on a largo scale and
+      under most highly skilled supervision, to be fit for general employment.
+    </p>
+    <p>
+      Fouch�, however, has since found the duty, per cubic foot of neat
+      acetylene consumed in a twin injector burner at the most advantageous rate
+      of 3.2 inches, to be as follows for mixtures with air in the proportions
+      stated:
+    </p>
+<pre xml:space="preserve">
+Percentage of air          0       17       27       33.5
+Candles per cubic feet    38.4     36.0     32.8     26.0
+</pre>
+    <p>
+      At lower pressures, the duty of the acetylene when diluted appears to be
+      relatively somewhat higher. Figures which have been published in regard to
+      a mixture of 30 volumes of air and 70 volumes of acetylene obtained by a
+      particular system of producing such a mixture, known as the "Molet-
+      Boistelle," indicate that the admixture of air causes a slight increase in
+      the illuminating duty obtained from the acetylene in burners of various
+      sizes. The type of burner and the pressure employed in these experiments
+      were not, however, stated. This system has been used at certain stations
+      on the "Midi" railway in France. Nevertheless even where the admixture of
+      air to acetylene is legally permissible, the risk of obtaining a really
+      dangerous product and the nebulous character of the advantages attainable
+      should preclude its adoption.
+    </p>
+    <p>
+      In Great Britain the manufacture, importation, storage, and use of
+      acetylene mixed with air or oxygen, in all proportions and at all
+      pressures, with or without the presence of other substances, is prohibited
+      by an Order in Council dated July 1900; to which prohibition the mixture
+      of acetylene and air that takes place in a burner or contrivance in which
+      the mixture is intended to be burnt, and the admixture of air with
+      acetylene that may unavoidably occur in the first use or recharging of an
+      apparatus (usually a water-to-carbide generator), properly designed and
+      constructed with a view to the production of pure acetylene, are the
+      solitary exceptions.
+    </p>
+    <p>
+      MIXED CARBIDES.--In fact the only processes for diluting acetylene which
+      possess real utility are that of adding vaporised petroleum spirit or
+      benzene to the gas, as was described in Chapter X. under the name of
+      carburetted acetylene, and one other possible method of obtaining a
+      diluted acetylene directly from the gas-generator, to which a few words
+      will now be devoted. [Footnote: Mixtures of acetylene with relatively
+      large proportions of other illuminating gases, such as are referred to on
+      subsequent pages, are also, from one aspect, forms of diluted acetylene.]
+      Calcium carbide is only one particular specimen of a large number of
+      similar metallic compounds, which can be prepared in the electric furnace,
+      or otherwise. Some of those carbides yield acetylene when treated with
+      water, some are not attacked, some give liquid products, and some yield
+      methane, or mixtures of methane and hydrogen. Among the latter is
+      manganese carbide. If, then, a mixture of manganese carbide and calcium
+      carbide is put into an ordinary acetylene generator, the gas evolved will
+      be a mixture of acetylene with methane and hydrogen in proportions
+      depending upon the composition of the carbide mixture. It is clear that a
+      suitable mixture of the carbides might be made by preparing them
+      separately and bulking the whole in the desired proportions; while since
+      manganese carbide can be won in the electric furnace, it might be feasible
+      to charge into such a furnace a mixture of lime, coke, and manganese oxide
+      calculated to yield a simple mixture of the carbides or a kind of double
+      carbide. Following the lines which have been adopted in writing the
+      present book, it is not proposed to discuss the possibility of making
+      mixed carbides; but it may be said in brief that Brame and Lewes have
+      carried out several experiments in this direction, using charges of lime
+      and coke containing (<i>a</i>) up to 20 per cent. of manganese oxide, and
+      (<i>b</i>) more than 60 per cent. of manganese oxide. In neither case did
+      they succeed in obtaining a material which gave a mixture of acetylene and
+      methane when treated with water; in case (<i>a</i>) they found the gas to
+      be practically pure acetylene, so that the carbide must have been calcium
+      carbide only; in case (<i>b</i>) the gas was mainly methane and hydrogen,
+      so that the carbide must have been essentially that of manganese alone.
+      Mixed charges containing between 20 and 60 per cent. of manganese oxide
+      remain to be studied; but whether they would give mixed carbides or no, it
+      would be perfectly simple to mix ready-made carbides of calcium and
+      manganese together, if any demand for a diluted acetylene should arise on
+      a sufficiently large scale. It is, however, somewhat difficult to
+      appreciate the benefits to be obtained from forms of diluted acetylene
+      other than those to which reference is made later in this chapter.
+    </p>
+    <p>
+      There is, nevertheless, one modification of calcium carbide which, in a
+      small but important sphere, finds a useful <i>r�le</i>. It has been
+      pointed out that a carbide containing much calcium phosphide is usually
+      objectionable, because the gas evolved from it requires extra
+      purification, and because there is the (somewhat unlikely) possibility
+      that the acetylene obtained from such material before purification may be
+      spontaneously inflammable. If, now, to the usual furnace charge of lime
+      and coke a sufficient quantity of calcium phosphate is purposely added, it
+      is possible to win a mixture of calcium phosphide and carbide, or, as
+      Bradley, Read, and Jacobs call it, a "carbophosphide of calcium," having
+      the formula Ca_5C_6P_2, which yields a spontaneously inflammable mixture
+      of acetylene, gaseous phosphine, and liquid phosphine when treated with
+      water, and which, therefore, automatically gives a flame when brought into
+      contact with the liquid. The value of this material will be described in
+      Chapter XIII.
+    </p>
+    <p>
+      GAS-ENRICHING.--Other methods of diluting acetylene consist in adding a
+      comparatively small proportion of it to some other gas, and may be
+      considered rather as processes for enriching that other gas with
+      acetylene. Provided the second gas is well chosen, such mixtures exhibit
+      properties which render them peculiarly valuable for special purposes.
+      They have, usually, a far lower upper limit of explosibility than that of
+      neat acetylene, and they admit of safe compression to an extent greatly
+      exceeding that of acetylene itself, while they do not lose illuminating
+      power on compression. The second characteristic is most important, and
+      depends on the phenomena of "partial pressure," which have been referred
+      to in Chapter VI. When a single gas is stored at atmospheric pressure, it
+      is insensibly withstanding on all sides and in all directions a pressure
+      of roughly 15 lb. per square inch, which is the weight of the atmosphere
+      at sea-level; and when a mixture of two gases, X and Y, in equal volumes
+      is similarly stored it, regarded as an entity, is also supporting a
+      pressure of 15 lb. per square inch. But in every 1 volume of that mixture
+      there is only half a volume of X and Y each; and, ignoring the presence of
+      its partner, each half-volume is evenly distributed throughout a space of
+      1 volume. But since the volume of a gas stands in inverse ratio to the
+      pressure under which it is stored, the half-volume of X in the 1 volume of
+      X + Y apparently stands at a pressure of half an atmosphere, for it has
+      expanded till it fills, from a chemical and physical aspect, the space of
+      1 volume: suitable tests proving that it exhibits the properties which a
+      gas stored at a pressure of half an atmosphere should do. Therefore, in
+      the mixture under consideration, X and Y are both said to be at a "partial
+      pressure" of half an atmosphere, which is manifestly 7.5 lb. per square
+      inch. Clearly, when a gas is an entity (either an element or one single
+      chemical compound) partial and total pressure are identical. Now, it has
+      been shown that acetylene ceases to be a safe gas to handle when it is
+      stored at a pressure of 2 atmospheres; but the limit of safety really
+      occurs when the gas is stored at a <i>partial</i> pressure of 2
+      atmospheres. Neat acetylene, accordingly, cannot be compressed above the
+      mark 30 lb. shown on a pressure gauge; but diluted acetylene (if the
+      diluent is suitable) may be compressed in safety till the partial pressure
+      of the acetylene itself reaches 2 atmospheres. For instance, a mixture of
+      equal volumes of X and Y (X being acetylene) contains X at a partial
+      pressure of half the total pressure, and may therefore be compressed to (2
+      / 1/2 =) 4 atmospheres before X reaches the partial pressure of 2
+      atmospheres; and therewith the mixture is brought just to the limit of
+      safety, any effect of Y one way or the other being neglected. Similarly, a
+      mixture of 1 volume of acetylene with 4 volumes of Y may be safely
+      compressed to a pressure of (2 / 1/5 =) 10 atmospheres, or, broadly, a
+      mixture in which the percentage of acetylene is <i>x</i> may be safely
+      compressed to a pressure not exceeding (2 / <i>x</i>/100) atmospheres.
+      This fact permits acetylene after proper dilution to be compressed in the
+      same fashion as is allowable in the case of the dissolved and absorbed gas
+      described above.
+    </p>
+    <p>
+      If the latent illuminating power of acetylene is not to be wasted, the
+      diluent must not be selected without thought. Acetylene burns with a very
+      hot flame, the luminosity of which is seriously decreased if the
+      temperature is lowered. As mentioned in Chapter VIII., this may be done by
+      allowing too much air to enter the flame; but it may also be effected to a
+      certain extent by mixing with the acetylene before combustion some
+      combustible gas or vapour which burns at a lower temperature than
+      acetylene itself. Manifestly, therefore, the ideal diluent for acetylene
+      is a substance which possesses as high a flame temperature as acetylene
+      and a certain degree of intrinsic illuminating power, while the lower the
+      flame temperature of the diluent and the less its intrinsic illuminating
+      power, the less efficiently will the acetylene act as an enriching
+      material. According to Love, Hempel, Wedding, and others, if acetylene is
+      mixed with coal-gas in amounts up to 8 per cent. or thereabouts, the
+      illuminating power of the mixture increases about 1 candle for every 1 per
+      cent. of acetylene present: a fact which is usually expressed by saying
+      that with coal-gas the enrichment value of acetylene is 1 candle per 1 per
+      cent. Above 8 per cent., the enrichment value of acetylene rises, Love
+      having found an increase in illuminating power, for each 1 per cent. of
+      acetylene in the mixture, of 1.42 candles with 11.28 per cent. of
+      acetylene; and of 1.54 candles with 17.62 per cent. of acetylene.
+      Theoretically, if the illuminating power of acetylene is taken at 240
+      candles, its enrichment value should be (240 / 100 =) 2.4 candles per 1
+      per cent.; and since, in the case of coal-gas, its actual enrichment value
+      falls seriously below this figure, it is clear that coal-gas is not an
+      economical diluent for it. Moreover, coal-gas can be enriched by other
+      methods much more cheaply than with acetylene. Simple ("blue") water-gas,
+      according to Love, requires more than 10 per cent. of acetylene to be
+      added to it before a luminous flame is produced; while a mixture of 20.3
+      per cent. of acetylene and 79.7 per cent. of water-gas had an illuminating
+      power of 15.47 candles. Every addition to the proportion of acetylene when
+      it amounted to 20 per cent. and upwards of the mixture had a very
+      appreciable effect on the illuminating power of the latter. Thus with
+      27.84 per cent. of acetylene, the illuminating power of the mixture was
+      40.87 candles; with 38.00 per cent. of acetylene it was 73.96 candles.
+      Acetylene would not be an economical agent to employ in order to render
+      water-gas an illuminating gas of about the quality of coal-gas, but the
+      economy of enrichment of water-gas by acetylene increases rapidly with the
+      degree of enrichment demanded of it. Carburetted water-gas which, after
+      compression under 16 atmospheres pressure, had an illuminating power of
+      about 17.5 candles, was enriched by additions of acetylene. 4.5 per cent.
+      of acetylene in the mixture gave an illuminating power of 22.69 candles;
+      8.4 per cent., 29.54 candles; 11.21 per cent., 35.05 candles; 15.06 per
+      cent., 42.19 candles; and 21.44 per cent., 52.61 candles. It is therefore
+      evident that the effect of additions of acetylene on the illuminating
+      power of carburetted water-gas is of the same order as its effect on
+      coal-gas. The enrichment value of the acetylene increases with its
+      proportion in the mixture; but only when the proportion becomes quite
+      considerable, and, therefore, the gas of high illuminating power, does
+      enrichment by acetylene become economical. Methane (marsh-gas), owing to
+      its comparatively high flame temperature, and to the fact that it has an
+      intrinsic, if small, illuminating power, is a better diluent of acetylene
+      than carbon monoxide or hydrogen, in that it preserves to a greater extent
+      the illuminative value of the acetylene.
+    </p>
+    <p>
+      Actually comparisons of the effect of additions of various proportions of
+      a richly illuminating gas, such as acetylene, on the illuminative value of
+      a gas which has little or no inherent illuminating power, are largely
+      vitiated by the want of any systematic method for arriving at the
+      representative illuminative value of any illuminating gas. A statement
+      that the illuminating power of a gas is <i>x</i> candles is, strictly
+      speaking, incomplete, unless it is supplemented by the information that
+      the gas during testing was burnt (1) in a specified type of burner, and
+      (2) either at a specified fixed rate of consumption or so as to afford a
+      light of a certain specified intensity. There is no general agreement,
+      even in respect of the statutory testing of the illuminating power of
+      coal-gas supplies, as to the observance of uniform conditions of burning
+      of the gas under test, and in regard to more highly illuminating gases
+      there is even greater diversity of conditions. Hence figures such as those
+      quoted above for the enrichment value of acetylene inevitably show a
+      certain want of harmony which is in reality due to the imperfection or
+      incompleteness of the modes of testing employed. Relatively to another,
+      one gas appears advantageously merely in virtue of the conditions of
+      assessing illuminating power having been more favourable to it. Therefore
+      enrichment values, such as those given, must always be regarded as only
+      approximately trustworthy in instituting comparisons between either
+      different diluent gases or different enriching agents.
+    </p>
+    <p>
+      ACETYLENE MIXTURES FOR RAILWAY-CARRIAGE LIGHTING.--In modern practice, the
+      gases which are most commonly employed for diluents of acetylene, under
+      the conditions now being considered, are cannel-coal gas (in France) and
+      oil-gas (elsewhere). Fowler has made a series of observations on the
+      illuminating value of mixtures of oil-gas and acetylene. 13.41 per cent.
+      of acetylene improved the illuminating power of oil-gas from 43 to 49
+      candles. Thirty-nine-candle-power oil-gas had its illuminating power
+      raised to about 60 candles by an admixture of 20 per cent. of acetylene,
+      to about 80 candles by 40 per cent. of acetylene, and to about 110 candles
+      by 60 per cent. of acetylene. The difficulty of employing mixtures fairly
+      rich in acetylene, or pure acetylene, for railway- carriage lighting, lies
+      in the poor efficiency of the small burners which yield from such rich gas
+      a light of 15 to 20 candle-power, such as is suitable for the purpose. For
+      the lighting of railway carriages it is seldom deemed necessary to have a
+      flame of more than 20 candle-power, and it is somewhat difficult to obtain
+      such a flame from oil-gas mixtures rich in acetylene, unless the
+      illuminative value of the gas is wasted to a considerable extent.
+      According to Bunte, 15 volumes of coal-gas, 8 volumes of German oil-gas,
+      and 1.5 volumes of acetylene all yield an equal amount of light; from
+      which it follows that 1 volume of acetylene is equivalent to 5.3 volumes
+      of German oil-gas.
+    </p>
+    <p>
+      A lengthy series of experiments upon the illuminating power of mixtures of
+      oil-gas and acetylene in proportions ranging between 10 and 50 per cent.
+      of the latter, consumed in different burners and at different pressures,
+      has been carried out by Borck, of the German State Railway Department. The
+      figures show that per unit of volume such mixtures may give anything up to
+      6.75 times the light evolved by pure oil-gas; but that the latent
+      illuminating power of the acetylene is less advantageously developed if
+      too much of it is employed. As 20 per cent. of acetylene is the highest
+      proportion which may be legally added to oil- gas in this country, Borck's
+      results for that mixture may be studied:
+    </p>
+<pre xml:space="preserve">
+ ______________________________________________________________________
+|           |        |       |          |         |          |         |
+|           |        |       |          |         |          | Propor- |
+|           |        |       | Consump- |         | Consump- | tionate |
+|  Kind of  | No. of | Pres- | tion per | Candle- | tion per | Illum-  |
+|  Burner.  | Burner | sure. | Hour.    | Power.  | Candle-  | inating |
+|           |        |  mm.  | Litres.  |         | Hour.    | Power   |
+|           |        |       |          |         | Litres.  | to Pure |
+|           |        |       |          |         |          | Oil-Gas.|
+|___________|________|_______|__________|_________|__________|_________|
+|           |        |       |          |         |          |         |
+| Bray      |   00   |  42   |   82     |  56.2   |   1.15   |  3.38   |
+| "         |  000   |  35   |   54     |  28.3   |   1.91   |  4.92   |
+| "         | 0000   |  35   |   43.3   |  16     |   2.71   |  4.90   |
+| Oil-gas   |        |       |          |         |          |         |
+|    burner |   15   |  24   |   21     |   7.25  |   2.89   |  4.53   |
+| "    "    |   30   |  15   |   22     |  10.5   |   2.09   |  3.57   |
+| "    "    |   40   |  16   |   33.5   |  20.2   |   1.65   |  3.01   |
+| "    "    |   60   |  33   |   73     |  45.2   |   1.62   |  3.37   |
+|                                                                      |
+|     The oil-gas from which this mixture was prepared showing:        |
+|                                                                      |
+| Bray      |   00   |  34   |   73.5   |  16.6   |   4.42   |   ...   |
+| "         |  000   |  30   |   48     |   6.89  |   6.96   |   ...   |
+| "         | 0000   |  28   |   39     |   3.26  |  11.6    |   ...   |
+| Oil-gas   |        |       |          |         |          |         |
+|   burner  |   15   |  21   |   19     |   1.6   |  11.8    |   ...   |
+| "    "    |   30   |  14   |   21.5   |   2.94  |   7.31   |   ...   |
+| "    "    |   40   |  15   |   33     |   6.7   |   4.92   |   ...   |
+| "    "    |   60   |  25   |   60     |  13.4   |   4.40   |   ...   |
+|___________|________|_______|__________|_________|__________|_________|
+</pre>
+    <p>
+      It will be seen that the original oil-gas, when compressed to 10
+      atmospheres, gave a light of 1 candle-hour for an average consumption of
+      7.66 litres in the Bray burners, and for a consumption of 7.11 litres in
+      the ordinary German oil-gas jets; while the mixture containing 20 per
+      cent. of acetylene evolved the same amount of light for a consumption of
+      2.02 litres in Bray burners, or of 2.06 litres in the oil-gas jets. Again,
+      taking No. 40 as the most popular and useful size of burner, 1 volume of
+      acetylene oil-gas may be said to be equal to 3 volumes of simple oil-gas,
+      which is the value assigned to the mixture by the German Government
+      officials, who, at the prices ruling there, hold the mixture to be twice
+      as expensive as plain oil-gas per unit of volume, which means that for a
+      given outlay 50 per cent. more light may be obtained from acetylene
+      oil-gas than from oil-gas alone.
+    </p>
+    <p>
+      This comparison of cost is not applicable, as it stands, to compressed
+      oil-gas, with and without enrichment by acetylene, in this country, owing
+      to the oils from which oil-gas is made being much cheaper and of better
+      quality here than in Germany, where a heavy duty is imposed on imported
+      petroleum. Oil-gas as made from Scotch and other good quality gas-oil in
+      this country, usually has, after compression, an illuminating duty of
+      about 8 candles per cubic foot, which is about double that of the
+      compressed German oil-gas as examined by Borck.
+    </p>
+    <p>
+      Hence the following table, containing a summary of results obtained by H.
+      Fowler with compressed oil-gas, as used on English railways, must be
+      accepted rather than the foregoing, in so far as conditions prevailing in
+      this country are concerned. It likewise refers to a mixture of oil-gas and
+      acetylene containing 20 per cent. of acetylene.
+    </p>
+<pre xml:space="preserve">
+ ______________________________________________________________________
+|             |         |           |      |           |               |
+|             |         |           |      |           |   Ratio of    |
+|             |         |Consumption|      |Candles per| Illuminating  |
+|   Burner.   |Pressure.| per Hour. |Candle| Cubic Foot| Power to that |
+|             | Inches. |Cubic Feet.|Power.| per Hour. |of Oil-gas [1] |
+|             |         |           |      |           |  in the same  |
+|             |         |           |      |           |    Burner.    |
+|_____________|_________|___________|______|___________|_______________|
+|             |         |           |      |           |               |
+| Oil-gas . . |   0.7   |   0.98    | 12.5 |   12.72   |      1.65     |
+| Bray 000  . |   0.7   |   1.17    | 14.4 |   12.30   |      1.57     |
+|  "   0000 . |   0.7   |   0.97    | 10.4 |   10.74   |      1.41     |
+|  "   00000  |   0.7   |   0.78    |  5.6 |    7.16   |      1.08     |
+|  "   000000 |   0.7   |   0.55    |  1.9 |    3.52   |      1.14     |
+|_____________|_________|___________|______|___________|_______________|
+</pre>
+    <p>
+      [Footnote 1: Data relating to the relative pecuniary values of acetylene
+      (carburetted or not), coal-gas, paraffin, and electricity as heating or
+      illuminating agents, are frequently presented to British readers after
+      simple recalculation into English equivalents of the figures which obtain
+      in France and Germany. Such a method of procedure is utterly incorrect, as
+      it ignores the higher prices of coal, coal-gas, and especially petroleum
+      products on the Continent of Europe, which arise partly from geographical,
+      but mainly from political causes.]
+    </p>
+    <p>
+      The mixture was tried also at higher pressures in the same burners, but
+      with less favourable results in regard to the duty realised. The oil-gas
+      was also tried at various pressures, and the most favourable result is
+      taken for computing the ratio in the last column. It is evident from this
+      table that 1 volume of this acetylene-oil-gas mixture is equal at the most
+      to 1.65 volume of the simple oil-gas. Whether the mixture will prove
+      cheaper under particular conditions must depend on the relative prices of
+      gas-oil and calcium carbide at the works where the gas is made and
+      compressed. At the prevailing prices in most parts of Britain, simple
+      oil-gas is slightly cheaper, but an appreciable rise in the price of gas-
+      oil would render the mixture with acetylene the cheaper illuminant. The
+      fact remains, however, that per unit weight or volume of cylinder into
+      which the gas is compressed, acetylene oil-gas evolves a higher candle-
+      power, or the same candle-power for a longer period, than simple,
+      unenriched British oil-gas. Latterly, however, the incandescent mantle has
+      found application for railway-carriage lighting, and poorer compressed
+      gases have thereby been rendered available. Thus coal-gas, to which a
+      small proportion of acetylene has been added, may advantageously displace
+      the richer oil-gas and acetylene mixtures.
+    </p>
+    <p>
+      Patents have been taken out by Schwander for the preparation of a mixture
+      of acetylene, air, and vaporised petroleum spirit. A current of naturally
+      damp, or artificially moistened, air is led over or through a mass of
+      calcium carbide, whereby the moisture is replaced by an equivalent
+      quantity of acetylene; and this mixture of acetylene and air is
+      carburetted by passing it through a vessel of petroleum spirit in the
+      manner adopted with air-gas. No details as to the composition,
+      illuminating power, and calorific values of the gas so made have been
+      published. It would clearly tend to be of highly indefinite constitution
+      and might range between what would be virtually inferior carburetted
+      acetylene, and a low-grade air-gas. It is also doubtful whether the
+      combustion of such gas would not be accompanied by too grave risks to
+      render the process useful. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkxii" id="xii">CHAPTER XII</a>
+    </h2>
+    <h3>
+      SUNDRY USES
+    </h3>
+    <p>
+      There are sundry uses for acetylene, and to some extent for carbide, which
+      are not included in what has been said in previous chapters of this book;
+      and to them a few words may be devoted.
+    </p>
+    <p>
+      In orchards and market gardens enormous damage is frequently done to the
+      crops by the ravages of caterpillars of numerous species. These
+      caterpillars cannot be caught by hand, and hitherto it has proved
+      exceedingly difficult to cope with them. However, when they have changed
+      into the perfect state, the corresponding butterflies and moths, like most
+      other winged insects, are strongly attracted by a bright light. As
+      acetylene can easily be burnt in a portable apparatus, and as the burners
+      can be supplied with gas at such comparatively high pressure that the
+      flames are capable of withstanding sharp gusts of wind even when not
+      protected by glass, the brilliant light given by acetylene forms an
+      excellent method of destroying the insects before they have had time to
+      lay their eggs. Two methods of using the light have been tried with
+      astonishing success: in one a naked flame is supported within some
+      receptacle, such as a barrel with one end knocked out, the interior of
+      which is painted heavily with treacle; in the other the flame is supported
+      over an open dish filled with some cheap heavy oil (or perhaps treacle
+      would do equally well). In the first case the insects are attracted by the
+      light and are caught by the adhesive surfaces; in the second they are
+      attracted and singed, and then drowned in, or caught by, the liquid.
+      Either a well-made, powerful, vehicular lamp with its bull's- eye (if any)
+      removed could be used for this purpose, or a portable generator of any
+      kind might be connected with the burner through a flexible tube. It is
+      necessary that the lights should be lit just before dusk when the weather
+      is fine and the nights dark, and for some twenty evenings in June or July,
+      exactly at the period of the year when the perfect insects are coming into
+      existence. In some of the vineyards of Beaujolais, in France, where great
+      havoc has been wrought by the pyralid, a set of 10-candle-power lamps were
+      put up during July 1901, at distances of 150 yards apart, using generators
+      containing 6 oz. of carbide, and dishes filled with water and petroleum 18
+      or 20 inches in diameter. In eighteen nights, some twenty lamps being
+      employed, the total catch of insects was 170,000, or an average of 3200
+      per lamp per night. At French prices, the cost is reported to have been 8
+      centimes per night, or 32 centimes per hectare (2.5 acres). In Germany,
+      where school children are occasionally paid for destroying noxious moths,
+      two acetylene lamps burning for twelve evenings succeeded in catching
+      twice as many insects as the whole juvenile population of a village during
+      August 1902. A similar process has been recommended for the destruction of
+      the malarial mosquito, and should prove of great service to mankind in
+      infected districts. The superiority of acetylene in respect of brilliancy
+      and portability will at once suggest its employment as the illuminant in
+      the "light" moth-traps which entomologists use for entrapping moths. In
+      these traps, the insects, attracted by the light, flutter down panes of
+      glass, so inclined that ultimate escape is improbable; while they are
+      protected from injury through contact with the flame by moans of an
+      intervening sheet of glass.
+    </p>
+    <p>
+      Methods of spraying with carbide dust have been found useful in treating
+      mildew in vines; while a process of burying small quantities of carbide at
+      the roots has proved highly efficacious in exterminating phylloxera in the
+      French and Spanish vineyards. It was originally believed that the
+      impurities of the slowly formed acetylene, the phosphine in particular,
+      acted as toxic agents upon the phylloxera; and therefore carbide
+      containing an extra amount of decomposable phosphides was specially
+      manufactured for the vine-growers. But more recently it has been argued,
+      with some show of reason, that the acetylene itself plays a part in the
+      process, the effects produced being said to be too great to be ascribed
+      wholly to the phosphine. It is well known that many hydrocarbon vapours,
+      such as the vapour of benzene or of naphthalene, have a highly toxic
+      action on low organisms, and the destructive effect of acetylene on
+      phylloxera may be akin to this action.
+    </p>
+    <p>
+      As gaseous acetylene will bear a certain amount of pressure in safety--a
+      pressure falling somewhat short of one effective atmosphere--and as
+      pressure naturally rises in a generating apparatus where calcium carbide
+      reacts with water, it becomes possible to use this pressure as a source of
+      energy for several purposes. The pressure of the gas may, in fact, be
+      employed either to force a stream of liquid through a pipe, or to propel
+      certain mechanism. An apparatus has been constructed in France on the
+      lines of some portable fire-extinguishing appliances in which the pressure
+      set up by the evolution of acetylene in a closed space produces a spray of
+      water charged with lime and gas under the pressure obtaining; the liquid
+      being thrown over growing vines or other plants in order to destroy
+      parasitic and other forms of life. The apparatus consists of a metal
+      cylinder fitted with straps so that it can be carried by man or beast. At
+      one end it has an attachment for a flexible pipe, at the other end a
+      perforated basket for carbide introduced and withdrawn through a
+      "man-hole" that can be tightly closed. The cylinder is filled with water
+      to a point just below the bottom of the basket when the basket is
+      uppermost; the carbide charge is then inserted, and the cover fastened
+      down. As long as the cylinder is carried in the same position, no reaction
+      between the carbide and the water occurs, and consequently no pressure
+      arises; but on inverting the vessel, the carbide is wetted, and acetylene
+      is liberated in the interior. On opening the cock on the outlet pipe, a
+      stream of liquid issues and may be directed as required. By charging the
+      cylinder in the first place with a solution of copper sulphate, the liquid
+      ejected becomes a solution and suspension of copper and calcium salts and
+      hydroxides, resembling "Bordeaux mixture," and may be employed as such. In
+      addition, it is saturated with acetylene which adds to its value as a
+      germicide.
+    </p>
+    <p>
+      The effective gas pressure set up in a closed generator has also been
+      employed in Italy to drive a gas-turbine, and so to produce motion. The
+      plant has been designed for use in lighthouses where acetylene is burnt,
+      and where a revolving or flashing light is required. The gas outlet from a
+      suitably arranged generator communicates with the inlet of a gas- turbine,
+      and the outlet of the turbine is connected to a pipe leading to the
+      acetylene burners. The motion of the turbine is employed to rotate
+      screens, coloured glasses, or any desired optical arrangements round the
+      flames; or, in other situations, periodically to open and close a cock on
+      the gas-main leading to the burners. In the latter case, a pilot flame fed
+      separately is always alight, and serves to ignite the gas issuing from the
+      main burners when the cock is opened.
+    </p>
+    <p>
+      Another use for acetylene, which is only dependent upon a suitably lowered
+      price for carbide to become of some importance, consists in the
+      preparation of a black pigment to replace ordinary lampblack. One method
+      for this purpose has been elaborated by Hubou. Acetylene is prepared from
+      carbide smalls or good carbide, according to price, and the gas is pumped
+      into small steel cylinders to a pressure of 2 atmospheres. An electric
+      spark is then passed, and the gas, standing at its limit of safety,
+      immediately dissociates, yielding a quantitative amount of hydrogen and
+      free carbon. The hydrogen is drawn off, collected in holders, and used for
+      any convenient purpose; the carbon is withdrawn from the vessel, and is
+      ready for sale. At present the pigment is much too expensive, at least in
+      British conditions, to be available in the manufacture of black paint; but
+      its price would justify its employment in the preparation of the best
+      grades of printers' ink. One of the authors has examined an average sample
+      and has found it fully equal in every way to blacks, such as those termed
+      "spirit blacks," which fetch a price considerably above their real value.
+      It has a pure black cast of tint, is free from greasy matter, and can
+      therefore easily be ground into water, or into linseed oil without
+      interfering with the drying properties of the latter. Acetylene black has
+      also been tried in calico printing, and has given far better results in
+      tone and strength than other blacks per unit weight of pigment. It may be
+      added that the actual yield of pigment from creosote oils, the commonest
+      raw material for the preparation of lampblack ("vegetable black"), seldom
+      exceeds 20 or 25 per cent., although the oil itself contains some 80 per
+      cent, of carbon. The yield from acetylene is clearly about 90 per cent.,
+      or from calcium carbide nearly 37.5 per cent, of the original weight.
+    </p>
+    <p>
+      An objection urged against the Hubou process is that only small quantities
+      of the gas can be treated with the spark at one time; if the cylinders are
+      too large, it is stated, tarry by-products are formed. A second method of
+      preparing lampblack (or graphite) from acetylene is that devised by Frank,
+      and depends on utilising the reactions between carbon monoxide or dioxide
+      and acetylene or calcium carbide, which have already been sketched in
+      Chapter VI. When acetylene is employed, the yield is pure carbon, for the
+      only by-product is water vapour; but if the carbide process is adopted,
+      the carbon remains mixed with calcium oxide. Possibly such a material as
+      Frank's carbide process would give, viz., 36 parts by weight of carbon
+      mixed with 56 parts of quicklime or 60 parts of carbon mixed with 112
+      parts of quicklime, might answer the purpose of a pigment in some black
+      paints where the amount of ash left on ignition is not subject to
+      specification. Naturally, however, the lime might be washed away from the
+      carbon by treatment with hydrochloric acid; but the cost of such a
+      purifying operation would probably render the residual pigment too
+      expensive to be of much service except (conceivably) in the manufacture of
+      certain grades of printers' ink, for which purpose it might compete with
+      the carbon obtainable by the Hubou process already referred to.
+    </p>
+    <p>
+      Acetylene tetrachloride, or tetrachlorethane, C_2H_2Cl_4, is now produced
+      for sale as a solvent for chlorine, sulphur, phosphorus, and organic
+      substances such as fats. It may be obtained by the direct combination of
+      acetylene and chlorine as explained in Chapter VI., but the liability of
+      the reaction to take place with explosive violence would preclude the
+      direct application of it on a commercial scale. Processes free from such
+      risk have now, however, been devised for the production of
+      tetrachlorethane. One patented by the Salzbergwerk Neu-Stassfurt consists
+      in passing acetylene into a mixture of finely divided iron and chloride of
+      sulphur. The iron acts as a catalytic. The liquid is kept cool, and as
+      soon as the acetylene passes through unabsorbed, its introduction is
+      stopped and chlorine is passed in. Acetylene and chlorine are then passed
+      in alternately until the liquid finally is saturated with acetylene. The
+      tetrachlorethane, boiling at 147� C., is then distilled off, and the
+      residual sulphur is reconverted to the chloride for use again in the
+      process. A similar process in which the chlorine is used in excess is
+      applicable also to the production of hexachlorethane.
+    </p>
+    <p>
+      Dependent upon price, again, are several uses for calcium carbide as a
+      metallurgical or reducing reagent; but as those are uses for carbide only
+      as distinguished from acetylene, they do not fall within the purview of
+      the present book.
+    </p>
+    <p>
+      When discussing, in Chapter III., methods for disposing of the lime sludge
+      coming from an acetylene generator, it was stated that on occasion a use
+      could be found for this material. If the carbide has been entirely
+      decomposed in an apparatus free from overheating, the waste lime is
+      recovered as a solid mass or as a cream of lime practically pure white in
+      colour. Sometimes, however, as explained in Chapter II., the lime sludge
+      is of a bluish grey tint, even in cases where the carbide decomposed was
+      of good quality and there was no overheating in the generator. Such
+      discoloration is of little moment for most of the uses to which the sludge
+      may be put. The residue withdrawn from a carbide-to-water generator is
+      usually quite fluid; but when allowed to rest in a suitable pit or tank,
+      it settles down to a semi-solid or pasty mass which contains on a rough
+      average 47 per cent. of water and 53 per cent. of solid matter, the amount
+      of lime present, calculated as calcium oxide, being about 40 per cent.
+      Since 64 parts by weight of pure calcium carbide yield 74 parts of dry
+      calcium hydroxide, it may be said that 1 part of ordinary commercial
+      carbide should yield approximately 1.1 parts of dry residue, or 2.1 parts
+      of a sludge containing 47 per cent. of moisture; and sludge of this
+      character has been stated by Vogel to weigh about 22.5 cwt. per cubic
+      yard.
+    </p>
+    <p>
+      Experience has shown that those pasty carbide residues can be employed
+      very satisfactorily, and to the best advantage from the maker's point of
+      view, by builders and decorators for the preparation of ordinary mortar or
+      lime-wash. The mortar made from acetylene lime has been found equal in
+      strength and other properties to mortar compounded from fresh slaked lime;
+      while the distemper prepared by diluting the sludge has been used most
+      successfully in all places where a lime-wash is required, <i>e.g.</i>, on
+      fruit-trees, on cattle-pens, farm-buildings, factories, and the "offices"
+      of a residence. Many of the village installations abroad sell their sludge
+      to builders for the above-mentioned purposes at such a price that their
+      revenue accounts are materially benefited by the additional income. The
+      sludge is also found serviceable for softening the feed-water of steam
+      boilers by the common liming process; although it has been stated that the
+      material contains certain impurities--notably "fatty matter"--which
+      becomes hydrolysed by the steam, yielding fatty acids that act corrosively
+      upon the boiler-plates. This assertion would appear to require
+      substantiation, but a patent has been taken out for a process of drying
+      the sludge at a temperature of 150� to 200� C. in order to remove the
+      harmful matter by the action of the steam evolved. So purified, it is
+      claimed, the lime becomes fit for treating any hard potable or boiler-
+      feed water. It is very doubtful, however, whether the intrinsic value of
+      acetylene lime is such in comparison with the price of fresh lime that,
+      with whatever object in view, it would bear the cost of any method of
+      artificial drying if obtained from the generators in a pasty state.
