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border-bottom: thin dotted red;} +ins.edcorr {text-decoration: none; border-bottom: thin solid red;} +ins.mycorr {text-decoration: none; border-bottom: thin dotted red;} + +/* page number */ + +span.pagenum {position: absolute; right: 2%; font-size: 95%; +font-weight: normal; font-style: normal; text-align: right; +text-indent: 0em;} +span.pagenum.left {right: 93%;} /* for Index */ + +/* Transcriber's Note */ + +div.mynote, p.mynote {background-color: #DDE; color: #000; +font-family: sans-serif; font-size: 90%;} +div.mynote {margin: 2em 5%; padding: .5em 1em 1em;} +p.mynote {margin: 1em 5%; padding: 1em;} +div.mynote a {text-decoration: none;} +div.index div.mynote p, table.toc p.mynote +{margin-left: 0; text-indent: 0; margin-top: 1em;} + + +div.endnote {padding: .5em 1em 1em; margin: 2em 1em; +border: 3px ridge #A9F;} +div.endnote, div.endnote td {font-family: sans-serif; font-size: 90%;} + +</style> +</head> + +<body> + +<pre> + +Project Gutenberg's Conversations on Chemistry, V. 1-2, by Jane Marcet + +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: Conversations on Chemistry, V. 1-2 + In Which the Elements of that Science Are Familiarly + Explained and Illustrated by Experiments + +Author: Jane Marcet + +Release Date: October 13, 2008 [EBook #26908] + +Language: English + +Character set encoding: UTF-8 + +*** START OF THIS PROJECT GUTENBERG EBOOK CONVERSATIONS ON CHEMISTRY, V. 1-2 *** + + + + +Produced by Louise Hope + + + + + +</pre> + +<div class="mynote"> +<p>Caution: DO NOT TRY THIS AT HOME.</p> + +<p><a name="start" id="start">This text</a> uses utf-8 (unicode) +file encoding. If the apostrophes and quotation marks in this paragraph +appear as garbage, you may have an incompatible browser or unavailable +fonts. First, make sure that the browser’s “character set” or “file +encoding” is set to Unicode (UTF-8). You may also need to change your +browser’s default font.</p> + +<p>The original book was published in two volumes. The format is +reproduced for this e-text, except that the author’s preface (originally +in Volume I) and the combined index (Volume II) are in this +introductory file.</p> + +<p>See the <a href="#endnotes">end of this file</a> for notes on +scientific terminology, spelling, Plates and chapter numbering.</p> + +</div> + + +<h1 class="two">CONVERSATIONS</h1> +<h1 class="seven">ON</h1> +<h1 class="one extended">CHEMISTRY;</h1> +<h1 class="seven">IN WHICH</h1> +<h1 class="three">THE ELEMENTS OF THAT SCIENCE</h1> +<h1 class="seven">ARE</h1> +<h1 class="five"><i>FAMILIARLY EXPLAINED</i></h1> +<h1 class="seven">AND</h1> +<h1 class="five">ILLUSTRATED BY EXPERIMENTS.</h1> + +<hr class="fat"> +<hr class="thin"> + +<h1 class="six">IN TWO VOLUMES.</h1> + +<hr class="thin"> +<hr class="fat"> + +<h1 class="six"><i>The Fifth Edition, revised, corrected, and +considerably enlarged.</i><br> + </h1> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<h1 class="five"><i>LONDON:</i></h1> +<h1 class="six">PRINTED FOR LONGMAN, HURST, REES, ORME, AND BROWN,<br> +PATERNOSTER-ROW.</h1> +<h1 class="five">1817.</h1> + +<div class="page"> + +<h6>Printed by A. Strahan,<br> +Printers-Street, London.</h6> + +</div> + +<div class="maintext"> + +<h3>ADVERTISEMENT.</h3> + +<hr class="thin"> +<hr class="fat"> + +<p><i><span class="firstword"><span class="firstletter">T</span>he</span> Author, in this fifth edition, has +endeavoured to give an account of the principal discoveries which have +been made within the last four years in Chemical Science, and of the +various important applications, such as the gas-lights, and the +miner’s-lamp, to which they have given rise. But in regard to doctrines +or principles, the work has undergone no material alteration.</i></p> + +<p class="smaller"><i>London</i>, <i>July</i>, 1817.</p> + + + + +<span class="pagenum">v</span> + +<h3><a name="preface" id="preface">PREFACE.</a></h3> + +<hr class="thin"> +<hr class="fat"> + +<p><span class="firstword"><span class="firstletter">I</span>n</span> venturing to offer to the public, and +more particularly to the female sex, an Introduction to Chemistry, the +author, herself a woman, conceives that some explanation may be +required; and she feels it the more necessary to apologise for the +present undertaking, as her knowledge of the subject is but recent, and +as she can have no real claims to the title of chemist.</p> + +<p>On attending for the first time experimental lectures, the author +found it almost impossible to derive any clear or satisfactory +information from the rapid demonstrations which are usually, and perhaps +necessarily, crowded into popular courses of this kind. But frequent +opportunities having +<span class="pagenum">vi</span> +afterwards occurred of conversing with a friend on the subject of +chemistry, and of repeating a variety of experiments, she became better +acquainted with the principles of that science, and began to feel highly +interested in its pursuit. It was then that she perceived, in attending +the excellent lectures delivered at the Royal Institution, by the +present Professor of Chemistry, the great advantage which her previous +knowledge of the subject, slight as it was, gave her over others who had +not enjoyed the same means of private instruction. Every fact or +experiment attracted her attention, and served to explain some theory to +which she was not a total stranger; and she had the gratification to +find that the numerous and elegant illustrations, for which that school +is so much distinguished, seldom failed to produce on her mind the +effect for which they were intended.</p> + +<p>Hence it was natural to infer, that familiar conversation was, in +studies of this kind, a most useful auxiliary source of +information; +<span class="pagenum">vii</span> +and more especially to the female sex, whose education is seldom +calculated to prepare their minds for abstract ideas, or scientific +language.</p> + +<p>As, however, there are but few women who have access to this mode of +instruction; and as the author was not acquainted with any book that +could prove a substitute for it, she thought that it might be useful for +beginners, as well as satisfactory to herself, to trace the steps by +which she had acquired her little stock of chemical knowledge, and to +record, in the form of dialogue, those ideas which she had first derived +from conversation.</p> + +<p>But to do this with sufficient method, and to fix upon a mode of +arrangement, was an object of some difficulty. After much hesitation, +and a degree of embarrassment, which, probably, the most competent +chemical writers have often felt in common with the most superficial, +a mode of division was adopted, which, though the most natural, +does not always admit of being +<span class="pagenum">viii</span> +strictly pursued—it is that of treating first of the simplest +bodies, and then gradually rising to the most intricate compounds.</p> + +<p>It is not the author’s intention to enter into a minute vindication +of this plan. But whatever may be its advantages or inconveniences, the +method adopted in this work is such, that a young pupil, who should +occasionally recur to it, with a view to procure information on +particular subjects, might often find it obscure or unintelligible; for +its various parts are so connected with each other as to form an +uninterrupted chain of facts and reasonings, which will appear +sufficiently clear and consistent to those only who may have patience to +go through the whole work, or have previously devoted some attention to +the subject.</p> + +<p>It will, no doubt, be observed, that in the course of these +Conversations, remarks are often introduced, which appear much too acute +for the young pupils, by whom +<span class="pagenum">ix</span> +they are supposed to be made. Of this fault the author is fully aware. +But, in order to avoid it, it would have been necessary either to omit a +variety of useful illustrations, or to submit to such minute +explanations and frequent repetitions, as would have rendered the work +tedious, and therefore less suited to its intended purpose.</p> + +<p>In writing these pages, the author was more than once checked in her +progress by the apprehension that such an attempt might be considered by +some, either as unsuited to the ordinary pursuits of her sex, or +ill-justified by her own recent and imperfect knowledge of the subject. +But, on the one hand, she felt encouraged by the establishment of those +public institutions, open to both sexes, for the dissemination of +philosophical knowledge, which clearly prove that the general opinion no +longer excludes women from an acquaintance with the elements of science; +and, on the other, she flattered herself that whilst the impressions +made upon her mind, by the wonders +<span class="pagenum">x</span> +of Nature, studied in this new point of view, were still fresh and +strong, she might perhaps succeed the better in communicating to others +the sentiments she herself experienced.</p> + +<p>The reader will soon perceive, in perusing this work, that he is +often supposed to have previously acquired some slight knowledge of +natural philosophy, a circumstance, indeed, which appears very +desirable. The author’s original intention was to commence this work by +a small tract, explaining, on a plan analogous to this, the most +essential rudiments of that science. This idea she has since abandoned; +but the manuscript was ready, and might, perhaps, have been printed at +some future period, had not an elementary work of a similar description, +under the tide of “Scientific Dialogues,” been pointed out to her, +which, on a rapid perusal, she thought very ingenious, and well +calculated to answer its intended object.</p> + +</div> + + +<h3><a name="contents" id="contents"> +CONTENTS</a></h3> + +<p class="mynote"> +Page numbers have been retained to give an idea of the relative length +of each Conversation.</p> + +<table class="toc" summary="contents"> +<tr> +<td class="chapnum"><a href="#conver1.pageconvI"> +CONVERSATION I.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE GENERAL PRINCIPLES OF CHEMISTRY.</td> +<td class="number">Page 1</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvII"> +CONVERSATION II.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON LIGHT AND HEAT.</td> +<td class="number">26</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvIII"> +CONVERSATION III.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">CONTINUATION OF THE SUBJECT.</td> +<td class="number">70</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvIV"> +CONVERSATION IV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT +AND LATENT HEAT.</td> +<td class="number">122</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvV"> +CONVERSATION V.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE CHEMICAL AGENCIES OF ELECTRICITY.</td> +<td class="number">160</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvVI"> +CONVERSATION VI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON OXYGEN AND NITROGEN.</td> +<td class="number">181</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvVII"> +CONVERSATION VII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON HYDROGEN.</td> +<td class="number">214</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvVIII"> +CONVERSATION VIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON SULPHUR AND PHOSPHORUS.</td> +<td class="number">256</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvIX"> +CONVERSATION IX.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON CARBON.</td> +<td class="number">282</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver1.pageconvX"> +CONVERSATION X.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON METALS.</td> +<td class="number">314</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXIII"> +CONVERSATION XIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE ATTRACTION OF COMPOSITION.</td> +<td class="number">1</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXIV"> +CONVERSATION XIV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ALKALIES.</td> +<td class="number">19</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXV"> +CONVERSATION XV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON EARTHS.</td> +<td class="number">44</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXVI"> +CONVERSATION XVI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ACIDS.</td> +<td class="number">69</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXVII"> +CONVERSATION XVII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname long"><p>OF THE SULPHURIC AND PHOSPHORIC ACIDS: +OR, THE COMBINATIONS OF OXYGEN WITH SULPHUR AND WITH PHOSPHORUS; AND OF +THE SULPHATS AND PHOSPHATS.</p></td> +<td class="number">80</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXVIII"> +CONVERSATION XVIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname long"><p>OF THE NITRIC AND CARBONIC ACIDS: OR THE +COMBINATION OF OXYGEN WITH NITROGEN AND WITH CARBON; AND OF THE NITRATS +AND CARBONATS.</p></td> +<td class="number">100</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXIX"> +CONVERSATION XIX.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED +MURIATIC ACIDS; AND ON MURIATS.</td> +<td class="number">131</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXX"> +CONVERSATION XX.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE NATURE AND COMPOSITION OF VEGETABLES.</td> +<td class="number">162</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXXI"> +CONVERSATION XXI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE DECOMPOSITION OF VEGETABLES.</td> +<td class="number">202</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXXII"> +CONVERSATION XXII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">HISTORY OF VEGETATION.</td> +<td class="number">243</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXXIII"> +CONVERSATION XXIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE COMPOSITION OF ANIMALS.</td> +<td class="number">276</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXXIV"> +CONVERSATION XXIV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE ANIMAL ECONOMY.</td> +<td class="number">297</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXXV"> +CONVERSATION XXV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ANIMALISATION, NUTRITION, AND +RESPIRATION.</td> +<td class="number">314</td> +</tr> + +<tr> +<td class="chapnum"><a href="#conver2.pageconvXXVI"> +CONVERSATION XXVI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ANIMAL HEAT; AND OF VARIOUS ANIMAL +PRODUCTS.</td> +<td class="number">336</td> +</tr> +</table> + + +<div class="page"> + +<span class="pagenum">I.xvi</span> + +<h5>ERRATA.</h5> + +<table class="smaller" summary="errors"> +<tr> +<td class="number">Vol. I. page 56.</td> +<td>last line but one, for “caloric,” read “calorific.”</td> +</tr> +<tr> +<td class="number">179.</td> +<td>Note, for “Plate XII.” r. “Plate XIII.”</td> +</tr> +</table> + +</div> + +<hr><hr> + +<h1 class="two">CONVERSATIONS</h1> +<h1 class="seven">ON</h1> +<h1 class="one extended">CHEMISTRY;</h1> +<h1 class="seven">IN WHICH</h1> +<h1 class="three">THE ELEMENTS OF THAT SCIENCE</h1> +<h1 class="seven">ARE</h1> +<h1 class="five"><i>FAMILIARLY EXPLAINED</i></h1> +<h1 class="seven">AND</h1> +<h1 class="five">ILLUSTRATED BY EXPERIMENTS.</h1> + +<hr class="fat"> +<hr class="thin"> + +<h1 class="six">IN TWO VOLUMES.</h1> + +<hr class="thin"> +<hr class="fat"> + +<h1 class="six"><i>The Fifth Edition, revised, corrected, and +considerably enlarged.</i><br> + </h1> + +<h1 class="four">VOL. I.</h1> +<h1 class="five">ON SIMPLE BODIES.</h1> + +<p class="illustration"> +<img src="images/dec_line.png" width="91" height="8" +alt="----"> +</p> + +<h1 class="five"><i>LONDON:</i></h1> +<h1 class="six">PRINTED FOR LONGMAN, HURST, REES, ORME, AND BROWN,<br> +PATERNOSTER-ROW.</h1> +<h1 class="five">1817.</h1> + +<p> <br> </p> + +<span class="pagenum">xi</span> + +<h3 class="three"><a name="contents1" id="contents1"> +CONTENTS</a></h3> +<h3 class="seven">OF</h3> +<h3 class="four"><i>THE FIRST VOLUME</i>.</h3> + +<hr class="fat"> +<hr class="thin"> + +<h3 class="five">ON SIMPLE BODIES.</h3> + +<hr class="thin"> +<hr class="fat"> + +<table class="toc" summary="table of contents"> +<tr> +<td class="chapnum"><a href="#convI"> +CONVERSATION I.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE GENERAL PRINCIPLES OF CHEMISTRY.</td> +<td class="number">Page 1</td> +</tr> +<tr> +<td><p>Connexion between Chemistry and Natural +Philosophy.—Improved State of modern Chemistry.—Its use in +the Arts.—The general Objects of Chemistry.—Definition of +Elementary Bodies.—Definition of Decomposition.—Integrant +and Constituent Particles.—Distinction between Simple and Compound +Bodies.—Classification of Simple Bodies.—Of Chemical +Affinity, or Attraction of Composition.—Examples of Composition +and Decomposition.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convII"> +CONVERSATION II.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON LIGHT AND HEAT.</td> +<td class="number">26</td> +</tr> +<tr> +<td><p>Light and Heat capable of being separated.—Dr. <ins +class="correction" title="body text has ‘Herschell’">Herschel’s</ins> +Experiments.—Phosphorescence.—Of Caloric.—Its two +Modifications.—Free Caloric.—Of the three +<span class="pagenum">xii</span> +<a name="conver1.pagexii" id="conver1.pagexii"> </a> +different States of Bodies, solid, fluid, and aeriform.—Dilatation +of solid Bodies.—Pyrometer.—Dilatation of +Fluids.—Thermometer.—Dilatation of Elastic Fluids.—Air +Thermometer.—Equal Diffusion of Caloric.—Cold a Negative +Quality.—Professor Prevost’s Theory of the Radiation of +Heat.—Professor Pictet’s Experiments on the Reflexion of +Heat.—Mr. Leslie’s Experiments on the Radiation of +Heat.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convIII"> +CONVERSATION III.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">CONTINUATION OF THE SUBJECT.</td> +<td class="number">70</td> +</tr> +<tr> +<td><p>Of the different Power of Bodies to conduct Heat.—Attempt +to account for this Power.—Count Rumford’s Theory of the +non-conducting Power of Fluids.—Phenomena of Boiling.—Of +Solution in general.—Solvent Power of Water.—Difference +between Solution and Mixture.—Solvent Power of Caloric.—Of +Clouds, Rain, Dr. Wells’ theory of Dew, Evaporation, +&c.—Influence of Atmospherical Pressure on +Evaporation.—Ignition.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convIV"> +CONVERSATION IV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT +AND LATENT HEAT.</td> +<td class="number">122</td> +</tr> +<tr> +<td><p>Of Specific Heat.—Of the different Capacities of Bodies for +Heat.—Specific Heat not perceptible by the Senses.—How to be +ascertained.—Of Latent Heat.—Distinction between Latent and +Specific Heat.—Phenomena attending the Melting of Ice and the +Formation of Vapour.—Phenomena attending the Formation of Ice, and +the Condensation of Elastic Fluids.—Instances of Condensation, and +consequent Disengagement of Heat, produced by Mixtures, by the Slaking +of Lime.—General +<span class="pagenum">xiii</span> +<a name="conver1.pagexiii" id="conver1.pagexiii"> </a> +Remarks on Latent Heat.—Explanation of the Phenomena of Ether +boiling, and Water freezing, at the same Temperature.—Of the +Production of Cold by +Evaporation.—Calorimeter.—Meteorological Remarks.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convV"> +CONVERSATION V.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE CHEMICAL AGENCIES OF ELECTRICITY.</td> +<td class="number">160</td> +</tr> +<tr> +<td><p>Of Positive and Negative Electricity.—Galvani’s +Discoveries.—Voltaic Battery.—Electrical +Machine.—Theory of Voltaic Excitement.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convVI"> +CONVERSATION VI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON OXYGEN AND NITROGEN.</td> +<td class="number">181</td> +</tr> +<tr> +<td><p>The Atmosphere composed of Oxygen and Nitrogen in the State of +Gas.—Definition of Gas.—Distinction between Gas and +Vapour.—Oxygen essential to Combustion and +Respiration.—Decomposition of the Atmosphere by +Combustion.—Nitrogen Gas obtained by this Process.—Of +Oxygenation in general.—Of the Oxydation of Metals.—Oxygen +Gas obtained from Oxyd of Manganese.—Description of a Water-Bath +for collecting and preserving Gases.—Combustion of Iron Wire in +Oxygen Gas.—Fixed and volatile Products of +Combustion.—Patent Lamps.—Decomposition of the Atmosphere by +Respiration.—Recomposition of the Atmosphere.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convVII"> +CONVERSATION VII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON HYDROGEN.</td> +<td class="number">214</td> +</tr> +<tr> +<td><p>Of Hydrogen.—Of the Formation of Water by the Combustion of +Hydrogen.—Of the Decomposition of Water. +<span class="pagenum">xiv</span> +<a name="conver1.pagexiii" id="conver1.pagexiv"> </a> +—Detonation of Hydrogen Gas.—Description of Lavoisier’s +Apparatus for the formation of Water.—Hydrogen Gas essential to +the Production of Flame.—Musical Tones produced by the Combustion +of Hydrogen Gas within a Glass Tube.—Combustion of Candles +explained.—Gas lights.—Detonation of Hydrogen Gas in Soap +Bubbles.—Air Balloons.—Meteorological Phenomena ascribed to +Hydrogen Gas.—Miner’s Lamp.</p> + +<p class="mynote"> +The final two pages of the Table of Contents for Volume I were +missing from the available text; everything after “Decomposition of +Water” was supplied from earlier and later editions, compared against +the body text. The section marked “Diamond” (Conv. IX) was called +“Diamond is +Carbon(e) in a state of perfect purity” in the 4th edn., “Diamond” +alone in later editions.</p> +</td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convVIII"> +CONVERSATION VIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON SULPHUR AND PHOSPHORUS.</td> +<td class="number">256</td> +</tr> +<tr> +<td><p>Natural History of +Sulphur.—Sublimation.—Alembic.—Combustion of Sulphur +in Atmospheric Air.—Of Acidification in +general.—Nomenclature of the Acids.—Combustion of Sulphur in +Oxygen Gas.—Sulphuric Acid.—Sulphurous +Acid.—Decomposition of Sulphur.—Sulphurated Hydrogen +Gas.—Harrogate, or Hydro-sulphurated +Waters.—Phosphorus.—History of its Discovery.—Its +Combustion in Oxygen Gas.—Phosphoric Acid.—Phosphorus +Acid.—Eudiometer.—Combination of Phosphorus with +Sulphur.—Phosphorated Hydrogen Gas.—Nomenclature of Binary +Compounds.—Phosphoret of Lime burning under Water.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convIX"> +CONVERSATION IX.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON CARBON.</td> +<td class="number">282</td> +</tr> +<tr> +<td><p>Method of obtaining pure Charcoal.—Method of making common +Charcoal.—Pure Carbon not to be obtained by +Art.—Diamond.—Properties of Carbon.—Combustion of +Carbon.—Production of Carbonic Acid Gas.—Carbon susceptible +of only one Degree of Acidification.—Gaseous Oxyd of +Carbon.—Of Seltzer Water and other Mineral +Waters.—Effervescence.—Decomposition of Water by +Carbon.—Of Fixed and Essential Oils.—Of the Combustion of +Lamps and Candles.—Vegetable Acids.—Of the Power of Carbon +to revive Metals.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convX"> +CONVERSATION X.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON METALS.</td> +<td class="number">314</td> +</tr> +<tr> +<td><p>Natural History of Metals.—Of Roasting, Smelting, +&c.—Oxydation of metals by the Atmosphere.—Change of +Colours produced by different degrees of Oxydation.—Combustion of +Metals.—Perfect Metals burnt by Electricity only.—Some +Metals revived by Carbon and other Combustibles.—Perfect Metals +revived by Heat alone.—Of the Oxydation of certain Metals by the +Decomposition of Water. Power of Acids to promote this +Effect.—Oxydation of Metals by Acids.—Metallic Neutral +Salts.—Previous oxydation of the Metal +requisite.—Crystallisation.—Solution distinguished from +Dissolution.—Five metals susceptible of +acidification.—Meteoric Stones.—Alloys, Soldering, Plating, +&c.—Of Arsenic, and of the caustic Effects of Oxygen.—Of +Verdigris, Sympathetic Ink, &c.—Of the new Metals discovered +by Sir H. Davy.</p></td> +<td></td> +</tr> +</table> + + +<div class="page"> + +<h2 class="two">CONVERSATIONS</h2> + +<h2 class="seven">ON</h2> + +<h2 class="one extended">CHEMISTRY.</h2> + +</div> + +<hr class="thin"> +<hr class="fat"> + +<div class="maintext"> + +<a name="conver1.page1" id="conver1.page1"> </a> + +<h4><a name="convI" id="convI">CONVERSATION I.</a><br> +<span class="subhead">ON THE GENERAL PRINCIPLES OF +CHEMISTRY.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstletter">A</span>S you have now acquired some +elementary notions of <span class="smallcaps">Natural +Philosophy</span>, I am going to propose to you another branch of +science, to which I am particularly anxious that you should devote a +share of your attention. This is <span class="smallcaps">Chemistry</span>, which is so closely connected with Natural +Philosophy, that the study of the one must be incomplete without some +knowledge of the other; for, it is obvious that we can derive but a very +imperfect idea of bodies from the study of the general laws by which +they are governed, if we remain totally ignorant of their intimate +nature.</p> + +<span class="pagenum">2</span> +<a name="conver1.page2" id="conver1.page2"> </a> +<p class="speaker">CAROLINE.</p> + +<p>To confess the truth, Mrs. B., I am not disposed to form a very +favourable idea of chemistry, nor do I expect to derive much +entertainment from it. I prefer the sciences which exhibit nature +on a grand scale, to those that are confined to the minutiæ of petty +details. Can the studies which we have lately pursued, the general +properties of matter, or the revolutions of the heavenly bodies, be +compared to the mixing up of a few insignificant drugs? I grant, +however, there may be entertaining experiments in chemistry, and should +not dislike to try some of them: the distilling, for instance, of +lavender, or rose water . . . . . .</p> + +<p class="speaker">MRS. B.</p> + +<p>I rather imagine, my dear Caroline, that your want of taste for +chemistry proceeds from the very limited idea you entertain of its +object. You confine the chemist’s laboratory to the narrow precincts of +the apothecary’s and perfumer’s shops, whilst it is subservient to an +immense variety of other useful purposes. Besides, my dear, chemistry is +by no means confined to works of art. Nature also has her laboratory, +which is the universe, and there she is incessantly employed in chemical +operations. You are surprised, Caroline, but I assure you that the most +wonderful and the most interesting phenomena of nature are +<span class="pagenum">3</span> +<a name="conver1.page3" id="conver1.page3"> </a> +almost all of them produced by chemical powers. What Bergman, in the +introduction to his history of chemistry, has said of this science, will +give you a more just and enlarged idea of it. The knowledge of nature +may be divided, he observes, into three periods. The first was that in +which the attention of men was occupied in learning the external forms +and characters of objects, and this is called <i>Natural History</i>. In +the second, they considered the effects of bodies acting on each other +by their mechanical power, as their weight and motion, and this +constitutes the science of <i>Natural Philosophy</i>. The third period +is that in which the properties and mutual action of the elementary +parts of bodies was investigated. This last is the science of <span +class="smallcaps">Chemistry</span>, and I have no doubt you will soon +agree with me in thinking it the most interesting.</p> + +<p>You may easily conceive, therefore, that without entering into the +minute details of practical chemistry, a woman may obtain such a +knowledge of the science as will not only throw an interest on the +common occurrences of life, but will enlarge the sphere of her ideas, +and render the contemplation of nature a source of delightful +instruction.</p> + +<p class="speaker">CAROLINE.</p> + +<p>If this is the case, I have certainly been much +<span class="pagenum">4</span> +<a name="conver1.page4" id="conver1.page4"> </a> +mistaken in the notion I had formed of chemistry. I own that I +thought it was chiefly confined to the knowledge and preparation of +medicines.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is only a branch of chemistry which is called Pharmacy; and, +though the study of it is certainly of great importance to the world at +large, it belongs exclusively to professional men, and is therefore the +last that I should advise you to pursue.</p> + +<p class="speaker">EMILY.</p> + +<p>But, did not the chemists formerly employ themselves in search of the +philosopher’s stone, or the secret of making gold?</p> + +<p class="speaker">MRS. B.</p> + +<p>These were a particular set of misguided philosophers, who dignified +themselves with the name of Alchemists, to distinguish their pursuits +from those of the common chemists, whose studies were confined to the +knowledge of medicines.</p> + +<p>But, since that period, chemistry has undergone so complete a +revolution, that, from an obscure and mysterious art, it is now become a +regular and beautiful science, to which art is entirely subservient. It +is true, however, that we are indebted to the alchemists for many very +useful discoveries, which sprung from their fruitless attempts +<span class="pagenum">5</span> +<a name="conver1.page5" id="conver1.page5"> </a> +to make gold, and which, undoubtedly, have proved of infinitely greater +advantage to mankind than all their chimerical pursuits.</p> + +<p>The modern chemists, instead of directing their ambition to the vain +attempt of producing any of the original substances in nature, rather +aim at analysing and imitating her operations, and have sometimes +succeeded in forming combinations, or effecting decompositions, no +instances of which occur in the chemistry of Nature. They have little +reason to regret their inability to make gold, whilst, by their +innumerable inventions and discoveries, they have so greatly stimulated +industry and facilitated labour, as prodigiously to increase the +luxuries as well as the necessaries of life.</p> + +<p class="speaker">EMILY.</p> + +<p>But, I do not understand by what means chemistry can facilitate +labour; is not that rather the province of the mechanic?</p> + +<p class="speaker">MRS. B.</p> + +<p>There are many ways by which labour may be rendered more easy, +independently of mechanics; but even the machine, the most wonderful in +its effects, the Steam-engine, cannot be understood without the +assistance of chemistry. In agriculture, a chemical knowledge of +the nature of soils, and of vegetation, is highly useful; and, in those +<span class="pagenum">6</span> +<a name="conver1.page6" id="conver1.page6"> </a> +arts which relate to the comforts and conveniences of life, it would be +endless to enumerate the advantages which result from the study of this +science.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, pray, tell us more precisely in what manner the discoveries of +chemists have proved so beneficial to society?</p> + +<p class="speaker">MRS. B.</p> + +<p>That would be an injudicious anticipation; for you would not +comprehend the nature of such discoveries and useful applications, as +well as you will do hereafter. Without a due regard to method, we cannot +expect to make any progress in chemistry. I wish to direct your +observations chiefly to the chemical operations of Nature; but those of +Art are certainly of too high importance to pass unnoticed. We shall +therefore allow them also some share of our attention.</p> + +<p class="speaker">EMILY.</p> + +<p>Well, then, let us now set to work regularly. I am very anxious +to begin.</p> + +<p class="speaker">MRS. B.</p> + +<p>The object of chemistry is to obtain a knowledge of the intimate +nature of bodies, and of their mutual action on each other. You find +therefore, +<span class="pagenum">7</span> +<a name="conver1.page7" id="conver1.page7"> </a> +Caroline, that this is no narrow or confined science, which comprehends +every thing material within our sphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>On the contrary, it must be inexhaustible; and I am a loss to +conceive how any proficiency can be made in a science whose objects are +so numerous.</p> + +<p class="speaker">MRS. B.</p> + +<p>If every individual substance were formed of different materials, the +study of chemistry would, indeed, be endless; but you must observe that +the various bodies in nature are composed of certain elementary +principles, which are not very numerous.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes; I know that all bodies are composed of fire, air, earth, and +water; I learnt that many years ago.</p> + +<p class="speaker">MRS. B.</p> + +<p>But you must now endeavour to forget it. I have already informed +you what a great change chemistry has undergone since it has become a +regular science. Within these thirty years especially, it has +experienced an entire revolution, and it is now proved, that neither +fire, air, earth, nor water, can be called elementary bodies. For an +<span class="pagenum">8</span> +<a name="conver1.page8" id="conver1.page8"> </a> +elementary body is one that has never been decomposed, that is to say, +separated into other substances; and fire, air, earth, and water, are +all of them susceptible of decomposition.</p> + +<p class="speaker">EMILY.</p> + +<p>I thought that decomposing a body was dividing it into its minutest +parts. And if so, I do not understand why an elementary substance +is not capable of being decomposed, as well as any other.</p> + +<p class="speaker">MRS. B.</p> + +<p>You have misconceived the idea of <i>decomposition</i>; it is very +different from mere <i>division</i>. The latter simply reduces a body +into parts, but the former separates it into the various ingredients, or +materials, of which it is composed. If we were to take a loaf of bread, +and separate the several ingredients of which it is made, the flour, the +yeast, the salt, and the water, it would be very different from cutting +or crumbling the loaf into pieces.</p> + +<p class="speaker">EMILY.</p> + +<p>I understand you now very well. To decompose a body is to separate +from each other the various elementary substances of which it +consists.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But flour, water, and other materials of bread, +<span class="pagenum">9</span> +<a name="conver1.page9" id="conver1.page9"> </a> +according to our definition, are not elementary substances?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, my dear; I mentioned bread rather as a familiar comparison, to +illustrate the idea, than as an example.</p> + +<p>The elementary substances of which a body is composed are called the +<i>constituent</i> parts of that body; in decomposing it, therefore, we +separate its constituent parts. If, on the contrary, we divide a body by +chopping it to pieces, or even by grinding or pounding it to the finest +powder, each of these small particles will still consist of a portion of +the several constituent parts of the whole body: these are called the +<i>integrant</i> parts; do you understand the difference?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, I think, perfectly. We <i>decompose</i> a body into its +<i>constituent</i> parts; and <i>divide</i> it into its <i>integrant</i> +parts.</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so. If therefore a body consists of only one kind of +substance, though it may be divided into its integrant parts, it is not +possible to decompose it. Such bodies are therefore called <i>simple</i> +or <i>elementary</i>, as they are the elements of which all other bodies +are composed. <i>Compound +<span class="pagenum">10</span> +<a name="conver1.page10" id="conver1.page10"> </a> +bodies</i> are such as consist of more than one of these elementary +principles.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But do not fire, air, earth, and water, consist, each of them, but of +one kind of substance?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, my dear; they are every one of them susceptible of being +separated into various simple bodies. Instead of four, chemists now +reckon upwards of forty elementary substances. The existence of most of +these is established by the clearest experiments; but, in regard to a +few of them, particularly the most subtle agents of nature, <i>heat</i>, +<i>light</i>, and <i>electricity</i>, there is yet much uncertainty, and +I can only give you the opinion which seems most probably deduced from +the latest discoveries. After I have given you a list of the elementary +bodies, classed according to their properties, we shall proceed to +examine each of them separately, and then consider them in their +combinations with each other.</p> + +<p>Excepting the more general agents of nature, heat, light, and +electricity, it would seem that the simple form of bodies is that of a +metal.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You astonish me! I thought the metals were only +<span class="pagenum">11</span> +<a name="conver1.page11" id="conver1.page11"> </a> +one class of minerals, and that there were besides, earths, stones, +rocks, acids, alkalies, vapours, fluids, and the whole of the animal and +vegetable kingdoms.</p> + +<p class="speaker">MRS. B.</p> + +<p>You have made a tolerably good enumeration, though I fear not +arranged in the most scientific order. All these bodies, however, it is +now strongly believed, may be ultimately resolved into metallic +substances. Your surprise at this circumstance is not singular, as the +decomposition of some of them, which has been but lately accomplished, +has excited the wonder of the whole philosophical world.</p> + +<p>But to return to the list of simple bodies—these being usually +found in combination with oxygen, I shall class them according to +their properties when so combined. This will, I think, facilitate +their future investigation.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>A simple body; at least one that is supposed to be so, as it has +never been decomposed. It is always found united with the negative +electricity. It will be one of the first of the elementary bodies whose +properties I shall explain to you, and, as +<span class="pagenum">12</span> +<a name="conver1.page12" id="conver1.page12"> </a> +you will soon perceive, it is one of the most important in nature; but +it would be irrelevant to enter upon this subject at present. We must +now confine our attention to the enumeration and classification of the +simple bodies in general. They may be arranged as follows:</p> + +<h5>CLASS I.</h5> + +<p class="listhead"> +Comprehending the imponderable agents, viz.</p> + +<div class="list"> +<p><span class="smallroman">HEAT</span> or <span class="smallroman">CALORIC</span>,</p> +<p><span class="smallroman">LIGHT</span>,</p> +<p><span class="smallroman">ELECTRICITY</span>.</p> +</div> + +<h5>CLASS II.</h5> + +<p class="listhead long"> +Comprehending agents capable of uniting with inflammable bodies, and in +most instances of effecting their combustion.</p> + +<div class="list"> +<p><span class="smallroman">OXYGEN</span>,</p> +<p><span class="smallroman">CHLORINE</span>,</p> +<p><span class="smallroman">IODINE</span>.<a class="tag" name="tag1" id="tag1" href="#note1">*</a></p> +</div> + +<h5>CLASS III.</h5> + +<p class="listhead long"> +Comprehending bodies capable of uniting with oxygen, and, forming with +it various compounds. This class may be divided as follows:</p> + +<h6>DIVISION 1.</h6> + +<div class="list"> +<p><span class="smallroman">HYDROGEN</span>, <i>forming</i> +water.</p> +</div> + +<span class="pagenum">13</span> +<a name="conver1.page13" id="conver1.page13"> </a> +<h6>DIVISION 2.</h6> + +<p class="listhead"> +Bodies forming acids.</p> + +<table class="list" summary="list of substances"> +<tr> +<td><span class="smallroman">NITROGEN</span>,</td> +<td><i>forming</i> nitric acid.</td> +</tr> +<tr> +<td><span class="smallroman">SULPHUR</span>,</td> +<td><i>forming</i> sulphuric acid.</td> +</tr> +<tr> +<td><span class="smallroman">PHOSPHORUS</span>,</td> +<td><i>forming</i> phosphoric acid.</td> +</tr> +<tr> +<td><span class="smallroman">CARBON</span>,</td> +<td><i>forming</i> carbonic acid.</td> +</tr> +<tr> +<td><span class="smallroman">BORACIUM</span>,</td> +<td><i>forming</i> boracic acid.</td> +</tr> +<tr> +<td><span class="smallroman">FLUORIUM</span>,</td> +<td><i>forming</i> fluoric acid.</td> +</tr> +<tr> +<td><span class="smallroman">MURIATIUM</span>,</td> +<td><i>forming</i> muriatic acid.</td> +</tr> +</table> + +<h6>DIVISION 3.</h6> + +<p class="listhead"> +Metallic bodies forming alkalies.</p> + +<table class="list" summary="list of substances"> +<tr> +<td><span class="smallroman">POTASSIUM</span>,</td> +<td><i>forming</i> potash.</td> +</tr> +<tr> +<td><span class="smallroman">SODIUM</span>,</td> +<td><i>forming</i> soda.</td> +</tr> +<tr> +<td><span class="smallroman">AMMONIUM</span>,</td> +<td><i>forming</i> ammonia.</td> +</tr> +</table> + +<h6>DIVISION 4.</h6> + +<p class="listhead"> +Metallic bodies forming earths.</p> + +<table class="list" summary="list of substances"> +<tr> +<td><span class="smallroman">CALCIUM</span>,</td> +<td><i>or metal forming</i> lime.</td> +</tr> +<tr> +<td><span class="smallroman">MAGNIUM</span>,</td> +<td><i>forming</i> magnesia.</td> +</tr> +<tr> +<td><span class="smallroman">BARIUM</span>,</td> +<td><i>forming</i> barytes.</td> +</tr> +<tr> +<td><span class="smallroman">STRONTIUM</span>,</td> +<td><i>forming</i> strontites.</td> +</tr> +<tr> +<td><span class="smallroman">SILICIUM</span>,</td> +<td><i>forming</i> silex.</td> +</tr> +<tr> +<td><span class="smallroman">ALUMIUM</span>,</td> +<td><i>forming</i> alumine.</td> +</tr> +<tr> +<td><span class="smallroman">YTTRIUM</span>,</td> +<td><i>forming</i> yttria.</td> +</tr> +<tr> +<td> +<span class="pagenum">14</span> +<a name="conver1.page14" id="conver1.page14"> </a> +<span class="smallroman">GLUCIUM</span>,</td> +<td><i>forming</i> glucina.</td> +</tr> +<tr> +<td><span class="smallroman">ZIRCONIUM</span>,</td> +<td><i>forming</i> zirconi.<a class="tag" name="tag2" id="tag2" +href="#note2">*</a></td> +</tr> +</table> + +<h6>DIVISION 5.</h6> + +<p class="listhead"> +Metals, either naturally metallic, or yielding their oxygen to carbon or +to heat alone.</p> + +<p class="listhead"> +Subdivision 1.</p> + +<p class="listhead"> +Malleable Metals.</p> + +<div class="list"> +<p><span class="smallroman">GOLD</span>,</p> +<p><span class="smallroman">PLATINA</span>,</p> +<p><span class="smallroman">PALLADIUM</span>,</p> +<p><span class="smallroman">SILVER</span><a class="tag" name="tag3" id="tag3" href="#note3">*</a></p> +<p><span class="smallroman">MERCURY</span><a class="tag" name="tag4" id="tag4" href="#note4">†</a></p> +<p><span class="smallroman">TIN</span>,</p> +<p><span class="smallroman">COPPER</span>,</p> +<p><span class="smallroman">IRON</span>,</p> +<p><span class="smallroman">LEAD</span>,</p> +<p><span class="smallroman">NICKEL</span>,</p> +<p><span class="smallroman">ZINC</span>.</p> +</div> + +<p class="listhead"> +Subdiv. 2.</p> + +<p class="listhead"> +Brittle Metals.</p> + +<div class="list"> +<p><span class="smallroman">ARSENIC</span>,</p> +<p><span class="smallroman">BISMUTH</span>,</p> +<p><span class="smallroman">ANTIMONY</span>,</p> +<p><span class="smallroman">MANGANESE</span>,</p> +<span class="pagenum">15</span> +<a name="conver1.page15" id="conver1.page15"> </a> +<p><span class="smallroman">TELLURIUM</span>,</p> +<p><span class="smallroman">COBALT</span>,</p> +<p><span class="smallroman">TUNGSTEN</span>,</p> +<p><span class="smallroman">MOLYBDENUM</span>,</p> +<p><span class="smallroman">TITANIUM</span>,</p> +<p><span class="smallroman">CHROME</span>,</p> +<p><span class="smallroman">URANIUM</span>,</p> +<p><span class="smallroman">COLUMBIUM</span> <i>or</i> <span class="smallroman">TANTALIUM</span>,</p> +<p><span class="smallroman">IRIDIUM</span>,</p> +<p><span class="smallroman">OSMIUM</span>,</p> +<p><span class="smallroman">RHODIUM</span>.<a class="tag" name="tag5" id="tag5" href="#note5">*</a></p> +</div> + +<p class="speaker">CAROLINE.</p> + +<p>Oh, what a formidable list! You will have much to do to explain it, +Mrs. B.; for I assure you it is perfectly unintelligible to me, and +I think rather perplexes than assists me.</p> + +<p class="speaker">MRS. B.</p> + +<p>Do not let that alarm you, my dear; I hope that hereafter this +classification will appear quite clear, and, so far from perplexing you, +will assist you in arranging your ideas. It would be in vain to attempt +forming a division that would appear perfectly clear to a beginner: for +you may easily conceive that a chemical division being necessarily +founded on properties with which you are almost wholly unacquainted, it +is impossible that you should at once be able to understand its meaning +or appreciate its utility.</p> + +<span class="pagenum">16</span> +<a name="conver1.page16" id="conver1.page16"> </a> +<p>But, before we proceed further, it will be necessary to give you some +idea of chemical attraction, a power on which the whole science +depends.</p> + +<p><i>Chemical Attraction</i>, or the <i>Attraction of Composition</i>, +consists in the peculiar tendency which bodies of a different nature +have to unite with each other. It is by this force that all the +compositions, and decompositions, are effected.</p> + +<p class="speaker">EMILY.</p> + +<p>What is the difference between chemical attraction, and the +attraction of cohesion, or of aggregation, which you often mentioned to +us, in former conversations?</p> + +<p class="speaker">MRS. B.</p> + +<p>The attraction of cohesion exists only between particles of the +<i>same</i> nature, whether simple or compound; thus it unites the +particles of a piece of metal which is a simple substance, and likewise +the particles of a loaf of bread which is a compound. The attraction of +composition, on the contrary, unites and maintains, in a state of +combination, particles of a <i>dissimilar</i> nature; it is this power +that forms each of the compound particles of which bread consists; and +it is by the attraction of cohesion that all these particles are +connected into a single mass.</p> + +<span class="pagenum">17</span> +<a name="conver1.page17" id="conver1.page17"> </a> +<p class="speaker">EMILY.</p> + +<p>The attraction of cohesion, then, is the power which unites the +integrant particles of a body: the attraction of composition that which +combines the constituent particles. Is it not so?</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely: and observe that the attraction of cohesion unites +particles of a similar nature, without changing their original +properties; the result of such an union, therefore, is a body of the +same kind as the particles of which it is formed; whilst the attraction +of composition, by combining particles of a dissimilar nature, produces +compound bodies, quite different from any of their constituents. If, for +instance, I pour on the piece of copper, contained in this glass, +some of this liquid (which is called nitric acid), for which it has a +strong attraction, every particle of the copper will combine with a +particle of acid, and together they will form a new body, totally +different from either the copper or the acid.</p> + +<p>Do you observe the internal commotion that already begins to take +place? It is produced by the combination of these two substances; and +yet the acid has in this case to overcome not only the resistance which +the strong cohesion of the particles of copper opposes to their +combination with it, but also to overcome the weight of the copper, +which +<span class="pagenum">18</span> +<a name="conver1.page18" id="conver1.page18"> </a> +makes it sink to the bottom of the glass, and prevents the acid from +having such free access to it as it would if the metal were suspended in +the liquid.</p> + +<p class="speaker">EMILY.</p> + +<p>The acid seems, however, to overcome both these obstacles without +difficulty, and appears to be very rapidly dissolving the copper.</p> + +<p class="speaker">MRS. B.</p> + +<p>By this means it reduces the copper into more minute parts than could +possibly be done by any mechanical power. But as the acid can act only +on the surface of the metal, it will be some time before the union of +these two bodies will be completed.</p> + +<p>You may, however, already see how totally different this compound is +from either of its ingredients. It is neither colourless, like the acid, +nor hard, heavy, and yellow like the copper. If you tasted it, you would +no longer perceive the sourness of the acid. It has at present the +appearance of a blue liquid; but when the union is completed, and the +water with which the acid is diluted is evaporated, the compound will +assume the form of regular crystals, of a fine blue colour, and +perfectly transparent<a class="tag" name="tag6" id="tag6" href="#note6">*</a>. Of these I can shew you a +<span class="pagenum">19</span> +<a name="conver1.page19" id="conver1.page19"> </a> +specimen, as I have prepared some for that purpose.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How very beautiful they are, in colour, form, and transparency!</p> + +<p class="speaker">EMILY.</p> + +<p>Nothing can be more striking than this example of chemical +attraction.</p> + +<p class="speaker">MRS. B.</p> + +<p>The term <i>attraction</i> has been lately introduced into chemistry +as a substitute for the word <i>affinity</i>, to which some chemists +have objected, because it originated in the vague notion that chemical +combinations depended upon a certain resemblance, or relationship, +between particles that are disposed to unite; and this idea is not only +imperfect, but erroneous, as it is generally particles of the most +dissimilar nature, that have the greatest tendency to combine.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Besides, there seems to be no advantage in using a variety of terms +to express the same meaning; on the contrary it creates confusion; and +as we are well acquainted with the term Attraction in natural +philosophy, we had better adopt it in chemistry likewise.</p> + +<span class="pagenum">20</span> +<a name="conver1.page20" id="conver1.page20"> </a> +<p class="speaker">MRS. B.</p> + +<p>If you have a clear idea of the meaning, I shall leave you at +liberty to express it in the terms you prefer. For myself, +I confess that I think the word Attraction best suited to the +general law that unites the integrant particles of bodies; and Affinity +better adapted to that which combines the constituent particles, as it +may convey an idea of the preference which some bodies have for others, +which the term <i>attraction of composition</i> does not so well +express.</p> + +<p class="speaker">EMILY.</p> + +<p>So I think; for though that preference may not result from any +relationship, or similitude, between the particles (as you say was once +supposed), yet, as it really exists, it ought to be expressed.</p> + +<p class="speaker">MRS. B.</p> + +<p>Well, let it be agreed that you may use the terms <i>affinity</i>, +<i>chemical attraction</i> and <i>attraction of composition</i>, +indifferently, provided you recollect that they have all the same +meaning.</p> + +<p class="speaker">EMILY.</p> + +<p>I do not conceive how bodies can be decomposed by chemical +attraction. That this power should be the means of composing them, is +very obvious; but that it should, at the same time, produce exactly the +contrary effect, appears to me very singular.</p> + +<span class="pagenum">21</span> +<a name="conver1.page21" id="conver1.page21"> </a> +<p class="speaker">MRS. B.</p> + +<p>To decompose a body is, you know, to separate its constituent parts, +which, as we have just observed, cannot be done by mechanical means.</p> + +<p class="speaker">EMILY.</p> + +<p>No: because mechanical means separate only the integrant particles; +they act merely against the attraction of cohesion, and only divide a +compound into smaller parts.</p> + +<p class="speaker">MRS. B.</p> + +<p>The decomposition of a body is performed by chemical powers. If you +present to a body composed of two principles, a third, which has a +greater affinity for one of them than the two first have for each other, +it will be decomposed, that is, its two principles will be separated by +means of the third body. Let us call two ingredients, of which the body +is composed, A and B. If we present to it another +ingredient C, which has a greater affinity for B than that which +unites A and B, it necessarily follows that B will quit A to +combine with C. The new ingredient, therefore, has effected a +decomposition of the original body A B; A has been left alone, +and a new compound, B C, has been formed.</p> + +<p class="speaker">EMILY.</p> + +<p>We might, I think, use the comparison of two +<span class="pagenum">22</span> +<a name="conver1.page22" id="conver1.page22"> </a> +friends, who were very happy in each other’s society, till a third +disunited them by the preference which one of them gave to the +new-comer.