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diff --git a/8144.txt b/8144.txt new file mode 100644 index 0000000..ef81570 --- /dev/null +++ b/8144.txt @@ -0,0 +1,18150 @@ +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: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK ACETYLENE *** + + + + +Produced by Richard Prairie, Tonya Allen, Juliet Sutherland, +Charles Franks, and the Online Distributed Proofreading Team + + + + + + + + +ACETYLENE + +THE PRINCIPLES OF ITS GENERATION AND USE + +A PRACTICAL HANDBOOK ON THE PRODUCTION, PURIFICATION, AND SUBSEQUENT +TREATMENT OF ACETYLENE FOR THE DEVELOPMENT OF LIGHT, HEAT, AND POWER + +Second Edition + +REVISED AND ENLARGED + +BY + +F. H. LEEDS, F.I.C. + +FOR SOME YEARS TECHNICAL EDITOR OF THE JOURNAL "ACETYLENE" + +AND + +W. J. ATKINSON BUTTERFIELD, M.A. + +AUTHOR OF "THE CHEMISTRY OF GAS MANUFACTURE" + + + + + + + +PREFATORY NOTE TO THE FIRST EDITION + +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: + +(1) Accompanying the generation of acetylene from calcium carbide and +water. + +(2) Accompanying the combustion of the gas in luminous or incandescent +burners, and + +(3) Its employment for any purpose--(a) neat, (b) compressed into +cylinders, (c) diluted, and (d) as an enriching material. + +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. + +_June_ 1903 + +NOTE TO THE SECOND EDITION + +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. + +W. J. ATKINSON BUTTERFIELD + +WESTMINSTER + +_August 1909_ + +CONTENTS + +CHAPTER I + +INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING + +Intrinsic advantages +Hygienic advantages +Acetylene and paraffin oil +Blackened ceilings +Cost of acetylene lighting +Cost of acetylene and coal-gas +Cost of acetylene and electric lighting +Cost of acetylene and paraffin oil +Cost of acetylene and air-gas +Cost of acetylene and candles +Tabular statement of costs (_to face_) +Illuminating power and effect + + +CHAPTER II + +THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER + +Nature of calcium carbide +Storage of calcium carbide +Fire risks of acetylene lighting +Purchase of carbide +Quality and sizes of carbide +Treated and scented carbide +Reaction between carbide and water + chemical nature + heat evolved + difference between heat and temperature + amount of heat evolved + effect of heat on process of generation +Reaction: + effects of heat + effect of heat on the chemical reaction + effects of heat on the acetylene + effects of heat on the carbide +Colour of spent carbide +Maximum attainable temperatures +Soft solder in generators +Reactions at low temperatures +Reactions at high temperatures +Pressure in generators + +CHAPTER III + +THE GENERAL PRINCIPLES OF ACETYLENE GENERATION ACETYLENE GENERATING +APPARATUS + +Automatic and non-automatic generators +Control of the chemical reaction +Non-automatic carbide-to-water generators +Non-automatic water-to-carbide generators +Automatic devices +Displacement gasholders +Action of water-to-carbide generators +Action of carbide-to-water generators +Use of oil in generator +Rising gasholder +Deterioration of acetylene on storage +Freezing and its avoidance +Corrosion in apparatus +Isolation of holder from generator +Water-seals +Vent pipes and safety valve +Frothing in generator +Dry process of generation +Artificial lighting of generator sheds + +CHAPTER IV + +THE SELECTION OF AN ACETYLENE GENERATOR + +Points to be observed +Recommendations of Home Office Committee +British and Foreign regulations for the construction and installation of + acetylene generating plant + +CHAPTER V + +THE TREATMENT OF ACETYLENE AFTER GENERATION + +Impurities in calcium carbide +Impurities of acetylene +Removal of moisture +Generator impurities in acetylene +Filters +Carbide impurities in acetylene +Washers +Reasons for purification +Necessary extent of purification +Quantity of impurities in acetylene +Purifying materials +Bleaching powder +Heratol, frankoline, acagine, and puratylene +Efficiency of purifying material +Minor reagent +Method of a gas purifier +Methods of determining exhaustion of purifying material +Regulations for purification +Drying +Position of purifier +Filtration +General arrangement of plans +Generator residues +Disposal of residue + +CHAPTER VI + +THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE + +Physical properties +Leakage +Heat of combustion +Explosive limits +Range of explosibility +Solubility in liquids +Toxicity +Endothermic nature +Polymerisation +Heats of formation and combustion +Colour of flame +Radiant efficiency +Chemical properties +Reactions with copper + +CHAPTER VII + +MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS + +Meters +Governors +Gasholder pressure +Pressure-gauges +Dimensions of mains and pipes +Velocity of flow in pipes +Service-pipes and mains +Leakage +Pipes and fittings +Laying mains +Expelling air from pipes +Tables of pipes and mains + +CHAPTER VIII + +COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION + +Nature of luminous flames +Illuminating power +Early burners +Injector and twin-flame burners +Illuminating power of self-luminous burners +Glassware for burners + +CHAPTER IX + +INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING + +Merits of incandescent lighting +Conditions for incandescent lighting +Illuminating power of incandescent burners +Durability of mantles +Typical incandescent burners +Acetylene for heating and cooking +Acetylene motors +Blowpipes +Autogenous soldering and welding + +CHAPTER X + +CARBURETTED ACETYLENE + +Carburetted acetylene +Illuminating power of carburetted acetylene +Carburetted acetylene for "power" + + +CHAPTER XI + +COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES + +Compression +Dissolved acetylene +Solution in acetone +Liquefied acetylene +Dilution with carbon dioxide +Dilution with air +Mixed carbides +Dilution with, methane and hydrogen +Self-inflammable acetylene +Enrichment with acetylene +Partial pressure +Acetylene-oil-gas + +CHAPTER XII + +SUNDRY USES + +Destruction of noxious moths +Destruction of phylloxera and mildew +Manufacture of lampblack +Production of tetrachlorethane +Utilisation of residues +Sundry uses for the gas + +CHAPTER XIII + +PORTABLE ACETYLENE LAMPS AND PLANT + +Table and vehicular lamps +Flare lamps +Cartridges of carbide +Cycle-lamp burners +Railway lighting + +CHAPTER XIV + +VALUATION AND ANALYSIS OF CARBIDE + +Regulations of British Acetylene Association +Regulations oL German Acetylene Association +Regulations of Austrian Acetylene Association +Sampling carbide +Yield of gas from small carbide +Correction of volumes for temperature and pressure +Estimation of impurities +Tabular numbers + +APPENDIX + +DESCRIPTIONS OP GENERATORS + +America: Canada +America: United States +Austria-Hungary +Belgium +France +Germany +Great Britain and Ireland + +INDEX + +INDEX TO APPENDIX + + + +ACETYLENE + + + +CHAPTER I + +INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING + +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. + +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. + +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. + +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. + +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. + +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. + +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. + +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, _e.g._, +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. + +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. + +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 anaemia +occasionally follow the constant inspiration of air rendered foul by +human exhalations. + +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. + +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. + +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. + +The efficiency (_i.e._, 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.e._, 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, _e.g._, 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. + +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. + +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-- +_e.g._, 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. + +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.e._, 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. + +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, &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. + +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. + +COST PER HOUR AND HYGIENIC EFFECT OF LIGHTING BY DIFFERENT MEANS + +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. + +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. + + ______________________________________________________________________ +| | | | | | | +| | |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 | +|____________|____________________|________|_________|_________|_______| + + ___________________________________________________________________ +| | | | | +| | | | | +| | | | 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 | +|____________|____________________|____________________|____________| + + _______________________________________________________________________ +| | | | | | | +| | |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 | +|____________|____________________|______|_________|__________|_________| + +[Footnote 1: Interest and depreciation charges on generating and +purifying plant = 0.15 penny. Purifying material and burner renewals = +0.05 penny.] + +[Footnote 2: Mantle renewals as for coal-gas.] + +[Footnote 3: Renewals of wicks and chimneys = 0.02 penny.] + +[Footnote 4: Renewals and mantles (and chimneys) at contract rate of 3s. +per burner per annum.] + +[Footnote 5: Renewals of lamps and fuses, at price indicated per lamp per +annum.] + +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.e._, 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.e._, 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, &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, +&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. + +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. + + + +CHAPTER II + +THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER + +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. + +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, &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. + +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. + +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. + +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: + +RULES FOR THE STORAGE OF CALCIUM CARBIDE. + +(_a_) 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. + +(_b_) 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. + +(_c_) 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. + +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." + +The following is a summary of the AUSTRIAN GOVERNMENT rules relating to +the storage and handling of carbide: + +(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. + +(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. + +(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. + +(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. + +(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. + +(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. + +(7) The breaking of carbide must be done by men provided with respirators +and goggles, and care taken to avoid the formation of dust. + +(8) Local or other authorities will issue from time to time special +regulations in regard to carbide trade premises. + +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. + +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. + +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. + +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. + +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-- + +(1) CaC_2 + H_2O = C_2H_2 + CaO. + +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: (_a_) that the substance referred to is a compound +of calcium and carbon only, and that it is therefore a carbide of +calcium; (_b_) that it is composed of one chemical part or atom of +calcium and two atoms of carbon; and (_c_) that it contains 40 parts +by weight of calcium combined with twice twelve, or 24, parts of carbon. +It follows from (_c_) 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. + +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-- + +CaO + H_2O = Ca(OH)_2. + +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-- + +(2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2. + +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.e._, 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 + +CaC_2 + 2H_2O = C_2H_2 + CaO.H_2O. + +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. + +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 deg. 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 (_a_) 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 +(_b_) 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. + +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.e._, 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. + +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 deg. 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 deg. 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. + +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 deg. 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 deg. C. the same +quantity will heat 1 kilo. of steel, whose specific heat is roughly 0.11, +through (10/011) = 9 deg. C., or, which comes to the same thing, will heat 9 +kilos, of steel through 1 deg. C.; and similarly, 1 large calorie will raise +4 kilos. of calcium carbide 1 deg. C. in temperature, or 1 kilo. 4 deg. 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, _per contra_, 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. + +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 deg. 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.e._, 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. + +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. _infra_). 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: + +_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 + +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.e._, that of a +solution), the amount of heat set free will be greater by those 3 +calories, _i.e._, 32.1 large calories altogether. + +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 deg. C., say from 10 deg. C. (50 deg. F., which is +roughly the temperature of ordinary cold water) to 38 deg. C. It is +sufficient (2) to raise 64 grammes of water (a weight equal to that of +the carbide decomposed) through 438 deg. C., if that were possible. It would +raise (3) 311 grammes of water through 90 deg. C., _i.e._, from 10 deg. 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 deg. C. into steam at +100 deg. C.; or (5) to change 46.7 grammes of water at 10 deg. 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 deg. 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 deg. 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. + +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. + +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. + +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.e._, 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 deg. and 100 deg. C.; but in two tests out of ten +he obtained temperatures of about 160 deg. 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 deg. C. were fused completely; in two tests +other alloys melting at 216 deg. and 240 deg. C. showed signs of fusion; and in +one test an alloy melting at 280 deg. C. began to soften. Working with an +experimental apparatus constructed on the "dripping" principle-- +_i.e._, 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 deg. 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 deg., 734 deg., 754 deg., and 807 deg. 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 deg. +and Lewes' maximum of 807 deg. 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 deg. C. is important; because this figure is appreciably +above the point 780 deg. C., at which acetylene decomposes into its elements +in the absence of air. + +Nevertheless the production of a temperature somewhat exceeding 100 deg. 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, Fouche has proposed that 130 deg. 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 deg. 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. Fouche +adopts this figure on the ground that 130 deg. 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 deg. 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 deg. to 90 deg. C., the average maximum +temperature being about 80 deg. 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 deg. C.; whereas the corresponding Italian code contains a +similar stipulation, but quotes the maximum temperature as 100 deg. C. +(_vide_ Chapter IV.). + +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--(_a_) upon the +gas generated, (_b_) upon the carbide decomposed, and (_c_) +upon the general chemical reaction taking place. + +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)-- + +(2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2 + +rather than in accordance with equation (1)-- + +(1) CaC_2 + H_2O = C_2H_2 + CaO. + +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-- + +(3) CaC_2 + Ca_2(OH) = C_2H_2 + 2CaO. + +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 deg. +to 430 deg. 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: + +_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 + +[1 Footnote: Into its elements, Ca, O_2, and H_2; _cf._ footnote, +p: 31.] + +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: + + +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 + +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 deg. 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.e._, 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 deg. 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. + +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 deg. 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-- + +(4) 3C_2H_2 = C_6H_6. + +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 formulae 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: + +(5) 2C_2H_2 + 5O_2 = 4CO_2 + 2H_2O. + +(6) 2C_6H_6 + 15O_2 = 12CO_2 + 6H_2O. + +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.e._, 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 deg. 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. + +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 deg. C. By other changes, some +"saturated hydrocarbons," _i.e._, 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 deg. to 807 deg. 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: + + 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 + +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. + +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-- + +(7) C_2H_2 -> C_2 + H_2 + +whenever it has the opportunity; and the opportunity arrives if the +temperature of the gas risen to 780 deg. 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 deg. 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. + +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 deg. 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 deg. 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 deg. 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 (_cf._ 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 deg. 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, &c., exceeds 480 deg. 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. + +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. + +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. + +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 deg. C., +_i.e._, from 44.6 deg. 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 deg. 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 deg. C. [Footnote: Let x = the number of large +calories absorbed by the water; then 28 - x = those taken up by the gas. +Then-- + +1000x / 302 = 1000 (28 - x) / (26 X 0.25) + +whence x = 27.41; and 28 - x = 0.59. + +Therefore, for water, the rise in temperature is-- + +27.41 X 1000 / 302 = 90.8 deg. C.; + +and for acetylene the rise is-- + +0.59 X 1000 / 26 / 0.25 = 90.8 deg. C.] + +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 deg. 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 deg. in the first instance, or 54 deg. 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. + +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 deg. 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 deg. +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. + +In less critical situations in an acetylene plant, such as the partitions +of a carbide container, &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, _e.g._, 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. + +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.e._, 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. + +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 deg. 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 _n_ thermometric degrees, will raise the temperature +of the same weight of water vapour through rather more than 2 _n_ +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, _e.g._, at a rate much above that +required to supply one or two burners with gas. + +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. _ante_). +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. + +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 deg. 