+    </p>
+    <p>
+      When, on the other hand, the residue is naturally dry, or nearly so, it is
+      exactly equal to an equivalent quantity of quick or slaked lime as a
+      dressing for soil. In this last connexion, however, it must be remembered
+      that only certain soils are improved by an addition of lime in any shape,
+      and therefore carbide residues must not be used blindly; but if analysis
+      indicates that a particular plot of ground would derive benefit from an
+      application of lime, acetylene lime is precisely as good as any other
+      description. Naturally a residue containing unspent carbide, or
+      contaminated with tarry matter, is essentially valueless (except as
+      mentioned below); while it must not be forgotten that a solid residue if
+      it is exposed to air, or a pasty residue if not kept under water, will
+      lose many of its useful properties, because it will be partially converted
+      into calcium carbonate or chalk.
+    </p>
+    <p>
+      Nevertheless, in some respects, the residue from a good acetylene
+      generator is a more valuable material, agriculturally speaking, than pure
+      lime. It contains a certain amount of sulphur, &amp;c., and it therefore
+      somewhat resembles the spent or gas lime of the coal-gas industry. This
+      sulphur, together, no doubt, with the traces of acetylene clinging to it,
+      renders the residue a valuable material for killing the worms and vermin
+      which tend to infest heavily manured and under-cultivated soil. Acetylene
+      lime has been found efficacious in exterminating the "finger-and-toe" of
+      carrots, the "peach-curl" of peach-trees, and in preventing cabbages from
+      being "clubbed." It may be applied to the ground alone, or after admixture
+      with some soil or stable manure. The residue may also be employed, either
+      alone or mixed with some agglomerate, in the construction of garden paths
+      and the like.
+    </p>
+    <p>
+      If the residues are suitably diluted with water and boiled with (say)
+      twice their original weight of flowers of sulphur, the product consists of
+      a mixture of various compounds of calcium and sulphur, or calcium
+      sulphides--which remain partly in solution and partly in the solid state.
+      This material, used either as a liquid spray or as a moist dressing, has
+      been said to prove a useful garden insecticide and weed-killer.
+    </p>
+    <p>
+      There are also numerous applications of the acetylene light, each of much
+      value, but involving no new principle which need be noticed. The light is
+      so actinic, or rich in rays acting upon silver salts, that it is
+      peculiarly useful to the photographer, either for portraiture or for his
+      various positive printing operations. Acetylene is very convenient for
+      optical lantern work on the small scale, or where the oxy-hydrogen or
+      oxy-coal-gas light cannot be used. Its intensity and small size make its
+      self-luminous flame preferable on optical grounds to the oil-lamp or the
+      coal-gas mantle; but the illuminating surface is nevertheless too large to
+      give the best results behind such condensers as have been carefully worked
+      to suit a source of light scarcely exceeding the dimensions of a point.
+      For lantern displays on very large screens, or for the projection of a
+      powerful beam of light to great distances in one direction (as in night
+      signalling, &amp;c.), the acetylene blowpipe fed with pure oxygen, or with
+      air containing more than its normal proportion of oxygen, which is
+      discussed in Chapter IX., is specially valuable, more particularly if the
+      ordinary cylinder of lime is replaced by one of magnesia, zirconia, or
+      other highly refractory oxide. <br /> <br /> <br />
+    </p>
+    <h2>
+      <a name="linkxiii" id="xiii">CHAPTER XIII</a>
+    </h2>
+    <h3>
+      PORTABLE ACETYLENE LAMPS AND PLANT
+    </h3>
+    <p>
+      It will be apparent from what has been said in past chapters that the
+      construction of a satisfactory generator for portable purposes must be a
+      problem of considerable complexity. A fixed acetylene installation tends
+      to work the more smoothly, and the gas evolved therefrom to burn the more
+      pleasantly, the more technically perfect the various subsidiary items of
+      the plant are; that is to say, the more thoroughly the acetylene is
+      purified, dried, and delivered at a strictly constant pressure to the
+      burners and stoves. Moreover, the efficient behaviour of the generator
+      itself will depend more upon the mechanical excellence and solidity of its
+      construction than (with one or two exceptions) upon the precise system to
+      which it belongs. And, lastly, the installation will, broadly speaking,
+      work the better, the larger the holder is in proportion to the demands
+      ever made upon it; while that holder will perform the whole duty of a
+      gasholder more effectually if it belongs to the rising variety than if it
+      is a displacement holder. All these requirements of a good acetylene
+      apparatus have to be sacrificed to a greater or less extent in portable
+      generators; and since the sacrifice becomes more serious as the generator
+      is made smaller and lighter in weight, it may be said in general terms
+      that the smaller a portable (or, indeed, other) acetylene apparatus is,
+      the less complete or permanent satisfaction will it give its user. Again,
+      small portable apparatus are only needed to develop intensities of light
+      insignificant in comparison with those which may easily be won from
+      acetylene on a larger scale; they are therefore fitted with smaller
+      burners, and those burners are not merely small in terms of consumption
+      and illuminating power, but not infrequently are very badly constructed,
+      and are relatively deficient in economy or duty. Thus any comparisons
+      which may be made on lines similar to those adopted in Chapter I., or
+      between unit weights, volumes, or monetary equivalents of calcium carbide,
+      paraffin, candles, and colza oil, become utterly incorrect if the carbide
+      is only decomposed in a small portable generator fitted with an
+      inefficient jet; first, because the latent illuminating power of the
+      acetylene evolved is largely wasted; secondly, because any gas produced
+      over and above that capable of instant combustion must be blown off from a
+      vent-pipe; and thirdly, because the carbide itself tends to be imperfectly
+      decomposed, either through a defect in the construction of the lamp, or
+      through the brief and interrupted requirements of the consumer.
+    </p>
+    <p>
+      In several important respects portable acetylene apparatus may be divided
+      into two classes from a practical point of view. There is the portable
+      table or stand lamp intended for use in an occupied room, and there is the
+      hand or supported lamp intended for the illumination of vehicles or
+      open-air spaces. Economy apart, no difficulty arises from imperfect
+      combustion or escape of unburnt gas from an outdoor lamp, but in a room
+      the presence of unburnt acetylene must always be offensive even if it is
+      not dangerous; while the combustion products of the impurities--and in a
+      portable generator acetylene cannot be chemically purified--are highly
+      objectionable. It is simply a matter of good design to render any form of
+      portable apparatus safe against explosion (employment of proper carbide
+      being assumed), for one or more vent-pipes can always be inserted in the
+      proper places; but from an indoor lamp those vent-pipes cannot be made to
+      discharge into a place of safety, while, as stated before, a generator in
+      which the vent-pipes come into action with any frequency is but an
+      extravagant piece of apparatus for the decomposition of so costly a
+      material as calcium carbide. Looked at from one aspect the holder of a
+      fixed apparatus is merely an economical substitute for the wasteful vent-
+      pipe, because it is a place in which acetylene can be held in reserve
+      whenever the make exceeds the consumption in speed. It is perhaps possible
+      to conceive of a large table acetylene lamp fitted with a water- sealed
+      rising holder; but for vehicular purposes the displacement holder is
+      practically the only one available, and in small apparatus it becomes too
+      minute in size to be of much service as a store for the gas produced by
+      after-generation. Other forms of holder have been suggested by inventors,
+      such as a collapsible bag of india-rubber or the like; but rubber is too
+      porous, weak, and perishable a material to be altogether suitable. If it
+      is possible, by bringing carbide and water into mutual contact in
+      predetermined quantities, to produce gas at a uniform rate, and at one
+      which corresponds with the requirements of the burner, in a small
+      apparatus--and experience has shown it to be possible within moderately
+      satisfactory limits--it is manifest that the holder is only needed to take
+      up the gas of after-generation; and in Chapters II. and III. it was
+      pointed out that after-generation only occurs when water is brought into
+      contact with an excess of carbide. If, then, the opposite system of
+      construction is adopted, and carbide is fed into water mechanically, no
+      after-generation can take place; and provided the make of gas can be
+      controlled in a small carbide-feed generator as accurately as is possible
+      in a small water-to-carbide generator, the carbide-feed principle will
+      exhibit even greater advantages in portable apparatus than it does in
+      plant of domestic size. Naturally almost every variety of carbide-feeding
+      gear, especially when small, requires or prefers granulated (or granulated
+      and "treated") carbide; and granulated carbide must inevitably be
+      considerably more expensive per unit of light evolved than the large
+      material, but probably in the application to which the average portable
+      acetylene apparatus is likely to be put, strict economy is not of first
+      consequence. In portable acetylene generators of the carbide-feed type,
+      the supply is generally governed by the movements of a mushroom-headed or
+      conical valve at the mouth of a conical carbide vessel; such movements
+      occurring in sympathy with the alterations in level of the water in the
+      decomposing chamber, which is essentially a small displacement holder
+      also, or being produced by the contraction of a flexible chamber through
+      which the gas passes on its way to the burner. So far as it is safe to
+      speak definitely on a matter of this kind, the carbide-feed device appears
+      to work satisfactorily in a stationary (<i>e.g.</i>, table) lamp; but it
+      is highly questionable whether it could be applied to a vehicular
+      apparatus exposed to any sensible amount of vibration. The device is
+      satisfactory on the table of an occupied room so far, be it understood, as
+      any small portable generators can be: it has no holder, but since no
+      after-generation occurs, no holder is needed; still the combustion
+      products contaminate the room with all the sulphur and phosphorus of the
+      crude acetylene.
+    </p>
+    <p>
+      For vehicular lamps, and probably for hand lanterns, the water-to-carbide
+      system has practically no alternative (among actual generators), and
+      safety and convenience have to be gained at the expense of the carbide. In
+      such apparatus the supply of water is usually controlled ultimately by
+      pressure, though a hand-operated needle-valve is frequently put on the
+      water tube. The water actually reaches the carbide either by dropping from
+      a jet, by passing along, upwards or downwards, a "wick" such as is used in
+      oil-lamps, or by percolating through a mass of porous material like felt.
+      The carbide is held in a chamber closed except at the gas exit to the
+      burner and at the inlet from the water reservoir: so that if gas is
+      produced more rapidly than the burner takes it, more water is prevented
+      from entering, or the water already present is driven backwards out of the
+      decomposing chamber into some adjoining receptacle. It is impossible to
+      describe in detail all the lamps which have been constructed or proposed
+      for vehicular use; and therefore the subject must be approached in general
+      terms, discussing simply the principles involved in the design of a safe
+      portable generator.
+    </p>
+    <p>
+      In all portable apparatus, and indeed in generators of larger dimensions,
+      the decomposing chamber must be so constructed that it can never, even by
+      wrong manipulation, be sealed hermetically against the atmosphere. If
+      there is a cock on the water inlet tube which is capable of being
+      completely shut, there must be no cock between the decomposing chamber and
+      the burner. If there is a cock between the carbide vessel and the burner,
+      the water inlet tube must only be closed by the water, being water-sealed,
+      in fact, so that if pressure rises among the carbide the surplus gas may
+      blow the seal or bubble through the water in the reservoir. If the
+      water-supply is mainly controlled by a needle-valve, it is useful to
+      connect the burner with the carbide vessel through a short length of
+      rubber tube; and if this plan is adopted, a cock can, if desired, be put
+      close to the burner. The rubber should not be allowed to form a bend
+      hanging down, or water vapour, &amp;c., may condense and extinguish the
+      flame. In any case there should be a steady fall from the burner to the
+      decomposing chamber, or to some separate catch-pit for the products of
+      condensation. Much of the success attainable with small generators will
+      depend on the water used. If it is contaminated with undissolved matter,
+      the dirt will eventually block the fine orifices, especially the
+      needle-valve, or will choke the pores of the wick or the felt pad. If the
+      water contains an appreciable amount of "temporary hardness," and if it
+      becomes heated much in the lamp, fur will be deposited sooner or later,
+      and will obviously give trouble. Where the water reservoir is at the upper
+      part of the lamp, and the liquid is exposed to the heat of the flame, fur
+      will appear quickly if the water is hard. Considerable benefit would
+      accrue to the user of a portable lamp by the employment of rain water
+      filtered, if necessary, through fabric or paper. The danger of freezing in
+      very severe weather may be prevented by the use of calcium chloride, or
+      preferably, perhaps, methylated spirit in the water (<i>cf.</i> Chapter
+      III., p. 92). The disfavour with which cycle and motor acetylene lamps are
+      frequently regarded by nocturnal travellers, other than the users thereof,
+      is due to thoughtless design in the optical part of such lamps, and is no
+      argument against the employment of acetylene. By proper shading or
+      deflection of the rays, the eyes of human beings and horses can be
+      sufficiently protected from the glare, and the whole of the illumination
+      concentrated more perfectly on the road surface and the lower part of
+      approaching objects--a beam of light never reaching a height of 5 feet
+      above the ground is all that is needed to satisfy all parties.
+    </p>
+    <p>
+      As the size of the generator rises, conditions naturally become more
+      suited to the construction of a satisfactory apparatus; until generators
+      intended to supply light to the whole of (say) a railway carriage, or the
+      head and cab lamps of a locomotive, or for the outside and inside lighting
+      of an omnibus are essentially generators of domestic dimensions somewhat
+      altered in internal construction to withstand vibration and agitation. As
+      a rule there is plenty of space at the side of a locomotive to carry a
+      generator fitted with a displacement holder of sufficient size, which is
+      made tall rather than wide, to prevent the water moving about more than
+      necessary. From the boiler, too, steam can be supplied to a coil to keep
+      the liquid from freezing in severe weather. Such apparatus need not be
+      described at length, for they can be, and are, made on lines resembling
+      those of domestic generators, though more compactly, and having always a
+      governor to give a constant pressure. For carriage lighting any ordinary
+      type of generator, preferably, perhaps, fitted with a displacement holder,
+      can be erected either in each corridor carriage, or in a brake van at the
+      end of the train. Purifiers may be added, if desired, to save the burners
+      from corrosion; but the consumption of unpurified gas will seldom be
+      attended by hygienic disadvantages, because the burners will be contained
+      in closed lamps, ventilating into the outside air. The generator, also,
+      may conveniently be so constructed that it is fed with carbide from above
+      the roof, and emptied of lime sludge from below the floor of the vehicle.
+      It can hardly be said that the use of acetylene generated on board adds a
+      sensible risk in case of collision. In the event of a subsequent fire, the
+      gas in the generator would burn, but not explode; but in view of the
+      greater illuminating power per unit volume of carbide than per equal
+      volume of compressed oil- gas, a portable acetylene generator should be
+      somewhat less objectionable than broken cylinders of oil-gas if a fire
+      should follow a railway accident of the usual kind. More particularly by
+      the use of "cartridges" of carbide, a railway carriage generator can be
+      constructed of sufficient capacity to afford light for a long journey, or
+      even a double journey, so that attention would be only required (in the
+      ordinary way) at one end of the line.
+    </p>
+    <p>
+      Passing on from the generators used for the lighting of vehicles and for
+      portable lamps for indoor lighting to the considerably larger portable
+      generators now constructed for the supply of acetylene for welding
+      purposes and for "flare" lamps, it will be evident that they may embody
+      most or all of the points which are essential to the proper working of a
+      fixed generator for the supply of a small establishment. The holder will
+      generally be of the displacement type, but some of these larger portable
+      generators are equipped with a rising holder. The generators are,
+      naturally, automatic in action, but may be either of the water-to-carbide
+      or carbide-to-water type--the latter being preferable in the larger sizes
+      intended for use with the oxy-acetylene blow-pipe for welding, &amp;c.,
+      for which use a relatively large though intermittent supply of acetylene
+      is called for. The apparatus is either carried by means of handles or
+      poles attached to it, or is mounted on a wheelbarrow or truck for
+      convenience of transport to the place where it is to be used. The so
+      called "flare" lamps, which are high power burners mounted, with or
+      without a reflector, above a portable generator, are extremely useful for
+      lighting open spaces where work has to be carried on temporarily after
+      nightfall, and are rapidly displacing oil-flares of the Lucigen type for
+      such purposes.
+    </p>
+    <p>
+      The use of "cartridges" of calcium carbide has already been briefly
+      referred to in Chapters II. and III. These cartridges are usually either
+      receptacles of thin sheet-metal, say tin plate, or packages of carbide
+      wrapped up in grease proof paper or the like. If of metal, they may have a
+      lid which is detached or perforated before they are put into the
+      generator, or the generator (when automatic and of domestic size) may be
+      so arranged that a cartridge is punctured in one or more places whenever
+      more gas is required. If wrapped in paper, the cartridges may be dropped
+      into water by an automatic generator at the proper times, the liquid then
+      loosening the gum and so gaining access to the interior; or one spot may
+      be covered by a drape of porous material (felt) only, through which the
+      water penetrates slowly. The substance inside the cartridge may be
+      ordinary, granulated, or "treated" carbide. Cartridges or "sticks" of
+      carbide are also made without wrappings, either by moistening powdered
+      carbide with oil and compressing the whole into moulds, or by compressing
+      dry carbide dust and immersing the sticks in oil or molten grease. The
+      former process is said to cause the carbide to take up too much oil, so
+      that sticks made by the second method are reputed preferable. All these
+      cartridges have the advantage over common carbide of being more permanent
+      in damp air, of being symmetrical in shape, of decomposing at a known
+      speed, and of liberating acetylene in known quantity; but evidently they
+      are more expensive, owing to the cost of preparing them, &amp;c. They may
+      be made more cheaply from the dust produced in the braking of carbide, but
+      in that case the yield of gas will be relatively low.
+    </p>
+    <p>
+      It is manifest that, where space is to spare, purifiers containing the
+      materials mentioned in Chapter V. can be added to any portable acetylene
+      apparatus, provided also that the extra weight is not prohibitive. Cycle
+      lamps and motor lamps must burn an unpurified gas unpurified from
+      phosphorus and sulphur; but it is always good and advisable to filter the
+      acetylene from dust by a plug of cotton wool or the like, in order to keep
+      the burners as clear as may be. A burner with a screwed needle for
+      cleaning is always advantageous. Formerly the burners used on portable
+      acetylene lamps were usually of the single jet or rat-tail, or the union
+      jet or fish tail type, and exhibited in an intensified form, on account of
+      their small orifices, all the faults of these types of burners for the
+      consumption of acetylene (see Chapter VIII.). Now, however, there are
+      numerous special burners adapted for use in acetylene cycle and motor
+      lamps, &amp;c., and many of these are of the impinging jet type, and some
+      have steatite heads to prevent distortion by the heat. One such cycle-
+      lamp burner, as sold in England by L. Wiener, of Fore Street, London, is
+      shown in Fig. 21. A burner constructed like the "Kona" (Chapter VIII.) is
+      made in small sizes (6, 8 and 10 litres per hour) for use in vehicular
+      lamps, under the name of the "Konette," by Falk, Stadelmann and Co., Ltd.,
+      of London, who also make a number of other small impinging jet burners. A
+      single jet injector burner on the "Ph�s" principle is made in small sizes
+      by the Ph�s Co., of London, specially for use in lamps on vehicles.
+    </p>
+    <p class="ctr">
+      <a href="images/304.png"><img src="images/304th.png"
+      alt="FIG. 21.--CYCLE-LAMP BURNER NO. 96042A" /></a>
+    </p>
+    <p>
+      Nevertheless, although satisfactory medium-sized vehicular lamps for the
+      generation of acetylene have been constructed, the best way of using
+      acetylene for all such employments as these is to carry it ready made in a
+      state of compression. For railway purposes, where an oil-gas plant is in
+      existence, and where it is merely desired to obtain a somewhat brighter
+      light, the oil-gas may be enriched with 20 per cent. of acetylene, and the
+      mixed gas pumped into the same cylinders to a pressure of 10 atmospheres,
+      as mentioned in Chapter XI.; the only alteration necessary being the
+      substitution of suitable small burners for the common oil-gas jets. As far
+      as the plant is concerned, all that is required is a good acetylene
+      generator, purifier, and holder from which the acetylene can be drawn or
+      forced through a meter into a larger storage holder, the meter being
+      connected by gearing with another meter on the pipe leading from the
+      oil-gas holder to the common holder, so that the necessary proportions of
+      the two gases shall be introduced into the common holder simultaneously.
+      From this final holder the enriched gas will be pumped into the cylinders
+      or into a storage cylinder, by means of a thoroughly cooled pump, so that
+      the heat set free by the compression may be safely dissipated.
+    </p>
+    <p>
+      Whenever still better light is required in railway carriages, as also for
+      the illumination of large, constantly used vehicles, such as omnibuses,
+      the acetone process (<i>cf.</i> Chapter XI.) exhibits notable advantages.
+      The light so obtained is the light of neat acetylene, but the gas is
+      acetylene having an upper limit of explosibility much lower than usual
+      because of the vapour of acetone in it. In all other respects the presence
+      of the acetone will be unnoticeable, for it is a fairly pure organic
+      chemical body, which burns in the flame completely to carbon dioxide and
+      water, exactly as acetylene itself does. If the acetylene is merely
+      compressed into porous matter without acetone, the gas burnt is acetylene
+      simply; but per unit of volume or weight the cylinders will not be capable
+      of developing so much light.
+    </p>
+    <p>
+      In the United States, at least one railway system (The Great Northern) has
+      a number of its passenger coaches lighted by means of plain acetylene
+      carried in a state of compression in cylinders without porous matter. The
+      gas is generated, filtered from dust, and stored in an ordinary rising
+      holder at a factory alongside the line; being drawn from this holder
+      through a drier to extract moisture, and through a safety device, by a
+      pump which, in three stages, compresses the acetylene into large storage
+      reservoirs. The safety device consists of a heavy steel cylinder filled
+      with some porous substance which, like the similar material of the acetone
+      cylinders, prevents any danger of the acetylene contained in the
+      water-sealed holder being implicated in an explosion starting backwards
+      from the compression, by extinguishing any spark which might be produced
+      there. The plant on the trains comprises a suitable number of cylinders,
+      filled by contact with the large stores of gas to a pressure of 10
+      atmospheres, pipes of fusible metal communicating with the lamps, and
+      ordinary half-foot acetylene burners. The cylinders are provided with
+      fusible plugs, so that, in the event of a fire, they and the service-
+      pipes would melt, allowing the gas to escape freely and burn in the air,
+      instead of exploding or dissociating explosively within the cylinders
+      should the latter be heated by any burning woodwork or the like. It is
+      stated that this plan of using acetylene enables a quantity of gas to be
+      carried under each coach which is sufficient for a run of from 53 to 70
+      hours' duration, or of over 3600 miles; that is to say, enables the train,
+      in the conditions obtaining on the line in question, to make a complete
+      "round trip" without exhaustion of its store of artificial light. The
+      system has been in operation for some years, and appears to have been so
+      carefully managed that no accident has arisen; but it is clear that
+      elements of danger are present which are eliminated when the cylinders are
+      loaded with porous matter and acetone. The use of a similar system of
+      compressed acetylene train lighting in South America has been attended
+      with a disastrous explosion, involving loss of life.
+    </p>
+    <p>
+      It may safely be said that the acetone system, or less conveniently
+      perhaps the mere compression into porous matter, is the best to adopt for
+      the table-lamp which is to be used in occupied rooms Small cylinders of
+      such shapes as to form an elegant base for a table-lamp on more or less
+      conventional lines would be easy to make. They would be perfectly safe to
+      handle. If accidentally or wilfully upset, no harm would arise. By
+      deliberate ill-treatment they might be burst, or the gas-pipe fractured
+      below the reducing valve, so that gas would escape under pressure for a
+      time; but short of this they would be as devoid of extra clangor in times
+      of fire as the candle or the coal-gas burner. Moreover, they would only
+      contaminate the air with carbon dioxide and water vapour, for the gas is
+      purified before compression; and modern investigations have conclusively
+      demonstrated that the ill effects produced in the air of an imperfectly
+      ventilated room by the extravagant consumption of coal-gas depend on the
+      accumulation of the combustion products of the sulphur in the gas rather
+      than upon the carbon dioxide set free.
+    </p>
+    <p>
+      One particular application of the portable acetylene apparatus is of
+      special interest. As calcium carbide evolves an inflammable gas when it
+      merely comes into contact with water, it becomes possible to throw into
+      the sea or river, by hand or by ejection from a mortar, a species of bomb
+      or portable generator which is capable of emitting a powerful beam of
+      light if only facilities are present for inflaming the acetylene
+      generated; and it is quite easy so to arrange the interior of such
+      apparatus that they can be kept ready for instant use for long periods of
+      time without sensible deterioration, and that they can be recharged after
+      employment. Three methods of firing the gas have been proposed. In one the
+      shock or contact with the water brings a small electric battery into play
+      which produces a spark between two terminals projecting across the burner
+      orifice; in the second, a cap at the head of the generator contains a
+      small quantity of metallic potassium, which decomposes water with such
+      energy that the hydrogen liberated catches fire; and in the third a
+      similar cap is filled with the necessary quantity of calcium phosphide, or
+      the "carbophosphide of calcium" mentioned in Chapter XI., which yields a
+      flame by the immediate ignition of the liquid phosphine produced on the
+      attack of water. During the two or three seconds consumed in the
+      production of the spark or pilot flame, the water is penetrating the main
+      charge of calcium carbide in the interior of the apparatus, until the
+      whole is ready to give a bright light for a time limited only by the
+      capacity of the generator. It is obvious that such apparatus may be of
+      much service at sea: they may be thrown overboard to illuminate separate
+      lifebuoys in case of accident, or be attached to the lifebuoys they are
+      required to illuminate, or be used as lifebuoys themselves if fitted with
+      suitable chains or ropes; they may be shot ahead to illuminate a difficult
+      channel, or to render an enemy visible in time of war. Several such
+      apparatus have already been constructed and severely tested; they appear
+      to give every satisfaction. They are, of course, so weighted that the
+      burner floats vertically, while buoyancy is obtained partly by the gas
+      evolved, and partly by a hollow portion of the structure containing air.
+      Cartridges of carbide and caps yielding a self- inflammable gas can be
+      carried on board ship, by means of which the torches or lifebuoys may be
+      renewed after service in a few minutes' time.
+    </p>
+    <h2>
+      <a name="linkxiv" id="xiv">CHAPTER XIV</a>
+    </h2>
+    <h3>
+      VALUATION AND ANALYSIS OF CARBIDE
+    </h3>
+    <p>
+      The sale and purchase of calcium carbide in this country will, under
+      existing conditions, usually be conducted in conformity with the set of
+      regulations issued by the British Acetylene Association, of which a copy,
+      revised to date, is given below:
+    </p>
+    <p>
+      "REGULATIONS AS TO CARBIDE OF CALCIUM."
+    </p>
+    <p>
+      1. The carbide shall be guaranteed by the seller to yield, when broken to
+      standard size, <i>i.e.</i>, in lumps varying from 1 to 2-1/2 inches or
+      larger, not less than 4.8 cubic feet per lb., at a barometric pressure of
+      30 inches and temperature of 60� Fahr. (15.55� Centigrade). The actual gas
+      yield shall be deemed to be the gas yield ascertained by the analyst, plus
+      5 per cent.
+    </p>
+    <p>
+      "Carbide yielding less than 4.8 cubic feet in the sizes given above shall
+      be paid for in proportion to the gas yield, <i>i.e.</i>, the price to be
+      paid shall bear the same relation to the contract price as the gas yield
+      bears to 4.8 cubic feet per lb.
+    </p>
+    <p>
+      "2. The customer shall have the right to refuse to take carbide yielding
+      in the sizes mentioned above less than 4.2 cubic foot, per lb., and it
+      shall lie, in case of refusal and as from the date of the result, of the
+      analysis being made known to either party, at the risk and expense of the
+      seller.
+    </p>
+    <p>
+      "3. The carbide shall not contain higher figures of impurities than shall
+      from time to time be fixed by the Association.
+    </p>
+    <p>
+      "4. No guarantee shall be given for lots of less than 3 cwt., or for
+      carbide crushed to smaller than the above sizes.
+    </p>
+    <p>
+      "5. In case of dispute as to quality, either the buyer or the seller shall
+      have the right to have one unopened drum per ton of carbide, or part of a
+      ton, sent for examination to one of the analysts appointed by the
+      Association, and the result of the examination shall be held to apply to
+      the whole of the consignment to which the drum belonged. "6. A latitude of
+      5 per cent, shall be allowed for analysis; consequently differences of 5
+      per cent. above or below the yields mentioned in 1 and 2 shall not be
+      taken into consideration.
+    </p>
+    <p>
+      "7. Should the yield of gas be less than 4.8 cubic feet less 5 per cent.,
+      the carriage of the carbide to and from the place of analysis and the cost
+      of the analysis shall be paid for by the seller. Should the yield be more
+      than 4.8 cubic feet less 5 per cent., the carriage and costs of analysis
+      shall be borne by the buyer, who, in addition, shall pay an increase of
+      price for the carbide proportionate to the gas yield above 4.8 cubic feet
+      plus 5 per cent.
+    </p>
+    <p>
+      "8. Carbide of 1 inch mesh and above shall not contain more than 5 per
+      cent. of dust, such dust to be defined as carbide capable of passing
+      through a mesh of one-sixteenth of an inch.
+    </p>
+    <p>
+      "9. The seller shall not be responsible for deterioration of quality
+      caused by railway carriage in the United Kingdom, unless he has sold
+      including carriage to the destination indicated by the buyer.
+    </p>
+    <p>
+      "10. Carbide destined for export shall, in case the buyer desires to have
+      it tested, be sampled at the port of shipment, and the guarantee shall
+      cease after shipment.
+    </p>
+    <p>
+      "11. The analyst shall take a sample of not less than 1 lb. each from the
+      top, centre, and bottom of the drum. The carbide shall be carefully broken
+      up into small pieces, due care being taken to avoid exposure to the air as
+      much as possible, carefully screened and tested for gas yield by
+      decomposing it in water, previously thoroughly saturated by exposure to
+      acetylene for a period of not less than 48 hours.
+    </p>
+    <p>
+      "12. Carbide which, when properly decomposed, yields acetylene containing
+      from all phosphorus compounds therein more than .05 per cent. by volume of
+      phosphoretted hydrogen, may be refused by the buyer, and any carbide found
+      to contain more than this figure, with a latitude of .01 per cent. for the
+      analysis, shall lie at the risk and expense of the seller in the manner
+      described in paragraph 2.
+    </p>
+    <p>
+      "The rules mentioned in paragraph 7 shall apply as regards the carriage
+      and costs of analysis; in other words, the buyer shall pay these costs if
+      the figure is below 0.05 per cent. plus 0.01 per cent., and the seller if
+      the figure is above 0.05 per cent. plus 0.01 per cent. "The sampling shall
+      take place in the manner prescribed in paragraphs 5 and 11, and the
+      analytical examination shall be effected in the manner prescribed by the
+      Association and obtainable upon application to the Secretary."
+    </p>
+    <hr />
+    <p>
+      The following is a translation of the corresponding rules issued by the
+      German Acetylene Association (<i>Der Deutsche Acetylenverein</i>) in
+      regard to business dealings in calcium carbide, as put into force on April
+      1, 1909:
+    </p>
+    <p>
+      "REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE.
+    </p>
+    <p>
+      "<i>Price</i>.
+    </p>
+    <p>
+      "The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of
+      carbide in packages containing about 100 kilogrammes.
+    </p>
+    <p>
+      "By packages containing about 100 kilogrammes are meant packages
+      containing within 10 per cent. above or below that weight.
+    </p>
+    <p>
+      "The carbide shall be packed in gas- and water-tight vessels of sheet-
+      iron of the strength indicated in the prescriptions of the carrying
+      companies.
+    </p>
+    <p>
+      "The prices for other descriptions of packing must be specially stated.
+    </p>
+    <p>
+      "<i>Place of Delivery</i>.
+    </p>
+    <p>
+      "For consignment for export, the last European shipping port shall be
+      taken as the place of delivery.
+    </p>
+    <p>
+      "<i>Quality</i>.
+    </p>
+    <p>
+      "Commercial carbide shall be of such quality that in the usual lumps of 15
+      to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield of at
+      least 300 litres at 15� C. and 760 mm. pressure of crude acetylene per
+      kilogramme for each consignment (= 4.81 cubic feet at 60� F. and 30 inches
+      per lb.). A margin of 2 per cent. shall be allowed for the analysis.
+      Carbide which yields less than 300 litres per kilogramme, but not less
+      than 270 litres (= 4.33 cubic feet) of crude acetylene per kilogramme
+      (with the above-stated 2 per cent. margin for analysis) must be accepted
+      by the buyer. The latter, however, is entitled to make a proportionate
+      deduction from the price and also to deduct the increased freight charges
+      to the destination or, if the latter is not settled at the time when the
+      transaction is completed, to the place of delivery. Carbide which yields
+      less than 270 litres of crude acetylene per kilogramme need not be
+      accepted.
+    </p>
+    <p>
+      "Carbide must not contain more than 5 per cent. of dust. By dust is to be
+      understood all which passes through a screen of 1 mm. (0.04 inch) square,
+      clear size of holes.
+    </p>
+    <p>
+      "Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (and
+      intermediate sizes) must yield on the average for each delivery at least
+      270 litres at 15� C. and 760 mm. pressure of crude acetylene per
+      kilogramme (= 4.33 cubic feet at 60� F. and 30 inches per lb.) A margin of
+      2 per cent. shall be allowed for the analysis. Small carbide of from 4 to
+      15 mm. in size (and intermediate sizes) which yields less than 270 litres
+      but not less than 250 litres (= 4.01 cubic feet per lb.) of crude
+      acetylene per kilogramme (with the above-stated 2 per cent. margin for
+      analysis) must be accepted by the buyer. The latter, however, is entitled
+      to make a proportionate deduction from the price and also to deduct the
+      increased freight charges to the destination or, if the latter is not
+      settled at the time when the transaction is completed, to the place of
+      delivery. Small carbide of from 4 to 15 mm. in size (and intermediate
+      sizes) which yields less than 250 litres per kilogramme need not be
+      accepted.
+    </p>
+    <p>
+      "Carbide shall only be considered fit for delivery if the proportion of
+      phosphoretted hydrogen in the crude acetylene does not amount to more than
+      0.04 volume per cent. A margin of 0.01 volume per cent. shall be allowed
+      for the analysis for phosphoretted hydrogen. The whole of the phosphorus
+      compounds contained in the gas are to be calculated as phosphoretted
+      hydrogen.
+    </p>
+    <p>
+      "<i>Period for Complaints.</i>
+    </p>
+    <p>
+      "An interval of four weeks from delivery shall be allowed for complaints
+      for consignments of 5000 kilogrammes (= 5 tons) and over, and an interval
+      of two weeks for smaller consignments. A complaint shall refer only to a
+      quantity of carbide remaining at the time of taking the sample.
+    </p>
+    <p>
+      "<i>Determination of Quality.</i>
+    </p>
+    <p>
+      "1. In case the parties do not agree that the consignee is to send to the
+      analyst for the determination of the quality one unopened and undamaged
+      drum when the consignment is less than 5000 kilogrammes, and two such
+      drums when it is over 5000 kilogrammes, a sample for the purpose of
+      testing the quality is to be taken in the following manner:
+    </p>
+    <p>
+      "A sample having a total weight of at least 2 kilogrammes (= 4.4 lb.) is
+      to be taken. If the delivery to be tested does not comprise more than ten
+      drums, the sample is to be taken from an unopened and undamaged drum
+      selected at random. With deliveries of more than ten drums, the sample is
+      to be drawn from not fewer than 10 per cent, of the lot, and from each of
+      the unopened and undamaged drums drawn for the purpose not less than 1
+      kilogramme (= 2.2 lb.) is to be taken.