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well. I shall now show you how this takes place in +chemistry.</p> + +<p>Let us suppose that we wish to decompose the compound we have just +formed by the combination of the two ingredients, copper and nitric +acid; we may do this by presenting to it a piece of iron, for which the +acid has a stronger attraction than for copper; the acid will, +consequently, quit the copper to combine with the iron, and the copper +will be what the chemists call <i>precipitated</i>, that is to say, it +will be thrown down in its separate state, and reappear in its simple +form.</p> + +<p>In order to produce this effect, I shall dip the blade of this knife +into the fluid, and, when I take it out, you will observe, that, instead +of being wetted with a bluish liquid, like that contained in the glass, +it will be covered with a thin coat of copper.</p> + +<p class="speaker">CAROLINE.</p> + +<p>So it is really! but then is it not the copper, instead of the acid, +that has combined with the iron blade?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; you are deceived by appearances: it is +<span class="pagenum">23</span> +<a name="conver1.page23" id="conver1.page23"> </a> +the acid which combines with the iron, and, in so doing, deposits or +precipitates the copper on the surface of the blade.</p> + +<p class="speaker">EMILY.</p> + +<p>But, cannot three or more substances combine together, without any of +them being precipitated?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is sometimes the case; but, in general, the stronger affinity +destroys the weaker; and it seldom happens that the attraction of +several substances for each other is so equally balanced as to produce +such complicated compounds.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, pray, Mrs. B., what is the cause of the chemical attraction of +bodies for each other? It appears to me more extraordinary or unnatural, +if I may use the expression, than the attraction of cohesion, which +unites particles of a similar nature.</p> + +<p class="speaker">MRS. B.</p> + +<p>Chemical attraction may, like that of cohesion or gravitation, be one +of the powers inherent in matter which, in our present state of +knowledge, admits of no other satisfactory explanation than an immediate +reference to a divine cause. Sir H. Davy, however, whose important +discoveries have +<span class="pagenum">24</span> +<a name="conver1.page24" id="conver1.page24"> </a> +opened such improved views in chemistry, has suggested an hypothesis +which may throw great light upon that science. He supposes that there +are two kinds of electricity, with one or other of which all bodies are +united. These we distinguish by the names of <i>positive</i> and +<i>negative</i> electricity; those bodies are disposed to combine, which +possess opposite electricities, as they are brought together by the +attraction which these electricities have for each other. But, whether +this hypothesis be altogether founded on truth or not, it is impossible +to question the great influence of electricity in chemical +combinations.</p> + +<p class="speaker">EMILY.</p> + +<p>So, that we must suppose that the two electricities always attract +each other, and thus compel the bodies in which they exist to +combine?</p> + +<p class="speaker">CAROLINE.</p> + +<p>And may not this be also the cause of the attraction of cohesion?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, for in particles of the same nature the same electricities must +prevail, and it is only the different or opposite electric fluids that +attract each other.</p> + +<p class="speaker">CAROLINE.</p> + +<p>These electricities seem to me to be a kind of +<span class="pagenum">25</span> +<a name="conver1.page25" id="conver1.page25"> </a> +chemical spirit, which animates the particles of bodies, and draws them +together.</p> + +<p class="speaker">EMILY.</p> + +<p>If it is known, then, with which of the electricities bodies are +united, it can be inferred which will, and which will not, combine +together?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly.—I should not omit to mention, that some doubts have +been entertained whether electricity be really a material agent, or +whether it might not be a power inherent in bodies, similar to, or, +perhaps identical with, attraction.</p> + +<p class="speaker">EMILY.</p> + +<p>But what then would be the electric spark which is visible, <ins +class="mycorr" title="text reads ‘aud’">and</ins> must therefore be +really material?</p> + +<p class="speaker">MRS. B.</p> + +<p>What we call the electric spark, may, Sir H. Davy says, be merely the +heat and light, or fire produced by the chemical combinations with which +these phenomena are always connected. We will not, however, enter more +fully on this important subject at present, but reserve the principal +facts which relate to it to a future conversation.</p> + +<p>Before we part, however, I must recommend you to fix in your memory +the names of the simple bodies, against our next interview.</p> + +<div class="footnote"> + +<p><a name="note1" id="note1" href="#tag1">*</a> +It has been questioned by some eminent chemists, whether these two last +agents should not be classed among the inflammable bodies, as they are +capable of combining with oxygen, as well as with inflammable bodies. +But they seem to be more distinctly characterised by their property of +supporting combustion than by any other quality.</p> + +<p><a name="note2" id="note2" href="#tag2">*</a> +Of all these earths, three or four only have as yet been distinctly +decomposed.</p> + +<p><a name="note3" id="note3" href="#tag3">*</a> +These first four metals have commonly been distinguished by the +appellation of perfect or noble metals, on account of their possessing +the characteristic properties of ductility, malleability, +inalterability, and great specific gravity, in an eminent degree.</p> + +<p><a name="note4" id="note4" href="#tag4">†</a> +Mercury, in its liquid state, cannot, of course, be called a malleable +metal. But when frozen, it possesses a considerable degree of +malleability.</p> + +<p><a name="note5" id="note5" href="#tag5">*</a> +These last four or five metallic bodies are placed under this class for +the sake of arrangement, though some of their properties have not been +yet fully investigated.</p> + +<p><a name="note6" id="note6" href="#tag6">*</a> +These crystals are more easily obtained from a mixture of sulphuric with +a little nitric acid.</p> + +</div> + + + +<span class="pagenum">26</span> +<a name="conver1.page26" id="conver1.page26"> </a> +<h4><a name="convII" id="convII">CONVERSATION II.</a><br> +<span class="subhead">ON LIGHT AND HEAT OR CALORIC.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">CAROLINE.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> have learned by heart the names of all +the simple bodies which you have enumerated, and we are now ready to +enter on the examination of each of them successively. You will begin, +I suppose, with <span class="smallroman">LIGHT</span>?</p> + +<p class="speaker">MRS. B.</p> + +<p>Respecting the nature of light we have little more than conjectures. +It is considered by most philosophers as a real substance, immediately +emanating from the sun, and from all luminous bodies, from which it is +projected in right lines with prodigious velocity. Light, however, being +imponderable, it cannot be confined and examined by itself; and +therefore it is to the effects it produces on other bodies, rather than +to its immediate nature, that we must direct our attention.</p> + +<p>The connection between light and heat is very obvious; indeed, it is +such, that it is extremely +<span class="pagenum">27</span> +<a name="conver1.page27" id="conver1.page27"> </a> +difficult to examine the one independently of the other.</p> + +<p class="speaker">EMILY.</p> + +<p>But, is it possible to separate light from heat; I thought they +were only different degrees of the same thing, fire?</p> + +<p class="speaker">MRS. B.</p> + +<p>I told you that fire was not now considered as a simple element. +Whether light and heat be altogether different agents, or not, +I cannot pretend to decide; but, in many cases, light may be +separated from heat. The first discovery of this was made by a +celebrated Swedish chemist, Scheele. Another very striking illustration +of the separation of heat and light was long after pointed out by Dr. +Herschell. This philosopher discovered that these two agents were +emitted in the rays of the sun, and that heat was less refrangible than +light; for, in separating the different coloured rays of light by a +prism (as we did some time ago), he found that the greatest heat was +beyond the spectrum, at a little distance from the red rays, which, you +may recollect, are the least refrangible.</p> + +<p class="speaker">EMILY.</p> + +<p>I should like to try that experiment.</p> + +<span class="pagenum">28</span> +<a name="conver1.page28" id="conver1.page28"> </a> +<p class="speaker">MRS. B.</p> + +<p>It is by no means an easy one: the heat of a ray of light, refracted +by a prism, is so small, that it requires a very delicate thermometer to +distinguish the difference of the degree of heat within and without the +spectrum. For in this experiment the heat is not totally separated from +the light, each coloured ray retaining a certain portion of it, though +the greatest part is not sufficiently refracted to fall within the +spectrum.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose, then, that those coloured rays which are the least +refrangible, retain the greatest quantity of heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>They do so.</p> + +<p class="speaker">EMILY.</p> + +<p>Though I no longer doubt that light and heat can be separated, Dr. +Herschell’s experiment does not appear to me to afford sufficient proof +that they are essentially different; for light, which you call a simple +body, may likewise be divided into the various coloured rays.</p> + +<p class="speaker">MRS. B.</p> + +<p>No doubt there must be some difference in the various coloured rays. +Even their chemical powers +<span class="pagenum">29</span> +<a name="conver1.page29" id="conver1.page29"> </a> +are different. The blue rays, for instance, have the greatest effect in +separating oxygen from bodies, as was found by Scheele; and there exist +also, as Dr. Wollaston has shown, rays more refrangible than the blue, +which produce the same chemical effect, and, what is very remarkable, +are invisible.</p> + +<p class="speaker">EMILY.</p> + +<p>Do you think it possible that heat may be merely a modification of +light?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is a supposition which, in the present state of natural +philosophy, can neither be positively affirmed nor denied. Let us, +therefore, instead of discussing theoretical points, be contented with +examining what is known respecting the chemical effects of light.</p> + +<p>Light is capable of entering into a kind of transitory union with +certain substances, and this is what has been called phosphorescence. +Bodies that are possessed of this property, after being exposed to the +sun’s rays, appear luminous in the dark. The shells of fish, the bones +of land animals, marble, limestone, and a variety of combinations of +earths, are more or less powerfully phosphorescent.</p> + +<span class="pagenum">30</span> +<a name="conver1.page30" id="conver1.page30"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I remember being much surprised last summer with the phosphorescent +appearance of some pieces of rotten wood, which had just been dug out of +the ground; they shone so bright that I at first supposed them to be +glow-worms.</p> + +<p class="speaker">EMILY.</p> + +<p>And is not the light of a glow-worm of a phosphorescent nature?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a very remarkable instance of phosphorescence in living +animals; this property, however, is not exclusively possessed by the +glow-worm. The insect called the lanthorn-fly, which is peculiar to warm +climates, emits light as it flies, producing in the dark a remarkably +sparkling appearance. But it is more common to see animal matter in a +dead state possessed of a phosphorescent quality; sea fish is often +eminently so.</p> + +<p class="speaker">EMILY.</p> + +<p>I have heard that the sea has sometimes had the appearance of being +illuminated, and that the light is supposed to proceed from the spawn of +fishes floating on its surface.</p> + +<span class="pagenum">31</span> +<a name="conver1.page31" id="conver1.page31"> </a> +<p class="speaker">MRS. B.</p> + +<p>This light is probably owing to that or some other animal matter. Sea +water has been observed to become luminous from the substance of a fresh +herring having been immersed in it; and certain insects, of the Medusa +kind, are known to produce similar effects.</p> + +<p>But the strongest phosphorescence is produced by chemical +compositions prepared for the purpose, the most common of which consists +of oyster shells and sulphur, and is known by the name of Canton’s +Phosphorus.</p> + +<p class="speaker">EMILY.</p> + +<p>I am rather surprised, Mrs. B., that you should have said so much of +the light emitted by phosphorescent bodies without taking any notice of +that which is produced by burning bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>The light emitted by the latter is so intimately connected with the +chemical history of combustion, that I must defer all explanation of it +till we come to the examination of that process, which is one of the +most interesting in chemical science.</p> + +<p>Light is an agent capable of producing various chemical changes. It +is essential to the welfare both of the animal and vegetable kingdoms; +for men and plants grow pale and sickly if deprived of +<span class="pagenum">32</span> +<a name="conver1.page32" id="conver1.page32"> </a> +its salutary influence. It is likewise remarkable for its property of +destroying colour, which renders it of great consequence in the process +of bleaching.</p> + +<p class="speaker">EMILY.</p> + +<p>Is it not singular that light, which in studying optics we were +taught to consider as the source and origin of colours, should have also +the power of destroying them?</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is a fact, however, that we every day experience; you know how it +fades the colours of linens and silks.</p> + +<p class="speaker">EMILY.</p> + +<p>Certainly. And I recollect that endive is made to grow white instead +of green, by being covered up so as to exclude the light. But by what +means does light produce these effects?</p> + +<p class="speaker">MRS. B.</p> + +<p>This I cannot attempt to explain to you until you have obtained a +further knowledge of chemistry. As the chemical properties of light can +be accounted for only in their reference to compound bodies, it would be +useless to detain you any longer on this subject; we may therefore pass +on to the examination of heat, or caloric, with which we are somewhat +better acquainted.</p> + +<span class="pagenum">33</span> +<a name="conver1.page33" id="conver1.page33"> </a> +<p><span class="smallcaps">Heat</span> and <span class="smallcaps">Light</span> may be always distinguished by the different +sensations they produce, <i>Light</i> affects the sense of sight; +<i>Caloric</i> that of feeling; the one produces <i>Vision</i>, the +other the sensation of <i>Heat</i>.</p> + +<p>Caloric is found to exist in a variety of forms or modifications, and +I think it will be best to consider it under the two following heads, +viz.</p> + +<div class="inset"> +<p>1. <span class="smallroman">FREE OR RADIANT CALORIC</span>.</p> + +<p>2. <span class="smallroman">COMBINED CALORIC</span>.</p> +</div> + +<p>The first, <span class="smallroman">FREE</span> or <span class="smallroman">RADIANT CALORIC</span>, is also called <span class="smallroman">HEAT OF TEMPERATURE</span>; it comprehends all heat which +is perceptible to the senses, and affects the thermometer.</p> + +<p class="speaker">EMILY.</p> + +<p>You mean such as the heat of the sun, of fire, of candles, of stoves; +in short, of every thing that burns?</p> + +<p class="speaker">MRS. B.</p> + +<p>And likewise of things that do not burn, as, for instance, the warmth +of the body; in a word, all heat that is <i>sensible</i>, whatever may +be its degree, or the source from which it is derived.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What then are the other modifications of caloric? +<span class="pagenum">34</span> +<a name="conver1.page34" id="conver1.page34"> </a> +It must be a strange kind of heat that cannot be perceived by our +senses.</p> + +<p class="speaker">MRS. B.</p> + +<p>None of the modifications of caloric should properly be called +<i>heat</i>; for heat, strictly speaking, is the sensation produced by +caloric, on animated bodies; this word, therefore, in the accurate +language of science, should be confined to express the sensation. But +custom has adapted it likewise to inanimate matter, and we say <i>the +heat of an oven</i>, <i>the heat of the sun</i>, without any reference +to the sensation which they are capable of exciting.</p> + +<p>It was in order to avoid the confusion which arose from thus +confounding the cause and effect, that modern chemists adopted the new +word <i>caloric</i>, to denote the principle which produces heat; yet +they do not always, in compliance with their own language, limit the +word <i>heat</i> to the expression of the sensation, since they still +frequently employ it in reference to the other modifications of caloric +which are quite independent of sensation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But you have not yet explained to us what these other modifications +of caloric are.</p> + +<p class="speaker">MRS. B.</p> + +<p>Because you are not acquainted with the properties +<span class="pagenum">35</span> +<a name="conver1.page35" id="conver1.page35"> </a> +of free caloric, and you know that we have agreed to proceed with +regularity.</p> + +<p>One of the most remarkable properties of free caloric is its power of +<i>dilating</i> bodies. This fluid is so extremely subtle, that it +enters and pervades all bodies whatever, forces itself between their +particles, and not only separates them, but frequently drives them +asunder to a considerable distance from each other. It is thus that +caloric dilates or expands a body so as to make it occupy a greater +space than it did before.</p> + +<p class="speaker">EMILY.</p> + +<p>The effect it has on bodies, therefore, is directly contrary to that +of the attraction of cohesion; the one draws the particles together, the +other drives them asunder.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely. There is a continual struggle between the attraction of +aggregation, and the expansive power of caloric; and from the action of +these two opposite forces, result all the various forms of matter, or +degrees of consistence, from the solid, to the liquid and aëriform +state. And accordingly we find that most bodies are capable of passing +from one of these forms to the other, merely in consequence of their +receiving different quantities of caloric.</p> + +<span class="pagenum">36</span> +<a name="conver1.page36" id="conver1.page36"> </a> +<p class="speaker">CAROLINE.</p> + +<p>That is very curious; but I think I understand the reason of it. If a +great quantity of caloric is added to a solid body, it introduces itself +between the particles in such a manner as to overcome, in a considerable +degree, the attraction of cohesion; and the body, from a solid, is then +converted into a fluid.</p> + +<p class="speaker">MRS. B.</p> + +<p>This is the case whenever a body is fused or melted; but if you add +caloric to a liquid, can you tell me what is the consequence?</p> + +<p class="speaker">CAROLINE.</p> + +<p>The caloric forces itself in greater abundance between the particles +of the fluid, and drives them to such a distance from each other, that +their attraction of aggregation is wholly destroyed: the liquid is then +transformed into vapour.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well; and this is precisely the case with boiling water, when it +is converted into steam or vapour, and with all bodies that assume an +aëriform state.</p> + +<p class="speaker">EMILY.</p> + +<p>I do not well understand the word aëriform?</p> + +<span class="pagenum">37</span> +<a name="conver1.page37" id="conver1.page37"> </a> +<p class="speaker">MRS. B.</p> + +<p>Any elastic fluid whatever, whether it be merely vapour or permanent +air, is called aëriform.</p> + +<p>But each of these various states, solid, liquid, and aëriform, admit +of many different degrees of density, or consistence, still arising +(chiefly at least) from the different quantities of caloric the bodies +contain. Solids are of various degrees of density, from that of gold, to +that of a thin jelly. Liquids, from the consistence of melted glue, or +melted metals, to that of ether, which is the lightest of all liquids. +The different elastic fluids (with which you are not yet acquainted) are +susceptible of no less variety in their degrees of density.</p> + +<p class="speaker">EMILY.</p> + +<p>But does not every individual body also admit of different degrees of +consistence, without changing its state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; and this I can immediately show you by a very simple +experiment. This piece of iron now exactly fits the frame, or ring, made +to receive it; but if heated red hot, it will no longer do so, for its +dimensions will be so much increased by the caloric that has penetrated +into it, that it will be much too large for the frame.</p> + +<p>The iron is now red hot; by applying it to the frame, we shall see +how much it is dilated.</p> + +<span class="pagenum">38</span> +<a name="conver1.page38" id="conver1.page38"> </a> +<p class="speaker">EMILY.</p> + +<p>Considerably so indeed! I knew that heat had this effect on bodies, +but I did not imagine that it could be made so conspicuous.</p> + +<p class="speaker">MRS. B.</p> + +<p>By means of this instrument (called a Pyrometer) we may estimate, in +the most exact manner, the various dilatations of any solid body by +heat. The body we are now going to submit to trial is this small iron +bar; I fix it to this apparatus, (<a class="smallcaps" href="#plateI">Plate I.</a> Fig. <ins class="mycorr" title="text reads ‘I’">1</ins>.) and then heat it by lighting the three lamps +beneath it: when the bar expands, it increases in length as well as +thickness; and, as one end communicates with this wheel-work, whilst the +other end is fixed and immoveable, no sooner does it begin to dilate +than it presses against the wheel-work, and sets in motion the index, +which points out the degrees of dilatation on the dial-plate.</p> + +<p class="figname"> +<a name="plateI" id="plateI">Plate I.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 38.</p> + +<p class="illustration"> +<img src="images/plate1_thumb.png" width="589" height="251" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1 +A.A Bar of Metal. +1.2.3 Lamps burning. +B.B Wheel work. +C Index.<br> +Fig. 2 +A.A Glass tubes with bulbs. +B.B Glasses of water in which they are immersed.</p> + +<p class="figlink"> +<a href="images/plate1_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">EMILY.</p> + +<p>This is, indeed, a very curious instrument; but I do not understand +the use of the wheels: would it not be more simple, and answer the +purpose equally well, if the bar, in dilating, pressed against the +index, and put it in motion without the intervention of the wheels?</p> + +<span class="pagenum">39</span> +<a name="conver1.page39" id="conver1.page39"> </a> +<p class="speaker">MRS. B.</p> + +<p>The use of the wheels is merely to multiply the motion, and therefore +render the effect of the caloric more obvious; for if the index moved no +more than the bar increased in length, its motion would scarcely be +perceptible; but by means of the wheels it moves in a much greater +proportion, which therefore renders the variations far more +conspicuous.</p> + +<p>By submitting different bodies to the test of the pyrometer, it is +found that they are far from dilating in the same proportion. Different +metals expand in different degrees, and other kinds of solid bodies vary +still more in this respect. But this different susceptibility of +dilatation is still more remarkable in fluids than in solid bodies, as I +shall show you. I have here two glass tubes, terminated at one end +by large bulbs. We shall fill the bulbs, the one with spirit of wine, +the other with water. I have coloured both liquids, in order that +the effect may be more conspicuous. The spirit of wine, you see, dilates +by the warmth of my hand as I hold the bulb.</p> + +<p class="speaker">EMILY.</p> + +<p>It certainly does, for I see it is rising into the tube. But water, +it seems, is not so easily affected by heat; for scarcely any change is +produced on it by the warmth of the hand.</p> + +<span class="pagenum">40</span> +<a name="conver1.page40" id="conver1.page40"> </a> +<p class="speaker">MRS. B.</p> + +<p>True; we shall now plunge the bulbs into hot water, (<a class="smallcaps" href="#plateI">Plate I.</a> Fig. 2.) and you will see +both liquids rise in the tubes; but the spirit of wine will ascend +highest.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How rapidly it expands! Now it has nearly reached the top of the +tube, though the water has hardly begun to rise.</p> + +<p class="speaker">EMILY.</p> + +<p>The water now begins to dilate. Are not these glass tubes, with +liquids rising within them, very like thermometers?</p> + +<p class="speaker">MRS. B.</p> + +<p>A thermometer is constructed exactly on the same principle, and these +tubes require only a scale to answer the purpose of thermometers: but +they would be rather awkward in their dimensions. The tubes and bulbs of +thermometers, though of various sizes, are in general much smaller than +these; the tube too is hermetically closed, and the air excluded from +it. The fluid most generally used in thermometers is mercury, commonly +called quicksilver, the dilatations and contractions of which correspond +more exactly to the additions, and subtractions, of caloric, than those +of any other fluid.</p> + +<span class="pagenum">41</span> +<a name="conver1.page41" id="conver1.page41"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Yet I have often seen coloured spirit of wine used in +thermometers.</p> + +<p class="speaker">MRS. B.</p> + +<p>The expansions and contractions of that liquid are not quite so +uniform as those of mercury; but in cases in which it is not requisite +to ascertain the temperature with great precision, spirit of wine will +answer the purpose equally well, and indeed in some respects better, as +the expansion of the latter is greater, and therefore more conspicuous. +This fluid is used likewise in situations and experiments in which +mercury would be frozen; for mercury becomes a solid body, like a piece +of lead or any other metal, at a certain degree of cold: but no degree +of cold has ever been known to freeze spirit of wine.</p> + +<p>A thermometer, therefore, consists of a tube with a bulb, such as you +see here, containing a fluid whose degrees of dilatation and contraction +are indicated by a scale to which the tube is fixed. The degree which +indicates the boiling point, simply means that, when the fluid is +sufficiently dilated to rise to this point, the heat is such that water +exposed to the same temperature will boil. When, on the other hand, the +fluid is so much condensed as to sink to the freezing point, we know +that water will freeze at that temperature. +<span class="pagenum">42</span> +<a name="conver1.page42" id="conver1.page42"> </a> +The extreme points of the scales are not the same in all thermometers, +nor are the degrees always divided in the same manner. In different +countries philosophers have chosen to adopt different scales and +divisions. The two thermometers most used are those of Fahrenheit, and +of Reaumur; the first is generally preferred by the English, the latter +by the French.</p> + +<p class="speaker">EMILY.</p> + +<p>The variety of scale must be very inconvenient, and I should think +liable to occasion confusion, when French and English experiments are +compared.</p> + +<p class="speaker">MRS. B.</p> + +<p>The inconvenience is but very trifling, because the different +gradations of the scales do not affect the principle upon which +thermometers are constructed. When we know, for instance, that +Fahrenheit’s scale is divided into 212 degrees, in which 32° corresponds +with the freezing point, and 212° with the point of boiling water: and +that Reaumur’s is divided only into 80 degrees, in which 0° denotes the +freezing point, and 80° that of boiling water, it is easy to compare the +two scales together, and reduce the one into the other. But, for greater +convenience, thermometers are sometimes constructed with both these +scales, one +<span class="pagenum">43</span> +<a name="conver1.page43" id="conver1.page43"> </a> +on either side of the tube; so that the correspondence of the different +degrees of the two scales is thus instantly seen. Here is one of these +scales, (<a class="smallcaps" href="#plateII">Plate II.</a> +Fig. 1.) by which you can at once perceive that each degree of +Reaumur’s corresponds to 2¼ of Fahrenheit’s division. But I believe the +French have, of late, given the preference to what they call the +centigrade scale, in which the space between the freezing and the +boiling point is divided into 100 degrees.</p> + +<p class="figname"> +<a name="plateII" id="plateII">Plate II.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 42.</p> + +<p class="illustration"> +<img src="images/plate2_thumb.png" width="253" height="554" +alt="see text"> +</p> + +<p class="figlink"> +<a href="images/plate2_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>That seems to me the most reasonable division, and I cannot guess why +the freezing point is called 32°, or what advantage is derived +from it.</p> + +<p class="speaker">MRS. B.</p> + +<p>There really is no advantage in it; and it originated in a mistaken +opinion of the instrument-maker, Fahrenheit, who first constructed these +thermometers. He mixed snow and salt together, and produced by that +means a degree of cold which he concluded was the greatest possible, and +therefore made his scale begin from that point. Between that and boiling +water he made 212 degrees, and the freezing point was found to be at +32°.</p> + +<span class="pagenum">44</span> +<a name="conver1.page44" id="conver1.page44"> </a> +<p class="speaker">EMILY.</p> + +<p>Are spirit of wine, and mercury, the only liquids used in the +construction of thermometers?</p> + +<p class="speaker">MRS. B.</p> + +<p>I believe they are the only liquids now in use, though some others, +such as linseed oil, would make tolerable thermometers: but for +experiments in which a very quick and delicate test of the changes of +temperature is required, air is the fluid sometimes employed. The bulb +of air thermometers is filled with common air only, and its expansion +and contraction are indicated by a small drop of any coloured liquor, +which is suspended within the tube, and moves up and down, according as +the air within the bulb and tube expands or contracts. But in general, +air thermometers, however sensible to changes of temperature, are by no +means accurate in their indications.</p> + +<p>I can, however, show you an air thermometer of a very peculiar +construction, which is remarkably well adapted for some chemical +experiments, as it is equally delicate and accurate in its +indications.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It looks like a double thermometer reversed, the tube being bent, and +having a large bulb at each of its extremities. (<a class="smallcaps" +href="#plateII">Plate II.</a> Fig. 2.)</p> + +<span class="pagenum">45</span> +<a name="conver1.page45" id="conver1.page45"> </a> +<p class="speaker">EMILY.</p> + +<p>Why do you call it an air thermometer; the tube contains a coloured +liquid?</p> + +<p class="speaker">MRS. B.</p> + +<p>But observe that the bulbs are filled with air, the liquid being +confined to a portion of the tube, and answering only the purpose of +showing, by its motion in the tube, the comparative dilatation or +contraction of the air within the bulbs, which afford an indication of +their relative temperature. Thus if you heat the bulb A, by the +warmth of your hand, the fluid will rise towards the bulb B, and +the contrary will happen if you reverse the experiment.</p> + +<p>But if, on the contrary, both tubes are of the same temperature, as +is the case now, the coloured liquid, suffering an equal pressure on +each side, no change of level takes place.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This instrument appears, indeed, uncommonly delicate. The fluid is +set in motion by the mere approach of my hand.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must observe, however, that this thermometer cannot indicate the +temperature of any particular body, or of the medium in which it is +<span class="pagenum">46</span> +<a name="conver1.page46" id="conver1.page46"> </a> +immersed; it serves only to point out the <i>difference</i> of +temperature between the two bulbs, when placed under different +circumstances. For this reason it has been called <ins class="mycorr" +title="missing ‘a’ or ‘the’?"><i>differential</i></ins> thermometer. +You will see by-and-bye to what particular purposes this instrument +applies.</p> + +<p class="speaker">EMILY.</p> + +<p>But do common thermometers indicate the exact quantity of caloric +contained either in the atmosphere, or in any body with which they are +in contact?</p> + +<p class="speaker">MRS. B.</p> + +<p>No: first, because there are other modifications of caloric which do +not affect the thermometer; and, secondly, because the temperature of a +body, as indicated by the thermometer, is only relative. When, for +instance, the thermometer remains stationary at the freezing point, we +know that the atmosphere (or medium in which it is placed, whatever it +may be) is as cold as freezing water; and when it stands at the boiling +point, we know that this medium is as hot as boiling water; but we do +not know the positive quantity of heat contained either in freezing or +boiling water, any more than we know the real extremes of heat and cold; +and consequently we cannot determine that of the body in which the +thermometer is placed.</p> + +<span class="pagenum">47</span> +<a name="conver1.page47" id="conver1.page47"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I do not quite understand this explanation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Let us compare a thermometer to a well, in which the water rises to +different heights, according as it is more or less supplied by the +spring which feeds it: if the depth of the well is unfathomable, it must +be impossible to know the absolute quantity of water it contains; yet we +can with the greatest accuracy measure the number of feet the water has +risen or fallen in the well at any time, and consequently know the +precise quantity of its increase or diminution, without having the least +knowledge of the whole quantity of water it contains.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now I comprehend it very well; nothing appears to me to explain a +thing so clearly as a comparison.</p> + +<p class="speaker">EMILY.</p> + +<p>But will thermometers bear any degree of heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for if the temperature were much above the highest degree marked +on the scale of the thermometer, the mercury would burst the tube in an +attempt to ascend. And at any rate, no thermometer can be applied to +temperatures higher than the boiling +<span class="pagenum">48</span> +<a name="conver1.page48" id="conver1.page48"> </a> +point of the liquid used in its construction, for the steam, on the +liquid beginning to boil, would burst the tube. In furnaces, or whenever +any very high temperature is to be measured, a pyrometer, invented +by Wedgwood, is used for that purpose. It is made of a certain +composition of baked clay, which has the peculiar property of +contracting by heat, so that the degree of contraction of this substance +indicates the temperature to which it has been exposed.</p> + +<p class="speaker">EMILY.</p> + +<p>But is it possible for a body to contract by heat? I thought +that heat dilated all bodies whatever.</p> + +<p class="speaker">MRS. B.</p> + +<p>This is not an exception to the rule. You must recollect that the +bulk of the clay is not compared, whilst hot, with that which it has +when cold; but it is from the change which the clay has undergone by +<i>having been</i> heated that the indications of this instrument are +derived. This change consists in a beginning fusion which tends to unite +the particles of clay more closely, thus rendering it less pervious or +spongy.</p> + +<p>Clay is to be considered as a spongy body, having many interstices or +pores, from its having contained water when soft. These interstices are +<span class="pagenum">49</span> +<a name="conver1.page49" id="conver1.page49"> </a> +by heat lessened, and would by extreme heat be entirely obliterated.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And how do you ascertain the degrees of contraction of Wedgwood’s +pyrometer?</p> + +<p class="speaker">MRS. B.</p> + +<p>The dimensions of a piece of clay are measured by a scale graduated +on the side of a tapered groove, formed in a brass ruler; the more the +clay is contracted by the heat, the further it will descend into the +narrow part of the tube.</p> + +<p>Before we quit the subject of expansion, I must observe to you +that, as liquids expand more readily than solids, so elastic fluids, +whether air or vapour, are the most expansible of all bodies.</p> + +<p>It may appear extraordinary that all elastic fluids whatever, undergo +the same degree of expansion from equal augmentations of +temperature.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose, then, that all elastic fluids are of the same density?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very far from it; they vary in density, more than either liquids or +solids. The uniformity of their expansibility, which at first may appear +singular, is, however, readily accounted for. For if the different +susceptibilities of expansion of bodies +<span class="pagenum">50</span> +<a name="conver1.page50" id="conver1.page50"> </a> +arise from their various degrees of attraction of cohesion, no such +difference can be expected in elastic fluids, since in these the +attraction of cohesion does not exist, their particles being on the +contrary possessed of an elastic or repulsive power; they will therefore +all be equally expanded by equal degrees of caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>True; as there is no power opposed to the expansive force of caloric +in elastic bodies, its effect must be the same in all of them.</p> + +<p class="speaker">MRS. B.</p> + +<p>Let us now proceed to examine the other properties of free +caloric.</p> + +<p>Free caloric always tends to diffuse itself equally, that is to say, +when two bodies are of different temperatures, the warmer gradually +parts with its heat to the colder, till they are both brought to the +same temperature. Thus, when a thermometer is applied to a hot body, it +receives caloric; when to a cold one, it communicates part of its own +caloric, and this communication continues until the thermometer and the +body arrive at the same temperature.</p> + +<p class="speaker">EMILY.</p> + +<p>Cold, then, is nothing but a negative quality, simply implying the +absence of heat.</p> + +<span class="pagenum">51</span> +<a name="conver1.page51" id="conver1.page51"> </a> +<p class="speaker">MRS. B.</p> + +<p>Not the total absence, but a diminution of heat; for we know of no +body in which some caloric may not be discovered.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But when I lay my hand on this marble table I feel it +<i>positively</i> cold, and cannot conceive that there is any caloric +in it.</p> + +<p class="speaker">MRS. B.</p> + +<p>The cold you experience consists in the loss of caloric that your +hand sustains in an attempt to bring its temperature to an equilibrium +with the marble. If you lay a piece of ice upon it, you will find that +the contrary effect will take place; the ice will be melted by the heat +which it abstracts from the marble.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it not in this case the air of the room, which being warmer than +the marble, melts the ice?</p> + +<p class="speaker">MRS. B.</p> + +<p>The air certainly acts on the surface which is exposed to it, but the +table melts that part with which it is in contact.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But why does caloric tend to an equilibrium? +<span class="pagenum">52</span> +<a name="conver1.page52" id="conver1.page52"> </a> +It cannot be on the same principle as other fluids, since it has no +weight?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very true, Caroline, that is an excellent objection. You might also, +with some propriety, object to the term <i>equilibrium</i> being applied +to a body that is without weight; but I know of no expression that would +explain my meaning so well. You must consider it, however, in a +figurative rather than a literal sense; its strict meaning is an +<i>equal diffusion</i>. We cannot, indeed, well say by what power it +diffuses itself equally, though it is not surprising that it should go +from the parts which have the most to those which have the least. This +subject is best explained by a theory suggested by Professor Prevost of +Geneva, which is now, I believe, generally adopted.</p> + +<p>According to this theory, caloric is composed of particles perfectly +separate from each other, every one of which moves with a rapid velocity +in a certain direction. These directions vary as much as imagination can +conceive, the result of which is, that there are rays or lines of these +particles moving with immense velocity in every possible direction. +Caloric is thus universally diffused, so that when any portion of space +happens to be in the neighbourhood of another, which contains more +caloric, the colder portion receives a +<span class="pagenum">53</span> +<a name="conver1.page53" id="conver1.page53"> </a> +quantity of calorific rays from the latter, sufficient to restore an +equilibrium of temperature. This radiation does not only take place in +free space, but extends also to bodies of every kind. Thus you may +suppose all bodies whatever constantly radiating caloric: those that are +of the same temperature give out and absorb equal quantities, so that no +variation of temperature is produced in them; but when one body contains +more free caloric than another, the exchange is always in favour of the +colder body, until an equilibrium is effected; this you found to be the +case when the marble table cooled your hand, and again when it melted +the ice.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This reciprocal radiation surprises me extremely; I thought, +from what you first said, that the hotter bodies alone emitted rays of +caloric which were absorbed by the colder; for it seems unnatural that a +hot body should receive any caloric from a cold one, even though it +should return a greater quantity.</p> + +<p class="speaker">MRS. B.</p> + +<p>It may at first appear so, but it is no more extraordinary than that +a candle should send forth rays of light to the sun, which, you know, +must necessarily happen.</p> + +<span class="pagenum">54</span> +<a name="conver1.page54" id="conver1.page54"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Well, Mrs. B—, I believe that I must give up the point. But I +wish I could <i>see</i> these rays of caloric; I should then have +greater faith in them.</p> + +<p class="speaker">MRS. B.</p> + +<p>Will you give no credit to any sense but that of sight? You may feel +the rays of caloric which you receive from any body of a temperature +higher than your own; the loss of the caloric you part with in return, +it is true, is not perceptible; for as you gain more than you lose, +instead of suffering a diminution, you are really making an acquisition +of caloric. It is, therefore, only when you are parting with it to a +body of a lower temperature, that you are sensible of the sensation of +cold, because you then sustain an absolute loss of caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>And in this case we cannot be sensible of the small quantity of heat +we receive in exchange from the colder body, because it serves only to +diminish the loss.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well, indeed, Emily. Professor Pictet, of Geneva, has made some +very interesting experiments, which prove not only that caloric radiates +from all bodies whatever, but that these rays may be reflected, +according to the laws of optics, in +<span class="pagenum">55</span> +<a name="conver1.page55" id="conver1.page55"> </a> +the same manner as light. I shall repeat these experiments before +you, having procured mirrors fit for the purpose; and it will afford us +an opportunity of using the differential thermometer, which is +particularly well adapted for these experiments.—I place an +iron bullet, (<a class="smallcaps" href="#plateIII">Plate III.</a> +Fig. <ins class="mycorr" title="text reads ‘I’">1</ins>.) about +two inches in diameter, and heated to a degree not sufficient to render +it luminous, in the focus of this large metallic concave mirror. The +rays of heat which fall on this mirror are reflected, agreeably to the +property of concave mirrors, in a parallel direction, so as to fall on a +similar mirror, which, you see, is placed opposite to the first, at the +distance of about ten feet; thence the rays converge to the focus of the +second mirror, in which I place one of the bulbs of this thermometer. +Now, observe in what manner it is affected by the caloric which is +reflected on it from the heated bullet.—The air is dilated in the +bulb which we placed in the focus of the mirror, and the liquor rises +considerably in the opposite leg.</p> + +<p class="figname"> +<a name="plateIII" id="plateIII">Plate III.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 54</p> + +<p class="illustration"> +<img src="images/plate3_thumb.png" width="531" height="238" +alt="see text and caption"> +</p> + +<p class="caption"> +A.A. & B.B Concave mirrors fixed on stands. +C Heated Bullet placed in the focus of the mirror A. +D Thermometer, with its bulb placed in the focus of the +mirror B.<br> +1.2.3.4 Rays of Caloric radiating from the bullet & falling on the +mirror A. +5.6.7.8 The same rays reflected from the mirror A to the mirror B. + +9.10.11.12 The same rays reflected by the mirror B to the +Thermometer.</p> + +<p class="figlink"> +<a href="images/plate3_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">EMILY.</p> + +<p>But would not the same effect take place, if the rays of caloric from +the heated bullet fell directly on the thermometer, without the +assistance of the mirrors?</p> + +<p class="speaker">MRS. B.</p> + +<p>The effect would in that case be so trifling, at +<span class="pagenum">56</span> +<a name="conver1.page56" id="conver1.page56"> </a> +the distance at which the bullet and the thermometer are from each +other, that it would be almost imperceptible. The mirrors, you know, +greatly increase the effect, by collecting a large quantity of rays into +a focus; place your hand in the focus of the mirror, and you will find +it much hotter there than when you remove it nearer to the bullet.</p> + +<p class="speaker">EMILY.</p> + +<p>That is very true; it appears extremely singular to feel the heat +diminish in approaching the body from which it proceeds.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And the mirror which produces so much heat, by converging the rays, +is itself quite cold.</p> + +<p class="speaker">MRS. B.</p> + +<p>The same number of rays that are dispersed over the surface of the +mirror are collected by it into the focus; but, if you consider how +large a surface the mirror presents to the rays, and, consequently, how +much they are diffused in comparison to what they are at the focus, +which is little more than a point, I think you can no longer wonder +that the focus should be so much hotter than the mirror.</p> + +<p>The principal use of the mirrors in this experiment is, to prove that +the <ins class="edcorr" title="corrected by author from ‘caloric’">calorific</ins> +emanation is reflected in the same manner as light.</p> + +<span class="pagenum">57</span> +<a name="conver1.page57" id="conver1.page57"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And the result, I think, is very conclusive.</p> + +<p class="speaker">MRS. B.</p> + +<p>The experiment may be repeated with a wax taper instead of the +bullet, with a view of separating the light from the caloric. For this +purpose a transparent plate of glass must be interposed between the +mirrors; for light, you know, passes with great facility through glass, +whilst the transmission of caloric is almost wholly impeded by it. We +shall find, however, in this experiment, that some few of the calorific +rays pass through the glass together with the light, as the thermometer +rises a little; but, as soon as the glass is removed, and a free passage +left to the caloric, it will rise considerably higher.</p> + +<p class="speaker">EMILY.</p> + +<p>This experiment, as well as that of Dr. Herschell’s, proves that +light and heat may be separated; for in the latter experiment the +separation was not perfect, any more than in that of Mr. Pictet.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I should like to repeat this experiment, with the difference of +substituting a cold body instead of the hot one, to see whether cold +would not be reflected as well as heat.</p> + +<span class="pagenum">58</span> +<a name="conver1.page58" id="conver1.page58"> </a> +<p class="speaker">MRS. B.</p> + +<p>That experiment was proposed to Mr. Pictet by an incredulous +philosopher like yourself, and he immediately tried it by substituting a +piece of ice in the place of the heated bullet.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Well, Mrs. B., and what was the result?</p> + +<p class="speaker">MRS. B.</p> + +<p>That we shall see; I have procured some ice for the purpose.</p> + +<p class="speaker">EMILY.</p> + +<p>The thermometer falls considerably!</p> + +<p class="speaker">CAROLINE.</p> + +<p>And does not that prove that cold is not merely a <i>negative</i> +quality, implying simply an inferior degree of heat? The cold must be +<i>positive</i>, since it is capable of reflection.</p> + +<p class="speaker">MRS. B.</p> + +<p>So it at first appeared to Mr. Pictet; but upon a little +consideration he found that it afforded only an additional proof of the +reflection of heat: this I shall endeavour to explain to you.</p> + +<p>According to Mr. Prevost’s theory, we suppose that all bodies +whatever radiate caloric; the thermometer used in these experiments +therefore emits calorific rays in the same manner as any other +<span class="pagenum">59</span> +<a name="conver1.page59" id="conver1.page59"> </a> +substance. When its temperature is in equilibrium with that of the +surrounding bodies, it receives as much caloric as it parts with, and no +change of temperature is produced. But when we introduce a body of a +lower temperature, such as a piece of ice, which parts with less caloric +than it receives, the consequence is, that its temperature is raised, +whilst that of the surrounding bodies is proportionally lowered.</p> + +<p class="speaker">EMILY.</p> + +<p>If, for instance, I was to bring a large piece of ice into this room, +the ice would in time be melted, by absorbing caloric from the general +radiation which is going on throughout the room; and as it would +contribute very little caloric in return for what is absorbed, the room +would necessarily be cooled by it.</p> + +<p class="speaker">MRS. B.</p> + +<p>Just so; and as in consequence of the mirrors, a more +considerable exchange of rays takes place between the ice and the +thermometer, than between these and any of the surrounding bodies, the +temperature of the thermometer must be more lowered than that of any +other adjacent object.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I confess I do not perfectly understand your explanation.</p> + +<span class="pagenum">60</span> +<a name="conver1.page60" id="conver1.page60"> </a> +<p class="speaker">MRS. B.</p> + +<p>This experiment is exactly similar to that made with the heated +bullet: for, if we consider the thermometer as the hot body (which it +certainly is in comparison to the ice), you may then easily understand +that it is by the loss of the calorific rays which the thermometer sends +to the ice, and not by any cold rays received from it, that the fall of +the mercury is occasioned: for the ice, far from emitting rays of cold, +sends forth rays of caloric, which diminish the loss sustained by the +thermometer.