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 +(_a_) to lift the gasholder bell, or to raise the water in a +displacement holder, (_b_) to drive the gas through the various +subsidiary items in the plant, such as washers and purifiers, (_c_) +to overcome the friction in the service-pipes, [Footnote: This friction +manifestly causes a loss of pressure, _i.e._, 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, (_c_) may be virtually neglected. When the +holder has a rising bell, (_a_) 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, &c.--attached to the +main. The pressure (_b_) 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.e._, 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. + +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. + + + +CHAPTER III + +THE GENERAL PRINCIPLES OF ACETYLENE GENERATION--ACETYLENE GENERATING +APPARATUS + +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. + +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. + +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 deg. 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. + +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. + +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. + +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 _compact_ 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. + +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. + +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. + +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. + +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. + +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. _infra_), 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. + +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.e._, 100 deg. +C.--provided always the natural convection currents of the water are +properly made use of. + +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. + +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 _a_, being either driven +out through the shoot or otherwise. Since the point _b_ of the shoot +extends further into the generator than _a_, 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 _a_ 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. + +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. + +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.e._, 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. + +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 +_l_, 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 _X_ 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 _X_ 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 _X_, 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 _X_ +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 +_S_ 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 _S_ +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 _S_, 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 _l_, below the mouth of a pipe +_P_; but when low, as in A^3(b), the water is raised to the point +_l'_, which is above _P_. Water therefore flows into _P_, +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 +_l_, lest the mouth of _P_ should not be covered whenever the +bell falls. + +[Illustration: FIG. 1.--TYPICAL METHODS OF AUTOMATIC GENERATION +CONTROLLED BY BELL GASHOLDER.] + +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 _l_, 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 +_l"_, rising in F to the dotted line _l'_. 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 _l_, 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 +_l_, 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 +_l"_, and _l'_, 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. + +[Illustration: FIG. 2.--TYPICAL METHODS OF AUTOMATIC GENERATION +CONTROLLED BY INTERNAL GAS PRESSURE.] + +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 _l_. 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 _l'_ and _l"_. 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 _l'_ and _l"_; 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, &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. + +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 (_a_) 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 _c_, 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 _e_ opens at its base into the gas space +of the generator, so that the pressure below the diaphragm in _a_ is +the same as that elsewhere in the apparatus, while the pressure in +_a_ above the diaphragm is that of the atmosphere. Being flexible +and but slightly stretched, the diaphragm is normally depressed by the +weight of _c_ until it occupies the position _b_; but if the +pressure in the generator (_i.e._, in _e_) rises, it lifts the +diaphragm to somewhat about the position _b'_--the extent of +movement being, as usual, exaggerated in the sketch. The movement of the +diaphragm is accompanied by a movement of the rod _c_, 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 _g_ 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. + +[Illustration: FIG. 3.--TYPICAL METHODS OF AUTOMATIC GENERATION +CONTROLLED BY A FLEXIBLE DIAPHRAM OR BAG.] + +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.e._, 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. + +[Illustration: FIG. 4.--TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TO +CARBIDE).] + +[Illustration: FIG. 5.--TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TO +CARBIDE).] + +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.e._, +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. + +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 _d_ 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 _c_ +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 _d_ 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. + +[Illustration: FIG. 6.--TYPICAL METHODS OF DECOMPOSING CARBIDE (CARBIDE +TO WATER).] + +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.e._, 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, _e.g._, 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. + +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. + +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 +_l'_ and _l"_ 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 _l_, 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 _l"_ 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. + +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, &c., a little smaller in +diameter than the boll, floating on the water of a plain tank. + +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 (_cf._ 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, +_e.g._, 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. + +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. + +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 deg. C. or 21.2 deg. +F.; a 15 per cent. solution has a density of 1.111, and freezes at -10 deg. +C. or 14 deg. 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 deg. C. or 17.6 deg. F. + + _Freezing-Points of Dilute Alcohol._ + _________________________________________________________ +| | | | +| 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 | +|_______________|___________________|__________|__________| + + _Freezing-Points of Dilute Glycerin._ + _________________________________________________________ +| | | | +| 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 | +|_______________|___________________|__________|__________| + + _Freezing-Points of Calcium Chloride Solutions._ + _________________________________________________________ +| | | | +| 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 | +|_______________|___________________|__________|__________| + +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 deg. C. (-43.6 deg. F.), and is completely solid at +-56 deg. C. (-69) deg. F.). Diluted with one-third its volume of water, it +freezes between -20 deg. and -28 deg. C. (-4 deg. and-l8.4 deg. F.). The makers recommend +that it should be mixed with an equal volume of water. Another material +known as "Gefrierschutzfluessigkeit" and made by the Floersheim chemical +works, freezes at -35 deg. C. (-3 deg. F.). Diluted with one-quarter its volume +of water, it solidifies at -18 deg. C. (-0.4 deg. F.); with equal parts of water +it freezes at -12 deg. C. (10.4 deg. 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-Beaupre'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. + +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, &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, &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. + +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.e._, 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 + +NaC_2H_3O_2 + 3H_2O = NaC_2H_3O_2.3H_2O + +(anhydrous acetate) (crystals) + +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 deg. 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 deg. C. (43 deg. +F.) or in 2.4 parts at 37 deg. C. (99 deg. 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 deg. and 43 deg. 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, &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. + +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, &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. + +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.e._, 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. + +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. + +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, &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 _b_, one variety of water-seal is shown at D in Fig. 7 on page +103. The water being at the level _l_, gas enters at _a_ and +bubbles through it, escaping from the apparatus at _c_. It cannot +return from _c_ to _a_ without driving the water out of the +vessel till its level falls from _f_ to _g_; 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 _a_. 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 _a_ from the spot at which +it was originally level or was given a fall to the seal, as well as that +condensing in _c_ as far as the spot where _c_ dips again; and +it equally acts as a washer to the gas, especially if the orifice +_g_ 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 _d_ and _e_. _d_ is a tunnel tube extending +almost to the bottom of the vessel, and _e_ is a curved run-off pipe +of the form shown. The lower part of the upper curve in _e_ is above +the level _f_, being higher than _f_ 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 +_f_, when the surplus overflows of itself. The operation thus not +only adjusts the quantity of water present to the desired level so that +_a_ 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 _e_, or to some +other spot where a large-bore draw-off cock could be fitted for the +purpose of extracting any sludge of lime, &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. + +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. + +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 +_l_ to the levels _l'_ and _l"_, 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 _l"_, 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 _l"_ in the +closed half of the apparatus, its level in the interior of the vent-pipe +stands at _l'_, 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 _l"_ there is an +amount of water inside the pipe equal in height to the distance between +_l'_ and _l"_; 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 _l'_ and +_l"_, 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. + +[Illustration: FIG. 7.--TYPICAL FORMS OF VENT-PIPES OR SAFETY-VALVES.] + +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, _h_, which is closed at its +upper end. _h_ 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 _h_ 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 _g_ to +_f_ 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 _a_ depresses the water in +the pipe below the level _f_ to an extent equal to the pressure at +which it enters that pipe--an extent normally less than the distance +_f_ to _g_; and therefore gas never passes into the body of the +vessel, but travels away by the side tube _b_ (which in former +references to this drawing was supposed to be absent). If, however, the +pressure at _a_ exceeds that of the vertical height _f_ to +_g_, gas escapes at _g_ through the water, and is then free to +reach the atmosphere by means of the vent _c_. As before, _d_ +serves to charge the apparatus with water, and _e_ 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. + +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-Beaupre, 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. + +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.e._, 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: + +5CaC_2 + Na_2CO_3.10H_2O = 5C_2H_2 + 5Ca(OH)_2 + Na_2CO_3. + +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. + +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.e._, 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. + +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 +(_a_) the low igniting-point of acetylene; (_b_) the high +temperature of its flame; and (_c_) 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, &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. + + + +CHAPTER IV + +THE SELECTION OF AN ACETYLENE GENERATOR + +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. + +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 +(_vide_ 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.e._, 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. + +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. + +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. + +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, &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, &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. + +ADDENDUM. + +BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OF +ACETYLENE GENERATING PLANT + +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: + +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 deg. 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. + +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. + +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. + +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. + +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. + +6. The apparatus should give no tarry or other heavy condensation +products from the decomposition of the carbide. + +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. + +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. + +9. The use of glass gauges should be avoided as far as possible, and, +where absolutely necessary, they should be effectively protected against +breakage. + +10. The air space in a generator before charging should be as small as +possible. + +11. The use of copper should be avoided in such parts of the apparatus as +are liable to come in contact with acetylene. + +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: + +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. + +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. + +3. The limit of pressure in service-pipes, within the house, shall not +exceed 10 inches of water. + +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. + +5. Generators shall have sufficient storage capacity to make a serious +blow-off impossible. + +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. + +7. It shall not be possible under any conditions, even by wrong +manipulation of cocks, to seal the generating chamber hermetically. + +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. + +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. + +10. The use of glass gauges shall be avoided as far as possible, and +where absolutely necessary they shall be effectively protected against +breakage. + +11. The air space in the generator before charging shall be as small as +possible, _i.e._, 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.e._, more than 18 per cent, of air. This shall not apply to the +initial charges of the gasholder, when reasonable precautions are taken. + +12. The apparatus shall produce no tarry or other heavy condensation +products from the decomposition of the carbide. + +13. The temperature of the gas, immediately on leaving the charge, shall +not exceed 212 deg. F. (100 deg. C.) + +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. + +15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING +ALLOWED." + +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. + +17. The Association strongly advise the use of an efficient purifier with +generating plant for indoor lighting. + +18. No composition piping shall be used in any part of a permanent +installation. + +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. + +20. After the fittings (pendants, brackets, &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. + +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. + +_Recommendation_.--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. + +THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15, +1907, of its Rules and Regulations _re_ artificial lighting on +insured premises, includes the following stipulations applicable to +acetylene: + +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. + +An acetylene portable apparatus is allowed, provided it holds a charge of +not more than 2 lb. of carbide. + +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. + +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. + +Liquid acetylene must not be used or stored on the premises. + +The pipe, whether flexible or not, connecting an incandescent gas lamp to +the gas-supply must be of metal with metal connexions. + +(The reference in these Rules to the storage of carbide has been quoted +in Chapter II. (page 19).) + +These rules are liable to revision from time to time. + +The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following +code of rules for the construction, erection, and manipulation of +acetylene apparatus: + +I. _Rules for Construction._ + +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. + +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: + + 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 + +When not constructed of cast-iron, the bottoms, covers, and "manhole" +lids must be 0.5 mm. thicker in each respective size. + +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. + +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. + +3. Generators, purifiers, and holders must be welded, riveted or folded +at the seams; soft solder is only permissible as a tightening material. + +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. + +5. When cast-iron is employed, the rules of the German Gas and Water +Engineers are to be followed. + +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.] + +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.] + +The gasholder space of apparatus where carbide is not stored must be at +least 30 litres for every normal (10-litre) flame. + +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. + +8. Acetylene plant must be provided with purifying apparatus which +contains a proper purifying material in a suitable condition. + +9. The dimensions of subsidiary apparatus, such as washers, purifiers, +condensers, pipes, and cocks must correspond with the capacity of the +plant. + +10. Purifiers and washers must be constructed of materials capable of +resisting the attack of the substances in them. + +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. + +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. + +II. _Rules for Erection_ + +1. Acetylene apparatus must not be erected in or under rooms occupied or +frequented (passages, covered courts, &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. + +2. The doors of apparatus sheds must open outwards, and must not +communicate directly with rooms where fires and artificial lights are +used. + +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. + +4. Permanent apparatus erected in the open air must be at least 15 feet +from an occupied building. + +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. + +6. The contacts of any electrical warning devices must be outside the +apparatus shed. + +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. + +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. + +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. + +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. + +III. Rules for Working the Apparatus. + +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. + +2. All work required by the plant, or by any portion of it, and all +ordinary attendance needed must be performed by daylight. + +3. All water-seals must be carefully kept full. + +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. + +5. Alterations to any part of an apparatus which involve the operations +of soldering or riveting, &c., _i.e._, 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. + +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. + +7. It in forbidden to enter the house with a burning lantern or lamp, to +strike matches, or to smoke therein. + +8. A search for leaks in the pipes must not be made with the aid of