+    </p>
+    <p>
+      "The sampling is to be carried out by a trustworthy person appointed by
+      the two parties, or by one of the experts regularly recognised by the
+      German Acetylene Association, thus: Each selected drum, before opening, is
+      to be turned over twice (to got rid of any local accumulation of dust) and
+      the requisite quantity is to he withdrawn with a shovel (not with the
+      hand) from any part of it. These samples are immediately shot into one or
+      more vessels which are closed air- and water-tight. The lid is secured by
+      a seal. No other description of package, such as cardboard cases, boxes,
+      &amp;c., is permissible.
+    </p>
+    <p>
+      "If there is disagreement as to the choice of a trustworthy person, each
+      of the two parties is to take the required quantity, as specified above.
+    </p>
+    <p>
+      "2. The yield of gas and the proportion of phosphoretted hydrogen
+      contained in it are to be determined by the methods prescribed by the
+      German Acetylene Association. If there are different analyses giving non-
+      concordant results, an analysis is to be made by the German Acetylene
+      Association, which shall be accepted as final and binding.
+    </p>
+    <p>
+      "In cases, however, where the first analysis has been made in the
+      Laboratory of the German Acetylene Association and arbitration is
+      required, the decisive analysis shall be made by the Austrian Acetylene
+      Association. If one of the parties prevents the arbitrator's analysis
+      being carried out, the analysis of the other party shall be absolutely
+      binding on him.
+    </p>
+    <p>
+      "3. The whole of the cost of sampling and analysis is to be borne by the
+      party in the wrong."
+    </p>
+    <hr />
+    <p>
+      The corresponding regulations issued by the Austrian Acetylene Association
+      (<i>Der Oesterreichische Acetylenverein</i>) are almost identical with
+      those of the German Association. They contain, however, provisions that
+      the price is to include packing, that the carbide must not be delivered in
+      lumps larger than the fist, that the sample may be sealed in a glass
+      vessel with well-ground glass stopper, that the sample is to be
+      transmitted to the testing laboratory with particulars of the size of the
+      lots and the number of drums drawn for sampling, and that the whole of it
+      is to be gasified in lots of upwards of 1 kilogramme (= 2.2 lb.) apiece.
+    </p>
+    <p>
+      In Italy, it is enacted by the Board of Agriculture, Commerce and Industry
+      that by calcium carbide is to be understood for legal purposes also any
+      other carbide, or carbide-containing mixture, which evolves acetylene by
+      interaction with water. Also that only calcium carbide, which on admixture
+      with water yields acetylene containing less than 1 per cent. of its volume
+      of sulphuretted hydrogen and phosphoretted hydrogen taken together, may be
+      put on the market.
+    </p>
+    <p>
+      It is evident from the regulations quoted that the determination of the
+      volume of gas which a particular sample of calcium carbide is capable of
+      yielding, when a given weight of it is decomposed under the most
+      favourable conditions, is a matter of the utmost practical importance to
+      all interested in the trafficking of carbide, <i>i.e.</i>, to the makers,
+      vendors, brokers, and purchasers of that material, as well as to all
+      makers and users of acetylene generating plant. The regulations of the
+      British Association do not, however, give details of the method which the
+      analyst should pursue in determining the yield of acetylene; and while
+      this may to a certain extent be advantageously left to the discretion of
+      the competent analyst, it is desirable that the results of the experience
+      already won by those who have had special opportunities for practising
+      this branch of analytical work should be embodied in a set of directions
+      for the analysis of carbide, which may be followed in all ordinary
+      analyses of that material. By the adoption of such a set of directions as
+      a provisional standard method, disputes as to the quantity of carbide will
+      be avoided, while it will still be open to the competent analyst to modify
+      the method of procedure to meet the requirements of special cases. It
+      would certainly be unadvisable in the present state of our analytical
+      methods to accept any hard and fast of rules for analysis for determining
+      the quality of carbide, but it is nevertheless well to have the best of
+      existing methods codified for the guidance of analysts. The substance of
+      the directions issued by the German Association (<i>Der Deutsche
+      Acetylenverein</i>) is reproduced below.
+    </p>
+    <p>
+      "METHODS FOR THE DETERMINATION OF TILE YIELD OF GAS FROM CALCIUM CARBIDE.
+    </p>
+    <p>
+      "The greatest precision is attained when the whole of the sample submitted
+      to the analyst is gasified in a carbide-to-water apparatus, and the gas
+      evolved is measured in an accurately graduated gasholder.
+    </p>
+    <p>
+      "The apparatus used for this analysis must not only admit of all the
+      precautionary rules of gas-analytical work being observed, but must also
+      fulfil certain other experimental conditions incidental to the nature of
+      the analysis.
+    </p>
+    <p>
+      "(<i>a</i>) The apparatus must be provided with an accurate thermometer to
+      show the temperature of the confining water, and with a pressure gauge,
+      which is in communication with the gasholder.
+    </p>
+    <p>
+      "(<i>b</i>) The generator must either be provided with a gasholder which
+      is capable of receiving the quantity of gas evolved from the whole amount
+      of carbide, or the apparatus must be so constructed that it becomes
+      possible with a gasholder which in not too large (up to 200 litres = say 7
+      cubic feet capacity) to gasify a larger amount of carbide.
+    </p>
+    <p>
+      "(<i>c</i>) The generator must be constructed so that escape of the
+      evolved gas from it to the outer air is completely avoided.
+    </p>
+    <p>
+      "(<i>d</i>) The gasholder must be graduated in parts up to 1/4 per cent.
+      of its capacity, must travel easily, and be kept, as far as may be in
+      suspension by counterweighting.
+    </p>
+    <p>
+      "(<i>e</i>) The water used for decomposing the carbide and the confining
+      water must be saturated, before use, with acetylene, and, further, the
+      generator must, before the analysis proper, be put under the pressure of
+      the confining (or sealing) liquid."
+    </p>
+    <p>
+      The following is a description of a typical form of apparatus
+      corresponding with the foregoing requirements:
+    </p>
+    <p>
+      "The apparatus, shown in the annexed figure, consists of the generator A,
+      the washer B, and the gasholder C.
+    </p>
+    <p class="ctr">
+      <a href="images/313.png"><img src="images/313th.png"
+      alt="FIG. 22.--LARGE-SCALE APPARATUS FOR DETERMINING YIELD OF GAS FROM CARBIDE" /></a>
+    </p>
+    <p>
+      "The generator A consists of a cylindrical vessel with sloping bottom,
+      provided with a sludge outlet <i>a</i>, a gas exit-pipe <i>b</i>, and a
+      lid <i>b'</i> fastened by screws. In the upper part ten boxes <i>c</i> are
+      installed for the purpose of receiving the carbide. The bottoms of those
+      boxes are flaps which rest through their wire projections on a revolvable
+      disc <i>d</i>, which is mounted on a shaft <i>l</i>. This shaft passes
+      through a stuffing-box to the outside of the generator and can be rotated
+      by moans of the chains <i>f</i>, the pulleys <i>g</i> and <i>h</i>, and
+      the winch <i>i</i>. Its rotation causes rotation of the disc <i>d</i>. The
+      disc <i>d</i>, on which the bottoms of the carbide- holders are supported,
+      is provided with a slot <i>e</i>. On rotating the disc, on which the
+      supporting wires of the bottoms of the carbide-holders rest, the slot is
+      brought beneath these wires in succession; and the bottoms, being thus
+      deprived of their support, drop down. It is possible in this way to effect
+      the discharge of the several carbide-holders by gradual turning of the
+      winch <i>i</i>.
+    </p>
+    <p>
+      "The washer B is provided with a thermometer <i>m</i> passing through a
+      sound stuffing-box and extending into the water.
+    </p>
+    <p>
+      "The gasholder C is provided with a scale and pointer, which indicate how
+      much gas there is in it. It is connected with the pressure-gauge <i>n</i>,
+      and is further provided with a control thermometer <i>o</i>. The gas
+      exit-pipe <i>q</i> can be shut off by a cock. There is a cock between the
+      gasholder and the washer for isolating one from the other.
+    </p>
+    <p>
+      "The dimensions of the apparatus are such that each carbide-holder can
+      contain readily about half a kilogramme (say l lb.) of carbide. The
+      gasholder is of about 200 litres (say 7 cubic feet) capacity; and if the
+      bell is 850 mm. (= 33-1/2 inches) high, and 550 mm. (= 21-1/2 inches) in
+      diameter it will admit of the position being read off to within half a
+      litre (say 0.02 cubic foot)."
+    </p>
+    <p>
+      The directions of the German Association for sampling a consignment of
+      carbide packed in drums each containing 100 kilogrammes (say 2 cwt.) have
+      already been given in the rules of that body. They differ somewhat from
+      those issued by the British Association (<i>vide ante</i>), and have
+      evidently been compiled with a view to the systematic and rapid sampling
+      of larger consignments than are commonly dealt with in this country.
+      Drawing a portion of the whole sample from every tenth drum is
+      substantially the same as the British Association's regulations for cases
+      of dispute, viz., to have one unopened drum (<i>i.e.</i>, one or two cwt.)
+      per ton of carbide placed at the analyst's disposal for sampling. Actually
+      the mode of drawing a portion of the whole sample from every tenth vessel,
+      or lot, where a large number is concerned, is one which would naturally be
+      adopted by analysts accustomed to sampling any other products so packed or
+      stored, and there in no reason why it should be departed from in the case
+      of large consignments of carbide. For lots of less than ten drums, unless
+      there is reason to suspect want of uniformity, it should usually suffice
+      to draw the sample from one drum selected at random by the sampler. The
+      analyst, or person who undertakes the sampling, must, however, exercise
+      discretion as to the scheme of sampling to be followed, especially if want
+      of uniformity of the several lots constituting the consignment in
+      suspected. The size of the lumps constituting a sample will be referred to
+      later.
+    </p>
+    <p>
+      The British Association's regulations lead to a sample weighing about 3
+      lb. being obtained from each drum. If only one drum is sampled, the
+      quantity taken from each position may be increased with advantage so as to
+      give a sample weighing about 10 lb., while if a large number of drums is
+      sampled, the several samples should be well mixed, and the ordinary method
+      of quartering and re-mixing followed until a representative portion
+      weighing about 10 lb. remains.
+    </p>
+    <p>
+      A sample representative of the bulk of the consignment having been
+      obtained, and hermetically sealed, the procedure of testing by means of
+      the apparatus already described may be given from the German Association's
+      directions:
+    </p>
+    <p>
+      "The first carbide receptacle is filled with 300 to 400 grammes (say 3/4
+      lb.) of any readily decomposable carbide, and is hung up in the apparatus
+      in such a position with regard to the slot <i>e</i> on the disc <i>d</i>
+      that it will be the first receptacle to be discharged when the winch <i>i</i>
+      is turned. The tin or bottle containing the sample for analysis is then
+      opened and weighed on a balance capable of weighing exactly to 1/2 gramme
+      (say 10 grains). The carbide in it is then distributed quickly, and as far
+      as may be equally, into the nine remaining carbide receptacles, which are
+      then shut and hung up quickly in the generator. The lid <i>b'</i> is then
+      screwed on the generator to close it, and the empty tin or bottle, from
+      which the sample of carbide has been removed, is weighed.
+    </p>
+    <p>
+      "The contents of the first carbide receptacle are then discharged by
+      turning the winch <i>i</i>. Their decomposition ensures on the one hand
+      that the sealing water and the generating water are saturated with
+      acetylene, and on the other hand that the dead space in the generator is
+      brought under the pressure of the seal, so that troublesome corrections
+      which would otherwise be entailed are avoided. After the carbide is
+      completely decomposed, but not before two hours at least have elapsed, the
+      cock <i>p</i> is shut, and the gasholder is run down to the zero mark by
+      opening the cock <i>q</i>. The cock <i>q</i> is then shut, <i>p</i> is
+      opened, and the analytical examination proper is begun by discharging the
+      several carbide receptacles by turning the winch <i>i</i>. After the first
+      receptacle has been discharged, five or ten minutes are allowed to elapse
+      for the main evolution of gas to occur, and the cock <i>p</i> is then
+      shut. Weights are added to the gasholder until the manometer <i>n</i>
+      gives the zero reading; the position of the gasholder C is then read off,
+      and readings of the barometer and of the thermometer <i>o</i> are made.
+      The gasholder is then emptied down to the zero mark by closing the cock <i>p</i>
+      and opening <i>q</i>. When this is done <i>q</i> is closed and <i>p</i> is
+      opened, and the winch <i>i</i> is turned until the contents of the next
+      carbide receptacle are discharged. This procedure is followed until the
+      carbide from the last receptacle has been gasified; then, after waiting
+      until all the carbide has been decomposed, but in any case not less than
+      two hours, the position of the gasholder is read, and readings of the
+      barometer and thermometer are again taken. The total of the values
+      obtained represents the yield of gas from the sample examined."
+    </p>
+    <p>
+      The following example is quoted:
+    </p>
+<pre xml:space="preserve">
+Weight of the tin received, with its contained |
+   carbide      .     .     .     .     .    ._| = 6325 grammes.
+Weight of the empty tin     .     .     .    .   = 1485    "
+                                                _______
+                   Carbide used   .     .    .   = 4840    " = 10670 lb.
+</pre>
+    <p>
+      The carbide in question was distributed among the nine receptacles and
+      gasified. The readings were:
+    </p>
+<pre xml:space="preserve">
+ ________________________________________________
+|      |          |              |               |
+| No.  |  Litres. |  Degrees C.  |  Millimetres. |
+|______|__________|______________|_______________|
+|      |          |              |               |
+|  1   |   152.5  |     13       |     762       |
+|  2   |   136.6  |      "       |      "        |
+|  3   |   138.5  |      "       |      "        |
+|  4   |   161.0  |      "       |      "        |
+|  5   |   131.0  |      "       |      "        |
+|  6   |   182.5  |     13.5     |      "        |
+|  7   |   146.0  |      "       |      "        |
+|  8   |   163.0  |     14.0     |      "        |
+|  9   |   178.5  |      "       |      "        |
+|______|__________|______________|_______________|
+</pre>
+    <p>
+      After two hours, the total of the readings was 1395.0 litres at 13.5� C.
+      and 762 mm., which is equivalent to 1403.7 litres (= 49.57 cubic feet) at
+      15� C. and 760 mm. (or 60� F. and 30 inches; there is no appreciable
+      change of volume of a gas when the conditions under which it is measured
+      are altered from 15� C. and 760 mm. to 60� F. and 30 inches, or <i>vice
+      vers�</i>).
+    </p>
+    <p>
+      The yield of gas from this sample is therefore 1403.7/4.840 = 290 litres
+      at 15� C. and 760 mm. per kilogramme, or 49.57/10.67 = 4.65 cubic feet at
+      60� F. and 30 inches per pound of carbide. The apparatus described can, of
+      course, be used when smaller samples of carbide only are available for
+      gasification, but the results will be less trustworthy if much smaller
+      quantities than those named are taken for the test.
+    </p>
+    <p>
+      Other forms of carbide-to-water apparatus may of course be devised, which
+      will equally well fulfil the requisite conditions for the test, viz.,
+      complete decomposition of the whole of the carbide without excessive rise
+      of temperature, and no loss of gas by solution or otherwise.
+    </p>
+    <p>
+      An experimental wet gas-motor, of which the water-line has been accurately
+      set (by means of the Gas Referees' 1/12 cubic foot measure, or a similar
+      meter-proving apparatus), may be used in place of the graduated gasholder
+      for measuring the volume of the gas evolved, provided the rate of flow of
+      the gas does not exceed 1/6 cubic foot, or say 5 litres per minute. If the
+      generation of gas is irregular, as when an apparatus of the type described
+      above is used, it is advisable to insert a small gasholder or large
+      bell-governor between the washer and the meter. The meter must be provided
+      with a thermometer, according to the indications of which the observed
+      volumes must be corrected to the corresponding volume at normal
+      temperature.
+    </p>
+    <p>
+      If apparatus such as that described above is not available, fairly
+      trustworthy results for practical purposes may be obtained by the
+      decomposition of smaller samples in the manner described below, provided
+      these samples are representative of the average composition of the larger
+      sample or bulk, and a number of tests are made in succession and the
+      results of individual tests do not differ by more than 10 litres of gas
+      per kilogramme (or 0.16 cubic foot per pound) of carbide.
+    </p>
+    <p>
+      It is necessary at the outset to reduce large lumps of carbide in the
+      sample to small pieces, and this must be done with as little exposure as
+      possible to the (moist) air. Failing a good pulverising machine of the
+      coffee-mill or similar type, which does its work quickly, the lumps must
+      be broken as rapidly as possible in a dry iron mortar, which may with
+      advantage be fitted with a leather or india-rubber cover, through a hole
+      in which the pestle passes. As little actual dust as possible should be
+      made during pulverisation. The decomposition of the carbide is best
+      effected by dropping it into water and measuring the volume of gas evolved
+      with the precautions usually practised in gas analysis. An example of one
+      of the methods of procedure described by the German Association will show
+      how this test can be satisfactorily carried out:
+    </p>
+    <p>
+      "A Woulff's bottle, <i>a</i> in the annexed figure, of blown glass and
+      holding about 1/4 litre is used as the generating vessel. One neck, about
+      15 mm. in internal diameter, is connected by flexible tubing with a
+      globular vessel <i>b</i>, having two tubulures, and this vessel is further
+      connected with a conical flask <i>c</i>, holding about 100 c.c. The other
+      neck is provided with tubing <i>d</i>, serving to convey the gas to the
+      inlet-tube, with tap <i>e</i>, of the 20-litre measuring vessel <i>f</i>,
+      which is filled with water saturated with acetylene, and communicates
+      through its lower tubulure with a similar large vessel <i>g</i>. The
+      generating vessel <i>a</i> is charged with about 150 c.c. of water
+      saturated with acetylene. The vessel <i>f</i> is filled up to the zero
+      mark by raising the vessel <i>g</i>; the tap <i>e</i> is then shut, and
+      connexion is made with the tube <i>d</i>. Fifty grammes (or say 2 oz.) of
+      the pulverised carbide are then weighed into the flask <i>c</i> and this
+      is connected by the flexible tubing with the vessel <i>b</i>. The carbide
+      is then decomposed by bringing it in small portions at a time into the
+      bulb <i>b</i> by raising the flask <i>c</i>, and letting it drop from <i>b</i>
+      into the generating vessel <i>a</i>, after having opened the cock <i>e</i>
+      and slightly raised the vessel <i>f</i>. After the last of the carbide has
+      been introduced two hours are allowed to elapse, and the volume of gas in
+      <i>f</i> is then read while the water stands at the same level in <i>f</i>
+      and <i>g</i>, the temperature and pressure being noted simultaneously."
+    </p>
+    <p>
+      A second, but less commendable method of decomposing the carbide is by
+      putting it in a dry two-necked bottle, one neck of which is connected with
+      <i>e</i>, and dropping water very slowly from a tap-funnel, which enters
+      the other neck, on to the carbide. The generating bottle should be stood
+      in water, in order to keep it cool, and the water should be dropped in at
+      the rate of about 50 c.c. in one hour. It will take about three hours
+      completely to gasify the 50 grammes of carbide under these conditions. The
+      gas is measured as before.
+    </p>
+    <p class="ctr">
+      <a href="images/318.png"><img src="images/318th.png"
+      alt="FIG. 23.--SMALL-SCALE APPARATUS FOR DETERMINING YIELD OF GAS FROM CARBIDE" /></a>
+    </p>
+    <p>
+      Cedercreutz has carried out trials to show the difference between the
+      yields found from large and small carbide taken from the same drum. One
+      sample consisted of the dust and smalls up to about 3/5 inch in size,
+      while the other contained large carbide as well as the small. The latter
+      sample was broken to the same size as the former for the analysis. Tests
+      were made both with a large testing apparatus, such as that shown in Fig.
+      22, and with a small laboratory apparatus, such as that shown in Fig. 23.
+      The dust was screened off for the tests made in the large apparatus. Two
+      sets of testings were made on different lots of carbide, distinguished
+      below as "A" and "B," and about 80 grammes wore taken for each
+      determination in the laboratory apparatus, and 500 grammes in the large
+      apparatus. The results are stated in litres (at normal temperature and
+      pressure) per kilogramme of carbide.
+    </p>
+<pre xml:space="preserve">
+ ___________________________________________________________________
+|                                                     |      |      |
+|                                                     | "A"  | "B"  |
+|_____________________________________________________|______|______|
+|                                                     |      |      |
+|                                                 Lot |Litres|Litres|
+| Small carbide, unscreened, in laboratory     \  (1) |  276 |  267 |
+|   apparatus   .     .     .     .     .      /  (2) |  273 |  270 |
+| Average sample of carbide, unscreened, in    \  (1) |  318 |  321 |
+|   laboratory apparatus     .     .     .     /  (2) |  320 |  321 |
+| Small carbide, dust freed, in large apparatus   (1) |  288 |  274 |
+| Average sample of carbide, dust freed, in    \  (2) |  320 |  322 |
+|   large apparatus    .     .     .     .     /      |      |      |
+|_____________________________________________________|______|______|
+</pre>
+    <p>
+      As the result of the foregoing researches Cedercreutz has recommended that
+      in order to sample the contents of a drum, they should be tipped out, and
+      about a kilogramme (say 2 to 3 lb.) taken at once from them with a shovel,
+      put on an iron base and broken with a hammer to pieces of about 2/5 inch,
+      mixed, and the 500 grammes required for the analysis in the form of
+      testing plant which he employs taken from this sample. Obviously a larger
+      sample can be taken in the same manner. On the other hand the British and
+      German Associations' directions for sampling the contents of a drum, which
+      have already been quoted, differ somewhat from the above, and must
+      generally be followed in cases of dispute.
+    </p>
+    <p>
+      Cedercreutz's figures, given in the above table, show that it would be
+      very unfair to determine the gas-making capacity of a given parcel of
+      carbide in which the lumps happened to vary considerably in size by
+      analysing only the smalls, results so obtained being possibly 15 per cent.
+      too low. This is due to two causes: first, however carefully it be stored,
+      carbide deteriorates somewhat by the attack of atmospheric moisture; and
+      since the superficies of a lump (where the attack occurs) is larger in
+      proportion to the weight of the lump as the lump itself is smaller, small
+      lumps deteriorate more on keeping than large ones. The second reason,
+      however, is more important. Not being a pure chemical substance, the
+      commercial material calcium carbide varies in hardness; and when it is
+      merely crushed (not reduced altogether to powder) the softer portions tend
+      to fall into smaller fragments than the hard portions. As the hard
+      portions are different in composition from the soft portions, if a parcel
+      is sampled by taking only the smalls, practically that sample contains an
+      excess of the softer part of the original material, and as such is not
+      representative. Originally the German Acetylene Association did not lay
+      down any rules as to the crushing of samples by the analyst, but
+      subsequently they specified that the material should be tested in the size
+      (or sizes) in which it was received. The British Association, on the
+      contrary, requires the sample to be broken in small pieces. If the
+      original sample is taken in such fashion as to include large and small
+      lumps as accurately as possible in the same proportion as that in which
+      they occur in the main parcel, no error will be introduced if that sample
+      is crushed to a uniform size, and then subdivided again; but a small
+      deficiency in gas yield will be produced, which will be in the consumer's
+      favour. It is not altogether easy to see the advantage of the British idea
+      of crushing the sample over the German plan of leaving it alone; because
+      the analytical generator will easily take, or its parts could be modified
+      to take, the largest lumps met with. If the sample is in very large
+      masses, and is decomposed too quickly, polymerisation of gas may be set
+      up; but on the other hand, the crushing and re-sampling will cause
+      wastage, especially in damp weather, or when the sampling has to be done
+      in inconvenient places. The British Association requires the test to be
+      made on carbide parcels ranging between 1 and 2-1/2 inches or larger,
+      because that is the "standard" size for this country, and because no
+      guarantee is to be had or expected from the makers as to the gas-producing
+      capacity of smaller material. Manifestly, if a consumer employs such a
+      form of generator that he is obliged to use carbide below "standard" size,
+      analyses may be made on his behalf in the ordinary way; but he will have
+      no redress if the yield of acetylene is less than the normal. This may
+      appear a defect or grievance; but since in many ways the use of small
+      carbide (except in portable lamps) is not advantageous--either technically
+      or pecuniarily--the rule simply amounts to an additional judicious
+      incentive to the adoption of apparatus capable of decomposing
+      standard-sized lumps. The German and Austrian Associations' regulations,
+      however, provide a standard for the quality of granulated carbide.
+    </p>
+    <p>
+      It has been pointed out that the German Association's direction that the
+      water used in the testing should be saturated with acetylene by a
+      preliminary decomposition of 1/2 kilogramme of carbide is not wholly
+      adequate, and it has been suggested that the preliminary decomposition
+      should be carried out twice with charges of carbide, each weighing not
+      less than 1 per cent. of the weight of water used. A further possible
+      source of error lies in the fact that the generating water is saturated at
+      the prevailing temperature of the room, and liberates some of its
+      dissolved acetylene when the temperature rises during the subsequent
+      generation of gas. This error, of course, makes the yield from the sample
+      appear higher than it actually is. Its effects may be compensated by
+      allowing time for the water in the generator or gasholder to cool to its
+      original temperature before the final reading is made.
+    </p>
+    <p>
+      With regard to the measurement of the temperature of the evolved gas in
+      the bell gasholder, it is usual to assume that the reading of a
+      thermometer which passes through the crown of the gasholder suffices. If
+      the thermometer has a very long stem, so that the bulb is at about the
+      mid-height of the filled bell, this plan is satisfactory, but if an
+      ordinary thermometer is used, it is better to take, as the average
+      temperature of the gas in the holder, the mean of the readings of the
+      thermometer in the crown, and of one dipping into the water of the holder
+      seal.
+    </p>
+    <p>
+      The following table gives factors for correcting volumes of gas observed
+      at any temperature and pressure falling within its range to the normal
+      temperature (60� F.) and normal barometric height (30 inches). The normal
+      volume thus found is, as already stated, not appreciably different from
+      the volume at 15� C. and 760 mm. (the normal conditions adopted by
+      Continental gas chemists). To use the table, find the observed temperature
+      and the observed reading of the barometer in the border of the table, and
+      in the space where these vertical and horizontal columns meet will be
+      found a number by which the observed volume of gas is to be multiplied in
+      order to find the corresponding volume under normal conditions. For
+      intermediate temperatures, &amp;c., the factors may be readily inferred
+      from the table by inspection. This table must only be applied when the gas
+      is saturated with aqueous vapour, as is ordinarily the case, and therefore
+      a drier must not be applied to the gas before measurement.
+    </p>
+    <p>
+      Hammerschmidt has calculated a similar table for the correction of volumes
+      of gas measured at temperatures ranging from 0� to 30� C., and under
+      pressures from 660 to 780 mm., to 15� C. and 760 mm. It is based on the
+      coefficient of expansion of acetylene given in Chapter VI., but, as was
+      there pointed out, this coefficient differs by so little from that of the
+      permanent gases for which the annexed table was compiled, that no
+      appreciable error results from the use of the latter for acetylene also. A
+      table similar to the annexed but of more extended range is given in the
+      "Notification of the Gas Referees," and in the text-book on "Gas
+      Manufacture" by one of the authors.
+    </p>
+    <p>
+      The determination of the amounts of other gases in crude or purified
+      acetylene is for the most part carried out by the methods in vogue for the
+      analysis of coal-gas and other illuminating gases, or by slight
+      modifications of them. For an account of these methods the textbook on
+      "Gas Manufacture" by one of the authors may be consulted. For instance,
+      two of the three principal impurities in acetylene, viz., ammonia and
+      sulphuretted hydrogen, may be detected and estimated in that gas in the
+      same manner as in coal gas. The detection and estimation of phosphine are,
+      however, analytical operations peculiar to acetylene among common
+      illuminating gases, and they must therefore be referred to.
+    </p>
+    <p>
+      <i>Table to facilitate the Correction of the Volume of Gas at different
+      Temperatures and under different Atmospheric Pressures.</i>
+    </p>
+<pre xml:space="preserve">
+ _____________________________________________________
+|     |                                               |
+|     |                  THERMOMETER.                 |
+| BAR.|_______________________________________________|
+|     |       |       |       |       |       |       |
+|     |  46�  |  48�  |  50�  |  52�  |  54�  |  56�  |
+|_____|_______|_______|_______|_______|_______|_______|
+|     |       |       |       |       |       |       |
+|28.4 | 0.979 | 0.974 | 0.970 | 0.965 | 0.960 | 0.955 |
+|28.5 | 0.983 | 0.978 | 0.973 | 0.968 | 0.964 | 0.959 |
+|28.6 | 0.986 | 0.981 | 0.977 | 0.972 | 0.967 | 0.962 |
+|28.7 | 0.990 | 0.985 | 0.980 | 0.975 | 0.970 | 0.966 |
+|28.8 | 0.993 | 0.988 | 0.984 | 0.979 | 0.974 | 0.969 |
+|28.9 | 0.997 | 0.992 | 0.987 | 0.982 | 0.977 | 0.973 |
+|29.0 | 1.000 | 0.995 | 0.990 | 0.986 | 0.981 | 0.976 |
+|29.1 | 1.004 | 0.999 | 0.994 | 0.989 | 0.984 | 0.979 |
+|29.2 | 1.007 | 1.002 | 0.997 | 0.992 | 0.988 | 0.982 |
+|29.3 | 1.011 | 1.005 | 1.001 | 0.996 | 0.991 | 0.986 |
+|29.4 | 1.014 | 1.009 | 1.004 | 0.999 | 0.995 | 0.990 |
+|29.5 | 1.018 | 1.013 | 1.008 | 1.003 | 0.998 | 0.993 |
+|29.6 | 1.021 | 1.016 | 1.011 | 1.006 | 1.001 | 0.996 |
+|29.7 | 1.025 | 1.019 | 1.015 | 1.010 | 1.005 | 1.000 |
+|29.8 | 1.028 | 1.023 | 1.018 | 1.013 | 1.008 | 1.003 |
+|29.9 | 1.031 | 1.026 | 1.022 | 1.017 | 1.012 | 1.007 |
+|30.0 | 1.035 | 1.030 | 1.025 | 1.020 | 1.015 | 1.010 |
+|30.1 | 1.038 | 1.033 | 1.029 | 1.024 | 1.019 | 1.014 |
+|30.2 | 1.042 | 1.037 | 1.032 | 1.027 | 1.022 | 1.017 |
+|30.3 | 1.045 | 1.040 | 1.036 | 1.030 | 1.025 | 1.020 |
+|30.4 | 1.049 | 1.044 | 1.039 | 1.034 | 1.029 | 1.024 |
+|30.5 | 1.052 | 1.047 | 1.042 | 1.037 | 1.032 | 1.027 |
+|_____|_______|_______|_______|_______|_______|_______|
+ _____________________________________________________
+|     |                                               |
+|     |                  THERMOMETER.                 |
+| BAR.|_______________________________________________|
+|     |       |       |       |       |       |       |
+|     |  58�  |  60�  |  62�  |  64�  |  66�  |  68�  |
+|_____|_______|_______|_______|_______|_______|_______|
+|     |       |       |       |       |       |       |
+|28.5 | 0.954 | 0.949 | 0.944 | 0.939 | 0.934 | 0.929 |
+|28.6 | 0.958 | 0.953 | 0.947 | 0.943 | 0.938 | 0.932 |
+|28.7 | 0.961 | 0.956 | 0.951 | 0.946 | 0.941 | 0.936 |
+|28.8 | 0.964 | 0.959 | 0.954 | 0.949 | 0.944 | 0.939 |
+|28.9 | 0.968 | 0.963 | 0.958 | 0.953 | 0.948 | 0.942 |
+|29.0 | 0.971 | 0.966 | 0.961 | 0.956 | 0.951 | 0.946 |
+|29.1 | 0.975 | 0.969 | 0.964 | 0.959 | 0.954 | 0.949 |
+|29.2 | 0.978 | 0.973 | 0.968 | 0.963 | 0.958 | 0.952 |
+|29.3 | 0.981 | 0.976 | 0.971 | 0.966 | 0.961 | 0.956 |
+|29.4 | 0.985 | 0.980 | 0.975 | 0.969 | 0.964 | 0.959 |
+|29.5 | 0.988 | 0.983 | 0.978 | 0.973 | 0.968 | 0.962 |
+|29.6 | 0.992 | 0.986 | 0.981 | 0.976 | 0.971 | 0.966 |
+|29.7 | 0.995 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
+|29.8 | 0.998 | 0.993 | 0.988 | 0.983 | 0.978 | 0.972 |
+|29.9 | 1.002 | 0.997 | 0.991 | 0.986 | 0.981 | 0.976 |
+|30.0 | 1.005 | 1.000 | 0.995 | 0.990 | 0.985 | 0.979 |
+|30.1 | 1.009 | 1.003 | 0.998 | 0.993 | 0.988 | 0.983 |
+|30.2 | 1.012 | 1.007 | 1.002 | 0.996 | 0.991 | 0.986 |
+|30.3 | 1.015 | 1.010 | 1.005 | 1.000 | 0.995 | 0.989 |
+|30.4 | 1.019 | 1.014 | 1.008 | 1.003 | 0.998 | 0.993 |
+|30.5 | 1.022 | 1.017 | 1.012 | 1.006 | 1.001 | 0.996 |
+|_____|_______|_______|_______|_______|_______|_______|
+ _____________________________________________
+|     |                                       |
+|     |                  THERMOMETER.         |
+| BAR.|_______________________________________|
+|     |       |       |       |       |       |
+|     |  70�  |  72�  |  74�  |  76�  |  78�  |
+|_____|_______|_______|_______|_______|_______|
+|     |       |       |       |       |       |
+|28.4 | 0.921 | 0.915 | 0.910 | 0.905 | 0.900 |
+|28.5 | 0.924 | 0.919 | 0.914 | 0.908 | 0.903 |
+|28.6 | 0.927 | 0.922 | 0.917 | 0.912 | 0.906 |
+|28.7 | 0.931 | 0.925 | 0.920 | 0.915 | 0.909 |
+|28.8 | 0.934 | 0.929 | 0.924 | 0.918 | 0.913 |
+|28.9 | 0.937 | 0.932 | 0.927 | 0.921 | 0.916 |
+|29.0 | 0.941 | 0.935 | 0.930 | 0.925 | 0.919 |
+|29.1 | 0.944 | 0.939 | 0.933 | 0.928 | 0.923 |
+|29.2 | 0.947 | 0.942 | 0.937 | 0.931 | 0.926 |
+|29.3 | 0.950 | 0.945 | 0.940 | 0.935 | 0.929 |
+|29.4 | 0.954 | 0.949 | 0.943 | 0.938 | 0.932 |
+|29.5 | 0.957 | 0.952 | 0.947 | 0.941 | 0.936 |
+|29.6 | 0.960 | 0.955 | 0.950 | 0.944 | 0.939 |
+|29.7 | 0.964 | 0.959 | 0.953 | 0.948 | 0.942 |
+|29.8 | 0.967 | 0.962 | 0.957 | 0.951 | 0.946 |
+|29.9 | 0.970 | 0.965 | 0.960 | 0.954 | 0.949 |
+|30.0 | 0.974 | 0.968 | 0.963 | 0.958 | 0.952 |
+|30.1 | 0.977 | 0.972 | 0.966 | 0.961 | 0.955 |
+|30.2 | 0.980 | 0.975 | 0.970 | 0.964 | 0.959 |
+|30.3 | 0.984 | 0.978 | 0.973 | 0.968 | 0.962 |
+|30.4 | 0.987 | 0.982 | 0.976 | 0.971 | 0.965 |
+|30.5 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
+|_____|_______|_______|_______|_______|_______|
+</pre>
+    <p>
+      For the detection of phosphine, Berg�'s solution may be used. It is a
+      "solution of 8 to 10 parts of corrosive sublimate in 80 parts of water and
+      20 parts of 30 per cent. hydrochloric acid." It becomes cloudy when gas
+      containing phosphine is passed into it. It is, however, applied most
+      conveniently in the form of Keppeler's test-papers, which have been
+      described in Chapter V. Test-papers for phosphine, the active body in
+      which has not yet been divulged, have recently been produced for sale by
+      F. B. Gatehouse.