</p> + +<p>Let us say, for instance, that the radiation of the thermometer +towards the ice is equal to 20, and that of the ice towards the +thermometer to 10: the exchange in favour of the ice is as 20 is to 10, +or the thermometer absolutely loses 10, whilst the ice +gains 10.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if the ice actually sends rays of caloric to the thermometer, +must not the latter fall still lower when the ice is removed?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for the space that the ice occupied, admits rays from all the +surrounding bodies to pass through it; and those being of the same +temperature as the thermometer, will not affect it, because as much heat +now returns to the thermometer as radiates from it.</p> + +<span class="pagenum">61</span> +<a name="conver1.page61" id="conver1.page61"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I must confess that you have explained this in so satisfactory a +manner, that I cannot help being convinced now that cold has no real +claim to the rank of a positive being.</p> + +<p class="speaker">MRS. B.</p> + +<p>Before I conclude the subject of radiation I must observe to you that +different bodies, (or rather surfaces,) possess the power of radiating +caloric in very different degrees.</p> + +<p>Some very curious experiments have been made by Mr. Leslie on this +subject, and it was for this purpose that he invented the differential +thermometer; with its assistance he ascertained that black surfaces +radiate most, glass next, and polished surfaces the least of all.</p> + +<p class="speaker">EMILY.</p> + +<p>Supposing these surfaces, of course, to be all of the same +temperature.</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly. I will now show you the very simple and ingenious +apparatus, by means of which he made these experiments. This cubical tin +vessel or canister, has each of its sides externally covered with +different materials; the one is simply blackened; the next is covered +with white +<span class="pagenum">62</span> +<a name="conver1.page62" id="conver1.page62"> </a> +paper; the third with a pane of glass, and in the fourth the polished +tin surface remains uncovered. We shall fill this vessel with hot water, +so that there can be no doubt but that all its sides will be of the same +temperature. Now let us place it in the focus of one of the mirrors, +making each of its sides front it in succession. We shall begin with the +black surface.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It makes the thermometer which is in the focus of the other mirror +rise considerably. Let us turn the paper surface towards the mirror. The +thermometer falls a little, therefore of course this side cannot emit or +radiate so much caloric as the blackened side.</p> + +<p class="speaker">EMILY.</p> + +<p>This is very surprising; for the sides are exactly of the same size, +and must be of the same temperature. But let us try the glass +surface.</p> + +<p class="speaker">MRS. B.</p> + +<p>The thermometer continues falling, and with the plain surface it +falls still lower; these two surfaces therefore radiate less and +less.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think I have found out the reason of this.</p> + +<span class="pagenum">63</span> +<a name="conver1.page63" id="conver1.page63"> </a> +<p class="speaker">MRS. B.</p> + +<p>I should be very happy to hear it, for it has not yet (to my +knowledge) been accounted for.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The water within the vessel gradually cools, and the thermometer in +consequence gradually falls.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is true that the water cools, but certainly in much less +proportion than the thermometer descends, as you will perceive if you +now change the tin surface for the black one.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I was mistaken certainly, for the thermometer rises again now that +the black surface fronts the mirror.</p> + +<p class="speaker">MRS. B.</p> + +<p>And yet the water in the vessel is still cooling, Caroline.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised that the tin surface should radiate the least <ins +class="mycorr" title="text reads ‘carolic’">caloric</ins>, for a +metallic vessel filled with hot water, a silver teapot, for +instance, feels much hotter to the hand than one of black earthen +ware.</p> + +<span class="pagenum"><ins class="mycorr" title="text reads ‘54’">64</ins></span> +<a name="conver1.page64" id="conver1.page64"> </a> + +<p class="speaker">MRS. B.</p> + +<p>That is owing to the different power which various bodies possess for +<i>conducting</i> caloric, a property which we shall presently +examine. Thus, although a metallic vessel feels warmer to the hand, +a vessel of this kind is known to preserve the heat of the liquid +within, better than one of any other materials; it is for this reason +that silver teapots make better tea than those of earthen ware.</p> + +<p class="speaker">EMILY.</p> + +<p>According to these experiments, light-coloured dresses, in cold +weather, should keep us warmer than black clothes, since the latter +radiate so much more than the former.</p> + +<p class="speaker">MRS. B.</p> + +<p>And that is actually the case.</p> + +<p class="speaker">EMILY.</p> + +<p>This property, of different surfaces to radiate in different degrees, +appears to me to be at variance with the equilibrium of caloric; since +it would imply that those bodies which radiate most, must ultimately +become coldest.</p> + +<p>Suppose that we were to vary this experiment, by using two metallic +vessels full of boiling water, the one blackened, the other not; would +not the black one cool the first?</p> + +<span class="pagenum">65</span> +<a name="conver1.page65" id="conver1.page65"> </a> +<p class="speaker">CAROLINE.</p> + +<p>True; but when they were both brought down to the temperature of the +room, the interchange of caloric between the canisters and the other +bodies of the room being then equal, their temperatures would remain the +same.</p> + +<p class="speaker">EMILY.</p> + +<p>I do not see why that should be the case; for if different surfaces +of the same temperature radiate in different degrees when heated, why +should they not continue to do so when cooled down to the temperature of +the room?</p> + +<p class="speaker">MRS. B.</p> + +<p>You have started a difficulty, Emily, which certainly requires +explanation. It is found by experiment that the power of absorption +corresponds with and is proportional to that of radiation; so that under +equal temperatures, bodies compensate for the greater loss they sustain +in consequence of their greater radiation by their greater absorption; +so that if you were to make your experiment in an atmosphere heated like +the canisters, to the temperature of boiling water, though it is true +that the canisters would radiate in different degrees, no change of +temperature would be produced in them, because they would each absorb +caloric in proportion to their respective radiation.</p> + +<span class="pagenum">66</span> +<a name="conver1.page66" id="conver1.page66"> </a> +<p class="speaker">EMILY.</p> + +<p>But would not the canisters of boiling water also absorb caloric in +different degrees in a room of the common temperature?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly they would. But the various bodies in the room would not, +at a lower temperature, furnish either of the canisters with a +sufficiency of caloric to compensate for the loss they undergo; for, +suppose the black canister to absorb 400 rays of caloric, whilst the +metallic one absorbed only 200; yet if the former radiate 800, whilst +the latter radiates only 400, the black canister will be the first +cooled down to the temperature of the room. But from the moment the +equilibrium of temperature has taken place, the black canister, both +receiving and giving out 400 rays, and the metallic one 200, no change +of temperature will take place.</p> + +<p class="speaker">EMILY.</p> + +<p>I now understand it extremely well. But what becomes of the surplus +of calorific rays, which good radiators emit and bad radiators refuse to +receive; they must wander about in search of a resting-place?</p> + +<p class="speaker">MRS. B.</p> + +<p>They really do so; for they are rejected and sent +<span class="pagenum">67</span> +<a name="conver1.page67" id="conver1.page67"> </a> +back, or, in other words, <i>reflected</i> by the bodies which are bad +radiators of caloric; and they are thus transmitted to other bodies +which happen to lie in their way, by which they are either absorbed or +again reflected, according as the property of reflection, or that of +absorption, predominates in these bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not well understand the difference between radiating and +reflecting caloric, for the caloric that is reflected from a body +proceeds from it in straight lines, and may surely be said to radiate +from it?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is true that there at first appears to be a great analogy between +<i>radiation</i> and <i>reflection</i>, as they equally convey the idea +of the transmission of caloric.</p> + +<p>But if you consider a little, you will perceive that when a body +<i>radiates</i> caloric, the heat which it emits not only proceeds from, +but has its origin in the body itself. Whilst when a body +<i>reflects</i> caloric, it parts with none of its own caloric, but only +reflects that which it receives from other bodies.</p> + +<p class="speaker">EMILY.</p> + +<p>Of this difference we have very striking examples before us, in the +tin vessel of water, and the concave mirrors; the first radiates its own +heat, +<span class="pagenum">68</span> +<a name="conver1.page68" id="conver1.page68"> </a> +the latter reflect the heat which they receive from other bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now, that I understand the difference, it no longer surprises me that +bodies which radiate, or part with their own caloric freely, should not +have the power of transmitting with equal facility that which they +receive from other bodies.</p> + +<p class="speaker">EMILY.</p> + +<p>Yet no body can be said to possess caloric of its own, if all caloric +is originally derived from the sun.</p> + +<p class="speaker">MRS. B.</p> + +<p>When I speak of a body radiating its own caloric, I mean that +which it has absorbed and incorporated either immediately from the sun’s +rays, or through the medium of any other substance.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It seems natural enough that the power of absorption should be in +opposition to that of reflection, for the more caloric a body receives, +the less it will reject.</p> + +<p class="speaker">EMILY.</p> + +<p>And equally so that the power of radiation should correspond with +that of absorption. It is, in fact, cause and effect; for a body cannot +radiate +<span class="pagenum">69</span> +<a name="conver1.page69" id="conver1.page69"> </a> +heat without having previously absorbed it; just as a spring that is +well fed flows abundantly.</p> + +<p class="speaker">MRS. B.</p> + +<p>Fluids are in general very bad radiators of caloric; and air neither +radiates nor absorbs caloric in any sensible degree.</p> + +<p>We have not yet concluded our observations on free caloric. But I +shall defer, till our next meeting, what I have further to say on this +subject. I believe it will afford us ample conversation for another +interview.</p> + + + + +<span class="pagenum">70</span> +<a name="conver1.page70" id="conver1.page70"> </a> +<h4><a name="convIII" id="convIII">CONVERSATION III.</a><br> +<span class="subhead">CONTINUATION OF THE SUBJECT.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">I</span>n</span> our last conversation, we began to +examine the tendency of caloric to restore an equilibrium of +temperature. This property, when once well understood, affords the +explanation of a great variety of facts which appeared formerly +unaccountable. You must observe, in the first place, that the effect of +this tendency is gradually to bring all bodies that are in contact to +the same temperature. Thus, the fire which burns in the grate, +communicates its heat from one object to another, till every part of the +room has an equal proportion of it.</p> + +<p class="speaker">EMILY.</p> + +<p>And yet this book is not so cold as the table on which it lies, +though both are at an equal distance from the fire, and actually in +contact with each other, so that, according to your theory, they should +be exactly of the same temperature.</p> + +<span class="pagenum">71</span> +<a name="conver1.page71" id="conver1.page71"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And the hearth, which is much nearer the fire than the carpet, is +certainly the colder of the two.</p> + +<p class="speaker">MRS. B.</p> + +<p>If you ascertain the temperature of these several bodies by a +thermometer (which is a much more accurate test than your feeling), you +will find that it is exactly the same.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if they are of the same temperature, why should the one feel +colder than the other?</p> + +<p class="speaker">MRS. B.</p> + +<p>The hearth and the table feel colder than the carpet or the book, +because the latter are not such good <i>conductors of heat</i> as the +former. Caloric finds a more easy passage through marble and wood, than +through leather and worsted; the two former will therefore absorb heat +more rapidly from your hand, and consequently give it a stronger +sensation of cold than the two latter, although they are all of them +really of the same temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>So, then, the sensation I feel on touching a cold body, is in +proportion to the rapidity with which my hand yields its heat to that +body?</p> + +<span class="pagenum">72</span> +<a name="conver1.page72" id="conver1.page72"> </a> +<p class="speaker">MRS. B.</p> + +<p>Precisely; and, if you lay your hand successively on every object in +the room, you will discover which are good, and which are bad conductors +of heat, by the different degrees of cold you feel. But, in order to +ascertain this point, it is necessary that the several substances should +be of the same temperature, which will not be the case with those that +are very near the fire, or those that are exposed to a current of cold +air from a window or door.</p> + +<p class="speaker">EMILY.</p> + +<p>But what is the reason that some bodies are better conductors of heat +than others?</p> + +<p class="speaker">MRS. B.</p> + +<p>This is a point not well ascertained. It has been conjectured that a +certain union or adherence takes place between the caloric and the +particles of the body through which it passes. If this adherence be +strong, the body detains the heat, and parts with it slowly and +reluctantly; if slight, it propagates it freely and rapidly. The +conducting power of a body is therefore, inversely, as its tendency to +unite with caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>That is to say, that the best conductors are those that have the +least affinity for caloric.</p> + +<span class="pagenum">73</span> +<a name="conver1.page73" id="conver1.page73"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes; but the term affinity is objectionable in this case, because, as +that word is used to express a chemical attraction (which can be +destroyed only by decomposition), it cannot be applicable to the slight +and transient union that takes place between free caloric and the bodies +through which it passes; an union which is so weak, that it constantly +yields to the tendency which caloric has to an equilibrium. Now you +clearly understand, that the passage of caloric, through bodies that are +good conductors, is much more rapid than through those that are bad +conductors, and that the former both give and receive it more quickly, +and therefore, in a given time, more abundantly, than bad conductors, +which makes them feel either hotter or colder, though they may be, in +fact, both of the same temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes, I understand it now; the table, and the book lying upon it, +being really of the same temperature, would each receive, in the same +space of time, the same quantity of heat from my hand, were their +conducting powers equal; but as the table is the best conductor of the +two, it will absorb the heat from my hand more rapidly, and consequently +produce a stronger sensation of cold than the book.</p> + +<span class="pagenum">74</span> +<a name="conver1.page74" id="conver1.page74"> </a> +<p class="speaker">MRS. B.</p> + +<p>Very well, my dear; and observe, likewise, that if you were to heat +the table and the book an equal number of degrees above the temperature +of your body, the table, which before felt the colder, would now feel +the hotter of the two; for, as in the first case it took the heat most +rapidly from your hand, so it will now impart heat most rapidly to it. +Thus the marble table, which seems to us colder than the mahogany one, +will prove the hotter of the two to the ice; for, if it takes heat more +rapidly from our hands, which are warmer, it will give out heat more +rapidly to the ice, which is colder. Do you understand the reason of +these apparently opposite effects?</p> + +<p class="speaker">EMILY.</p> + +<p>Perfectly. A body which is a good conductor of caloric, affords it a +free passage; so that it penetrates through that body more rapidly than +through one which is a bad conductor; and consequently, if it is colder +than your hand, you lose more caloric, and if it is hotter, you gain +more than with a bad conductor of the same temperature.</p> + +<p class="speaker">MRS. B.</p> + +<p>But you must observe that this is the case only when the conductors +are either hotter or colder than your hand; for, if you heat different +conductors +<span class="pagenum">75</span> +<a name="conver1.page75" id="conver1.page75"> </a> +to the temperature of your body, they will all feel equally warm, since +the exchange of caloric between bodies of the same temperature is equal. +Now, can you tell me why flannel clothing, which is a very bad conductor +of heat, prevents our feeling cold?</p> + +<p class="speaker">CAROLINE.</p> + +<p>It prevents the cold from penetrating . +. . . . . . .</p> + +<p class="speaker">MRS. B.</p> + +<p>But you forget that cold is only a negative quality.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; it only prevents the heat of our bodies from escaping so +rapidly as it would otherwise do.</p> + +<p class="speaker">MRS. B.</p> + +<p>Now you have explained it right; the flannel rather keeps in the +heat, than keeps out the cold. Were the atmosphere of a higher +temperature than our bodies, it would be equally efficacious in keeping +their temperature at the same degree, as it would prevent the free +access of the external heat, by the difficulty with which it +conducts it.</p> + +<p class="speaker">EMILY.</p> + +<p>This, I think, is very clear. Heat, whether external or internal, +cannot easily penetrate flannel; +<span class="pagenum">76</span> +<a name="conver1.page76" id="conver1.page76"> </a> +therefore in cold weather it keeps us warm; and if the weather was +hotter than our bodies, it would keep us cool.</p> + +<p class="speaker">MRS. B.</p> + +<p>The most dense bodies are, generally speaking, the best conductors of +heat; probably because the denser the body the greater are the number of +points or particles that come in contact with caloric. At the common +temperature of the atmosphere a piece of metal will feel much colder +than a piece of wood, and the latter than a piece of woollen cloth; this +again will feel colder than flannel; and down, which is one of the +lightest, is at the same time one of the warmest bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This is, I suppose, the reason that the plumage of birds preserves +them so effectually from the influence of cold in winter?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but though feathers in general are an excellent preservative +against cold, down is a kind of plumage peculiar to aquatic birds, and +covers their chest, which is the part most exposed to the water; for +though the surface of the water is not of a lower temperature than the +atmosphere, yet, as it is a better conductor of heat, it feels much +<span class="pagenum">77</span> +<a name="conver1.page77" id="conver1.page77"> </a> +colder, consequently the chest of the bird requires a warmer covering +than any other part of its body. Besides, the breasts of aquatic birds +are exposed to cold not only from the temperature of the water, but also +from the velocity with which the breast of the bird strikes against it; +and likewise from the rapid evaporation occasioned in that part by the +air against which it strikes, after it has been moistened by dipping +from time to time into the water.</p> + +<p>If you hold a finger of one hand motionless in a glass of water, and +at the same time move a finger of the other hand swiftly through water +of the same temperature, a different sensation will be soon +perceived in the different fingers.</p> + +<p>Most animal substances, especially those which Providence has +assigned as a covering for animals, such as fur, wool, hair, skin, +&c. are bad conductors of heat, and are, on that account, such +excellent preservatives against the inclemency of winter, that our +warmest apparel is made of these materials.</p> + +<p class="speaker">EMILY.</p> + +<p>Wood is, I dare say, not so good a conductor as metal, and it is for +that reason, no doubt, that silver teapots have always wooden +handles.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and it is the facility with which metals +<span class="pagenum">78</span> +<a name="conver1.page78" id="conver1.page78"> </a> +conduct caloric that made you suppose that a silver pot radiated more +caloric than an earthen one. The silver pot is in fact hotter to the +hand when in contact with it; but it is because its conducting power +more than counterbalances its deficiency in regard to radiation.</p> + +<p>We have observed that the most dense bodies are in general the best +conductors; and metals, you know, are of that class. Porous bodies, such +as the earths and wood, are worse conductors, chiefly, I believe, +on account of their pores being filled with air; for air is a remarkably +bad conductor.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is a very fortunate circumstance that air should be a bad +conductor, as it tends to preserve the heat of the body when exposed to +cold weather.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is one of the many benevolent dispensations of Providence, in +order to soften the inclemency of the seasons, and to render almost all +climates habitable to man.</p> + +<p>In fluids of different densities, the power of conducting heat varies +no less remarkably; if you dip your hand into this vessel full of +mercury, you will scarcely conceive that its temperature is not lower +than that of the atmosphere.</p> + +<span class="pagenum">79</span> +<a name="conver1.page79" id="conver1.page79"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Indeed I know not how to believe it, it feels so extremely +cold.—But we may easily ascertain its true temperature by the +thermometer.—It is really not colder than the air;—the +apparent difference then is produced merely by the difference of the +conducting power in mercury and in air.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; hence you may judge how little the sense of feeling is to be +relied on as a test of the temperature of bodies, and how necessary a +thermometer is for that purpose.</p> + +<p>It has indeed been doubted whether fluids have the power of +conducting caloric in the same manner as solid bodies. Count Rumford, +a very few years since, attempted to prove, by a variety of +experiments, that fluids, when at rest, were not at all endowed with +this property.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How is that possible, since they are capable of imparting cold or +heat to us; for if they did not conduct heat, they would neither take it +from, nor give it to us?</p> + +<p class="speaker">MRS. B.</p> + +<p>Count Rumford did not mean to say that fluids would not communicate +their heat to solid bodies; +<span class="pagenum">80</span> +<a name="conver1.page80" id="conver1.page80"> </a> +but only that heat does not pervade fluids, that is to say, is not +transmitted from one particle of a fluid to another, in the same manner +as in solid bodies.</p> + +<p class="speaker">EMILY.</p> + +<p>But when you heat a vessel of water over the fire, if the particles +of water do not communicate heat to each other, how does the water +become hot throughout?</p> + +<p class="speaker">MRS. B.</p> + +<p>By constant agitation. Water, as you have seen, expands by heat in +the same manner as solid bodies; the heated particles of water, +therefore, at the bottom of the vessel, become specifically lighter than +the rest of the liquid, and consequently ascend to the surface, where, +parting with some of their heat to the colder atmosphere, they are +condensed, and give way to a fresh succession of heated particles +ascending from the bottom, which having thrown off their heat at the +surface, are in their turn displaced. Thus every particle is +successively heated at the bottom, and cooled at the surface of the +liquid; but as the fire communicates heat more rapidly than the +atmosphere cools the succession of surfaces, the whole of the liquid in +time becomes heated.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This accounts most ingeniously for the propagation +<span class="pagenum">81</span> +<a name="conver1.page81" id="conver1.page81"> </a> +of heat upwards. But suppose you were to heat the upper surface of a +liquid, the particles being specifically lighter than those below, could +not descend: how therefore would the heat be communicated downwards?</p> + +<p class="speaker">MRS. B.</p> + +<p>If there were no agitation to force the heated surface downwards, +Count Rumford assures us that the heat would not descend. In proof of +this he succeeded in making the upper surface of a vessel of water boil +and evaporate, while a cake of ice remained frozen at the bottom.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is very extraordinary indeed!</p> + +<p class="speaker">MRS. B.</p> + +<p>It appears so, because we are not accustomed to heat liquids by their +upper surface; but you will understand this theory better if I show you +the internal motion that takes place in liquids when they experience a +change of temperature. The motion of the liquid itself is indeed +invisible from the extreme minuteness of its particles; but if you mix +with it any coloured dust, or powder, of nearly the same specific +gravity as the liquid, you may judge of the internal motion of the +latter by that of the coloured dust it contains.—Do you see the +<span class="pagenum">82</span> +<a name="conver1.page82" id="conver1.page82"> </a> +small pieces of amber moving about in the liquid contained in this +phial?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes, perfectly.</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall now immerse the phial in a glass of hot water, and the +motion of the liquid will be shown, by that which it communicates to the +amber.</p> + +<p class="speaker">EMILY.</p> + +<p>I see two currents, the one rising along the sides of the phial, the +other descending in the centre: but I do not understand the reason of +this.</p> + +<p class="speaker">MRS. B.</p> + +<p>The hot water communicates its caloric, through the medium of the +phial, to the particles of the fluid nearest to the glass; these dilate +and ascend laterally to the surface, where, in parting with their heat, +they are condensed, and in descending, form the central current.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This is indeed a very clear and satisfactory experiment; but how much +slower the currents now move than they did at first?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because the circulation of particles has +<span class="pagenum">83</span> +<a name="conver1.page83" id="conver1.page83"> </a> +nearly produced an equilibrium of temperature between the liquid in the +glass and that in the phial.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But these communicate laterally, and I thought that heat in liquids +could be propagated only upwards.</p> + +<p class="speaker">MRS. B.</p> + +<p>You do not take notice that the heat is imparted from one liquid to +the other, through the medium of the phial itself, the external surface +of which receives the heat from the water in the glass, whilst its +internal surface transmits it to the liquid it contains. Now take the +phial out of the hot water, and observe the effect of its cooling.</p> + +<p class="speaker">EMILY.</p> + +<p>The currents are reversed; the external current now descends, and the +internal one rises.—I guess the reason of this +change:—the phial being in contact with cold air instead of hot +water, the external particles are cooled instead of being heated; they +therefore descend and force up the central particles, which, being +warmer, are consequently lighter.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is just so. Count Rumford hence infers that no alteration of +temperature can take place in a fluid, without an internal motion of its +particles, +<span class="pagenum">84</span> +<a name="conver1.page84" id="conver1.page84"> </a> +and as this motion is produced only by the comparative levity of the +heated particles, heat cannot be propagated downwards.</p> + +<p>But though I believe that Count Rumford’s theory as to heat being +incapable of pervading fluids is not strictly correct, yet there is, no +doubt, much truth in his observation, that the communication is +materially promoted by a motion of the parts; and this accounts for the +cold that is found to prevail at the bottom of the lakes in Switzerland, +which are fed by rivers issuing from the snowy Alps. The water of these +rivers being colder, and therefore more dense than that of the lakes, +subsides to the bottom, where it cannot be affected by the warmer +temperature of the surface; the motion of the waves may communicate this +temperature to some little depth, but it can descend no further than the +agitation extends.</p> + +<p class="speaker">EMILY.</p> + +<p>But when the atmosphere is colder than the lake, the colder surface +of the water will descend, for the very reason that the warmer will +not.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly: and it is on this account that neither a lake, nor any +body of water whatever, can be frozen until every particle of the water +has risen to the surface to give off its caloric to the colder +<span class="pagenum">85</span> +<a name="conver1.page85" id="conver1.page85"> </a> +atmosphere; therefore the deeper a body of water is, the longer will be +the time it requires to be frozen.</p> + +<p class="speaker">EMILY.</p> + +<p>But if the temperature of the whole body of water be brought down to +the freezing point, why is only the surface frozen?</p> + +<p class="speaker">MRS. B.</p> + +<p>The temperature of the whole body is lowered, but not to the freezing +point. The diminution of heat, as you know, produces a contraction in +the bulk of fluids, as well as of solids. This effect, however, does not +take place in water below the temperature of 40 degrees, which is 8 +degrees above the freezing point. At that temperature, therefore, the +internal motion, occasioned by the increased specific gravity of the +condensed particles, ceases; for when the water at the surface no longer +condenses, it will no longer descend, and leave a fresh surface exposed +to the atmosphere: this surface alone, therefore, will be further +exposed to its severity, and will soon be brought down to the freezing +point, when it becomes ice, which being a bad conductor of heat, +preserves the water beneath a long time from being affected by the +external cold.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And the sea does not freeze, I suppose, because +<span class="pagenum">86</span> +<a name="conver1.page86" id="conver1.page86"> </a> +its depth is so great, that a frost never lasts long enough to bring +down the temperature of such a great body of water to 40 degrees?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is one reason why the sea, as a large mass of water, does not +freeze. But, independently of this, salt water does not freeze till it +is cooled much below 32 degrees, and with respect to the law of +condensation, salt water is an exception, as it condenses even many +degrees below the freezing point. When the caloric of fresh water, +therefore, is imprisoned by the ice on its surface, the ocean still +continues throwing off heat into the atmosphere, which is a most signal +dispensation of Providence to moderate the intensity of the cold in +winter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This theory of the non-conducting power of liquids, does not, +I suppose, hold good with respect to air, otherwise the atmosphere +would not be heated by the rays of the sun passing through it?</p> + +<p class="speaker">MRS. B.</p> + +<p>Nor is it heated in that way. The pure atmosphere is a perfectly +transparent medium, which neither radiates, absorbs, nor conducts +caloric, but transmits the rays of the sun to us without in any way +<span class="pagenum">87</span> +<a name="conver1.page87" id="conver1.page87"> </a> +diminishing their intensity. The air is therefore not more heated, by +the sun’s rays passing through it, than diamond, glass, water, or any +other transparent medium.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is very extraordinary! Are glass windows not heated then by the +sun shining on them?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; not if the glass be perfectly transparent. A most convincing +proof that glass transmits the rays of the sun without being heated by +them is afforded by the burning lens, which by converging the rays to a +focus will set combustible bodies on fire, without its own temperature +being raised.</p> + +<p class="speaker">EMILY.</p> + +<p>Yet, Mrs. B., if I hold a piece of glass near the fire it is almost +immediately warmed by it; the glass therefore must retain some of the +caloric radiated by the fire? Is it that the solar rays alone pass +freely through glass without paying tribute? It seems unaccountable that +the radiation of a common fire should have power to do what the sun’s +rays cannot accomplish.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not because the rays from the fire have more power, but rather +because they have less, that +<span class="pagenum">88</span> +<a name="conver1.page88" id="conver1.page88"> </a> +they heat glass and other transparent bodies. It is true, however, that +as you approach the source of heat the rays being nearer each other, the +heat is more condensed, and can produce effects of which the solar rays, +from the great distance of their source, are incapable. Thus we should +find it impossible to roast a joint of meat by the sun’s rays, though it +is so easily done by culinary heat. Yet caloric emanated from burning +bodies, which is commonly called <i>culinary heat</i>, has neither the +intensity nor the velocity of solar rays. All caloric, we have said, is +supposed to proceed originally from the sun; but after having been +incorporated with terrestrial bodies, and again given out by them, +though its nature is not essentially altered, it retains neither the +intensity nor the velocity with which it first emanated from that +luminary; it has therefore not the power of passing through transparent +mediums, such as glass and water, without being partially retained by +those bodies.</p> + +<p class="speaker">EMILY.</p> + +<p>I recollect that in the experiment on the reflection of heat, the +glass <ins class="correction" title="unchanged">skreen</ins> which +you interposed between the burning taper and the mirror, arrested the +rays of caloric, and suffered only those of light to pass +through it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Glass windows, then, though they cannot be +<span class="pagenum">89</span> +<a name="conver1.page89" id="conver1.page89"> </a> +heated by the sun shining on them, may be heated internally by a fire in +the room? But, Mrs. B., since the atmosphere is not warmed by the +solar rays passing through it, how does it obtain heat; for all the +fires that are burning on the surface of the earth would contribute very +little towards warming it?</p> + +<p class="speaker">EMILY.</p> + +<p>The radiation of heat is not confined to burning bodies: for all +bodies, you know, have that property; therefore, not only every thing +upon the surface of the earth, but the earth itself, must radiate heat; +and this terrestrial caloric, not having, I suppose, sufficient +power to traverse the atmosphere, communicates heat to it.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your inference is extremely well drawn, Emily; but the foundation on +which it rests is not sound; for the fact is, that terrestrial or +culinary heat, though it cannot pass through the denser transparent +mediums, such as glass or water, without loss, traverses the atmosphere +completely: so that all the heat which the earth radiates, unless it +meet with clouds or any foreign body to intercept its passage, passes +into the distant regions of the universe.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a pity that so much heat should be wasted!</p> + +<span class="pagenum">90</span> +<a name="conver1.page90" id="conver1.page90"> </a> +<p class="speaker">MRS. B.</p> + +<p>Before you are tempted to object to any law of nature, reflect +whether it may not prove to be one of the numberless dispensations of +Providence for our good. If all the heat which the earth has received +from the sun, since the creation had been accumulated in it, its +temperature by this time would, no doubt, have been more elevated than +any human being could have borne.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I spoke indeed very inconsiderately. But, Mrs. B., though the +earth, at such a high temperature, might have scorched our feet, we +should always have had a cool refreshing air to breathe, since the +radiation of the earth does not heat the atmosphere.</p> + +<p class="speaker">EMILY.</p> + +<p>The cool air would have afforded but very insufficient refreshment, +whilst our bodies were exposed to the burning radiation of the +earth.</p> + +<p class="speaker">MRS. B.</p> + +<p>Nor should we have breathed a cool air; for though it is true that +heat is not communicated to the atmosphere by radiation, yet the air is +warmed by contact with heated bodies, in the same manner as solids or +liquids. The stratum of air which is immediately in contact with the +earth is heated by +<span class="pagenum">91</span> +<a name="conver1.page91" id="conver1.page91"> </a> +it; it becomes specifically lighter and rises, making way for another +stratum of air which is in its turn heated and carried upwards; and thus +each successive stratum of air is warmed by coming in contact with the +earth. You may perceive this effect in a sultry day, if you attentively +observe the strata of air near the surface of the earth; they appear in +constant agitation, for though it is true the air is itself invisible, +yet the sun shining on the vapours floating in it, render them visible, +like the amber dust in the water. The temperature of the surface of the +earth is therefore the source from whence the atmosphere derives its +heat, though it is communicated neither by radiation, nor transmitted +from one particle of it to another by the conducting power; but every +particle of air must come in contact with the earth in order to receive +heat from it.</p> + +<p class="speaker">EMILY.</p> + +<p>Wind then by agitating the air should contribute to cool the earth +and warm the atmosphere, by bringing a more rapid succession of fresh +strata of air in contact with the earth, and yet in general wind feels +cooler than still air?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the agitation of the air carries off heat from the surface of +our bodies more rapidly than +<span class="pagenum">92</span> +<a name="conver1.page92" id="conver1.page92"> </a> +still air, by occasioning a greater number of points of contact in a +given time.</p> + +<p class="speaker">EMILY.</p> + +<p>Since it is from the earth and not the sun that the atmosphere +receives its heat, I no longer wonder that elevated regions should +be colder than plains and valleys; it was always a subject of +astonishment to me, that in ascending a mountain and approaching the +sun, the air became colder instead of being more heated.</p> + +<p class="speaker">MRS. B.</p> + +<p>At the distance of about a hundred million of miles, which we are +from the sun, the approach of a few thousand feet makes no sensible +difference, whilst it produces a very considerable effect with regard to +the warming the atmosphere at the surface of the earth.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet as the warm air rises from the earth and the cold air descends to +it, I should have supposed that heat would have accumulated in the +upper regions of the atmosphere, and that we should have felt the air +warmer as we ascended?</p> + +<p class="speaker">MRS. B.</p> + +<p>The atmosphere, you know, diminishes in density, and consequently in +weight, as it is more distant +<span class="pagenum">93</span> +<a name="conver1.page93" id="conver1.page93"> </a> +from the earth; the warm air, therefore, rises only till it meets with a +stratum of air of its own density; and it will not ascend into the upper +regions of the atmosphere until all the parts beneath have been +previously heated. The length of summer even in warm climates does not +heat the air sufficiently to melt the snow which has accumulated during +the winter on very high mountains, although they are almost constantly +exposed to the heat of the sun’s rays, being too much elevated to be +often enveloped in clouds.</p> + +<p class="speaker">EMILY.</p> + +<p>These explanations are very satisfactory; but allow me to ask you one +more question respecting the increased levity of heated liquids. You +said that when water was heated over the fire, the particles at the +bottom of the vessel ascended as soon as heated, in consequence of their +specific levity: why does not the same effect continue when the water +boils, and is converted into steam? and why does the steam rise from the +surface, instead of the bottom of the liquid?</p> + +<p class="speaker">MRS. B.</p> + +<p>The steam or vapour does ascend from the bottom, though it seems to +arise from the surface of the liquid. We shall boil some water in this +Florence flask, (<a class="smallcaps" href="#plateIV">Plate IV.</a> +<ins class="mycorr" title="error for ‘Fig. 2’">Fig. 1</ins>.) in order that +<span class="pagenum">94</span> +<a name="conver1.page94" id="conver1.page94"> </a> +you may be well acquainted with the process of ebullition;—you +will then see, through the glass, that the vapour rises in bubbles from +the bottom. We shall make it boil by means of a lamp, which is more +convenient for this purpose than the chimney fire.</p> + +<p class="figname"> +<a name="plateIV" id="plateIV">Plate IV.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 84.</p> + +<p class="illustration"> +<img src="images/plate4b_thumb.png" width="118" height="310" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 2. Boiling water in a flask over a Patent lamp.</p> + +<p class="figlink"> +<a href="images/plate4_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">EMILY.</p> + +<p>I see some small bubbles ascend, and a great many appear all over the +inside of the flask; does the water begin to boil already?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; what you now see are bubbles of air, which were either dissolved +in the water, or attached to the inner surface of the flask, and which, +being rarefied by the heat, ascend in the water.</p> + +<p class="speaker">EMILY.</p> + +<p>But the heat which rarefies the air inclosed in the water must rarefy +the water at the same time; therefore, if it could remain stationary in +the water when both were cold, I do not understand why it should +not when both are equally heated?</p> + +<p class="speaker">MRS. B.</p> + +<p>Air being much less dense than water, is more easily rarefied; the +former, therefore, expands to a great extent, whilst the latter +continues to occupy +<span class="pagenum">95</span> +<a name="conver1.page95" id="conver1.page95"> </a> +nearly the same space; for water dilates comparatively but very little +without changing its state and becoming vapour. Now that the water in +the flask begins to boil, observe what large bubbles rise from the +bottom of it.</p> + +<p class="speaker">EMILY.</p> + +<p>I see them perfectly; but I wonder that they have sufficient power to +force themselves through the water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>They <i>must</i> rise, you know, from their specific levity.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are right, Caroline; but vapour has not in all liquids (when +brought to the degree of vaporization) the power of overcoming the +pressure of the less heated surface. Metals, for instance, mercury +excepted, evaporate only from the surface; therefore no vapour will +ascend from them till the degree of heat which is necessary to form it +has reached the surface; that is to say, till the whole of the liquid is +brought to a state of ebullition.</p> + +<p class="speaker">EMILY.</p> + +<p>I have observed that steam, immediately issuing from the spout of a +teakettle, is less visible than at a further distance from it; yet it +must be more +<span class="pagenum">96</span> +<a name="conver1.page96" id="conver1.page96"> </a> +dense when it first evaporates, than when it begins to diffuse itself in +the air.</p> + +<p class="speaker">MRS. B.</p> + +<p>When the steam is first formed, it is so perfectly dissolved by +caloric, as to be invisible. In order however to understand this, it +will be necessary for me to enter into some explanation respecting the +nature of <span class="smallroman">SOLUTION</span>. Solution takes +place whenever a body is melted in a fluid. In this operation the body +is reduced to such a minute state of division by the fluid, as to become +invisible in it, and to partake of its fluidity; but in common solutions +this happens without any decomposition, the body being only divided into +its integrant particles by the fluid in which it is melted.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is then a mode of destroying the attraction of aggregation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly.—The two principal solvent fluids are <i>water</i>, +and <i>caloric</i>. You may have observed that if you melt salt in +water, it totally disappears, and the water remains clear, and +transparent as before; yet though the union of these two bodies appears +so perfect, it is not produced by any chemical combination; both the +salt and the water remain unchanged; and if you were to separate +<span class="pagenum">97</span> +<a name="conver1.page97" id="conver1.page97"> </a> +them by evaporating the latter, you would find the salt in the same +state as before.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose that water is a solvent for solid bodies, and caloric for +liquids?</p> + +<p class="speaker">MRS. B.</p> + +<p>Liquids of course can only be converted into vapour by caloric. But +the solvent power of this agent is not at all confined to that class of +bodies; a great variety of solid substances are dissolved by heat: +thus metals, which are insoluble in water, can be dissolved by intense +heat, being first fused or converted into a liquid, and then rarefied +into an invisible vapour. Many other bodies, such as salt, gums, &c. +yield to either of these solvents.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And that, no doubt, is the reason why hot water will melt them so +much better than cold water?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is so. Caloric may, indeed, be considered as having, in every +instance, some share in the solution of a body by water, since water, +however low its temperature may be, always contains more or less +caloric.</p> + +<span class="pagenum">98</span> +<a name="conver1.page98" id="conver1.page98"> </a> +<p class="speaker">EMILY.</p> + +<p>Then, perhaps, water owes its solvent power merely to the caloric +contained in it?</p> + +<p class="speaker">MRS. B.</p> + +<p>That, probably, would be carrying the speculation too far; +I should rather think that water and caloric unite their efforts to +dissolve a body, and that the difficulty or facility of effecting this, +depend both on the degree of attraction of aggregation to be overcome, +and on the arrangement of the particles which are more or less disposed +to be divided and penetrated by the solvent.</p> + +<p class="speaker">EMILY.</p> + +<p>But have not all liquids the same solvent power as water?</p> + +<p class="speaker">MRS. B.</p> + +<p>The solvent power of other liquids varies according to their nature, +and that of the substances submitted to their action. Most of these +solvents, indeed, differ essentially from water, as they do not merely +separate the integrant particles of the bodies which they dissolve, but +attack their constituent principles by the power of chemical attraction, +thus producing a true decomposition. These more complicated operations +we must consider in another place, and confine our attention +<span class="pagenum">99</span> +<a name="conver1.page99" id="conver1.page99"> </a> +at present to the solutions by water and caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But there are a variety of substances which, when dissolved in water, +make it thick and muddy, and destroy its transparency.</p> + +<p class="speaker">MRS. B.</p> + +<p>In this case it is not a solution, but simply a mixture. I shall +show you the difference between a solution and a mixture, by +putting some common salt into one glass of water, and some powder of +chalk into another; both these substances are white, but their effect on +the water will be very different.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Very different indeed! The salt entirely disappears and leaves the +water transparent, whilst the chalk changes it into an opaque liquid +like milk.</p> + +<p class="speaker">EMILY.</p> + +<p>And would lumps of chalk and salt produce similar effects on +water?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, but not so rapidly; salt is, indeed, soon melted though in a +lump; but chalk, which does not mix so readily with water, would require +a +<span class="pagenum">100</span> +<a name="conver1.page100" id="conver1.page100"> </a> +much greater length of time; I therefore preferred showing you the +experiment with both substances reduced to powder, which does not in any +respect alter their nature, but facilitates the operation merely by +presenting a greater quantity of surface to the water.</p> + +<p>I must not forget to mention a very curious circumstance respecting +solutions, which is, that a fluid is not nearly so much increased in +bulk by holding a body in solution, as it would by mere mixture with the +body.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That seems impossible; for two bodies cannot exist together in the +same space.</p> + +<p class="speaker">MRS. B.</p> + +<p>Two bodies may, by condensation, occupy less space when in union than +when separate, and this I can show you by an easy experiment.</p> + +<p>This phial, which contains some salt, I shall fill with water, +pouring it in quickly, so as not to dissolve much of the salt; and when +it is quite full I cork it.—If I now shake the phial till the salt +is dissolved, you will observe that it is no longer full.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I shall try to add a little more salt.—But now, you see, +Mrs. B., the water runs over.</p> + +<span class="pagenum">101</span> +<a name="conver1.page101" id="conver1.page101"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes; but observe that the last quantity of salt you put in remains +solid at the bottom, and displaces the water; for it has already melted +all the salt it is capable of holding in solution. This is called the +point of <i>saturation</i>; and the water in this case is said to be +<i>saturated</i> with salt.</p> + +<p class="speaker">EMILY.</p> + +<p>I think I now understand the solution of a solid body by water +perfectly: but I have not so clear an idea of the solution of a liquid +by caloric.