a +light. + +9. Alterations to the service must not be made while the pipes are under +pressure, but only after the main cock has been shut. + +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. + +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. + +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. + +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. + +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. + +13. Carbide drums must not be opened with the aid of a flame or a red-hot +iron instrument. + +14. Acetylene apparatus must only be attended to by trustworthy and +responsible persons. + +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: + +1. The preparation and use of liquid acetylene is forbidden. + +2. Gaseous acetylene, alone, in admixture, or in solution, must not be +compressed above 2 atmospheres absolute except under special permission. + +3. The storage of mixtures of acetylene with air or other gases +containing or evolving free oxygen is forbidden. + +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. + +5. The firms and fitters undertaking the installation of acetylene plant +must be licensed. + +The special enactments fall under four headings, viz., (_a_) +apparatus; (_b_) plant houses; (_c_) pipes; (_d_) +residues. + +In regard to apparatus it is enacted that: + +1. The type of apparatus to be employed must be one which has been +approved by one of certain public authorities in the country. + +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. + +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. + +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. + +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. + +6. Generators exceeding 50 litres per hour productive capacity must be +arranged so that they can be freed from air before use. + +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. + +8. Automatic generators of which the decomposing chambers are built +inside the gasholder must not exceed 300 litres per hour productive +capacity. + +9. Generators must be arranged so that after-generation cannot produce +objectionable results. + +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. + +11. The maximum pressure permissible in any part of the apparatus is 1.1 +atmosphere absolute. + +12. The temperature in the gas space of a generator must never exceed 80 deg. +C. + +13. Generating apparatus, &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, &c., of brass, bronze, &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. + +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. + +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. + +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. + +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. + +18. Signal devices to show the position of the gasholder bell must not be +capable of producing sparks inside the apparatus house. + +19. Leaks must not be sought for with an open flame and repairs requiring +the use of a blow-pipe, &c., must only be carried out after the apparatus +has been taken to pieces or freed from gas by flooding. + +20. Apparatus must only be attended to by trustworthy and responsible +adults. + +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. + +In regard to (_b_), plant houses, it is enacted that: + +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. + +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. + +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. + +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. + +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. + +6. All acetylene installations must be known to the local fire brigade. + +In regard to (_c_), pipes, it is enacted that: + +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. + +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. + +In regard to (_d_), 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. + +The second section relates to acetylene installations, which are +classified in four groups, viz., (_a_) fixed or portable apparatus +supplying not more than thirty burners consuming 20 litres per hour; +(_b_) private installations supplying between 30 and 200 such +burners; (_c_) public or works installations supplying between 30 +and 200 such burners; (_d_) installations supplying more than 200 +such burners. + +The installations must comply with the following general conditions: + +1. No part of the generator when working at its utmost capacity should +attain a temperature of more than 100 deg. C. + +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. + +3. The apparatus must preclude the escape of lime into the gas and water +connexions. + +4. Glass parts must be adequately protected. + +5. Rubber connexions between the generator, gasholder, and main are +absolutely prohibited with installations supplying more than 30 burners. + +6. Cocks must be provided for cutting off the main and connexions from +the generator and gasholder. + +7. Each burner must have an independent tap. + +8. Generators of groups (_b_), (_c_), and (_d_) 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. + +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 (_b_) 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 +(_c_) 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 (_d_) must be at least 50 +feet from occupied premises and the gasholder and generator must not be +in the same building. + +The fourth section deals with the question of authorisation for the +installation of acetylene plant. Apparatus of group (_a_) 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. + +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. + +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 (_a_) is not subject to these periodical +inspections. + +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. + +The eighth section refers to the notification of the position and +description of all carbide works, stores, and acetylene installations to +the local authorities. + +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 deg. C., in that of a portable +apparatus 80 deg. C. The maximum effective pressure permissible is 0.15 +atmosphere. + +The CONSEIL D'HYGIENE 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. + +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." + +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.] + +The use of liquid acetylene or gas generated therefrom is absolutely +prohibited. + +Failure to observe these rules is as liable to endanger life as property. + +To secure the largest measure of safety to life and property, the +following rules for the installation of acetylene gas machines must be +observed. + +_Class A.--Stationary Automatic Apparatus._ + +1. FOUNDATIONS.--(_a_) 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. + +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. + +(_b_) Must be so arranged that the machine will be level and unequal +strain will not be placed on the generator or connexions. + +2. LOCATION.--(_a_) 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. + +(_b_) 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. + +(_c_) 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. + +(_d_) Generators must be placed where water will not freeze. + +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. + +The hood must be constructed in such a manner that it cannot be +obstructed by rain, snow, ice, insects or birds. + +4. CAPACITY.--(_a_) 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. + +(_b_) 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. + +(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. + +(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. + +(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. + +(_c_) 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. _An overworked generator adds to the cost of +producing acetylene gas_. + +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. + +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. + +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. + +7. PIPING.--(_a_) 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. + +(_b_) 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. + +(_c_) 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. + +(_d_) 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. + +The following schedule is advocated: + + 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. + +(_e_) 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. + +(_f_) 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. + +(_g_) Piping and connexions must be installed by persons experienced +in the installation of acetylene apparatus. + +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. + +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. + +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. + +Always observe a regular time, during daylight hours only, for attending +to and charging the apparatus. + +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. + +Whenever recharging with carbide always replenish the water-supply. + +Never deposit residuum or exhausted material from water-feed machines in +sewer-pipes or near inflammable material. + +Always keep water-tanks and water-seals filled with clean water. + +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. + +Never use a lighted match, lamp, candle, lantern or any open light near +the machine. + +Failure to observe the above cautions is as liable to endanger life as +property. + +9. OUTSIDE GENERATOR HOUSES.--(_a_) 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. + +(_b_) 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. + +(_c_) Generator houses must be thoroughly ventilated, and any +artificial heating necessary to prevent freezing shall be done by steam +or hot-water systems. + +(_d_) Generator houses must not be used for the storage of calcium +carbide except in accordance with the rules relating to that subject +(_vide_ Chapter II.). + +_Class B.--Stationary Non-Automatic Apparatus_. + +10. FOUNDATIONS.--(_a_) Must be of brick, stone or concrete. + +(_b_) Must be so arranged that the machine will be level and so that +strain will not be brought upon the connexions. + +11. GAS-HOUSES.--(_a_) Must be constructed entirely of non- +combustible material and must not be lighted by any system of +illumination involving open flames. + +(_b_) 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. + +(_c_) Must be kept closed and locked excepting during daylight +hours. + +(_d_) 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. + +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. + +The hood must be constructed in such a manner that it cannot be +obstructed by rain, snow, ice, insects or birds. + +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. + +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. + +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. + +(Rule 14, referring to the storage of carbide, has been quoted in Chapter +II. (page 19)). + +RULES FOR THE CONSTRUCTION OF GENERATORS. + +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. + +_Class A.--Stationary Apparatus for Isolated Installations._ + +15. GENERAL RULES. GENERATORS.--(_a_) Must be made of iron or steel, +and in a manner and of material to insure stability and durability. + +(_b_) 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 deg. F.) or abnormal +pressure at any stage of the process when using carbide of any degree of +fineness. + +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. + +(_c_) 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. + +This is intended to prevent the dangerous escape of gas. + +(_d_) 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. + +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. + +(_e_) 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. + +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. + +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. + +(_f_) The apparatus must be capable of withstanding fire from +outside causes. + +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. + +This prohibits the use of wood or of joints relying entirely upon solder. + +(_g_) Gauge glasses, the breakage of which would allow the escape of +gas, must not be used. + +(_h_) The use of mercury seals is prohibited. + +Mercury has been found unreliable as a seal in acetylene apparatus.(_i_) +Combustible oils must not be used in connexion with the +apparatus. + +(_j_) The construction must be such that liquid seals shall not +become thickened by the deposit of lime or other foreign matter. + +(_k_) The apparatus must be constructed so that accidental siphoning +of water will be impossible. + +(_l_) 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. + +Floats must not be used excepting in cases where failure will result only +in rendering the machine inoperative. + +(_m_) 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. + +16. GENERATING CHAMBERS.--(_a_) 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. + +(_b_) 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. + +This prevents dangerous pressure within or the escape of gas from the +generating chamber. + +(_c_) 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. + +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. + +(_d_) 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. + +(_e_) Must be so designed that the residuum will not clog or affect +the working of the machine and can conveniently be handled and removed. + +(_f_) 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. + +This applies to machines of the carbide-feed type. + +(_g_) 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. + +17. CARBIDE CHAMBERS.--(_a_) 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. + +(_b_) Must have sufficient carbide capacity to supply the full +number of burners continuously and automatically during the maximum +lighting period. + +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. + +(_c_) Must be arranged so that the carbide holders or charges may be +easily and entirely removed in case of necessity. + +18. GASHOLDERS.--(_a_) 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. + +Gas-bells, if used, may be two gauges lighter than holders. + +Condensation chambers, if placed under holders, to be of same gauge as +holders. + +(_b_) Must be of sufficient capacity to contain all gas generated +after all lights have been extinguished. + +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. + +(_c_) 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. + +(_d_) 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. + +(_e_) 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. + +This tends to insure the proper action of the bell and decreases the +liability of escaping gas. + +(_f_) A space of at least three-quarters of an inch must be allowed +between the sides of the tank and the bell. + +(_g_) All water-seals must be so arranged that the water-level may +be readily seen and maintained. + +19. WATER-SUPPLY.--(_a_) 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, +(_c_), (_d_), and (_e_) may be retained under all +conditions. This provides for the proper level of water in the gasholder. + +(_b_) 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. + +This is to prevent the expulsion of explosive mixtures through the +filling trap in refilling. + +20. RELIEFS OR SAFETY BLOW-OFFS.--(_a_) 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. + +Both the above-mentioned vents may be connected, with the same escape- +pipe. + +(_b_) 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. + +(_c_) Must be constructed without valves or other mechanical working +parts. + +(_d_) 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. + +This is intended to prevent the possibility of undue pressure in the +service-pipes due to failure of the pressure regulator. + +21. PRESSURES.--(_a_) 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. + +(_b_) Apparatus not requiring pressure regulators must be so +arranged that the gas pressure cannot exceed sixty-tenths (6) inches +water column. + +This requires the use of the pressure relief provided for in Rule No. 20 +(_a_). + +(_c_) Apparatus requiring pressure regulators must be so arranged +that the gas pressure cannot exceed three pounds to the square inch. + +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. + +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. + +Owing to the explosive properties of acetylene mixed with air, machines +must be so designed that such mixtures are impossible. + +23. PURIFIERS.--(_a_) Must be constructed of galvanised iron or +steel not less than No. 24 U.S. Standard gauge in thickness. + +(_b_) Where installed, purifiers must conform to the general rules +for the construction of other acetylene apparatus and allow the free +passage of gas. + +(_c_) Purifiers must contain no carbide for drying purposes. + +(_d_) 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. + +24. PRESSURE REGULATORS.--(_a_) 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. + +(_b_) Must be capable of maintaining a uniform pressure, not varying +more than four-tenths inch water column, at any load within their rating. + +(_c_) Must be installed between valves in such a manner as to +facilitate inspection and repairs. + +_Class B.--Stationary Apparatus for Central Station Service._ + +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. + +25. GENERAL RULES. GENERATORS.--(_a_) Must be substantially +constructed of iron or steel and be protected against depreciation by an +effective and durable preventive of corrosion. + +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. + +(_b_) Must contain no copper or alloy of copper in contact with +acetylene, excepting in valves. + +(_c_) Must be so arranged that generation will take place without +overheating; temperatures in excess of 500 deg. F. to be considered +excessive. + +(_d_) Must be provided with means for automatic removal of +condensation from gas passages. + +(_e_) Must be provided with suitable protection against freezing of +any water contained in the apparatus. + +No salt or other corrosive chemical is permissible as a protection +against freezing. + +(_f_) Must in general comply with the requirements governing the +construction of apparatus for isolated installations so far as they are +applicable. + +(_g_) Must be so arranged as to insure correct procedure in +recharging and cleaning. + +(_h_) 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. + +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. + +26. GENERATING CHAMBERS.--(_a_) 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. + +(_b_) Must be so arranged as to guard against appreciable escape of +gas to the room at any time during the introduction of the charges. + +(_c_) Must be so designed that the residuum will not clog or affect +the operation of the machine and can conveniently be handled and removed. + +(_d_) 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. + +27. GASHOLDERS.--(_a_) 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. + +(_b_) Must be provided with suitable guides to direct the movement +of the bell throughout its entire travel. + +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. + +29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of +approximately 25-tenths (2.5) inches water column in the mains. + + + +CHAPTER V + +THE TREATMENT OF ACETYLENE AFTER GENERATION + +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. + +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, &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. + +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, _e.g._, 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. + +GENERATOR IMPURITIES.--The generator impurities present in the crudest +acetylene consist of oxygen and nitrogen, _i.e._, 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 deg. 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. + +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, &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. + +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, &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. + +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.e._, 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.] + +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 deg. 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. + +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. + +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.e._, +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. + +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). + +The British Acetylene Association's regulations relating to carbide of +calcium (_vide_ 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. + +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-Beaupre 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 (_aqua regia_), 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. + +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. + +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 deg. to -40 deg. 