+    </p>
+    <p>
+      The estimation of phosphine will usually require to be carried out either
+      (1) on gas directly evolved from carbide in order to ascertain if the
+      carbide in question yields an excessive proportion of phosphine, or (2)
+      upon acetylene which is presumably purified, drawn either from the outlet
+      of the purifier or from the service-pipes, with the object of ascertaining
+      whether an adequate purification in regard to phosphine has been
+      accomplished. In either case, the method of estimation is the same, but in
+      the first, acetylene should be specially generated from a small
+      representative sample of the carbide and led directly into the apparatus
+      for the absorption of the phosphine. If the acetylene passes into the
+      ordinary gasholder, the amount of phosphine in gas drawn off from the
+      holder will vary from time to time according to the temperature and the
+      degree of saturation of the water in the holder-tank with phosphine, as
+      well as according to the amount of phosphine in the gas generated at the
+      time.
+    </p>
+    <p>
+      A method frequently employed for the determination of phosphine in
+      acetylene is one devised by Lunge and Cedercreutz. If the acetylene is to
+      be evolved from a sample of carbide in order to ascertain how much
+      phosphine the latter yields to the gas, about 50 to 70 grammes of the
+      carbide, of the size of peas, are brought into a half-litre flask, and a
+      tap-funnel, with the mouth of its stem contracted, is passed through a
+      rubber plug fitting the mouth of the flask. A glass tube passing through
+      the plug serves to convey the gas evolved to an absorption apparatus,
+      which is charged with about 75 c.c. of a 2 to 3 per cent. solution of
+      sodium hypochlorite. The absorption apparatus may be a ten-bulbed
+      absorption tube or any convenient form of absorption bulbs which subject
+      the gas to intimate contact with the solution. If acetylene from a
+      service-pipe is to be tested, it is led direct from the nozzle of a gas-
+      tap to the absorption tube, the outlet of which is connected with an
+      aspirator or the inlet of an experimental meter, by which the volume of
+      gas passed through the solution is measured. But if the generating flask
+      is employed, water is allowed to drop from the tap-funnel on to the
+      carbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnel
+      being filled up from time to time), and all the carbide will thus be
+      decomposed in 3 to 4 hours. The flask is then filled to the neck with
+      water, and disconnected from the absorption apparatus, through which a
+      little air is then drawn. The absorbing liquid is then poured, and washed
+      out, into a beaker; hydrochloric acid is added to it, and it is boiled in
+      order to expel the liberated chlorine. It is then usual to precipitate the
+      sulphuric acid by adding solution of barium chloride to the boiling
+      liquid, allowing it to cool and settle, and then filtering. The weight of
+      barium sulphate obtained by ignition of the filter and its contents,
+      multiplied by 0.137, gives the amount of sulphur present in the acetylene
+      in the form of sulphuretted hydrogen. The filtrate and washings from this
+      precipitate are rendered slightly ammoniacal, and a small excess of
+      "magnesia mixture" is added; the whole is stirred, left to stand for 12
+      hours, filtered, the precipitate washed with water rendered slightly
+      ammoniacal, dried, ignited, and weighed. The weight so found multiplied by
+      0.278 gives the weight of phosphorus in the form of phosphine in the
+      volume of gas passed through the absorbent liquid.
+    </p>
+    <p>
+      Objection may rightly be raised to the Lunge and Cedercreutz method of
+      estimating the phosphine in crude acetylene on the ground that explosions
+      are apt to occur when the gas is being passed into the hypochlorite
+      solution. Also it must be borne in mind that it aims at estimating only
+      the phosphorus which is contained in the gas in the form of phosphine, and
+      that there may also be present in the gas organic compounds of phosphorus
+      which are not decomposed by the hypochlorite. But when the acetylene is
+      evolved from the carbide in proper conditions for the avoidance of
+      appreciable heating it appears fairly well established that phosphorus
+      compounds other than phosphine exist in the gas only in practically
+      negligible amount, unless the carbide decomposed is of an abnormal
+      character. Various methods of burning the acetylene and estimating the
+      phosphorus in the products of combustion have, however been proposed for
+      the purpose of determining the total amount of phosphorus in acetylene.
+      Some of them are applicable to the simultaneous determination of the total
+      sulphur in the acetylene, and in this respect become akin to the Gas
+      Referees' method for the determination of the sulphur compounds in
+      coal-gas.
+    </p>
+    <p>
+      Eitner and Keppeler have proposed to burn the acetylene on which the
+      estimation is to be made in a current of neat oxygen. But this procedure
+      is rather inconvenient, and by no means essential. Lidholm liberated
+      acetylene slowly from 10 grammes of carbide by immersing the carbide in
+      absolute alcohol and gradually adding water, while the gas mixed with a
+      stream of hydrogen leading to a burner within a flask. The flow of
+      hydrogen was reduced or cut off entirely while the acetylene was coming
+      off freely, but hydrogen was kept burning for ten minutes after the flame
+      had ceased to be luminous in order to ensure the burning of the last
+      traces of acetylene. The products of combustion were aspirated through a
+      condenser and a washing bottle, which at the close were rinsed out with
+      warm solution of ammonia. The whole of the liquid so obtained was
+      concentrated by evaporation, filtered in order to remove particles of soot
+      or other extraneous matter, and acidified with nitric acid. The phosphoric
+      acid was then precipitated by addition of ammonium molybdate.
+    </p>
+    <p>
+      J. W. Gatehouse burns the acetylene in an ordinary acetylene burner of
+      from 10 to 30 litres per hour capacity, and passes the products of
+      combustion through a spiral condensing tube through which water is dropped
+      at the rate of about 75 c.c. per hour, and collected in a beaker. The
+      burner is placed in a glass bell-shaped combustion chamber connected at
+      the top through a right-angled tube with the condenser, and closed below
+      by a metal base through which the burner is passed. The amount of gas
+      burnt for one determination is from 50 to 100 litres. When the gas is
+      extinguished, the volume consumed is noted, and after cooling, the
+      combustion chamber and condenser are washed out with the liquid collected
+      in the beaker and finally with distilled water, and the whole, amounting
+      to about 400 c.c., is neutralised with solution of caustic alkali (if
+      decinormal alkali is used, the total acidity of the liquid thus
+      ascertained may be taken as a convenient expression of the aggregate
+      amount of the sulphuric, phosphoric and silicic acids resulting from the
+      combustion of the total corresponding impurities in the gas), acidified
+      with hydrochloric acid, and evaporated to dryness with the addition
+      towards the end of a few drops of nitric acid. The residue is taken up in
+      dilute hydrochloric acid; and silica filtered off and estimated if
+      desired. To the filtrate, ammonia and magnesia mixture are added, and the
+      magnesium pyrophosphate separated and weighed with the usual precautions.
+      Sulphuric acid may, if desired, be estimated in the filtrate, but in that
+      case care must be taken that the magnesia mixture used was free from it.
+    </p>
+    <p>
+      Mauricheau-Beaupr� has elaborated a volumetric method for the estimation
+      of the phosphine in crude acetylene depending on its decomposition by a
+      known volume of excess of centinormal solution of iodine, addition of
+      excess of standard solution of sodium thiosulphate, and titrating back
+      with decinormal solution of iodine with a few drops of starch solution as
+      an indicator. One c.c. of centinormal solution of iodine is equivalent to
+      0.0035 c.c. of phosphine. This method of estimation is quickly carried out
+      and is sufficiently accurate for most technical purposes.
+    </p>
+    <p>
+      In carrying out these analytical operations many precautions have to be
+      taken with which the competent analyst is familiar, and they cannot be
+      given in detail in this work, which is primarily intended for ordinary
+      users of acetylene, and not for the guidance of analysts. It may, however,
+      be pointed out that many useful tests in connexion with acetylene supply
+      can be conducted by a trained analyst, which are not of a character to be
+      serviceable to the untrained experimentalist. Among such may be named the
+      detection of traces of phosphine in acetylene which has passed through a
+      purifier with a view to ascertaining if the purifying material is
+      exhausted, and the estimation of the amount of air or other diluents in
+      stored acetylene or acetylene generated in a particular manner. Advice on
+      these points should be sought from competent analysts, who will already
+      have the requisite information for the carrying out of any such tests, or
+      know where it is to be found. The analyses in question are not such as can
+      be undertaken by untrained persons. The text-book on "Gas Manufacture" by
+      one of the authors gives much information on the operations of gas
+      analysis, and may be consulted, along with Hempel's "Gas Analysis" and
+      Winkler and Lunge's "Technical Gas Analysis."
+    </p>
+    <h2>
+      <a name="linkappendix" id="appendix">APPENDIX</a>
+    </h2>
+    <p>
+      DESCRIPTIONS OF A NUMBER OF ACETYLENE GENERATORS AS MADE IN THE YEAR 1909
+    </p>
+    <p>
+      (<i>The purpose of this Appendix is explained in Chapter IV., page 111,
+      and a special index to it follows the general index at the end of this
+      book.</i>)
+    </p>
+    <p>
+      AMERICA--CANADA.
+    </p>
+    <p>
+      <i>Maker</i>: SICHE GAS CO., LTD., GEORGETOWN, ONTARIO.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Siche" generator made by this firm consists of a water-tank <i>A</i>,
+      having at the bottom a sludge agitator <i>N</i> and draw-off faucet <i>O</i>,
+      and rigidly secured within it a bell-shaped generating chamber <i>B</i>,
+      above which rises a barrel containing the feed chamber <i>C</i>,
+      surmounted by the carbide chamber <i>D</i>. The carbide used is granulated
+      or of uniform size. In the generating chamber <i>B</i> is an annular float
+      <i>E</i>, nearly filling the area of the chamber, and connected, by two
+      rods passing, with some lateral play, through apertures in the conical
+      bottom of the feed chamber <i>C</i>, to the T-shaped tubular valve <i>F</i>.
+      Consequently when the float shifts vertically or laterally the rods and
+      valves at once move with it. The angle of the cone of the feed chamber and
+      the curve of the tubular valve are based on the angle of rest of the size
+      of carbide used, with the object of securing sensitiveness of the feed.
+      The feed is thus operated by a very small movement of the float, and
+      consequently there is but very slight rise and fall of the water in the
+      generating chamber. Owing to the lateral play, the feed valve rarely
+      becomes concentric with its seat. There is a cover <i>G</i> over the feed
+      valve <i>F</i>, designed to distribute the carbide evenly about the feed
+      aperture and to prevent it passing down the hollow of the valve and the
+      holes through which the connecting-rods pass. It also directs the course
+      of the evolved gas on its way to the service-pipe through the carbide in
+      the feed chamber <i>C</i>, whereby the gas is dried. The carbide chamber
+      <i>D</i> has at its bottom a conical valve, normally open, but closed by
+      means of the spindle <i>H</i>, which is engaged at its upper end by the
+      closing screw-cap <i>J</i>, which is furnished with a safelocking device
+      to prevent its removal until the conical valve is closed and the hopper
+      chamber <i>D</i> thereby cut off from the gas-supply. The cap <i>J</i>, in
+      addition to a leather washer to make a gas-tight joint when down, has a
+      lower part fitting to make an almost gas-tight joint. Thus when the cap is
+      off; the conical valve fits gas-tight; when it is on and screwed down it
+      is gas-tight; and when on but not screwed down, it is almost gas-tight.
+      Escape of gas is thus avoided. A special charging funnel <i>K</i>, shown
+      in half-scale, is provided for inserting in place of the screw cap. The
+      carbide falls from the funnel into the chamber <i>D</i> when the chain is
+      pulled. A fresh charge of carbide may be put in while the apparatus is in
+      action. The evolved gas goes into the chamber <i>C</i> through a pipe,
+      with cock, to a dust-arrester <i>L</i>, which contains a knitted stocking
+      lightly filled with raw sheep's wool through which the gas passes to the
+      service- pipe. The dust-arrester needs its contents renewing once in one,
+      two, or three years, according to the make of gas. The pressure of the gas
+      is varied as desired by altering the height of water in the tank <i>A</i>.
+      When cleaning the machine, the water must never be run below the top of
+      the generating chamber.
+    </p>
+    <p class="ctr">
+      <a href="images/328.png"><img src="images/328th.png"
+      alt="FIG. 24.--'SICHE' GENERATOR" /></a>
+    </p>
+    <p>
+      AMERICA--UNITED STATES.
+    </p>
+    <p>
+      <i>Maker:</i> J. B. COLT CO., 21 BARCLAY STREET, NEW YORK.
+    </p>
+    <p>
+      <i>Type:</i> Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Colt" generator made by this firm comprises a carbide hopper mounted
+      above a generating tank containing water, and an equalising bell gasholder
+      mounted above a seal-pot having a vent-pipe <i>C</i> communicating with
+      the outer air. The carbide hopper is charged with 1/4 x 1/12 inch carbide,
+      which is delivered from it into the water in the generating tank in small
+      portions at a time through a double valve, which is actuated through
+      levers connected to the crown of the equalising gasholder. As the bell of
+      the gasholder falls the lever rotates a rock shaft, which enters the
+      carbide hopper, and through a rigidly attached lever raises the inner
+      plunger of the feed-valve. The inner plunger in turn raises the concentric
+      outer stopper, thereby leaving an annular space at the base of the carbide
+      hopper, through which a small delivery of carbide to the water in the
+      generating tank then ensues. The gas evolved follows the course shown by
+      the arrows in the figure into the gasholder, and raises the bell, thereby
+      reversing the action of the levers and allowing the valve to fall of its
+      own weight and so cut off the delivery of carbide. The outer stopper of
+      the valve descends before the inner plunger and so leaves the conical
+      delivery mouth of the hopper free from carbide. The inner plunger, which
+      is capped at its lower end with rubber, then falls and seats itself
+      moisture-tight on the clear delivery mouth of the hopper. The weight of
+      the carbide in the hopper is taken by its sides and a projecting flange of
+      the valve casing, so that the pressure of the carbide at the delivery
+      point is slight and uniform. The outside of the delivery mouth is finished
+      by a drip collar with double lip to prevent condensed moisture creeping
+      upwards to the carbide in the hopper. A float in the generating tank, by
+      its descent when the water falls below a certain level, automatically
+      draws a cut off across the delivery mouth of the carbide hopper and so
+      prevents the delivery of carbide either automatically or by hand until the
+      water in the generating tank has been restored to its proper level.
+      Interlocking levers, (11) and (12) in the figure, prevent the opening of
+      the feed valve while the cap (10) of the carbide hopper is open for
+      recharging the hopper. There is a stirrer actuated by a handle (9) for
+      preventing the sludge choking the sludge cock. The gas passes into the
+      gasholder through a floating seal, which serves the dual purpose of
+      washing it in the water of the gasholder tank and of preventing the return
+      of gas from the holder to the generating tank. From the gasholder the gas
+      passes to the filter (6) where it traverses a strainer of closely woven
+      cotton felt for the purpose of the removal of any lime.
+    </p>
+    <p class="ctr">
+      <a href="images/330.png"><img src="images/330th.png"
+      alt="FIG. 25.--'COLT' GENERATING PLANT" /></a>
+    </p>
+    <p>
+      Drip pipes (30) and (31) connected to the inlet- and outlet-pipes of the
+      gasholder are sealed in water to a depth of 6 inches, so that in the event
+      of the pressure in the generator or gasholder rising above that limit the
+      surplus gas blows through the seal and escapes through the vent-pipe <i>C</i>.
+      There is also a telescopic blow-off (32) and (33), which automatically
+      comes into play if the gasholder bell rises above a certain height.
+    </p>
+    <p>
+      <i>Maker:</i> DAVIS ACETYLENE CO., ELKHARDT, INDIANA.
+    </p>
+    <p>
+      <i>Type:</i> Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Davis" generator made by this firm comprises an equalising bell
+      gasholder with double walls, the inner wall surrounding a central tube
+      rising from the top of the generating chamber, in which is placed a
+      water-sealed carbide chamber with a rotatory feeding mechanism which is
+      driven by a weight motor. The carbide falls from the chamber on to a wide
+      disc from which it is pushed off a lump at a time by a swinging displacer,
+      so arranged that it will yield in every direction and prevent clogging of
+      the feeding mechanism. Carbide falls from the disk into the water of the
+      generating chamber, and the evolved gas raises the bell and so allows a
+      weighted lever to interrupt the action of the clockwork, until the bell
+      again descends. The gas passes through a washer in the gasholder tank, and
+      then through an outside scrubber to the service-pipe. There is an outside
+      chamber connected by a pipe with the generating chamber, which
+      automatically prevents over-filling with water, and also acts as a
+      drainage chamber for the service- and blow-off-pipes. There is an agitator
+      for the residuum and a sludge-cock through which to remove same. The
+      feeding mechanism permits the discharge of lump carbide, and the weight
+      motor affords independent power for feeding the carbide, at the same time
+      indicating the amount of unconsumed carbide and securing uniform gas
+      pressure.
+    </p>
+    <p class="ctr">
+      <a href="images/332.png"><img src="images/332th.png"
+      alt="FIG. 26.--'DAVIS' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker:</i> SUNLIGHT GAS MACHINE CO., 49 WARREN STREET, NEW YORK.
+    </p>
+    <p>
+      <i>Type:</i> Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Omega" apparatus made by this firm consists of a generating tank
+      containing water, and surmounted by a hopper which is filled with carbide
+      of 1/4-inch size. The carbide is fed from the hopper into the generating
+      tank through a mechanism consisting of a double oscillating cup so
+      weighted that normally the feed is closed. The fall of the bell of the
+      equalising gasholder, into which the gas evolved passes, operates a lever
+      <i>B</i>, which rotates the weighted cup in the neck of the hopper and so
+      causes a portion of carbide to fall into the water in the generating tank.
+      The feed-cup consists of an upper cup into which the carbide is first
+      delivered. It is then tipped from the upper cup into the lower cup while,
+      at the same time, further delivery from the hopper is prevented. Thus only
+      the portion of carbide which has been delivered into the lower cup is
+      emptied at one discharge into the generator. There is a safety lock to the
+      hopper cap which prevents the feeding mechanism coming into operation
+      until the hopper cap is screwed down tightly. Provision is made for a
+      limited hand-feed of carbide to start the apparatus. The gasholder is
+      fitted with a telescoping vent-pipe, by which gas escapes to the open in
+      the event of the bell being raised above a certain height. There is also
+      an automatic cut-off of the carbide feed, which comes into operation it
+      the gas is withdrawn too rapidly whether through leakage in the pipes or
+      generating plant, or through the consumption being increased above the
+      normal generating capacity of the apparatus. The gas evolved passes into a
+      condensing or washing chamber placed beneath the gasholder tank and thence
+      it travels to the gasholder. From the gasholder it goes through a purifier
+      containing "chemically treated coke and cotton" to the supply-pipe.
+    </p>
+    <p class="ctr">
+      <a href="images/334.png"><img src="images/334th.png"
+      alt="FIG. 27.--'OMEGA' GENERATOR" /></a>
+    </p>
+    <p>
+      1 Vent-cock handle. 2 Residuum-cock handle. 3 Agitator handle. 4 Filling
+      funnel. 5 Water overflow. 6 Hopper cap and lever. 7 Starting feed. 8
+      Rocker arm. 9 Feed connecting-rod. A Pawl. B Lever for working feed
+      mechanism. C Guide frame. D Residuum draw-off cock. G Chain from hopper
+      cap to feed mechanism. H Blow-off and vent-pipe connexion. I Gas outlet
+      from generator. J Gas service-cock. K Filling funnel for gasholder tank. L
+      Funnel for condensing chamber. M Gas outlet at top of purifier. N Guides
+      on gas-bell. O Crosshead on swinging pawl. P Crane carrying pawl. Q Shaft
+      connecting feed mechanism. R Plug in gas outlet-pipe. S Guide-frame
+      supports. U Removable plate to clean purifier. Z Removable plate to expose
+      feed-cups for cleaning same.
+    </p>
+    <p>
+      AUSTRIA-HUNGARY
+    </p>
+    <p>
+      <i>Maker:</i> RICH. KLINGER, GUMPOLDSKIRCHEN, NEAR VIENNA.
+    </p>
+    <p>
+      <i>Type:</i> Non-automatic; carbide-to-water.
+    </p>
+    <p>
+      The generating plant made by this firm consists of the generator <i>A</i>
+      which is supported in a concrete water and sludge tank <i>B</i>, a storage
+      gasholder <i>J</i>, and purifiers <i>K</i>. In the top of the generator
+      are guide-ways <i>F</i>, through each of which is passed a plunger <i>C</i>
+      containing a perforated cage charged with about 8 lb. of lump carbide. The
+      plungers are supported by ropes passing over pulleys <i>D</i>, and when
+      charged they are lowered through the guide-ways <i>F</i> into the water in
+      the tank <i>B</i>. The charge of carbide is thus plunged at once into the
+      large body of water in the tank, and the gas evolved passes through
+      perforations in the washer <i>G</i> to the condenser <i>H</i> and thence
+      to the storage gasholder <i>J</i>. After exhaustion of the charge the
+      plungers are withdrawn and a freshly charged cage of carbide inserted
+      ready for lowering into the generating tank. There is a relief seal <i>f</i>
+      through which gas will blow and escape by a pipe <i>g</i> to the open
+      should the pressure within the apparatus exceed the depth of the seal,
+      viz., about 9 inches. There is a syphon pot <i>N</i> for the collection
+      and withdrawal of condensed water. The sludge is allowed to accumulate in
+      the bottom of the concrete tank <i>B</i> until it becomes necessary to
+      remove it at intervals of about three months. Water is added to the tank
+      daily to replace that used up in the generation of the gas. The gas passes
+      from the storage holder through one of the pair of purifiers <i>K</i>,
+      with water-sealed lids, which are charged with a chemical preparation for
+      the removal of phosphoretted hydrogen. This purifying material also acts
+      as a desiccating agent. From the purifiers the gas passes through the
+      meter <i>L</i> to the service- pipes.
+    </p>
+    <p class="ctr">
+      <a href="images/335.png"><img src="images/335th.png"
+      alt="FIG. 28.--KLINGER'S GENERATING PLANT" /></a>
+    </p>
+    <p>
+      BELGIUM.
+    </p>
+    <p>
+      <i>Maker</i>: SOC. AN. DE L'AC�TYLITHE, 65 RUE DU MARCHE, BRUSSELS.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; contact.
+    </p>
+    <p>
+      The generating apparatus made by this firm uses, instead of ordinary
+      carbide, a preparation known as "ac�tylithe," which is carbide treated
+      specially with mineral oil, glucose and sugar. The object of using this
+      treated carbide is to avoid the effects of the attack of atmospheric
+      humidity or water vapour, which, with ordinary carbide, give rise to the
+      phenomena of after-generation. The generator comprises a water-tank <i>A</i>
+      with conical base, a basket <i>C</i> containing the treated carbide
+      inserted within a cylindrical case <i>B</i> which is open at the bottom
+      and is surmounted by a cylindrical filter <i>D</i>. At starting, the tank
+      <i>A</i> is filled with water to the level <i>N N'</i>. The water rises
+      within the cylindrical case until it comes in contact with the treated
+      carbide, which thereupon begins to evolve gas. The gas passes through the
+      filter <i>D</i>, which is packed with dry cotton-wool, and escapes through
+      the tap <i>M</i>. As soon as the contained air has been displaced by gas
+      the outlet of the tap <i>M</i> is connected by a flexible tube to the pipe
+      leading to a purifier and the service-pipe. When the tap <i>M</i> is
+      closed, or when the rate of evolution of the gas exceeds the rate of
+      consumption, the evolved gas accumulates within the cylindrical case <i>B</i>
+      and begins to displace the water, the level of which within the case is
+      lowered from <i>S S'</i>, first to <i>S1 S'1</i> and ultimately to, say,
+      <i>S2 S'2</i>. The evolution of gas is thereby gradually curtailed or
+      stopped until more is required for consumption. The water displacement
+      causes the water-level in the outer tank to rise to <i>N1 N'1</i> and
+      ultimately to, say <i>N2 N'2</i>. The lime formed by the decomposition of
+      the carbide is loosened from the unattacked portion and taken more or less
+      into solution as sucrate of lime, which is a soluble salt which the
+      glucose or sugar in the treated carbide forms with lime. The solution is
+      eventually run off through the cock <i>R</i>. The cover <i>T</i> of the
+      filter is screwed down on rubber packing until gas- tight. The purifier is
+      charged with puratylene or other purifying material.
+    </p>
+    <p class="ctr">
+      <a href="images/337.png"><img src="images/337th.png"
+      alt="FIG. 29.--AC�TYLITHE GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: L. DEBRUYNE, 22 PLACE MASUI, BRUSSELS.
+    </p>
+    <p>
+      <i>Type</i>: (1) Automatic; carbide-to-water.
+    </p>
+    <p>
+      The generating plant made by this firm, using granulated carbide,
+      comprises an equalising gasholder <i>E</i> alongside a generating tank <i>B</i>,
+      which is surmounted by a closed carbide receptacle <i>A</i> and a
+      distributing appliance. The carbide receptacle is filled with granulated
+      carbide and the lid <i>N</i> screwed down; the carbide is then withdrawn
+      from the base of the receptacle by the distributing appliance and
+      discharged in measured quantities as required into the water in the
+      generating tank. The distributing appliance is actuated by a weighted cord
+      <i>H</i> attached to the bell <i>I</i> of the gasholder and discharges at
+      each time a quantity of carbide only sufficient nearly to fill the
+      gasholder with acetylene. The gas passes from the generator through the
+      pipe <i>J</i> and seal-pot <i>D</i>, or bypass <i>F</i>, to the gasholder.
+      The generating tank is provided with a funnel <i>G</i> for replacing the
+      water consumed, a sludge-stirrer and a draw-off cock <i>L</i>, and a
+      water-level cock <i>C</i>. The gas passes from the gasholder through a
+      purifier <i>K</i>, charged with heratol, to the service-pipe.
+    </p>
+    <p class="ctr">
+      <a href="images/338.png"><img src="images/338th.png"
+      alt="FIG. 30.--L. DEBRUYNE'S GENERATING PLANT FOR GRANULATED CARBIDE" /></a>
+    </p>
+    <p>
+      (2) Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Debruyne" generator comprises an equalising bell gasholder <i>A</i>
+      placed alongside a generating tank <i>B</i> containing water into which
+      lump carbide is discharged as necessary from each in turn of a series of
+      chambers mounted in a ring above the generating tank. The chambers are
+      removable for refilling, and when charged are hermetically sealed until
+      opened in turn above the shoot <i>C</i>, through which their contents are
+      discharged into the generating tank. The carbide contained in each chamber
+      yields sufficient gas nearly to fill the gasholder. The discharging
+      mechanism is operated through an arm <i>E</i> attached to the bell <i>G</i>
+      of the gasholder, which sets the mechanism in motion when the bell has
+      fallen nearly to its lowest position. The lip <i>L</i> serves for renewing
+      the water in the generator, and the gas evolved goes through the pipe <i>K</i>
+      with tap <i>F</i> to the gasholder. There is an eccentric stirrer for the
+      sludge and a large-bore cock for discharging it. The gas passes from the
+      gasholder through the pipe <i>J</i> to the purifier <i>H</i>, charged with
+      heratol, and thence to the service-pipe.
+    </p>
+    <p class="ctr">
+      <a href="images/339.png"><img src="images/339th.png"
+      alt="FIG. 3l.--THE 'DEBRUYNE' GENERATING PLANT FOR LUMP CARBIDE" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: DE SMET VAN OVERBERGE, ALOST.
+    </p>
+    <p>
+      <i>Type</i>: (1) Automatic; carbide-to-water.
+    </p>
+    <p>
+      This generating apparatus comprises an equalising gasholder <i>A</i>
+      placed alongside a generating tank <i>B</i>, above which is mounted on a
+      rotating spindle a series of chambers <i>C</i>, arranged in a circle,
+      which are filled with carbide. The generating tank is closed at the top,
+      but on one side there is a shoot <i>D</i> through which the carbide is
+      discharged from the chambers in turn into the water in the tank. The
+      series of chambers are rotated by means of a cord passing round a pulley
+      <i>E</i> and having a weight <i>F</i> at one end, and being attached to
+      the bell of the gasholder at the other. When the bell falls, owing to the
+      consumption of gas, to a certain low position, the carbide chamber, which
+      has been brought by the rotation of the pulley over the shoot, is opened
+      at the bottom by the automatic liberation of a catch, and its contents are
+      discharged into the generating tank. The contents of one carbide chamber
+      suffice to fill the gasholder to two-thirds of its total capacity. The
+      carbide chambers after filling remain hermetically closed until the bottom
+      is opened for the discharge of the carbide. There is a sludge-cock <i>G</i>
+      at the bottom of the generating tank. The gas passes from the gasholder
+      through a purifier <i>H</i>, which is ordinarily charged with puratylene.
+    </p>
+    <p class="ctr">
+      <a href="images/340.png"><img src="images/340th.png"
+      alt="FIG. 32.--AUTOMATIC GENERATING PLANT OF DE SMET VAN OVERBERGE" /></a>
+    </p>
+    <p>
+      (2) Non-automatic; carbide-to-water. This apparatus comprises a storage
+      bell gasholder <i>J</i> placed alongside a generating tank in the top of
+      which is a funnel <i>E</i> with a counter-weighted lever pivoted on the
+      arm <i>B</i>. The base of the funnel is closed by a flap valve <i>C</i>
+      hinged at <i>D</i>. When it is desired to generate gas the counter-weight
+      <i>A</i> of the lever is raised and the valve at the bottom of the funnel
+      is thereby opened. A charge of carbide is then tipped into the funnel and
+      drops into the water in the generating tank. The valve is then closed and
+      the gas evolved goes through the pipe <i>G</i> to the gasholder, whence it
+      passes through a purifier to the service-pipe. There is a sludge-cock on
+      the generating tank.
+    </p>
+    <p class="ctr">
+      <a href="images/341.png"><img src="images/341th.png"
+      alt="FIG. 33.--NON-AUTOMATIC GENERATING PLANT OF DE SMET VAN OVERBERGE" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: SOC. AN. BELGE DE LA PHOTOLITHE, 2 RUE DE HUY, LI�GE.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Photolithe" generating plant made by this firm comprises an
+      equalising bell gasholder <i>A</i> in the tank <i>O</i>, alongside a
+      generating tank <i>B</i> which is surmounted by a carbide storage
+      receptacle divided into a number of compartments. These compartments are
+      fitted with flap bottoms secured by catches, and are charged with carbide.
+      Through the middle of the storage receptacle passes a spindle, to the
+      upper end of which is attached a pulley <i>b</i>. Round the pulley passes
+      a chain, one end of which carries a weight <i>n</i>, while in the other
+      direction it traverses guide pulleys and is attached to a loop on the
+      crown of the gasholder bell. When the bell falls below a certain point
+      owing to the consumption of gas, it pulls the chain and rotates the pulley
+      <i>b</i> and therewith an arm <i>d</i>, which liberates the catch
+      supporting the flap-bottom of the next in order of the carbide
+      compartments. The contents of this compartment are thereby discharged
+      through the shoot <i>C</i> into the generating tank <i>B</i>. The gas
+      evolved passes through the cock <i>R</i> and the pipe <i>T</i> into the
+      gasholder, the rise of the bell of which takes the pull off the chain and
+      allows the weight at its other end to draw it up until it is arrested by
+      the stop <i>f</i>. The arm <i>d</i> is thereby brought into position to
+      liberate the catch of the next carbide receptacle. The generating tank is
+      enlarged at its base to form a sludge receptacle <i>E</i>, which is
+      provided with a sludge draw-off cock <i>S</i> and a hand-hole <i>P</i>.
+      Between the generating tank proper and the sludge receptacle is a grid,
+      which is cleaned by means of a rake with handle <i>L</i>. The gas passes
+      from the gasholder through a purifier <i>H</i> charged with puratylene, to
+      the service-pipe.
+    </p>
+    <p class="ctr">
+      <a href="images/342.png"><img src="images/342th.png"
+      alt="FIG. 34.--'PHOTOLITHE' GENERATING PLANT" /></a>
+    </p>
+    <p>
+      The same firm also makes a portable generating apparatus in which the
+      carbide is placed in a basket in the crown of the bell of the gasholder.
+      This apparatus is supplied on a trolley for use in autogenous soldering or
+      welding.
+    </p>
+    <p>
+      FRANCE.
+    </p>
+    <p>
+      <i>Maker</i>: LA SOC. DES APPLICATIONS DE L'AC�TYL�NE, 26 RUE CADET,
+      PARIS.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Javal" generating plant made by this firm consists of an equalising
+      bell gasholder <i>A</i> in the tank <i>B</i> with a series of buckets <i>D</i>,
+      with removable bottoms <i>h</i>, mounted on a frame <i>F</i> round the
+      guide framing of the holder. Alongside the gasholder stands the generating
+      tank <i>H</i> with shoot <i>K</i>, into which the carbide discharged from
+      the buckets falls. On top of the generator is a tipping water-bucket <i>I</i>
+      supplied with water through a ball cock. The bell of the gasholder is
+      connected by chains <i>a</i> and <i>c</i>, and levers <i>b</i> and <i>d</i>
+      with an arm which, when the bell descends to a certain point, comes in
+      contact with the catch by which the bottom of the carbide bucket is held
+      in place, and, liberating the same, allows the carbide to fall into the
+      shoot. When the bell rises, in consequence of the evolved gas, the ring of
+      carbide buckets is rotated sufficiently to bring the next bucket over the
+      shoot. Thus the buckets are discharged in turn as required through the
+      rise and fall of the gasholder bell.
+    </p>
+    <p class="ctr">
+      <a href="images/344.png"><img src="images/344th.png"
+      alt="FIG. 35.--'JAVAL' GENERATOR" /></a>
+    </p>
+    <p>
+      The carbide falling from the opened bucket strikes the end <i>i</i> of the
+      lever <i>k</i>, and thereby tips the water-bucket <i>I</i> and discharges
+      its contents into the shoot of the generator. The rise in the level of the
+      water in the generator, due to the discharge of the water from the bucket
+      <i>I</i>, lifts the float <i>L</i> and therewith, through the attached rod
+      and chain <i>u</i>, the ball <i>s</i> of the valve <i>t</i>. The sludge,
+      which has accumulated in the base <i>N</i> of the generator from the
+      decomposition of the previous portion of carbide, is thereby discharged
+      automatically into a special drain. The discharge- valve closes
+      automatically when the float <i>L</i> has sunk to its original level. The
+      gas evolved passes from the generator through the seal-pot <i>M</i> and
+      the pipe <i>r</i> with cock <i>q</i> into the gasholder, from which it
+      passes through the pipe <i>x</i>; with condensation chamber and discharge
+      tap <i>y</i> into the purifier <i>R</i>, which is charged with heratol.
+    </p>
+    <p>
+      <i>Maker</i>: L'HERMITE, LOUVIERS, EURE.
+    </p>
+    <p>
+      <i>Type</i>: (1) Automatic; carbide-to-water.
+    </p>
+    <p>
+      The generating plant known as "L'�clair," by this firm comprises an
+      equalising bell gasholder <i>A</i> floating in an annular water-seal <i>N</i>,
+      formed in the upper part of a generating tank <i>B</i> into which carbide
+      enters through the shoot <i>K</i>. Mounted at the side of the tank is the
+      carbide delivery device, which consists of the carbide containers <i>J</i>
+      supported on an axis beneath the water-sealed cover <i>H</i>. The
+      containers are filled with ordinary lump carbide when the cover <i>H</i>
+      is removed. The tappet <i>O</i> attached to the bell of the gasholder come
+      in contact with a pawl when the gasholder bell descends to a certain level
+      and thereby rotates a pinion on the protruding end of the axis which
+      carries the carbide containers <i>J</i>. Each time the bell falls and the
+      tappet strikes the pawl, one compartment of the carbide containers
+      discharges its contents down the shoot <i>K</i> into the generating tank
+      <i>B</i>. The gas evolved passes upwards and causes the bell <i>A</i> to
+      rise. The gas is prevented from rising into the shoot by the deflecting
+      plates <i>G</i>. The natural level of the water in the generating tank,
+      when the apparatus is in use, is shown by the dotted lines <i>L</i>. The
+      lime sludge is discharged from time to time through the cock <i>E</i>,
+      being stirred up by means of the agitator <i>C</i> with handle <i>D</i>.