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is probably of a similar nature; but as caloric is an invisible +fluid, its action as a solvent is not so obvious as that of water. +Caloric, we may conceive, dissolves water, and converts it into vapour +by the same process as water dissolves salt; that is to say, the +particles of water are so minutely divided by the caloric as to become +invisible. Thus, you are now enabled to understand why the vapour of +boiling water, when it first issues from the spout of a kettle, is +invisible; it is so, because it is then completely dissolved by caloric. +But the air with which it comes in contact, being much colder than the +vapour, the latter yields to it a quantity of its caloric. The particles +of vapour being thus in a great measure deprived +<span class="pagenum">102</span> +<a name="conver1.page102" id="conver1.page102"> </a> +of their solvent, gradually collect, and become visible in the form of +steam, which is water in a state of imperfect solution; and if you were +further to deprive it of its caloric, it would return to its original +liquid state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That I understand very well. If you hold a cold plate over a tea-urn, +the steam issuing from it will be immediately converted into drops of +water by parting with its caloric to the plate; but in what state is the +steam, when it becomes invisible by being diffused in the air?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not merely diffused, but is again dissolved by the air.</p> + +<p class="speaker">EMILY.</p> + +<p>The air, then, has a solvent power, like water and caloric?</p> + +<p class="speaker">MRS. B.</p> + +<p>This was formerly believed to be the case. But it appears from more +recent enquiries that the solvent power of the atmosphere depends solely +upon the caloric contained in it. Sometimes the watery vapour diffused +in the atmosphere is but imperfectly dissolved, as is the case in the +formation of clouds and fogs; but if it gets into a region sufficiently +warm, it becomes perfectly invisible.</p> + +<span class="pagenum">103</span> +<a name="conver1.page103" id="conver1.page103"> </a> +<p class="speaker">EMILY.</p> + +<p>Can any water dissolve in the atmosphere without its being previously +converted into vapour by boiling?</p> + +<p class="speaker">MRS. B.</p> + +<p>Unquestionably; and this constitutes the difference between +<i>vaporization</i> and <i>evaporation</i>. Water, when heated to the +boiling point, can no longer exist in the form of water, and must +necessarily be converted into vapour or steam, whatever may be the state +and temperature of the surrounding medium; this is called vaporization. +But the atmosphere, by means of the caloric it contains, can take up a +certain portion of water at any temperature, and hold it in a state of +solution. This is simply evaporation. Thus the atmosphere is continually +carrying off moisture from the surface of the earth, until it is +saturated with it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is the case, no doubt, when we feel the atmosphere damp.</p> + +<p class="speaker">MRS. B.</p> + +<p>On the contrary, when the moisture is well dissolved it occasions no +humidity: it is only when in a state of imperfect solution and floating +in the atmosphere, in the form of watery vapour, that it produces +dampness. This happens more frequently +<span class="pagenum">104</span> +<a name="conver1.page104" id="conver1.page104"> </a> +in winter than in summer; for the lower the temperature of the +atmosphere, the less water it can dissolve; and in reality it never +contains so much moisture as in a dry hot summer’s day.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You astonish me! But why, then, is the air so dry in frosty weather, +when its temperature is at the lowest?</p> + +<p class="speaker">EMILY.</p> + +<p>This, I conjecture, proceeds not so much from the moisture being +dissolved, as from its being frozen; is not that the case?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is; and the freezing of the watery vapour which the atmospheric +heat could not dissolve, produces what is called a hoar frost; for the +particles descend in freezing, and attach themselves to whatever they +meet with on the surface of the earth.</p> + +<p>The tendency of free caloric to an equilibrium, together with its +solvent power, are likewise connected with the phenomena of rain, of +dew, &c. When moist air of a certain temperature happens to +pass through a colder region of the atmosphere, it parts with a portion +of its heat to the surrounding air; the quantity of caloric, therefore, +which served to keep the water in a state of +<span class="pagenum">105</span> +<a name="conver1.page105" id="conver1.page105"> </a> +vapour, being diminished, the watery particles approach each other, and +form themselves into drops of water, which being heavier than the +atmosphere, descend to the earth. There are also other circumstances, +and particularly the variation in the weight of the atmosphere, which +may contribute to the formation of rain. This, however, is an intricate +subject, into which we cannot more fully enter at present.</p> + +<p class="speaker">EMILY.</p> + +<p>In what manner do you account for the formation of dew?</p> + +<p class="speaker">MRS. B.</p> + +<p>Dew is a deposition of watery particles or minute drops from the +atmosphere, precipitated by the coolness of the evening.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This precipitation is owing, I suppose, to the cooling of the +atmosphere, which prevents its retaining so great a quantity of watery +vapour in solution as during the heat of the day.</p> + +<p class="speaker">MRS. B.</p> + +<p>Such was, from time immemorial, the generally received opinion +respecting the cause of dew; but it has been very recently proved by a +course of ingenious experiments of Dr. Wells, that the deposition +<span class="pagenum">106</span> +<a name="conver1.page106" id="conver1.page106"> </a> +of dew is produced by the cooling of the surface of the earth, which he +has shown to take place previously to the cooling of the atmosphere; for +on examining the temperature of a plot of grass just before the +dew-fall, he found that <ins class="mycorr" title="text reads ‘is’">it</ins> +was considerably colder than the air a few feet above it, +from which the dew was shortly after precipitated.</p> + +<p class="speaker">EMILY.</p> + +<p>But why should the earth cool in the evening sooner than the +atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because it parts with its heat more readily than the air; the earth +is an excellent radiator of caloric, whilst the atmosphere does not +possess that property, at least in any sensible degree. Towards evening, +therefore, when the solar heat declines, and when after sunset it +entirely ceases, the earth rapidly cools by radiating heat towards the +skies; whilst the air has no means of parting with its heat but by +coming into contact with the cooled surface of the earth, to which it +communicates its caloric. Its solvent power being thus reduced, it is +unable to retain so large a portion of watery vapour, and deposits those +pearly drops which we call dew.</p> + +<p class="speaker">EMILY.</p> + +<p>If this be the cause of dew, we need not be apprehensive +<span class="pagenum">107</span> +<a name="conver1.page107" id="conver1.page107"> </a> +of receiving any injury from it; for it can be deposited only on +surfaces that are colder than the atmosphere, which is never the case +with our bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very true; yet I would not advise you for this reason to be too +confident of escaping all the ill effects which may arise from exposure +to the dew; for it may be deposited on your clothes, and chill you +afterwards by its evaporation from them. Besides, whenever the dew is +copious, there is a chill in the atmosphere which it is not always safe +to encounter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Wind, then, must promote the deposition of dew, by bringing a more +rapid succession of particles of air in contact with the earth, just as +it promotes the cooling of the earth and warming of the atmosphere +during the heat of the day?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; provided the wind be unattended with clouds, for these +accumulations of moisture not only prevent the free radiation of the +earth towards the upper regions, but themselves radiate towards the +earth; under these circumstances much less dew is formed than on fine +clear nights, when the radiation of the earth passes without obstacle +through the atmosphere to the distant regions of space, whence it +<span class="pagenum">108</span> +<a name="conver1.page108" id="conver1.page108"> </a> +receives no caloric in exchange. The dew continues to be deposited +during the night, and is generally most abundant towards morning, when +the contrast between the temperature of the earth and that of the air is +greatest. After sunrise the equilibrium of temperature between these two +bodies is gradually restored by the solar rays passing freely through +the atmosphere to the earth; and later in the morning the temperature of +the earth gains the ascendency, and gives out caloric to the air by +contact, in the same manner as it receives it from the air during the +night.—Can you tell me, now, why a bottle of wine taken fresh from +the cellar (in summer particularly), will soon be covered with dew; and +even the glasses into which the wine is poured will be moistened with a +similar vapour?</p> + +<p class="speaker">EMILY.</p> + +<p>The bottle being colder than the surrounding air, must absorb caloric +from it; the moisture therefore which that air contained becomes +visible, and forms the dew which is deposited on the bottle.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well, Emily. Now, Caroline, can you inform me why, in a warm +room, or close carriage, the contrary effect takes place; that is to +say, that the inside of the windows is covered with vapour?</p> + +<span class="pagenum">109</span> +<a name="conver1.page109" id="conver1.page109"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I have heard that it proceeds from the breath of those within the +room or the carriage; and I suppose it is occasioned by the windows +which, being colder than the breath, deprive it of part of its caloric, +and by this means convert it into watery vapour.</p> + +<p class="speaker">MRS. B.</p> + +<p>You have both explained it extremely well. Bodies attract dew in +proportion as they are good radiators of caloric, as it is this quality +which reduces their temperature below that of the atmosphere; hence we +find that little or no dew is deposited on rocks, sand, water; while +grass and living vegetables, to which it is so highly beneficial, +attract it in abundance—another remarkable instance of the wise +and bountiful dispensations of Providence.</p> + +<p class="speaker">EMILY.</p> + +<p>And we may again observe it in the abundance of dew in summer, and in +hot climates, when its cooling effects are so much required; but I do +not understand what natural cause increases the dew in hot weather?</p> + +<p class="speaker">MRS. B.</p> + +<p>The more caloric the earth receives during the day, the more it will +radiate afterwards, and consequently the more rapidly its temperature +will be reduced in the evening, in comparison to that of the +<span class="pagenum">110</span> +<a name="conver1.page110" id="conver1.page110"> </a> +atmosphere. In the West-Indies especially, where the intense heat of the +day is strongly contrasted with the coolness of the evening, the dew is +prodigiously abundant. During a drought, the dew is less plentiful, as +the earth is not sufficiently supplied with moisture to be able to +saturate the atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have often observed, Mrs. B., that when I walk out in frosty +weather, with a veil over my face, my breath freezes upon it. Pray what +is the reason of that?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because the cold air immediately seizes on the caloric of your +breath, and, by robbing it of its solvent, reduces it to a denser fluid, +which is the watery vapour that settles on your veil, and there it +continues parting with its caloric till it is brought down to the +temperature of the atmosphere, and assumes the form of ice.</p> + +<p>You may, perhaps, have observed that the breath of animals, or rather +the moisture contained in it, is visible in damp weather, or during a +frost. In the former case, the atmosphere being over-saturated with +moisture, can dissolve no more. In the latter, the cold condenses it +into visible vapour; and for the same reason, the steam arising from +water that is warmer than the atmosphere, +<span class="pagenum">111</span> +<a name="conver1.page111" id="conver1.page111"> </a> +becomes visible. Have you never taken notice of the vapour rising from +your hands after having dipped them into warm water?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Frequently, especially in frosty weather.</p> + +<p class="speaker">MRS. B.</p> + +<p>We have already observed that pressure is an obstacle to evaporation: +there are liquids that contain so great a quantity of caloric, and whose +particles consequently adhere so slightly together, that they may be +rapidly converted into vapour without any elevation of temperature, +merely by taking off the weight of the atmosphere. In such liquids, you +perceive, it is the pressure of the atmosphere alone that connects their +particles, and keeps them in a liquid state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not well understand why the particles of such fluids should be +disunited and converted into vapour, without any elevation of +temperature, in spite of the attraction of cohesion.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because the degree of heat at which we usually observe these +fluids is sufficient to overcome their attraction of cohesion. Ether is +of this description; +<span class="pagenum">112</span> +<a name="conver1.page112" id="conver1.page112"> </a> +it will boil and be converted into vapour, at the common temperature of +the air, if the pressure of the atmosphere be taken off.</p> + +<p class="speaker">EMILY.</p> + +<p>I thought that ether would evaporate without either the pressure of +the atmosphere being taken away, or heat applied; and that it was for +that reason so necessary to keep it carefully corked up?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is true it will evaporate, but without ebullition; what I am now +speaking of is the vaporization of ether, or its conversion into vapour +by boiling. I am going to show you how suddenly the ether in this +phial will be converted into vapour, by means of the +air-pump.—Observe with what rapidity the bubbles ascend, as I take +off the pressure of the atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It positively boils: how singular to see a liquid boil without +heat!</p> + +<p class="speaker">MRS. B.</p> + +<p>Now I shall place the phial of ether in this glass, which it nearly +fits, so as to leave only a small space, which I fill with water; and in +this state I put it again under the receiver. +<span class="pagenum">113</span> +<a name="conver1.page113" id="conver1.page113"> </a> +(<a class="smallcaps" href="#plateIVa">Plate IV.</a> Fig. 1.)<a +class="tag" name="tag7" id="tag7" href="#note7">*</a> You will +observe, as I exhaust the air from it, that whilst the ether boils, the +water freezes.</p> + +<p class="figname"> +<a name="plateIVa" id="plateIVa">Plate IV.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 84.</p> + +<p class="illustration"> +<img src="images/plate4a_thumb.png" width="245" height="251" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. Ether evaporated & water frozen in the air pump. +A Phial of Ether. +B Glass vessel containing water. +C.C Thermometers<ins class="correction" title="comma missing or invisible">, </ins>one +in the Ether, the other in the water.</p> + +<p class="figlink"> +<a href="images/plate4_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is indeed wonderful to see water freeze in contact with a boiling +fluid!</p> + +<p class="speaker">EMILY.</p> + +<p>I am at a loss to conceive how the ether can pass to the state of +vapour without an addition of caloric. Does it not contain more caloric +in a state of vapour, than in a state of liquidity?</p> + +<p class="speaker">MRS. B.</p> + +<p>It certainly does; for though it is the pressure of the atmosphere +which condenses it into a liquid, it is by forcing out the caloric that +belongs to it when in an aëriform state.</p> + +<span class="pagenum">114</span> +<a name="conver1.page114" id="conver1.page114"> </a> +<p class="speaker">EMILY.</p> + +<p>You have, therefore, two difficulties to explain, +Mrs. B.—First, from whence the ether obtains the caloric +necessary to convert it into vapour when it is relieved from the +pressure of the atmosphere; and, secondly, what is the reason that the +water, in which the bottle of ether stands, is frozen?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now, I think, I can answer both these questions. The ether +obtains the addition of caloric required, from the water in the glass; +and the loss of caloric, which the latter sustains, is the occasion of +its freezing.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are perfectly right; and if you look at the thermometer which I +have placed in the water, whilst I am working the pump, you will see +that every time bubbles of vapour are produced, the mercury descends; +which proves that the heat of the water diminishes in proportion as the +ether boils.</p> + +<p class="speaker">EMILY.</p> + +<p>This I understand now very well; but if the water freezes in +consequence of yielding its caloric to the ether, the equilibrium of +heat must, in this case, be totally destroyed. Yet you have told us, +that the exchange of caloric between two bodies of +<span class="pagenum">115</span> +<a name="conver1.page115" id="conver1.page115"> </a> +equal temperature, was always equal; how, then, is it that the water, +which was originally of the same temperature as the ether, gives out +caloric to it, till the water is frozen, and the ether made to boil?</p> + +<p class="speaker">MRS. B.</p> + +<p>I suspected that you would make these objections; and, in order to +remove them, I enclosed two thermometers in the air-pump; one which +stands in the glass of water, the other in the phial of ether; and you +may see that the equilibrium of temperature is not destroyed; for as the +thermometer descends in the water, that in the ether sinks in the same +manner; so that both thermometers indicate the same temperature, though +one of them is in a boiling, the other in a freezing liquid.</p> + +<p class="speaker">EMILY.</p> + +<p>The ether, then, becomes colder as it boils? This is so contrary to +common experience, that I confess it astonishes me exceedingly.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is, indeed, a most extraordinary circumstance. But pray, how do +you account for it?</p> + +<p class="speaker">MRS. B.</p> + +<p>I cannot satisfy your curiosity at present; for before we can attempt +to explain this apparent +<span class="pagenum">116</span> +<a name="conver1.page116" id="conver1.page116"> </a> +paradox, it is necessary to become acquainted with the subject of <span +class="smallroman">LATENT HEAT</span>: and that, I think, we must +defer till our next interview.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I believe, Mrs. B., that you are glad to put off the explanation; for +it must be a very difficult point to account for.</p> + +<p class="speaker">MRS. B.</p> + +<p>I hope, however, that I shall do it to your complete +satisfaction.</p> + +<p class="speaker">EMILY.</p> + +<p>But before we part, give me leave to ask you one question. Would not +water, as well as ether, boil with less heat, if deprived of the +pressure of the atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly. You must always recollect that there are two forces to +overcome, in order to make a liquid boil or evaporate; the attraction of +aggregation, and the weight of the atmosphere. On the summit of a high +mountain (as Mr. De Saussure ascertained on Mount Blanc) much less heat +is required to make water boil, than in the plain, where the weight of +the atmosphere is +<span class="pagenum">117</span> +<a name="conver1.page117" id="conver1.page117"> </a> +greater.<a class="tag" name="tag8" id="tag8" href="#note8">*</a> +Indeed if the weight of the atmosphere be entirely removed by means of a +good air-pump, and if water be placed in the exhausted receiver, it will +evaporate so fast, however cold it maybe, as to give it the appearance +of boiling from the surface. But without the assistance of the air-pump, +I can show you a very pretty experiment, which proves the effect of +the pressure of the atmosphere in this respect.</p> + +<p>Observe, that this Florence flask is about half full of water, and +the upper half of invisible vapour, the water being in the act of +boiling.—I take it from the lamp, and cork it +carefully—the water, you see, immediately ceases +boiling.—I shall now dip the flask into a bason of cold +water.<a class="tag" name="tag9" id="tag9" href="#note9">†</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>But look, Mrs. B., the hot water begins to boil again, although the +cold water must rob it more and more of its caloric! What can be the +reason of that?</p> + +<span class="pagenum">118</span> +<a name="conver1.page118" id="conver1.page118"> </a> +<p class="speaker">MRS. B.</p> + +<p>Let us examine its temperature. You see the thermometer immersed in +it remains stationary at 180 degrees, which is about 30 degrees below +the boiling point. When I took the flask from the lamp, I observed +to you that the upper part of it was filled with vapour; this being +compelled to yield its caloric to the cold water, was again condensed +into water—What, then, filled the upper part of the flask?</p> + +<p class="speaker">EMILY.</p> + +<p>Nothing; for it was too well corked for the air to gain admittance, +and therefore the upper part of the flask must be a vacuum.</p> + +<p class="speaker">MRS. B.</p> + +<p>The water below, therefore, no longer sustains the pressure of the +atmosphere, and will consequently boil at a much lower temperature. +Thus, you see, though it had lost many degrees of heat, it began boiling +again the instant the vacuum was formed above it. The boiling has now +ceased, the temperature of the water being still farther reduced; if it +had been ether, instead of water, it would have continued boiling much +longer, for ether boils, under the usual atmospheric pressure, at a +temperature as low as 100 degrees; and in a vacuum it boils at almost +any temperature; but +<span class="pagenum">119</span> +<a name="conver1.page119" id="conver1.page119"> </a> +water being a more dense fluid, requires a more considerable quantity of +caloric to make it evaporate quickly, even when the pressure of the +atmosphere is removed.</p> + +<p class="speaker">EMILY.</p> + +<p>What proportion of vapour can the atmosphere contain in a state of +solution?</p> + +<p class="speaker">MRS. B.</p> + +<p>I do not know whether it has been exactly ascertained by experiment; +but at any rate this proportion must vary, both according to the +temperature and the weight of the atmosphere; for the lower the +temperature, and the greater the pressure, the smaller must be the +proportion of vapour that the atmosphere can contain.</p> + +<p>To conclude the subject of free caloric, I should mention +<i>Ignition</i>, by which is meant that emission of light which is +produced in bodies at a very high temperature, and which is the effect +of accumulated caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>You mean, I suppose, that light which is produced by a burning +body?</p> + +<p class="speaker">MRS. B.</p> + +<p>No: ignition is quite independent of combustion. Clay, chalk, and +indeed all incombustible +<span class="pagenum">120</span> +<a name="conver1.page120" id="conver1.page120"> </a> +substances, may be made red hot. When a body burns, the light emitted is +the effect of a chemical change which takes place, whilst ignition is +the effect of caloric alone, and no other change than that of +temperature is produced in the ignited body.</p> + +<p>All solid bodies, and most liquids, are susceptible of ignition, or, +in other words, of being heated so as to become luminous; and it is +remarkable that this takes place pretty nearly at the same temperature +in all bodies, that is, at about 800 degrees of Fahrenheit’s scale.</p> + +<p class="speaker">EMILY.</p> + +<p>But how can liquids attain so high a temperature, without being +converted into vapour?</p> + +<p class="speaker">MRS. B.</p> + +<p>By means of confinement and pressure. Water confined in a strong iron +vessel (called Papin’s digester) can have its temperature raised to +upwards of 400 degrees. Sir James Hall has made some very curious +experiments on the effects of heat assisted by pressure; by means of +strong gun-barrels, he succeeded in melting a variety of substances +which were considered as infusible: and it is not unlikely that, by +similar methods, water itself might be heated to redness.</p> + +<span class="pagenum">121</span> +<a name="conver1.page121" id="conver1.page121"> </a> +<p class="speaker">EMILY.</p> + +<p>I am surprised at that: for I thought that the force of steam was +such as to destroy almost all mechanical resistance.</p> + +<p class="speaker">MRS. B.</p> + +<p>The expansive force of steam is prodigious; but in order to subject +water to such high temperatures, it is prevented by confinement from +being converted into steam, and the expansion of heated water is +comparatively trifling.—But we have dwelt so long on the subject +of free caloric, that we must reserve the other modifications of that +agent to our next meeting, when we shall endeavour to proceed more +rapidly.</p> + +<div class="footnote"> + +<p><a name="note7" id="note7" href="#tag7">*</a> +Two pieces of thin glass tubes, sealed at one end, might answer this +purpose better. The experiment, however, as here described, is +difficult, and requires a very nice apparatus. But if, instead of phials +or tubes, two watch-glasses be used, water may be frozen almost +instantly in the same manner. The two glasses are placed over one +another, with a few drops of water interposed between them, and the +uppermost glass is filled with ether. After working the pump for a +minute or two, the glasses are found to adhere strongly together, and a +thin layer of ice is seen between them.</p> + +<p><a name="note8" id="note8" href="#tag8">*</a> +On the top of Mount Blanc, water boiled when heated only to 187 degrees, +instead of 212 degrees.</p> + +<p><a name="note9" id="note9" href="#tag9">†</a> +The same effect may be produced by wrapping a cold wet linen cloth round +the upper part of the flask. In order to show how much the water cools +whilst it is boiling, a thermometer, graduated on the tube itself, +may be introduced into the bottle through the cork.</p> + +</div> + + +<span class="pagenum">122</span> +<a name="conver1.page122" id="conver1.page122"> </a> +<h4><a name="convIV" id="convIV">CONVERSATION IV.</a><br> +<span class="subhead">ON COMBINED CALORIC, COMPREHENDING SPECIFIC AND +LATENT HEAT.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> are now to examine the other +modifications of caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am very curious to know of what nature they can be; for I have no +notion of any kind of heat that is not perceptible to the senses.</p> + +<p class="speaker">MRS. B.</p> + +<p>In order to enable you to understand them, it will be necessary to +enter into some previous explanations.</p> + +<p>It has been discovered by modern chemists, that bodies of a different +nature, heated to the same temperature, do not contain the same quantity +of caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How could that be ascertained? Have you not told us that it is +impossible to discover the absolute quantity of caloric which bodies +contain?</p> + +<span class="pagenum">123</span> +<a name="conver1.page123" id="conver1.page123"> </a> +<p class="speaker">MRS. B.</p> + +<p>True; but at the same time I said that we were enabled to form a +judgment of the proportions which bodies bore to each other in this +respect. Thus it is found that, in order to raise the temperature of +different bodies the same number of degrees, different quantities of +caloric are required for each of them. If, for instance, you place a +pound of lead, a pound of chalk, and a pound of milk, in a hot +oven, they will be gradually heated to the temperature of the oven; but +the lead will attain it first, the chalk next, and the milk last.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is a natural consequence of their different bulks; the lead +being the smallest body, will be heated soonest, and the milk, which is +the largest, will require the longest time.</p> + +<p class="speaker">MRS. B.</p> + +<p>That explanation will not do, for if the lead be the least in bulk, +it offers also the least surface to the caloric, the quantity of heat +therefore which can enter into it in the same space of time is +proportionally smaller.</p> + +<p class="speaker">EMILY.</p> + +<p>Why, then, do not the three bodies attain the temperature of the oven +at the same time?</p> + +<span class="pagenum">124</span> +<a name="conver1.page124" id="conver1.page124"> </a> +<p class="speaker">MRS. B.</p> + +<p>It is supposed to be on account of the different capacity of these +bodies for caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What do you mean by the capacity of a body for caloric?</p> + +<p class="speaker">MRS. B.</p> + +<p>I mean a certain disposition of bodies to require more or less +caloric for raising their temperature to any degree of heat. Perhaps the +fact may be thus explained:</p> + +<p>Let us put as many marbles into this glass as it will contain, and +pour some sand over them—observe how the sand penetrates and +lodges between them. We shall now fill another glass with pebbles of +various forms—you see that they arrange themselves in a more +compact manner than the marbles, which, being globular, can touch each +other by a single point only. The pebbles, therefore, will not admit so +much sand between them; and consequently one of these glasses will +necessarily contain more sand than the other, though both of them be +equally full.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This I understand perfectly. The marbles and the pebbles represent +two bodies of different kinds, and the sand the caloric contained in +them; +<span class="pagenum">125</span> +<a name="conver1.page125" id="conver1.page125"> </a> +it appears very plain, from this comparison, that one body may admit of +more caloric between its particles than another.</p> + +<p class="speaker">MRS. B.</p> + +<p>You can no longer be surprised, therefore, that bodies of a different +capacity for caloric should require different proportions of that fluid +to raise their temperatures equally.</p> + +<p class="speaker">EMILY.</p> + +<p>But I do not conceive why the body that contains the most caloric +should not be of the highest temperature; that is to say, feel hot in +proportion to the quantity of caloric it contains?</p> + +<p class="speaker">MRS. B.</p> + +<p>The caloric that is employed in filling the capacity of a body, is +not free caloric; but is imprisoned as it were in the body, and is +therefore imperceptible: for we can feel only the caloric which the body +parts with, and not that which it retains.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It appears to me very extraordinary that heat should be confined in a +body in such a manner as to be imperceptible.</p> + +<span class="pagenum">126</span> +<a name="conver1.page126" id="conver1.page126"> </a> +<p class="speaker">MRS. B.</p> + +<p>If you lay your hand on a hot body, you feel only the caloric which +leaves it, and enters your hand; for it is impossible that you should be +sensible of that which remains in the body. The thermometer, in the same +manner, is affected only by the free caloric which a body transmits to +it, and not at all by that which it does not part with.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I begin to understand it: but I confess that the idea of insensible +heat is so new and strange to me, that it requires some time to render +it familiar.</p> + +<p class="speaker">MRS. B.</p> + +<p>Call it insensible caloric, and the difficulty will appear much less +formidable. It is indeed a sort of contradiction to call it heat, when +it is so situated as to be incapable of producing that sensation. Yet +this modification of caloric is commonly called <span class="smallroman">SPECIFIC HEAT</span>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But it certainly would have been more correct to have called it +<i>specific caloric</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>I do not understand how the term <i>specific</i> applies to this +modification of caloric?</p> + +<span class="pagenum">127</span> +<a name="conver1.page127" id="conver1.page127"> </a> +<p class="speaker">MRS. B.</p> + +<p>It expresses the relative quantity of caloric which different +<i>species</i> of bodies of the same weight and temperature are capable +of containing. This modification is also frequently called <i>heat of +capacity</i>, a term perhaps preferable, as it explains better its +own meaning.</p> + +<p>You now understand, I suppose, why the milk and chalk required a +longer portion of time than the lead to raise their temperature to that +of the oven?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes: the milk and chalk having a greater capacity for caloric than +the lead, a greater proportion of that fluid became insensible in +those bodies: and the more slowly, therefore, their temperature was +raised.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But might not this difference proceed from the different conducting +powers of heat in these three bodies, since that which is the best +conductor must necessarily attain the temperature of the oven first?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well observed, Caroline. This objection would be insurmountable, +if we could not, by reversing the experiment, prove that the milk, the +chalk, and the lead, actually absorbed different +<span class="pagenum">128</span> +<a name="conver1.page128" id="conver1.page128"> </a> +quantities of caloric, and we know that if the different time they took +in heating, proceeded merely from their different conducting powers, +they would each have acquired an equal quantity of caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Certainly. But how can you reverse this <ins class="mycorr" title="text reads ‘expe-/periment’ at line break">experiment</ins>?</p> + +<p class="speaker">MRS. B.</p> + +<p>It may be done by cooling the several bodies to the same degree in an +apparatus adapted to receive and measure the caloric which they give +out. Thus, if you plunge them into three equal quantities of water, each +at the same temperature, you will be able to judge of the relative +quantity of caloric which the three bodies contained, by that, which, in +cooling, they communicated to their respective portions of water: for +the same quantity of caloric which they each absorbed to raise their +temperature, will abandon them in lowering it; and on examining the +three vessels of water, you will find the one in which you immersed the +lead to be the least heated; that which held the chalk will be the next; +and that which contained the milk will be heated the most of all. The +celebrated Lavoisier has invented a machine to estimate, upon this +principle, the specific heat of bodies in a more perfect manner; but I +cannot +<span class="pagenum">129</span> +<a name="conver1.page129" id="conver1.page129"> </a> +explain it to you, till you are acquainted with the next modification of +caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>The more dense a body is, I suppose, the less is its capacity for +caloric?</p> + +<p class="speaker">MRS. B.</p> + +<p>This is not always the case with bodies of different nature; iron, +for instance, contains more specific heat than tin, though it is more +dense. This seems to show that specific heat does hot merely depend upon +the interstices between the particles; but, probably, also upon some +peculiar constitution of the bodies which we do not comprehend.</p> + +<p class="speaker">EMILY.</p> + +<p>But, Mrs. B., it would appear to me more proper to compare bodies by +<i>measure</i>, rather than by <i>weight</i>, in order to estimate their +specific heat. Why, for instance, should we not compare <i>pints</i> of +milk, of chalk, and of lead, rather than <i>pounds</i> of those +substances; for equal weights may be composed of very different +quantities?</p> + +<p class="speaker">MRS. B.</p> + +<p>You are mistaken, my dear; equal weight must contain equal quantities +of matter; and when we wish to know what is the relative quantity of +caloric, +<span class="pagenum">130</span> +<a name="conver1.page130" id="conver1.page130"> </a> +which substances of various kinds are capable of containing under the +same temperature, we must compare equal weights, and not equal bulks of +those substances. Bodies of the same weight may undoubtedly be of very +different dimensions; but that does not change their real quantity of +matter. A pound of feathers does not contain one atom more than a +pound of lead.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have another difficulty to propose. It appears to me, that if the +temperature of the three bodies in the oven did not rise equally, they +would never reach the same degree; the lead would always keep its +advantage over the chalk and milk, and would perhaps be boiling before +the others had attained the temperature of the oven. I think you +might as well say that, in the course of time, you and I should be of +the same age?</p> + +<p class="speaker">MRS. B.</p> + +<p>Your comparison is not correct, Caroline. As soon as the lead reached +the temperature of the oven, it would remain stationary; for it would +then give out as much heat as it would receive. You should recollect +that the exchange of radiating heat, between two bodies of equal +temperature, is equal: it would be impossible, therefore, for the lead +to accumulate heat after having attained +<span class="pagenum">131</span> +<a name="conver1.page131" id="conver1.page131"> </a> +the temperature of the oven; and that of the chalk and milk therefore +would ultimately arrive at the same standard. Now I fear that this will +not hold good with respect to our ages, and that, as long as I live, +I shall never cease to keep my advantage over you.</p> + +<p class="speaker">EMILY.</p> + +<p>I think that I have found a comparison for specific heat, which is +very applicable. Suppose that two men of equal weight and bulk, but who +required different quantities of food to satisfy their appetites, sit +down to dinner, both equally hungry; the one would consume a much +greater quantity of provisions than the other, in order to be equally +satisfied.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, that is very fair; for the quantity of food necessary to satisfy +their respective appetites, varies in the same manner as the quantity of +caloric requisite to raise equally the temperature of different +bodies.</p> + +<p class="speaker">EMILY.</p> + +<p>The thermometer, then, affords no indication of the specific heat of +bodies?</p> + +<p class="speaker">MRS. B.</p> + +<p>None at all: no more than satiety is a test of the quantity of food +eaten. The thermometer, as +<span class="pagenum">132</span> +<a name="conver1.page132" id="conver1.page132"> </a> +I have repeatedly said, can be affected only by free caloric, which +alone raises the temperature of bodies.</p> + +<p>But there is another mode of proving the existence of specific heat, +which affords a very satisfactory illustration of that modification. +This, however, I did not enlarge upon before, as I thought it might +appear to you rather complicated.—If you mix two fluids of +different temperatures, let us say the one at 50 degrees, and the other +at 100 degrees, of what temperature do you suppose the mixture +will be?</p> + +<p class="speaker">CAROLINE.</p> + +<p>It will be no doubt the medium between the two, that is to say, 75 +degrees.</p> + +<p class="speaker">MRS. B.</p> + +<p>That will be the case if the two bodies happen to have the same +capacity for caloric; but if not, a different result will be +obtained. Thus, for instance, if you mix together a pound of mercury, +heated at 50 degrees, and a pound of water heated at 100 degrees, the +temperature of the mixture, instead of being 75 degrees, will be <ins +class="mycorr" title="error for 88?">80</ins> degrees; so that the +water will have lost only 12 degrees, whilst the mercury will have +gained 38 degrees; from which you will conclude that the capacity of +mercury for heat is less than that of water.</p> + +<span class="pagenum">133</span> +<a name="conver1.page133" id="conver1.page133"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I wonder that mercury should have so little specific heat. Did we not +see it was a much better conductor of heat than water?</p> + +<p class="speaker">MRS. B.</p> + +<p>And it is precisely on that account that its specific heat is less. +For since the conductive power of bodies depends, as we have observed +before, on their readiness to receive heat and part with it, it is +natural to expect that those bodies which are the worst conductors +should absorb the most caloric before they are disposed to part with it +to other bodies. But let us now proceed to <span class="smallroman">LATENT HEAT</span>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And pray what kind of heat is that?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is another modification of combined caloric, which is so analogous +to specific heat, that most chemists make no distinction between them; +but Mr. Pictet, in his Essay on Fire, has so clearly discriminated them, +that I am induced to adopt his view of the subject. We therefore call +<i>latent heat</i> that portion of insensible caloric which is employed +in changing the state of bodies; that is to say, in converting solids +into liquids, or liquids; into vapour. When a body changes its state +from +<span class="pagenum">134</span> +<a name="conver1.page134" id="conver1.page134"> </a> +solid to liquid, or from liquid to vapour, its expansion occasions a +sudden and considerable increase of capacity for heat, in consequence of +which it immediately absorbs a quantity of caloric, which becomes fixed +in the body which it has transformed; and, as it is perfectly concealed +from our senses, it has obtained the name of <i>latent</i> heat.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think it would be much more correct to call this modification +latent caloric instead of latent heat, since it does not excite the +sensation of heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>This modification of heat was discovered and named by Dr. Black long +before the French chemists introduced the term caloric, and we must not +presume to alter it, as it is still used by much better chemists than +ourselves. And, besides, you are not to suppose that the nature of heat +is altered by being variously modified: for if latent heat and specific +heat do not excite the same sensations as free caloric, it is owing to +their being in a state of confinement, which prevents them from acting +upon our organs; and consequently, as soon as they are extricated from +the body in which they are imprisoned, they return to their state of +free caloric.</p> + +<span class="pagenum">135</span> +<a name="conver1.page135" id="conver1.page135"> </a> +<p class="speaker">EMILY.</p> + +<p>But I do not yet clearly see in what respect latent heat differs from +specific heat; for they are both of them imprisoned and concealed in +bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>Specific heat is that which is employed in filling the capacity of a +body for caloric, in the state in which this body actually exists; while +latent heat is that which is employed only in effecting a change of +state, that is, in converting bodies from a solid to a liquid, or from a +liquid to an aëriform state. But I think that, in a general point of +view, both these modifications might be comprehended under the name of +<i>heat of capacity</i>, as in both cases the caloric is equally engaged +in filling the capacities of bodies.</p> + +<p>I shall now show you an experiment, which I hope will give you a +clear idea of what is understood by latent heat.</p> + +<p>The snow which you see in this phial has been cooled by certain +chemical means (which I cannot well explain to you at present), to 5 or +6 degrees below the freezing point, as you will find indicated by the +thermometer which is placed in it. We shall expose it to the heat of a +lamp, and you will see the thermometer gradually rise, till it reaches +the freezing point——</p> + +<span class="pagenum">136</span> +<a name="conver1.page136" id="conver1.page136"> </a> +<p class="speaker">EMILY.</p> + +<p>But there it stops, Mrs. B., and yet the lamp burns just as well as +before. Why is not its heat communicated to the thermometer?</p> + +<p class="speaker">CAROLINE.</p> + +<p>And the snow begins to melt, therefore it must be rising above the +freezing point?</p> + +<p class="speaker">MRS. B.</p> + +<p>The heat no longer affects the thermometer, because it is wholly +employed in converting the ice into water. As the ice melts, the caloric +becomes <i>latent</i> in the new-formed liquid, and therefore cannot +raise its temperature; and the thermometer will consequently remain +stationary, till the whole of the ice be melted.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now it is all melted, and the thermometer begins to rise again.</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the conversion of the ice into water being completed, the +caloric no longer becomes latent; and therefore the heat which the water +now receives raises its temperature, as you find the thermometer +indicates.</p> + +<span class="pagenum">137</span> +<a name="conver1.page137" id="conver1.page137"> </a> +<p class="speaker">EMILY.</p> + +<p>But I do not think that the thermometer rises so quickly in the water +as it did in the ice, previous to its beginning to melt, though the lamp +burns equally well?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is owing to the different specific heat of ice and water. The +capacity of water for caloric being greater than that of ice, more heat +is required to raise its temperature, and therefore the thermometer +rises slower in the water than in the ice.</p> + +<p class="speaker">EMILY.</p> + +<p>True; you said that a solid body always increased its capacity for +heat by becoming fluid; and this is an instance of it.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, and the latent heat is that which is absorbed in consequence of +the greater capacity which the water has for heat, in comparison to +ice.</p> + +<p>I must now tell you a curious calculation founded on that +consideration. I have before observed to you that though the +thermometer shows us the comparative warmth of bodies, and enables us to +determine the same point at different times and places, it gives us no +idea of the absolute quantity of heat in any body. We cannot tell how +low it ought to fall by the privation of all heat, but an +<span class="pagenum">138</span> +<a name="conver1.page138" id="conver1.page138"> </a> +attempt has been made to infer it in the following manner. It has been +found by experiment, that the capacity of water for heat, when compared +with that of ice, is as 10 to 9, so that, at the same temperature, ice +contains one tenth of caloric less than water. By experiment also it is +observed, that in order to melt ice, there must be added to it as much +heat, as would, if it did not melt it, raise its temperature 140 +degrees. This quantity of heat is therefore absorbed when the ice, by +being converted into water, is made to contain one-ninth more caloric +than it did before. Therefore 140 degrees is a ninth part of the heat +contained in ice at 30 degrees; and the point of zero, or the absolute +privation of heat, must consequently be 1260 degrees below 32 +degrees.</p> + +<p>This mode of investigating so curious a question is ingenious, but +its correctness is not yet established by similar calculations for other +bodies. The points of absolute cold, indicated by this method in various +bodies, are very remote from each other; it is however possible, that +this may arise from some imperfection in the experiments.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is indeed very ingenious—but we must now attend to our +present experiment. The water begins to boil, and the thermometer is +again stationary.</p> + +<span class="pagenum">139</span> +<a name="conver1.page139" id="conver1.page139"> </a> +<p class="speaker">MRS. B.</p> + +<p>Well, Caroline, it is your turn to explain the phenomenon.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is wonderfully curious! The caloric is now busy in changing the +water into steam, in which it hides itself, and becomes insensible. This +is another example of latent heat, producing a change of form. At first +it converted a solid body into a liquid, and now it turns the liquid +into vapour!</p> + +<p class="speaker">MRS. B.</p> + +<p>You see, my dear, how easily you have become acquainted with these +modifications of insensible heat, which at first appeared so +unintelligible. If, now, we were to reverse these changes, and condense +the vapour into water, and the water into ice, the latent heat would +re-appear entirely, in the form of free caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray do let us see the effect of latent heat returning to its free +state.</p> + +<p class="speaker">MRS. B.</p> + +<p>For the purpose of showing this, we need simply conduct the vapour +through this tube into this vessel of cold water, where it will part +with its latent heat and return to its liquid form.</p> + +<span class="pagenum">140</span> +<a name="conver1.page140" id="conver1.page140"> </a> +<p class="speaker">EMILY.</p> + +<p>How rapidly the steam heats the water!</p> + +<p class="speaker">MRS. B.</p> + +<p>That is because it does not merely impart its free caloric to the +water, but likewise its latent heat. This method of heating liquids, has +been turned to advantage, in several economical establishments. The +steam-kitchens, which are getting into such general use, are upon the +same principle. The steam is conveyed through a pipe in a similar +manner, into the several vessels which contain the provisions to be +dressed, where it communicates to them its latent caloric, and returns +to the state of water. Count Rumford makes great use of this principle +in many of his fire-places: his grand maxim is to avoid all unnecessary +waste of caloric, for which purpose he confines the heat in such a +manner, that not a particle of it shall unnecessarily escape; and while +he economises the free caloric, he takes care also to turn the latent +heat to advantage. It is thus that he is enabled to produce a degree of +heat superior to that which is obtained in common fire-places, though he +employs less fuel.</p> + +<p class="speaker">EMILY.</p> + +<p>When the advantages of such contrivances are so clear and plain, +I cannot understand why they are not universally used.</p> + +<span class="pagenum">141</span> +<a name="conver1.page141" id="conver1.page141"> </a> +<p class="speaker">MRS. B.</p> + +<p>A long time is always required before innovations, however useful, +can be reconciled with the prejudices of the vulgar.</p> + +<p class="speaker">EMILY.</p> + +<p>What a pity it is that there should be a prejudice against new +inventions; how much more rapidly the world would improve, if such +useful discoveries were immediately and universally adopted!</p> + +<p class="speaker">MRS. B.</p> + +<p>I believe, my dear, that there are as many novelties attempted to be +introduced, the adoption of which would be prejudicial to society, as +there are of those which would be beneficial to it. The well-informed, +though by no means exempt from error, have an unquestionable advantage +over the illiterate, in judging what is likely or not to prove +serviceable; and therefore we find the former more ready to adopt such +discoveries as promise to be really advantageous, than the latter, who +having no other test of the value of a novelty but time and experience, +at first oppose its introduction. The well-informed, however, are +frequently disappointed in their most sanguine expectations, and the +prejudices of the vulgar, though they often retard the progress of +knowledge, yet sometimes, it must be +<span class="pagenum">142</span> +<a name="conver1.page142" id="conver1.page142"> </a> +admitted, prevent the propagation of error.—But we are deviating +from our subject.