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. Berge 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. + +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. + +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 +(_see_ 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. + +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.e._, 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. + +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. + + _________________________________________________ +| | | | +| | Litres | Cubic Feet | +| | per Kilogramme. | per Lb. | +|______________|___________________|______________| +| | | | +| Heratol | 5,000 | 80 | +| Frankoline | 9,000 | 144 | +| Puratylene | 10,000 | 160 | +| Acagine | 13,000 | 208 | +|______________|___________________|______________| + +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. + +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. + +EPURENE.--A purifying material to which the name of epurene has been +given has been described, by Mauricheau-Beaupre, 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: + +8Fe_2Cl_6 + 4Fe_2O_3 + 3PH_3 = 12Fe_2Cl_4 + 3H_3PO_4. + +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 epurene 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 _in situ_ 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-Beaupre, +suffices to double the purifying capacity of one charge of the material, +while a larger proportion would achieve its continuous revivification. +Epurene 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. + +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. + +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: + + __________________________________________________________ +| | | | | +| | 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 | +|_____________|____________|________________|______________| + +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.e._, 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. + +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, _e.g._, a purifier +charged with 132 lb. of heratol should purify 144 cubic feet of acetylene +per hour. + +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 +Berge's solution for the detection of phosphine (_vide_ 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. + +REGULATIONS AS TO PURIFICATION.--The British Acetylene +Association has issued the following set of regulations as to purifying +material and purifiers for acetylene: + +Efficient purifying material and purifiers shall comply with the +following requirements: + +(1) The purifying material shall remove phosphorus and sulphur compounds +to a commercially satisfactory degree; _i.e._, not to a greater +degree than will allow easy detection of escaping gas through its odour. + +(2) The purifying material shall not yield any products capable of +corroding the gas-mains or fittings. + +(3) The purifying material shall, if possible, be efficient as a drying +agent, but the Association does not consider this an absolute necessity. + +(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. + +(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. + +(6) The containers in purifiers shall be made of such materials as are +not dangerously affected by the respective purifying materials used. + +(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. + +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. + +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. + +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. + +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. + +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. + +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. + + + +CHAPTER VI + +THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE + +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. + +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 +(_vide_ 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, +_e.g._, 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 _v_ = the loss of acetylene from a +distributing system and _v'_ = 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 + +(1) (_v_/_v'_) = (0.40 / 0.91)^(1/2) = 0.663 + +or, _v_ = 0.663_v'_, + +which signifies that the loss of acetylene by leakage under the same +conditions of pressure, &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 _p_, and the corresponding +pressure of the coal-gas _p'_, the relative losses by leakage are-- + +(2) (_v_/_v'_) = (0.40 / 0.91)^(1/2) x (_p_/_p'_)^(1/2) + +_v_ = 0.663_v'_ x (_p_/_p'_)^(1/2) + +It will be evident that whenever the value of the fraction +(_p_/_p'_)^(1/2), is less than 1.5, _i.e._, 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, &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, _coeteris paribus_, 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. + +The critical temperature of acetylene, _i.e._, the temperature below +which an abrupt change from the gaseous to the liquid state takes place +if the pressure is sufficiently high, is 37 deg. C., and the critical +pressure, _i.e._, 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.e._, at 13.5 deg. C. a pressure of 32.77 atmospheres, at 0 deg. C., 21.53 +atmospheres (Ansdell, _cf._ 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. + +The mean coefficient of expansion of gaseous acetylene between 0 deg. C. and +100 deg. 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 deg. 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. + +Ansdell has found the density of liquid acetylene to range from 0.460 at +-7 deg. C. to 0.364 at +35.8 deg. C., being 0.451 at 0 deg. C. Taking the volume of +the liquid at -7 deg. as unity, it becomes 1.264 at 35.8 deg., and thence Ansdell +infers that the mean coefficient of expansion per degree is 0.00489 deg. 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 Fouche As mentioned before, data referring to +liquid (_i.e._, 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 +(_k_ 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 _k_ 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. + +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 + +26 C_p - 26 C_v = 2 cal., + +and + +C_p = 1.26 C_v. + +From this it follows that C_p, _i.e._, the specific heat at constant +pressure of acetylene, should be 0.373.] It will be seen that this value +for _k_ 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: + + 0 deg. 1000 deg. 1500 deg. 2000 deg. 2500 deg. 3000 deg. 3500 deg. +0.247 0.271 0.296 0.325 0.344 0.363 0.381 + +The molecular volume of acetylene is 0.8132 (oxygen = 1). + +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 deg. 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 deg. 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 deg./0 deg. 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 deg. F. and 30 inches of mercury) become approximately: + + 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. + +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 deg. 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.e._, 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. + +HEAT OF COMBUSTION, &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: + + Dry. Dry. Saturated. + 0 deg. C. & 760 mm. 60 deg. F & 30 ins. 60 deg. F. & 30 ins. + +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 " + +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 deg. C. V. Meyer and +Muench in 1893 found that a mixture of acetylene and oxygen ignited +between 509 deg. and 515 deg. C. Recent (1909) investigations by H. B. Dixon and +H. F. Coward show, however, that the ignition temperature in neat oxygen +is between 416 deg. and 440 deg. (mean 428 deg. C.) and in air between 406 deg. and 440 deg., +with a mean of 429 deg. C. The corresponding mean temperature of ignition +found by the same investigators for other gases are: hydrogen, 585 deg.; +carbon monoxide, moist 664 deg., dry 692 deg.; ethylene, in oxygen 510 deg., in air +543 deg.; and methane, in oxygen between 550 deg. and 700 deg., and in air, between +650 deg. and 750 deg. C. + +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 deg. C. +- +20 deg., which is 120 deg. 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 deg. and 2400 deg., while Lewes had found for the dark zone 459 deg., +for the luminous zone 1410 deg., and for the tip 1517 deg. C, Fery and Mahler +have also made measurements of the temperatures afforded by acetylene and +other fuels, some of their results being quoted below. Fery 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 deg. C. and a constant pressure of 760 mm. + +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 + +Catani has published the following determinations of the temperature +yielded by acetylene when burnt with cold and hot air and also with +oxygen: + +Acetylene and cold air . . . . . . 2568 deg. C. + " air at 500 deg. C . . . . 2780 deg. C. + " air at 1000 deg. C . . . . 3000 deg. C. + " oxygen . . . . . . 4160 deg. C. + +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 deg. 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 (_cf._ 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 (_cf._ 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 deg. 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 deg. 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 (_cf._ Chapter XI.). + +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, &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. + +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: + +_Explosive Limits of Acetylene mixed with Air._--(Le Chatelier.) + + ___________________________________________________________ +| | | | +| | 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 | ... | ... | ... | +|__________________|___________|___________|________________| + +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. + +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 deg. to 65 deg. F., was saturated with +aqueous vapour, and was fired by electric spark. + +_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._--(Eitner.) + + ____________________________________________________________________ +| | | | | +| 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 | +|__________________|___________|___________|_________________________| + +These figures are of great practical significance. They indicate that a +mixture of acetylene and air becomes explosive (_i.e._, 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.e._, mixtures of benzene with +toluene, &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, +&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. + +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. + +_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._--(Teclu). + + ____________________________________________________________________ +| | | | +| | 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 | +|__________________|________________________|________________________| + +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. + +_Solubility of Acetylene in Various Liquids._ + + _____________________________________________________________________ +| | | | | +| | | 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. Mueller | +| " " . | 15 | 110 | Lewes | +| " " . | 18 | 100 | Berthelot | +| " " . | -- | 100 | E. Davy (in 1836)| +| " " . | 19.5 | 97.5 | E. Mueller | +| 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. Mueller | +| " " " | 12 | 21.0 | " | +| " " " | 18 | 20.4 | " | +| Solution of calcium | | | Hammerschmidt | +| chloride (saturated) . | 15 | 6.0 | and Sandmann | +| Berge and Reychler's re- | | | | +| agent . . . . | -- | 95 | Nieuwland | +|___________________________|_________|____________|__________________| + +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, &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. + +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 deg. 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 deg. 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. + + _________________________________________________ +| | | | +| 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 | +|_______________|_______________|_________________| + +Figures showing the solubility of acetylene in plain water at different +temperatures have been published in Landolt-Boernstein's Physico- +Chemical Tables. These are reproduced below. The "Coefficient of +Absorption" is the volume of the gas, measured at 0 deg. 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. + + _____________________________________________ +| | | | +| 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 | +|______________|________________|_____________| + +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 deg. 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. + +Turning to the other end of the scale of solubility, the most valuable +liquids for serving as seals of gasholders, &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 +(_vide_ 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. + +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 deg. +C., the corresponding figure for benzene in place of water being 1.40 deg. C. +These figures indicate that 100 parts by weight of water should dissolve +0.1118 part by weight of acetylene at 0 deg. C., and that 100 parts of +benzene should dissolve about 0.687 part of acetylene at 5 deg. 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 deg. C. Other measurements of the +solubility of acetylene in water at 0 deg. C. have given the figure 0.1162 +per cent. by weight. + +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 +_per se_ 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 _nil_. The toxic action of the impurities of crude +acetylene is discussed in Chapter V. + +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 deg. C. and upwards, +or at a pressure of two atmospheres absolute, or higher. If that +temperature or that pressure is exceeded, dissociation (_i.e._, +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 deg. 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 Dupre 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. + +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 (_see_ 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 _maximum_ illuminative value obtainable +from them either by combustion alone or in admixture with some non- +illuminating or feebly-illuminating gas: + + ________________________________________________ +| | | | +| | | 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 | +|______________|___________________|_____________| + +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. + +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: + + _______________________________________________________________ +| | | | | +| 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 | +|________________________________|_________|___________|________| + +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). + +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, Muensterberg has given the following table for the composition +of the several lights mentioned: + + ______________________________________________________________________ +| | | | | | +| | 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 | +|__________|______|_________|________|_________|_______|_______|_______| + +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. + +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: + + __________________________________________________________________ +| | | | | +| | | | 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 | +|___________|_______________|______________|________|______________| + +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. + + ____________________________________________________________________ +| | | | +| | 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 | +|____________________________|___________________|___________________| + +Violle and Fery, also Erdmann, have proposed the use of acetylene as a +standard of light. As a standard burner Fery 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. + +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. + +Numerous investigators have studied the optical or radiant efficiency of +artificial lights, _i.e._, 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. + +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: + + _______________________________________________________________________ +| | | | | | +| | 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 | +|____________________|____________|____________|____________|___________| + +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 (_see_ 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, Woehler, 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: + +C_2H_2 + 2Cl_2 = C_2H_2Cl_4; + +but when the reaction is violent some hexachlorethane is formed, +presumably thus: + +2C_2H_2 + 5Cl_2 = 4HCl + C_2 + C_2Cl_6. + +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; + +C_2H_2 + Cl_2 = 2HCl + C_2. + +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. + +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. + +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. Schroeter has made similar +investigations on the action of strongly fuming sulphuric acid on +acetylene. These investigations have not yet acquired any commercial +significance. + +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 deg. or 250 deg. C., the second +product in this case being calcium oxide. The equations representing +these actions are: + +C_2H_2 + CO = H_2O + 3C + +2C_2H_2 + CO_2 = 2H_2O + 5C + +CaC_2 + CO = CaO + 3C + +2CaC_2 + CO_2 = 2CaO + 5C + +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 (_cf._ Chapter +XII.). + +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.e._, 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. + +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 deg. and 70 deg. 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 deg. 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 deg. or 60 deg. 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. + +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. + +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. + +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. (_Cf._ Chapter IV., +page 127.) + +When acetylene is passed over finely divided copper or iron (obtained by +reduction of the oxide by hydrogen) heated to from 130 deg. C. to 250 deg. 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. + + + +CHAPTER VII + +MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS + +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, &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. + +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. + +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.e._, 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. + +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 (_see_ 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. + +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. + +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. + +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. + +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 _d_ is the diameter in inches of the +(cylindrical) bell, the surface of the water displaced will have an area +of _d^2_ x 0.7854. If the level of the water is depressed _p_ +inches, then the water displaced amounts to _p_(_d^2_ x 0.7854) +cubic inches, and its weight will be (at 62 deg. F.): + +(0.7854_pd^2_ x 0.03604) = 0.028302_pd^2_ lb. + +Consequently a bell which is _d_ inches in diameter, and gives a +pressure of _p_ inches of water, will weigh 0.028302_pd^2_ lb. +Or, if W = the weight of the bell in lb., the pressure thrown by it will +be W/0.028302_d^2_ or 35.333W/_d^2_. This is the fundamental +formula, which is sometimes given as _p_ = 550W/_d^2_, in which +W = the weight of the bell in tons, and _d_ the diameter in feet. +This value of _p_, 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, _mutatis mutandis_, 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 _h_(1 - +_d_)/828 where _d_ is the specific gravity of the gas and +_h_ 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 _h_ here must be taken as equal to the +height of the top of the sides above the water-level (= _h'_), plus +the height of a cylinder having the same capacity as the crown, and the +same diameter as the bell, that is to say, _h_=_h'_ + +_d_/40 where _d_ = 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_h_ + 0.0000027_d_, where _h_ is the +height in inches of the top of the sides of the bell above the water- +level, and _d_ 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 formulae 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 formulae. + +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, _h_ the height +in inches of the top of the sides of the gasholder above the water-level, +and _w_ = 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 - _h_)/H, and the buoyancy is (H - _h_)/H x +_w_/S + pi/4_d^2_, 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_w_(H - _h_)) / (7.78Hpi_d^2_) lb. per square inch +(_d_ being inches and _w_ lb.), which is equivalent to +(4_w_(H - _h_)) / (0.03604 x 7.78Hpi_d^2_) = +(4.54_w_(H - _h_)) / (H_d^2_) inches of water. Hence the +complete formula for acetylene gasholders is: + +_p_ = 35.333W / _d^2_ - 4.54_w_(H - _h_) / +H_d^2_ + +It follows that _p_ 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. + +Now, according to the rules of the "Acetylen-Verein" (_cf._ 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, +_h_ is very nearly equal to H, and _p_ = (35.333 x 443) / 48^2 += 6.79 inches. If the holder stands only 1 foot above