+      When the sludge is discharged water is added through <i>M</i> to the
+      proper level. The gas evolved passes from the holder through the pipe with
+      tap <i>F</i> to the service-pipe. A purifier is supplied if desired.
+    </p>
+    <p class="ctr">
+      <a href="images/345a.png"><img src="images/345ath.png"
+      alt="FIG. 36.--'L'�CLAIR,' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>References</i>
+    </p>
+    <p>
+      A Gasholder. B Generator. C Agitator. D Handle of agitator. E Sludge-cock.
+      F Gas outlet. G Deflecting plates. H Cover. I Carbide. J Automatic
+      distributor. K Shoot. L Water-level. M Water-inlet. N Water-seal. O
+      Tappet.
+    </p>
+    <p>
+      (2) Automatic; water-to-carbide; contact.
+    </p>
+    <p>
+      A generating plant known as "L'�toile" made by this firm. A tappet on the
+      bell of an equalising gasholder depresses a lever which causes water to
+      flow into a funnel, the outlet of which leads to a generating chamber
+      containing carbide.
+    </p>
+    <p>
+      <i>Maker</i>: MAISON SIRIUS, FR. MANGIAMELI &amp; CO., 34 RUE DES PETITS-
+      H�TELS, PARIS.
+    </p>
+    <p>
+      <i>Type</i>: (1) Automatic; carbide-to-water.
+    </p>
+    <p>
+      The generating plant made by this firm comprises a drum-shaped carbide
+      holder mounted above a generating tank, a condenser, a washer, an
+      equalising gasholder, and a purifier. The drum <i>A</i> is divided into
+      eight chambers <i>a</i> each closed by a fastening on the periphery of the
+      drum. These chambers are packed with lump carbide, which is discharged
+      from them in turn through the funnel <i>B</i> into the generating tank,
+      which is filled with water to the level of the overflow cock <i>b</i>. A
+      deflecting plate <i>d</i> in the tank distributes the carbide and prevents
+      the evolved gas passing out by way of the funnel <i>B</i>. The gas evolved
+      passes through the pipe <i>O</i> into the condenser, which is packed with
+      coke, through which the gas goes to the pipe <i>E</i> and so to the washer
+      <i>P</i> through the water, in which it bubbles and issues by the pipe <i>G</i>
+      into the gasholder. The bell <i>L</i> of the gasholder is connected by a
+      chain <i>C</i> to the axis of the drum <i>A</i>, on which is a pinion with
+      pawl so arranged that the pull on the chain caused by the fall of the bell
+      of the gasholder rotates the drum by 1/8 of a turn. The catch on the
+      outside of the carbide chamber, which has thereby been brought to the
+      lowest position, is at the same time freed, so that the contents of the
+      chamber are discharged through the funnel <i>B</i>. The evolved gas causes
+      the bell to rise and the drum remains at rest until, owing to the
+      consumption of gas, the bell again falls and rotates the drum by another
+      1/8 of a turn. Each chamber of the drum holds sufficient carbide to make a
+      volume of gas nearly equal to the capacity of the gasholder. Thus each
+      discharge of carbide very nearly fills the gasholder, but cannot over-fill
+      it. The bell is provided with a vent-pipe <i>i</i>, which comes into
+      operation should the bell rise so high that it is on the point of becoming
+      unsealed. From the gasholder the gas passes through the pipe <i>J</i>,
+      with cock <i>e</i>, to the purifier, which is charged with frankoline,
+      puratylene, or other purifying material, whence it passes to the pipe <i>N</i>
+      leading to the place of combustion. The generating tank is provided with a
+      sludge-cock <i>g</i>, and a cleaning opening with lid <i>f</i>. This
+      generating plant has been primarily designed for the use of acetylene for
+      autogenous welding, and is made also mounted on a suitable trolley for
+      transport for this purpose.
+    </p>
+    <p class="ctr">
+      <a href="images/347.png"><img src="images/347th.png"
+      alt="FIG. 37.--'SIRIUS' GENERATOR" /></a>
+    </p>
+    <p>
+      (2) Automatic; carbide-to-water.
+    </p>
+    <p>
+      A later design of generating plant, known as the Type G, also primarily
+      intended for the supply of acetylene for welding, has the carbide store
+      mounted in the crown of the bell of the equalising gasholder, to the
+      framing of the tank of which are attached a purifier, charged with
+      frankoline, and a safety water-seal or valve. The whole plant is mounted
+      on a four-legged stand, and is provided with handles for carrying as a
+      whole without dismounting. It is made in two sizes, for charges of 5-1/2
+      and 11 lb. of carbide respectively.
+    </p>
+    <p>
+      GERMANY.
+    </p>
+    <p>
+      <i>Maker</i>: KELLER AND KNAPPICH, G.m.b.H., AUGSBURG.
+    </p>
+    <p>
+      <i>Type</i>: Non-automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Knappich" generating plant made by this firm embodies a generating
+      tank, one-half of which is closed, and the other half of which is open at
+      the top, containing water. A small drum containing carbide is attached by
+      a clamp to the end of a lever which projects above the open half of the
+      tank. The lever is fastened to a horizontal spindle which is turned
+      through 180� by means of a counter-weighted lever handle. The carbide
+      container is thus carried into the water within the closed half of the
+      tank, and is opened automatically in transit. The carbide is thus exposed
+      to the water and the evolved gas passes through a pipe from the top of the
+      generating tank to a washer acting on the Livesey principle, and thence to
+      a storage gasholder. The use of closed carbide containers in charging is
+      intended to preclude the introduction of air into the generator, and the
+      evolution and escape of gas to the air while the carbide is being
+      introduced. Natural circulation of the water in the generating tank is
+      encouraged with a view to the dissipation of heat and washing of the
+      evolved gas. From the gasholder the gas passes in a downward direction
+      through two purifiers arranged in series, charged with a material supplied
+      under the proprietary name of "Carburylen." This material is stated to act
+      as a desiccating as well as a purifying agent. The general arrangement of
+      the plant is shown in the illustration. (Fig. 38).
+    </p>
+    <p class="ctr">
+      <a href="images/348.png"><img src="images/348th.png"
+      alt="FIG. 38.--'KNAPPICH' GENERATING PLANT" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: NORDISCHE AZETYLEN-INDUSTRIE; ALTONA-OTTENSEN.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; "drawer."
+    </p>
+    <p>
+      The apparatus made by this firm consists of an equalising gasholder with
+      bell <i>D</i> and tank <i>E</i>, a water-tank <i>O</i>, and two drawer
+      generators <i>C</i> situated in the base of the gasholder tank. The
+      water-supply from the tank <i>O</i> through the pipe <i>P</i> with valve
+      <i>Q</i> is controlled by the rise and fall of the bell through the medium
+      of the weight <i>J</i> attached to the bell. When the bell descends this
+      weight rests on <i>K</i> and so moves a counter-weighted lever, which
+      opens the valve <i>Q</i>. The water then flows through the nozzle <i>B</i>
+      into one division of the funnel <i>A</i> and down the corresponding pipe
+      to one of the generators. The generators contain trays with compartments
+      intended to be half filled with carbide. The gas evolved passes up the
+      pipe <i>T</i> and through the seal <i>U</i> into the bell of the
+      gasholder. There is a safety pipe <i>F</i>, the upper end of which is
+      carried outside the generator house. From the gasholder the gas is
+      delivered through the cock <i>M</i> to a purifier charged with a special
+      purifying material mixed with cork waste and covered with wadding. There
+      is a drainage cock <i>N</i> at the base of the purifier. The nozzle <i>B</i>
+      of the water-supply pipe is shifted to discharge into either compartment
+      of the funnel <i>A</i>, according to which of the two generators is
+      required to be in action. The other generator may then be recharged
+      without interfering with the continuous working of the plant.
+    </p>
+    <p class="ctr">
+      <a href="images/350.png"><img src="images/350th.png"
+      alt="FIG. 39.--GENERATING PLANT OF THE NORDISCHE AZETYLEN-INDUSTRIE" /></a>
+    </p>
+    <p>
+      GREAT BRITAIN AND IRELAND.
+    </p>
+    <p>
+      <i>Maker:</i> THE ACETYLENE CORPORATION OF GREAT BRITAIN LTD., 49 VICTORIA
+      STREET, LONDON, S.W.
+    </p>
+    <p>
+      <i>Type:</i> (1) Automatic; water-to-carbide; contact, superposed pans.
+    </p>
+    <p>
+      The "A1" generating plant made by this firm comprises a bell gasholder,
+      with central guide, standing alongside the generator. The generator
+      consists of a rectangular tank in which is a generating chamber having a
+      water-sealed lid with pressure test-cock <i>I</i>. Into the generating
+      chamber fit a number of pans <i>J</i>, which are charged with carbide.
+      Water is supplied to the generating chamber from an overhead tank <i>B</i>
+      through the starting tap <i>D</i> and the funnel <i>E</i>. It flows out of
+      the supply-pipe near the top of the generating chamber through a slot in
+      the side of the pipe facing the corner of the chamber, so that it runs
+      down the latter without splashing the carbide in the upper pans. It enters
+      first the lowest carbide pan through the perforations, which are at
+      different levels in the side of the pan. It thus attacks the carbide from
+      the bottom upwards. The evolved gas passes from the generating chamber
+      through a pipe opening near the top of the same to the washer <i>A</i>,
+      which forms the base of the generating tank. It bubbles through the water
+      in the washer, which therefore also serves as a water-seal, and passes
+      thence to the gasholder. On the bell of the gasholder is an arm <i>C</i>
+      which, when the holder descends nearly to its lowest point, depresses the
+      rod <i>C</i>, which is connected by a chain to a piston in the outlet-pipe
+      from the water-tank <i>B</i>. The fall of the gasholder thereby raises the
+      piston and allows water to flow out of the tank <i>B</i> through the tap
+      <i>D</i> to the funnel <i>E</i>. The generating tank is connected by a
+      pipe, with tap <i>G</i>, with the washer <i>A</i>, and the water in the
+      generating tank is run off through this pipe each time the generating
+      chamber is opened for recharging, thereby flushing out the washer <i>A</i>
+      and renewing the water in the same. There is a sludge discharging tap <i>F</i>.
+      With a view to the ready dissipation of the heat of generation the
+      generating chamber is made rectangular and is placed in a water-tank as
+      described. Some of the heat of generation is also communicated to the
+      underlying washer and warms the water in it, so that the washing of the
+      gas is effected by warm water. Water condensing in the gasholder
+      inlet-pipe falls downwards to the washer. There is a water lip <i>H</i> by
+      which the level of the water in the washer is automatically kept constant.
+      The gasholder is provided with a safety-pipe <i>K</i>, which allows gas to
+      escape through it to the open before the sides of the holder become
+      unsealed, should the holder for any reason become over-filled. The holder
+      is of a capacity to take the whole of the gas evolved from the carbide in
+      one pan, and the water- tank <i>B</i> holds just sufficient water for the
+      decomposition of one charge of the generator. From the gasholder the gas
+      passes through a purifier, which is ordinarily charged with "Klenzal," and
+      a baffle-box for abstraction of dust, to the service-pipe. With plants
+      intended to supply more than forty lights for six hours, two or more
+      generating chambers are employed, placed in separate compartments of one
+      rectangular generating tank. The water delivery from the water-tank <i>B</i>
+      then takes place into a trough with outlets at different levels for each
+      generating chamber. By inspection of this trough it may be seen at once
+      whether the charge in any generating chamber is unattacked, in course of
+      attack, or exhausted.
+    </p>
+    <p class="ctr">
+      <a href="images/352.png"><img src="images/352th.png"
+      alt="FIG. 40.--THE 'A1' GENERATING PLANT OF THE ACETYLENE CORPORATION OF GREAT BRITAIN, LTD" /></a>
+    </p>
+    <p>
+      (2) Automatic; water-to-carbide; contact.
+    </p>
+    <p>
+      The same firm also makes the "Corporation Flexible-Tube Generator," which
+      is less costly than the "A1" (<i>vide supra</i>). The supply of water to
+      the generating vessels takes place from the tank of the equalising bell
+      gasholder and is controlled by a projection on the bell which depresses a
+      flexible tube delivering into the generating vessels below the level of
+      the water inlet to the tube.
+    </p>
+    <p>
+      (3) Automatic; water-to-carbide; "drawer."
+    </p>
+    <p>
+      The same firm also makes a generator known as the "A-to-Z," which is less
+      costly than either of the above. In it water is supplied from the tank of
+      a bell gasholder to a drawer type of generator placed in the base of the
+      gasholder tank. The supply of water is controlled by an external piston-
+      valve actuated through the rise and fall of the bell of the gasholder. The
+      flow of water to the generator is visible.
+    </p>
+    <p>
+      <i>Maker</i>: THE ACETYLENE GAS AND CARBIDE OF CALCIUM CO., PONTARDAWE,
+      R.S.O., GLAM.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; flooded compartment.
+    </p>
+    <p>
+      The "Owens" generator made by this firm comprises an equalising bell
+      gasholder alongside which are placed two or more inclined generating
+      cylinders. The front lower end of each cylinder is fitted with a lid which
+      is closed by a screw clamp. There is inserted in each cylinder a
+      cylindrical trough, divided into ten compartments, each of which contains
+      carbide. Water is supplied to the upper ends of the cylinders from a
+      high-level tank placed at the back of the gasholder. In the larger sizes
+      the tank is automatically refilled from a water service through a
+      ball-cock. The outlet-valve of this tank is operated through a counter-
+      weighted lever, the unweighted end of which is depressed by a loop,
+      attached to the crown of the gasholder bell, when the bell has nearly
+      reached its lowest position. This action of the bell on the lever opens
+      the outlet-valve of the tank and allows water to flow thence into one of
+      the generating cylinders. It is discharged into the uppermost of the
+      compartments of the carbide trough, and when the carbide in that
+      compartment is exhausted it flows over the partition into the next
+      compartment, and so on until the whole trough is flooded. The gas passes
+      from the generating cylinders through a water-seal and a baffle plate
+      condenser placed within the water link of the gasholder to the bell of the
+      latter. There is a water seal on the water supply-pipe from the tank to
+      the generators, which would be forced should the pressure within the
+      generators for any reason become excessive. There is also a sealed vent-
+      pipe which allows of the escape of gas from the holder to the open should
+      the holder for any reason be over filled. The gas passes from the holder
+      through a purifier charged with "Owens" purifying material to the service
+      pipe. The plant is shown in Fig 41.
+    </p>
+    <p class="ctr">
+      <a href="images/354.png"><img src="images/354th.png"
+      alt="FIG. 41.--'OWENS' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker</i> ACETYLENE ILLUMINATING CO, LTD, 268-270 SOUTH LAMBETH ROAD,
+      LONDON, SW
+    </p>
+    <p>
+      <i>Type</i> (1) Non automatic, carbide to water
+    </p>
+    <p>
+      The generator <i>A</i> of this type made by this firm is provided with a
+      loading box <i>B</i>, with gas tight lid, into which the carbide is put.
+      It is then discharged by moving a lever which tilts the hinged bottom <i>D</i>
+      of the box <i>B</i>, and so tips the carbide through the shoot <i>E</i> on
+      to the conical distributor <i>F</i> and into the water in the generating
+      chamber. There is a sludge cock <i>G</i> at the base of the generator. Gas
+      passes as usual from the generator to a washer and storage gasholder.
+      Heratol is the purifying material supplied.
+    </p>
+    <p class="ctr">
+      <a href="images/355.png"><img src="images/355th.png"
+      alt="FIG. 42.--CARBIDE-TO-WATER GENERATOR OF THE ACETYLENE ILLUMINATING CO., LTD" /></a>
+    </p>
+    <p>
+      (2) Non-automatic; water-to-carbide; contact.
+    </p>
+    <p>
+      The generator <i>A</i> is provided with a carbide container with
+      perforated base, and water is supplied to it from a delivery-pipe through
+      a scaled overflow. The gas evolved passes through the pipe <i>E</i> to the
+      washer <i>B</i>, which contains a distributor, and thence to the storage
+      gasholder <i>G</i>. There is a sludge-cock <i>F</i> at the base of the
+      generator. From the gasholder the gas passes through the purifier <i>D</i>,
+      charged with heratol, to the service-pipe.
+    </p>
+    <p class="ctr">
+      <a href="images/356.png"><img src="images/356th.png"
+      alt="FIG. 43.--WATER-TO-CARBIDE GENERATING PLANT OF THE ACETYLENE ILLUMINATING CO., LTD" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: THE ALLEN CO., 106 VICTORIA STREET, LONDON, S.W.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      The generating plant made by this firm comprises an equalising bell
+      gasholder, from the tank of which water is supplied through a flexible
+      tube to the top of a water-scaled generating chamber in which is a
+      vertical cylinder containing a cage packed with carbide. The open end of
+      the flexible tube is supported by a projection from the bell of the
+      gasholder, so that as the bell rises it is raised above the level of the
+      water in the tank and so ceases to deliver water to the generator until
+      the bell again falls. The water supplied flows by way of the water-seal of
+      the cover of the generating chamber to the cylinder containing the carbide
+      cage. Larger sizes have two generating chambers, and the nozzle of the
+      water delivery-pipe may be switched over from one to the other. There is
+      an overflow connexion which brings the second chamber automatically into
+      action when the first is exhausted. One chamber may be recharged while the
+      other is in action. Spare cylinders and cages are provided for use when
+      recharging. There is a cock for drawing off water condensing in the
+      outlet-pipe from the gasholder. The gas passes from the holder to the
+      lower part of a purifier with water-scaled cover, through the purifying
+      material in which it rises to the outlet leading to the service-pipe.
+      Purifying material under the proprietary name of the "Allen" compound is
+      supplied. The plant is shown in Fig. 44.
+    </p>
+    <p class="ctr">
+      <a href="images/357.png"><img src="images/357th.png"
+      alt="FIG. 44.--'ALLEN' FLEXIBLE-TUBE GENERATOR" /></a>
+    </p>
+    <p>
+      Maker: THE BON-ACCORD ACETYLENE GAS CO., 285 KING STREET, ABERDEEN.
+    </p>
+    <p>
+      Type: Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      The "Bon Accord" generating plant made by this firm comprises an
+      equalising displacement gasholder <i>B</i> immersed in a water-tank <i>A</i>.
+      Alongside the tank are placed two water-jacketed generating chambers <i>G1</i>
+      and <i>G2</i> containing cages <i>K</i> charged with carbide. Water passes
+      from within the gasholder through the water inlet- pipes <i>L1 L2</i>, the
+      cock <i>H</i>, and the pipes <i>F1 F2</i> to the generating chambers, from
+      which the gas evolved travels to the holder <i>B</i>, in which it
+      displaces water until the water-level falls below the mouths of the pipes
+      <i>L1</i> and <i>L2</i>, and so cuts off the supply of water to the
+      generating chambers. The gas passes from the holder <i>B</i> through the
+      pipe with outlet-cock <i>T</i> to a washer containing an acid solution for
+      the neutralisation of ammonia, then through a purifier containing a
+      "special mixture of chloride of lime." After that through a tower packed
+      with lime, and finally through a pressure regulator, the outlet of which
+      is connected to the service-pipe. There is an indicator <i>I</i> to show
+      the amount of gas in the holder. One generator may be charged while the
+      other is in action.
+    </p>
+    <p class="ctr">
+      <a href="images/358.png"><img src="images/358th.png"
+      alt="FIG. 45.--'BON-ACCORD' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: FREDK. BRABY AND CO., LTD., ASHTON GATE WORKS, BRISTOL; AND
+      352-364 EUSTON ROAD, LONDON.
+    </p>
+    <p>
+      <i>Type:</i> (I) Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "A" type of generator made by this firm comprises an equalising bell
+      gasholder, round the bell of which are arranged a series of buckets which
+      are charged with carbide. Those buckets are discharged in turn as the bell
+      falls from time to time through a mechanism operated by a weight suspended
+      from a wire cord on a revolving spindle. The carbide is discharged on to a
+      different spot in the generating tank from each bucket. There is a cock
+      for the periodical removal of sludge. Gas passes through a purifier
+      charged with puratylene to the service-pipe. The disposition of the parts
+      of the plant and the operating mechanism arc shown in the accompanying
+      figure, which represents the generating apparatus partly in elevation and
+      partly in section. The carbide buckets (1) are loosely hooked on the flat
+      ring (2) bolted to the gasholder tank (3). The buckets discharge through
+      the annular water-space (4) between the tank and the generator (5). The
+      rollers (6), fitted on the generator, support a ring (7) carrying radial
+      pins (8) projecting outwards, one pin for each bucket. The ring can travel
+      round on the rollers. Superposed on the ring is a tray (9) closed at the
+      bottom except for an aperture beneath the throat (11), on which is mounted
+      an inclined striker (12), which strikes the projecting tongues (1<i>a</i>)
+      of the lids of the buckets in turn. There is fixed to the sides of the
+      generator a funnel (13) with open bottom (13<i>a</i>) to direct the
+      carbide, on to the rocking grid (14) which is farther below the funnel
+      than appears from the figure. Gas passing up behind the funnel escapes
+      through a duct (15) to the gasholder. The ring (7) is rotated through the
+      action of the weight (16) suspended by the chain or rope (17) which passes
+      round the shaft (18), which is supported by the bracket (19) and has a
+      handle for winding up. An escapement, with upper limb (20<i>a</i>) and
+      lower limb (20<i>b</i>), is pivotally centred at (21) in the bracket (19)
+      and normally restrains the turning of the shaft by the weight. There is a
+      fixed spindle (24) supported on the bracket (23)--which is fixed to the
+      tank or one of the guide-rods--having centred on it a curved bar or
+      quadrant (25) running loose on the spindle (24) and having a crank arm
+      (26) to which is connected one end of a rod (27) which, at the other end,
+      is connected to the arm (28) of the escapement. The quadrant bears at both
+      extremities against the flat bar (29) when the bell (22) is sufficiently
+      raised. The bar (29) extends above the bell and carries an arm (30) on
+      which is a finger (30<i>a</i>). There is fixed on the shaft (18) a wheel
+      (31), with diagonal divisions or ways extending from side to side of its
+      rim, and stop-pins (32) on one side at each division. A clutch prevents
+      the rotation of the wheel during winding up.
+    </p>
+    <p class="ctr">
+      <a href="images/360.png"><img src="images/360th.png"
+      alt="FIG. 46.--THE 'A' GENERATOR OF FRED K. BRABY AND CO., LTD" /></a>
+    </p>
+    <p>
+      (2) Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      The type "B" generator made by this firm comprises an equalising bell
+      gasholder, a crescent-shaped feed water-tank placed on one side of the
+      gasholder, and mechanism for controlling a tap on the pipe by which the
+      feed water passes to a washer whence it overflows through a seal into a
+      horizontal generating chamber containing cells packed with carbide. The
+      mechanism controlling the water feed embodies the curved bar (25),
+      connecting-rod (27) and flat guide-bar (29) as used for controlling the
+      carbide feed in the "A" type of generator (Fig. 46). When the bell
+      descends water is fed into the washer, and the water-level of the seal is
+      thus automatically maintained. The gas evolved passes through a pipe,
+      connecting the seal on the top of the generating chamber with the washer,
+      into the gasholder. Plants of large size have two generating chambers with
+      connexions to a single washer.
+    </p>
+    <p>
+      <i>Maker:</i> THE DARGUE ACETYLENE GAS CO., 57 GREY STREET, NEWCASTLE-ON-
+      TYNE.
+    </p>
+    <p>
+      <i>Type:</i> Automatic; water-to-carbide; "drawer."
+    </p>
+    <p>
+      The "Dargue" acetylene generator made by this firm comprises an equalising
+      bell gasholder <i>B</i> floating in a water-tank <i>A</i>, which is deeper
+      than is necessary to submerge the bell of the gasholder. In the lower part
+      of this tank are placed two or more horizontal generating chambers which
+      receive carbide-containing trays divided by partitions into a number of
+      compartments which are half filled with carbide. Water is supplied from
+      the gasholder tank through the tap <i>E</i> and pipe <i>F</i> to the
+      generating chambers in turn. It rises in the latter and floods the first
+      compartment containing carbide before gaining access to the second, and so
+      on throughout the series of compartments. As soon as the carbide in the
+      first generating chamber is exhausted, the water overflows from it through
+      the pipe with by-pass tap <i>J</i> to the second generating chamber. The
+      taps <i>G</i> and <i>H</i> serve to disconnect one of the generating
+      chambers from the water-supply during recharging or while another chamber
+      is in action. The gas evolved passes from each generating chamber through
+      a pipe <i>L</i>, terminating in the dip-pipe <i>M</i>, which is provided
+      with a baffle-plate having very small perforations by which the stream of
+      gas is broken up, thereby subjecting it to thorough washing by the upper
+      layers of water in the gasholder tank. The washed gas, which thus enters
+      the gasholder, passes from it through the pipe <i>N</i> with main cock <i>R</i>
+      to the service- pipes. The water-supply to the generator is controlled
+      through the tap <i>E</i>, which is operated by a chain connected to an arm
+      attached to the bell of the gasholder.
+    </p>
+    <p>
+      The water in the gasholder tank is accordingly made to serve for the
+      supply of the generating chambers, for the washing of the gas, and as a
+      jacket to the generating chambers. The heat evolved by the decomposition
+      of the carbide in the latter creates a circulation of the water, ensuring
+      thereby thorough mixing of the fresh water, which is added from time to
+      time to replace that removed for the decomposition of the carbide, with
+      the water already in the tank. Thus the impurities acquired by the water
+      from the washing of the gas do not accumulate in it to such an extent as
+      to render it necessary to run off the whole of the water and refill,
+      except at long intervals. A purifier, ordinarily charged with puratylene,
+      is inserted in many cases after the main cock <i>R</i>. The same firm
+      makes an automatic generator on somewhat similar lines, specially designed
+      for use in autogenous welding, the smaller sizes of which are readily
+      portable.
+    </p>
+    <p class="ctr">
+      <a href="images/362.png"><img src="images/362th.png"
+      alt="FIG. 47.--'DARGUE' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: J. AND J. DRUMMOND, 162 MARKET STREET, ABERDEEN.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; contact.
+    </p>
+    <p>
+      The generating plant made by this firm comprises two or more generating
+      vessels <i>B</i> in which carbide is contained in removable cases
+      perforated at different levels. Water is supplied to these generating
+      vessels, entering them at the bottom, from an elevated tank <i>A</i>
+      through a pipe <i>C</i>, in which is a tap <i>F</i> connected by a lever
+      and chain <i>L</i> with the bell <i>G</i> of the equalising gasholder <i>H</i>,
+      into which the evolved gas passes. The lever of the tap <i>F</i> is
+      counter-weighted so that when the bell <i>G</i> descends the tap is
+      opened, and when the bell rises the tap is closed. The gas passes from the
+      generating chambers <i>B</i> through the pipe <i>D</i> to the
+      washer-cooler <i>E</i> and thence to the gasholder. From the latter it
+      passes through the dry purifier <i>J</i> to the service-pipe. The
+      gasholder bell is sealed in oil contained in an annular tank instead of in
+      the usual single-walled tank containing water. The purifying material
+      ordinarily supplied is puratylene. The apparatus is also made to a large
+      extent in a compact form specially for use on board ships.
+    </p>
+    <p class="ctr">
+      <a href="images/363.png"><img src="images/363th.png"
+      alt="FIG. 48.--J. AND J. DRUMMOND'S GENERATING PLANT" /></a>
+    </p>
+    <p>
+      <i>Agents</i>: FITTINGS, LTD., 112 VICTORIA STREET, S.W.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; carbide-to-water.
+    </p>
+    <p>
+      The "Westminster" generator supplied by this firm is the "Davis" generator
+      described in the section of the United States. The rights for the sale of
+      this generator in Great Britain are held by this firm.
+    </p>
+    <p>
+      <i>Maker</i>: LOCKERBIE AND WILKINSON, TIPTON, STAFFS.
+    </p>
+    <p>
+      <i>Type</i>: (1) Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      The "Thorscar" generator of this firm comprises an equalising gasholder,
+      the gas-space of the bell <i>B</i> of which is reduced by conical upper
+      walls. When the bell descends and this lining enters the water in the tank
+      <i>A</i> the displacement of water is increased and its level raised until
+      it comes above the mouths of the pipes <i>E</i>, through which a portion
+      then flows to the generators <i>D</i>. The evolution of the gas in the
+      latter causes the bell to rise and the conical lining to be lifted out of
+      the water, the level of which thereupon falls below the mouths of the
+      pipes <i>E</i> in consequence of the reduced displacement of the bell. The
+      supply of water to the generators is thus cut off until the bell again
+      falls and the level of the water in the tank is raised above the mouths of
+      the pipes <i>E</i>. The generating chambers <i>D</i> are provided with
+      movable cages <i>F</i> in which the carbide is arranged on trays. The gas
+      evolved travels through a scrubbing-box <i>G</i> containing charcoal, and
+      the pipe <i>J</i> with drainage-pipe <i>P</i> to the water-seal or washer
+      <i>K</i> inside the holder, into which it then passes. The outlet-pipe for
+      gas from the holder leads through the condensing coil <i>L</i> immersed in
+      the water in the tank to the condensed water-trap <i>N</i>, and thence by
+      the tap <i>Q</i> to the supply-pipe. The generating chambers are
+      water-jacketed and provided with gauge-glasses <i>H</i> to indicate when
+      recharging is necessary, and also with sludge-cocks <i>M</i>. The object
+      of the displacement cone in the upper part of the bell is to obtain
+      automatic feed of water to the carbide without the use of cocks or movable
+      parts. There is a funnel- shaped indicator in front of the tank for
+      regulating the height of water to a fixed level, and also an independent
+      purifier, the purifying material or which is supplied under the
+      proprietary name of "Thorlite."
+    </p>
+    <p class="ctr">
+      <a href="images/365.png"><img src="images/365th.png"
+      alt="FIG. 49.--'THORSCAR' GENERATOR" /></a>
+    </p>
+    <p>
+      (2) Non-automatic; water-to-carbide; "drawer."
+    </p>
+    <p>
+      This generating plant, the "Thorlite," comprises a water-tank <i>A</i>
+      from which water is admitted to the drawer generating chambers <i>B</i>,
+      one of which may be recharged while the other is in operation. The gas
+      evolved passes through a seal <i>C</i> to the gasholder <i>D</i>, whence
+      it issues as required for use through the purifier <i>E</i> to the
+      supply-pipe. For the larger sixes a vertical generating chamber is used.
+      The purifier and purifying material are the same as for the automatic
+      plant of the same firm.
+    </p>
+    <p class="ctr">
+      <a href="images/366.png"><img src="images/366th.png"
+      alt="FIG. 50.--'THORLITE' GENERATING PLANT" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: THE MANCHESTER ACETYLENE GAS CO., LTD., ACRE WORKS, CLAYTON,
+      MANCHESTER.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; "drawer."
+    </p>
+    <p>
+      The plant made by this firm comprises an equalising gasholder <i>A</i>
+      from the tank of which water is supplied to generating cylinders <i>B</i>
+      placed at the side of the tank, the number of which varies with the
+      capacity of the plant. The cylinders receive tray carbide-containers
+      divided into compartments perforated at different levels so that they are
+      flooded in turn by the inflowing water. A weight <i>C</i> carried by a
+      chain <i>D</i> from one end of a lever <i>E</i> pivoted to the framing of
+      the gasholder is supported by the bell of the gasholder when the latter
+      rises; but when the holder falls the weight <i>C</i>, coming upon the
+      lever <i>E</i>, raises the rod <i>F</i>, which thereupon opens the valve
+      <i>G</i>, which then allows water to flow from the gasholder tank through
+      the pipe <i>H</i> to one of the generating cylinders. When the carbide in
+      the first cylinder is exhausted, the water passes on to a second. One
+      generating cylinder may be recharged while another is in action. The
+      rising of the holder, due to the evolved gas, causes the bell to support
+      the weight <i>C</i> and thus closes the water supply-valve <i>G</i>. The
+      gas evolved passes through vertical condensers <i>J</i> into washing-
+      boxes <i>K</i>, which are placed within the tank. The gas issues from the
+      washing-boxes into the gasholder bell, whence it is withdrawn through the
+      pipe <i>L</i> which leads to the purifier. Puratylene is the purifying
+      material ordinarily supplied by this firm.
+    </p>
+    <p class="ctr">
+      <a href="images/367.png"><img src="images/367th.png"
+      alt="FIG. 51.--GENERATING PLANT OF THE MANCHESTER ACETYLENE GAS CO., LTD" /></a>
+    </p>
+    <p>
+      <i>Maker:</i> R,. J. MOSS AND SONS, 98 SNOW HILL, BIRMINGHAM.
+    </p>
+    <p>
+      <i>Type:</i> (1) Automatic; water-to-carbide; superposed trays.
+    </p>
+    <p>
+      The "Moss" generator, "Type A," made by this firm comprises an equalising
+      gasholder, four, three, or two generating chambers, and an intermediate
+      water-controlling chamber. Each generating chamber consists of a frame in
+      which are arranged about a central tube trays half filled with carbide,
+      having water inlet-holes at several different levels, and each divided
+      into two compartments. Over this frame is put a bell-shaped cover or cap,
+      and the whole is placed in an outer tank or bucket, in the upper part of
+      which is a water inlet-orifice. The water entering by this orifice passes
+      down the outside of the bell, forming a water-seal, and rises within the
+      bell to the perforations in the carbide trays from the lowest upwards, and
+      so reaches the carbide in successive layers until the whole has been
+      exhausted. The gas evolved passes through the central tube to a water-
+      seal and condensing tank, through which it escapes to the controlling
+      chamber, which consists of a small water displacement chamber, the gas
+      outlet of which is connected to the equalising gasholder. The bell of the
+      equalising gasholder is weighted or balanced so that when it rises to a
+      certain point the pressure is increased to a slight extent and
+      consequently the level of the water in the displacement controlling
+      chamber is lowered. In this chamber is a pipe perforated at about the
+      water-level, so that when the level is lowered through the increased
+      pressure thrown by the rising gasholder the water is below the
+      perforations and cannot enter the pipe. The pipe leads to the water
+      inlet-orifices of the generating tanks and when the equalising gasholder
+      falls, and so reduces the pressure within the controlling chamber, the
+      water in the latter rises and flows through the pipe to the generating
+      tanks. The water supplied to the carbide is thus under the dual control of
+      the controlling chamber and of the differential pressure within the
+      generating tank. The four generators are coupled so that they come into
+      action in succession automatically, and their order of operation is
+      naturally reversed after each recharging. An air-cock is provided in the
+      crown of the bell of each generator and, in case there should be need of
+      examination when charged, cocks are provided in other parts of the
+      apparatus for withdrawing water. There is a sludge-cock on each generator.
+      The gas passes from the equalising gasholder through a purifier, for which
+      the material ordinarily supplied is puratylene.
+    </p>
+    <p class="ctr">
+      <a href="images/369.png"><img src="images/369th.png"
+      alt="FIG. 52.--'MOSS TYPE A' GENERATOR" /></a>
+    </p>
+    <p>
+      The "Moss Type B" generator is smaller and more compact than "Type A." It
+      has ordinarily only two generating chambers, and the displacement water
+      controlling chamber is replaced by a bell governor, the bell of which is
+      balanced through a lever and chains by a weight suspended over the bell of
+      the equalising gasholder, which on rising supports this counter-weight and
+      so allows the governor bell to fall, thereby cutting off the flow of water
+      to the generating chambers.