</p> + +<p>We have converted steam into water, and are now to change water into +ice, in order to render the latent heat sensible, as it escapes from the +water on its becoming solid. For this purpose we must produce a degree +of cold that will make water freeze.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That must be very difficult to accomplish in this warm room.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not so much as you think. There are certain chemical mixtures which +produce a rapid change from the solid to the fluid state, or the +reverse, in the substances combined, in consequence of which change +latent heat is either extricated or absorbed.</p> + +<p class="speaker">EMILY.</p> + +<p>I do not quite understand you.</p> + +<p class="speaker">MRS. B.</p> + +<p>This snow and salt, which you see me mix together, are melting +rapidly; heat, therefore, must be absorbed by the mixture, and cold +produced.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It feels even colder than ice, and yet the snow is melted. This is +very extraordinary.</p> + +<span class="pagenum">143</span> +<a name="conver1.page143" id="conver1.page143"> </a> +<p class="speaker">MRS. B.</p> + +<p>The cause of the intense cold of the mixture is to be attributed to +the change from a solid to a fluid state. The union of the snow and salt +produces a new arrangement of their particles, in consequence of which +they become liquid; and the quantity of caloric, required to effect this +change, is seized upon by the mixture wherever it can be obtained. This +eagerness of the mixture for caloric, during its liquefaction, is such, +that it converts part of its own free caloric into latent heat, and it +is thus that its temperature is lowered.</p> + +<p class="speaker">EMILY.</p> + +<p>Whatever you put in this mixture, therefore, would freeze?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; at least any fluid that is susceptible of freezing at that +temperature. I have prepared this mixture of salt and snow for the +purpose of freezing the water from which you are desirous of seeing the +latent heat escape. I have put a thermometer in the glass of water +that is to be frozen, in order that you may see how it cools.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The thermometer descends, but the heat which the water is now losing, +is its <i>free</i>, not its <i>latent</i> heat.</p> + +<span class="pagenum">144</span> +<a name="conver1.page144" id="conver1.page144"> </a> +<p class="speaker">MRS. B.</p> + +<p>Certainly; it does not part with its latent heat till it changes its +state and is converted into ice.</p> + +<p class="speaker">EMILY.</p> + +<p>But here is a very extraordinary circumstance! The thermometer is +fallen below the freezing point, and yet the water is not frozen.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is always the case previous to the freezing of water when it is +in a state of rest. Now it begins to congeal, and you may observe that +the thermometer again rises to the freezing point.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It appears to me very strange that the thermometer should rise the +very moment that the water freezes; for it seems to imply that the water +was colder before it froze than when in the act of freezing.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is so; and after our long dissertation on this circumstance, +I did not think it would appear so surprising to you. Reflect a +little, and I think you will discover the reason of it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It must be, no doubt, the extrications of latent heat, at the instant +the water freezes, that raises the temperature.</p> + +<span class="pagenum">145</span> +<a name="conver1.page145" id="conver1.page145"> </a> +<p class="speaker">MRS. B.</p> + +<p>Certainly; and if you now examine the thermometer, you will find that +its rise was but temporary, and lasted only during the disengagement of +the latent heat—now that all the water is frozen it falls again, +and will continue to fall till the ice and mixture are of an equal +temperature.</p> + +<p class="speaker">EMILY.</p> + +<p>And can you show us any experiments in which liquids, by being mixed, +become solid, and disengage latent heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>I could show you several; but you are not yet sufficiently advanced +to understand them well. I shall, however, try one, which will +afford you a striking instance of the fact. The fluid which you see in +this phial consists of a quantity of a certain salt called <i>muriat of +lime</i>, dissolved in water. Now, if I pour into it a few drops of this +other fluid, called <i>sulphuric acid</i>, the whole, or very nearly the +whole, will be instantaneously converted into a solid mass.</p> + +<p class="speaker">EMILY.</p> + +<p>How white it turns! I feel the latent heat escaping, for the bottle +is warm, and the fluid is changed to a solid white substance like +chalk!</p> + +<span class="pagenum">146</span> +<a name="conver1.page146" id="conver1.page146"> </a> +<p class="speaker">CAROLINE.</p> + +<p>This is, indeed, the most curious experiment we have seen yet. But +pray what is that white vapour that ascends from the mixture?</p> + +<p class="speaker">MRS. B.</p> + +<p>You are not yet enough of a chemist to understand that.—But +take care, Caroline, do not approach too near it, for it has a very +pungent smell.</p> + +<p>I shall show you another instance similar to that of the water, which +you observed to become warmer as it froze. I have in this phial a +solution of a salt called sulphat of soda or Glauber’s salt, made very +strong, and corked up when it was hot, and kept without agitation till +it became cold, as you may feel the phial is. Now when I take out the +cork and let the air fall upon it, (for being closed when boiling, there +was a vacuum in the upper part) observe that the salt will suddenly +crystallize. . . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>Surprising! how beautifully the needles of salt have shot through the +whole phial!</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, it is very striking—but pray do not forget the object of +the experiment. Feel how warm the phial has become by the conversion of +part of the liquid into a solid.</p> + +<span class="pagenum">147</span> +<a name="conver1.page147" id="conver1.page147"> </a> +<p class="speaker">EMILY.</p> + +<p>Quite warm I declare! this is a most curious experiment of the +disengagement of latent heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>The slakeing of lime is another remarkable instance of the +extrication of latent heat. Have you never observed how quick-lime +smokes when water is poured upon it, and how much heat it produces?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes; but I do not understand what change of state takes place in the +lime that occasions its giving out latent heat; for the quick-lime, +which is solid, is (if I recollect right) reduced to powder, by this +operation, and is, therefore, rather expanded than condensed.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is from the water, not the lime, that the latent heat is set free. +The water incorporates with, and becomes solid in the lime; in +consequence of which, the heat, which kept it in a liquid state, is +disengaged, and escapes in a sensible form.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I always thought that the heat originated in the lime. It seems very +strange that water, and cold water too, should contain so much heat.</p> + +<span class="pagenum">148</span> +<a name="conver1.page148" id="conver1.page148"> </a> +<p class="speaker">EMILY.</p> + +<p>After this extrication of caloric, the water must exist in a state of +ice in the lime, since it parts with the heat which kept it liquid.</p> + +<p class="speaker">MRS. B.</p> + +<p>It cannot properly be called ice, since ice implies a degree of cold, +at least equal to the freezing point. Yet as water, in combining with +lime, gives out more heat than in freezing, it must be in a state of +still greater solidity in the lime, than it is in the form of ice; and +you may have observed that it does not moisten or liquefy the lime in +the smallest degree.</p> + +<p class="speaker">EMILY.</p> + +<p>But, Mrs. B., the smoke that rises is white; if it was only pure +caloric which escaped, we might feel, but could not see it.</p> + +<p class="speaker">MRS. B.</p> + +<p>This white vapour is formed by some of the particles of lime, in a +state of fine dust, which are carried off by the caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>In all changes of state, then, a body either absorbs or disengages +latent heat?</p> + +<span class="pagenum">149</span> +<a name="conver1.page149" id="conver1.page149"> </a> +<p class="speaker">MRS. B.</p> + +<p>You cannot exactly say <i>absorbs latent heat</i>, as the heat +becomes latent only on being confined in the body; but you may say, +generally, that bodies, in passing from a solid to a liquid form, or +from the liquid state to that of vapour, absorb heat; and that when the +reverse takes place, heat is disengaged.<a class="tag" name="tag10" +id="tag10" href="#note10">*</a></p> + +<p class="speaker">EMILY.</p> + +<p>We can now, I think, account for the ether boiling, and the water +freezing in vacuo, at the same temperature.<a class="tag" name="tag11" id="tag11" href="#note11">†</a></p> + +<p class="speaker">MRS. B.</p> + +<p>Let me hear how you explain it.</p> + +<p class="speaker">EMILY.</p> + +<p>The latent heat, which the water gave out in freezing, was +immediately absorbed by the ether, during its conversion into vapour; +and therefore, from a latent state in one liquid, it passed into a +latent state in the other.</p> + +<p class="speaker">MRS. B.</p> + +<p>But this only partly accounts for the result of the experiment; it +remains to be explained why the +<span class="pagenum">150</span> +<a name="conver1.page150" id="conver1.page150"> </a> +temperature of the ether, while in a state of ebullition, is brought +down to the freezing temperature of the water.—It is because the +ether, during its evaporation, reduces its own temperature, in the same +proportion as that of the water, by converting its free caloric into +latent heat: so that, though one liquid boils, and the other freezes, +their temperatures remain in a state of equilibrium.</p> + +<p class="speaker">EMILY.</p> + +<p>But why does not water, as well as ether, reduce its own temperature +by evaporating?</p> + +<p class="speaker">MRS. B.</p> + +<p>The fact is that it does, though much less rapidly than ether. Thus, +for instance, you may often have observed, in the heat of summer, how +much any particular spot may be cooled by watering, though the water +used for that purpose be as warm as the air itself. Indeed so much cold +may be produced by the mere evaporation of water, that the inhabitants +of India, by availing themselves of the most favourable circumstances +for this process which their warm climate can afford, namely, the cool +of the night, and situations most exposed to the night breeze, succeed +in causing water to freeze, though the temperature of the air be as high +as 60 degrees. The water is put into shallow earthen trays, so as to +expose an extensive +<span class="pagenum">151</span> +<a name="conver1.page151" id="conver1.page151"> </a> +surface to the process of evaporation, and in the morning, the water is +found covered with a thin cake of ice, which is collected in sufficient +quantity to be used for purposes of luxury.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How delicious it must be to drink liquids so cold in those tropical +climates! But, Mrs. B., could we not try that experiment?</p> + +<p class="speaker">MRS. B.</p> + +<p>If we were in the country, I have no doubt but that we should be able +to freeze water, by the same means, and under similar circumstances. But +we can do it immediately, upon a small scale, in this very room, in +which the thermometer stands at 70 degrees. For this purpose we need +only place some water in a little cup under the receiver of the air-pump +(<a class="smallcaps" href="#plateV">Plate V.</a> fig. 1.), and +exhaust the air from it. What will be the consequence, Caroline?</p> + +<p class="figname"> +<a name="plateV" id="plateV">Plate V.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> page 138.</p> + +<p class="illustration"> +<img src="images/plate5a_thumb.png" width="291" height="217" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. +The air-pump & receiver for M<sup>r</sup>. Leslie’s experiment. + +C a saucer with sulphuric Acid. +B a glass or earthen cup containing Water. +D a stand for the cup with its legs made of Glass. +A a Thermometer.</p> + +<p class="figlink"> +<a href="images/plate5_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>Of course the water will evaporate more quickly, since there will no +longer be any atmospheric pressure on its surface: but will this be +sufficient to make the water freeze?</p> + +<span class="pagenum">152</span> +<a name="conver1.page152" id="conver1.page152"> </a> +<p class="speaker">MRS. B.</p> + +<p>Probably not, because the vapour will not be carried off fast enough; +but this will be accomplished without difficulty if we introduce into +the receiver (fig. 1.), in a saucer, or other large shallow vessel, +some strong sulphuric acid, a substance which has a great +attraction for water, whether in the form of vapour, or in the liquid +state. This attraction is such that the acid will instantly absorb the +moisture as it rises from the water, so as to make room for the +formation of fresh vapour; this will of course hasten the process, and +the cold produced from the rapid evaporation of the water, will, in a +few minutes, be sufficient to freeze its surface.<a class="tag" name="tag12" id="tag12" href="#note12">*</a> We shall now exhaust the air +from the receiver.</p> + +<p class="speaker">EMILY.</p> + +<p>Thousands of small bubbles already rise through the water from the +internal surface of the cup; what is the reason of this?</p> + +<p class="speaker">MRS. B.</p> + +<p>These are bubbles of air which were partly attached to the vessel, +and partly diffused in the water itself; and they expand and rise in +consequence of the atmospheric pressure being removed.</p> + +<span class="pagenum">153</span> +<a name="conver1.page153" id="conver1.page153"> </a> +<p class="speaker">CAROLINE.</p> + +<p>See, Mrs. B.; the thermometer in the cup is sinking fast; it has +already descended to 40 degrees!</p> + +<p class="speaker">EMILY.</p> + +<p>The water seems now and then violently agitated on the surface, as if +it was boiling; and yet the thermometer is descending fast!</p> + +<p class="speaker">MRS. B.</p> + +<p>You may call it <i>boiling</i>, if you please, for this appearance +is, as well as boiling, owing to the rapid formation of vapour; but +here, as you have just observed, it takes place from the surface, for it +is only when heat is applied to the bottom of the vessel that the vapour +is formed there.—Now crystals of ice are actually shooting all +over the surface of the water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How beautiful it is! The surface is now entirely frozen—but the +thermometer remains at 32 degrees.</p> + +<p class="speaker">MRS. B.</p> + +<p>And so it will, conformably with our doctrine of latent heat, until +the whole of the water is frozen; but it will then again begin to +descend lower and lower, in consequence of the evaporation which goes on +from the surface of the ice.</p> + +<span class="pagenum">154</span> +<a name="conver1.page154" id="conver1.page154"> </a> +<p class="speaker">EMILY.</p> + +<p>This is a most interesting experiment; but it would be still more +striking if no sulphuric acid were required.</p> + +<p class="speaker">MRS. B.</p> + +<p>I will show you a freezing instrument, contrived by Dr. Wollaston, +upon the same principle as Mr. Leslie’s experiment, by which water may +be frozen by its own evaporation alone, without the assistance of +sulphuric acid.</p> + +<p>This tube, which, as you see (<a class="smallcaps" href="#plateVb">Plate V.</a> fig. 2.), is terminated at each extremity +by a bulb, one of which is half full of water, is internally perfectly +exhausted of air; the consequence of this is, that the water in the bulb +is always much disposed to evaporate. This evaporation, however, does +not proceed sufficiently fast to freeze the water; but if the empty ball +be cooled by some artificial means, so as to condense quickly the vapour +which rises from the water, the process may be thus so much promoted as +to cause the water to freeze in the other ball. Dr. Wollaston has called +this instrument <i>Cryophorus</i>.</p> + +<p class="figname"> +<a name="plateVb" id="plateVb">Plate V.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> page 138.</p> + +<p class="illustration"> +<img src="images/plate5b_thumb.png" width="295" height="304" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 2. D<sup>r</sup>. Wollaston’s Cryophorus.<br> +Fig. 5. D<sup>r</sup>. Marcet’s mode of using the Cryophorus.<br> +Fig. 3. & 4. the different parts of Fig. 5. seen +separate.</p> + +<p class="figlink"> +<a href="images/plate5_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>So that cold seems to perform here the same part which the sulphuric +acid acted in Mr. Leslie’s experiment?</p> + +<span class="pagenum">155</span> +<a name="conver1.page155" id="conver1.page155"> </a> +<p class="speaker">MRS. B.</p> + +<p>Exactly so; but let us try the experiment.</p> + +<p class="speaker">EMILY.</p> + +<p>How will you cool the instrument? You have neither ice nor snow.</p> + +<p class="speaker">MRS. B.</p> + +<p>True: but we have other means of effecting this.<a class="tag" name="tag13" id="tag13" href="#note13">*</a> You recollect what an +intense cold can be produced by the evaporation of ether in an exhausted +receiver. We shall inclose the bulb in this little bag of fine flannel +(fig. 3.), then soke it in ether, and introduce it into the +receiver of the air-pump. (Fig. 5.) For this purpose we shall find +it more convenient to use a cryophorus of this shape (fig. 4.), as +its elongated bulb passes easily through a brass plate which closes the +top of the receiver. If we now exhaust the receiver quickly, you will +see, in less than a minute, the water freeze in the other bulb, out of +the receiver.</p> + +<p class="speaker">EMILY.</p> + +<p>The bulb already looks quite dim, and small drops of water are +condensing on its surface.</p> + +<span class="pagenum">156</span> +<a name="conver1.page156" id="conver1.page156"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And now crystals of ice shoot all over the water. This is, indeed, +a very curious experiment!</p> + +<p class="speaker">MRS. B.</p> + +<p>You will see, some other day, that, by a similar method, even +quicksilver may be frozen.—But we cannot at present indulge in any +further digression.</p> + +<p>Having advanced so far on the subject of heat, I may now give +you an account of the calorimeter, an instrument invented by Lavoisier, +upon the principles just explained, for the purpose of estimating the +specific heat of bodies. It consists of a vessel, the inner surface of +which is lined with ice, so as to form a sort of hollow globe of ice, in +the midst of which the body, whose specific heat is to be ascertained, +is placed. The ice absorbs caloric from this body, till it has brought +it down to the freezing point; this caloric converts into water a +certain portion of the ice which runs out through an aperture at the +bottom of the machine; and the quantity of ice changed to water is a +test of the quantity of caloric which the body has given out in +descending from a certain temperature to the freezing point.</p> + +<p class="speaker">CAROLINE.</p> + +<p>In this apparatus, I suppose, the milk, chalk, +<span class="pagenum">157</span> +<a name="conver1.page157" id="conver1.page157"> </a> +and lead, would melt different quantities of ice, in proportion to their +different capacities for caloric?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly: and thence we are able to ascertain, with precision, their +respective capacities for heat. But the calorimeter affords us no more +idea of the absolute quantity of heat contained in a body, than the +thermometer; for though by means of it we extricate both the free and +combined caloric, yet we extricate them only to a certain degree, which +is the freezing point; and we know not how much they contain of either +below that point.</p> + +<p class="speaker">EMILY.</p> + +<p>According to the theory of latent heat, it appears to me that the +weather should be warm when it freezes, and cold in a thaw: for latent +heat is liberated from every substance that it freezes, and such a large +supply of heat must warm the atmosphere; whilst, during a thaw, that +very quantity of free heat must be taken from the atmosphere, and return +to a latent state in the bodies which it thaws.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your observation is very natural; but consider that in a frost the +atmosphere is so much colder than the earth, that all the caloric which +it takes +<span class="pagenum">158</span> +<a name="conver1.page158" id="conver1.page158"> </a> +from the freezing bodies is insufficient to raise its temperature above +the freezing point; otherwise the frost must cease. But if the quantity +of latent heat extricated does not destroy the frost, it serves to +moderate the suddenness of the change of temperature of the atmosphere, +at the commencement both of frost, and of a thaw. In the first instance, +its extrication diminishes the severity of the cold; and, in the latter, +its absorption moderates the warmth occasioned by a thaw: it even +sometimes produces a discernible chill, at the breaking up of a +frost.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what are the general causes that produce those sudden changes in +the weather, especially from hot to cold, which we often experience?</p> + +<p class="speaker">MRS. B.</p> + +<p>This question would lead us into meteorological discussions, to which +I am by no means competent. One circumstance, however, we can easily +understand. When the air has passed over cold countries, it will +probably arrive here at a temperature much below our own, and then it +must absorb heat from every object it meets with, which will produce a +general fall of temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But pray, now that we know so much of the +<span class="pagenum">159</span> +<a name="conver1.page159" id="conver1.page159"> </a> +effects of heat, will you inform us whether it is really a distinct +body, or, as I have heard, a peculiar kind of motion produced in +bodies?</p> + +<p class="speaker">MRS. B.</p> + +<p>As I before told you, there is yet much uncertainty as to the nature +of these subtle agents. But I am inclined to consider heat not as mere +motion, but as a separate substance. Late experiments too appear to make +it a compound body, consisting of the two electricities, and in our next +conversation I shall inform you of the principal facts on which that +opinion is founded.</p> + +<div class="footnote"> + +<p><a name="note10" id="note10" href="#tag10">*</a> +This rule, if not universal, admits of very few exceptions.</p> + +<p><a name="note11" id="note11" href="#tag11">†</a> +See <a href="#page102">page 102</a>.</p> + +<p><a name="note12" id="note12" href="#tag12">*</a> +This experiment was first devised by Mr. Leslie, and has since been +modified in a variety of forms.</p> + +<p><a name="note13" id="note13" href="#tag13">*</a> +This mode of making the experiment was proposed, and the particulars +detailed, by Dr. Marcet, in the 34th vol. of Nicholson’s Journal, page +119.</p> + +</div> + + +<span class="pagenum">160</span> +<a name="conver1.page160" id="conver1.page160"> </a> +<h4><a name="convV" id="convV">CONVERSATION V.</a><br> +<span class="subhead">ON THE CHEMICAL AGENCIES OF +ELECTRICITY.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">B</span>efore</span> we proceed further it will be +necessary to give you some account of certain properties of electricity, +which have of late years been discovered to have an essential connection +with the phenomena of chemistry.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is <span class="smallroman">ELECTRICITY</span>, if I recollect +right, which comes next in our list of simple substances?</p> + +<p class="speaker">MRS. B.</p> + +<p>I have placed electricity in that list, rather from the necessity of +classing it somewhere, than from any conviction that it has a right to +that situation, for we are as yet so ignorant of its intimate nature, +that we are unable to determine, not only whether it is simple or +compound, but whether it is in fact a material agent; or, as Sir H. Davy +has hinted, whether it may not be merely a property inherent +<span class="pagenum">161</span> +<a name="conver1.page161" id="conver1.page161"> </a> +in matter. As, however, it is necessary to adopt some hypothesis for the +explanation of the discoveries which this agent has enabled us to make, +I have chosen the opinion, at present most prevalent, which +supposes the existence of two kinds of electricity, distinguished by the +names of <i>positive</i> and <i>negative</i> electricity.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Well, I must confess, I do not feel nearly so interested in a +science in which so much uncertainty prevails, as in those which rest +upon established principles; I never was fond of electricity, +because, however beautiful and curious the phenomena it exhibits may be, +the theories, by which they were explained, appeared to me so various, +so obscure and inadequate, that I always remained dissatisfied. +I was in hopes that the new discoveries in electricity had thrown +so great a light on the subject, that every thing respecting it would +now have been clearly explained.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is a point which we are yet far from having attained. But, in +spite of the imperfection of our theories, you will be amply repaid by +the importance and novelty of the subject. The number of new facts which +have already been ascertained, and the immense prospect of discovery +<span class="pagenum">162</span> +<a name="conver1.page162" id="conver1.page162"> </a> +which has lately been opened to us, will, I hope, ultimately lead +to a perfect elucidation of this branch of natural science; but at +present you must be contented with studying the effects, and in some +degree explaining the phenomena, without aspiring to a precise knowledge +of the remote cause of electricity.</p> + +<p>You have already obtained some notions of electricity: in our present +conversation, therefore, I shall confine myself to that part of the +science which is of late discovery, and is more particularly connected +with chemistry.</p> + +<p>It was a trifling and accidental circumstance which first gave rise +to this new branch of physical science. Galvani, a professor of +natural philosophy at Bologna, being engaged (about twenty years ago) in +some experiments on muscular irritability, observed, that when a piece +of metal was laid on the nerve of a frog, recently dead, whilst the limb +supplied by that nerve rested upon some other metal, the limb suddenly +moved, on a communication being made between the two pieces of +metal.</p> + +<p class="speaker">EMILY.</p> + +<p>How is this communication made?</p> + +<p class="speaker">MRS. B.</p> + +<p>Either by bringing the two metals into contact, or by connecting them +by means of a metallic conductor. +<span class="pagenum">163</span> +<a name="conver1.page163" id="conver1.page163"> </a> +But without subjecting a frog to any cruel experiments, I can +easily make you sensible of this kind of electric action. Here is a +piece of zinc, (one of the metals I mentioned in the list of elementary +bodies)—put it <i>under</i> your tongue, and this piece of silver +<i>upon</i> your tongue, and let both the metals project a little beyond +the tip of the tongue—very well—now make the projecting +parts of the metals touch each other, and you will instantly perceive a +peculiar sensation.</p> + +<p class="speaker">EMILY.</p> + +<p>Indeed I did, a singular taste, and I think a degree of heat: but I +can hardly describe it.</p> + +<p class="speaker">MRS. B.</p> + +<p>The action of these two pieces of metal on the tongue is, +I believe, precisely similar to that made on the nerve of a frog. +I shall not detain you by a detailed account of the theory by which +Galvani attempted to account for this fact, as his explanation was soon +overturned by subsequent experiments, which proved that <i>Galvanism</i> +(the name this new power had obtained) was nothing more than +electricity. Galvani supposed that the virtue of this new agent resided +in the nerves of the frog, but Volta, who prosecuted this subject with +much greater success, shewed that the phenomena did not depend on the +organs of the frog, but upon +<span class="pagenum">164</span> +<a name="conver1.page164" id="conver1.page164"> </a> +the electrical agency of the metals, which is excited by the moisture of +the animal, the organs of the frog being only a delicate test of the +presence of electric influence.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I suppose, then, the saliva of the mouth answers the same purpose as +the moisture of the frog, in exciting the electricity of the pieces of +silver and zinc with which Emily tried the experiment on her tongue.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely. It does not appear, however, necessary that the fluid used +for this purpose should be of an animal nature. Water, and acids very +much diluted by water, are found to be the most effectual in promoting +the developement of electricity in metals; and, accordingly, the +original apparatus which Volta first constructed for this purpose, +consisted of a pile or succession of plates of zinc and copper, each +pair of which was connected by pieces of cloth or paper impregnated with +water; and this instrument, from its original inconvenient structure and +limited strength, has gradually arrived at its present state of power +and improvement, such as is exhibited in the Voltaic battery. In this +apparatus, a specimen of which you see before you (<a class="smallcaps" href="#plateVI">Plate VI.</a> fig. 1.), the plates of +zinc and copper are soldered together in pairs, each pair being placed +at regular +<span class="pagenum">165</span> +<a name="conver1.page165" id="conver1.page165"> </a> +distances in wooden <ins class="mycorr" title="text reads ‘throughs’">troughs</ins> +and the interstices being filled with fluid.</p> + +<p class="figname"> +<a name="plateVI" id="plateVI">Plate VI.</a></p> + +<p class="figpage"> +p. 151.</p> + +<p class="illustration"> +<img src="images/plate6a_thumb.png" width="324" height="328" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. 2. & 4. Voltaic Batteries</p> + +<p class="figlink"> +<a href="images/plate6_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>Though you will not allow us to enquire into the precise cause of +electricity, may we not ask in what manner the fluid acts on the metals +so as to produce it?</p> + +<p class="speaker">MRS. B.</p> + +<p>The action of the fluid on the metals, whether water or acid be used, +is entirely of a chemical nature. But whether electricity is excited by +this chemical action, or whether it is produced by the contact of the +two metals, is a point upon which philosophers do not yet perfectly +agree.</p> + +<p class="speaker">EMILY.</p> + +<p>But can the mere contact of two metals, without any intervening +fluid, produce electricity?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, if they are afterwards separated. It is an established fact, +that when two metals are put in contact, and afterwards separated, that +which has the strongest attraction for oxygen exhibits signs of +positive, the other of negative electricity.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It seems then but reasonable to infer that the +<span class="pagenum">166</span> +<a name="conver1.page166" id="conver1.page166"> </a> +power of the Voltaic battery should arise from the contact of the plates +of zinc and copper.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is upon this principle that Volta and Sir H. Davy explain the +phenomena of the pile; but notwithstanding these two great authorities, +many philosophers entertain doubts on the truth of this theory. The +principal difficulty which occurs in explaining the phenomena of the +Voltaic battery on this principle, is, that two such plates show no +signs of different states of electricity whilst in contact, but only on +being separated after contact. Now in the Voltaic battery, those plates +that are in contact always continue so, being soldered together: and +they cannot therefore receive a succession of charges. Besides, if we +consider the mere disturbance of the balance of electricity by the +contact of the plates, as the sole cause of the production of Voltaic +electricity, it remains to be explained how this disturbed balance +becomes an inexhaustible source of electrical energy, capable of pouring +forth a constant and copious supply of electrical fluid, though without +any means of replenishing itself from other sources. This subject, it +must be owned, is involved in too much obscurity to enable us to speak +very decidedly in favour of any theory. But, in order to avoid +perplexing you with different explanations, +<span class="pagenum">167</span> +<a name="conver1.page167" id="conver1.page167"> </a> +I shall confine myself to one which appears to me to be least encumbered +with difficulties, and most likely to accord with truth.<a class="tag" +name="tag14" id="tag14" href="#note14">*</a></p> + +<p>This theory supposes the electricity to be excited by the chemical +action of the acid on the zinc; but you are yet such novices in +chemistry, that I think it will be necessary to give you some previous +explanation of the nature of this action.</p> + +<p>All metals have a strong attraction for oxygen, and this element is +found in great abundance both in water and in acids. The action of the +diluted acid on the zinc consists therefore in its oxygen combining with +it, and dissolving its surface.</p> + +<p class="speaker">CAROLINE.</p> + +<p>In the same manner I suppose as we saw an acid dissolve copper?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but in the Voltaic battery the diluted acid is not strong enough +to produce so complete +<span class="pagenum">168</span> +<a name="conver1.page168" id="conver1.page168"> </a> +an effect; it acts only on the surface of the zinc, to which it yields +its oxygen, forming upon it a film or crust, which is a compound of the +oxygen and the metal.</p> + +<p class="speaker">EMILY.</p> + +<p>Since there is so strong a chemical attraction between oxygen and +metals, I suppose they are naturally in different states of +electricity?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; it appears that all metals are united with the positive, and +that oxygen is the grand source of the negative electricity.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Does not then the acid act on the plates of copper, as well as on +those of zinc?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for though copper has an affinity for oxygen, it is less strong +than that of zinc; and therefore the energy of the acid is only exerted +upon the zinc.</p> + +<p>It will be best, I believe, in order to render the action of the +Voltaic battery more intelligible, to confine our attention at first to +the effect produced on two plates only. (<a class="smallcaps" href="#plateVI">Plate VI.</a> fig. 2.)</p> + +<p>If a plate of zinc be placed opposite to one of copper, or any other +metal less attractive of oxygen, +<span class="pagenum">169</span> +<a name="conver1.page169" id="conver1.page169"> </a> +and the space between them (suppose of half an inch in thickness), be +filled with an acid or any fluid capable of oxydating the zinc, the +oxydated surface will have its capacity for electricity diminished, so +that a quantity of electricity will be evolved from that surface. This +electricity will be received by the contiguous fluid, by which it will +be transmitted to the opposite metallic surface, the copper, which is +not oxydated, and is therefore disposed to receive it; so that the +copper plate will thus become positive, whilst the zinc plate will be in +the negative state.</p> + +<p>This evolution of electrical fluid however will be very limited; for +as these two plates admit of but very little accumulation of +electricity, and are supposed to have no communication with other +bodies, the action of the acid, and further developement of electricity, +will be immediately stopped.</p> + +<p class="speaker">EMILY.</p> + +<p>This action, I suppose, can no more continue to go on, than that of a +common electrical machine, which is not allowed to communicate with +other bodies?</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely; the common electrical machine, when excited by the +friction of the rubber, gives out both the positive and negative +electricities.—(<a class="smallcaps" href="#plateVIb">Plate +VI.</a> Fig. 3.) The positive, by the rotation +<span class="pagenum">170</span> +<a name="conver1.page170" id="conver1.page170"> </a> +of the glass cylinder, is conveyed into the conductor, whilst the +negative goes into the rubber. But unless there is a communication made +between the rubber and the ground, but a very inconsiderable quantity of +electricity can be excited; for the rubber, like the plates of the +battery, has too small a capacity to admit of an accumulation of +electricity. Unless therefore the electricity can pass out of the +rubber, it will not continue to go into it, and consequently no +additional accumulation will take place. Now as one kind of electricity +cannot be given out without the other, the developement of the positive +electricity is stopped as well as that of the negative, and the +conductor therefore cannot receive a succession of charges.</p> + +<p class="figname"> +<a name="plateVIb" id="plateVIb">Plate VI.</a></p> + +<p class="figpage"> +p. 151.</p> + +<p class="illustration"> +<img src="images/plate6b_thumb.png" width="321" height="257" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 3. +A the Cylinder. +B the Conductor. +R the Rubber. +C the Chain.</p> + +<p class="figlink"> +<a href="images/plate6_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>But does not the conductor, as well as the rubber, require a +communication with the earth, in order to get rid of its +electricity?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for it is susceptible of receiving and containing a considerable +quantity of electricity, as it is much larger than the rubber, and +therefore has a greater capacity; and this continued accumulation of +electricity in the conductor is what is called a charge.</p> + +<span class="pagenum">171</span> +<a name="conver1.page171" id="conver1.page171"> </a> +<p class="speaker">EMILY.</p> + +<p>But when an electrical machine is furnished with two conductors to +receive the two electricities, I suppose no communication with the +earth is required?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly not, until the two are fully charged; for the two +conductors will receive equal quantities of electricity.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I thought the use of the chain had been to convey the electricity +<i>from</i> the ground into the machine?</p> + +<p class="speaker">MRS. B.</p> + +<p>That was the idea of Dr. Franklin, who supposed that there was but +one kind of electricity, and who, by the terms positive and negative +(which he first introduced), meant only different quantities of the same +kind of electricity. The chain was in that case supposed to convey +electricity <i>from</i> the ground through the rubber into the +conductor. But as we have adopted the hypothesis of two electricities, +we must consider the chain as a vehicle to conduct the negative +electricity into the earth.</p> + +<p class="speaker">EMILY.</p> + +<p>And are both kinds of electricity produced whenever electricity is +excited?</p> + +<span class="pagenum">172</span> +<a name="conver1.page172" id="conver1.page172"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes, invariably. If you rub a tube of glass with a woollen cloth, the +glass becomes positive, and the cloth negative. If, on the contrary, you +excite a stick of sealing-wax by the same means, it is the rubber which +becomes positive, and the wax negative.</p> + +<p>But with regard to the Voltaic battery, in order that the acid may +act freely on the zinc, and the two electricities be given out without +interruption, some method must be devised, by which the plates may part +with their electricities as fast as they receive them.—Can you +think of any means by which this might be effected?</p> + +<p class="speaker">EMILY.</p> + +<p>Would not two chains or wires, suspended from either plate to the +ground, conduct the electricities into the earth, and thus answer the +purpose?</p> + +<p class="speaker">MRS. B.</p> + +<p>It would answer the purpose of carrying off the electricity, +I admit; but recollect, that though it is necessary to find a vent +for the electricity, yet we must not lose it, since it is the power +which we are endeavouring to obtain. Instead, therefore, of conducting +it into the ground, let us make the wires, from either plate, meet: the +two electricities will thus be brought together, and will combine +<span class="pagenum">173</span> +<a name="conver1.page173" id="conver1.page173"> </a> +and neutralize each other; and as long as this communication continues, +the two plates having a vent for their respective electricities, the +action of the acid will go on freely and uninterruptedly.</p> + +<p class="speaker">EMILY.</p> + +<p>That is very clear, so far as two plates only are concerned; but I +cannot say I understand how the energy of the succession of plates, or +rather pairs of plates, of which the Galvanic trough is composed, is +propagated and accumulated throughout a battery?</p> + +<p class="speaker">MRS. B.</p> + +<p>In order to shew you how the intensity of the electricity is +increased by increasing the number of plates, we will examine the action +of four plates; if you understand these, you will readily comprehend +that of any number whatever. In this figure (<a class="smallcaps" href="#plateVI">Plate VI.</a> Fig. 4.), you will observe that the two +central plates are united; they are soldered together, (as we observed +in describing the Voltaic trough,) so as to form but one plate which +offers two different surfaces, the one of copper, the other of zinc.</p> + +<p>Now you recollect that, in explaining the action of two plates, we +supposed that a quantity of electricity was evolved from the surface of +the first zinc plate, in consequence of the action of the acid, and was +conveyed by the interposed fluid to the copper +<span class="pagenum">174</span> +<a name="conver1.page174" id="conver1.page174"> </a> +plate, No. 2, which thus became positive. This copper plate +communicates its electricity to the contiguous zinc plate, No. 3, +in which, consequently, some accumulation of electricity takes place. +When, therefore, the fluid in the next cell acts upon the zinc plate, +electricity is extricated from it in larger quantity, and in a more +concentrated form, than before. This concentrated electricity is again +conveyed by the fluid to the next pair of plates, No. 4 and 5, when +it is farther increased by the action of the fluid in the third cell, +and so on, to any number of plates of which the battery may consist; so +that the electrical energy will continue to accumulate in proportion to +the number of double plates, the first zinc plate of the series being +the most negative, and the last copper plate the most positive.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But does the battery become more and more strongly charged, merely by +being allowed to stand undisturbed?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, for the action will soon stop, as was explained before, unless a +vent be given to the accumulated electricities. This is easily done, +however, by establishing a communication by means of the wires +(Fig. 1.), between the two ends of the battery: these being brought +into contact, the two +<span class="pagenum">175</span> +<a name="conver1.page175" id="conver1.page175"> </a> +electricities meet and neutralize each other, producing the shock and +other effects of electricity; and the action goes on with renewed +energy, being no longer obstructed by the accumulation of the two +electricities which impeded its progress.</p> + +<p class="speaker">EMILY.</p> + +<p>Is it the union of the two electricities which produces the electric +spark?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and it is, I believe, this circumstance which gave rise to Sir +H. Davy’s opinion that caloric may be a compound of the two +electricities.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet surely caloric is very different from the electrical spark?</p> + +<p class="speaker">MRS. B.</p> + +<p>The difference may consist probably only in intensity: for the heat +of the electric spark is considerably more intense, though confined to a +very minute spot, than any heat we can produce by other means.</p> + +<p class="speaker">EMILY.</p> + +<p>Is it quite certain that the electricity of the Voltaic battery is +precisely of the same nature as that of the common electrical +machine?</p> + +<span class="pagenum">176</span> +<a name="conver1.page176" id="conver1.page176"> </a> +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; the shock given to the human body, the spark, the +circumstance of the same substances which are conductors of the one +being also conductors of the other, and of those bodies, such as glass +and sealing-wax, which are non-conductors of the one, being also +non-conductors of the other, are striking proofs of it. Besides, Sir H. +Davy has shewn in his Lectures, that a Leyden jar, and a common electric +battery, can be charged with electricity obtained from a Voltaic +battery, the effect produced being perfectly similar to that obtained by +a common machine.</p> + +<p>Dr. Wollaston has likewise proved that similar chemical +decompositions are effected by the electric machine and by the Voltaic +battery; and has made other experiments which render it highly probable, +that the origin of both electricities is essentially the same, as they +show that the rubber of the common electrical machine, like the zinc in +the Voltaic battery, produces the two electricities by combining with +oxygen.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But I do not see whence the rubber obtains oxygen, for there is +neither acid nor water used in the common machine, and I always +understood that the electricity was excited by the friction.</p> + +<span class="pagenum">177</span> +<a name="conver1.page177" id="conver1.page177"> </a> +<p class="speaker">MRS. B.</p> + +<p>It appears that by friction the rubber obtains oxygen from the +atmosphere, which is partly composed of that element. The oxygen +combines with the amalgam of the rubber, which is of a metallic nature, +much in the same way as the oxygen of the acid combines with the zinc in +the Voltaic battery, and it is thus that the two electricities are +disengaged.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, if the electricities of both machines are similar, why not use +the common machine for chemical decompositions?</p> + +<p class="speaker">MRS. B.</p> + +<p>Though its effects are similar to those of the Voltaic battery, they +are incomparably weaker. Indeed Dr. Wollaston, in using it for chemical +decompositions, was obliged to act upon the most minute quantities of +matter, and though the result was satisfactory in proving the similarity +of its effects to those of the Voltaic battery, these effects were too +small in extent to be in any considerable degree applicable to chemical +decomposition.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How terrible, then, the shock must be from a Voltaic battery, since +it is so much more powerful than an electrical machine!</p> + +<span class="pagenum">178</span> +<a name="conver1.page178" id="conver1.page178"> </a> +<p class="speaker">MRS. B.</p> + +<p>It is not nearly so formidable as you think; at least it is by no +means proportional to the chemical effect. The great superiority of the +Voltaic battery consists in the large <i>quantity</i> of electricity +that passes; but in regard to the <i>rapidity</i> or <i>intensity</i> of +the charge, it is greatly surpassed by the common electrical machine. It +would seem that the shock or sensation depends chiefly upon the +intensity; whilst, on the contrary, for chemical purposes, it is +quantity which is required. In the Voltaic battery, the electricity, +though copious, is so weak as not to be able to force its way through +the fluid which separates the plates, whilst that of a common machine +will pass through any space of water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Would not it be possible to increase the intensity of the Voltaic +battery till it should equal that of the common machine?</p> + +<p class="speaker">MRS. B.</p> + +<p>It can actually be increased till it imitates a weak electrical +machine, so as to produce a visible spark when accumulated in a Leyden +jar. But it can never be raised sufficiently to pass through any +considerable extent of air, because of the ready communication through +the fluids employed.</p> + +<p>By increasing the number of plates of a battery, +<span class="pagenum">179</span> +<a name="conver1.page179" id="conver1.page179"> </a> +you increase its <i>intensity</i>, whilst, by enlarging the dimensions +of the plates, you augment its <i>quantity</i>; and, as the superiority +of the battery over the common machine consists entirely in the quantity +of electricity produced, it was at first supposed that it was the size, +rather than the number of plates that was essential to the augmentation +of power. It was, however, found upon trial, that the quantity of +electricity produced by the Voltaic battery, even when of a very +moderate size, was sufficiently copious, and that the chief advantage in +this apparatus was obtained by increasing the intensity, which, however, +still falls very short of that of the common machine.</p> + +<p>I should not omit to mention, that a very splendid, and, at the same +time, most powerful battery, was, a few years ago, constructed +under the direction of Sir H. Davy, which he repeatedly exhibited in his +course of electro-chemical lectures. It consists of two thousand double +plates of zinc and copper, of six square inches in dimensions, arranged +in troughs of Wedgwood-ware, each of which contains twenty of these +plates. The troughs are furnished with a contrivance for lifting the +plates out of them in a very convenient and expeditious manner.<a class="tag" name="tag15" id="tag15" href="#note15">*</a></p> + +<span class="pagenum">180</span> +<a name="conver1.page180" id="conver1.page180"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Well, now that we understand the nature of the action of the <ins +class="mycorr" title="text reads ‘Votaic’">Voltaic</ins> battery, +I long to hear an account of the discoveries to which it has given +rise.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must restrain your impatience, my dear, for I cannot with any +propriety introduce the subject of these discoveries till we come to +them in the regular course of our studies. But, as almost every +substance in nature has already been exposed to the influence of the +Voltaic battery, we shall very soon have occasion to notice its +effects.</p> + +<div class="footnote"> + +<p><a name="note14" id="note14" href="#tag14">*</a> +This mode of explaining the phenomena of the Voltaic pile is called the +<i>chemical theory</i> of electricity, because it ascribes the cause of +these phenomena to certain chemical changes which take place during +their appearance. In the preceding edition of this work, the same theory +was presented in a more elaborate, but less easy form than it is in +this. The mode of viewing the subject which is here sketched was long +since suggested by Dr. Bostock, of whose theory, however, this is by no +means to be considered as a complete statement.</p> + +<p><a name="note15" id="note15" href="#tag15">*</a> +A model of this mode of construction is exhibited in <a class="smallcaps" href="#plateXIIIa">Plate <ins class="edcorr" title="corrected by author from XII">XIII</ins>.</a> Fig. 1.</p> + +</div> + +<p class="figname"> +<a name="plateXIIIa" id="plateXIIIa">Plate XIII.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. II.</span> page 16.</p> + +<p class="illustration"> +<img src="images/plate13a_thumb.png" width="301" height="269" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. Voltaic Battery of improved construction with the Plates +out of the Cells.