the water-level, +then _p_ = 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: + +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 _p_ = (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 _s'_ times as great as when the liquid is water, +if _s'_ 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 (_vide_ 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 _p_ becomes = (35.333 x 389.1) / 48^2 = 5.97 inches, +instead of 6.07 inches.] + +The value of _p_ 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, &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. + +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 _w_ 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 _x_ lb. of steel is added to the +rim its weight in computing the value of W in the formula _p_ = +35.333W / _d_^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. + +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 _difference_ that is meant when the +_pressure_ 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 _exceeds_ 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. + +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. + +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.) + +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. + +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 _Journal of Gas +Lighting_ 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: + +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.: + +(1) The length of pipe = _l_ feet. + +(2) The internal diameter of the pipe = _d_ inches. + +(3) The actuating pressure = _h_ inches of head of water. (4) The +specific gravity or density of the gas = _d_ times that of air. + +(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. + +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_ld_); (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., _s_). + +Thus the force (_f_) necessary to maintain the motion of the gas in +the pipe is seen to vary (1) as pi_ld_, of which pi is a constant; +(2) as _v^2_, where _v_ = the velocity in feet per hour; and +(3) as _s_. Hence, combining these and deleting the constant pi, it +appears that + +_f_ varies as _ldsv^2_. + +Now the actuating force is equal to _f_, and is represented by the +difference of pressure at the two ends of the pipe, _i.e._, the +initial pressure, viz., that at the place whence gas is distributed or +issues from a larger pipe will be greater by the quantity _f_ 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.e._, at the inlet head of service-pipe) p_1, it +follows that p_1 - p_0 = _f_. Now the cross-section of the pipe has +an area (pi/4)_d^2_, and if _h_ represents the difference of +pressure between the two ends of the pipe per square inch of its area, it +follows that _f_ = _h(pi/4)d^2_. But since _f_ has been +found above to vary as _ldsv^2_ , it is evident that + +_h(pi/4)d^2_ varies as _ldsv^2_. + +Hence + +_v^2_ varies as _hd/ls_, + +and putting in some constant M, the value of which must be determined by +experiment, this becomes + +_v^2_ = M_hd/ls_. + +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_d^2v_, +it was found that for coal-gas Q = 780(_hd/sl_)^(1/2) + +This formula, in its usual form, is + +Q = 1350_d^2_(_hd/sl_)^(1/2) + +in which _l_ = 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. + +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, _cateria +paribus_, 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: + +Q = 0.001253_d^2_(_hd/sl_)^(1/2) + +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.e._, Q being cubic feet +per hour, _l_ feet, and _d_ and _h_ inches) becomes + +Q = 1313.5_d^2_(_hd/sl_)^(1/2) + +or, more simply, + +Q = 1313.4(_hd^5/sl_)^(1/2) + +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 + +Q = 1376.9(_hd^5/l_)^(1/2) + +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 + +d = 0.05552(Q^2_l/h_)^(1/5) + +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 + +D = 1.155(Q^2_l/h_)^(1/5) + +in which D = the diameter of the pipe in centimetres, Q = the number of +cubic metres of gas passing per hour, _l_ = the length of pipe in +metres, and _h_ = 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.e._, _l_ feet, Q cubic feet, and +_h_ and _d_ inches) it becomes + +(i) d = 0.045122(Q^2_l/h_)^(1/5) + +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: + +(ii) Q = 2312.2(_hd^5/l_)^(1/2) + +(iii) _h_ = 0.000000187011(Q^2_l/d^5_) + +and (iv) _l_ = 5,346,340(_hd^5_/Q^2) + +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 formulae 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. + +When dealing with coal-gas, it is highly important to bear in mind that +the ordinary distributing formulae 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. + +The distributing formulae 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 _l_ in +formulae (i), (ii), or (iii), the values then found for Q, _d_, or +_h_ will be trustworthy for all practical purposes. + +It may now be useful to give an example of the manner of using the +foregoing formulae 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? + +In the first instance, it is convenient to suppose that the trunk pipe +may be of uniform diameter throughout. Then the value of _l_ 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 _h_ will be 1 - 2.5 - 1.5. +Then using formula (i), we have: + +d = 0.045122((85^2 x 400)/1.5)^(1/5) = 0.045122(1,926,667)^(1/5) + += 0.045122 x 18.0713 = 0.8154. + +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. + +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 _d_ inches, its +cross-sectional area is _d^2_ 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 _d_ inches a length of + +1728/(_d^2_ x 0.7854) linear inches or 183/_d^2_^ linear feet. + +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 + +183/_d^2_ x Q/3600 = Q/(19 x 7_d^2_) linear feet per second. + +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 + +Q/(19.7_d^2_) = 22 or more; + +_i.e._, Q/_d^2_=433.4 + +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. + +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 formulae 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. + +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, &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.e._, 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, &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. + +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. + +Caro has stated that a loss of 15 to 20 litres per kilometre per hour +(_i.e._, 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 (Doese, 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.e._, 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. + +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, &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 _vice +versa_, 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. + +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, &c., and protected from blows, &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. + +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, &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, +&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. + +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. + +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. + +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. + +The mains for very large installations of acetylene--_e.g._, 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, &c. This +plan, however, will usually only be adopted in the case of very large +pipes, &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, &c., they are easy to hire and use. + +TABLE (B). + +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.) + + _________________________________________________________ +| | | +| 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 | +|________________|_______|_______|_______|_______|_______| + +TABLE (A). + +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.) + + ____________________________________________________________________ +| | | | | | | | | | | | | +| 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| +|__________|____|____|____|_____|_____|_____|____|____|____|____|____| + +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. + +TABLE (C). + +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.) + + ____________________________________________________________________ +| | | +| 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| +|____________|______|______|______|______|______|______|______|______| + +TABLE (D). + +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.) + + ____________________________________________________________________ +| | | +| 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 | +|____________|______|______|______|______|______|______|______|______| + +TABLE (E). + +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.) + + __________________________________________________________________ +| | | +| 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| +|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____| + + + +CHAPTER VIII + +COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION + +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, &c., occurs. Being +larger, too, the heat produced is less concentrated. + +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. + +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. + +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 aesthetic 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: + +1.377 / 5 = 77 / x hence x = 280. + +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. + +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.e._, 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. + +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.e._, 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. + +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 deg. 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. + +Some experiments reported by R. Granjon and P. Mauricheau-Beaupre 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. + +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. + +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. + +[Illustration: FIG. 8.--TYPICAL ACETYLENE BURNERS.] + +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 deg., 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 Phos 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 Phos 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 Phos burner is +shown in Fig. 9, in which _A_ is the burner tip, _B_ the wire +or needle, and _C_ the milled head by which the wire is screwed in +and out of the burner tube. + +[Illustration: FIG. 9.--IMPROVED PHOS BURNER.] + +[Illustration: FIG. 10.--"WONDER" SINGLE AND TWO-FLAME BURNERS.] + +[Illustration: FIG. 11.--"SUPREMA" NO. 266651, TWO-FLAME BURNER.] + +[Illustration: FIG. 12.--BRAY'S MODIFIED NAPHEY INJECTOR BURNER TIP.] + +[Illustration: FIG. 13.--BRAY'S "ELTA" BURNER.] + +[Illustration: FIG. 14.--BRAY'S "LUTA" BURNER.] + +[Illustration: FIG. 15.--BRAY'S "SANSAIR" BURNER.] + +[Illustration: FIG. 16.--ADJUSTABLE "KONA" BURNER.] + +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 Phos +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. + +[Illustration: FIG. 17.--"ORKA" BURNER.] + +[Illustration: FIG. 18.--"SUPREMA" NO. 216469 BURNER.] + +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: + + ___________________________________________________________ +| | | | | | +| | | 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 | +|_________|___________|____________|__________|_____________| + +From burners of the Billwiller type Lewes obtained in 1899 the values: + + ___________________________________________________________ +| | | | | | +| | | 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 | +|_________|___________|____________|__________|_____________| + +Neuberg gives these figures for different burners (1900) as supplied by +Pintsch: + + ______________________________________________________________________ +| | | | | | +| | Gas | | Candles | |"w +| 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 | +|____________________|___________|____________|__________|_____________| + +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. + +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 _bougie decimale_ equals 0.98 +standard English candle, which is the value he himself ascribes to it (1 +_bougie decimale_ equals 1.02 candles is the value now accepted). + + _____________________________________________________________________ +| | | | | | +| 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 | +|_____________|_________|_____________________|__________|____________| + +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. + + ___________________________________________________________________ +| | | | | +| | 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 | +|_______________________|_____________|___________|_________________| + +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. + +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 + +1 Hefner unit = 0.913 English candle + +1 English candle = 1.095 Hefner units, + +works out to an efficiency of 37 candles per foot in burners probably +consuming between 0.5 and 0.7 foot per hour. + +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: + + _______________________________________________________ +| | | | +| 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 | +|______________________|______________|_________________| + +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. + +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: + +ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE. + + _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. + +If the two streams of gas impinge at an angle of 90 deg., 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. + +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 deg., 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. + +GLOBES, &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.e._, 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. + + + +CHAPTER IX + +INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING + +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. + +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. + +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.e._, 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." + +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. + +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: + + ILLUMINATING POWER OF INCANDESCENT ACETYLENE. + HALF-FOOT BURNERS. + + 1 litre = 3.65 candles | 1 candle = 0.274 litre. + 1 cubic foot = 103.40 candles. | 1 candle = 0.0097 cubic foot. + +A number of tests of the Guentner 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: + _________________________________________________________________ +| | | | | +| 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 | +|______________|____________|____________|__________|_____________| + +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. + +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 Fouche showed: + + _________________________________________________________________ +| | | | | | +| 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 | +|________________|__________|____________|__________|_____________| + +By increasing the pressure at which acetylene is introduced into burners +of this type, still larger duties may be obtained from them: + + _________________________________________________________________ +| | | | | | +| 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 | +|________________|__________|____________|__________|_____________| + +High-power burners such as these are only fit for special purposes, such +as lighthouse illumination, or optical lantern work, &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. + +In 1902, working apparently with acetylene dissolved under pressure in +acetone (_cf._ Chapter XI.), Lewes obtained the annexed results with +the incandescent gas: + + ________________________________________________________ +| | | | | +| 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 | +|___________|_____________|______________|______________| + +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. + +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 Oleron. 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.e._, 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. + + ___________________________________________________________ +| | | | +| | 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 | +|_____________________|__________________|__________________| + +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): + + _Luminosity in Hefner Units._ + + ________________________________________________________ +| | | | | | +| 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 | +|_________|_______|____________|____________|____________| + +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. + +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. + +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 Fouche, 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). + +The more recent burners which have been somewhat extensively used include +the "Schimek," made by W. Guentner 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. + +[Illustration: FIG. 19.--"SCHIMEK" BURNER.] + +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. + +The "Zenith" burner, made by the firm of Gebrueder 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. + +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'Acetylene 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. + +[Illustration: FIG. 20.--BRAY'S INCANDESCENT BURNER.] + +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. + +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, &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. + +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. + +ACETYLENE MOTORS.--The question as to the feasibility of developing +"power" from acetylene, _i.e._, 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.e._, 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, &c. + +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.e._, 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.e._, 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. + +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 Fouche 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 Fouche'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 +Fouche 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 (_cf._ +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.e._, 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, Fouche +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. + +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 Fouche, 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 _in situ_), 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. + +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 +"Linde-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. + + + +CHAPTER X + +CARBURETTED ACETYLENE + +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. + +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.e._, 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 (_cf._ +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. + +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. + +The illuminating power of acetylene carburetted with petroleum spirit has +been examined by Caro, whose average figures, worked out in British +units, are: + + ILLUMINATING POWER OF CARBURETTED ACETYLENE. + HALF-FOOT BURNERS. + + _Self-luminous._ | _Incandescent_ +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. + +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. + +The calorific values of carburetted acetylene (Caro), and those of other +gaseous fuels are: + + 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 + + +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: + + ______________________________________________________________________ +| | | | | +| | 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 | --- | --- | +|________________________|______|______|________|_________|____________| + +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 15L 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. + +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.e._, 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. + +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 (_cf._ 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.e._, 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. + +Lepinay 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. Lepinay 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. + + + +CHAPTER XI + +COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES + +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. + +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 deg. 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. + +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 deg. 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, &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 (_cf._ Chapter VI.). + +DISSOLVED ACETYLENE.