+    </p>
+    <p class="ctr">
+      <a href="images/370.png"><img src="images/370th.png"
+      alt="FIG. 53.--'MOSS TYPE B' GENERATOR" /></a>
+    </p>
+    <p>
+      The "Moss Type C" generator is smaller than either "Type A" or "B," and
+      contains only one generating chamber, which is suspended in a pocket in
+      the crown of the equalising gasholder. Water enters through a hole near
+      the top of the bucket of the generating chamber, when it descends with the
+      holder through the withdrawal of gas from the latter.
+    </p>
+    <p class="ctr">
+      <a href="images/370a.png"><img src="images/370ath.png"
+      alt="FIG. 54.--'MOSS TYPE C' GENERATOR" /></a>
+    </p>
+    <p>
+      (2) Semi-automatic; water-to-carbide; superposed trays.
+    </p>
+    <p>
+      The "Moss Semi-Non-Auto" generating plant resembles the automatic plant
+      described above, but a storage gasholder capable of holding the gas
+      evolved from one charging of the whole of the generating chambers is
+      provided in place of the equalising gasholder, and the generation of gas
+      proceeds continuously at a slow rate.
+    </p>
+    <p>
+      The original form of the "Acetylite" generator (<i>vide infra</i>) adapted
+      for lantern use is also obtainable of R. J. Moss and Sons.
+    </p>
+    <p>
+      <i>Maker:</i> WM. MOYES AND SONS, 115 BOTHWELL STREET, GLASGOW.
+    </p>
+    <p>
+      <i>Type:</i> Automatic; carbide-to-water. The "Acetylite" generator made
+      by this firm consists of an equalising gasholder and one or more
+      generating tanks placed alongside it. On the top of each generating tank
+      is mounted a chamber, with conical base, charged with granulated carbide
+      1/8 to 1/2 inch in size. There is an opening at the bottom of the conical
+      base through which passes a rod with conical head, which, when the rod is
+      lowered, closes the opening. The rod is raised and lowered through levers
+      by the rise and fall of the bell of the equalising gasholder, which, when
+      it has risen above a certain point, supports a counter-weight, the pull of
+      which on the lever keeps the conical feed-valve open. The gas evolved in
+      the generating tanks passes through a condensing chamber situated at the
+      base of the tank into the equalising gasholder and so automatically
+      controls the feed of carbide and the evolution of gas according to the
+      rate of withdrawal of the gas from the holder to the service-pipes. The
+      water in the gasholder tank acts as a scrubbing medium to the gas. The
+      generating tanks are provided with sludge-cocks and a tap for drawing off
+      condensed water. The gas passes from the equalising gasholder, through a
+      purifier and dryer charged with heratol or other purifying material to the
+      service-pipes. The original form of the "Acetylite" generator is shown in
+      elevation and vertical section in Fig. 55. Wm. Moyes and Sons now make it
+      also with a detached equalising gasholder connected with the generator by
+      a pipe in which is inserted a lever cock actuated automatically through a
+      lever and cords by a weight above the bell of the gasholder. Some other
+      changes have been made with a view to securing constancy of action over
+      long periods and uniformity of pressure. In this form the apparatus is
+      also made provided with a clock-work mechanism for the supply of
+      lighthouses, in which the light is flashed on periodically. The flasher is
+      operated through a pilot jet, which serves to ignite the gas at the
+      burners when the supply is turned on to them at the prescribed intervals
+      by the clock- work mechanism.
+    </p>
+    <p class="ctr">
+      <a href="images/372.png"><img src="images/372th.png"
+      alt="FIG. 55.--'ACETYLITE' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: THE PH�S CO., 205 AND 207 BALLS POND ROAD, LONDON, N. <i>Type</i>:
+      Non-automatic; water-to-carbide; drip.
+    </p>
+    <p>
+      The type "E" generator made by this firm consists of a generating chamber
+      placed below a water chamber having an opening with cap <i>E</i> for
+      refilling. The generating chamber in closed by a door <i>B</i>, with
+      rubber washer <i>C</i>, held in position by the rod <i>A</i>, the ends of
+      which pass into slots, and the screw <i>A'</i>. The movable carbide
+      chamber <i>D</i> has its upper perforated part half filled with carbide,
+      which is pressed upwards by a spring <i>D'</i>. The carbide chamber when
+      filled is placed in the generating chamber, which is closed, and the lever
+      <i>F</i> of one of the taps <i>F'</i> is turned from "off" to "on,"
+      whereupon water drips from the tank on to the carbide. The evolution of
+      gas is stopped by reversing the lever of the tap. The second tap is
+      provided for use when the evolution of gas, through the water-supply from
+      the first tap, has been stopped and it is desired to start the apparatus
+      without waiting for water from the first tap to soak through a layer of
+      spent carbide. The two taps are not intended for concurrent use. The
+      evolved gas passes through a purifier containing any suitable purifying
+      material to the pipes leading to the burners.
+    </p>
+    <p class="ctr">
+      <a href="images/373.png"><img src="images/373th.png"
+      alt="FIG. 56.--'PH�S TYPE E' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker:</i> ROSCO ACETYLENE COMPANY, BELFAST.
+    </p>
+    <p>
+      <i>Type:</i> Non-automatic; carbide-to-water
+    </p>
+    <p>
+      The "Rosco" generating plant made by this firm comprises a generating tank
+      <i>A</i> which is filled with water to a given level by means of the
+      funnel-mouthed pipe <i>B</i> and the overflow <i>O</i>. On the top of the
+      water-sealed lid of the generating tank is mounted the carbide feed-valve
+      <i>L</i>, which consists of a hollow plug-tap with handle <i>M</i>. When
+      the handle <i>M</i> is turned upwards the hollow of the tap can be filled
+      from the top of the barrel with carbide. On giving the tap a third of a
+      turn the hollow of the plug is cut off from the outer air and is opened to
+      the generating tank so that the carbide contained in it is discharged over
+      a distributor <i>E</i> on to the tray <i>N</i> in the water in the
+      generating tank. The gas evolved passes through the scrubber and seal-pot
+      <i>J</i> to the storage gasholder <i>Q</i>. From the latter the gas passes
+      through the dry purifier <i>T</i> to the service-pipe. A sludge- cock <i>P</i>
+      is provided at the bottom of the generating tank and is stated to be
+      available for use while generation of gas is proceeding. The purifying
+      material ordinarily supplied is "Roscoline."
+    </p>
+    <p class="ctr">
+      <a href="images/374.png"><img src="images/374th.png"
+      alt="FIG. 57.--'ROSCO' GENERATING PLANT" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: THE RURAL DISTRICTS GAS LIGHT CO., 28 VICTORIA STREET, S.W.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      The "Signal-Arm" generating apparatus made by this firm comprises a bell
+      gasholder <i>A</i>, from the tank <i>B</i> of which water is supplied
+      through a swivelled pipe <i>C</i> to a generating chamber <i>D</i>. One
+      end of the swivelled pipe is provided with a delivery nozzle, the other
+      end is closed and counter-weighted, so that normally the open end of the
+      pipe is raised above the level of the water in the tank. A tappet <i>E</i>
+      on the bell of the gasholder comes into contact with, and depresses, the
+      open end of the swivelled pipe when the bell falls below a certain point.
+      As soon as the open end of the swivelled pipe has thus been lowered below
+      the level of the water in the tank, water flows through it into the
+      funnel-shaped mouth <i>F</i> of a pipe leading to the bottom of the
+      generating chamber. The latter is filled with cages containing carbide,
+      which is attacked by the water rising in the chamber. The gas evolved
+      passing into and raising the bell of the gasholder causes the open end of
+      the swivelled pipe to rise, through the weight of the counterpoise <i>G</i>,
+      above the level of the water in the tank and so cuts off the supply of
+      water to the generating chamber until the bell again descends and
+      depresses the swivelled pipe. The tappet on the bell also displaces a cap
+      <i>H</i> which covers the funnel-shaped mouth of the pipe leading to the
+      generating chamber, which cap, except when the swivelled supply-pipe is
+      being brought into play, prevents any extraneous moisture or other matter
+      entering the mouth of the funnel. Between the generating chamber and the
+      gasholder is a three-way cock <i>J</i> in the gas connexion, which, when
+      the gasholder is shut off from the generator, brings the latter into
+      communication with a vent-pipe <i>K</i> leading to the open. The gas
+      passes from the holder to a chamber <i>L</i> under grids packed with
+      purifying material, through which it passes to the outlet of the purifier
+      and thence to the service-pipe. Either heratol or chloride of lime is used
+      in the purifier, the lid of which, like the cover of the generator, is
+      water-sealed.
+    </p>
+    <p class="ctr">
+      <a href="images/375.png"><img src="images/375th.png"
+      alt="FIG. 58.--'SIGNAL-ARM' GENERATING PLANT" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: ST. JAMES' ILLUMINATING CO., LTD., 3 VICTORIA STREET,
+      LONDON, S.W.
+    </p>
+    <p>
+      <i>Type</i>: (1) Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      This plant consists of the generators <i>A</i>, the washer <i>B</i>, the
+      equalising gasholder <i>C</i>, the purifier <i>D</i>, and the water-tank
+      <i>E</i>. The carbide is arranged in baskets in the generators to which
+      water is supplied from the cistern <i>E</i> through the pipe <i>F</i>. The
+      supply is controlled by means of the valve <i>H</i>, which is actuated
+      through the rod <i>G</i> by the rise and fall of the gasholder <i>C</i>.
+      Gas travels from the gasholder through the purifier <i>D</i> to the
+      service-pipe. The purifier is packed with heratol resting on a layer of
+      pumice. The washer <i>B</i> contains a grid, the object of which is to
+      distribute the stream of gas through the water. There is a syphon-pot <i>J</i>
+      for the reception of condensed moisture. Taps <i>K</i> are provided for
+      shutting off the supply of water from the generators during; recharging,
+      and there is an overflow connexion <i>L</i> for conveying the water to the
+      second generator as soon as the first is exhausted. There is a sludge-cock
+      <i>M</i> at the base of each generator.
+    </p>
+    <p>
+      (2) Non-automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      This resembles the preceding plant except that the supply of water from
+      the cistern to the generators takes place directly through the pipe <i>N</i>
+      (shown in dotted lines in the diagram) and is controlled by hand through
+      the taps <i>K</i>. The automatic control-valve <i>H</i> and the rod <i>G</i>
+      are omitted. The gasholder <i>C</i> is increased in size so that it
+      becomes a storage holder capable of containing the whole of the gas
+      evolved from one charging.
+    </p>
+    <p class="ctr">
+      <a href="images/377.png"><img src="images/377th.png"
+      alt="FIG. 59.--GENERATING PLANT OF THE ST. JAMES' ILLUMINATING CO., LTD. (SECTIONAL ELEVATION AND PLAN.)" /></a>
+    </p>
+    <p>
+      <i>Maker</i>: THE STANDARD ACETYLENE CO., 123 VICTORIA STREET, LONDON,
+      S.W.
+    </p>
+    <p>
+      <i>Type</i>: (1) Non-automatic; carbide-to-water.
+    </p>
+    <p>
+      This plant comprises the generator <i>A</i>, the washer <i>B</i>, the
+      storage gasholder <i>C</i>, and the purifier <i>D</i>. The generator is
+      first filled with water to the crown of the cover, and carbide is then
+      thrown into the water by hand through the gas-tight lock, which is opened
+      and closed as required by the horizontal handle <i>P</i>. A cast-iron grid
+      prevents the lumps of carbide falling into the sludge in the conical base
+      of the generator. At the base of the cone is a sludge-valve <i>G</i>. The
+      gas passes from the generator through the pipe <i>H</i> into the washer <i>B</i>,
+      and after bubbling through the water therein goes by way of the pipe <i>K</i>
+      into the gasholder <i>C</i>. The syphon- pot <i>E</i> is provided for the
+      reception of condensed moisture, which is removed from time to time by the
+      pump <i>M</i>. From the gasholder the gas flows through the valve <i>R</i>
+      to the purifier <i>D</i>, whence it passes to the service-pipes. The
+      purifier is charged with material supplied under the proprietary name of
+      "Standard."
+    </p>
+    <p class="ctr">
+      <a href="images/378.png"><img src="images/378th.png"
+      alt="FIG. 60.--CARBIDE-TO-WATER GENERATING PLANT OF THE STANDARD ACETYLENE CO" /></a>
+    </p>
+    <p>
+      (2) Automatic; water-to-carbide; contact, superposed trays.
+    </p>
+    <p>
+      This plant comprises the generators <i>A</i>, the washer <i>B</i>, the
+      equalising gasholder <i>C</i>, the purifier <i>D</i>, and the water-tank
+      <i>E</i>. The carbide is arranged on a series of wire trays in each
+      generator, to which water is supplied from the water-tank <i>E</i> through
+      the pipe <i>Y</i> and the control-tap <i>U</i>. The gas passes through the
+      pipes <i>H</i> to the washer <i>B</i> and thence to the holder <i>C</i>.
+      The supply of water to the generators is controlled by the tap <i>U</i>
+      which is actuated by the rise and fall of the gasholder bell through the
+      rod <i>F</i>. The gas passes, as in the non-automatic plant, through a
+      purifier <i>D</i> to the service-pipes. Taps <i>W</i> are provided for
+      cutting off the flow of water to either of the generators during
+      recharging and an overflow pipe <i>h</i> serves to convey the water to the
+      second generator as soon as the carbide in the first is exhausted. A
+      sludge-cook <i>G</i> is put at the base of each generator.
+    </p>
+    <p class="ctr">
+      <a href="images/380.png"><img src="images/380th.png"
+      alt="FIG. 61.--AUTOMATIC, WATER-TO-CARBIDE GENERATING PLANT OF THE STANDARD ACETYLENE CO" /></a>
+    </p>
+    <p>
+      (3) Non-automatic; water-to-carbide; contact, superposed-trays.
+    </p>
+    <p>
+      This apparatus resembles the preceding except that the supply of water to
+      the generators is controlled by hand through the taps <i>W</i>, the
+      control valve <i>U</i> being omitted, and the gasholder <i>C</i> being a
+      storage holder of sufficient dimensions to contain the whole of the
+      acetylene evolved from one charging.
+    </p>
+    <p>
+      <i>Maker</i>: THORN AND HODDLE ACETYLENE CO., 151 VICTORIA STREET, S.W.
+    </p>
+    <p>
+      <i>Type</i>: Automatic; water-to-carbide; "drawer."
+    </p>
+    <p>
+      The "Incanto" generating plant made by this firm consists of a rising bell
+      gasholder which acts mainly on an equaliser. The fall of the bell
+      depresses a ball valve immersed in the tank, and so allows water to flow
+      from the tank past an outside tap, which is closed only during recharging,
+      to a generating chamber. The generating chamber is horizontal and is fixed
+      in the base of the tank, so that its outer case is surrounded by the water
+      in the tank, with the object of keeping it cool. The charge of carbide is
+      placed in a partitioned container, and is gradually attacked on the
+      flooding principle by the water which enters from the gasholder tank when
+      the ball valve is depressed. The gas evolved passes from the generating
+      chamber by a pipe which extends above the level of the water in the tank,
+      and is then bent down so that its end dips several inches below the level
+      of the water. The gas issuing from the end of the pipe is thus washed by
+      the water in the gasholder tank. From the gasholder the gas is taken off
+      as required for use by a pipe, the mouth of which is just below the crown
+      of the holder. There is a lip in the upper edge of the gasholder tank into
+      which water is poured from time to time to replace that consumed in the
+      generation of the gas. There are from one to three generating chambers in
+      each apparatus according to its size. The purifier is independent, and a
+      purifying mixture under the proprietary name of "Curazo" is supplied for
+      use in it.
+    </p>
+    <p class="ctr">
+      <a href="images/381.png"><img src="images/381th.png"
+      alt="FIG. 62.--'INCANTO' GENERATOR" /></a>
+    </p>
+    <p>
+      <i>Maker:</i> WELDREN AND BLERIOT, 54 LONG ACRE, LONDON, W.C.
+    </p>
+    <p>
+      <i>Type:</i> Automatic; contact.
+    </p>
+    <p>
+      This firm supplies the "Ac�tylithe" apparatus (<i>see</i> Belgium). <br />
+      <br /> <br />
+    </p>
+    <h2>
+      <a name="linkindex" id="index">INDEX</a>
+    </h2>
+<pre xml:space="preserve">
+Absorbed acetylene,
+Acagine,
+Accidents, responsibility for,
+Acetone, effect of, on acetylene,
+  solution of acetylene in,
+Acetylene-copper,
+Acetylene-oil-gas,
+Acetylene Association (Austrian)--regulations as to carbide,
+Acetylene Association (British)--analysis of carbide,
+  generator rules,
+  pressure gauges,
+  purification rules,
+Acetylene Association (German)--analysis of carbide,
+  holders,
+  generator rules,
+  standard carbide,
+Acetylene tetrachloride, production of,
+Ackermann burner,
+Advantages of acetylene, general,
+  hygienic,
+  intrinsic,
+  pecuniary,
+"After generation,"
+Air, admission of, to burners,
+  and acetylene, ignition temperature of,
+  composition of,
+  dilution of acetylene with, before combustion,
+  effect of acetylene lighting on,
+    coal-gas lighting on,
+    on illuminating power of acetylene,
+    paraffin lighting on,
+  in acetylene,
+  in flames, effect of,
+  in generators, danger of,
+    objections to,
+  in incandescent acetylene,
+  in service-pipes,
+  proportion of, rendering acetylene explosive,
+  removing, from pipes,
+  specific gravity of,
+  sterilised by flames,
+Air-gas,
+  and acetylene, comparison between,
+  and carburetted acetylene, comparison between,
+  effect of cold on,
+  illuminating power of,
+Alcohol, action of, on carbide,
+  for carburetting acetylene,
+    holder seals,
+  from acetylene, production of,
+Allgemeine Carbid und Acetylen Gesellschaft burner,
+Alloys, fusible, for testing generators,
+Alloys of copper. See <i>Copper (alloyed)</i>
+Aluminium sulphide, in carbide
+America (U.S.), regulations of the National Board of Fire Underwriters,
+American gallon, value of,
+Ammonia, in acetylene,
+  in coal-gas,
+  removal of,
+  solubility of, in water,
+Analysis of carbide,
+Ansdell, compressed and liquid acetylene,
+Anthracene, formation of, from acetylene,
+Anti-freezing agents,
+Area of purifiers,
+Argand burners,
+Aromatic hydrocarbons,
+Arrangement of generating plant,
+Arsenious oxide purifier,
+Atkins, dry process of generation,
+Atmospheric moisture and carbide,
+Atomic weights,
+Attention needed by generators,
+Austrian Acetylene Association, regulations as to carbide,
+Austrian Government Regulations,
+Autogenous soldering and welding,
+Automatic generators. See <i>Generators (automatic)</i>
+
+
+
+B
+
+Baking of carbide
+Ball-sockets for acetylene,
+Barium peroxide purifier,
+  sulphate in bleaching-powder,
+Barrel, gas, for acetylene, quality of
+Bell gasholders. See <i>Holders (rising)</i>
+Benz purifying material,
+Benzene,
+  for carburetting acetylene,
+  production of, from acetylene,
+Benzine. See <i>Petroleum spirit</i>
+Berg�, detection of phosphorus,
+  and Reychler, purification of acetylene,
+  and Reychler's reagent, solubility of acetylene in,
+Bernat, formula for mains and pipes,
+Berthelot, addition of chlorine to acetylene,
+  sodium acetate,
+  sulphuric acid and acetylene,
+Berthelot and Matignon, thermochemical data,
+  and Vieille, dissolved acetylene,
+Billwiller burners,
+Black, acetylene,
+Blagden, sodium hypochlorite,
+Bleaching-powder purifier (simple),
+Blochmann, copper acetylide,
+Blow-off pipes. See <i>Vent-pipes</i>
+Blowpipe, acetylene,
+Boiling-ring,
+Boistelle. See <i>Molet</i>
+Borek, enrichment of oil-gas,
+<i>Bougie d�cimale</i>,
+Brackets for acetylene,
+Bradley, Read, and Jacobs, calcium carbophosphide,
+Brame and Lewes, manganese carbide,
+Bray burners,
+British Acetylene Association. See <i>Acetylene Association
+(British)</i>,
+  Fire Offices Committee Regulations,
+  regulations. See <i>Acetylene Association (British); Home Office;
+    Orders in Council</i>
+Bromine-water purifier,
+Bullier, effect of heat on burners,
+  phosphorus in acetylene,
+  and Maquenne purifier,
+Bunsen burner, principle of,
+Bunte, enrichment of oil-gas,
+Burner orifices and gas density,
+Burners,
+  atmospheric,
+    principle of,
+  design of,
+  glassware for,
+  heating,
+  incandescent,
+    Ackermann,
+    Allgemeine Carbid und Acetylen Gesellschaft,
+    Bray,
+    firing back in,
+    Fouch�,
+    G�nther's,
+    illuminating power of,
+    Jacob, Gebr�der,
+    Keller and Knappich,
+    Knappich,
+    O.C.A.,
+    pressure for,
+    principles of construction of,
+    Schimek,
+    Sirius,
+    Trendel,
+    typical,
+    Weber,
+    Zenith,
+  self-luminous,
+    Argand,
+    as standard of light,
+    Billwiller,
+    Bray,
+    choking of,
+    corrosion of,
+    cycle,
+      Falk, Stadelmann and Co.'s,
+      Konette,
+      Ph�s,
+      Wiener's,
+    Dolan,
+    Drake,
+    effect of heat on,
+    Elta,
+    Falk, Stadelmann and Co.'s,
+    firing back in,
+    fish-tail,
+    Forbes,
+    Hannam's,
+    illuminating power of,
+ self-luminous injector,
+    Javal,
+    Kona,
+    Luta,
+    Naphey,
+    Orka,
+    Ph�s,
+    Pintsch,
+    pressure for,
+    rat-tail,
+    Sansair,
+    Schwarz's,
+    Stadelmann,
+    Suprema,
+    twin, angle of impingement in,
+      injector,
+      non-injector,
+    warping of,
+    Wiener's,
+    Wonder,
+By-products, See also <i>Residues</i>
+
+
+
+C
+
+
+
+Cadenel, shape of incandescent acetylene mantle,
+"Calcidum,"
+Calcium carbide, action of heat on,
+  action of non-aqueous liquids on,
+  analysis of,
+  and carbon bisulphide, reaction between,
+  and hydroxide, reaction between,
+  and ice, reaction between,
+  and steam, reaction between,
+  and water, reaction between,
+  as drying material,
+  baking of,
+  balls and cartridges. See <i>Cartridges</i>
+  bulk of,
+  chemical properties of,
+  crushing of,
+  decomposition of,
+    by solids containing water,
+    heat evolved during,
+    imperfect,
+    speed of,
+    temperature attained during,
+  deterioration of, on storage,
+  drums of,
+  dust in,
+  explosibility of,
+  fire, risk of,
+  formula for,
+  granulated,
+  heat-conducting power of,
+    of formation of,
+  impurities in,
+  inertness of,
+  in residues,
+  physical properties of,
+  purity of,
+  quality, regulations as to,
+  sale and purchase of, regulations as to,
+  scented,
+  shape of lumps of,
+  sizes of,
+  small, yield of gas from,
+  specific gravity of,
+    heat of,
+  standard, British,
+    German,
+  "sticks,"
+  storage regulations for,
+  subdivided charges of,
+  sundry uses of,
+  swelling of, during decomposition,
+  "treated,"
+  yield of acetylene from,
+Calcium carbophosphide,
+Calcium chloride, cause of frothing in generators,
+  for seals,
+  purifier,
+  solubility of acetylene in,
+Calcium hydroxide,
+  adhesion of, to carbide,
+  and carbide, reaction between,
+  milk of, solubility of acetylene in,
+  physical properties of,
+  space occupied by,
+Calcium hypochlorite,
+Calcium oxide,
+  and water, reaction between,
+  hydration of,
+  hygroscopic nature of,
+  physical properties of,
+Calcium phosphide,
+Calcium sulphide,
+Calorie, definition of,
+Calorific power of acetylene,
+  various gases,
+Candle-power. See <i>Illuminating power</i>
+Capelle, illuminating power of acetylene,
+Carbide. See <i>Calcium carbide</i>
+Carbide-containers,
+  air in,
+  filling of,
+  partitions in,
+  water-jacketing,
+Carbide-feed generators. See <i>Generators (carbide-to-water)</i>
+Carbide impurities in acetylene,
+Carbide-to-water generators. See <i>Generators (carbide-to-water)</i>
+Carbides, mixed,
+Carbolic acid, production of, from acetylene,
+Carbon, combustion of, in flames,
+  deposition of, in burners,
+  gaseous, heat of combustion of,
+  heat of combustion of,
+    vaporisation of,
+  pigment, production of,
+Carbon bisulphide and acetylene, reaction between,
+  and calcium carbide, reaction between,
+  in coal-gas,
+Carbon dioxide, addition of, to acetylene,
+  dissociation of,
+  effect of, on explosibility of acetylene,
+  for removing air from pipes,
+  heat of formation of,
+  produced by respiration,
+    benzene,
+    coal-gas,
+    in flame of acetylene,
+Carbon monoxide, in acetylene,
+  heat of combustion of,
+  formation of,
+  temperature of ignition of,
+Carbonic acid. See <i>Carbon dioxide</i>
+Carburetted acetylene, composition of,
+  effect of cold on,
+  illuminating power of,
+  manufacture of,
+  pecuniary value of,
+Carburetted water-gas, enrichment of,
+Carburine. See <i>Petroleum spirit</i>
+Carlson, specific heat of carbide,
+Caro, acetone vapour in acetylene,
+  addition of petroleum spirit to generator water,
+  air in incandescent acetylene,
+  calorific power of gases,
+  colour of incandescent acetylene,
+  composition of mantles,
+  durability of mantles,
+  heat production in generators,
+  illuminating power of carburetted acetylene,
+    of incandescent acetylene,
+  oil of mustard,
+  silicon in crude acetylene,
+Caro and Saulmann, "Calcidum,"
+Carriage, cost of, and artificial lighting,
+Cartridges of carbide,
+Cast-iron pipe for acetylene,
+Castor oil for acetylene joints,
+Catani, temperature of acetylene flame,
+Caustic potash purifier,
+Cedercreutz, yield of gas from carbide,
+  and Lunge, purification,
+Ceilings, blackening of,
+Ceria, proportion of, in mantles,
+Cesspools for residues,
+Chandeliers, hydraulic, for acetylene,
+Charcoal and chlorine purifier,
+Charging generators after dark,
+  at irregular intervals,
+Chassiron lighthouse,
+Chemical formul�, meaning of,
+Chemical reactions and heat,
+  of acetylene,
+Chimneys for stoves, &amp;c.,
+  glass, for burners,
+Chloride of lime. See <i>Bleaching-powder</i>
+Chlorine and acetylene, compounds of,
+  and charcoal purifier,
+  in acetylene,
+Chromic acid purifier,
+Cigars, lighted, danger of,
+Claude and Hess, dissolved acetylene,
+Coal-gas, enrichment of, with acetylene,
+  illuminating power of,
+  impurities in,
+  vitiation of air by,
+Cocks, hand-worked, in generators,
+Coefficient of expansion of acetone,
+  air,
+  dissolved acetylene,
+  gaseous acetylene,
+  liquid acetylene,
+  simple gases,
+Coefficient of friction of acetylene,
+  of coal-gas,
+Coke filters for acetylene,
+Cold, effect of, on acetylene,
+  on air-gas,
+  on carburetted acetylene,
+  on generation,
+Colour judging by acetylene,
+  of acetylene flame,
+  of air-gas flame,
+Colour of atmospheric acetylene flame,
+  of coal-gas flame,
+  of electric light,
+  of incandescent acetylene flame,
+  of spent carbide,
+Combustion of acetylene,
+  deposit from,
+Composition pipe for acetylene,
+Compounds, endo- and exo-thermic,
+  explosive, of acetylene and copper,
+"Compounds," of phosphorus and sulphur,
+  silicon,
+Compressed acetylene,
+Condensed matter in pipes, removal of,
+Condensers,
+Connexions, flexible, for acetylene,
+Construction of generators, principles of,
+  regulations as to,
+Contact generators,
+Convection of heat,
+Cooking-stoves,
+Copper acetylide,
+  (alloyed) in acetylene apparatus,
+  (unalloyed) in acetylene apparatus,
+  and acetylene, reactions between,
+  carbides,
+  chloride purifier
+Corrosion in apparatus,
+  avoidance of,
+Corrosive sublimate purifier,
+  as test for phosphorus
+Cost of acetylene lighting,
+Cotton-wool filters for acetylene,
+Council, Orders in. See <i>Orders in Council</i>
+Counterpoises for rising holders,
+Couples, galvanic,
+Coward. See <i>Dixon</i>
+Critical pressure and temperature of acetylene,
+Crushing of carbide,
+"Cuprene,"
+Cuprous chloride purifier,
+Cycle lamps,
+  burners for,
+  dilute alcohol for,
+Cylinders for absorbed acetylene,
+
+
+
+D
+
+
+
+Davy, addition of chlorine to acetylene,
+Davy's lamp for generator sheds,
+Decomposing vessels. See <i>Carbide containers</i>
+Decomposition of acetylene,
+  of carbide, See <i>Calcium carbide (decomposition of)</i>
+De Forcrand, heat of formation of carbide,
+Density. See <i>Specific gravity</i>
+Deposit at burner orifices,
+  on reflectors from combustion of acetylene,
+Deterioration of carbide in air,
+Diameter of pipes and explosive limits,
+Diaphragms, flexible, in generators,
+Diffusion through gasholder seals,
+Diluted acetylene,
+Dimensions of mains and pipes,
+Dipping generators,
+Displacement gasholders. See <i>Holders (displacement)</i>
+Dissociation of acetylene,
+  carbon dioxide,
+  water vapour,
+Dissolution of acetylene, depression of freezing-point by,
+  of gas in generators,
+Dissolved acetylene,
+Dixon and Coward, ignition temperature of acetylene,
+  of various gases,
+Dolan burners,
+Doors of generator sheds,
+Drainage of mains,
+Drake burners,
+Driers, chemical,
+Dripping generators,
+Drums of carbide,
+Dry process of generation,
+Dufour, addition of air to acetylene,
+"Dummies" in gasholder tanks,
+Dust and incandescent lighting,
+  in acetylene,
+  carbide,
+
+
+
+E
+
+
+
+Effusion of gases,
+Eitner, explosive limits of acetylene,
+  and Keppeler, estimation of phosphine,
+  phosphorus in crude acetylene,
+Electric lamps in generator sheds,
+  lighting, cost, and efficiency of,
+Elta burner,
+Endothermic compounds,
+  nature of acetylene,
+Engines, use of acetylene in,
+Enrichment, value of acetylene for,
+  with acetylene,
+�pur�ne purifying material,
+Equations, chemical, meaning of,
+Erdmann, acetylene as a standard of light,
+  colour of acetylene flame,
+  production of alcohol,
+Ethylene, formation of from acetylene,
+  heats of formation and combustion of,
+  ignition temperature of,
+Exhaustion of air by flames,
+Exothermic compounds,
+Expansion of gaseous acetylene, coefficient of,
+  of liquid acetylene coefficient of,
+  various coefficients of,
+Explosibility of carbide,
+Explosion of chlorine and acetylene,
+  of compressed acetylene,
+Explosive compounds of acetylene and copper,
+  effects of acetylene dissociation,
+  limits, meaning of term,
+    of acetylene,
+    of various gases,
+  nature of acetylene,
+  wave, speed of, in gases,
+Expulsion of air from mains,
+
+
+
+F
+
+
+
+Faced joints for acetylene,
+Falk, Stadelmann and Co., boiling-ring,
+  burners,
+  cycle-lamp burner,
+Ferric hydroxide purifier,
+F�ry, temperature of flames,
+  and Violle, acetylene as standard of light,
+Filters for acetylene,
+Filtration,
+Fire Offices Committee Regulations (British),
+  risks of acetylene apparatus,
+    carbide,
+    flame illuminants,
+  Underwriters, United States, Regulations,
+"Firing back" in incandescent burners,
+  self-luminous burners,
+Fish, action of lime on,
+Fittings for acetylene, quality of,
+Flame, colour of, air-gas,
+  atmospheric acetylene,
+  coal-gas,
+  incandescent, acetylene,
+  self-luminous acetylene,
+Flame illuminants, risk of fire with,
+  of acetylene containing air,
+  steadiness of acetylene,
+Flame temperature of acetylene,
+  temperature of various gases,
+Flames, distortion of, by solid matter,
+  effect of air on,
+    nitrogen on,
+  evolution of heat in,
+    light in,
+  jumping of,
+  liberation of carbon from,
+  loss of heat from,
+  shading of acetylene,
+  size of,
+Flare lamps,
+Flash-point of paraffin,
+Flexible connexions for acetylene,
+Floats in holder seals,
+Flooded-compartment generators,
+Flow of gases in pipes,
+Flues for heating burners,
+Fog, transmission of light through,
+Forbes burner,
+Foreign regulations,
+Formul�, meaning of chemical,
+Fouch�, absorbed acetylene,
+  burner,
+  dissolved acetylene,
+  illuminating power of acetylene air mixtures,
+  incandescent acetylene,
+  liquid acetylene,
+  oxy-acetylene blowpipe,
+Fournier. See <i>Maneuvrier</i>
+Fowler, enrichment of oil-gas,
+Fraenkel, deposit on reflectors from combustion of acetylene,
+  silicon in acetylene,
+France, regulations of the Conseil d'Hygi�ne de la Seine,
+  village acetylene mains in,
+Frank, freezing-point of calcium chloride solutions,
+  preparation of black pigment,
+  purifier,
+Frankoline,
+Freezing of generators,
+  of holder seals,
+Freezing of portable lamps,
+  of pressure-gauges,
+Freezing-point, depression of by dissolution of acetylene,
+  of calcium chloride solutions,
+  of dilute alcohol,
+  of dilute glycerin,
+Freund and Mai, copper acetylide,
+Friction of acetylene, coefficient of,
+  coal-gas, coefficient of,
+  gas in pipes,
+Frost, effect of, on air-gas,
+  on carburetted acetylene,
+Froth, lime, in acetylene,
+Frothing in generators,
+Fuchs and Schiff, olive oil,
+Furnace gases for removing air from pipes,
+
+
+
+G
+
+
+
+Gallon, American, value of,
+Galvanic action,
+Garelli and Falciola, depression of freezing-point by dissolution of
+   acetylene,
+Gas barrel for acetylene, objection to,
+  drying of,