</p> + +<p class="figlink"> +<a href="images/plate13_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + + +<span class="pagenum">181</span> +<a name="conver1.page181" id="conver1.page181"> </a> +<h4><a name="convVI" id="convVI">CONVERSATION VI.</a><br> +<span class="subhead">ON OXYGEN AND NITROGEN.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">T</span>o-day</span> we shall examine the chemical +properties of the <span class="smallroman">ATMOSPHERE</span>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I thought that we were first to learn the nature of <span class="smallcaps">Oxygen</span>, which <ins class="mycorr" title="error for ‘comes’?">come</ins> +next in our table of simple bodies?</p> + +<p class="speaker">MRS. B.</p> + +<p>And so you shall; the atmosphere being composed of two principles, +<span class="smallcaps">Oxygen</span> and <span class="smallcaps">Nitrogen</span>, we shall proceed to analyse it, and +consider its component parts separately.</p> + +<p class="speaker">EMILY.</p> + +<p>I always thought that the atmosphere had been a very complicated +fluid, composed of all the variety of exhalations from the earth.</p> + +<p class="speaker">MRS. B.</p> + +<p>Such substances may be considered rather as heterogeneous +<span class="pagenum">182</span> +<a name="conver1.page182" id="conver1.page182"> </a> +and accidental, than as forming any of its component parts; and the +proportion they bear to the whole mass is quite inconsiderable.</p> + +<p><span class="smallcaps">Atmospherical air</span> is composed of two +gasses, known by the names of <span class="smallroman">OXYGEN +GAS</span> and <span class="smallroman">NITROGEN</span> or <span class="smallroman">AZOTIC GAS</span>.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is a gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>The name of gas is given to any fluid capable of existing constantly +in an aeriform state, under the pressure and at the temperature of the +atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is not water, or any other substance, when evaporated by heat, called +gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, my dear; vapour is, indeed, an elastic fluid, and bears a strong +resemblance to a gas; there are, however, several points in which they +essentially differ, and by which you may always distinguish them. Steam, +or vapour, owes its elasticity merely to a high temperature, which is +equal to that of boiling water. And it differs from boiling water only +by being united with more caloric, which, as we before explained, is in +a latent state. When +<span class="pagenum">183</span> +<a name="conver1.page183" id="conver1.page183"> </a> +steam is cooled, it instantly returns to the form of water; but air, or +gas, has never yet been rendered liquid or solid by any degree of +cold.</p> + +<p class="speaker">EMILY.</p> + +<p>But does not gas, as well as vapour, owe its elasticity to +caloric?</p> + +<p class="speaker">MRS. B.</p> + +<p>It was the prevailing opinion; and the difference of gas or vapour +was thought to depend on the different manner in which caloric was +united with the basis of these two kinds of elastic fluids. In vapour, +it was considered as in a latent state; in gas, it was said to be +chemically combined. But the late researches of Sir H. Davy have given +rise to a new theory respecting gasses; and there is now reason to +believe that these bodies owe their permanently elastic state, not +solely to caloric, but likewise to the prevalence of either the one or +the other of the two electricities.</p> + +<p class="speaker">EMILY.</p> + +<p>When you speak, then, of the simple bodies oxygen and nitrogen, you +mean to express those substances which are the basis of the two +gasses?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, in strict propriety, for they can properly be called gasses only +when brought to an aeriform state.</p> + +<span class="pagenum">184</span> +<a name="conver1.page184" id="conver1.page184"> </a> +<p class="speaker">CAROLINE.</p> + +<p>In what proportions are they combined in the atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>The oxygen gas constitutes a little more than one-fifth, and the +nitrogen gas a little less than four-fifths. When separated, they are +found to possess qualities totally different from each other. For oxygen +gas is essential both to respiration and combustion, while neither of +these processes can be performed in nitrogen gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if nitrogen gas is unfit for respiration, how does it happen that +the large proportion of it which enters into the composition of the +atmosphere is not a great impediment to breathing?</p> + +<p class="speaker">MRS. B.</p> + +<p>We should breathe more freely than our lungs could bear, if we +respired oxygen gas alone. The nitrogen is no impediment to respiration, +and probably, on the contrary, answers some useful purpose, though we do +not know in what manner it acts in that process.</p> + +<p class="speaker">EMILY.</p> + +<p>And by what means can the two gasses, which compose the atmospheric +air, be separated?</p> + +<span class="pagenum">185</span> +<a name="conver1.page185" id="conver1.page185"> </a> +<p class="speaker">MRS. B.</p> + +<p>There are many ways of analysing the atmosphere: the two gasses may +be separated first by combustion.</p> + +<p class="speaker">EMILY.</p> + +<p>You surprise me! how is it possible that combustion should separate +them?</p> + +<p class="speaker">MRS. B.</p> + +<p>I should previously remind you that oxygen is supposed to be the only +simple body naturally combined with negative electricity. In all the +other elements the positive electricity prevails, and they have +consequently, all of them, an attraction for oxygen.<a class="tag" +name="tag16" id="tag16" href="#note16">*</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>Oxygen the only negatively electrified body! that surprises me +extremely; how then are the combinations of the other bodies performed, +if, according to your explanation of chemical attraction, bodies are +supposed only to combine in virtue of their opposite states of +electricity?</p> + +<span class="pagenum">186</span> +<a name="conver1.page186" id="conver1.page186"> </a> +<p class="speaker">MRS. B.</p> + +<p>Observe that I said, that oxygen was the only <i>simple</i> body, +naturally negative. Compound bodies, in which oxygen prevails over the +other component parts, are also negative, but their negative energy is +greater or less in proportion as the oxygen predominates. Those +compounds into which oxygen enters in less proportion than the other +constituents, are positive, but their positive energy is diminished in +proportion to the quantity of oxygen which enters into their +composition.</p> + +<p>All bodies, therefore, that are not already combined with oxygen, +will attract it, and, under certain circumstances, will absorb it from +the atmosphere, in which case the nitrogen gas will remain alone, and +may thus be obtained in its separate state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not understand how a gas can be absorbed?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is only the oxygen, or basis of the gas, which is absorbed; and +the two electricities escaping, that is to say, the negative from the +oxygen, the positive from the burning body, unite and produce +caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>And what becomes of this caloric?</p> + +<span class="pagenum">187</span> +<a name="conver1.page187" id="conver1.page187"> </a> +<p class="speaker">MRS. B.</p> + +<p>We shall make this piece of dry wood attract oxygen from the +atmosphere, and you will see what becomes of the caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You are joking, Mrs. B—; you do not mean to decompose the +atmosphere with a piece of dry stick?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not the whole body of the atmosphere, certainly; but if we can make +this piece of wood attract any quantity of oxygen from it, +a proportional quantity of atmospherical air will be +decomposed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>If wood has so strong an attraction for oxygen, why does it not +decompose the atmosphere spontaneously?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is found by experience, that an elevation of temperature is +required for the commencement of the union of the oxygen and the +wood.</p> + +<p>This elevation of temperature was formerly thought to be necessary, +in order to diminish the cohesive attraction of the wood, and enable the +oxygen to penetrate and combine with it more readily. But since the +introduction of the new theory of chemical combination, another cause +has +<span class="pagenum">188</span> +<a name="conver1.page188" id="conver1.page188"> </a> +been assigned, and it is now supposed that the high temperature, by +exalting the electrical energies of bodies, and consequently their force +of attraction, facilitates their combination.</p> + +<p class="speaker">EMILY.</p> + +<p>If it is true, that caloric is composed of the two electricities, an +elevation of temperature must necessarily augment the electric energies +of bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>I doubt whether that would be a necessary consequence; for, admitting +this composition of caloric, it is only by its being decomposed that +electricity can be produced. Sir H. Davy, however, in his numerous +experiments, has found it to be an almost invariable rule that the +electrical energies of bodies are increased by elevation of +temperature.</p> + +<p>What means then shall we employ to raise the temperature of the wood, +so as to enable it to attract oxygen from the atmosphere?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Holding it near the fire, I should think, would answer the +purpose.</p> + +<p class="speaker">MRS. B.</p> + +<p>It may, provided you hold it sufficiently close +<span class="pagenum">189</span> +<a name="conver1.page189" id="conver1.page189"> </a> +to the fire; for a very considerable elevation of temperature is +required.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It has actually taken fire, and yet I did not let it touch the coals, +but I held it so very close that I suppose it caught fire merely from +the intensity of the heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>Or you might say, in other words, that the caloric which the wood +imbibed, so much elevated its temperature, and exalted its electric +energy, as to enable it to attract oxygen very rapidly from the +atmosphere.</p> + +<p class="speaker">EMILY.</p> + +<p>Does the wood absorb oxygen while it is burning?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, and the heat and light are produced by the union of the two +electricities which are set at liberty, in consequence of the oxygen +combining with the wood.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You astonish me! the heat of a burning body proceeds then as much +from the atmosphere as from the body itself?</p> + +<p class="speaker">MRS. B.</p> + +<p>It was supposed that the caloric, given out +<span class="pagenum">190</span> +<a name="conver1.page190" id="conver1.page190"> </a> +during combustion, proceeded entirely, or nearly so, from the +decomposition of the oxygen gas; but, according to Sir H. Davy’s new +view of the subject, both the oxygen gas, and the combustible body, +concur in supplying the heat and light, by the union of their opposite +electricities.</p> + +<p class="speaker">EMILY.</p> + +<p>I have not yet met with any thing in chemistry that has surprised or +delighted me so much as this explanation of combustion. I was at +first wondering what connection there could be between the affinity of a +body for oxygen and its combustibility; but I think I understand it now +perfectly.</p> + +<p class="speaker">MRS. B.</p> + +<p>Combustion then, you see, is nothing more than the rapid combination +of a body with oxygen, attended by the disengagement of light and +heat.</p> + +<p class="speaker">EMILY.</p> + +<p>But are there no combustible bodies whose attraction for oxygen is so +strong, that they will combine with it, without the application of +heat?</p> + +<p class="speaker">CAROLINE.</p> + +<p>That cannot be; otherwise we should see bodies burning +spontaneously.</p> + +<span class="pagenum">191</span> +<a name="conver1.page191" id="conver1.page191"> </a> +<p class="speaker">MRS. B.</p> + +<p>But there are some instances of this kind, such as phosphorus, +potassium, and some compound bodies, which I shall hereafter make you +acquainted with. These bodies, however, are prepared by art, for in +general, all the combustions that could occur spontaneously, at the +temperature of the atmosphere, have already taken place; therefore new +combustions cannot happen without the temperature of the body being +raised. Some bodies, however, will burn at a much lower temperature than +others.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the common way of burning a body is not merely to approach it to +one already on fire, but rather to put the one in actual contact with +the other, as when I burn this piece of paper by holding it in the flame +of the fire.</p> + +<p class="speaker">MRS. B.</p> + +<p>The closer it is in contact with the source of caloric, the sooner +will its temperature be raised to the degree necessary for it to burn. +If you hold it near the fire, the same effect will be produced; but more +time will be required, as you found to be the case with the piece of +stick.</p> + +<p class="speaker">EMILY.</p> + +<p>But why is it not necessary to continue applying +<span class="pagenum">192</span> +<a name="conver1.page192" id="conver1.page192"> </a> +caloric throughout the process of combustion, in order to keep up the +electric energy of the wood, which is required to enable it to combine +with the oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>The caloric which is gradually produced by the two electricities +during combustion, keeps up the temperature of the burning body; so that +when once combustion has begun, no further application of caloric is +required.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Since I have learnt this wonderful theory of combustion, +I cannot take my eyes from the fire; and I can scarcely conceive +that the heat and light, which I always supposed to proceed entirely +from the coals, are really produced as much by the atmosphere.</p> + +<p class="speaker">EMILY.</p> + +<p>When you blow the fire, you increase the combustion, I suppose, +by supplying the coals with a greater quantity of oxygen gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; but of course no blowing will produce combustion, unless +the temperature of the coals be first raised. A single spark, +however, is sometimes sufficient to produce that effect; for, as I said +before, when once combustion has commenced, +<span class="pagenum">193</span> +<a name="conver1.page193" id="conver1.page193"> </a> +the caloric disengaged is sufficient to elevate the temperature of the +rest of the body, provided that there be a free access of oxygen. It +however sometimes happens that if a fire be ill made, it will be +extinguished before all the fuel is consumed, from the very circumstance +of the combustion being so slow that the caloric disengaged is +insufficient to keep up the temperature of the fuel. You must recollect +that there are three things required in order to produce combustion; +a combustible body, oxygen, and a temperature at which the one will +combine with the other.</p> + +<p class="speaker">EMILY.</p> + +<p>You said that combustion was one method of decomposing the +atmosphere, and obtaining the nitrogen gas in its simple state; but how +do you secure this gas, and prevent it from mixing with the rest of the +atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is necessary for this purpose to burn the body within a close +vessel, which is easily done.—We shall introduce a small lighted +taper (<a class="smallcaps" href="#plateVII">Plate VII.</a> +Fig. 1.) under this glass receiver, which stands in a bason over +water, to prevent all communication with the external air.</p> + +<p class="figname"> +<a name="plateVII" id="plateVII">Plate VII.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 181.</p> + +<p class="illustration"> +<img src="images/plate7_thumb.png" width="584" height="223" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. Combustion of a taper under a receiver.<br> +Fig. 2. A Retort on a stand.<br> +Fig. 3. +A Furnace. +B Earthen Retort in the furnace. +C Water bath. +D Receiver. +E.E Tube conveying the gas from the Retort through the water into +the Receiver. +F.F.F Shelf perforated on which the Receiver stands.<br> +Fig. 4. Combustion of iron wire in oxygen gas.</p> + +<p class="figlink"> +<a href="images/plate7_large.jpg" target="_blank">Larger +view</a></p> + +<span class="pagenum">194</span> +<a name="conver1.page194" id="conver1.page194"> </a> +<p class="speaker">CAROLINE.</p> + +<p>How dim the light burns already!—It is now extinguished.</p> + +<p class="speaker">MRS. B.</p> + +<p>Can you tell us why it is extinguished?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Let me consider.—The receiver was full of atmospherical air; +the taper, in burning within it, must have combined with the oxygen +contained in that air, and the caloric that was disengaged produced the +light of the taper. But when the whole of the oxygen was absorbed, the +whole of its electricity was disengaged; consequently no more caloric +could be produced, the taper ceased to burn, and the flame was +extinguished.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your explanation is perfectly correct.</p> + +<p class="speaker">EMILY.</p> + +<p>The two constituents of the oxygen gas being thus disposed of, what +remains under the receiver must be pure nitrogen gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>There are some circumstances which prevent the nitrogen gas, thus +obtained, from being perfectly pure; but we may easily try whether the +<span class="pagenum">195</span> +<a name="conver1.page195" id="conver1.page195"> </a> +oxygen has disappeared, by putting another lighted taper under +it.—You see how instantaneously the flame is extinguished, for +want of oxygen to supply the negative electricity required for the +formation of caloric; and were you to put an animal under the receiver, +it would immediately be suffocated. But that is an experiment which I do +not think your curiosity will tempt you to try.</p> + +<p class="speaker">EMILY.</p> + +<p>Certainly not.—But look, Mrs. B., the receiver is full of a +thick white smoke. Is that nitrogen gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, my dear; nitrogen gas is perfectly transparent and invisible, +like common air. This cloudiness proceeds from a variety of exhalations, +which arise from the burning taper, and the nature of which you cannot +yet understand.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The water within the receiver has now risen a little above its level +in the bason. What is the reason of this?</p> + +<p class="speaker">MRS. B.</p> + +<p>With a moment’s reflection, I dare say, you would have explained it +yourself. The water rises in consequence of the oxygen gas within it +<span class="pagenum">196</span> +<a name="conver1.page196" id="conver1.page196"> </a> +having been destroyed, or rather decomposed, by the combustion of the +taper.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Then why did not the water rise immediately when the oxygen gas was +destroyed?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the heat of the taper, whilst burning, produced a dilatation +of the air in the vessel, which at first counteracted this effect.</p> + +<p>Another means of decomposing the atmosphere is the <i>oxygenation</i> +of certain metals. This process is very analogous to combustion; it is, +indeed, only a more general term to express the combination of a body +with oxygen.</p> + +<p class="speaker">CAROLINE.</p> + +<p>In what respect, then, does it differ from combustion?</p> + +<p class="speaker">MRS. B.</p> + +<p>The combination of oxygen in combustion is always accompanied by a +disengagement of light and heat; whilst this circumstance is not a +necessary consequence of simple oxygenation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how can a body absorb oxygen without the combination of the two +electricities which produce caloric?</p> + +<span class="pagenum">197</span> +<a name="conver1.page197" id="conver1.page197"> </a> +<p class="speaker">MRS. B.</p> + +<p>Oxygen does not always present itself in a gaseous state; it is a +constituent part of a vast number of bodies, both solid and liquid, in +which it exists in a much denser state than in the atmosphere; and from +these bodies it may be obtained without much disengagement of caloric. +It may likewise, in some cases, be absorbed from the atmosphere without +any sensible production of light and heat; for, if the process be slow, +the caloric is disengaged in such small quantities, and so gradually, +that it is not capable of producing either light or heat. In this case +the absorption of oxygen is called <i>oxygenation</i> or +<i>oxydation</i>, instead of <i>combustion</i>, as the production of +sensible light and heat is essential to the latter.</p> + +<p class="speaker">EMILY.</p> + +<p>I wonder that metals can unite with oxygen; for, as they are so +dense, their attraction of aggregation must be very great; and I should +have thought that oxygen could never have penetrated such bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>Their strong attraction for oxygen counterbalances this obstacle. +Most metals, however, require to be made red-hot before they are capable +of attracting oxygen in any considerable quantity. +<span class="pagenum">198</span> +<a name="conver1.page198" id="conver1.page198"> </a> +By this combination they lose most of their metallic properties, and +fall into a kind of powder, formerly called <i>calx</i>, but now much +more properly termed an <i>oxyd</i>; thus we have <i>oxyd of lead</i>, +<i>oxyd of iron</i>, &c.</p> + +<p class="speaker">EMILY.</p> + +<p>And in the Voltaic battery, it is, I suppose, an oxyd of zinc, that +is formed by the union of the oxygen with that metal?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, it is.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The word oxyd, then, simply means a metal combined with oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but the term is not confined to metals, though chiefly applied +to them. Any body whatever, that has combined with a certain quantity of +oxygen, either by means of oxydation or combustion, is called an +<i>oxyd</i>, and is said to be <i>oxydated</i> or <i>oxygenated</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>Metals, when converted into oxyds, become, I suppose, +negative?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not in general; because in most oxyds the positive energy of the +metal more than counterbalances +<span class="pagenum">199</span> +<a name="conver1.page199" id="conver1.page199"> </a> +the native energy of the oxygen with which it combines.</p> + +<p>This black powder is an oxyd of manganese, a metal which has so +strong an affinity for oxygen, that it attracts that substance from the +atmosphere at any known temperature: it is therefore never found in its +metallic form, but always in that of an oxyd, in which state, you see, +it has very little of the appearance of a metal. It is now heavier than +it was before oxydation, in consequence of the additional weight of the +oxygen with which it has combined.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am very glad to hear that; for I confess I could not help having +some doubts whether oxygen was really a substance, as it is not to be +obtained in a simple and palpable state; but its weight is, +I think, a decisive proof of its being a real body.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is easy to estimate its weight, by separating it from the +manganese, and finding how much the latter has lost.</p> + +<p class="speaker">EMILY.</p> + +<p>But if you can take the oxygen from the metal, shall we not then have +it in its palpable simple state?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for I can only separate the oxygen from +<span class="pagenum">200</span> +<a name="conver1.page200" id="conver1.page200"> </a> +the manganese, by presenting to it some other body, for which it has a +greater affinity than for the manganese. Caloric affording the two +electricities is decomposed, and one of them uniting with the oxygen, +restores it to the aëriform state.</p> + +<p class="speaker">EMILY.</p> + +<p>But you said just now, that manganese would attract oxygen from the +atmosphere in which it is combined with the negative electricity; how, +therefore, can the oxygen have a superior affinity for that electricity, +since it abandons it to combine with the manganese?</p> + +<p class="speaker">MRS. B.</p> + +<p>I give you credit for this objection, Emily; and the only answer I +can make to it is, that the mutual affinities of metals for oxygen, and +of oxygen for electricity, vary at different temperatures; +a certain degree of heat will, therefore, dispose a metal to +combine with oxygen, whilst, on the contrary, the former will be +compelled to part with the latter, when the temperature is further +increased. I have put some oxyd of manganese into a retort, which +is an earthen vessel with a bent neck, such as you see here. (<a class="smallcaps" href="#plateVII">Plate VII.</a> Fig. 2.)—The +retort containing the manganese you cannot see, as I have enclosed it in +this furnace, where it is now red-hot. But, in order to +<span class="pagenum">201</span> +<a name="conver1.page201" id="conver1.page201"> </a> +make you sensible of the escape of the gas, which is itself invisible, +I have connected the neck of the retort with this bent tube, the +extremity of which is immersed in this vessel of water. (<a class="smallcaps" href="#plateVII">Plate VII.</a> Fig. 3.)—Do you +see the bubbles of air rise through the water?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Perfectly. This, then, is pure oxygen gas; what a pity it should be +lost! Could you not preserve it?</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall collect it in this receiver.—For this purpose, you +observe, I first fill it with water, in order to exclude the +atmospherical air; and then place it over the bubbles that issue from +the retort, so as to make them rise through the water to the upper part +of the receiver.</p> + +<p class="speaker">EMILY.</p> + +<p>The bubbles of oxygen gas rise, I suppose, from their specific +levity?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; for though oxygen forms rather a heavy gas, it is light compared +to water. You see how it gradually displaces the water from the +receiver. It is now full of gas, and I may leave it inverted in water on +this shelf, where I can keep the gas +<span class="pagenum">202</span> +<a name="conver1.page202" id="conver1.page202"> </a> +as long as I choose, for future experiments. This apparatus (which is +indispensable in all experiments in which gases are concerned) is called +a water-bath.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is a very clever contrivance, indeed; equally simple and useful. +How convenient the shelf is for the receiver to rest upon under water, +and the holes in it for the gas to pass into the receiver! I long +to make some experiments with this apparatus.</p> + +<p class="speaker">MRS. B.</p> + +<p>I shall try your skill that way, when you have a little more +experience. I am now going to show you an experiment, which proves, +in a very striking manner, how essential oxygen is to combustion. You +will see that iron itself will burn in this gas, in the most rapid and +brilliant manner.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Really! I did not know that it was possible to burn iron.</p> + +<p class="speaker">EMILY.</p> + +<p>Iron is a simple body, and you know, Caroline, that all simple bodies +are naturally positive, and therefore must have an affinity for +oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>Iron will, however, not burn in atmospherical +<span class="pagenum">203</span> +<a name="conver1.page203" id="conver1.page203"> </a> +air without a very great elevation of temperature; but it is eminently +combustible in pure oxygen gas; and what will surprise you still more, +it can be set on fire without any considerable rise of temperature. You +see this spiral iron wire—I fasten it at one end to this +cork, which is made to fit an opening at the top of the glass-receiver. +(<a class="smallcaps" href="#plateVII">Plate VII.</a> +Fig. 4.)</p> + +<p class="speaker">EMILY.</p> + +<p>I see the opening in the receiver; but it is carefully closed by a +ground glass-stopper.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is in order to prevent the gas from escaping; but I shall take +out the stopper, and put in the cork, to which the wire hangs.—Now +I mean to burn this wire in the oxygen gas, but I must fix a small piece +of lighted tinder to the extremity of it, in order to give the first +impulse to combustion; for, however powerful oxygen is in promoting +combustion, you must recollect that it cannot take place without some +elevation of temperature. I shall now introduce the wire into the +receiver, by quickly changing the stoppers.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is there no danger of the gas escaping while you change the +stoppers?</p> + +<span class="pagenum">204</span> +<a name="conver1.page204" id="conver1.page204"> </a> +<p class="speaker">MRS. B.</p> + +<p>Oxygen gas is a little heavier than atmospherical air, therefore it +will not mix with it very rapidly; and, if I do not leave the opening +uncovered, we shall not lose any——</p> + +<p class="speaker">CAROLINE.</p> + +<p>Oh, what a brilliant and beautiful flame!</p> + +<p class="speaker">EMILY.</p> + +<p>It is as white and dazzling as the sun!—Now a piece of the +melted wire drops to the bottom: I fear it is extinguished; but no, +it burns again as bright as ever.</p> + +<p class="speaker">MRS. B.</p> + +<p>It will burn till the wire is entirely consumed, provided the oxygen +is not first expended: for you know it can burn only while there is +oxygen to combine with it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I never saw a more beautiful light. My eyes can hardly bear it! How +astonishing to think that all this caloric was contained in the small +quantity of gas and iron that was enclosed in the receiver; and that, +without producing any sensible heat!</p> + +<p class="speaker">CAROLINE.</p> + +<p>How wonderfully quick combustion goes on in pure oxygen gas! But +pray, are these drops of burnt iron as heavy as the wire was before?</p> + +<span class="pagenum">205</span> +<a name="conver1.page205" id="conver1.page205"> </a> +<p class="speaker">MRS. B.</p> + +<p>They are even heavier; for the iron, in burning, has acquired exactly +the weight of the oxygen which has disappeared, and is now combined with +it. It has become an oxyd of iron.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not know what you mean by saying that the oxygen has +<i>disappeared</i>, Mrs. B., for it was always invisible.</p> + +<p class="speaker">MRS. B.</p> + +<p>True, my dear; the expression was incorrect. But though you could not +see the oxygen gas, I believe you had no doubt of its presence, as +the effect it produced on the wire was sufficiently evident.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes, indeed; yet you know it was the caloric, and not the oxygen gas +itself, that dazzled us so much.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are not quite correct in your turn, in saying the caloric dazzled +you; for caloric is invisible; it affects only the sense of feeling; it +was the light which dazzled you.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; but light and caloric are such constant companions, that it is +difficult to separate them, even in idea.</p> + +<span class="pagenum">206</span> +<a name="conver1.page206" id="conver1.page206"> </a> +<p class="speaker">MRS. B.</p> + +<p>The easier it is to confound them, the more careful you should be in +making the distinction.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But why has the water now risen, and filled part of the receiver?</p> + +<p class="speaker">MRS. B.</p> + +<p>Indeed, Caroline, I did not suppose you would have asked such a +question! I dare say, Emily, you can answer it.</p> + +<p class="speaker">EMILY.</p> + +<p>Let me reflect . . . . . . The oxygen has combined with the wire; the +caloric has escaped; consequently nothing can remain in the receiver, +and the water will rise to fill the vacuum.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I wonder that I did not think of that. I wish that we had weighed the +wire and the oxygen gas before combustion; we might then have found +whether the weight of the oxyd was equal to that of both.</p> + +<p class="speaker">MRS. B.</p> + +<p>You might try the experiment if you particularly wished it; but I can +assure you, that, if accurately performed, it never fails to show that +the additional weight of the oxyd is precisely equal to that +<span class="pagenum">207</span> +<a name="conver1.page207" id="conver1.page207"> </a> +of the oxygen absorbed, whether the process has been a real combustion, +or a simple oxygenation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But this cannot be the case with combustions in general; for when any +substance is burnt in the common air, so far from increasing in weight, +it is evidently diminished, and sometimes entirely consumed.</p> + +<p class="speaker">MRS. B.</p> + +<p>But what do you mean by the expression <i>consumed</i>? You cannot +suppose that the smallest particle of any substance in nature can be +actually destroyed. A compound body is decomposed by combustion; +some of its constituent parts fly off in a gaseous form, while others +remain in a concrete state; the former are called the <i>volatile</i>, +the latter the <i>fixed products</i> of combustion. But if we collect +the whole of them, we shall always find that they exceed the weight of +the combustible body, by that of the oxygen which has combined with them +during combustion.</p> + +<p class="speaker">EMILY.</p> + +<p>In the combustion of a coal fire, then, I suppose that the ashes +are what would be called the fixed product, and the smoke the volatile +product?</p> + +<span class="pagenum">208</span> +<a name="conver1.page208" id="conver1.page208"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yet when the fire burns best, and the quantity of volatile products +should be the greatest, there is no smoke; how can you account for +that?</p> + +<p class="speaker">EMILY.</p> + +<p>Indeed I cannot; therefore I suppose that I was not right in my +conjecture.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not quite: ashes, as you supposed, are a fixed product of combustion; +but smoke, properly speaking, is not one of the volatile products, as it +consists of some minute undecomposed particles of the coals that are +carried off by the heated air without being burnt, and are either +deposited in the form of soot, or dispersed by the wind. Smoke, +therefore, ultimately, becomes one of the <i>fixed</i> products of +combustion. And you may easily conceive that the stronger the fire is, +the less smoke is produced, because the fewer particles escape +combustion. On this principle depends the invention of Argand’s Patent +Lamps; a current of air is made to pass through the cylindrical +wick of the lamp, by which means it is so plentifully supplied with +oxygen, that scarcely a particle of oil escapes combustion, nor is there +any smoke produced.</p> + +<p class="speaker">EMILY.</p> + +<p>But what then are the volatile products of combustion?</p> + +<span class="pagenum">209</span> +<a name="conver1.page209" id="conver1.page209"> </a> +<p class="speaker">MRS. B.</p> + +<p>Various new compounds, with which you are not yet acquainted, and +which being converted by caloric either into vapour or gas, are +invisible; but they can be collected, and we shall examine them at some +future period.</p> + +<p class="speaker">CAROLINE.</p> + +<p>There are then other gases, besides the oxygen and nitrogen +gases.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, several: any substance that can assume and maintain the form of +an elastic fluid at the temperature of the atmosphere, is called a gas. +We shall examine the several gases in their respective places; but we +must now confine our attention to those that compose the atmosphere.</p> + +<p>I shall show you another method of decomposing the atmosphere, which +is very simple. In breathing, we retain a portion of the oxygen, and +expire the nitrogen gas; so that if we breathe in a closed vessel, for a +certain length of time, the air within it will be deprived of its oxygen +gas. Which of you will make the experiment?</p> + +<p class="speaker">CAROLINE.</p> + +<p>I should be very glad to try it.</p> + +<span class="pagenum">210</span> +<a name="conver1.page210" id="conver1.page210"> </a> +<p class="speaker">MRS. B.</p> + +<p>Very well; breathe several times through this glass tube into the +receiver with which it is connected, until you feel that your breath is +exhausted.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am quite out of breath already!</p> + +<p class="speaker">MRS. B.</p> + +<p>Now let us try the gas with a lighted taper.</p> + +<p class="speaker">EMILY.</p> + +<p>It is very pure nitrogen gas, for the taper is immediately +extinguished.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is not a proof of its being pure, but only of the absence of +oxygen, as it is that principle alone which can produce combustion, +every other gas being absolutely incapable of it.</p> + +<p class="speaker">EMILY.</p> + +<p>In the methods which you have shown us, for decomposing the +atmosphere, the oxygen always abandons the nitrogen; but is there no way +of taking the nitrogen from the oxygen, so as to obtain the latter pure +from the atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>You must observe, that whenever oxygen is +<span class="pagenum">211</span> +<a name="conver1.page211" id="conver1.page211"> </a> +taken from the atmosphere, it is by decomposing the oxygen gas; we +cannot do the same with the nitrogen gas, because nitrogen has a +stronger affinity for caloric than for any other known principle: it +appears impossible therefore to separate it from the atmosphere by the +power of affinities. But if we cannot obtain the oxygen gas, by this +means, in its separate state, we have no difficulty (as you have seen) +to procure it in its gaseous form, by taking it from those substances +that have absorbed it from the atmosphere, as we did with the oxyd of +manganese.</p> + +<p class="speaker">EMILY.</p> + +<p>Can atmospherical air be recomposed, by mixing due proportions of +oxygen and nitrogen gases?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes: if about one part of oxygen gas be mixed with about four parts +of nitrogen gas, atmospherical air is produced.<a class="tag" name="tag17" id="tag17" href="#note17">*</a></p> + +<p class="speaker">EMILY.</p> + +<p>The air, then, must be an oxyd of nitrogen?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, my dear; for there must be a chemical +<span class="pagenum">212</span> +<a name="conver1.page212" id="conver1.page212"> </a> +combination between oxygen and nitrogen in order to produce an oxyd; +whilst in the atmosphere these two substances are separately combined +with caloric, forming two distinct gases, which are simply mixed in the +formation of the atmosphere.</p> + +<p>I shall say nothing more of oxygen and nitrogen at present, as we +shall continually have occasion to refer to them in our future +conversations. They are both very abundant in nature; nitrogen is the +most plentiful in the atmosphere, and exists also in all animal +substances; oxygen forms a constituent part, both of the animal and +vegetable kingdoms, from which it may be obtained by a variety of +chemical means. But it is now time to conclude our lesson. I am +afraid you have learnt more to-day than you will be able to +remember.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I assure you that I have been too much interested in it, ever to +forget it. In regard to nitrogen there seems to be but little to +remember; it makes a very insignificant figure in comparison to oxygen, +although it composes a much larger portion of the atmosphere.</p> + +<p class="speaker">MRS. B.</p> + +<p>Perhaps this insignificance you complain of may arise from the +compound nature of nitrogen, for though I have hitherto considered it as +a simple +<span class="pagenum">213</span> +<a name="conver1.page213" id="conver1.page213"> </a> +body, because it is not known in any natural process to be decomposed, +yet from some experiments of Sir H. Davy, there appears to be reason for +suspecting that nitrogen is a compound body, as we shall see afterwards. +But even in its simple state, it will not appear so insignificant when +you are better acquainted with it; for though it seems to perform but a +passive part in the atmosphere, and has no very striking properties, +when considered in its separate state, yet you will see by-and-bye what +a very important agent it becomes, when combined with other bodies. But +no more of this at present; we must reserve it for its proper place.</p> + +<div class="footnote"> + +<p><a name="note16" id="note16" href="#tag16">*</a> +If chlorine or oxymuriatic gas be a simple body, according to Sir H. +Davy’s view of the subject, it must be considered as an exception to +this statement; but this subject cannot be discussed till the properties +and nature of chlorine come under examination.</p> + +<p><a name="note17" id="note17" href="#tag17">*</a> +The proportion of oxygen in the atmosphere varies from 21 to 22 per +cent.</p> + +</div> + + +<span class="pagenum">214</span> +<a name="conver1.page214" id="conver1.page214"> </a> +<h4><a name="convVII" id="convVII">CONVERSATION VII.</a><br> +<span class="subhead">ON HYDROGEN.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">CAROLINE.</p> + +<p><span class="firstword"><span class="firstletter">T</span>he</span> next simple bodies we come to are <span +class="smallroman">CHLORINE</span> and <span class="smallroman">IODINE</span>. Pray what kinds of substances are these; are +they also invisible?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for chlorine, in the state of gas, has a distinct greenish +colour, and is therefore visible; and iodine, in the same state, has a +beautiful claret-red colour. The knowledge of these two bodies, however, +and the explanation of their properties, imply various considerations, +which you would not yet be able to understand; we shall therefore defer +their examination to some future conversation, and we shall pass on to +the next simple substance, <span class="smallcaps">Hydrogen</span>, +which we cannot, any more than oxygen, obtain in a visible or palpable +form. We are acquainted with it only in its gaseous state, as we are +with oxygen and nitrogen.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But in its gaseous state it cannot be called a +<span class="pagenum">215</span> +<a name="conver1.page215" id="conver1.page215"> </a> +simple substance, since it is combined with heat and electricity?</p> + +<p class="speaker">MRS. B.</p> + +<p>True, my dear; but as we do not know in nature of any substance which +is not more or less combined with caloric and electricity, we are apt to +say that a substance is in its pure state when combined with those +agents only.</p> + +<p>Hydrogen was formerly called <i>inflammable air</i>, as it is +extremely combustible, and burns with a great flame. Since the invention +of the new nomenclature, it has obtained the name of hydrogen, which is +derived from two Greek words, the meaning of which is, <i>to produce +water</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>And how does hydrogen produce water?</p> + +<p class="speaker">MRS. B.</p> + +<p>By its combustion. Water is composed of eighty-five parts, by weight, +of oxygen, combined with fifteen parts of hydrogen; or of two parts, by +bulk of hydrogen gas, to one part of oxygen gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Really! is it possible that water should be a combination of two +gases, and that one of these +<span class="pagenum">216</span> +<a name="conver1.page216" id="conver1.page216"> </a> +should be inflammable air! Hydrogen must be a most extraordinary gas +that will produce both fire and water.</p> + +<p class="speaker">EMILY.</p> + +<p>But I thought you said that combustion could take place in no gas but +oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Do you recollect what the process of combustion consists in?</p> + +<p class="speaker">EMILY.</p> + +<p>In the combination of a body with oxygen, with disengagement of light +and heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>Therefore when I say that hydrogen is combustible, I mean that +it has an affinity for oxygen; but, like all other combustible +substances, it cannot burn unless supplied with oxygen, and also heated +to a proper temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The simply mixing fifteen parts of hydrogen, with eighty-five parts +of oxygen gas, will not, therefore, produce water?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; water being a much denser fluid than gases, in order to reduce +these gases to a liquid, it is +<span class="pagenum">217</span> +<a name="conver1.page217" id="conver1.page217"> </a> +necessary to diminish the quantity of caloric or electricity which +maintains them in an elastic form.</p> + +<p class="speaker">EMILY.</p> + +<p>That I should think might be done by combining the oxygen and +hydrogen together; for in combining they would give out their respective +electricities in the form of caloric, and by this means would be +condensed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But you forget, Emily, that in order to make the oxygen and hydrogen +combine, you must begin by elevating their temperature, which increases, +instead of diminishing, their electric energies.</p> + +<p class="speaker">MRS. B.</p> + +<p>Emily is, however, right; for though it is necessary to raise their +temperature, in order to make them combine, as that combination affords +them the means of parting with their electricities, it is eventually the +cause of the diminution of electric energy.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You love to deal in paradoxes to-day, Mrs. B.—Fire, then, +produces water?</p> + +<p class="speaker">MRS. B.</p> + +<p>The combustion of hydrogen gas certainly does; +<span class="pagenum">218</span> +<a name="conver1.page218" id="conver1.page218"> </a> +but you do not seem to have remembered the theory of combustion so well +as you thought you would. Can you tell me what happens in the combustion +of hydrogen gas?</p> + +<p class="speaker">CAROLINE.</p> + +<p>The hydrogen combines with the oxygen, and their opposite +electricities are disengaged in the form of caloric.—Yes, +I think I understand it now—by the loss of this caloric, the +gases are condensed into a liquid.</p> + +<p class="speaker">EMILY.</p> + +<p>Water, then, I suppose, when it evaporates and incorporates with the +atmosphere, is decomposed and converted into hydrogen and oxygen +gases?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, my dear—there you are quite mistaken: the decomposition of +water is totally different from its evaporation; for in the latter case +(as you should recollect) water is only in a state of very minute +division; and is merely suspended in the atmosphere, without any +chemical combination, and without any separation of its constituent +parts. As long as these remain combined, they form <span class="smallroman">WATER</span>, whether in a state of liquidity, or in that +of an elastic fluid, as vapour, or under the solid form of ice.</p> + +<p>In our experiments on latent heat, you may recollect +<span class="pagenum">219</span> +<a name="conver1.page219" id="conver1.page219"> </a> +that we caused water successively to pass through these three forms, +merely by an increase or diminution of caloric, without employing any +power of attraction, or effecting any decomposition.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But are there no means of decomposing water?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, several: charcoal, and metals, when heated red hot, will attract +the oxygen from water, in the same manner as they will from the +atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Hydrogen, I see, is like nitrogen, a poor dependant friend of +oxygen, which is continually forsaken for greater favourites.</p> + +<p class="speaker">MRS. B.</p> + +<p>The connection, or friendship, as you choose to call it, is much more +intimate between oxygen and hydrogen, in the state of water, than +between oxygen and nitrogen, in the atmosphere; for, in the first case, +there is a chemical union and condensation of the two substances; in the +latter, they are simply mixed together in their gaseous state. You will +find, however, that, in some cases, nitrogen is quite as intimately +connected with oxygen, as hydrogen is.—But this is foreign to our +present subject.</p> + +<span class="pagenum">220</span> +<a name="conver1.page220" id="conver1.page220"> </a> +<p class="speaker">EMILY.</p> + +<p>Water, then, is an oxyd, though the atmospherical air is not?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not commonly called an oxyd, though, according to our +definition, it may, no doubt, be referred to that class of bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I should like extremely to see water decomposed.</p> + +<p class="speaker">MRS. B.</p> + +<p>I can gratify your curiosity by a much more easy process than the +oxydation of charcoal or metals: the decomposition of water by these +latter means takes up a great deal of time, and is attended with much +trouble; for it is necessary that the charcoal or metal should be made +red hot in a furnace, that the water should pass over them in a state of +vapour, that the gas formed should be collected over the water-bath, +&c. In short, it is a very complicated affair. But the same effect +may be produced with the greatest facility, by the action of the Voltaic +battery, which this will give me an opportunity of exhibiting.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am very glad of that, for I longed to see the power of this +apparatus in decomposing bodies.</p> + +<span class="pagenum">221</span> +<a name="conver1.page221" id="conver1.page221"> </a> +<p class="speaker">MRS. B.</p> + +<p>For this purpose I fill this piece of glass-tube (<a class="smallcaps" href="#plateVIII">Plate VIII.</a> fig. 1.) with +water, and cork it up at both ends; through one of the corks I introduce +that wire of the battery which conveys the positive electricity; and the +wire which conveys the negative electricity is made to pass through the +other cork, so that the two wires approach each other sufficiently near +to give out their respective electricities.</p> + +<p class="figname"> +<a name="plateVIII" id="plateVIII">Plate VIII.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 206</p> + +<p class="illustration"> +<img src="images/plate8a_thumb.png" width="239" height="74" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. Apparatus for the decomposition of water by the +Voltaic Battery.</p> + +<p class="figlink"> +<a href="images/plate8_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>It does not appear to me that you approach the wires so near as you +did when you made the battery act by itself.</p> + +<p class="speaker">MRS. B.</p> + +<p>Water being a better conductor of electricity than air, the two wires +will act on each other at a greater distance in the former than in the +latter.</p> + +<p class="speaker">EMILY.</p> + +<p>Now the electrical effect appears: I see small bubbles of air emitted +from each wire.</p> + +<p class="speaker">MRS. B.</p> + +<p>Each wire decomposes the water, the positive by combining with its +oxygen which is negative, the negative by combining with its hydrogen +which is positive.</p> + +<span class="pagenum">222</span> +<a name="conver1.page222" id="conver1.page222"> </a> +<p class="speaker">CAROLINE.</p> + +<p>That is wonderfully curious! But what are the small bubbles of +air?</p> + +<p class="speaker">MRS. B.</p> + +<p>Those that appear to proceed from the positive wire, are the result +of the decomposition of the water by that wire. That is to say, the +positive electricity having combined with some of the oxygen of the +water, the particles of hydrogen which were combined with that portion +of oxygen are set at liberty, and appear in the form of small bubbles of +gas or air.</p> + +<p class="speaker">EMILY.</p> + +<p>And I suppose the negative fluid having in the same manner combined +with some of the hydrogen of the water, the particles of oxygen that +were combined with it, are set free, and emitted in a gaseous form.