--According to Fouche, 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 (Fouche), or 0.00489 (Ansdell) _i.e._, +three or five times as much. The specific gravity of liquid acetylene is +0.420 at 16.4 deg. C. (Ansdell), or 0.528 at 20.6 deg. C. (Willson and Suckert); +while the density of acetylene dissolved in acetone is 0.71 at 15 deg. C. +(Claude). The tension of liquefied acetylene is 21.53 atmospheres at 0 deg. +C., and 39.76 atmospheres at 20.15 deg. C. (Ansdell); 21.53 at 0 deg. C., and +39.76 at 19.5 deg. C. (Willson and Suckert); or 26.5 at 0 deg. C., and 42.8 at +20.0 deg. C. (Villard). Averaging those results, it may be said that the +tension rises from 23.2 atmospheres at 0 deg. C. to 40.77 at 20 deg. C., which is +an increment of 1/26 or 0.88 atmosphere, per 1 deg. Centigrade; while, of +course, liquefied acetylene cannot be kept at all at a temperature of 0 deg. +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 (_a_) 301 grammes of acetone are +charged with 69 grammes of acetylene, a pressure of 6.74 atmospheres at +14.0 deg. C. rises to 10.55 atmospheres at 35.7 deg. C.; (_b_) 315 grammes +of acetone are charged with 118 grammes of acetylene, a pressure of 12.25 +atmospheres at 14.0 deg. C. rises to 19.46 at 36.0 deg. C.; (_c_) 315 +grammes of acetone are charged with 203 grammes of acetylene, a pressure +of 19.98 atmospheres at 13.0 deg. C. rises to 30.49 at 36.0 deg. C. Therefore in +(_a_) the increase in pressure is 0.18 atmosphere, in (_b_) +O.33 atmosphere, and in (_c_) 0.46 atmosphere per 1 deg. Centigrade +within the temperature limits quoted. Taking case (_b_) as the +normal, it follows that the increment in pressure per 1 deg. 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. + +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 deg. 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. + +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. + +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 (_a_) 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, (_b_) that +the gas does not escape smoothly enough to be convenient from large +vessels unless those vessels are agitated, and (_c_) 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. + +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. + +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, &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. + +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 Fouche, 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. + +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.e._, 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. + +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 _nil_; 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. + +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. + +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. + +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 (_cf._ +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. + +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. + +Fouche, 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: + +Percentage of air 0 17 27 33.5 +Candles per cubic feet 38.4 36.0 32.8 26.0 + +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. + +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. + +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 (_a_) up to 20 per cent. of +manganese oxide, and (_b_) 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 +(_a_) they found the gas to be practically pure acetylene, so that +the carbide must have been calcium carbide only; in case (_b_) 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. + +There is, nevertheless, one modification of calcium carbide which, in a +small but important sphere, finds a useful _role_. 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. + +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 _partial_ +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 _x_ may be safely compressed to a pressure not exceeding (2 / +_x_/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. + +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. + +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 _x_ 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. + +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. + +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: + + ______________________________________________________________________ +| | | | | | | | +| | | | | | | 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 | ... | +|___________|________|_______|__________|_________|__________|_________| + +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. + +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. + +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. + + ______________________________________________________________________ +| | | | | | | +| | | | | | 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 | +|_____________|_________|___________|______|___________|_______________| + +[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.] + +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. + +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. + + + +CHAPTER XII + +SUNDRY USES + +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. + +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. + +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. + +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. + +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. + +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. + +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. + +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 deg. 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. + +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. + +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. + +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, +_e.g._, 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 deg. to 200 deg. 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. + +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. + +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, &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. + +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. + +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, &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. + + + +CHAPTER XIII + +PORTABLE ACETYLENE LAMPS AND PLANT + +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. + +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 +(_e.g._, 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. + +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. + +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, &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 (_cf._ 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. + +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. + +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, &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. + +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, &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. + +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, &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 "Phos" principle is made in +small sizes by the Phos Co., of London, specially for use in lamps on +vehicles. + +[Illustration: FIG. 21.--CYCLE-LAMP BURNER NO. 96042A.] + +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. + +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 (_cf._ 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. + +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. + +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. + +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. + + + +CHAPTER XIV + +VALUATION AND ANALYSIS OF CARBIDE + +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: + +"REGULATIONS AS TO CARBIDE OF CALCIUM." + +1. The carbide shall be guaranteed by the seller to yield, when broken +to standard size, _i.e._, 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 deg. Fahr. (15.55 deg. Centigrade). The actual +gas yield shall be deemed to be the gas yield ascertained by the analyst, +plus 5 per cent. + +"Carbide yielding less than 4.8 cubic feet in the sizes given above shall +be paid for in proportion to the gas yield, _i.e._, 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. + +"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. + +"3. The carbide shall not contain higher figures of impurities than shall +from time to time be fixed by the Association. + +"4. No guarantee shall be given for lots of less than 3 cwt., or for +carbide crushed to smaller than the above sizes. + +"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. + +"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. + +"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. + +"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. + +"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. + +"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. + +"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. + +"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." + + * * * * * + +The following is a translation of the corresponding rules issued by the +German Acetylene Association (_Der Deutsche Acetylenverein_) in +regard to business dealings in calcium carbide, as put into force on +April 1, 1909: + +"REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE. + +"_Price_. + +"The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of +carbide in packages containing about 100 kilogrammes. + +"By packages containing about 100 kilogrammes are meant packages +containing within 10 per cent. above or below that weight. + +"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. + +"The prices for other descriptions of packing must be specially stated. + +"_Place of Delivery_. + +"For consignment for export, the last European shipping port shall be +taken as the place of delivery. + +"_Quality_. + +"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 deg. C. and 760 mm. pressure of crude acetylene per +kilogramme for each consignment (= 4.81 cubic feet at 60 deg. 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. + +"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. + +"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 deg. C. and 760 mm. pressure of crude acetylene per +kilogramme (= 4.33 cubic feet at 60 deg. 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. + +"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. + +"_Period for Complaints._ + +"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. + +"_Determination of Quality._ + +"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: + +"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. + +"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 be 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, +&c., is permissible. + +"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. + +"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. + +"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. + +"3. The whole of the cost of sampling and analysis is to be borne by the +party in the wrong." + + * * * * * + +The corresponding regulations issued by the Austrian Acetylene +Association (_Der Oesterreichische Acetylenverein_) 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. + +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. + +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.e._, 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 (_Der Deutsche +Acetylenverein_) is reproduced below. + +"METHODS FOR THE DETERMINATION OF TILE YIELD OF GAS FROM CALCIUM CARBIDE. + +"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. + +"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. + +"(_a_) 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. + +"(_b_) 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. + +"(_c_) The generator must be constructed so that escape of the +evolved gas from it to the outer air is completely avoided. + +"(_d_) 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. + +"(_e_) 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." + +The following is a description of a typical form of apparatus +corresponding with the foregoing requirements: + +"The apparatus, shown in the annexed figure, consists of the generator A, +the washer B, and the gasholder C. + +[Illustration: FIG. 22.--LARGE-SCALE APPARATUS FOR DETERMINING YIELD OF +GAS FROM CARBIDE.] + +"The generator A consists of a cylindrical vessel with sloping bottom, +provided with a sludge outlet _a_, a gas exit-pipe _b_, and a +lid _b'_ fastened by screws. In the upper part ten boxes _c_ +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 _d_, which is mounted on a shaft _l_. This +shaft passes through a stuffing-box to the outside of the generator and +can be rotated by moans of the chains _f_, the pulleys _g_ and +_h_, and the winch _i_. Its rotation causes rotation of the +disc _d_. The disc _d_, on which the bottoms of the carbide- +holders are supported, is provided with a slot _e_. 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_. + +"The washer B is provided with a thermometer _m_ passing through a +sound stuffing-box and extending into the water. + +"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 +_n_, and is further provided with a control thermometer _o_. +The gas exit-pipe _q_ can be shut off by a cock. There is a cock +between the gasholder and the washer for isolating one from the other. + +"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)." + +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 (_vide ante_), 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.e._, 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. + +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. + +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: + +"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 _e_ on the disc _d_ +that it will be the first receptacle to be discharged when the winch +_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 _b'_ 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. + +"The contents of the first carbide receptacle are then discharged by +turning the winch _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 _p_ is shut, and the gasholder is run down to the zero mark +by opening the cock _q_. The cock _q_ is then shut, _p_ is +opened, and the analytical examination proper is begun by discharging the +several carbide receptacles by turning the winch _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 _p_ is +then shut. Weights are added to the gasholder until the manometer +_n_ gives the zero reading; the position of the gasholder C is then +read off, and readings of the barometer and of the thermometer _o_ +are made. The gasholder is then emptied down to the zero mark by closing +the cock _p_ and opening _q_. When this is done _q_ is +closed and _p_ is opened, and the winch _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." + +The following example is quoted: + +Weight of the tin received, with its contained | + carbide . . . . . ._| = 6325 grammes. +Weight of the empty tin . . . . = 1485 " + _______ + Carbide used . . . = 4840 " = 10670 lb. + +The carbide in question was distributed among the nine receptacles and +gasified. The readings were: + + ________________________________________________ +| | | | | +| 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 | " | " | +|______|__________|______________|_______________| + +After two hours, the total of the readings was 1395.0 litres at 13.5 deg. C. +and 762 mm., which is equivalent to 1403.7 litres (= 49.57 cubic feet) at +15 deg. C. and 760 mm. (or 60 deg. 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 deg. C. and 760 mm. to 60 deg. F. and 30 inches, or _vice +versa_). + +The yield of gas from this sample is therefore 1403.7/4.840 = 290 litres +at 15 deg. C. and 760 mm. per kilogramme, or 49.57/10.67 = 4.65 cubic feet at +60 deg. 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. + +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. + +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. + +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. + +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: + +"A Woulff's bottle, _a_ 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 _b_, having two tubulures, and this vessel is +further connected with a conical flask _c_, holding about 100 c.c. +The other neck is provided with tubing _d_, serving to convey the +gas to the inlet-tube, with tap _e_, of the 20-litre measuring +vessel _f_, which is filled with water saturated with acetylene, and +communicates through its lower tubulure with a similar large vessel +_g_. The generating vessel _a_ is charged with about 150 c.c. +of water saturated with acetylene. The vessel _f_ is filled up to +the zero mark by raising the vessel _g_; the tap _e_ is then +shut, and connexion is made with the tube _d_. Fifty grammes (or say +2 oz.) of the pulverised carbide are then weighed into the flask _c_ +and this is connected by the flexible tubing with the vessel _b_. +The carbide is then decomposed by bringing it in small portions at a time +into the bulb _b_ by raising the flask _c_, and letting it drop +from _b_ into the generating vessel _a_, after having opened +the cock _e_ and slightly raised the vessel _f_. After the last +of the carbide has been introduced two hours are allowed to elapse, and +the volume of gas in _f_ is then read while the water stands at the +same level in _f_ and _g_, the temperature and pressure being +noted simultaneously." + +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 _e_, 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. + +[Illustration: FIG. 23.--SMALL-SCALE APPARATUS FOR DETERMINING YIELD OF +GAS FROM CARBIDE.] + +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. + + ___________________________________________________________________ +| | | | +| | "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 . . . . / | | | +|_____________________________________________________|______|______| + +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. + +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. + +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. + +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. + +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 deg. F.) and normal barometric height (30 inches). The normal +volume thus found is, as already stated, not appreciably different from +the volume at 15 deg. 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, &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. + +Hammerschmidt has calculated a similar table for the correction of +volumes of gas measured at temperatures ranging from 0 deg. to 30 deg. C., and +under pressures from 660 to 780 mm., to 15 deg. 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. + +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. + +_Table to facilitate the Correction of the Volume of Gas at different +Temperatures and under different Atmospheric Pressures._ + + _____________________________________________________ +| | | +| | THERMOMETER. | +| BAR.|_______________________________________________| +| | | | | | | | +| | 46 deg. | 48 deg. | 50 deg. | 52 deg. | 54 deg. | 56 deg. | +|_____|_______|_______|_______|_______|_______|_______| +| | | | | | | | +|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 deg. | 60 deg. | 62 deg. | 64 deg. | 66 deg. | 68 deg. | +|_____|_______|_______|_______|_______|_______|_______| +| | | | | | | | +|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 deg. | 72 deg. | 74 deg. | 76 deg. | 78 deg. | +|_____|_______|_______|_______|_______|_______| +| | | | | | | +|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 | +|_____|_______|_______|_______|_______|_______| + +For the detection of phosphine, Berge'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. + +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. + +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. + +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. + +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. + +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. + +Mauricheau-Beaupre 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. + +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." + +APPENDIX + +DESCRIPTIONS OF A NUMBER OF ACETYLENE GENERATORS AS MADE IN THE YEAR 1909 + +(_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._) + +AMERICA--CANADA. + +_Maker_: SICHE GAS CO., LTD., GEORGETOWN, ONTARIO. + +_Type_: Automatic; carbide-to-water. + +The "Siche" generator made by this firm consists of a water-tank +_A_, having at the bottom a sludge agitator _N_ and draw-off +faucet _O_, and rigidly secured within it a bell-shaped generating +chamber _B_, above which rises a barrel containing the feed chamber +_C_, surmounted by the carbide chamber _D_. The carbide used is +granulated or of uniform size. In the generating chamber _B_ is an +annular float _E_, 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 _C_, to the T-shaped +tubular valve _F_. 