+  engines, acetylene for,
+  escape of, from generators,
+  firing, effects of,
+  volumes, correction of, for temperature and pressure,
+  yield of, from carbide,
+    determining,
+    standard,
+Gases, calorific value of,
+  effusion of,
+  explosive limits of,
+  flame temperature of,
+  illuminating power of,
+  inflammable properties of,
+  speed of explosive wave in,
+  temperature of ignition of,
+Gasfitters' paint,
+Gasholders. See <i>Holders</i>
+Gatehouse, F. B., test-papers,
+  J. W., estimation of phosphine,
+Gaud, blocking of burners,
+  polymerisation of acetylene,
+Generation, dry process of,
+Generating plant, regulations as to construction of,
+Generator impurities in acetylene,
+  pressure, utilisation of,
+  sheds,
+    lighting of,
+    smoking in,
+  water, addition of bleaching-powder to,
+    of petroleum spirit to,
+Generators and holders, isolation of,
+  attention needed by,
+Generators, charging after dark,
+  chemical reactions in,
+  construction of,
+  copper in,
+  corrosion in,
+  dissolution of gas in,
+  effect of tarry matter in,
+  escape of gas from,
+  failure of,
+  for analytical purposes,
+  for welding,
+  frothing in,
+  frozen, thawing of,
+  gauge of sheet-metal for,
+  heat dissipation in,
+    economy in,
+    produced in,
+  high temperatures and impurities in,
+  instructions for using,
+  joints in, making,
+  "lagging" for,
+  lead solder in,
+  materials for construction of,
+  maximum pressure in,
+  output of gas from,
+  overheating in,
+  polymerisation in,
+  pressure in,
+  protection of, from frost,
+  purchase of,
+  regulations as to,
+    American (National Board of Fire Underwriters),
+    Austrian Government,
+    British Acetylene Association,
+      Fire Offices Committee,
+      Home Office Committee(1901),
+    French (Council d' Hygiene de la Seine),
+    German Acetylene Association,
+    Hungarian Government,
+    Italian Government,
+  responsibility for accidents with,
+  selection of,
+  temperatures in,
+  typical,
+  vent-pipes for,
+  waste-pipes for,
+  water-jackets for,
+  water-scale in,
+Generators (automatic),
+    advantages of,
+    carbide-to-water,
+    definition of,
+    flexible diaphragms for,
+    holders of,
+    interlocking in,
+    mechanism for,
+    pressure thrown by,
+    speed of reaction in,
+    store of gas in,
+    supply of water to,
+    use of oil in,
+    water-to-carbide,
+    worked by holder bell,
+      by pressure,
+Generators (carbide-to-water),
+    advantages of,
+    frothing of,
+    grids for,
+    loss of gas in,
+    maximum temperature in,
+    pressure in,
+    quantity of water required by,
+Generators (contact),
+  (dipping),
+    temperatures in,
+  (dripping),
+    temperatures in,
+  (flooded compartment),
+  (non-automatic),
+    advantages of,
+    carbide-to-water,
+      hand-charging of,
+      water required for,
+    definition of,
+    speed of reaction in,
+    water-to-carbide,
+  (portable),
+  (shoot),
+  (water-to-carbide),
+    overheating in,
+  with carbide in excess,
+  with water in excess,
+Gerard, silicon in crude acetylene,
+Gerdes, acetylene copper,
+German Acetylene Association. (See <i>Acetylene Association, German</i>
+Gin, heat of formation of carbide,
+Glassware, for burners,
+Glow-lamps, electric, in generator sheds,
+Glucose for treatment of carbide,
+Glycerin for holder-seals,
+  for wet meters,
+Governor, displacement holder as,
+Governors,
+Graham, effusion of gases,
+Gramme-molecules,
+Granjon, illuminating power of self-luminous burners,
+  phosphine in acetylene,
+  pressure,
+  purifier,
+Granulated carbide. See <i>Calcium carbide, (granulated)</i>
+Graphite, artificial, production of,
+Grease for treatment of carbide,
+Grids for carbide-to-water generators,
+  in purifiers,
+Grittner, acetylene, and copper,
+Guides for rising holders,
+G�ntner burner,
+
+
+
+H
+
+
+
+Haber, effect of heat on acetylene,
+Haldane, toxicity of sulphuretted hydrogen,
+Hammcrschmidt, correction of gas volumes,
+  and Sandmann, milk of lime,
+Hannam's Ltd., burners,
+Hartmann, acetylene flame,
+Haze, on combustion of acetylene,
+Heat absorbed during change of physical state,
+  action on acetylene. See <i>Overheating</i>
+    carbide,
+  and temperature, difference between,
+  conducting power of carbide
+    iron and steel,
+    water,
+  convected,
+  developed by acetylene lighting,
+    coal-gas lighting,
+    electric lighting,
+    paraffin lighting,
+  dissipation of, in generators,
+  economy in generators,
+  effect of, on acetylene. (See <i>Overheating</i>)
+    on burners,
+  evolution of, in flames,
+  expansion of gaseous acetylene by,
+    liquid acetylene by,
+  from acetylene, production of,
+  latent. See <i>Latent heat</i>
+  loss of, from flames,
+  of chemical reactions,
+  of combustion of acetylene,
+    carbon,
+    carbon monoxide,
+    ethylene,
+  of formation of acetylene,
+    calcium carbide,
+      hydroxide,
+      oxide,
+    carbon dioxide,
+      monoxide,
+    ethylene,
+    water,
+  of hydration of calcium oxide,
+  of reaction between carbide and calcium hydroxide,
+    between carbide and water,
+  of solution of calcium hydroxide,
+  of vaporisation of carbon,
+    water,
+  radiant,
+  specific. See <i>Specific heat</i>
+Heating apparatus for generator sheds,
+Hefner unit,
+Heil, atmospheric acetylene flame,
+  carburetted acetylene,
+Heise, acetylene flame,
+Hempel, enrichment of coal-gas,
+Heratol,
+Hess. See <i>Claude</i>
+Hexachlorethane, production of,
+High houses, supply of acetylene to,
+Holder-bells, for testing mains,
+  supplying water to automatic generators,
+  weighting of,
+Holder-seals, freezing of,
+  level of liquid in,
+  liquids in,
+    and pressure,
+  solubility of acetylene in,
+  use of floats in,
+    liquids in, for decomposing carbide,
+    oil in,
+    water in, for washing the gas,
+Holders (gas) and generators, isolation of,
+  and pressure, relationship between,
+  and purifiers, relative position of,
+  exposed, roofs over,
+  false interiors for,
+  freezing of,
+  gauge of sheet-metal for,
+  loss of pressure in,
+  moistening of gas in,
+  of automatic generators,
+  preservation of, from corrosion,
+  situation of,
+  size of,
+  vent-pipes for,
+  value of,
+Holders (displacement),
+    action of,
+    pressure given by,
+  (rising),
+    guides and counterpoises for,
+    pressure thrown by,
+      equalisation of,
+    tanks for,
+Home Office, maximum pressure permitted by,
+  prohibition of air in acetylene by,
+  Committee, 1901, recommendations,
+    report,
+Home Secretary's Orders. See <i>Orders in Council</i>
+Hoxie. See <i>Stewart</i>,
+Hubou, acetylene black,
+Hungarian rules for apparatus,
+Hydraulic pendants for acetylene,
+Hydrocarbons formed by polymerisation,
+  illuminating power of,
+  volatile, names of,
+Hydrochloric acid in purified acetylene,
+Hydrogen and acetylene, reactions between,
+  effect of, on acetylene flame,
+  ignition temperature of,
+  in acetylene,
+  liberated by heat from acetylene,
+  silicide in crude acetylene,
+Hygienic advantages of acetylene,
+
+
+
+I
+
+
+
+Ice, reaction between carbide and,
+Ignition temperature of acetylene,
+  various gases,
+Illuminating power and illuminating effect,
+  definition of,
+  of acetylene, after storage,
+    carburetted,
+    effect of air on,
+    incandescent,
+    nominal,
+    self-luminous,
+  of acetylene-oil-gas,
+  of air-gas,
+  of polymerised acetylene,
+  of candles,
+  of coal-gas,
+  of electric lamps,
+  of hydrocarbons, various,
+  of paraffin,
+Illumination, amount of, required in rooms,
+  of lighthouses,
+  of optical lanterns,
+Impurities in acetylene, carbide,
+    detection and estimation of,
+    effect of, on air,
+  generator,
+  harmfullness of,
+  water soluble,
+    See also <i>Ammonia</i> and <i>Sulphuretted hydrogen</i>
+  in coal-gas,
+  in purified acetylene,
+    maximum limits of,
+Incandescent acetylene,
+  burners. See <i>Burners (incandescent)</i>
+  mantles,
+Inertness of carbide,
+Inflaming-point of acetylene,
+Inflammability, spontaneous,
+Installations, new, removal of air from,
+Interlocking of automatic generators,
+Iron and acetylene, reactions between,
+  and steel, heat-conducting power of,
+  silicide in carbide,
+Insecticide, carbide residues as,
+Isolation of apparatus parts,
+Intensity, specific, of acetylene light,
+  of oil light,
+Italian Government rules,
+
+
+
+J
+
+
+
+Jackets for generators,
+Jacob, Gebr�der, burner,
+Jacobs. See <i>Bradley</i>
+Jaubert, arsenious oxide purifier,
+Javal burners,
+    blocking of,
+  purifier,
+Jet photometer of acetylene,
+Joint-making in generators,
+  pipes,
+
+
+
+K
+
+
+
+Keller and Knappich burner,
+Keppeler, lead chromate in acagine,
+Keppeler, purification,
+  silicon in acetylene,
+  test-papers,
+  See also <i>Eitner</i>
+Kerosene. See <i>Paraffin oil</i>
+Klinger, vent-pipes,
+Knappich burner,
+Kona burner,
+Konette cycle-lamp burner,
+
+
+
+L
+
+
+
+La Belle boiling ring,
+Labour required in acetylene lighting,
+Lagging for generators,
+Lamps for generator sheds
+  paraffin,
+  portable,
+    acetone process for,
+Landolt-B�rnstein, solubility of acetylene in water,
+Landriset. See <i>Rossel</i>
+Lantern, optical, illumination of,
+Latent heat,
+Lead chromate in bleaching-powder,
+  objection to, in generators,
+  pipes for acetylene,
+  salts in bleaching-powder,
+  wire, &amp;c., for faced joints,
+Leakage of acetylene,
+Leaks, search for,
+Le Chatelier, explosive limits,
+  temperature of acetylene flame,
+  thermo-couple
+Leduc, specific gravity of acetylene,
+L�pinay, acetylene for engines,
+Level alteration and pressure in mains,
+Lewes, ammonia in crude acetylene,
+  blocking of burners,
+  haze,
+  heat of decomposition of carbide,
+    production in generators,
+  illuminating power of acetylene,
+  phosphorus in crude acetylene,
+  polymerisation of acetylene,
+  presence of hydrogen and carbon monoxide in acetylene,
+  reaction between carbide and calcium hydroxide,
+  silicon in crude acetylene,
+  temperature of acetylene flame,
+Lewes and Brame, manganese carbide,
+Lidholm, estimation of phosphine,
+Lifebuoys, acetylene for,
+Lifetime of burners,
+  mantles,
+Lifting power of acetylene in holders,
+Light, acetylene as a standard of,
+  colour of acetylene, incandescent,
+    self-luminous,
+  evolution of, in flames,
+  from acetylene, production of,
+  transmission of through fog,
+Lights, single, disadvantages of,
+  strong and weak, comparison between,
+Lighthouse illumination,
+Lighting by acetylene, scope of,
+  of generator sheds,
+Lime dust in acetylene,
+  reaction with sodium carbonate,
+  sludge. See <i>Residues</i>
+  solubility of, in sugar solutions,
+  water, solubility of gas in,
+Lime-light, acetylene for the,
+Limits, explosive, of acetylene,
+Lind�-air,
+Linseed oil for acetylene joints,
+Liquid acetylene, properties of,
+  condensation in pipes,
+  in holder-seals and pressure,
+  in pressure-gauge,
+Liquids, corrosive action of, on metals,
+  for seals,
+  purification by,
+  solubility of acetylene in,
+Locomotive lighting,
+Loss of gas in generators,
+  of pressure in holders,
+    in mains,
+    in purifiers,
+  on distribution,
+Love, enrichment by acetylene,
+Lubricating oil for seals,
+Luminous burners. See <i>Burners, self-luminous</i>
+Lunge and Cedercreutz, determination of phosphorus in acetylene,
+    purification,
+Luta burner,
+Lutes for holders. See <i>Seals</i>
+
+
+
+M
+
+
+
+Mahler, temperature of flames,
+Mai and Freund, copper acetylide,
+Mains, deposition of liquid in,
+  diameter of, and explosive limits,
+  dimensions of,
+  escapes from,
+  friction in,
+  laying of,
+  lead,
+  quality of,
+  removing air from,
+  testing of,
+Make of acetylene from carbide,
+  in generators,
+Manchester burners,
+Maneuvrier and Fournier, specific heat of acetylene,
+Manganese carbide,
+Mantles for acetylene,
+Manure for generator protection,
+Manurial value of generator residue,
+Maquenne. See <i>Bullier</i>
+Marsh gas, enrichment with acetylene,
+  formed from acetylene,
+Matignon. See <i>Berthelot</i>,
+Mauricheau-Beaupr�, �pur�ne,
+  estimation of phosphine,
+  frothing in generators,
+  phosphine in acetylene,
+  silicon in acetylene,
+Mechanism for automatic generators,
+Mercaptans in acetylene,
+Mercuric chloride purifier,
+  test for phosphorus,
+Merck test-papers,
+Metals for generators,
+  gauge of,
+Meters for acetylene,
+Methane, enrichment with acetylene,
+  formed from acetylene,
+  ignition temperature of,
+Methylated spirit for generators,
+  for holder seals,
+Meyer and M�nch, ignition temperatures,
+Mildew in vines, use of acetylene in,
+Milk of lime, solubility of acetylene in,
+Mineral oil for lighting. (See <i>Paraffin oil</i>)
+  for seals,
+Miner's lamp for generator sheds,
+Mist, transmission of light through,
+Mixter, thermo-chemical data,
+Mixtures of acetylene and air,
+  illuminating duty of,
+Moisture, effect of, on carbide,
+  in acetylene,
+Molecular volume of acetylene,
+  weight of acetylene,
+  weights, various,
+Molet-Boistelle acetylene-air mixture,
+Morel, formula for acetylene pipes,
+  sodium plumbate purifier,
+  specific heat of acetylene,
+    of carbide,
+Mosquitoes, destruction of,
+Moths, catching of,
+Motion of fluids in pipes,
+Motors, acetylene for,
+M�nch. See <i>Meyer</i>
+M�nsterberg, acetylene flame,
+Mustard, oil of,
+
+
+
+N
+
+
+
+Naphey burners,
+Naphthalene, formation of, from acetylene,
+Neuberg, illuminating power of acetylene,
+  radiant efficiency of acetylene,
+Nieuwland, mixtures of acetylene and chlorine,
+Nichols, illuminating power of acetylene after storage,
+  temperature of acetylene flame,
+Nickel and acetylene, reactions between,
+Nipples, burner, materials for,
+Nitrides in carbide,
+Nitrogen in flames, effect of,
+Non-automatic generators. See <i>Generators (non-automatic)</i>
+Non-luminous acetylene flame, appearance of,
+  burners. See <i>Burners (atmospheric)</i>
+Non-return valves,
+
+
+
+O
+
+
+
+O. C. A. burner,
+Odour of acetylene,
+Oil, action of, on carbide,
+  castor, for acetylene joints,
+  in generators,
+  in residues,
+  in seals,
+  linseed, for acetylene joints,
+  mustard,
+  olive, for seals,
+  (See also <i>Paraffin oil</i>)
+Olive oil for seals,
+Oil-gas, enrichment of,
+Optical efficiency of acetylene,
+Orders in Council, air in acetylene,
+  compression of absorbed acetylene,
+    acetylene-oil-gas,
+    neat acetylene,
+Origin of petroleum,
+Orka burner,
+Ortloff, friction of acetylene,
+Overheating in generators,
+  See also <i>Polymerisation</i>
+Oxide of iron purifier,
+Oxy-acetylene blowpipe,
+Oxygen required for combustion of acetylene,
+    of benzene,
+  combustion of acetylene with,
+  flames burning in,
+
+
+
+P
+
+
+
+Paint, cause of frothing in generators,
+  gas-fitters',
+Paraffin oil,
+  action of, on carbide,
+  flash-point of,
+  illuminating power of,
+  in residues,
+  lamps,
+  lighting, effect of on air,
+    heat developed by,
+  quality of different grades of,
+  use of in automatic generators,
+     seals,
+Paraffin wax, treatment of carbide with,
+Partial pressure,
+Pendants, water-slide for acetylene,
+Petroleum oil.  See <i>Paraffin oil</i>
+  spirit, addition of, to generator water,
+    composition of,
+      for carburetted acetylene,
+  spirits, nomenclature of,
+  theory of origin of,
+Pfeiffer, purifier,
+Pfleger, puratylene,
+Phenol, production of, from acetylene,
+Ph�s burners,
+Phosphine, cause of deposit at burner orifices,
+  composition of,
+  in crude acetylene,
+    amount of,
+  toxicity of,
+Phosphoretted hydrogen. See <i>Phosphine</i>
+Phosphorus and incandescent mantles,
+  "compounds,"
+  in crude acetylene,
+  in purified acetylene,
+    detection and determination of,
+    removal of,
+"Phossy-jaw,"
+Photometer, jet of acetylene,
+Phylloxera, use of acetylene for,
+Physical properties of acetylene,
+Pickering, freezing-points of calcium chloride solutions,
+Pictet, freezing-points of dilute alcohol,
+  purification of acetylene,
+Pintsch burners,
+Pipes, blow-off. See <i>Vent-pipes</i>
+  diameter of, and explosive limits,
+    vent. See <i>Vent-pipes</i> (See also <i>Mains</i>)
+Plant, acetylene, fire risks of,
+  order of items in,
+Platinum in burners,
+Poisonous nature of acetylene,
+Pole, motion of fluids in pipes,
+  pressure thrown by holders,
+Polymerisation, definition of,
+  of acetylene,
+    See also <i>Overheating</i>
+Porous matter, absorption of acetylene in,
+Portable lamps,
+    acetone process for,
+    temperature in,
+Potassium bichromate purifier,
+  hydroxide purifier,
+  permanganate purifier,
+Power from acetylene, production of,
+Precautions with generators,
+  with new installations,
+Presence of moisture in acetylene,
+Pressure and leakage,
+  after explosions of acetylene,
+  atmospheric,
+  automatic generators working by,
+  correction of gas volumes for,
+  critical, of acetylene,
+  definition of (gas),
+  for incandescent burners,
+    self-luminous burners,
+  gauge,
+    liquid for,
+  given by displacement holders,
+    rising holders,
+  in generators,
+    utilisation of,
+  in mains and pipes,
+  in purifiers, loss of,
+  irregular, caused by vent-pipes,
+  maximum safe, for acetylene,
+  necessity for regular,
+  partial,
+  regulators. See <i>Governors</i>
+Protection of generators from frost,
+  holders from frost,
+Puratylene,
+Purchase of a generator,
+  carbide, regulations as to,
+Purification by liquids and solids,
+  in portable lamps,
+  necessary extent of,
+  reasons for,
+  regulations as to,
+  speed of,
+Purified acetylene, chlorine in,
+    hydrochloric acid in,
+    phosphorus in,
+    sulphur in,
+Purifiers and holder, relative positions of,
+  construction of,
+  duplication of,
+  exhaustion of,
+  foul, emptying of,
+  loss of pressure in,
+  mechanical, for acetylene,
+Purifying materials, density of,
+    efficiency of,
+    quantity required,
+Pyralid, destruction of the,
+
+
+
+Q
+
+
+
+Quality of carbide, regulations as to,
+Quicklime. See <i>Calcium oxide</i>
+
+
+
+R
+
+
+
+Radiant efficiency of acetylene,
+  heat,
+Railway lighting by acetylene,
+Ramie mantles for acetylene,
+Range of explosibility, meaning of term,
+    of acetylene,
+Rat-tail burner,
+Reactions between copper and acetylene,
+  chemical, of acetylene,
+  physical, of acetylene,
+Reaction grids in generators,
+Read and Jacobs. See <i>Bradley</i>
+Rod lead for acetylene joints,
+Regulations, American (National Board of Fire Underwriters of U.S.A.),
+  Austrian Acetylene Association,
+    Government,
+  British Acetylene Association,
+    Fire Offices Committee,
+    Home Office Committee (1901),
+  for analysis of carbide,
+  for construction of generating plant,
+  for generators,
+  for purification,
+  for sale and purchase of carbide,
+  for sampling carbide,
+  for storing carbide,
+  French (Conseil d'Hygi�ne de la Seine),
+  German Acetylene Association,
+  Hungarian Government,
+  Italian Government,
+Residue from dry process of generation,
+Residues, carbide in,
+  colour of,
+  composition of,
+  consistency of,
+  disposal of,
+    containing oil,
+  manurial value of,
+  utilisation of,
+Respiration of acetylene,
+Reversibility of reaction between calcium oxide and water,
+Reychler. See <i>Berg�</i>
+Rising holders. See <i>Holders (rising)</i>
+Rossel and Landriset, ammonia in crude acetylene,
+  purifier,
+  sulphur in crude acetylene,
+Roofs over exposed holders,
+Rooms, amount of illumination required in,
+Rubber tubes for acetylene,
+Ruby for burners,
+Rules. See <i>Regulations</i>
+
+
+
+S
+
+
+
+Safety lamp, Davy's, for generator sheds,
+  valves. See <i>Vent-pipes</i>
+Sale of carbide, regulations as to,
+Salt, common, in holder-seals,
+Salzbergwerk Neu Stassfurt, production of tetrachlorethane,
+Sampling carbide,
+Sandmann. See <i>Hammerschmidt</i>
+Sansair burner,
+Saulmann. See <i>Caro</i>
+Sawdust in bleaching-powder,
+Scale, water, in generators,
+Scented carbide,
+Schiff. See <i>Fuchs</i>
+Schimek burner,
+Schwander, carburetted acetylene,
+Schwarz burners,
+Seal-pots,
+Seals (holder). See <i>Holder-seals</i>
+Seams in generator-making,
+Self-luminous burners. See <i>Burners (self-luminous)</i>
+Sensible heat,
+Separation of holder from generator,
+Service-pipes. See <i>Mains</i>
+Shoot generators,
+Silicon compounds,
+  in acetylene,
+  in carbide,
+Sirius burner,
+Slaked lime. See <i>Calcium hydroxide</i>
+Sludge. See <i>Residues</i>
+Sludge-cocks, automatic locking of,
+Sludge-pipes, blocked, clearance of,
+Smell of crude and purified acetylene,
+Smith, purification,
+Smoke, production of, by flames,
+Smoking,  danger of, in generator sheds,
+Soap, use of, in testing pipes,
+Soda, washing, for decomposing carbide,
+Sodium acetate solution for generator jackets,
+Sodium carbonate and lime, reaction between,
+    crystallised, for decomposing carbide,
+  chloride for holder-seals,
+    solubility of acetylene in,
+  hypochlorite purifier,
+  plumbate purifier,
+  sulphate in bleaching-powder,
+Soil, carbide residues as dressing for,
+Solder in generators,
+Soldering, autogenous,
+Solids containing water, decomposition of carbide by,
+  purification by,
+Solubility of acetylene,
+    in generators,
+    in holders,
+    in liquids,
+Soot, production by, of flames,
+Space occupied by purifying materials,
+Sparks from steel tools, danger of,
+Specific gravity and holder pressure,
+      leakage,
+    of acetylene, dissolved,
+      gaseous,
+      liquid,
+    of air,
+    of carbide,
+    of gases, and burner construction,
+    of water,
+  heat of acetylene,
+    of carbide,
+  heats, various,
+  intensity. See <i>Intensity, specific</i>
+Speed of reactions between carbide, water, and calcium hydroxide,
+  of purification,
+Spent lime. See <i>Residues</i>
+Spontaneous inflammability,
+Spraying apparatus,
+Stable manure for warming generators,
+Stadelmann burners,
+Standard of illumination in rooms,
+  of light, acetylene as,
+Steam, latent heat of, use of,
+  specific heat of,
+  reaction between carbide and,
+Steam-barrel for acetylene mains,
+Steatite for burners,
+Steel, heat-conducting power of,
+  tools, danger of
+Sterilisation of air by flames,
+Stewart and Hoxie, radiant efficiency of acetylene,
+Storage regulations for carbide,
+vessels for carbide, temporary,
+Styrolene. formation of, from acetylene,
+Suckert. See <i>Willson</i>
+Suffocation by acetylene,
+Sugar solutions, solubility of lime in,
+Sulphur "compounds,"
+  in coal-gas,
+  in crude acetylene,
+  in purified acetylene,
+  removal of,
+Sulphuretted hydrogen, solubility of, in water,
+  toxicity of,
+Sulphuric acid and acetylene, reactions between
+  as purifying material,
+Superficial area in purifiers,
+Supply of water to automatic generators,
+Suprenia burners,
+Swelling of carbide during decomposition,
+Symbols, chemical, meaning of,
+Syphons for removing water,
+
+
+
+T
+
+
+
+Table-lamps, acetone process for,
+Tabular numbers,
+Tanks for rising holders, construction of,
+"Tantalus Cup,"
+Taps for acetylene pipes,
+Tar, cause of frothing in generators,
+Tarry matter in generators,
+Telescopic gasholders. <i>See Holder (rising)</i>
+Temperature and heat, difference between,
+  correction of volumes for,
+  critical, of acetylene,
+  high, effect of, on acetylene. See <i>Polymerization</i>
+  of acetylene blowpipe,
+    flame,
+  of dissociation of acetylene,
+  of ignition of acetylene,
+    various gases,
+  of reaction between carbide and calcium hydroxide,
+    between carbide and water,
+Temperatures in generators,
+    calculation of,
+    determination of,
+Tension of liquid acetylene,
+Test-papers,
+Tetrachlorethane, production of,
+Tetrachloride, acetylene, production of,
+Thawing of frozen apparatus,
+Thermo-chemical data,
+Thermo-couple, Le Chatelier's,
+Thomson, radiant efficiency of acetylene,
+  thermo-chemical data,
+Tools, steel or iron, danger of,
+Town supplies,
+Toxicity of acetylene,
+  of sulphur and phosphorus compounds,
+Train-lighting by acetylene,
+Treated carbide. See <i>Calcium carbide (treated)</i>
+Trondol burner,
+Tubes, diameter of, and explosive limits,
+Tubes for acetylene. See <i>Mains</i>
+Tubing, flexible, for acetylene,
+Typical generators,
+
+
+
+U
+
+
+
+Ullmax purifier,
+Unaccounted-for gas,
+Underwriters, United States Fire,
+United States. See <i>America</i>
+Uses, sundry, for acetylene,
+
+
+
+V
+
+
+
+Valuation of carbide,
+Value of acetylene, hygienic,
+    enriching,
+    pecuniary,
+  of purifying materials,
+Valves, screw-down, for generators,
+Vapour, water, in acetylene, objections to,
+  removal of,
+  value of,
+Vehicular lamps,
+Ventilation of generator sheds,
+Vent-pipes, economy of,
+  for carbide vessels,
+    generators,
+    holders,
+  noise in,
+  position of mouths of,
+  size of,
+Vibration and incandescent lighting,
+Vieille, dissolved acetylene,
+Vigouroux, silicon in acetylene,
+Village installations, mains for,
+    leakage in,
+  supplies,
+Villard, liquid acetylene,
+Vines, treatment by acetylene of, for mildew and phylloxera,
+Violle and F�ry, acetylene as standard of light,
+Vitiation of air by flames,
+Volume, alteration of, on dissociation,
+  and weight of acetylene,
+  molecular, of acetylene,
+Volume of acetylene passing through pipes,
+Volumes, gas, correction for temperature and pressure,
+
+
+
+W
+
+
+
+Washers, oil,
+  water,
+Waste-pipes of generators,
+Water and calcium oxide, reaction between,
+  and carbide, heat of reaction between,
+  boiling-point, evolution of gas at,
+  condensation of, in pipes,
+  consumption of, in generators,
+  convection currents in,
+  freezing-point, evolution of gas at,
+  heat absorbed in warming,
+    conducting power of,
+    of formation of,
+  in excess, generators with,
+  in holders, freezing of,
+    use for decomposition,
+    use for washing,
+  jackets for generators,
+  quality of, for portable generators,
+  quantity required in carbide-to-water generators,
+  scale in generators,
+  solubility of acetylene in,
+    of impurities in,
+    of load in,
+  specific gravity of,
+  supply for automatic generators,
+  non-automatic generators,
+  yield of gas per unit of,
+Water-gas, enrichment with acetylene,
+Water-seals, as not-return valves,
+  setting water-level in,
+Water-slide pendants for acetylene,
+Water-soluble impurities in acetylene,
+  See also <i>Ammonia and Sulphuretted hydrogen</i>
+Water-to-carbide generators. See <i>Generators (water-to-carbide)</i>
+Water-vapour, dissociation of,
+  existence of, at low temperatures,
+  in acetylene, objections to,
+    removal of,
+    value of,
+  reaction between carbide and,
+Weber burner,
+Wedding, enrichment of coal-gas,
+Weed-killer, carbide residues as,
+Weight and volume of acetylene,
+Weights, atomic,
+  molecular,
+Welding, acetylene,
+White lead, for acetylene joints,
+Wiener burners,
+Willgerodt, purification,
+Willson and Suckert, liquid acetylene,
+Windows in generator sheds,
+Winter, manipulation of generators during,
+W�hler, addition of chlorine to acetylene,
+Wolff, acetone in acetylene,
+  illuminating power of acetylene,
+  purifier,
+  silicon in acetylene,
+Wonder burner,
+Work done in actuating automatic generators,
+
+
+
+Y
+
+
+
+Yield of gas, deficient, cause of,
+  from carbide,
+    determining,
+    (British standard),
+    (German standard),
+  from water,
+
+
+
+Z
+
+
+
+Zenith burner,
+</pre>
+    <h2>
+      <a name="linkindex2" id="index2">INDEX TO APPENDIX</a>
+    </h2>
+<pre xml:space="preserve">
+
+A
+
+
+
+"A" Generator (of Braby and Co., Ltd.),
+"A1" generator (of Acetylene Corporation of Great Britain),
+"A-to-Z" generator (of Acetylene Corporation of Great Britain),
+Acetylene Corporation of Great Britain,
+Acetylene Gas and Carbide of Calcium Co.,
+Acetylene Illuminating Co., Ltd.,
+"Acetylite" generator,
+"Ac�tylithe" generator,
+Ac�tylithe, Soc. An. de l',
+Allen Co.,
+"Allen" Flexible-tube generator,
+"Allen" purifying material,
+American generators,
+Applications de l'Ac�tyl�ne, La Soc. des.,
+Austrian generator,
+Automatic generators,
+
+
+
+B
+
+
+
+"B" generator (of Braby and Co., Ltd.),
+Belgian generators,
+Bon Accord Acetylene Gas Co.,
+"Bon Accord" generator,
+Braby, Frederick and Co., Ltd.,
+British generators,
+
+
+
+C
+
+
+
+Canadian generators,
+Carbide-to-water generators,
+"Carburlen" purifying material,
+Chloride of lime purifying material,
+Colt Co., J. G.,
+"Colt" generator,
+Compartment, flooded, generator,
+Contact generators,
+Cork waste and wadding purifying material,
+"Corporation Flexible Tube Generator,"
+"Curaze" purifying material,
+
+
+
+D
+
+
+
+"Dargue" generator,
+Dargue Acetylene Gas Co.,
+Davis Acetylene Co.,
+"Davis" generator,
+Debruyne, L.,
+Debruyne's generators,
+Drawer generators,
+Drip generator,
+Drummond, J. and J.,
+
+
+
+E
+
+
+
+English generators,
+
+
+
+F
+
+
+
+Flooded compartment generator,
+Fittings, Ltd.,
+Frankoline purifying material,
+French generators,
+
+
+
+G
+
+
+
+German generators,
+
+
+
+H
+
+
+
+Heratol, purifying material,
+
+
+
+I
+
+
+
+"Incanto" generator,
+Irish generator,
+
+
+
+J
+
+
+
+"Javal" generator,
+
+
+
+K
+
+
+
+Keller and Knappich, G.m.b.H.,
+"Klenzal" purifying material,
+Klinger, Rich.,
+Klinger's generator,
+"Knappich" generator,
+
+
+
+L
+
+
+
+"L'�clair" generator,
+"L'�toile" generator,
+L'Hermite,
+Lockerbie and Wilkinson,
+
+
+
+M
+
+
+
+Manchester Acetylene Gas Col., Ltd.,
+Mangiameli, Fr. and Co.,
+Moss, R. J. and Sons,
+  "Semi-Non-Auto" generator,
+  "Type A" generator,
+  "Type B" generator,
+  "Type C" generator,
+Moyes Wm., and Sons,
+
+
+
+N
+
+
+
+Non-automatic generators,
+Nordische Azetylen Industrie,
+
+
+
+O
+
+
+
+"Omega" generator,
+Overberge, De Smet van,
+"Owens" generator,
+"Owens" purifying material,
+
+
+
+P
+
+
+
+Ph�s Co.,
+"Ph�s Type E" generator,
+"Photolithe" generator,
+Photolithe, Soc. An. Belg de la,
+Pumice purifying material,
+Puratylene purifying material,
+Purifying material, "Allen,"
+  "Carburylen,"
+  chloride of lime,
+  coke and cotton, chemically treated,
+  cork waste and wadding,
+  "Curaze,"
+  frankoline,
+  heratol,
+  "Klenzal,"
+  "Owens,"
+  pumice,
+  puratylene,
+  "Roscoline,"
+  "Standard,"
+  "Thorlite,"
+
+
+
+R
+
+
+
+Rosco Acetylene Co.,
+"Rosco" generator,
+"Roscoline" purifying material,
+Rural Districts Gas Light Co.,
+
+
+
+S
+
+
+
+St. James' Illuminating Co., Ltd.,
+Scotch generators,
+Semi-automatic generator,
+Siche Gas Co., Ltd.,
+"Siche" generator,
+"Signal-Arm" generator,
+"Sirius" generator,
+Sirius, Maison,
+Standard Acetylene Co.,
+"Standard" purifying material,
+Sunlight Gas Machine Co.,
+Superposed pans or trays,
+
+
+
+T
+
+
+
+"Thorlite" generator,
+  purifying material,
+Thorn and Hoddle Co.,
+"Thorscar" generator,
+Trays, superposed,
+
+
+
+U
+
+
+
+United States generators,
+
+
+
+W
+
+
+
+Wadding and cork waste purifying material,
+Water-to-carbide generators,
+Weldhen and Bleriot,
+Welsh generator,
+"Westminster" generator,
+</pre>
+    <p>
+      <br /> <br /> <br /> <br />
+    </p>
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Acetylene, The Principles Of Its
+Generation And Use, by F. H. Leeds and W. J. Atkinson Butterfield
+
+*** END OF THIS PROJECT GUTENBERG EBOOK ACETYLENE ***
+
+***** This file should be named 8144-h.htm or 8144-h.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/8/1/4/8144/
+
+Produced by Richard Prairie, Tonya Allen, Juliet Sutherland,
+Charles Franks, and the Online Distributed Proofreading Team
+
+
+Updated editions will replace the previous one--the old editions
+will be renamed.
+
+Creating the works from public domain print editions means that no
+one owns a United States copyright in these works, so the Foundation
+(and you!) can copy and distribute it in the United States without
+permission and without paying copyright royalties.  Special rules,
+set forth in the General Terms of Use part of this license, apply to
+copying and distributing Project Gutenberg-tm electronic works to
+protect the PROJECT GUTENBERG-tm concept and trademark.  Project
+Gutenberg is a registered trademark, and may not be used if you
+charge for the eBooks, unless you receive specific permission.  If you
+do not charge anything for copies of this eBook, complying with the
+rules is very easy.  You may use this eBook for nearly any purpose
+such as creation of derivative works, reports, performances and
+research.  They may be modified and printed and given away--you may do
+practically ANYTHING with public domain eBooks.  Redistribution is
+subject to the trademark license, especially commercial
+redistribution.
+
+
+
+*** START: FULL LICENSE ***
+
+THE FULL PROJECT GUTENBERG LICENSE
+PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
+
+To protect the Project Gutenberg-tm mission of promoting the free
+distribution of electronic works, by using or distributing this work
+(or any other work associated in any way with the phrase "Project
+Gutenberg"), you agree to comply with all the terms of the Full Project
+Gutenberg-tm License available with this file or online at
+  www.gutenberg.org/license.
+
+
+Section 1.  General Terms of Use and Redistributing Project Gutenberg-tm
+electronic works
+
+1.A.  By reading or using any part of this Project Gutenberg-tm
+electronic work, you indicate that you have read, understand, agree to
+and accept all the terms of this license and intellectual property
+(trademark/copyright) agreement.  If you do not agree to abide by all
+the terms of this agreement, you must cease using and return or destroy
+all copies of Project Gutenberg-tm electronic works in your possession.
+If you paid a fee for obtaining a copy of or access to a Project
+Gutenberg-tm electronic work and you do not agree to be bound by the
+terms of this agreement, you may obtain a refund from the person or
+entity to whom you paid the fee as set forth in paragraph 1.E.8.