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely so. But I should not forget to observe, that the wires used +in this experiment are made of platina, a metal which is not +capable of combining with oxygen; for otherwise the wire would combine +with the oxygen, and the hydrogen alone would be disengaged.</p> + +<span class="pagenum">223</span> +<a name="conver1.page223" id="conver1.page223"> </a> +<p class="speaker">CAROLINE.</p> + +<p>But could not water be decomposed without the electric circle being +completed? If, for instance, you immersed only the positive wire in the +water, would it not combine with the oxygen, and the hydrogen gas be +given out?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for as you may recollect, the battery cannot act unless the +circle be completed; since the positive wire will not give out its +electricity, unless attracted by that of the negative wire.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I understand it now.—But look, Mrs. B., the decomposition of +the water which has now been going on for some time, does not sensibly +diminish its quantity—what is the reason of that?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the quantity decomposed is so extremely small. If you compare +the density of water with that of the gases into which it is resolved, +you must be aware that a single drop of water is sufficient to produce +thousands of such small bubbles as those you now perceive.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But in this experiment, we obtain the oxygen +<span class="pagenum">224</span> +<a name="conver1.page224" id="conver1.page224"> </a> +and hydrogen gases mixed together. Is there any means of procuring the +two gases separately?</p> + +<p class="speaker">MRS. B.</p> + +<p>They can be collected separately with great ease, by modifying a +little the experiment. Thus if instead of one tube, we employ two, as +you see here, (c, d, <a class="smallcaps" href="#plateVIIIb">Plate VIII.</a> fig. <ins class="correction" title="text reads ‘2,’">2.</ins>) both tubes being closed at one end, and +open at the other; and if after filling these tubes with water, we place +them standing in a glass of water (e), with their open end +downwards, you will see that the moment we connect the wires (a, b) +which proceed upwards from the interior of each tube, the one with one +end of the battery, and the other with the other end, the water in the +tubes will be decomposed; hydrogen will be given out round the wire in +the tube connected with the positive end of the battery, and oxygen in +the other; and these gases will be evolved, exactly in the proportions +which I have before mentioned, namely, two measures of hydrogen for one +of oxygen. We shall now begin the experiment, but it will be some time +before any sensible quantity of the gases can be collected.</p> + +<p class="figname"> +<a name="plateVIIIb" id="plateVIIIb">Plate VIII.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 206</p> + +<p class="illustration"> +<img src="images/plate8b_thumb.png" width="150" height="144" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 2. Apparatus for decomposing water by Voltaic +Electricity & obtaining the gasses separate.</p> + +<p class="figlink"> +<a href="images/plate8_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">EMILY.</p> + +<p>The decomposition of water in this way, slow as it is, is certainly +very striking; but I confess that I should be still more gratified, if +you could shew it us on a larger scale, and by a quicker process. +<span class="pagenum">225</span> +<a name="conver1.page225" id="conver1.page225"> </a> +I am sorry that the decomposition of water by charcoal or metals is +attended with so much inconvenience.</p> + +<p class="speaker">MRS. B.</p> + +<p>Water may be decomposed by means of metals without any difficulty; +but for this purpose the intervention of an acid is required. Thus, if +we add some sulphuric acid (a substance with the nature of which +you are not yet acquainted) to the water which the metal is to +decompose, the acid disposes the metal to combine with the oxygen of the +water so readily and abundantly, that no heat is required to hasten the +process. Of this I am going to shew you an instance. I put into +this bottle the water that is to be decomposed, as also the metal that +is to effect that decomposition by combining with the oxygen, and the +acid which is to facilitate the combination of the metal and the oxygen. +You will see with what violence these will act on each other.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what metal is it that you employ for this purpose?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is iron; and it is used in the state of filings, as these present +a greater surface to the acid than a solid piece of metal. For as it is +the surface of the metal which is acted upon by the acid, and is +disposed to receive the oxygen produced by the +<span class="pagenum">226</span> +<a name="conver1.page226" id="conver1.page226"> </a> +decomposition of the water, it necessarily follows that the greater is +the surface, the more considerable is the effect. The bubbles which are +now rising are hydrogen gas——</p> + +<p class="speaker">CAROLINE.</p> + +<p>How disagreeably it smells!</p> + +<p class="speaker">MRS. B.</p> + +<p>It is indeed unpleasant, though, I believe, not particularly hurtful. +We shall not, however, suffer any more to escape, as it will be wanted +for experiments. I shall, therefore, collect it in a +glass-receiver, by making it pass through this bent tube, which will +conduct it into the water-bath. (<a class="smallcaps" href="#plateVIIIc">Plate VIII.</a> fig. 3.)</p> + +<p class="figname"> +<a name="plateVIIIc" id="plateVIIIc">Plate VIII.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 206</p> + +<p class="illustration"> +<img src="images/plate8c_thumb.png" width="542" height="265" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 3. Apparatus for preparing & collecting hydrogen +gas.<br> +Fig. 4. Receiver full of hydrogen gas inverted over +water.<br> +Fig. 5. Slow combustion of hydrogen gas.<br> +Fig. 6. Apparatus for illustrating the formation of water by +the combustion of hydrogen gas.<br> +Fig. 7. Apparatus for producing harmonic sounds by the +combustion of hydrogen gas.</p> + +<p class="figlink"> +<a href="images/plate8_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">EMILY.</p> + +<p>How very rapidly the gas escapes! it is perfectly transparent, and +without any colour whatever.—Now the receiver is +full——</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall, therefore, remove it, and substitute another in its place. +But you must observe, that when the receiver is full, it is necessary to +keep it inverted with the mouth under water, otherwise the gas would +escape. And in order that it may not be in the way, I introduce +within the bath, under the water, a saucer, into which I slide the +receiver, so that it can be taken out of the bath +<span class="pagenum">227</span> +<a name="conver1.page227" id="conver1.page227"> </a> +and conveyed any where, the water in the saucer being equally effectual +in preventing its escape as that in the bath. (<a class="smallcaps" +href="#plateVIIIc">Plate VIII.</a> fig. 4.)</p> + +<p class="speaker">EMILY.</p> + +<p>I am quite surprised to see what a large quantity of hydrogen gas can +be produced by such a small quantity of water, especially as oxygen is +the principal constituent of water.</p> + +<p class="speaker">MRS. B.</p> + +<p>In weight it is; but not in volume. For though the proportion, by +weight, is nearly six parts of oxygen to one of hydrogen, yet the +proportion of the volume of the gases, is about one part of oxygen to +two of hydrogen; so much heavier is the former than the latter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But why is the vessel in which the water is decomposed so hot? As the +water changes from a liquid to a gaseous form, cold should be produced +instead of heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for if one of the constituents of water is converted into a gas, +the other becomes solid in combining with the metal.</p> + +<p class="speaker">EMILY.</p> + +<p>In this case, then, neither heat nor cold should be produced?</p> + +<span class="pagenum">228</span> +<a name="conver1.page228" id="conver1.page228"> </a> +<p class="speaker">MRS. B.</p> + +<p>True: but observe that the sensible heat which is disengaged in this +operation, is not owing to the decomposition of the water, but to an +extrication of heat produced by the mixture of water and sulphuric acid. +I will mix some water and sulphuric acid together in this glass, +that you may feel the surprising quantity of heat that is disengaged by +their union—now take hold of the glass——</p> + +<p class="speaker">CAROLINE.</p> + +<p>Indeed I cannot; it feels as hot as boiling water. I should have +imagined there would have been heat enough disengaged to have rendered +the liquid solid.</p> + +<p class="speaker">MRS. B.</p> + +<p>As, however, it does not produce that effect, we cannot refer this +heat to the modification called latent heat. We may, however, +I think, consider it as heat of capacity, as the liquid is +condensed by its loss; and if you were to repeat the experiment, in a +graduated tube, you would find that the two liquids, when mixed, occupy +considerably less space than they did separately.—But we will +reserve this to another opportunity, and attend at present to the +hydrogen gas which we have been producing.</p> + +<p>If I now set the hydrogen gas, which is contained in this receiver, +at liberty all at once, and +<span class="pagenum">229</span> +<a name="conver1.page229" id="conver1.page229"> </a> +kindle it as soon as it comes in contact with the atmosphere, by +presenting it to a candle, it will so suddenly and rapidly decompose the +oxygen gas, by combining with its basis, that an explosion, or a +<i>detonation</i> (as chemists commonly call it), will be produced. For +this purpose, I need only take up the receiver, and quickly present +its open mouth to the candle——so . . . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>It produced only a sort of hissing noise, with a vivid flash of +light. I had expected a much greater report.</p> + +<p class="speaker">MRS. B.</p> + +<p>And so it would have been, had the gases been closely confined at the +moment they were made to explode. If, for instance, we were to put in +this bottle a mixture of hydrogen gas and atmospheric air; and if, after +corking the bottle, we should kindle the mixture by a very small +orifice, from the sudden dilatation of the gases at the moment of their +combination, the bottle must either fly to pieces, or the cork be blown +out with considerable violence.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But in the experiment which we have just seen, if you did not kindle +the hydrogen gas, would it not equally combine with the oxygen?</p> + +<span class="pagenum">230</span> +<a name="conver1.page230" id="conver1.page230"> </a> +<p class="speaker">MRS. B.</p> + +<p>Certainly not; for, as I have just explained to you, it is necessary +that the oxygen and hydrogen gases be burnt together, in order to +combine chemically and produce water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is true; but I thought this was a different combination, for I +see no water produced.</p> + +<p class="speaker">MRS. B.</p> + +<p>The water resulting from this detonation was so small in quantity, +and in such a state of minute division, as to be invisible. But water +certainly was produced; for oxygen is incapable of combining with +hydrogen in any other proportions than those that form water; therefore +water must always be the result of their combination.</p> + +<p>If, instead of bringing the hydrogen gas into sudden contact with the +atmosphere (as we did just now) so as to make the whole of it explode +the moment it is kindled, we allow but a very small surface of gas to +burn in contact with the atmosphere, the combustion goes on quietly and +gradually at the point of contact, without any detonation, because the +surfaces brought together are too small for the immediate union of +gases. The experiment is a very easy one. This phial, with a narrow +neck, (<a class="smallcaps" href="#plateVIIIc">Plate VIII.</a> +fig. 5.) is full +<span class="pagenum">231</span> +<a name="conver1.page231" id="conver1.page231"> </a> +of hydrogen gas, and is carefully corked. If I take out the cork without +moving the phial, and quickly approach the candle to the orifice, you +will see how different the result will be——</p> + +<p class="speaker">EMILY.</p> + +<p>How prettily it burns, with a blue flame! The flame is gradually +sinking within the phial—now it has entirely disappeared. But does +not this combustion likewise produce water?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly. In order to make the formation of the water sensible to +you, I shall procure a fresh supply of hydrogen gas, by putting +into this bottle (<a class="smallcaps" href="#plateVIIIc">Plate +VIII.</a> fig. 6.) iron filings, water, and sulphuric acid, +materials similar to those which we have just used for the same purpose. +I shall then cork up the bottle, leaving only a small orifice in +the cork, with a piece of glass-tube fixed to it, through which the gas +will issue in a continued rapid stream.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I hear already the hissing of the gas through the tube, and I can +feel a strong current against my hand.</p> + +<p class="speaker">MRS. B.</p> + +<p>This current I am going to kindle with the candle—see how +vividly it burns——</p> + +<span class="pagenum">232</span> +<a name="conver1.page232" id="conver1.page232"> </a> +<p class="speaker">EMILY.</p> + +<p>It burns like a candle with a long flame. But why does this +combustion last so much longer than in the former experiment?</p> + +<p class="speaker">MRS. B.</p> + +<p>The combustion goes on uninterruptedly as long as the new gas +continues to be produced. Now if I invert this receiver over the flame, +you will soon perceive its internal surface covered with a very fine +dew, which is pure water——</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes, indeed; the glass is now quite dim with moisture! How glad I am +that we can see the water produced by this combustion.</p> + +<p class="speaker">EMILY.</p> + +<p>It is exactly what I was anxious to see; for I confess I was a little +incredulous.</p> + +<p class="speaker">MRS. B.</p> + +<p>If I had not held the glass-bell over the flame, the water would have +escaped in the state of vapour, as it did in the former experiment. We +have here, of course, obtained but a very small quantity of water; but +the difficulty of procuring a proper apparatus, with sufficient +quantities of +<span class="pagenum">233</span> +<a name="conver1.page233" id="conver1.page233"> </a> +gases, prevents my showing it you on a larger scale.</p> + +<p>The composition of water was discovered about the same period, both +by Mr. Cavendish, in this country, and by the celebrated French chemist +Lavoisier. The latter invented a very perfect and ingenious apparatus to +perform, with great accuracy, and upon a large scale, the formation of +water by the combination of oxygen and hydrogen gases. Two tubes, +conveying due proportions, the one of oxygen, the other of hydrogen gas, +are inserted at opposite sides of a large globe of glass, previously +exhausted of air; the two streams of gas are kindled within the globe, +by the electrical spark, at the point where they come in contact; they +burn together, that is to say, the hydrogen combines with the oxygen, +the caloric is set at liberty, and a quantity of water is produced +exactly equal, in weight, to that of the two gases introduced into the +globe.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And what was the greatest quantity of water ever formed in this +apparatus?</p> + +<p class="speaker">MRS. B.</p> + +<p>Several ounces; indeed, very nearly a pound, if I recollect right; +but the operation lasted many days.</p> + +<span class="pagenum">234</span> +<a name="conver1.page234" id="conver1.page234"> </a> +<p class="speaker">EMILY.</p> + +<p>This experiment must have convinced all the world of the truth of the +discovery. Pray, if improper proportions of the gases were mixed and set +fire to, what would be the result?</p> + +<p class="speaker">MRS. B.</p> + +<p>Water would equally be formed, but there would be a residue of either +one or other of the gases, because, as I have already told you, hydrogen +and oxygen will combine only in the proportions requisite for the +formation of water.</p> + +<p class="speaker">EMILY.</p> + +<p>Look, Mrs. B., our experiment with the Voltaic battery (<a class="smallcaps" href="#plateVIIIb">Plate VIII.</a> fig. 2.) has made +great progress; a quantity of gas has been formed in each tube, but +in one of them there is twice as much gas as in the other.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; because, as I said before, water is composed of two volumes of +hydrogen to one of oxygen—and if we should now mix these gases +together and set fire to them by an electrical spark, both gases would +entirely disappear, and a small quantity of water would be formed.</p> + +<p>There is another curious effect produced by the combustion of +hydrogen gas, which I shall show +<span class="pagenum">235</span> +<a name="conver1.page235" id="conver1.page235"> </a> +you, though I must acquaint you first, that I cannot well explain the +cause of it. For this purpose, I must put some materials into our +apparatus, in order to obtain a stream of hydrogen gas, just as we have +done before. The process is already going on, and the gas is rushing +through the tube—I shall now kindle it with the +taper——</p> + +<p class="speaker">EMILY.</p> + +<p>It burns exactly as it did before——What is the curious +effect which you were mentioning?</p> + +<p class="speaker">MRS. B.</p> + +<p>Instead of the receiver, by means of which we have just seen the +drops of water form, we shall invert over the flame this piece of tube, +which is about two feet in length, and one inch in diameter (<a class="smallcaps" href="#plateVIIIc">Plate VIII.</a> fig. 7.); but you +must observe that it is open at both ends.</p> + +<p class="speaker">EMILY.</p> + +<p>What a strange noise it makes! something like the Æolian harp, but +not so sweet.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is very singular, indeed; but I think rather too powerful to be +pleasing. And is not this sound accounted for?</p> + +<span class="pagenum">236</span> +<a name="conver1.page236" id="conver1.page236"> </a> +<p class="speaker">MRS. B.</p> + +<p>That the percussion of glass, by a rapid stream of gas, should +produce a sound, is not extraordinary: but the sound here is so +peculiar, that no other gas has a similar effect. Perhaps it is owing to +a brisk vibratory motion of the glass, occasioned by the successive +formation and condensation of small drops of water on the sides of the +glass tube, and the air rushing in to replace the vacuum formed.<a class="tag" name="tag18" id="tag18" href="#note18">*</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>How very much this flame resembles the burning of a candle.</p> + +<p class="speaker">MRS. B.</p> + +<p>The burning of a candle is produced by much the same means. +A great deal of hydrogen is contained in candles, whether of tallow +or wax. This hydrogen being converted into gas by the heat of the +candle, combines with the oxygen of the atmosphere, and flame and water +result from this combination. So that, in fact, the flame of a candle is +owing to the combustion of hydrogen gas. An elevation of temperature, +such as is produced by a lighted match or taper, is required to give the +first impulse to the combustion; but afterwards +<span class="pagenum">237</span> +<a name="conver1.page237" id="conver1.page237"> </a> +it goes on of itself, because the candle finds a supply of caloric in +the successive quantities of heat which results from the union of the +two electricities given out by the gases during their combustion. But +there are other circumstances connected with the combustion of candles +and lamps, which I cannot explain to you till you are acquainted with +<i>carbon</i>, which is one of their constituent parts. In general, +however, whenever you see flame, you may infer that it is owing to the +formation and burning of hydrogen gas<a class="tag" name="tag19" id="tag19" href="#note19">*</a>; for flame is the peculiar mode of +burning hydrogen gas, which, with only one or two apparent exceptions, +does not belong to any other combustible.</p> + +<p class="speaker">EMILY.</p> + +<p>You astonish me! I understood that flame was the caloric produced by +the union of the two electricities, in all combustions whatever?</p> + +<p class="speaker">MRS. B.</p> + +<p>Your error proceeded from your vague and incorrect idea of flame; you +have confounded it with light and caloric in general. Flame always +implies caloric, since it is produced by the combustion of hydrogen gas; +but all caloric does not +<span class="pagenum">238</span> +<a name="conver1.page238" id="conver1.page238"> </a> +imply flame. Many bodies burn with intense heat without producing flame. +Coals, for instance, burn with flame until all the hydrogen which they +contain is evaporated; but when they afterwards become red hot, much +more caloric is disengaged than when they produce flame.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the iron wire, which you burnt in oxygen gas, appeared to me to +emit flame; yet, as it was a simple metal, it could contain no +hydrogen?</p> + +<p class="speaker">MRS. B.</p> + +<p>It produced a sparkling dazzling blaze of light, but no real +flame.</p> + +<p class="speaker">EMILY.</p> + +<p>And what is the cause of the regular shape of the flame of a +candle?</p> + +<p class="speaker">MRS. B.</p> + +<p>The regular stream of hydrogen gas which exhales from its combustible +matter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the hydrogen gas must, from its great levity, ascend into the +upper regions of the atmosphere; why therefore does not the flame +continue to accompany it?</p> + +<span class="pagenum">239</span> +<a name="conver1.page239" id="conver1.page239"> </a> +<p class="speaker">MRS. B.</p> + +<p>The combustion of the hydrogen gas is completed at the point where +the flame terminates; it then ceases to be hydrogen gas, as it is +converted by its combination with oxygen into watery vapour; but in a +state of such minute division as to be invisible.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not understand what is the use of the wick of a candle, since +the hydrogen gas burns so well without it?</p> + +<p class="speaker">MRS. B.</p> + +<p>The combustible matter of the candle must be decomposed in order to +emit the hydrogen gas, and the wick is instrumental in effecting this +decomposition. Its combustion first melts the combustible matter, and . +. . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>But in lamps the combustible matter is already fluid, and yet they +also require wicks?</p> + +<p class="speaker">MRS. B.</p> + +<p>I am going to add that, afterwards, the burning wick (by the power of +capillary attraction) gradually draws up the fluid to the point where +combustion +<span class="pagenum">240</span> +<a name="conver1.page240" id="conver1.page240"> </a> +takes place; for you must have observed that the wick does not burn +quite to the bottom.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes; but I do not understand why it does not.</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the air has not so free an access to that part of the wick +which is immediately in contact with the candle, as to the part just +above, so that the heat there is not sufficient to produce its +decomposition; the combustion therefore begins a little above this +point.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, Mrs. B., in those beautiful lights, called <i>gas-lights</i>, +which are now seen in many streets, and will, I hope, be soon +adopted every where<ins class="correction" title="text has .">, +</ins>I can perceive no wick at all. How are these lights +managed?</p> + +<p class="speaker">MRS. B.</p> + +<p>I am glad you have put me in mind of saying a few words on this very +useful and interesting improvement. In this mode of lighting, the gas is +conveyed to the extremity of a tube, where it is kindled, and burns as +long as the supply continues. There is, therefore, no occasion for a +wick, or any other fuel whatever.</p> + +<span class="pagenum">241</span> +<a name="conver1.page241" id="conver1.page241"> </a> +<p class="speaker">EMILY.</p> + +<p>But how is all this gas procured in such large quantities?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is obtained from coal, by distillation.—Coal, when exposed +to heat in a close vessel, is decomposed; and hydrogen, which is one of +its constituents, rises in the state of gas, combined with another of +its component parts, carbon, forming a compound gas, called +<i>Hydrocarbonat</i>, the nature of which we shall again have an +opportunity of noticing when we treat of carbon. This gas, like +hydrogen, is perfectly transparent, invisible, and highly inflammable; +and in burning it emits that vivid light which you have so often +observed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And does the process for procuring it require nothing but heating the +coals, and conveying the gas through tubes?</p> + +<p class="speaker">MRS. B.</p> + +<p>Nothing else; except that the gas must be made to pass, immediately +at its formation, through two or three large vessels of water, in which +it deposits some other ingredients, and especially water, tar, and oil, +which also arise from the distillation of coals. The gas-light +apparatus, therefore, consists simply in a large iron vessel, in which +the coals are exposed to the heat of a furnace,—some reservoirs +<span class="pagenum">242</span> +<a name="conver1.page242" id="conver1.page242"> </a> +of water, in which the gas deposits its impurities,—and tubes that +convey it to the desired spot, being propelled with uniform velocity +through the tubes by means of a certain degree of pressure which is made +upon the reservoir.</p> + +<p class="speaker">EMILY.</p> + +<p>What an admirable contrivance! Do you not think, Mrs. B., that +it will soon get into universal use?</p> + +<p class="speaker">MRS. B.</p> + +<p>Most probably, as to the lighting of streets, offices, and public +places, as it far surpasses any former invention for that purpose; but +as to the interior of private houses, this mode of lighting has not yet +been sufficiently tried to know whether it will be found generally +desirable, either in regard to economy or convenience. It may, however, +be considered as one of the happiest applications of chemistry to the +comforts of life; and there is every reason to suppose that it will +answer the full extent of public, expectation.</p> + +<p>I have another experiment to show you with hydrogen gas, which I +think will entertain you. Have you ever blown bubbles with soap and +water?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, often, when I was a child; and I used to make them float in the +air by blowing them upwards.</p> + +<span class="pagenum">243</span> +<a name="conver1.page243" id="conver1.page243"> </a> +<p class="speaker">MRS. B.</p> + +<p>We shall fill some such bubbles with hydrogen gas, instead of +atmospheric air, and you will see with what ease and rapidity they will +ascend, without the assistance of blowing, from the lightness of the +gas.—Will you mix some soap and water whilst I fill this bladder +with the gas contained in the receiver which stands on the shelf in the +water-bath?</p> + +<p class="speaker">CAROLINE.</p> + +<p>What is the use of the brass-stopper and turn-cock at the top of the +receiver?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is to afford a passage to the gas when required. There is, you +see, a similar stop-cock fastened to this bladder, which is made to +fit that on the receiver. I screw them one on the other, and now +turn the two cocks, to open a communication between the receiver and the +bladder; then, by sliding the receiver off the shelf, and gently sinking +it into the bath, the water rises in the receiver and forces the gas +into the bladder. (<a class="smallcaps" href="#plateIX">Plate +IX.</a> fig. 1.)</p> + +<p class="figname"> +<a name="plateIX" id="plateIX">Plate IX.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 228</p> + +<p class="illustration"> +<img src="images/plate9_thumb.png" width="528" height="264" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. Apparatus for transferring gases from a Receiver into a +bladder.<br> +Fig. 2. Apparatus for blowing Soap bubbles.</p> + +<p class="figlink"> +<a href="images/plate9_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes, I see the bladder swell as the water rises in the receiver.</p> + +<span class="pagenum">244</span> +<a name="conver1.page244" id="conver1.page244"> </a> +<p class="speaker">MRS. B.</p> + +<p>I think that we have already a sufficient quantity in the bladder for +our purpose; we must be careful to stop both the cocks before we +separate the bladder from the receiver, lest the gas should +escape.—Now I must fix a pipe to the stopper of the bladder, and +by dipping its mouth into the soap and water, take up a few +drops—then I again turn the cock, and squeeze the bladder in order +to force the gas into the soap and water at the mouth of the pipe. (<a +class="smallcaps" href="#plateIX">Plate IX.</a> fig. 2.)</p> + +<p class="speaker">EMILY.</p> + +<p>There is a bubble—but it bursts before it leaves the mouth of +the pipe.</p> + +<p class="speaker">MRS. B.</p> + +<p>We must have patience and try again; it is not so easy to blow +bubbles by means of a bladder, as simply with the breath.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Perhaps there is not soap enough in the water; I should have had +warm water, it would have dissolved the soap better.</p> + +<p class="speaker">EMILY.</p> + +<p>Does not some of the gas escape between the bladder and the pipe?</p> + +<span class="pagenum">245</span> +<a name="conver1.page245" id="conver1.page245"> </a> +<p class="speaker">MRS. B.</p> + +<p>No, they are perfectly air tight; we shall succeed presently, +I dare say.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now a bubble ascends; it moves with the rapidity of a balloon. How +beautifully it refracts the light!</p> + +<p class="speaker">EMILY.</p> + +<p>It has burst against the ceiling—you succeed now wonderfully; +but why do they all ascend and burst against the ceiling?</p> + +<p class="speaker">MRS. B.</p> + +<p>Hydrogen gas is so much lighter than atmospherical air, that it +ascends rapidly with its very light envelope, which is burst by the +force with which it strikes the ceiling.</p> + +<p>Air-balloons are filled with this gas, and if they carried no other +weight than their covering, would ascend as rapidly as these +bubbles.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet their covering must be much heavier than that of these +bubbles?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not in proportion to the quantity of gas they contain. I do not +know whether you have ever +<span class="pagenum">246</span> +<a name="conver1.page246" id="conver1.page246"> </a> +been present at the filling of a large balloon. The apparatus for that +purpose is very simple. It consists of a number of vessels, either jars +or barrels, in which the materials for the formation of the gas are +mixed, each of these being furnished with a tube, and communicating with +a long flexible pipe, which conveys the gas into the balloon.</p> + +<p class="speaker">EMILY.</p> + +<p>But the fire-balloons which were first invented, and have been since +abandoned, on account of their being so dangerous, were constructed, +I suppose, on a different principle.</p> + +<p class="speaker">MRS. B.</p> + +<p>They were filled simply with atmospherical air, considerably rarefied +by heat; and the necessity of having a fire underneath the balloon, in +order to preserve the rarefaction of the air within it, was the +circumstance productive of so much danger.</p> + +<p>If you are not yet tired of experiments, I have another to show +you. It consists in filling soap-bubbles with a mixture of hydrogen and +oxygen gases, in the proportions that form water; and afterwards setting +fire to them.</p> + +<p class="speaker">EMILY.</p> + +<p>They will detonate, I suppose?</p> + +<span class="pagenum">247</span> +<a name="conver1.page247" id="conver1.page247"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes, they will. As you have seen the method of transferring the gas +from the receiver into the bladder, it is not necessary to repeat it. +I have therefore provided a bladder which contains a due proportion +of oxygen and hydrogen gases, and we have only to blow bubbles +with it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Here is a fine large bubble rising—shall I set fire to it with +the candle?</p> + +<p class="speaker">MRS. B.</p> + +<p>If you please . . . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>Heavens, what an explosion!—It was like the report of a gun: +I confess it frightened me much. I never should have imagined +it could be so loud.</p> + +<p class="speaker">EMILY.</p> + +<p>And the flash was as vivid as lightning.</p> + +<p class="speaker">MRS. B.</p> + +<p>The combination of the two gases takes place during that instant of +time that you see the flash, and hear the detonation.</p> + +<span class="pagenum">248</span> +<a name="conver1.page248" id="conver1.page248"> </a> +<p class="speaker">EMILY.</p> + +<p>This has a strong resemblance to thunder and lightning.</p> + +<p class="speaker">MRS. B.</p> + +<p>These phenomena, however, are generally of an electrical nature. Yet +various meteorological effects may be attributed to accidental +detonations of hydrogen gas in the atmosphere; for nature abounds with +hydrogen: it constitutes a very considerable portion of the whole mass +of water belonging to our globe, and from that source almost every other +body obtains it. It enters into the composition of all animal +substances, and of a great number of minerals; but it is most abundant +in vegetables. From this immense variety of bodies, it is often +spontaneously disengaged; its great levity makes it rise into the +superior regions of the atmosphere; and when, either by an electrical +spark, or any casual elevation of temperature, it takes fire, it may +produce such meteors or luminous appearances as are occasionally seen in +the atmosphere. Of this kind are probably those broad flashes which we +often see on a summer-evening, without hearing any detonation.</p> + +<p class="speaker">EMILY.</p> + +<p>Every flash, I suppose, must produce a quantity of water?</p> + +<span class="pagenum">249</span> +<a name="conver1.page249" id="conver1.page249"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And this water, naturally, descends in the form of rain?</p> + +<p class="speaker">MRS. B.</p> + +<p>That probably is often the case, though it is not a necessary +consequence; for the water may be dissolved by the atmosphere, as it +descends towards the lower regions, and remain there in the form of +clouds.</p> + +<p>The application of electrical attraction to chemical phenomena is +likely to lead to many very interesting discoveries in meteorology; for +electricity evidently acts a most important part in the atmosphere. This +subject however, is, as yet, not sufficiently developed for me to +venture enlarging upon it. The phenomena of the atmosphere are far from +being well understood; and even with the little that is known, I am +but imperfectly acquainted.</p> + + +<p class="space"> +But before we take leave of hydrogen, I must not omit to mention to you +a most interesting discovery of Sir H. Davy, which is connected with +this subject.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You allude, I suppose, to the new miner’s lamp, which has of late +been so much talked of? I have long been desirous of knowing what +that discovery was, and what purpose it was intended to answer.</p> + +<span class="pagenum">250</span> +<a name="conver1.page250" id="conver1.page250"> </a> +<p class="speaker">MRS. B.</p> + +<p>It often happens in coal-mines, that quantities of the gas, called by +chemists <i>hydro-carbonat</i>, or by the miners <i>fire-damp</i>, (the +same from which the gas-lights are obtained,) ooze out from fissures in +the beds of coal, and fill the cavities in which the men are at work; +and this gas being inflammable, the consequence is, that when the men +approach those places with a lighted candle, the gas takes fire, and +explosions happen which destroy the men and horses employed in that part +of the colliery, sometimes in great numbers.</p> + +<p class="speaker">EMILY.</p> + +<p>What tremendous accidents these must be! But whence does that gas +originate?</p> + +<p class="speaker">MRS. B.</p> + +<p>Being the chief product of the combustion of coal, no wonder that +inflammable gas should occasionally appear in situations in which this +mineral abounds, since there can be no doubt that processes of +combustion are frequently taking place at a great depth under the +surface of the earth; and therefore those accumulations of gas may arise +either from combustions actually going on, or from former combustions, +the gas having perhaps been confined there for ages.</p> + +<span class="pagenum">251</span> +<a name="conver1.page251" id="conver1.page251"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And how does Sir H. Davy’s lamp prevent those dreadful +explosions?</p> + +<p class="speaker">MRS. B.</p> + +<p>By a contrivance equally simple and ingenious; and one which does no +less credit to the philosophical views from which it was deduced, than +to the philanthropic motives from which the enquiry sprung. The +principle of the lamp is shortly this: It was ascertained, two or three +years ago, both by Mr. Tennant and by Sir Humphry himself, that the +combustion of inflammable gas could not be propagated through small +tubes; so that if a jet of an inflammable gaseous mixture, issuing from +a bladder or any other vessel, through a small tube, be set fire to, it +burns at the orifice of the tube, but the flame never penetrates into +the vessel. It is upon this fact that Sir Humphry’s safety-lamp is +founded.</p> + +<p class="speaker">EMILY.</p> + +<p>But why does not the flame ever penetrate through the tube into the +vessel from which the gas issues, so as to explode at once the whole of +the gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because, no doubt, the inflamed gas is so much cooled in its passage +through a small tube as to +<span class="pagenum">252</span> +<a name="conver1.page252" id="conver1.page252"> </a> +cease to burn before the combustion reaches the reservoir.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And how can this principle be applied to the construction of a +lamp?</p> + +<p class="speaker">MRS. B.</p> + +<p>Nothing easier. You need only suppose a lamp enclosed all round in +glass or horn, but having a number of small open tubes at the bottom, +and others at the top, to let the air in and out. Now, if such a lamp or +lanthorn be carried into an atmosphere capable of exploding, an +explosion or combustion of the gas will take place within the lamp; and +although the vent afforded by the tubes will save the lamp from +bursting, yet, from the principle just explained, the combustion will +not be propagated to the external air through the tubes, so that no +farther consequence will ensue.</p> + +<p class="speaker">EMILY.</p> + +<p>And is that all the mystery of that valuable lamp?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; in the early part of the enquiry a lamp of this kind was actually +proposed; but it was but a rude sketch compared to its present state of +improvement. Sir H. Davy, after a succession of trials, by which he +brought his lamp nearer and nearer +<span class="pagenum">253</span> +<a name="conver1.page253" id="conver1.page253"> </a> +to perfection, at last conceived the happy idea that if the lamp were +surrounded with a wire-work or wire-gauze, of a close texture, instead +of glass or horn, the tubular contrivance I have just described would be +entirely superseded, since each of the interstices of the gauze would +act as a tube in preventing the propagation of explosions; so that this +pervious metallic covering would answer the various purposes of +transparency, of permeability to air, and of protection against +explosion. This idea, Sir Humphry immediately submitted to the test of +experiment, and the result has answered his most sanguine expectations, +both in his laboratory and in the collieries, where it has already been +extensively tried. And he has now the happiness of thinking that his +invention will probably be the means of saving every year a number of +lives, which would have been lost in digging out of the bowels of the +earth one of the most valuable necessaries of life. Here is one of these +lamps, every part of which you will at once comprehend. (See <a class="smallcaps" href="#plateX">Plate X.</a> fig. 1.)</p> + +<p class="figname"> +<a name="plateX" id="plateX">Plate X.</a></p> + +<p class="illustration"> +<img src="images/plate10a_thumb.png" width="144" height="543" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. +A. the cistern containing the Oil +B. the rim or screw by which the gauze cage is fixed to the cistern. + +C. apperture for supplying Oil. +E. a wire for trimming the wick. +D. F. the wire gauze cylinder. +G. a double top.</p> + +<p class="figlink"> +<a href="images/plate10_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>How very simple and ingenious! But I do not yet well see why an +explosion taking place within the lamp should not communicate to the +external air around it, through the interstices of the wire?</p> + +<span class="pagenum">254</span> +<a name="conver1.page254" id="conver1.page254"> </a> +<p class="speaker">MRS. B.</p> + +<p>This has been and is still a subject of wonder, even to philosophers; +and the only mode they have of explaining it is, that flame or ignition +cannot pass through a fine wire-work, because the metallic wire cools +the flame sufficiently to extinguish it in passing through the gauze. +This property of the wire-gauze is quite similar to that of the tubes +which I mentioned on introducing the subject; for you may consider each +interstice of the gauze as an extremely short tube of a very small +diameter.</p> + +<p class="speaker">EMILY.</p> + +<p>But I should expect the wire would often become red-hot, by the +burning of the gas within the lamp?</p> + +<p class="speaker">MRS. B.</p> + +<p>And this is actually the case, for the top of the lamp is very apt to +become red-hot. But, fortunately, inflammable gaseous mixtures cannot be +exploded by red-hot wire, the intervention of actual flame being +required for that purpose; so that the wire does not set fire to the +explosive gas around it.</p> + +<p class="speaker">EMILY.</p> + +<p>I can understand that; but if the wire be red-hot, how can it cool +the flame within, and prevent its passing through the gauze?</p> + +<span class="pagenum">255</span> +<a name="conver1.page255" id="conver1.page255"> </a> +<p class="speaker">MRS. B.</p> + +<p>The gauze, though red-hot, is not so hot as the flame by which it has +been heated; and as metallic wire is a good conductor, the heat does not +much accumulate in it, as it passes off quickly to the other parts of +the lamp, as well as to any contiguous bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This is indeed a most interesting discovery, and one which shows at +once the immense utility with which science may be practically applied +to some of the most important purposes.</p> + +<div class="footnote"> + +<p><a name="note18" id="note18" href="#tag18">*</a> +This ingenious explanation was first suggested by Dr. +Delarive.—See Journals of the Royal Institution, vol. i. p. +259.</p> + +<p><a name="note19" id="note19" href="#tag19">*</a> +Or rather, <i>hydro-carbonat</i>, a gas composed of hydrogen and +carbon, which will be noticed under the head <i>Carbon</i>.</p> + +</div> + + +<span class="pagenum">256</span> +<a name="conver1.page256" id="conver1.page256"> </a> +<h4><a name="convVIII" id="convVIII">CONVERSATION VIII.</a><br> +<span class="subhead">ON SULPHUR AND PHOSPHORUS.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="smallcaps">Sulphur</span> is the next substance that +comes under our consideration. It differs in one essential point from +the preceding, as it exists in a solid form at the temperature of the +atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am glad that we have at last a solid body to examine; one that we +can see and touch. Pray, is it not with sulphur that the points of +matches are covered, to make them easily kindle?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, it is; and you therefore already know that <ins class="mycorr" +title="text reads ‘sulpur’">sulphur</ins> is a very combustible +substance. It is seldom discovered in nature in a pure unmixed state; so +great is its affinity for other substances, that it is almost constantly +found combined with some of them. It is most commonly united with +<span class="pagenum">257</span> +<a name="conver1.page257" id="conver1.page257"> </a> +metals, under various forms, and is separated from them by a very simple +process. It exists likewise in many mineral waters, and some vegetables +yield it in various proportions, especially those of the cruciform +tribe. It is also found in animal matter; in short, it may be discovered +in greater or less quantity, in the mineral, vegetable, and animal +kingdoms.</p> + +<p class="speaker">EMILY.</p> + +<p>I have heard of <i>flowers of sulphur</i>, are they the produce of +any plant?</p> + +<p class="speaker">MRS. B.</p> + +<p>By no means: they consist of nothing more than common sulphur, +reduced to a very fine powder by a process called +<i>sublimation</i>.—You see some of it in this phial; it is +exactly the same substance as this lump of sulphur, only its colour is a +paler yellow, owing to its state of very minute division.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is sublimation?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is the evaporation, or, more properly speaking, the volatilisation +of solid substances, which, in cooling, condense again in a concrete +form. +<span class="pagenum">258</span> +<a name="conver1.page258" id="conver1.page258"> </a> +The process, in this instance, must be performed in a closed vessel, +both to prevent combustion, which would take place if the access of air +were not carefully precluded, and likewise in order to collect the +substance after the operation. As it is rather a slow process, we shall +not try the experiment now; but you will understand it perfectly if I +show you the apparatus used for the purpose. (<a class="smallcaps" +href="#plateXI">Plate XI.</a> fig. 1.) Some lumps of sulphur are +put into a receiver of this kind, which is called a <i>cucurbit</i>. Its +shape, you see, somewhat resembles that of a pear, and is open at the +top, so as to adapt itself exactly to a kind of conical receiver of this +sort, called the head. The cucurbit, thus covered with its head, is +placed over a sand-bath; this is nothing more than a vessel full of +sand, which is kept heated by a furnace, such as you see here, so as to +preserve the apparatus in a moderate and uniform temperature. The +sulphur then soon begins to melt, and immediately after this, +a thick white smoke rises, which is gradually deposited within the +head, or upper part of the apparatus, where it condenses against the +sides, somewhat in the form of a vegetation, whence it has obtained the +name of flowers of sulphur. This apparatus, which is called an +<i>alembic</i>, is highly useful in all kinds of distillations, as you +will see when we come to treat of those operations. Alembics are not +commonly +<span class="pagenum">259</span> +<a name="conver1.page259" id="conver1.page259"> </a> +made of glass, like this, which is applicable only to distillations upon +a very small scale. Those used in manufactures are generally made of +copper, and are, of course, considerably larger. The principal +construction, however, is always the same, although their shape admits +of some variation.</p> + +<p class="figname"> +<a name="plateXI" id="plateXI">Plate XI.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. I.</span> p. 237.</p> + +<p class="illustration"> +<img src="images/plate11_thumb.png" width="576" height="264" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. +A Alembic. +B Sand-bath. +C Furnace.<br> +Fig. 2. Eudiometer.<br> +Fig. 3. +A Retort containing water. +B Lamp to heat the water. +C.C Porcelain tube containing Carbone. +D Furnace through which the tube passes. +E Receiver for the gas produced. +F Water bath.</p> + +<p class="figlink"> +<a href="images/plate11_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>What is the use of that neck, or tube, which bends down from the +upper piece of the apparatus?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is of no use in sublimations; but in distillations (the general +object of which is to evaporate, by heat, in closed vessels, the +volatile parts of a compound body, and to condense them again into a +liquid,) it serves to carry off the condensed fluid, which otherwise +would fall back into the cucurbit. But this is rather foreign to our +present subject. Let us return to the sulphur. You now perfectly +understand, I suppose, what is meant by sublimation?</p> + +<p class="speaker">EMILY.</p> + +<p>I believe I do. Sublimation appears to consist in destroying, by +means of heat, the attraction of aggregation of the particles of a solid +body, which are thus volatilised; and as soon as they lose the +<span class="pagenum">260</span> +<a name="conver1.page260" id="conver1.page260"> </a> +caloric which produced that effect, they are deposited in the form of a +fine powder.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It seems to me to be somewhat similar to the transformation of water +into vapour, which returns to its liquid state when deprived of +caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>There is this difference, however, that the sulphur does not return +to its former state, since, instead of lumps, it changes to a fine +powder.</p> + +<p class="speaker">MRS. B.</p> + +<p>Chemically speaking, it is exactly the same substance, whether in the +form of lump or powder. For if this powder be melted again by heat, it +will, in cooling, be restored to the same solid state in which it was +before its sublimation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if there be no real change, produced by the sublimation of the +sulphur, what is the use of that operation?</p> + +<p class="speaker">MRS. B.</p> + +<p>It divides the sulphur into very minute parts, and thus disposes it +to enter more readily into combination with other bodies. It is used +also as a means of purification.</p> + +<span class="pagenum">261</span> +<a name="conver1.page261" id="conver1.page261"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Sublimation appears to me like the beginning of combustion, for the +completion of which one circumstance only is wanting, the absorption of +oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>But that circumstance is every thing. No essential alteration is +produced in sulphur by sublimation; whilst in combustion it combines +with the oxygen, and forms a new compound totally different in every +respect from sulphur in its pure state.—We shall now <i>burn</i> +some sulphur, and you will see how very different the result will be. +For this purpose I put a small quantity of flowers of sulphur into this +cup, and place it in a dish, into which I have poured a little water: +I now set fire to the sulphur with the point of this hot wire; for +its combustion will not begin unless its temperature be considerably +raised.—You see that it burns with a faint blueish flame; and as I +invert over it this receiver, white fumes arise from the sulphur, and +fill the vessel.—You will soon perceive that the water is rising +within the receiver, a little above its level in the +plate.—Well, Emily, can you account for this?</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose that the sulphur has absorbed the oxygen from the +atmospherical air within the receiver, and that we shall find some +oxygenated +<span class="pagenum">262</span> +<a name="conver1.page262" id="conver1.page262"> </a> +sulphur in the cup. As for the white smoke, I am quite at a loss to +guess what it may be.