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 +_G_ over the feed valve _F_, 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 _C_, whereby the gas is +dried. The carbide chamber _D_ has at its bottom a conical valve, +normally open, but closed by means of the spindle _H_, which is +engaged at its upper end by the closing screw-cap _J_, which is +furnished with a safelocking device to prevent its removal until the +conical valve is closed and the hopper chamber _D_ thereby cut off +from the gas-supply. The cap _J_, 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 _K_, shown in half-scale, is +provided for inserting in place of the screw cap. The carbide falls from +the funnel into the chamber _D_ 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 _C_ through a pipe, with cock, to +a dust-arrester _L_, 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 _A_. +When cleaning the machine, the water must never be run below the top of +the generating chamber. + +[Illustration: FIG. 24.--"SICHE" GENERATOR.] + +AMERICA--UNITED STATES. + +_Maker:_ J. B. COLT CO., 21 BARCLAY STREET, NEW YORK. + +_Type:_ Automatic; carbide-to-water. + +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 _C_ +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. + +[Illustration: FIG. 25.--"COLT" GENERATING PLANT.] + +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 _C_. There is also a telescopic blow-off (32) and (33), +which automatically comes into play if the gasholder bell rises above a +certain height. + +_Maker:_ DAVIS ACETYLENE CO., ELKHARDT, INDIANA. + +_Type:_ Automatic; carbide-to-water. + +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. + +[Illustration: FIG. 26.--"DAVIS" GENERATOR.] + +_Maker:_ SUNLIGHT GAS MACHINE CO., 49 WARREN STREET, NEW YORK. + +_Type:_ Automatic; carbide-to-water. + +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 +_B_, 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. + +[Illustration: FIG. 27.--"OMEGA" GENERATOR.] + +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. + +AUSTRIA-HUNGARY + +_Maker:_ RICH. KLINGER, GUMPOLDSKIRCHEN, NEAR VIENNA. + +_Type:_ Non-automatic; carbide-to-water. + +The generating plant made by this firm consists of the generator _A_ +which is supported in a concrete water and sludge tank _B_, a +storage gasholder _J_, and purifiers _K_. In the top of the +generator are guide-ways _F_, through each of which is passed a +plunger _C_ containing a perforated cage charged with about 8 lb. of +lump carbide. The plungers are supported by ropes passing over pulleys +_D_, and when charged they are lowered through the guide-ways +_F_ into the water in the tank _B_. 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 _G_ to the +condenser _H_ and thence to the storage gasholder _J_. 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 _f_ through which gas will blow and escape by +a pipe _g_ to the open should the pressure within the apparatus +exceed the depth of the seal, viz., about 9 inches. There is a syphon pot +_N_ for the collection and withdrawal of condensed water. The sludge +is allowed to accumulate in the bottom of the concrete tank _B_ +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 _K_, 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 _L_ to the service- +pipes. + +[Illustration: FIG. 28.--KLINGER'S GENERATING PLANT.] + +BELGIUM. + +_Maker_: SOC. AN. DE L'ACETYLITHE, 65 RUE DU MARCHE, BRUSSELS. + +_Type_: Automatic; contact. + +The generating apparatus made by this firm uses, instead of ordinary +carbide, a preparation known as "acetylithe," 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 +_A_ with conical base, a basket _C_ containing the treated +carbide inserted within a cylindrical case _B_ which is open at the +bottom and is surmounted by a cylindrical filter _D_. At starting, +the tank _A_ is filled with water to the level _N N'_. 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 _D_, which is packed with dry cotton-wool, and +escapes through the tap _M_. As soon as the contained air has been +displaced by gas the outlet of the tap _M_ is connected by a +flexible tube to the pipe leading to a purifier and the service-pipe. +When the tap _M_ is closed, or when the rate of evolution of the gas +exceeds the rate of consumption, the evolved gas accumulates within the +cylindrical case _B_ and begins to displace the water, the level of +which within the case is lowered from _S S'_, first to _S1 S'1_ +and ultimately to, say, _S2 S'2_. 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 _N1 N'1_ and ultimately to, say _N2 N'2_. 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 _R_. The +cover _T_ of the filter is screwed down on rubber packing until gas- +tight. The purifier is charged with puratylene or other purifying +material. + +[Illustration: FIG. 29.--ACETYLITHE GENERATOR.] + +_Maker_: L. DEBRUYNE, 22 PLACE MASUI, BRUSSELS. + +_Type_: (1) Automatic; carbide-to-water. + +The generating plant made by this firm, using granulated carbide, +comprises an equalising gasholder _E_ alongside a generating tank +_B_, which is surmounted by a closed carbide receptacle _A_ and +a distributing appliance. The carbide receptacle is filled with +granulated carbide and the lid _N_ 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 _H_ attached to the bell _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 _J_ and seal-pot _D_, or bypass _F_, to +the gasholder. The generating tank is provided with a funnel _G_ for +replacing the water consumed, a sludge-stirrer and a draw-off cock +_L_, and a water-level cock _C_. The gas passes from the +gasholder through a purifier _K_, charged with heratol, to the +service-pipe. + +[Illustration: FIG. 30.--L. DEBRUYNE'S GENERATING PLANT FOR GRANULATED +CARBIDE.] + +(2) Automatic; carbide-to-water. + +The "Debruyne" generator comprises an equalising bell gasholder _A_ +placed alongside a generating tank _B_ 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 _C_, 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 _E_ attached to the +bell _G_ of the gasholder, which sets the mechanism in motion when +the bell has fallen nearly to its lowest position. The lip _L_ +serves for renewing the water in the generator, and the gas evolved goes +through the pipe _K_ with tap _F_ 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 _J_ to the +purifier _H_, charged with heratol, and thence to the service-pipe. + +[Illustration: FIG. 3l.--THE "DEBRUYNE" GENERATING PLANT FOR LUMP +CARBIDE.] + +_Maker_: DE SMET VAN OVERBERGE, ALOST. + +_Type_: (1) Automatic; carbide-to-water. + +This generating apparatus comprises an equalising gasholder _A_ +placed alongside a generating tank _B_, above which is mounted on a +rotating spindle a series of chambers _C_, 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 _D_ 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 +_E_ and having a weight _F_ 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 _G_ at the bottom of the generating tank. The gas passes +from the gasholder through a purifier _H_, which is ordinarily +charged with puratylene. + +[Illustration: FIG. 32.--AUTOMATIC GENERATING PLANT OF DE SMET VAN +OVERBERGE.] + +(2) Non-automatic; carbide-to-water. + +This apparatus comprises a storage bell gasholder _J_ placed +alongside a generating tank in the top of which is a funnel _E_ with +a counter-weighted lever pivoted on the arm _B_. The base of the +funnel is closed by a flap valve _C_ hinged at _D_. When it is +desired to generate gas the counter-weight _A_ 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 _G_ to the gasholder, whence it passes through a +purifier to the service-pipe. There is a sludge-cock on the generating +tank. + +[Illustration: FIG. 33.--NON-AUTOMATIC GENERATING PLANT OF DE SMET VAN +OVERBERGE.] + +_Maker_: SOC. AN. BELGE DE LA PHOTOLITHE, 2 RUE DE HUY, LIEGE. + +_Type_: Automatic; carbide-to-water. + +The "Photolithe" generating plant made by this firm comprises an +equalising bell gasholder _A_ in the tank _O_, alongside a +generating tank _B_ 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 _b_. Round the pulley +passes a chain, one end of which carries a weight _n_, 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 _b_ and therewith an arm _d_, 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 _C_ into the generating tank _B_. The gas +evolved passes through the cock _R_ and the pipe _T_ 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 _f_. The arm _d_ 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 _E_, which is +provided with a sludge draw-off cock _S_ and a hand-hole _P_. +Between the generating tank proper and the sludge receptacle is a grid, +which is cleaned by means of a rake with handle _L_. The gas passes +from the gasholder through a purifier _H_ charged with puratylene, +to the service-pipe. + +[Illustration: FIG. 34.--"PHOTOLITHE" GENERATING PLANT.] + +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. + +FRANCE. + +_Maker_: LA SOC. DES APPLICATIONS DE L'ACETYLENE, 26 RUE CADET, +PARIS. + +_Type_: Automatic; carbide-to-water. + +The "Javal" generating plant made by this firm consists of an equalising +bell gasholder _A_ in the tank _B_ with a series of buckets +_D_, with removable bottoms _h_, mounted on a frame _F_ +round the guide framing of the holder. Alongside the gasholder stands the +generating tank _H_ with shoot _K_, into which the carbide +discharged from the buckets falls. On top of the generator is a tipping +water-bucket _I_ supplied with water through a ball cock. The bell +of the gasholder is connected by chains _a_ and _c_, and levers +_b_ and _d_ 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. + +[Illustration: FIG. 35.--"JAVAL" GENERATOR.] + +The carbide falling from the opened bucket strikes the end _i_ of +the lever _k_, and thereby tips the water-bucket _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_, lifts the float _L_ and therewith, through +the attached rod and chain _u_, the ball _s_ of the valve +_t_. The sludge, which has accumulated in the base _N_ 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 _L_ has sunk to its +original level. The gas evolved passes from the generator through the +seal-pot _M_ and the pipe _r_ with cock _q_ into the +gasholder, from which it passes through the pipe _x_; with +condensation chamber and discharge tap _y_ into the purifier +_R_, which is charged with heratol. + +_Maker_: L'HERMITE, LOUVIERS, EURE. + +_Type_: (1) Automatic; carbide-to-water. + +The generating plant known as "L'Eclair," by this firm comprises an +equalising bell gasholder _A_ floating in an annular water-seal +_N_, formed in the upper part of a generating tank _B_ into +which carbide enters through the shoot _K_. Mounted at the side of +the tank is the carbide delivery device, which consists of the carbide +containers _J_ supported on an axis beneath the water-sealed cover +_H_. The containers are filled with ordinary lump carbide when the +cover _H_ is removed. The tappet _O_ 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 _J_. +Each time the bell falls and the tappet strikes the pawl, one compartment +of the carbide containers discharges its contents down the shoot _K_ +into the generating tank _B_. The gas evolved passes upwards and +causes the bell _A_ to rise. The gas is prevented from rising into +the shoot by the deflecting plates _G_. The natural level of the +water in the generating tank, when the apparatus is in use, is shown by +the dotted lines _L_. The lime sludge is discharged from time to +time through the cock _E_, being stirred up by means of the agitator +_C_ with handle _D_. When the sludge is discharged water is +added through _M_ to the proper level. The gas evolved passes from +the holder through the pipe with tap _F_ to the service-pipe. A +purifier is supplied if desired. + +[Illustration: FIG. 36.--"L'ECLAIR," GENERATOR.] + +_References_ + +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. + +(2) Automatic; water-to-carbide; contact. + +A generating plant known as "L'Etoile" 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. + +_Maker_: MAISON SIRIUS, FR. MANGIAMELI & CO., 34 RUE DES PETITS- +HOTELS, PARIS. + +_Type_: (1) Automatic; carbide-to-water. + +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 _A_ is divided into +eight chambers _a_ 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 _B_ into the +generating tank, which is filled with water to the level of the overflow +cock _b_. A deflecting plate _d_ in the tank distributes the +carbide and prevents the evolved gas passing out by way of the funnel +_B_. The gas evolved passes through the pipe _O_ into the +condenser, which is packed with coke, through which the gas goes to the +pipe _E_ and so to the washer _P_ through the water, in which +it bubbles and issues by the pipe _G_ into the gasholder. The bell +_L_ of the gasholder is connected by a chain _C_ to the axis of +the drum _A_, 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 _B_. 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_, 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 _J_, with cock _e_, +to the purifier, which is charged with frankoline, puratylene, or other +purifying material, whence it passes to the pipe _N_ leading to the +place of combustion. The generating tank is provided with a sludge-cock +_g_, and a cleaning opening with lid _f_. 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. + +[Illustration: FIG. 37.--"SIRIUS" GENERATOR.] + +(2) Automatic; carbide-to-water. + +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. + +GERMANY. + +_Maker_: KELLER AND KNAPPICH, G.m.b.H., AUGSBURG. + +_Type_: Non-automatic; carbide-to-water. + +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 deg. 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). + +[Illustration: FIG. 38.--"KNAPPICH" GENERATING PLANT.] + +_Maker_: NORDISCHE AZETYLEN-INDUSTRIE; ALTONA-OTTENSEN. + +_Type_: Automatic; water-to-carbide; "drawer." + +The apparatus made by this firm consists of an equalising gasholder with +bell _D_ and tank _E_, a water-tank _O_, and two drawer +generators _C_ situated in the base of the gasholder tank. The +water-supply from the tank _O_ through the pipe _P_ with valve +_Q_ is controlled by the rise and fall of the bell through the +medium of the weight _J_ attached to the bell. When the bell +descends this weight rests on _K_ and so moves a counter-weighted +lever, which opens the valve _Q_. The water then flows through the +nozzle _B_ into one division of the funnel _A_ 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 _T_ and through the seal _U_ into +the bell of the gasholder. There is a safety pipe _F_, the upper end +of which is carried outside the generator house. From the gasholder the +gas is delivered through the cock _M_ to a purifier charged with a +special purifying material mixed with cork waste and covered with +wadding. There is a drainage cock _N_ at the base of the purifier. +The nozzle _B_ of the water-supply pipe is shifted to discharge into +either compartment of the funnel _A_, 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. + +[Illustration: FIG. 39.--GENERATING PLANT OF THE NORDISCHE AZETYLEN- +INDUSTRIE.] + +GREAT BRITAIN AND IRELAND. + +_Maker:_ THE ACETYLENE CORPORATION OF GREAT BRITAIN LTD., 49 +VICTORIA STREET, LONDON, S.W. + +_Type:_ (1) Automatic; water-to-carbide; contact, superposed pans. + +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_. Into the generating +chamber fit a number of pans _J_, which are charged with carbide. +Water is supplied to the generating chamber from an overhead tank +_B_ through the starting tap _D_ and the funnel _E_. 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 _A_, 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 _C_ which, when the holder descends nearly to +its lowest point, depresses the rod _C_, which is connected by a +chain to a piston in the outlet-pipe from the water-tank _B_. The +fall of the gasholder thereby raises the piston and allows water to flow +out of the tank _B_ through the tap _D_ to the funnel _E_. +The generating tank is connected by a pipe, with tap _G_, with the +washer _A_, 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 _A_ and renewing the water in the +same. There is a sludge discharging tap _F_. 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 _H_ by which the level of the water +in the washer is automatically kept constant. The gasholder is provided +with a safety-pipe _K_, 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 _B_ 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 _B_ 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. + +[Illustration: FIG. 40.--THE "A1" GENERATING PLANT OF THE ACETYLENE +CORPORATION OF GREAT BRITAIN, LTD.] + +(2) Automatic; water-to-carbide; contact. + +The same firm also makes the "Corporation Flexible-Tube Generator," which +is less costly than the "A1" (_vide supra_). 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. + +(3) Automatic; water-to-carbide; "drawer." + +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. + +_Maker_: THE ACETYLENE GAS AND CARBIDE OF CALCIUM CO., PONTARDAWE, +R.S.O., GLAM. + +_Type_: Automatic; water-to-carbide; flooded compartment. + +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. + +[Illustration: FIG. 41.--"OWENS" GENERATOR.] + +_Maker_ ACETYLENE ILLUMINATING CO, LTD, 268-270 SOUTH LAMBETH ROAD, +LONDON, SW + +_Type_ (1) Non automatic, carbide to water + +The generator _A_ of this type made by this firm is provided with a +loading box _B_, with gas tight lid, into which the carbide is put. +It is then discharged by moving a lever which tilts the hinged bottom +_D_ of the box _B_, and so tips the carbide through the shoot +_E_ on to the conical distributor _F_ and into the water in the +generating chamber. There is a sludge cock _G_ 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. + +[Illustration: FIG. 42.--CARBIDE-TO-WATER GENERATOR OF THE ACETYLENE +ILLUMINATING CO., LTD.] + +(2) Non-automatic; water-to-carbide; contact. + +The generator _A_ 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 _E_ to +the washer _B_, which contains a distributor, and thence to the +storage gasholder _G_. There is a sludge-cock _F_ at the base +of the generator. From the gasholder the gas passes through the purifier +_D_, charged with heratol, to the service-pipe. + +[Illustration: FIG. 43.--WATER-TO-CARBIDE GENERATING PLANT OF THE +ACETYLENE ILLUMINATING CO., LTD.] + +_Maker_: THE ALLEN CO., 106 VICTORIA STREET, LONDON, S.W. + +_Type_: Automatic; water-to-carbide; contact, superposed trays. + +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. + +[Illustration: FIG. 44.--"ALLEN" FLEXIBLE-TUBE GENERATOR.] + +Maker: THE BON-ACCORD ACETYLENE GAS CO., 285 KING STREET, ABERDEEN. + +Type: Automatic; water-to-carbide; contact, superposed trays. + +The "Bon Accord" generating plant made by this firm comprises an +equalising displacement gasholder _B_ immersed in a water-tank +_A_. Alongside the tank are placed two water-jacketed generating +chambers _G1_ and _G2_ containing cages _K_ charged with +carbide. Water passes from within the gasholder through the water inlet- +pipes _L1 L2_, the cock _H_, and the pipes _F1 F2_ to the +generating chambers, from which the gas evolved travels to the holder +_B_, in which it displaces water until the water-level falls below +the mouths of the pipes _L1_ and _L2_, and so cuts off the +supply of water to the generating chambers. The gas passes from the +holder _B_ through the pipe with outlet-cock _T_ 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_ to show the amount of gas in the holder. +One generator may be charged while the other is in action. + +[Illustration: FIG. 45.--"BON-ACCORD" GENERATOR.] + +_Maker_: FREDK. BRABY AND CO., LTD., ASHTON GATE WORKS, BRISTOL; AND +352-364 EUSTON ROAD, LONDON. + +_Type:_ (I) Automatic; carbide-to-water. + +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_a_) of the lids of the +buckets in turn. There is fixed to the sides of the generator a funnel +(13) with open bottom (13_a_) 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_a_) and lower limb +(20_b_), 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_a_). 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. + +[Illustration: FIG. 46.--THE "A" GENERATOR OF FRED K. BRABY AND CO., +LTD.] + +(2) Automatic; water-to-carbide; contact, superposed trays. + +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. + +_Maker:_ THE DARGUE ACETYLENE GAS CO., 57 GREY STREET, NEWCASTLE-ON- +TYNE. + +_Type:_ Automatic; water-to-carbide; "drawer." + +The "Dargue" acetylene generator made by this firm comprises an +equalising bell gasholder _B_ floating in a water-tank _A_, +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 +_E_ and pipe _F_ 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 +_J_ to the second generating chamber. The taps _G_ and _H_ +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 _L_, terminating +in the dip-pipe _M_, 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 _N_ with main cock _R_ to the service- +pipes. The water-supply to the generator is controlled through the tap +_E_, which is operated by a chain connected to an arm attached to +the bell of the gasholder. + +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 _R_. 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. + +[Illustration: FIG. 47.--"DARGUE" GENERATOR.] + +_Maker_: J. AND J. DRUMMOND, 162 MARKET STREET, ABERDEEN. + +_Type_: Automatic; water-to-carbide; contact. + +The generating plant made by this firm comprises two or more generating +vessels _B_ 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 _A_ +through a pipe _C_, in which is a tap _F_ connected by a lever +and chain _L_ with the bell _G_ of the equalising gasholder +_H_, into which the evolved gas passes. The lever of the tap +_F_ is counter-weighted so that when the bell _G_ descends the +tap is opened, and when the bell rises the tap is closed. The gas passes +from the generating chambers _B_ through the pipe _D_ to the +washer-cooler _E_ and thence to the gasholder. From the latter it +passes through the dry purifier _J_ 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. + +[Illustration: FIG. 48.