+
+1.B.  "Project Gutenberg" is a registered trademark.  It may only be
+used on or associated in any way with an electronic work by people who
+agree to be bound by the terms of this agreement.  There are a few
+things that you can do with most Project Gutenberg-tm electronic works
+even without complying with the full terms of this agreement.  See
+paragraph 1.C below.  There are a lot of things you can do with Project
+Gutenberg-tm electronic works if you follow the terms of this agreement
+and help preserve free future access to Project Gutenberg-tm electronic
+works.  See paragraph 1.E below.
+
+1.C.  The Project Gutenberg Literary Archive Foundation ("the Foundation"
+or PGLAF), owns a compilation copyright in the collection of Project
+Gutenberg-tm electronic works.  Nearly all the individual works in the
+collection are in the public domain in the United States.  If an
+individual work is in the public domain in the United States and you are
+located in the United States, we do not claim a right to prevent you from
+copying, distributing, performing, displaying or creating derivative
+works based on the work as long as all references to Project Gutenberg
+are removed.  Of course, we hope that you will support the Project
+Gutenberg-tm mission of promoting free access to electronic works by
+freely sharing Project Gutenberg-tm works in compliance with the terms of
+this agreement for keeping the Project Gutenberg-tm name associated with
+the work.  You can easily comply with the terms of this agreement by
+keeping this work in the same format with its attached full Project
+Gutenberg-tm License when you share it without charge with others.
+
+1.D.  The copyright laws of the place where you are located also govern
+what you can do with this work.  Copyright laws in most countries are in
+a constant state of change.  If you are outside the United States, check
+the laws of your country in addition to the terms of this agreement
+before downloading, copying, displaying, performing, distributing or
+creating derivative works based on this work or any other Project
+Gutenberg-tm work.  The Foundation makes no representations concerning
+the copyright status of any work in any country outside the United
+States.
+
+1.E.  Unless you have removed all references to Project Gutenberg:
+
+1.E.1.  The following sentence, with active links to, or other immediate
+access to, the full Project Gutenberg-tm License must appear prominently
+whenever any copy of a Project Gutenberg-tm work (any work on which the
+phrase "Project Gutenberg" appears, or with which the phrase "Project
+Gutenberg" is associated) is accessed, displayed, performed, viewed,
+copied or distributed:
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+1.E.2.  If an individual Project Gutenberg-tm electronic work is derived
+from the public domain (does not contain a notice indicating that it is
+posted with permission of the copyright holder), the work can be copied
+and distributed to anyone in the United States without paying any fees
+or charges.  If you are redistributing or providing access to a work
+with the phrase "Project Gutenberg" associated with or appearing on the
+work, you must comply either with the requirements of paragraphs 1.E.1
+through 1.E.7 or obtain permission for the use of the work and the
+Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
+1.E.9.
+
+1.E.3.  If an individual Project Gutenberg-tm electronic work is posted
+with the permission of the copyright holder, your use and distribution
+must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
+terms imposed by the copyright holder.  Additional terms will be linked
+to the Project Gutenberg-tm License for all works posted with the
+permission of the copyright holder found at the beginning of this work.
+
+1.E.4.  Do not unlink or detach or remove the full Project Gutenberg-tm
+License terms from this work, or any files containing a part of this
+work or any other work associated with Project Gutenberg-tm.
+
+1.E.5.  Do not copy, display, perform, distribute or redistribute this
+electronic work, or any part of this electronic work, without
+prominently displaying the sentence set forth in paragraph 1.E.1 with
+active links or immediate access to the full terms of the Project
+Gutenberg-tm License.
+
+1.E.6.  You may convert to and distribute this work in any binary,
+compressed, marked up, nonproprietary or proprietary form, including any
+word processing or hypertext form.  However, if you provide access to or
+distribute copies of a Project Gutenberg-tm work in a format other than
+"Plain Vanilla ASCII" or other format used in the official version
+posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
+you must, at no additional cost, fee or expense to the user, provide a
+copy, a means of exporting a copy, or a means of obtaining a copy upon
+request, of the work in its original "Plain Vanilla ASCII" or other
+form.  Any alternate format must include the full Project Gutenberg-tm
+License as specified in paragraph 1.E.1.
+
+1.E.7.  Do not charge a fee for access to, viewing, displaying,
+performing, copying or distributing any Project Gutenberg-tm works
+unless you comply with paragraph 1.E.8 or 1.E.9.
+
+1.E.8.  You may charge a reasonable fee for copies of or providing
+access to or distributing Project Gutenberg-tm electronic works provided
+that
+
+- You pay a royalty fee of 20% of the gross profits you derive from
+     the use of Project Gutenberg-tm works calculated using the method
+     you already use to calculate your applicable taxes.  The fee is
+     owed to the owner of the Project Gutenberg-tm trademark, but he
+     has agreed to donate royalties under this paragraph to the
+     Project Gutenberg Literary Archive Foundation.  Royalty payments
+     must be paid within 60 days following each date on which you
+     prepare (or are legally required to prepare) your periodic tax
+     returns.  Royalty payments should be clearly marked as such and
+     sent to the Project Gutenberg Literary Archive Foundation at the
+     address specified in Section 4, "Information about donations to
+     the Project Gutenberg Literary Archive Foundation."
+
+- You provide a full refund of any money paid by a user who notifies
+     you in writing (or by e-mail) within 30 days of receipt that s/he
+     does not agree to the terms of the full Project Gutenberg-tm
+     License.  You must require such a user to return or
+     destroy all copies of the works possessed in a physical medium
+     and discontinue all use of and all access to other copies of
+     Project Gutenberg-tm works.
+
+- You provide, in accordance with paragraph 1.F.3, a full refund of any
+     money paid for a work or a replacement copy, if a defect in the
+     electronic work is discovered and reported to you within 90 days
+     of receipt of the work.
+
+- You comply with all other terms of this agreement for free
+     distribution of Project Gutenberg-tm works.
+
+1.E.9.  If you wish to charge a fee or distribute a Project Gutenberg-tm
+electronic work or group of works on different terms than are set
+forth in this agreement, you must obtain permission in writing from
+both the Project Gutenberg Literary Archive Foundation and Michael
+Hart, the owner of the Project Gutenberg-tm trademark.  Contact the
+Foundation as set forth in Section 3 below.
+
+1.F.
+
+1.F.1.  Project Gutenberg volunteers and employees expend considerable
+effort to identify, do copyright research on, transcribe and proofread
+public domain works in creating the Project Gutenberg-tm
+collection.  Despite these efforts, Project Gutenberg-tm electronic
+works, and the medium on which they may be stored, may contain
+"Defects," such as, but not limited to, incomplete, inaccurate or
+corrupt data, transcription errors, a copyright or other intellectual
+property infringement, a defective or damaged disk or other medium, a
+computer virus, or computer codes that damage or cannot be read by
+your equipment.
+
+1.F.2.  LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
+of Replacement or Refund" described in paragraph 1.F.3, the Project
+Gutenberg Literary Archive Foundation, the owner of the Project
+Gutenberg-tm trademark, and any other party distributing a Project
+Gutenberg-tm electronic work under this agreement, disclaim all
+liability to you for damages, costs and expenses, including legal
+fees.  YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
+LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
+PROVIDED IN PARAGRAPH 1.F.3.  YOU AGREE THAT THE FOUNDATION, THE
+TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
+LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
+INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
+DAMAGE.
+
+1.F.3.  LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
+defect in this electronic work within 90 days of receiving it, you can
+receive a refund of the money (if any) you paid for it by sending a
+written explanation to the person you received the work from.  If you
+received the work on a physical medium, you must return the medium with
+your written explanation.  The person or entity that provided you with
+the defective work may elect to provide a replacement copy in lieu of a
+refund.  If you received the work electronically, the person or entity
+providing it to you may choose to give you a second opportunity to
+receive the work electronically in lieu of a refund.  If the second copy
+is also defective, you may demand a refund in writing without further
+opportunities to fix the problem.
+
+1.F.4.  Except for the limited right of replacement or refund set forth
+in paragraph 1.F.3, this work is provided to you 'AS-IS', WITH NO OTHER
+WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE.
+
+1.F.5.  Some states do not allow disclaimers of certain implied
+warranties or the exclusion or limitation of certain types of damages.
+If any disclaimer or limitation set forth in this agreement violates the
+law of the state applicable to this agreement, the agreement shall be
+interpreted to make the maximum disclaimer or limitation permitted by
+the applicable state law.  The invalidity or unenforceability of any
+provision of this agreement shall not void the remaining provisions.
+
+1.F.6.  INDEMNITY - You agree to indemnify and hold the Foundation, the
+trademark owner, any agent or employee of the Foundation, anyone
+providing copies of Project Gutenberg-tm electronic works in accordance
+with this agreement, and any volunteers associated with the production,
+promotion and distribution of Project Gutenberg-tm electronic works,
+harmless from all liability, costs and expenses, including legal fees,
+that arise directly or indirectly from any of the following which you do
+or cause to occur: (a) distribution of this or any Project Gutenberg-tm
+work, (b) alteration, modification, or additions or deletions to any
+Project Gutenberg-tm work, and (c) any Defect you cause.
+
+
+Section  2.  Information about the Mission of Project Gutenberg-tm
+
+Project Gutenberg-tm is synonymous with the free distribution of
+electronic works in formats readable by the widest variety of computers
+including obsolete, old, middle-aged and new computers.  It exists
+because of the efforts of hundreds of volunteers and donations from
+people in all walks of life.
+
+Volunteers and financial support to provide volunteers with the
+assistance they need are critical to reaching Project Gutenberg-tm's
+goals and ensuring that the Project Gutenberg-tm collection will
+remain freely available for generations to come.  In 2001, the Project
+Gutenberg Literary Archive Foundation was created to provide a secure
+and permanent future for Project Gutenberg-tm and future generations.
+To learn more about the Project Gutenberg Literary Archive Foundation
+and how your efforts and donations can help, see Sections 3 and 4
+and the Foundation information page at www.gutenberg.org
+
+
+Section 3.  Information about the Project Gutenberg Literary Archive
+Foundation
+
+The Project Gutenberg Literary Archive Foundation is a non profit
+501(c)(3) educational corporation organized under the laws of the
+state of Mississippi and granted tax exempt status by the Internal
+Revenue Service.  The Foundation's EIN or federal tax identification
+number is 64-6221541.  Contributions to the Project Gutenberg
+Literary Archive Foundation are tax deductible to the full extent
+permitted by U.S. federal laws and your state's laws.
+
+The Foundation's principal office is located at 4557 Melan Dr. S.
+Fairbanks, AK, 99712., but its volunteers and employees are scattered
+throughout numerous locations.  Its business office is located at 809
+North 1500 West, Salt Lake City, UT 84116, (801) 596-1887.  Email
+contact links and up to date contact information can be found at the
+Foundation's web site and official page at www.gutenberg.org/contact
+
+For additional contact information:
+     Dr. Gregory B. Newby
+     Chief Executive and Director
+     gbnewby@pglaf.org
+
+Section 4.  Information about Donations to the Project Gutenberg
+Literary Archive Foundation
+
+Project Gutenberg-tm depends upon and cannot survive without wide
+spread public support and donations to carry out its mission of
+increasing the number of public domain and licensed works that can be
+freely distributed in machine readable form accessible by the widest
+array of equipment including outdated equipment.  Many small donations
+($1 to $5,000) are particularly important to maintaining tax exempt
+status with the IRS.
+
+The Foundation is committed to complying with the laws regulating
+charities and charitable donations in all 50 states of the United
+States.  Compliance requirements are not uniform and it takes a
+considerable effort, much paperwork and many fees to meet and keep up
+with these requirements.  We do not solicit donations in locations
+where we have not received written confirmation of compliance.  To
+SEND DONATIONS or determine the status of compliance for any
+particular state visit www.gutenberg.org/donate
+
+While we cannot and do not solicit contributions from states where we
+have not met the solicitation requirements, we know of no prohibition
+against accepting unsolicited donations from donors in such states who
+approach us with offers to donate.
+
+International donations are gratefully accepted, but we cannot make
+any statements concerning tax treatment of donations received from
+outside the United States.  U.S. laws alone swamp our small staff.
+
+Please check the Project Gutenberg Web pages for current donation
+methods and addresses.  Donations are accepted in a number of other
+ways including checks, online payments and credit card donations.
+To donate, please visit:  www.gutenberg.org/donate
+
+
+Section 5.  General Information About Project Gutenberg-tm electronic
+works.
+
+Professor Michael S. Hart was the originator of the Project Gutenberg-tm
+concept of a library of electronic works that could be freely shared
+with anyone.  For forty years, he produced and distributed Project
+Gutenberg-tm eBooks with only a loose network of volunteer support.
+
+Project Gutenberg-tm eBooks are often created from several printed
+editions, all of which are confirmed as Public Domain in the U.S.
+unless a copyright notice is included.  Thus, we do not necessarily
+keep eBooks in compliance with any particular paper edition.
+
+Most people start at our Web site which has the main PG search facility:
+
+     www.gutenberg.org
+
+This Web site includes information about Project Gutenberg-tm,
+including how to make donations to the Project Gutenberg Literary
+Archive Foundation, how to help produce our new eBooks, and how to
+subscribe to our email newsletter to hear about new eBooks.
+
+
+
+</pre>
+
+  </body>
+</html>
diff --git a/8144-h/images/081.png b/8144-h/images/081.png
new file mode 100644
index 0000000..d3a5ba4
--- /dev/null
+++ b/8144-h/images/081.png
diff --git a/8144-h/images/081th.png b/8144-h/images/081th.png
new file mode 100644
index 0000000..6e892b5
--- /dev/null
+++ b/8144-h/images/081th.png
diff --git a/8144-h/images/084.png b/8144-h/images/084.png
new file mode 100644
index 0000000..ec5f2a6
--- /dev/null
+++ b/8144-h/images/084.png
diff --git a/8144-h/images/084th.png b/8144-h/images/084th.png
new file mode 100644
index 0000000..624087d
--- /dev/null
+++ b/8144-h/images/084th.png
diff --git a/8144-h/images/086.png b/8144-h/images/086.png
new file mode 100644
index 0000000..770e2ff
--- /dev/null
+++ b/8144-h/images/086.png
diff --git a/8144-h/images/086th.png b/8144-h/images/086th.png
new file mode 100644
index 0000000..908479a
--- /dev/null
+++ b/8144-h/images/086th.png
diff --git a/8144-h/images/088.png b/8144-h/images/088.png
new file mode 100644
index 0000000..0e43851
--- /dev/null
+++ b/8144-h/images/088.png
diff --git a/8144-h/images/088th.png b/8144-h/images/088th.png
new file mode 100644
index 0000000..810b089
--- /dev/null
+++ b/8144-h/images/088th.png
diff --git a/8144-h/images/089.png b/8144-h/images/089.png
new file mode 100644
index 0000000..f3ae6e2
--- /dev/null
+++ b/8144-h/images/089.png
diff --git a/8144-h/images/089th.png b/8144-h/images/089th.png
new file mode 100644
index 0000000..dfc74b9
--- /dev/null
+++ b/8144-h/images/089th.png
diff --git a/8144-h/images/092.png b/8144-h/images/092.png
new file mode 100644
index 0000000..2c6fb94
--- /dev/null
+++ b/8144-h/images/092.png
diff --git a/8144-h/images/092th.png b/8144-h/images/092th.png
new file mode 100644
index 0000000..4cb0a60
--- /dev/null
+++ b/8144-h/images/092th.png
diff --git a/8144-h/images/111.png b/8144-h/images/111.png
new file mode 100644
index 0000000..e21906b
--- /dev/null
+++ b/8144-h/images/111.png
diff --git a/8144-h/images/111th.png b/8144-h/images/111th.png
new file mode 100644
index 0000000..0b79ac5
--- /dev/null
+++ b/8144-h/images/111th.png
diff --git a/8144-h/images/239.png b/8144-h/images/239.png
new file mode 100644
index 0000000..64f6b31
--- /dev/null
+++ b/8144-h/images/239.png
diff --git a/8144-h/images/239th.png b/8144-h/images/239th.png
new file mode 100644
index 0000000..dbdd7a5
--- /dev/null
+++ b/8144-h/images/239th.png
diff --git a/8144-h/images/241.png b/8144-h/images/241.png
new file mode 100644
index 0000000..2d83a91
--- /dev/null
+++ b/8144-h/images/241.png
diff --git a/8144-h/images/241a.png b/8144-h/images/241a.png
new file mode 100644
index 0000000..a6e228a
--- /dev/null
+++ b/8144-h/images/241a.png
diff --git a/8144-h/images/241ath.png b/8144-h/images/241ath.png
new file mode 100644
index 0000000..b444027
--- /dev/null
+++ b/8144-h/images/241ath.png
diff --git a/8144-h/images/241th.png b/8144-h/images/241th.png
new file mode 100644
index 0000000..73a0254
--- /dev/null
+++ b/8144-h/images/241th.png
diff --git a/8144-h/images/242.png b/8144-h/images/242.png
new file mode 100644
index 0000000..ee31a10
--- /dev/null
+++ b/8144-h/images/242.png
diff --git a/8144-h/images/242a.png b/8144-h/images/242a.png
new file mode 100644
index 0000000..06d5d43
--- /dev/null
+++ b/8144-h/images/242a.png
diff --git a/8144-h/images/242ath.png b/8144-h/images/242ath.png
new file mode 100644
index 0000000..68959f1
--- /dev/null
+++ b/8144-h/images/242ath.png
diff --git a/8144-h/images/242th.png b/8144-h/images/242th.png
new file mode 100644
index 0000000..90d9231
--- /dev/null
+++ b/8144-h/images/242th.png
diff --git a/8144-h/images/243a.png b/8144-h/images/243a.png
new file mode 100644
index 0000000..6830e7e
--- /dev/null
+++ b/8144-h/images/243a.png
diff --git a/8144-h/images/243ath.png b/8144-h/images/243ath.png
new file mode 100644
index 0000000..74d75d5
--- /dev/null
+++ b/8144-h/images/243ath.png
diff --git a/8144-h/images/243b.png b/8144-h/images/243b.png
new file mode 100644
index 0000000..bac6640
--- /dev/null
+++ b/8144-h/images/243b.png
diff --git a/8144-h/images/243bth.png b/8144-h/images/243bth.png
new file mode 100644
index 0000000..bf391f0
--- /dev/null
+++ b/8144-h/images/243bth.png
diff --git a/8144-h/images/243c.png b/8144-h/images/243c.png
new file mode 100644
index 0000000..e0bf53a
--- /dev/null
+++ b/8144-h/images/243c.png
diff --git a/8144-h/images/243cth.png b/8144-h/images/243cth.png
new file mode 100644
index 0000000..37a405e
--- /dev/null
+++ b/8144-h/images/243cth.png
diff --git a/8144-h/images/243d.png b/8144-h/images/243d.png
new file mode 100644
index 0000000..9321352
--- /dev/null
+++ b/8144-h/images/243d.png
diff --git a/8144-h/images/243dth.png b/8144-h/images/243dth.png
new file mode 100644
index 0000000..6f4b5dc
--- /dev/null
+++ b/8144-h/images/243dth.png
diff --git a/8144-h/images/244a.png b/8144-h/images/244a.png
new file mode 100644
index 0000000..1955780
--- /dev/null
+++ b/8144-h/images/244a.png
diff --git a/8144-h/images/244ath.png b/8144-h/images/244ath.png
new file mode 100644
index 0000000..48f6a84
--- /dev/null
+++ b/8144-h/images/244ath.png
diff --git a/8144-h/images/244b.png b/8144-h/images/244b.png
new file mode 100644
index 0000000..4502289
--- /dev/null
+++ b/8144-h/images/244b.png
diff --git a/8144-h/images/244bth.png b/8144-h/images/244bth.png
new file mode 100644
index 0000000..bf16b2b
--- /dev/null
+++ b/8144-h/images/244bth.png
diff --git a/8144-h/images/259.png b/8144-h/images/259.png
new file mode 100644
index 0000000..748e328
--- /dev/null
+++ b/8144-h/images/259.png
diff --git a/8144-h/images/259th.png b/8144-h/images/259th.png
new file mode 100644
index 0000000..2ee3c24
--- /dev/null
+++ b/8144-h/images/259th.png
diff --git a/8144-h/images/260.png b/8144-h/images/260.png
new file mode 100644
index 0000000..ecf3ad4
--- /dev/null
+++ b/8144-h/images/260.png
diff --git a/8144-h/images/260th.png b/8144-h/images/260th.png
new file mode 100644
index 0000000..6203dc7
--- /dev/null
+++ b/8144-h/images/260th.png
diff --git a/8144-h/images/304.png b/8144-h/images/304.png
new file mode 100644
index 0000000..110ac75
--- /dev/null
+++ b/8144-h/images/304.png
diff --git a/8144-h/images/304th.png b/8144-h/images/304th.png
new file mode 100644
index 0000000..8de236c
--- /dev/null
+++ b/8144-h/images/304th.png
diff --git a/8144-h/images/313.png b/8144-h/images/313.png
new file mode 100644
index 0000000..5a1b8b5
--- /dev/null
+++ b/8144-h/images/313.png
diff --git a/8144-h/images/313th.png b/8144-h/images/313th.png
new file mode 100644
index 0000000..0019934
--- /dev/null
+++ b/8144-h/images/313th.png
diff --git a/8144-h/images/318.png b/8144-h/images/318.png
new file mode 100644
index 0000000..948ef31
--- /dev/null
+++ b/8144-h/images/318.png
diff --git a/8144-h/images/318th.png b/8144-h/images/318th.png
new file mode 100644
index 0000000..30cb285
--- /dev/null
+++ b/8144-h/images/318th.png
diff --git a/8144-h/images/328.png b/8144-h/images/328.png
new file mode 100644
index 0000000..3e1c5f6
--- /dev/null
+++ b/8144-h/images/328.png
diff --git a/8144-h/images/328th.png b/8144-h/images/328th.png
new file mode 100644
index 0000000..75af87d
--- /dev/null
+++ b/8144-h/images/328th.png
diff --git a/8144-h/images/330.png b/8144-h/images/330.png
new file mode 100644
index 0000000..dcfad67
--- /dev/null
+++ b/8144-h/images/330.png
diff --git a/8144-h/images/330th.png b/8144-h/images/330th.png
new file mode 100644
index 0000000..d328376
--- /dev/null
+++ b/8144-h/images/330th.png
diff --git a/8144-h/images/332.png b/8144-h/images/332.png
new file mode 100644
index 0000000..422b639
--- /dev/null
+++ b/8144-h/images/332.png
diff --git a/8144-h/images/332th.png b/8144-h/images/332th.png
new file mode 100644
index 0000000..26b084e
--- /dev/null
+++ b/8144-h/images/332th.png
diff --git a/8144-h/images/334.png b/8144-h/images/334.png
new file mode 100644
index 0000000..2cd997b
--- /dev/null
+++ b/8144-h/images/334.png
diff --git a/8144-h/images/334th.png b/8144-h/images/334th.png
new file mode 100644
index 0000000..99582a3
--- /dev/null
+++ b/8144-h/images/334th.png
diff --git a/8144-h/images/335.png b/8144-h/images/335.png
new file mode 100644
index 0000000..0f40ac6
--- /dev/null
+++ b/8144-h/images/335.png
diff --git a/8144-h/images/335th.png b/8144-h/images/335th.png
new file mode 100644
index 0000000..aa16b52
--- /dev/null
+++ b/8144-h/images/335th.png
diff --git a/8144-h/images/337.png b/8144-h/images/337.png
new file mode 100644
index 0000000..e7f28e2
--- /dev/null
+++ b/8144-h/images/337.png
diff --git a/8144-h/images/337th.png b/8144-h/images/337th.png
new file mode 100644
index 0000000..9832c07
--- /dev/null
+++ b/8144-h/images/337th.png
diff --git a/8144-h/images/338.png b/8144-h/images/338.png
new file mode 100644
index 0000000..937c873
--- /dev/null
+++ b/8144-h/images/338.png
diff --git a/8144-h/images/338th.png b/8144-h/images/338th.png
new file mode 100644
index 0000000..dcb71ac
--- /dev/null
+++ b/8144-h/images/338th.png
diff --git a/8144-h/images/339.png b/8144-h/images/339.png
new file mode 100644
index 0000000..00c041b
--- /dev/null
+++ b/8144-h/images/339.png
diff --git a/8144-h/images/339th.png b/8144-h/images/339th.png
new file mode 100644
index 0000000..088de2c
--- /dev/null
+++ b/8144-h/images/339th.png
diff --git a/8144-h/images/340.png b/8144-h/images/340.png
new file mode 100644
index 0000000..c026128
--- /dev/null
+++ b/8144-h/images/340.png
diff --git a/8144-h/images/340th.png b/8144-h/images/340th.png
new file mode 100644
index 0000000..c2ba986
--- /dev/null
+++ b/8144-h/images/340th.png
diff --git a/8144-h/images/341.png b/8144-h/images/341.png
new file mode 100644
index 0000000..6555e87
--- /dev/null
+++ b/8144-h/images/341.png
diff --git a/8144-h/images/341th.png b/8144-h/images/341th.png
new file mode 100644
index 0000000..7e34f44
--- /dev/null
+++ b/8144-h/images/341th.png
diff --git a/8144-h/images/342.png b/8144-h/images/342.png
new file mode 100644
index 0000000..6f940ca
--- /dev/null
+++ b/8144-h/images/342.png
diff --git a/8144-h/images/342th.png b/8144-h/images/342th.png
new file mode 100644
index 0000000..2eba560
--- /dev/null
+++ b/8144-h/images/342th.png
diff --git a/8144-h/images/344.png b/8144-h/images/344.png
new file mode 100644
index 0000000..c73b060
--- /dev/null
+++ b/8144-h/images/344.png
diff --git a/8144-h/images/344th.png b/8144-h/images/344th.png
new file mode 100644
index 0000000..799e628
--- /dev/null
+++ b/8144-h/images/344th.png
diff --git a/8144-h/images/345a.png b/8144-h/images/345a.png
new file mode 100644
index 0000000..ac555a8
--- /dev/null
+++ b/8144-h/images/345a.png
diff --git a/8144-h/images/345ath.png b/8144-h/images/345ath.png
new file mode 100644
index 0000000..6976554
--- /dev/null
+++ b/8144-h/images/345ath.png
diff --git a/8144-h/images/347.png b/8144-h/images/347.png
new file mode 100644
index 0000000..08cc403
--- /dev/null
+++ b/8144-h/images/347.png
diff --git a/8144-h/images/347th.png b/8144-h/images/347th.png
new file mode 100644
index 0000000..3ec473e
--- /dev/null
+++ b/8144-h/images/347th.png
diff --git a/8144-h/images/348.png b/8144-h/images/348.png
new file mode 100644
index 0000000..0d2f039
--- /dev/null
+++ b/8144-h/images/348.png
diff --git a/8144-h/images/348th.png b/8144-h/images/348th.png
new file mode 100644
index 0000000..c3d3a75
--- /dev/null
+++ b/8144-h/images/348th.png
diff --git a/8144-h/images/350.png b/8144-h/images/350.png
new file mode 100644
index 0000000..923579f
--- /dev/null
+++ b/8144-h/images/350.png
diff --git a/8144-h/images/350th.png b/8144-h/images/350th.png
new file mode 100644
index 0000000..670b9d0
--- /dev/null
+++ b/8144-h/images/350th.png
diff --git a/8144-h/images/352.png b/8144-h/images/352.png
new file mode 100644
index 0000000..a368540
--- /dev/null
+++ b/8144-h/images/352.png
diff --git a/8144-h/images/352th.png b/8144-h/images/352th.png
new file mode 100644
index 0000000..1b636ae
--- /dev/null
+++ b/8144-h/images/352th.png
diff --git a/8144-h/images/354.png b/8144-h/images/354.png
new file mode 100644
index 0000000..ccd5fcf
--- /dev/null
+++ b/8144-h/images/354.png
diff --git a/8144-h/images/354th.png b/8144-h/images/354th.png
new file mode 100644
index 0000000..027d5f6
--- /dev/null
+++ b/8144-h/images/354th.png
diff --git a/8144-h/images/355.png b/8144-h/images/355.png
new file mode 100644
index 0000000..61fab94
--- /dev/null
+++ b/8144-h/images/355.png
diff --git a/8144-h/images/355th.png b/8144-h/images/355th.png
new file mode 100644
index 0000000..e5cea50
--- /dev/null
+++ b/8144-h/images/355th.png
diff --git a/8144-h/images/356.png b/8144-h/images/356.png
new file mode 100644
index 0000000..71e4bf6
--- /dev/null
+++ b/8144-h/images/356.png
diff --git a/8144-h/images/356th.png b/8144-h/images/356th.png
new file mode 100644
index 0000000..239e15e
--- /dev/null
+++ b/8144-h/images/356th.png
diff --git a/8144-h/images/357.png b/8144-h/images/357.png
new file mode 100644
index 0000000..2af9f4b
--- /dev/null
+++ b/8144-h/images/357.png
diff --git a/8144-h/images/357th.png b/8144-h/images/357th.png
new file mode 100644
index 0000000..69e5d82
--- /dev/null
+++ b/8144-h/images/357th.png
diff --git a/8144-h/images/358.png b/8144-h/images/358.png
new file mode 100644
index 0000000..6d5195f
--- /dev/null
+++ b/8144-h/images/358.png
diff --git a/8144-h/images/358th.png b/8144-h/images/358th.png
new file mode 100644
index 0000000..e3284f3
--- /dev/null
+++ b/8144-h/images/358th.png
diff --git a/8144-h/images/360.png b/8144-h/images/360.png
new file mode 100644
index 0000000..cf9f1e3
--- /dev/null
+++ b/8144-h/images/360.png
diff --git a/8144-h/images/360th.png b/8144-h/images/360th.png
new file mode 100644
index 0000000..dd33f45
--- /dev/null
+++ b/8144-h/images/360th.png
diff --git a/8144-h/images/362.png b/8144-h/images/362.png
new file mode 100644
index 0000000..332d8a4
--- /dev/null
+++ b/8144-h/images/362.png
diff --git a/8144-h/images/362th.png b/8144-h/images/362th.png
new file mode 100644
index 0000000..7be6a13
--- /dev/null
+++ b/8144-h/images/362th.png
diff --git a/8144-h/images/363.png b/8144-h/images/363.png
new file mode 100644
index 0000000..69dd725
--- /dev/null
+++ b/8144-h/images/363.png
diff --git a/8144-h/images/363th.png b/8144-h/images/363th.png
new file mode 100644
index 0000000..131e692
--- /dev/null
+++ b/8144-h/images/363th.png
diff --git a/8144-h/images/365.png b/8144-h/images/365.png
new file mode 100644
index 0000000..239ad9b
--- /dev/null
+++ b/8144-h/images/365.png
diff --git a/8144-h/images/365th.png b/8144-h/images/365th.png
new file mode 100644
index 0000000..0b50646
--- /dev/null
+++ b/8144-h/images/365th.png
diff --git a/8144-h/images/366.png b/8144-h/images/366.png
new file mode 100644
index 0000000..04b78b5
--- /dev/null
+++ b/8144-h/images/366.png
diff --git a/8144-h/images/366th.png b/8144-h/images/366th.png
new file mode 100644
index 0000000..2a527af
--- /dev/null
+++ b/8144-h/images/366th.png
diff --git a/8144-h/images/367.png b/8144-h/images/367.png
new file mode 100644
index 0000000..66be08f
--- /dev/null
+++ b/8144-h/images/367.png
diff --git a/8144-h/images/367th.png b/8144-h/images/367th.png
new file mode 100644
index 0000000..0807603
--- /dev/null
+++ b/8144-h/images/367th.png
diff --git a/8144-h/images/369.png b/8144-h/images/369.png
new file mode 100644
index 0000000..6cd7163
--- /dev/null
+++ b/8144-h/images/369.png
diff --git a/8144-h/images/369th.png b/8144-h/images/369th.png
new file mode 100644
index 0000000..25d2d9c
--- /dev/null
+++ b/8144-h/images/369th.png
diff --git a/8144-h/images/370.png b/8144-h/images/370.png
new file mode 100644
index 0000000..19c5127
--- /dev/null
+++ b/8144-h/images/370.png
diff --git a/8144-h/images/370a.png b/8144-h/images/370a.png
new file mode 100644
index 0000000..73c7846
--- /dev/null
+++ b/8144-h/images/370a.png
diff --git a/8144-h/images/370ath.png b/8144-h/images/370ath.png
new file mode 100644
index 0000000..a912fe0
--- /dev/null
+++ b/8144-h/images/370ath.png
diff --git a/8144-h/images/370th.png b/8144-h/images/370th.png
new file mode 100644
index 0000000..935ec01
--- /dev/null
+++ b/8144-h/images/370th.png
diff --git a/8144-h/images/372.png b/8144-h/images/372.png
new file mode 100644
index 0000000..6434669
--- /dev/null
+++ b/8144-h/images/372.png
diff --git a/8144-h/images/372th.png b/8144-h/images/372th.png
new file mode 100644
index 0000000..cd79288
--- /dev/null
+++ b/8144-h/images/372th.png
diff --git a/8144-h/images/373.png b/8144-h/images/373.png
new file mode 100644
index 0000000..9d77a74
--- /dev/null
+++ b/8144-h/images/373.png
diff --git a/8144-h/images/373th.png b/8144-h/images/373th.png
new file mode 100644
index 0000000..5cd8a18
--- /dev/null
+++ b/8144-h/images/373th.png
diff --git a/8144-h/images/374.png b/8144-h/images/374.png
new file mode 100644
index 0000000..3a4a068
--- /dev/null
+++ b/8144-h/images/374.png
diff --git a/8144-h/images/374th.png b/8144-h/images/374th.png
new file mode 100644
index 0000000..688de52
--- /dev/null
+++ b/8144-h/images/374th.png
diff --git a/8144-h/images/375.png b/8144-h/images/375.png
new file mode 100644
index 0000000..3ce3920
--- /dev/null
+++ b/8144-h/images/375.png
diff --git a/8144-h/images/375th.png b/8144-h/images/375th.png
new file mode 100644
index 0000000..c7c6285
--- /dev/null
+++ b/8144-h/images/375th.png
diff --git a/8144-h/images/377.png b/8144-h/images/377.png
new file mode 100644
index 0000000..e9db4cb
--- /dev/null
+++ b/8144-h/images/377.png
diff --git a/8144-h/images/377th.png b/8144-h/images/377th.png
new file mode 100644
index 0000000..2984356
--- /dev/null
+++ b/8144-h/images/377th.png
diff --git a/8144-h/images/378.png b/8144-h/images/378.png
new file mode 100644
index 0000000..4893851
--- /dev/null
+++ b/8144-h/images/378.png
diff --git a/8144-h/images/378th.png b/8144-h/images/378th.png
new file mode 100644
index 0000000..18eeda5
--- /dev/null
+++ b/8144-h/images/378th.png
diff --git a/8144-h/images/380.png b/8144-h/images/380.png
new file mode 100644
index 0000000..da4ff99
--- /dev/null
+++ b/8144-h/images/380.png
diff --git a/8144-h/images/380th.png b/8144-h/images/380th.png
new file mode 100644
index 0000000..341e8aa
--- /dev/null
+++ b/8144-h/images/380th.png
diff --git a/8144-h/images/381.png b/8144-h/images/381.png
new file mode 100644
index 0000000..4cb99c9
--- /dev/null
+++ b/8144-h/images/381.png
diff --git a/8144-h/images/381th.png b/8144-h/images/381th.png
new file mode 100644
index 0000000..08b5623
--- /dev/null
+++ b/8144-h/images/381th.png
author	Roger Frank <rfrank@pglaf.org>	2025-10-15 05:31:01 -0700
committer	Roger Frank <rfrank@pglaf.org>	2025-10-15 05:31:01 -0700
commit	29ea61f647bf83c6f5b7b5e8e69aa9940e65a477 (patch)
tree	eaadfc4e66cf2820ae6edfe9f150c3abbab89ffa /8144-h