--J. AND J. DRUMMOND'S GENERATING PLANT.] + +_Agents_: FITTINGS, LTD., 112 VICTORIA STREET, S.W. + +_Type_: Automatic; carbide-to-water. + +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. + +_Maker_: LOCKERBIE AND WILKINSON, TIPTON, STAFFS. + +_Type_: (1) Automatic; water-to-carbide; contact, superposed trays. + +The "Thorscar" generator of this firm comprises an equalising gasholder, +the gas-space of the bell _B_ of which is reduced by conical upper +walls. When the bell descends and this lining enters the water in the +tank _A_ the displacement of water is increased and its level raised +until it comes above the mouths of the pipes _E_, through which a +portion then flows to the generators _D_. 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 _E_ 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 _E_. The generating chambers _D_ are +provided with movable cages _F_ in which the carbide is arranged on +trays. The gas evolved travels through a scrubbing-box _G_ +containing charcoal, and the pipe _J_ with drainage-pipe _P_ to +the water-seal or washer _K_ inside the holder, into which it then +passes. The outlet-pipe for gas from the holder leads through the +condensing coil _L_ immersed in the water in the tank to the +condensed water-trap _N_, and thence by the tap _Q_ to the +supply-pipe. The generating chambers are water-jacketed and provided with +gauge-glasses _H_ to indicate when recharging is necessary, and also +with sludge-cocks _M_. 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." + +[Illustration: FIG. 49.--"THORSCAR" GENERATOR.] + +(2) Non-automatic; water-to-carbide; "drawer." + +This generating plant, the "Thorlite," comprises a water-tank _A_ +from which water is admitted to the drawer generating chambers _B_, +one of which may be recharged while the other is in operation. The gas +evolved passes through a seal _C_ to the gasholder _D_, whence +it issues as required for use through the purifier _E_ 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. + +[Illustration: FIG. 50.--"THORLITE" GENERATING PLANT.] + +_Maker_: THE MANCHESTER ACETYLENE GAS CO., LTD., ACRE WORKS, +CLAYTON, MANCHESTER. + +_Type_: Automatic; water-to-carbide; "drawer." + +The plant made by this firm comprises an equalising gasholder _A_ +from the tank of which water is supplied to generating cylinders _B_ +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 _C_ carried by a +chain _D_ from one end of a lever _E_ 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 _C_, coming upon the +lever _E_, raises the rod _F_, which thereupon opens the valve +_G_, which then allows water to flow from the gasholder tank through +the pipe _H_ 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 _C_ and thus closes the water supply-valve _G_. The +gas evolved passes through vertical condensers _J_ into washing- +boxes _K_, which are placed within the tank. The gas issues from the +washing-boxes into the gasholder bell, whence it is withdrawn through the +pipe _L_ which leads to the purifier. Puratylene is the purifying +material ordinarily supplied by this firm. + +[Illustration: FIG. 51.--GENERATING PLANT OF THE MANCHESTER ACETYLENE GAS +CO., LTD.] + +_Maker:_ R,. J. MOSS AND SONS, 98 SNOW HILL, BIRMINGHAM. + +_Type:_ (1) Automatic; water-to-carbide; superposed trays. + +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. + +[Illustration: FIG. 52.--"MOSS TYPE A" GENERATOR.] + +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. + +[Illustration: FIG 53.--"MOSS TYPE B" GENERATOR.] + +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. + +[Illustration: FIG 54.--"MOSS TYPE C" GENERATOR.] + +(2) Semi-automatic; water-to-carbide; superposed trays. + +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. + +The original form of the "Acetylite" generator (_vide infra_) +adapted for lantern use is also obtainable of R. J. Moss and Sons. + +_Maker:_ WM. MOYES AND SONS, 115 BOTHWELL STREET, GLASGOW. + +_Type:_ 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. + +[Illustration: FIG. 55.--"ACETYLITE" GENERATOR.] + +_Maker_: THE PHOS CO., 205 AND 207 BALLS POND ROAD, LONDON, N. +_Type_: Non-automatic; water-to-carbide; drip. + +The type "E" generator made by this firm consists of a generating chamber +placed below a water chamber having an opening with cap _E_ for +refilling. The generating chamber in closed by a door _B_, with +rubber washer _C_, held in position by the rod _A_, the ends of +which pass into slots, and the screw _A'_. The movable carbide +chamber _D_ has its upper perforated part half filled with carbide, +which is pressed upwards by a spring _D'_. The carbide chamber when +filled is placed in the generating chamber, which is closed, and the +lever _F_ of one of the taps _F'_ 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. + +[Illustration: FIG. 56.--"PHOS TYPE E" GENERATOR.] + +_Maker:_ ROSCO ACETYLENE COMPANY, BELFAST. + +_Type:_ Non-automatic; carbide-to-water + +The "Rosco" generating plant made by this firm comprises a generating +tank _A_ which is filled with water to a given level by means of the +funnel-mouthed pipe _B_ and the overflow _O_. On the top of the +water-sealed lid of the generating tank is mounted the carbide feed-valve +_L_, which consists of a hollow plug-tap with handle _M_. When +the handle _M_ 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 _E_ on to the tray _N_ in the water in the +generating tank. The gas evolved passes through the scrubber and seal-pot +_J_ to the storage gasholder _Q_. From the latter the gas +passes through the dry purifier _T_ to the service-pipe. A sludge- +cock _P_ 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." + +[Illustration: FIG. 57.--"ROSCO" GENERATING PLANT.] + +_Maker_: THE RURAL DISTRICTS GAS LIGHT CO., 28 VICTORIA STREET, S.W. + +_Type_: Automatic; water-to-carbide; contact, superposed trays. + +The "Signal-Arm" generating apparatus made by this firm comprises a bell +gasholder _A_, from the tank _B_ of which water is supplied +through a swivelled pipe _C_ to a generating chamber _D_. 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 +_E_ 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 _F_ 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 _G_, 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 _H_ 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 _J_ in the +gas connexion, which, when the gasholder is shut off from the generator, +brings the latter into communication with a vent-pipe _K_ leading to +the open. The gas passes from the holder to a chamber _L_ 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. + +[Illustration: FIG. 58.--"SIGNAL-ARM" GENERATING PLANT.] + +_Maker_: ST. JAMES' ILLUMINATING CO., LTD., 3 VICTORIA STREET, +LONDON, S.W. + +_Type_: (1) Automatic; water-to-carbide; contact, superposed trays. + +This plant consists of the generators _A_, the washer _B_, the +equalising gasholder _C_, the purifier _D_, and the water-tank +_E_. The carbide is arranged in baskets in the generators to which +water is supplied from the cistern _E_ through the pipe _F_. +The supply is controlled by means of the valve _H_, which is +actuated through the rod _G_ by the rise and fall of the gasholder +_C_. Gas travels from the gasholder through the purifier _D_ to +the service-pipe. The purifier is packed with heratol resting on a layer +of pumice. The washer _B_ contains a grid, the object of which is to +distribute the stream of gas through the water. There is a syphon-pot +_J_ for the reception of condensed moisture. Taps _K_ are +provided for shutting off the supply of water from the generators during; +recharging, and there is an overflow connexion _L_ for conveying the +water to the second generator as soon as the first is exhausted. There is +a sludge-cock _M_ at the base of each generator. + +(2) Non-automatic; water-to-carbide; contact, superposed trays. + +This resembles the preceding plant except that the supply of water from +the cistern to the generators takes place directly through the pipe +_N_ (shown in dotted lines in the diagram) and is controlled by hand +through the taps _K_. The automatic control-valve _H_ and the +rod _G_ are omitted. The gasholder _C_ is increased in size so +that it becomes a storage holder capable of containing the whole of the +gas evolved from one charging. + +[Illustration: FIG. 59.--GENERATING PLANT OF THE ST. JAMES' ILLUMINATING +CO., LTD. (SECTIONAL ELEVATION AND PLAN.)] + +_Maker_: THE STANDARD ACETYLENE CO., 123 VICTORIA STREET, LONDON, +S.W. + +_Type_: (1) Non-automatic; carbide-to-water. + +This plant comprises the generator _A_, the washer _B_, the +storage gasholder _C_, and the purifier _D_. 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 _P_. 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 +_G_. The gas passes from the generator through the pipe _H_ +into the washer _B_, and after bubbling through the water therein +goes by way of the pipe _K_ into the gasholder _C_. The syphon- +pot _E_ is provided for the reception of condensed moisture, which +is removed from time to time by the pump _M_. From the gasholder the +gas flows through the valve _R_ to the purifier _D_, whence it +passes to the service-pipes. The purifier is charged with material +supplied under the proprietary name of "Standard." + +[Illustration: FIG. 60.--CARBIDE-TO-WATER GENERATING PLANT OF THE STANDARD +ACETYLENE CO.] + +(2) Automatic; water-to-carbide; contact, superposed trays. + +This plant comprises the generators _A_, the washer _B_, the +equalising gasholder _C_, the purifier _D_, and the water-tank +_E_. The carbide is arranged on a series of wire trays in each +generator, to which water is supplied from the water-tank _E_ +through the pipe _Y_ and the control-tap _U_. The gas passes +through the pipes _H_ to the washer _B_ and thence to the +holder _C_. The supply of water to the generators is controlled by +the tap _U_ which is actuated by the rise and fall of the gasholder +bell through the rod _F_. The gas passes, as in the non-automatic +plant, through a purifier _D_ to the service-pipes. Taps _W_ +are provided for cutting off the flow of water to either of the +generators during recharging and an overflow pipe _h_ serves to +convey the water to the second generator as soon as the carbide in the +first is exhausted. A sludge-cook _G_ is put at the base of each +generator. + +[Illustration: FIG. 61.--AUTOMATIC, WATER-TO-CARBIDE GENERATING PLANT OF +THE STANDARD ACETYLENE CO.] + +(3) Non-automatic; water-to-carbide; contact, superposed-trays. + +This apparatus resembles the preceding except that the supply of water to +the generators is controlled by hand through the taps _W_, the +control valve _U_ being omitted, and the gasholder _C_ being a +storage holder of sufficient dimensions to contain the whole of the +acetylene evolved from one charging. + +_Maker_: THORN AND HODDLE ACETYLENE CO., 151 VICTORIA STREET, S.W. + +_Type_: Automatic; water-to-carbide; "drawer." + +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. + +[Illustration: FIG. 62.--"INCANTO" GENERATOR.] + +_Maker:_ WELDREN AND BLERIOT, 54 LONG ACRE, LONDON, W.C. + +_Type:_ Automatic; contact. + +This firm supplies the "Acetylithe" apparatus (_see_ Belgium). + + + +INDEX + +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 _Copper (alloyed)_ +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 _Generators (automatic)_ + +B + +Baking of carbide +Ball-sockets for acetylene, +Barium peroxide purifier, + sulphate in bleaching-powder, +Barrel, gas, for acetylene, quality of +Bell gasholders. See _Holders (rising)_ +Benz purifying material, +Benzene, + for carburetting acetylene, + production of, from acetylene, +Benzine. See _Petroleum spirit_ +Berge, 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 _Vent-pipes_ +Blowpipe, acetylene, +Boiling-ring, +Boistelle. See _Molet_ +Borek, enrichment of oil-gas, +_Bougie decimale_, +Brackets for acetylene, +Bradley, Read, and Jacobs, calcium carbophosphide, +Brame and Lewes, manganese carbide, +Bray burners, +British Acetylene Association. See _Acetylene Association +(British)_, + Fire Offices Committee Regulations, + regulations. See _Acetylene Association (British); Home Office; + Orders in Council_ +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, + Fouche, + Guenther's, + illuminating power of, + Jacob, Gebrueder, + 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, + Phos, + 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, + Phos, + 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 _Residues_ + +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 _Cartridges_ + 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 _Illuminating power_ +Capelle, illuminating power of acetylene, +Carbide. See _Calcium carbide_ +Carbide-containers, + air in, + filling of, + partitions in, + water-jacketing, +Carbide-feed generators. See _Generators (carbide-to-water)_ +Carbide impurities in acetylene, +Carbide-to-water generators. See _Generators (carbide-to-water)_ +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 _Carbon dioxide_ +Carburetted acetylene, composition of, + effect of cold on, + illuminating power of, + manufacture of, + pecuniary value of, +Carburetted water-gas, enrichment of, +Carburine. See _Petroleum spirit_ +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 formulae, meaning of, +Chemical reactions and heat, + of acetylene, +Chimneys for stoves, &c., + glass, for burners, +Chloride of lime. See _Bleaching-powder_ +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 _Orders in Council_ +Counterpoises for rising holders, +Couples, galvanic, +Coward. See _Dixon_ +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 _Carbide containers_ +Decomposition of acetylene, + of carbide, See _Calcium carbide (decomposition of)_ +De Forcrand, heat of formation of carbide, +Density. See _Specific gravity_ +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 _Holders (displacement)_ +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, +epurene 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, +Fery, 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, +Formulae, meaning of chemical, +Fouche, absorbed acetylene, + burner, + dissolved acetylene, + illuminating power of acetylene air mixtures, + incandescent acetylene, + liquid acetylene, + oxy-acetylene blowpipe, +Fournier. See _Maneuvrier_ +Fowler, enrichment of oil-gas, +Fraenkel, deposit on reflectors from combustion of acetylene, + silicon in acetylene, +France, regulations of the Conseil d'Hygiene 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 _Holders_ +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 _Acetylene Association, German_) +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 _Calcium carbide, (granulated)_ +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, +Guentner 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 _Overheating_ + 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 _Overheating_) + on burners, + evolution of, in flames, + expansion of gaseous acetylene by, + liquid acetylene by, + from acetylene, production of, + latent. See _Latent heat_ + 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 _Specific heat_ +Heating apparatus for generator sheds, +Hefner unit, +Heil, atmospheric acetylene flame, + carburetted acetylene, +Heise, acetylene flame, +Hempel, enrichment of coal-gas, +Heratol, +Hess. See _Claude_ +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 _Orders in Council_ +Hoxie. See _Stewart_, +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 _Ammonia_ and _Sulphuretted hydrogen_ + in coal-gas, + in purified acetylene, + maximum limits of, +Incandescent acetylene, + burners. See _Burners (incandescent)_ + 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, Gebrueder, burner, +Jacobs. See _Bradley_ +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 _Eitner_ +Kerosene. See _Paraffin oil_ +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-Boernstein, solubility of acetylene in water, +Landriset. See _Rossel_ +Lantern, optical, illumination of, +Latent heat, +Lead chromate in bleaching-powder, + objection to, in generators, + pipes for acetylene, + salts in bleaching-powder, + wire, &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, +Lepinay, 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 _Residues_ + solubility of, in sugar solutions, + water, solubility of gas in, +Lime-light, acetylene for the, +Limits, explosive, of acetylene, +Linde-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 _Burners, self-luminous_ +Lunge and Cedercreutz, determination of phosphorus in acetylene, + purification, +Luta burner, +Lutes for holders. See _Seals_ + +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 _Bullier_ +Marsh gas, enrichment with acetylene, + formed from acetylene, +Matignon. See _Berthelot_, +Mauricheau-Beaupre, epurene, + 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 Muench, ignition temperatures, +Mildew in vines, use of acetylene in, +Milk of lime, solubility of acetylene in, +Mineral oil for lighting. (See _Paraffin oil_) + 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, +Muench. See _Meyer_ +Muensterberg, 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 _Generators (non-automatic)_ +Non-luminous acetylene flame, appearance of, + burners. See _Burners (atmospheric)_ +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 _Paraffin oil_) +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 _Polymerisation_ +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 _Paraffin oil_ + 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, +Phos burners, +Phosphine, cause of deposit at burner orifices, + composition of, + in crude acetylene, + amount of, + toxicity of, +Phosphoretted hydrogen. See _Phosphine_ +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 _Vent-pipes_ + diameter of, and explosive limits, + vent. See _Vent-pipes_ (See also _Mains_) +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 _Overheating_ +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 _Governors_ +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 _Calcium oxide_ + +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 _Bradley_ +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'Hygiene 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 _Berge_ +Rising holders. See _Holders (rising)_ +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 _Regulations_ + +S + +Safety lamp, Davy's, for generator sheds, + valves. See _Vent-pipes_ +Sale of carbide, regulations as to, +Salt, common, in holder-seals, +Salzbergwerk Neu Stassfurt, production of tetrachlorethane, +Sampling carbide, +Sandmann. See _Hammerschmidt_ +Sansair burner, +Saulmann. See _Caro_ +Sawdust in bleaching-powder, +Scale, water, in generators, +Scented carbide, +Schiff. See _Fuchs_ +Schimek burner, +Schwander, carburetted acetylene, +Schwarz burners, +Seal-pots, +Seals (holder). See _Holder-seals_ +Seams in generator-making, +Self-luminous burners. See _Burners (self-luminous)_ +Sensible heat, +Separation of holder from generator, +Service-pipes. See _Mains_ +Shoot generators, +Silicon compounds, + in acetylene, + in carbide, +Sirius burner, +Slaked lime. See _Calcium hydroxide_ +Sludge. See _Residues_ +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 _Intensity, specific_ +Speed of reactions between carbide, water, and calcium hydroxide, + of purification, +Spent lime. See _Residues_ +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 _Willson_ +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. _See Holder (rising)_ +Temperature and heat, difference between, + correction of volumes for, + critical, of acetylene, + high, effect of, on acetylene. See _Polymerization_ + 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 _Calcium carbide (treated)_ +Trondol burner, +Tubes, diameter of, and explosive limits, +Tubes for acetylene. See _Mains_ +Tubing, flexible, for acetylene, +Typical generators, + +U + +Ullmax purifier, +Unaccounted-for gas, +Underwriters, United States Fire, +United States. See _America_ +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 Fery, 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 _Ammonia and Sulphuretted hydrogen_ +Water-to-carbide generators. See _Generators (water-to-carbide)_ +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, +Woehler, 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, + + +INDEX TO APPENDIX + +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, +"Acetylithe" generator, +Acetylithe, Soc. An. de l', +Allen Co., +"Allen" Flexible-tube generator, +"Allen" purifying material, +American generators, +Applications de l'Acetylene, 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'Eclair" generator, +"L'Etoile" 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 + +Phos Co., +"Phos 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, + + + + + + + +End of the Project Gutenberg EBook of Acetylene, The Principles Of Its +Generation And Use, by F. 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