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your first conjecture is very right: but you are mistaken in the +last; for nothing will be left in the cup. The white vapour is the +oxygenated sulphur, which assumes the form of an elastic fluid of a +pungent and offensive smell, and is a powerful acid. Here you see a +chemical combination of oxygen and sulphur, producing a true gas, which +would continue such under the pressure and at the temperature of the +atmosphere, if it did not unite with the water in the plate, to which it +imparts its acid taste, and all its acid properties.—You see, now, +with what curious effects the combustion of sulphur is attended.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This is something quite new; and I confess that I do not perfectly +understand why the sulphur turns acid.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because it unites with oxygen, which is the acidifying +principle. And, indeed, the word <i>oxygen</i> is derived from two Greek +words signifying <i>to produce an acid</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Why, then, is not water, which contains such a quantity of oxygen, +acid?</p> + +<span class="pagenum">263</span> +<a name="conver1.page263" id="conver1.page263"> </a> +<p class="speaker">MRS. B.</p> + +<p>Because hydrogen, which is the other constituent of water, is not +susceptible of acidification.—I believe it will be necessary, +before we proceed further, to say a few words of the general nature of +acids, though it is rather a deviation from our plan of examining the +simple bodies separately, before we consider them in a state of +combination.</p> + +<p>Acids may be considered as a peculiar class of <i>burnt</i> bodies, +which during their combustion, or combination with oxygen, have acquired +very characteristic properties. They are chiefly discernible by their +sour taste, and by turning red most of the blue vegetable colours. These +two properties are common to the whole class of acids; but each of them +is distinguished by other peculiar qualities. Every acid consists of +some particular substance, (which constitutes its basis, and is +different in each,) and of oxygen, which is common to them all.</p> + +<p class="speaker">EMILY.</p> + +<p>But I do not clearly see the difference between acids and oxyds.</p> + +<p class="speaker">MRS. B.</p> + +<p>Acids were, in fact, oxyds, which, by the addition of a sufficient +quantity of oxygen, have been converted into acids. For acidification, +you must observe, always implies previous oxydation, as a body must have +combined with the quantity of +<span class="pagenum">264</span> +<a name="conver1.page264" id="conver1.page264"> </a> +oxygen requisite to constitute it an oxyd, before it can combine with +the greater quantity that is necessary to render it an acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Are all oxyds capable of being converted into acids?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very far from it; it is only certain substances which will enter into +that peculiar kind of union with oxygen that produces acids, and the +number of these is proportionally very small; but all burnt bodies may +be considered as belonging either to the class of oxyds, or to that of +acids. At a future period, we shall enter more at large into this +subject. At present, I have but one circumstance further to point +out to your observation respecting acids: it is, that most of them are +susceptible of two degrees of acidification, according to the different +quantities of oxygen with which their basis combines.</p> + +<p class="speaker">EMILY.</p> + +<p>And how are these two degrees of acidification distinguished?</p> + +<p class="speaker">MRS. B.</p> + +<p>By the peculiar properties which result from them. The acid we have +just made is the first or weakest degree of acidification, and is called +<i>sulphureous acid</i>; if it were fully saturated with oxygen, +<span class="pagenum">265</span> +<a name="conver1.page265" id="conver1.page265"> </a> +it would be called <i>sulphuric acid</i>. You must therefore remember, +that in this, as in all acids, the first degree of acidification is +expressed by the termination in <i>ous</i>; the stronger, by the +termination in <i>ic</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And how is the sulphuric acid made?</p> + +<p class="speaker">MRS. B.</p> + +<p>By burning sulphur in pure oxygen gas, and thus rendering its +combustion much more complete. I have provided some oxygen gas for +this purpose; it is in that bottle, but we must first decant the gas +into the glass receiver which stands on the shelf in the bath, and is +full of water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, let me try to do it, Mrs. B.</p> + +<p class="speaker">MRS. B.</p> + +<p>It requires some little dexterity—hold the bottle completely +under water, and do not turn the mouth upwards, till it is immediately +under the aperture in the shelf, through which the gas is to pass into +the receiver, and then turn it up gradually.—Very well, you have +only let a few bubbles escape, and that must be expected at a first +trial.—Now I shall put this piece of sulphur into the receiver, +through the opening at the top, and +<span class="pagenum">266</span> +<a name="conver1.page266" id="conver1.page266"> </a> +introduce along with it a small piece of lighted tinder to set fire to +it.—This requires being done very quickly, lest the atmospherical +air should get in, and mix with the pure oxygen gas.</p> + +<p class="speaker">EMILY.</p> + +<p>How beautifully it burns!</p> + +<p class="speaker">CAROLINE.</p> + +<p>But it is already buried in the thick vapour. This, I suppose, +is sulphuric acid?</p> + +<p class="speaker">EMILY.</p> + +<p>Are these acids always in a gaseous state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Sulphureous acid, as we have already observed, is a permanent gas, +and can be obtained in a liquid form only by condensing it in water. In +its pure state, the sulphureous acid is invisible, and it now appears in +the form of a white smoke, from its combining with the moisture. But the +vapour of sulphuric acid, which you have just seen to rise during the +combustion, is not a gas, but only a vapour, which condenses into liquid +sulphuric acid, by losing its caloric. But it appears from Sir H. Davy’s +experiments, that this formation and condensation of sulphuric acid +requires the presence of water, for which purpose the vapour is received +<span class="pagenum">267</span> +<a name="conver1.page267" id="conver1.page267"> </a> +into cold water, which may afterwards be separated from the acid by +evaporation.</p> + +<p>Sulphur has hitherto been considered as a simple substance; but Sir +H. Davy has suspected that it contains a small portion of hydrogen, and +perhaps also of oxygen.</p> + +<p>On submitting sulphur to the action of the Voltaic battery, he +observed that the negative wire gave out hydrogen; and the existence of +hydrogen in sulphur was rendered still more probable by his observing +that a small quantity of water was produced during the combustion of +sulphur.</p> + +<p class="speaker">EMILY.</p> + +<p>And pray of what nature is sulphur when perfectly pure?</p> + +<p class="speaker">MRS. B.</p> + +<p>Sulphur has probably never been obtained perfectly free from +combination, so that its radical may possibly possess properties very +different from those of common sulphur. It has been suspected to be of a +metallic nature; but this is mere conjecture.</p> + +<p>Before we quit the subject of sulphur, I must tell you that it is +susceptible of combining with a great variety of substances, and +especially with hydrogen, with which you are already acquainted. +Hydrogen gas can dissolve a small portion of it.</p> + +<span class="pagenum">268</span> +<a name="conver1.page268" id="conver1.page268"> </a> +<p class="speaker">EMILY.</p> + +<p>What! can a gas dissolve a solid substance?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; a solid substance may be so minutely divided by heat, as to +become soluble in a gas: and there are several instances of it. But you +must observe, that, in this case, a chemical union or combination +of the sulphur with the hydrogen gas is produced. In order to effect +this, the sulphur must be strongly heated in contact with the gas; the +heat reduces the sulphur to such a state of extreme division, and +diffuses it so thoroughly through the gas, that they combine and +incorporate together. And as a proof that there must be a chemical union +between the sulphur and the gas, it is sufficient to remark that they +are not separated when the sulphur loses the caloric by which it was +volatilized. Besides, it is evident, from the peculiar fetid smell of +this gas, that it is a new compound totally different from either of its +constituents; it is called <i>sulphuretted hydrogen gas</i>, and is +contained in great abundance in sulphureous mineral waters.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Are not the Harrogate waters of this nature?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; they are naturally impregnated with sulphuretted +<span class="pagenum">269</span> +<a name="conver1.page269" id="conver1.page269"> </a> +hydrogen gas, and there are many other springs of the same kind, which +shows that this gas must often be formed in the bowels of the earth by +spontaneous processes of nature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And could not such waters be made artificially by impregnating common +water with this gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; they can be so well imitated, as perfectly to resemble the +Harrogate waters.</p> + +<p>Sulphur combines likewise with phosphorus, and with the alkalies, and +alkaline earths, substances with which you are yet unacquainted. We +cannot, therefore, enter into these combinations at present. In our next +lesson we shall treat of phosphorus.</p> + +<p class="speaker">EMILY.</p> + +<p>May we not begin that subject to-day; this lesson has been so +short?</p> + +<p class="speaker">MRS. B.</p> + +<p>I have no objection, if you are not tired. What do you say, +Caroline?</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am as desirous as Emily of prolonging the lesson to-day, especially +as we are to enter on a new +<span class="pagenum">270</span> +<a name="conver1.page270" id="conver1.page270"> </a> +subject; for I confess that sulphur has not appeared to me so +interesting as the other simple bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>Perhaps you may find phosphorus more entertaining. You must not, +however, be discouraged when you meet with some parts of a study less +amusing than others; it would answer no good purpose to select the most +pleasing parts, since, if we did not proceed with some method, in order +to acquire a general idea of the whole, we could scarcely expect to take +interest in any particular subjects.</p> + + +<h5 class="section">PHOSPHORUS.</h5> + +<p><span class="smallcaps">Phosphorus</span> is considered as a simple +body; though, like sulphur, it has been suspected of containing +hydrogen. It was not known by the earlier chemists. It was first +discovered by Brandt, a chemist of Hamburgh, whilst employed in +researches after the philosopher’s stone; but the method of obtaining it +remained a secret till it was a second time discovered both by Kunckel +and Boyle, in the year 1680. You see a specimen of phosphorus in this +phial; it is generally moulded into small sticks of a yellowish colour, +as you find it here.</p> + +<span class="pagenum">271</span> +<a name="conver1.page271" id="conver1.page271"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I do not understand in what the discovery consisted; there may be a +secret method of making an artificial composition, but how can you talk +of <i>making</i> a substance which naturally exists?</p> + +<p class="speaker">MRS. B.</p> + +<p>A body may exist in nature so closely combined with other substances, +as to elude the observation of chemists, or render it extremely +difficult to obtain it in its separate state. This is the case with +phosphorus, which is always so intimately combined with other +substances, that its existence remained unnoticed till Brandt discovered +the means of obtaining it free from other combinations. It is found in +all animal substances, and is now chiefly extracted from bones, by a +chemical process. It exists also in some plants, that bear a strong +analogy to animal matter in their chemical composition.</p> + +<p class="speaker">EMILY.</p> + +<p>But is it never found in its pure separate state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Never, and this is the reason that it has remained so long +undiscovered.</p> + +<p>Phosphorus is eminently combustible; it melts and takes fire at the +temperature of one hundred +<span class="pagenum">272</span> +<a name="conver1.page272" id="conver1.page272"> </a> +degrees, and absorbs in its combustion nearly once and a half its own +weight of oxygen.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What! will a pound of phosphorus consume a pound and half of +oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>So it appears from accurate experiments. I can show you with +what violence it combines with oxygen, by burning some of it in that +gas. We must manage the experiment in the same manner as we did the +combustion of sulphur. You see I am obliged to cut this little bit of +phosphorus under water, otherwise there would be danger of its taking +fire by the heat of my fingers. I now <ins class="mycorr" title="missing ‘it’?">put into</ins> the receiver, and kindle it by means of a +hot wire.</p> + +<p class="speaker">EMILY.</p> + +<p>What a blaze! I can hardly look at it. I never saw any thing so +brilliant. Does it not hurt your eyes, Caroline?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes; but still I cannot help looking at it. A prodigious +quantity of oxygen must indeed be absorbed, when so much light and +caloric are disengaged!</p> + +<span class="pagenum">273</span> +<a name="conver1.page273" id="conver1.page273"> </a> +<p class="speaker">MRS. B.</p> + +<p>In the combustion of a pound of phosphorus, a sufficient +quantity of caloric is set free to melt upwards of a hundred pounds of +ice; this has been computed by direct experiments with the +calorimeter.</p> + +<p class="speaker">EMILY.</p> + +<p>And is the result of this combustion, like that of sulphur, an +acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; phosphoric acid. And had we duly proportioned the phosphorus and +the oxygen, they would have been completely converted into phosphoric +acid, weighing together, in this new state, exactly the sum of their +weights separately. The water would have ascended into the receiver, on +account of the vacuum formed, and would have filled it entirely. In this +case, as in the combustion of sulphur, the acid vapour formed is +absorbed and condensed in the water of the receiver. But when this +combustion is performed without any water or moisture being present, the +acid then appears in the form of concrete whitish flakes, which are, +however, extremely ready to melt upon the least admission of +moisture.</p> + +<p class="speaker">EMILY.</p> + +<p>Does phosphorus, in burning in atmospherical +<span class="pagenum">274</span> +<a name="conver1.page274" id="conver1.page274"> </a> +air, produce, like sulphur, a weaker sort of the same acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>No: for it burns in atmospherical air, nearly at the same temperature +as in pure oxygen gas; and it is in both cases so strongly disposed to +combine with the oxygen, that the combustion is perfect, and the product +similar; only in atmospherical air, being less rapidly supplied with +oxygen, the process is performed in a slower manner.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But is there no method of acidifying phosphorus in a slighter manner, +so as to form <i>phosphorus</i> acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, there is. When simply exposed to the atmosphere, phosphorus +undergoes a kind of slow combustion at any temperature above zero.</p> + +<p class="speaker">EMILY.</p> + +<p>But is not the process in this case rather an oxydation than a +combustion? For if the oxygen is too slowly absorbed for a sensible +quantity of light and heat to be disengaged, it is not a true +combustion.</p> + +<p class="speaker">MRS. B.</p> + +<p>The case is not as you suppose: a faint light is +<span class="pagenum">275</span> +<a name="conver1.page275" id="conver1.page275"> </a> +emitted which is very discernible in the dark; but the heat evolved is +not sufficiently strong to be sensible: a whitish vapour arises +from this combustion, which, uniting with water, condenses into liquid +phosphorus acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it not very singular that phosphorus should burn at so low a +temperature in atmospherical air, whilst it does not burn in pure oxygen +without the application of heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>So it at first appears. But this circumstance seems to be owing to +the nitrogen gas of the atmosphere. This gas dissolves small particles +of phosphorus, which being thus minutely divided and diffused in the +atmospherical air, combines with the oxygen, and undergoes this slow +combustion. But the same effect does not take place in oxygen gas, +because it is not capable of dissolving phosphorus; it is therefore +necessary, in this case, that heat should be applied to effect that +division of particles, which, in the former instance, is produced by the +nitrogen.</p> + +<p class="speaker">EMILY.</p> + +<p>I have seen letters written with phosphorus, which are invisible by +day-light, but may be read +<span class="pagenum">276</span> +<a name="conver1.page276" id="conver1.page276"> </a> +in the dark by their own light. They look as if they were written with +fire; yet they do not seem to burn.</p> + +<p class="speaker">MRS. B.</p> + +<p>But they do really burn; for it is by their slow combustion that the +light is emitted; and phosphorus acid is the result of this +combustion.</p> + +<p>Phosphorus is sometimes used as a test to estimate the purity of +atmospherical air. For this purpose, it is burnt in a graduated tube, +called an <i>Eudiometer</i> (<a class="smallcaps" href="#plateXI">Plate XI.</a> fig. 2.), and from the quantity of air +which the phosphorus absorbs, the proportion of oxygen in the air +examined is deduced; for the phosphorus will absorb all the oxygen, and +the nitrogen alone will remain.</p> + +<p class="speaker">EMILY.</p> + +<p>And the more oxygen is contained in the atmosphere, the purer, +I suppose, it is esteemed?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly. Phosphorus, when melted, combines with a great variety of +substances. With sulphur it forms a compound so extremely combustible, +that it immediately takes fire on coming in contact with the air. It is +with this composition that phosphoric matches are prepared, which kindle +as soon as they are taken out of their case and are exposed to the +air.</p> + +<span class="pagenum">277</span> +<a name="conver1.page277" id="conver1.page277"> </a> +<p class="speaker">EMILY.</p> + +<p>I have a box of these curious matches; but I have observed, that in +very cold weather, they will not take fire without being previously +rubbed.</p> + +<p class="speaker">MRS. B.</p> + +<p>By rubbing them you raise their temperature; for, you know, friction +is one of the means of extricating heat.</p> + +<p class="speaker">EMILY.</p> + +<p>Will phosphorus combine with hydrogen gas, as sulphur does?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and the compound gas which results from this combination has a +smell still more fetid than the sulphuretted hydrogen; it resembles that +of garlic.</p> + +<p>The <i>phosphoretted hydrogen gas</i> has this remarkable +peculiarity, that it takes fire spontaneously in the atmosphere, at any +temperature. It is thus, probably, that are produced those transient +flames, or flashes of light, called by the vulgar <i>Will-of-the +Whisp</i>, or more properly <i>Ignes-fatui</i>, which are often seen in +church-yards, and places where the putrefactions of animal matter exhale +phosphorus and hydrogen gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Country people, who are so much frightened by +<span class="pagenum">278</span> +<a name="conver1.page278" id="conver1.page278"> </a> +those appearances, would soon be reconciled to them, if they knew from +what a simple cause they proceed.</p> + +<p class="speaker">MRS. B.</p> + +<p>There are other combinations of phosphorus that have also very +singular properties, particularly that which results from its union with +lime.</p> + +<p class="speaker">EMILY.</p> + +<p>Is there any name to distinguish the combination of two substances, +like phosphorus and lime, neither of which are oxygen, and which cannot +therefore produce either an oxyd or an acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>The names of such combinations are composed from those of their +ingredients, merely by a slight change in their termination. Thus the +combination of sulphur with lime is called a <i>sulphuret</i>, and that +of phosphorus, a <i>phosphuret of lime</i>. This latter compound, +I was going to say, has the singular property of decomposing water, +merely by being thrown into it. It effects this by absorbing the oxygen +of water, in consequence of which bubbles of hydrogen gas ascend, +holding in solution a small quantity of phosphorus.</p> + +<span class="pagenum">279</span> +<a name="conver1.page279" id="conver1.page279"> </a> +<p class="speaker">EMILY.</p> + +<p>These bubbles then are <i>phosphoretted hydrogen gas</i>?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and they produce the singular appearance of a flash of fire +issuing from water, as the bubbles kindle and detonate on the surface of +the water, at the instant that they come in contact with the +atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is not this effect nearly similar to that produced by the combination +of phosphorus and sulphur, or, more properly speaking, the <i>phosphuret +of sulphur</i>?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but the phenomenon appears more extraordinary in this case, from +the presence of water, and from the gaseous form of the combustible +compound. Besides, the experiment surprises by its great simplicity. You +only throw a piece of phosphoret of lime into a glass of water, and +bubbles of fire will immediately issue from it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Cannot we try the experiment?</p> + +<span class="pagenum">280</span> +<a name="conver1.page280" id="conver1.page280"> </a> +<p class="speaker">MRS. B.</p> + +<p>Very easily: but we must do it in the open air; for the smell of the +phosphorated hydrogen gas is so extremely fetid, that it would be +intolerable in the house. But before we leave the room, we may produce, +by another process, some bubbles of the same gas, which are much less +offensive.</p> + +<p>There is in this little glass retort a solution of potash in water; +I add to it a small piece of phosphorus. We must now heat the +retort over the lamp, after having engaged its neck under +water—you see it begins to boil; in a few minutes bubbles will +appear, which take fire and detonate as they issue from the water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>There is one—and another. How curious it is!—But I do not +understand how this is produced.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is the consequence of a display of affinities too complicated, +I fear, to be made perfectly intelligible to you at present.</p> + +<p>In a few words, the reciprocal action of the potash, phosphorus, +caloric, and water are such, that some of the water is decomposed, and +the hydrogen gas thereby formed carries off some minute particles of +phosphorus, with which it forms phosphoretted +<span class="pagenum">281</span> +<a name="conver1.page281" id="conver1.page281"> </a> +hydrogen gas, a compound which spontaneously takes fire at almost +any temperature.</p> + +<p class="speaker">EMILY.</p> + +<p>What is that circular ring of smoke which slowly rises from each +bubble after its detonation<ins class="mycorr" title="text has .">? </ins></p> + +<p class="speaker">MRS. B.</p> + +<p>It consists of water and phosphoric acid in vapour, which are +produced by the combustion of hydrogen and phosphorus.</p> + + + + +<span class="pagenum">282</span> +<a name="conver1.page282" id="conver1.page282"> </a> +<h4><a name="convIX" id="convIX">CONVERSATION IX.</a><br> +<span class="subhead">ON CARBON.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">CAROLINE.</p> + +<p><span class="firstword"><span class="firstletter">T</span>o-day</span>, Mrs. B., I believe we are to +learn the nature and properties of <span class="smallroman">CARBON</span>. This substance is quite new to me; +I never heard it mentioned before.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not so new as you imagine; for carbon is nothing more than charcoal +in a state of purity, that is to say, unmixed with any foreign +ingredients.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But charcoal is made by art, Mrs. B., and a body consisting of one +simple substance cannot be fabricated?</p> + +<p class="speaker">MRS. B.</p> + +<p>You again confound the idea, of making a simple body, with that of +separating it from a compound. The chemical processes by which a simple +body is obtained in a state of purity, consist in <i>unmaking</i> the +compound in which it is contained, +<span class="pagenum">283</span> +<a name="conver1.page283" id="conver1.page283"> </a> +in order to separate from it the simple substance in question. The +method by which charcoal is usually obtained, is, indeed, commonly +called <i>making</i> it; but, upon examination, you will find this +process to consist simply in separating it from other substances with +which it is found combined in nature.</p> + +<p>Carbon forms a considerable part of the solid matter of all organised +bodies; but it is most abundant in the vegetable creation, and it is +chiefly obtained from wood. When the oil and water (which are other +constituents of vegetable matter) are evaporated, the black, porous, +brittle substance that remains, is charcoal.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if heat be applied to the wood in order to evaporate the oil and +water, will not the temperature of the charcoal be raised so as to make +it burn; and if it combines with oxygen, can we any longer call it +pure?</p> + +<p class="speaker">MRS. B.</p> + +<p>I was going to say, that, in this operation, the air must be +excluded.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How then can the vapour of the oil and water fly off?</p> + +<span class="pagenum">284</span> +<a name="conver1.page284" id="conver1.page284"> </a> +<p class="speaker">MRS. B.</p> + +<p>In order to produce charcoal in its purest state (which is, even +then, but a less imperfect sort of carbon), the operation should be +performed in an earthen retort. Heat being applied to the body of the +retort, the evaporable part of the wood will escape through its neck, +into which no air can penetrate as long as the heated vapour continues +to fill it. And if it be wished to collect these volatile products of +the wood, this can easily be done by introducing the neck of the retort +into the water-bath apparatus, with which you are acquainted. But the +preparation of common charcoal, such as is used in kitchens and +manufactures, is performed on a much larger scale, and by an easier and +less expensive process.</p> + +<p class="speaker">EMILY.</p> + +<p>I have seen the process of making common charcoal. The wood is ranged +on the ground in a pile of a pyramidical form, with a fire underneath; +the whole is then covered with clay, a few holes only being left +for the circulation of air.</p> + +<p class="speaker">MRS. B.</p> + +<p>These holes are closed as soon as the wood is fairly lighted, so that +the combustion is checked, or at least continues but in a very imperfect +manner; but the heat produced by it is sufficient to +<span class="pagenum">285</span> +<a name="conver1.page285" id="conver1.page285"> </a> +force out and volatilize, through the earthy cover, most part of the +oily and watery principles of the wood, although it cannot reduce it to +ashes.</p> + +<p class="speaker">EMILY.</p> + +<p>Is pure carbon as black as charcoal?</p> + +<p class="speaker">MRS. B.</p> + +<p>The purest charcoal we can prepare is so; but chemists have never yet +been able to separate it entirely from hydrogen. Sir H. Davy says, that +the most perfect carbon that is prepared by art contains about five per +cent. of hydrogen; he is of opinion, that if we could obtain it quite +free from foreign ingredients, it would be metallic, in common with +other simple substances.</p> + +<p>But there is a form in which charcoal appears, that I dare say will +surprise you.—This ring, which I wear on my finger, owes its +brilliancy to a small piece of carbon.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Surely, you are jesting, Mrs. B.?</p> + +<p class="speaker">EMILY.</p> + +<p>I thought your ring was diamond?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is so. But diamond is nothing more than carbon in a crystallized +state.</p> + +<span class="pagenum">286</span> +<a name="conver1.page286" id="conver1.page286"> </a> +<p class="speaker">EMILY.</p> + +<p>That is astonishing! Is it possible to see two things apparently more +different than diamond and charcoal?</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is, indeed, curious to think that we adorn ourselves with jewels +of charcoal!</p> + +<p class="speaker">MRS. B.</p> + +<p>There are many other substances, consisting chiefly of carbon, that +are remarkably white. Cotton, for instance, is almost wholly carbon.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That, I own, I could never have imagined!—But pray, +Mrs. B., since it is known of what substance diamond and cotton are +composed, why should they not be manufactured, or imitated, by some +chemical process, which would render them much cheaper, and more +plentiful than the present mode of obtaining them?</p> + +<p class="speaker">MRS. B.</p> + +<p>You might as well, my dear, propose that we should make flowers and +fruit, nay, perhaps even animals, by a chemical process; for it is known +of what these bodies consist, since every thing which we are acquainted +with in nature is formed from the various simple substances that we have +<span class="pagenum">287</span> +<a name="conver1.page287" id="conver1.page287"> </a> +enumerated. But you must not suppose that a knowledge of the component +parts of a body will in every case enable us to imitate it. It is much +less difficult to decompose bodies, and discover of what materials they +are made, than it is to recompose them. The first of these processes is +called <i>analysis</i>, the last <i>synthesis</i>. When we are able to +ascertain the nature of a substance by both these methods, so that the +result of one confirms that of the other, we obtain the most complete +knowledge of it that we are capable of acquiring. This is the case with +water, with the atmosphere, with most of the oxyds, acids, and neutral +salts, and with many other compounds. But the more complicated +combinations of nature, even in the mineral kingdom, are in general +beyond our reach, and any attempt to imitate organised bodies must ever +prove fruitless; their formation is a secret that rests in the bosom of +the Creator. You see, therefore, how vain it would be to attempt to make +cotton by chemical means. But, surely, we have no reason to regret our +inability in this instance, when nature has so clearly pointed out a +method of obtaining it in perfection and abundance.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I did not imagine that the principle of life could be imitated by the +aid of chemistry; but it did not appear to me ridiculous to suppose that +chemists +<span class="pagenum">288</span> +<a name="conver1.page288" id="conver1.page288"> </a> +might attain a perfect imitation of inanimate nature.</p> + +<p class="speaker">MRS. B.</p> + +<p>They have succeeded in this point in a variety of instances; but, as +you justly observe, the principle of life, or even the minute and +intimate organisation of the vegetable kingdom, are secrets that have +almost entirely eluded the researches of philosophers; nor do I imagine +that human art will ever be capable of investigating them with complete +success.</p> + +<p class="speaker">EMILY.</p> + +<p>But diamond, since it consists of one simple unorganised substance, +might be, one would think, perfectly imitable by art?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is sometimes as much beyond our power to obtain a simple body in a +state of perfect purity, as it is to imitate a complicated combination; +for the operations by which nature separates bodies are frequently as +inimitable as those which she uses for their combination. This is the +case with carbon; all the efforts of chemists to separate it entirely +from other substances have been fruitless, and in the purest state in +which it can be obtained by art, it still retains a portion of hydrogen, +and probably of some other foreign ingredients. We are ignorant +<span class="pagenum">289</span> +<a name="conver1.page289" id="conver1.page289"> </a> +of the means which nature employs to crystallize it. It may probably be +the work of ages, to purify, arrange, and unite the particles of carbon +in the form of diamond. Here is some charcoal in the purest state we can +procure it: you see that it is a very black, brittle, light, porous +substance, entirely destitute of either taste or smell. Heat, without +air, produces no alteration in it, as it is not volatile; but, on the +contrary, it invariably remains at the bottom of the vessel after all +the other parts of the vegetable are evaporated.</p> + +<p class="speaker">EMILY.</p> + +<p>Yet carbon is, no doubt, combustible, since you say that charcoal +would absorb oxygen if air were admitted during its preparation?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Unquestionably. Besides, you know, Emily, how much it is used in +cooking. But pray what is the reason that charcoal burns without smoke, +whilst a wood fire smokes so much?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because, in the conversion of wood into charcoal, the volatile +particles of the former have been evaporated.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet I have frequently seen charcoal burn with +<span class="pagenum">290</span> +<a name="conver1.page290" id="conver1.page290"> </a> +flame; therefore it must, in that case, contain some hydrogen.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very true; but you must recollect that charcoal, especially that +which is used for common purposes, is not perfectly pure. It generally +retains some remains of the various other component parts of vegetables, +and hydrogen particularly, which accounts for the flame in question.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what becomes of the carbon itself during its combustion?</p> + +<p class="speaker">MRS. B.</p> + +<p>It gradually combines with the oxygen of the atmosphere, in the same +way as sulphur and phosphorus, and, like those substances, it is +converted into a peculiar acid, which flies off in a gaseous form. There +is this difference, however, that the acid is not, in this instance, as +in the two cases just mentioned, a mere condensable vapour, but a +permanent elastic fluid, which always remains in the state of gas, under +any pressure and at any temperature. The nature of this acid was first +ascertained by Dr. Black, of Edinburgh; and, before the introduction of +the new nomenclature, it was called <i>fixed air</i>. It is now +distinguished by the more appropriate name of <i>carbonic acid +gas</i>.</p> + +<span class="pagenum">291</span> +<a name="conver1.page291" id="conver1.page291"> </a> +<p class="speaker">EMILY.</p> + +<p>Carbon, then, can be volatilized by burning, though, by heat alone, +no such effect is produced?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but then it is no longer simple carbon, but an acid of which +carbon forms the basis. In this state, carbon retains no more appearance +of solidity or corporeal form, than the basis of any other gas. And you +may, I think, from this instance, derive a more clear idea of the +basis of the oxygen, hydrogen, and nitrogen gases, the existence of +which, as real bodies, you seemed to doubt, because they were not to be +obtained simply in a solid form.</p> + +<p class="speaker">EMILY.</p> + +<p>That is true; we may conceive the basis of the oxygen, and of the +other gases, to be solid, heavy substances, like carbon; but so much +expanded by caloric as to become invisible.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But does not the carbonic acid gas partake of the blackness of +charcoal?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not in the least. Blackness, you know, does not appear to be +essential to carbon, and it is pure carbon, and not charcoal, that we +must consider +<span class="pagenum">292</span> +<a name="conver1.page292" id="conver1.page292"> </a> +as the basis of carbonic acid. We shall make some carbonic acid, and, in +order to hasten the process, we shall burn the carbon in oxygen gas.</p> + +<p class="speaker">EMILY.</p> + +<p>But do you mean then to burn diamond?</p> + +<p class="speaker">MRS. B.</p> + +<p>Charcoal will answer the purpose still better, being softer and more +easy to inflame; besides the experiments on diamond are rather +expensive.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But is it possible to burn diamond?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, it is; and in order to effect this combustion, nothing more is +required than to apply a sufficient degree of heat by means of the +blow-pipe, and of a stream of oxygen gas. Indeed it is by burning +diamond that its chemical nature has been ascertained. It has long been +known as a combustible substance, but it is within these few years only +that the product of its combustion has been proved to be pure carbonic +acid. This remarkable discovery is due to Mr. Tennant.</p> + +<p>Now let us try to make some carbonic acid.—Will you, Emily, +decant some oxygen gas from this large jar into the receiver in which we +are to +<span class="pagenum">293</span> +<a name="conver1.page293" id="conver1.page293"> </a> +<ins class="mycorr" title="text reads ‘bnrn’">burn</ins> the carbon; +and I shall introduce this small piece of charcoal, with a little +lighted tinder, which will be necessary to give the first impulse to the +combustion.</p> + +<p class="speaker">EMILY.</p> + +<p>I cannot conceive how so small a piece of tinder, and that but just +lighted, can raise the temperature of the carbon sufficiently to set +fire to it; for it can produce scarcely any sensible heat, and it hardly +touches the carbon.</p> + +<p class="speaker">MRS. B.</p> + +<p>The tinder thus kindled has only heat enough to begin its own +combustion, which, however, soon becomes so rapid in the oxygen gas, as +to raise the temperature of the charcoal sufficiently for this to burn +likewise, as you see is now the case.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised that the combustion of carbon is not more brilliant; +it does not give out near so much light or caloric as phosphorus, or +sulphur. Yet since it combines with so much oxygen, why is not a +proportional quantity of light and heat disengaged from the +decomposition of the oxygen gas, and the union of its electricity with +that of the charcoal?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not surprising that less light and heat should be liberated in +this than in almost any other combustion, +<span class="pagenum">294</span> +<a name="conver1.page294" id="conver1.page294"> </a> +since the oxygen, instead of entering into a solid or liquid +combination, as it does in the phosphoric and sulphuric acids, is +employed in forming another elastic fluid; it therefore parts with less +of its caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>True; and, on second consideration, it appears, on the contrary, +surprising that the oxygen should, in its combination with carbon, +retain a sufficient portion of caloric to maintain both substances in a +gaseous state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>We may then judge of the degree of solidity in which oxygen is +combined in a burnt body, by the quantity of caloric liberated during +its combustion?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; provided that you take into the account the quantity of oxygen +absorbed by the combustible body, and observe the proportion which the +caloric bears to it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But why should the water, after the combustion of carbon, rise in the +receiver, since the gas within it retains an aëriform state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the carbonic acid gas is gradually absorbed +<span class="pagenum">295</span> +<a name="conver1.page295" id="conver1.page295"> </a> +by the water; and this effect would be promoted by shaking the +receiver.</p> + +<p class="speaker">EMILY.</p> + +<p>The charcoal is now extinguished, though it is not nearly consumed; +it has such an extraordinary avidity for oxygen, I suppose, that +the receiver did not contain enough to satisfy the whole.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is certainly the case; for if the combustion were performed in +the exact proportions of 28 parts of carbon to 72 of oxygen, both these +ingredients would disappear, and 100 parts of carbonic acid would be +produced.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Carbonic acid must be a very strong acid, since it contains so great +a proportion of oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is a very natural inference; yet it is erroneous. For the +carbonic is the weakest of all the acids. The strength of an acid seems +to depend upon the nature of its basis, and its mode of combination, as +well as upon the proportion of the acidifying principle. The same +quantity of oxygen that will convert some bodies into strong acids, will +only be sufficient simply to oxydate others.</p> + +<span class="pagenum">296</span> +<a name="conver1.page296" id="conver1.page296"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Since this acid is so weak, I think chemists should have called it +the <i>carbonous</i>, instead of the <i>carbonic</i> acid.</p> + +<p class="speaker">EMILY.</p> + +<p>But, I suppose, the carbonous acid is still weaker, and is formed by +burning carbon in atmospherical air.</p> + +<p class="speaker">MRS. B.</p> + +<p>It has been lately discovered, that carbon may be converted into a +gas, by uniting with a smaller proportion of oxygen; but as this gas +does not possess any acid properties, it is no more than an oxyd; it is +called <i>gaseous oxyd of carbon</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray is not carbonic acid a very wholesome gas to breathe, as it +contains so much oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>On the contrary, it is extremely pernicious. Oxygen, when in a state +of combination with other substances, loses, in almost every instance, +its respirable properties, and the salubrious effects which it has on +the animal economy when in its unconfined state. Carbonic acid is not +only unfit for respiration, but extremely deleterious if taken into the +lungs.</p> + +<span class="pagenum">297</span> +<a name="conver1.page297" id="conver1.page297"> </a> +<p class="speaker">EMILY.</p> + +<p>You know, Caroline, how very unwholesome the fumes of burning +charcoal are reckoned.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes; but, to confess the truth, I did not consider that a charcoal +fire produced carbonic acid gas.—Can this gas be condensed into a +liquid?</p> + +<p class="speaker">MRS. B.</p> + +<p>No: for, as I told you before, it is a permanent elastic fluid. But +water can absorb a certain quantity of this gas, and can even be +impregnated with it, in a very strong degree, by the assistance of +agitation and pressure, as I am going to show you. I shall decant +some carbonic acid gas into this bottle, which I fill first with water, +in order to exclude the atmospherical air; the gas is then introduced +through the water, which you see it displaces, for it will not mix with +it in any quantity, unless strongly agitated, or allowed to stand over +it for some time. The bottle is now about half full of carbonic acid +gas, and the other half is still occupied by the water. By corking the +bottle, and then violently shaking it, in this way, I can mix the +gas and water together.—Now will you taste it?</p> + +<p class="speaker">EMILY.</p> + +<p>It has a distinct acid taste.</p> + +<span class="pagenum">298</span> +<a name="conver1.page298" id="conver1.page298"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Yes, it is sensibly sour, and appears full of little bubbles.</p> + +<p class="speaker">MRS. B.</p> + +<p>It possesses likewise all the other properties of acids, but, of +course, in a less degree than the pure carbonic acid gas, as it is so +much diluted by water.</p> + +<p>This is a kind of artificial Seltzer water. By analysing that which +is produced by nature, it was found to contain scarcely any thing more +than common water impregnated with a certain proportion of carbonic acid +gas. We are, therefore, able to imitate it, by mixing those proportions +of water and carbonic acid. Here, my dear, is an instance, in which, by +a chemical process, we can exactly copy the operations of nature; for +the artificial Seltzer waters can be made in every respect similar to +those of nature; in one point, indeed, the former have an advantage, +since <ins class="mycorr" title="text reads ‘thay’">they</ins> may +be prepared stronger, or weaker, as occasion requires.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I thought I had tasted such water before. But what renders it so +brisk and sparkling?</p> + +<p class="speaker">MRS. B.</p> + +<p>This sparkling, or effervescence, as it is called, is always +occasioned by the action of an elastic fluid escaping from a liquid; in +the <ins class="mycorr" title="text reads ‘artifical’">artificial</ins> Seltzer +<span class="pagenum">299</span> +<a name="conver1.page299" id="conver1.page299"> </a> +water, it is produced by the carbonic acid, which being lighter than the +water in which it was strongly condensed, flies off with great rapidity +the instant the bottle is uncorked; this makes it necessary to drink it +immediately. The bubbling that took place in this bottle was but +trifling, as the water was but very slightly impregnated with carbonic +acid. It requires a particular apparatus to prepare the gaseous +artificial mineral waters.</p> + +<p class="speaker">EMILY.</p> + +<p>If, then, a bottle of Seltzer water remains for any length of time +uncorked, I suppose it returns to the state of common water?</p> + +<p class="speaker">MRS. B.</p> + +<p>The whole of the carbonic acid gas, or very nearly so, will soon +disappear; but there is likewise in Seltzer water a very small quantity +of soda, and of a few other saline or earthy ingredients, which will +remain in the water, though it should be kept uncorked for any length of +time.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have often heard of people drinking soda-water. Pray what sort of +water is that?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a kind of artificial Seltzer water, holding +<span class="pagenum">300</span> +<a name="conver1.page300" id="conver1.page300"> </a> +in solution, besides the gaseous acid, a particular saline +substance, called soda, which imparts to the water certain medicinal +qualities.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how can these waters be so wholesome, since carbonic acid is so +pernicious?</p> + +<p class="speaker">MRS. B.</p> + +<p>A gas, we may conceive, though very prejudicial to breathe, may be +beneficial to the stomach.—But it would be of no use to attempt +explaining this more fully at present.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Are waters never impregnated with other gases?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; there are several kinds of gaseous waters. I forgot to tell +you that waters have, for some years past, been prepared, impregnated +both with oxygen and hydrogen gases. These are not an imitation of +nature, but are altogether obtained by artificial means. They have been +lately used medicinally, particularly on the continent, where, +I understand, they have acquired some reputation.</p> + +<p class="speaker">EMILY.</p> + +<p>If I recollect right, Mrs. B., you told us that +<span class="pagenum">301</span> +<a name="conver1.page301" id="conver1.page301"> </a> +carbon was capable of decomposing water; the affinity between oxygen and +carbon must, therefore, be greater than between oxygen and hydrogen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but this is not the case unless their temperature be raised to a +certain degree. It is only when carbon is red-hot, that it is capable of +separating the oxygen from the hydrogen. Thus, if a small quantity of +water be thrown on a red-hot fire, it will increase rather than +extinguish the combustion; for the coals or wood (both of which contain +a quantity of carbon) decompose the water, and thus supply the fire both +with oxygen and hydrogen gases. If, on the contrary, a large mass +of water be thrown over the fire, the diminution of heat thus produced +is such, that the combustible matter loses the power of decomposing the +water, and the fire is extinguished.</p> + +<p class="speaker">EMILY.</p> + +<p>I have heard that fire-engines sometimes do more harm than good, and +that they actually increase the fire when they cannot throw water enough +to extinguish it. It must be owing, no doubt, to the decomposition of +the water by the carbon during the conflagration.</p> + +<span class="pagenum">302</span> +<a name="conver1.page302" id="conver1.page302"> </a> +<p class="speaker">MRS. B.</p> + +<p>Certainly.—The apparatus which you see here (<a class="smallcaps" href="#plateXI">Plate XI.</a> fig. 3.), may be used +to exemplify what we have just said. It consists in a kind of open +furnace, through which a porcelain tube, containing charcoal, passes. To +one end of the tube is adapted a glass retort with water in it; and the +other end communicates with a receiver placed on the water-bath. +A lamp being applied to the retort, and the water made to boil, the +vapour is gradually conveyed through the red-hot charcoal, by which it +is decomposed; and the hydrogen gas which results from this +decomposition is collected in the receiver. But the hydrogen thus +obtained is far from being pure; it retains in solution a minute portion +of carbon, and contains also a quantity of carbonic acid. This renders +it heavier than pure hydrogen gas, and gives it some peculiar +properties; it is distinguished by the name of <i>carbonated hydrogen +gas</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And whence does it obtain the carbonic acid that is mixed +with it?</p> + +<p class="speaker">EMILY.</p> + +<p>I believe I can answer that question, Caroline.—From the union +of the oxygen (proceeding from +<span class="pagenum">303</span> +<a name="conver1.page303" id="conver1.page303"> </a> +the decomposed water) with the carbon, which, you know, makes carbonic +acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; I should have recollected that.—The product of the +decomposition of water by red-hot charcoal, therefore, is carbonated +hydrogen gas, and carbonic acid gas.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are perfectly right now.</p> + +<p>Carbon is frequently found combined with hydrogen in a state of +solidity, especially in coals, which owe their combustible nature to +these two principles.</p> + +<p class="speaker">EMILY.</p> + +<p>Is it the hydrogen, then, that produces the flame of coals?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is so; and when all the hydrogen is consumed, the carbon continues +to burn without flame. But again, as I mentioned when speaking of the +gas-lights, the hydrogen gas produced by the burning of coals is not +pure; for, during the combustion, particles of carbon are successively +volatilized with the hydrogen, with which they form what is called a +<i>hydro-carbonat</i>, which is the principal product of this +combustion.</p> + +<p>Carbon is a very bad conductor of heat; for +<span class="pagenum">304</span> +<a name="conver1.page304" id="conver1.page304"> </a> +this reason, it is employed (in conjunction with other ingredients) for +coating furnaces and other chemical apparatus.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is the use of coating furnaces?</p> + +<p class="speaker">MRS. B.</p> + +<p>In most cases, in which a furnace is used, it is necessary to produce +and preserve a great degree of heat, for which purpose every possible +means are used to prevent the heat from escaping by communicating with +other bodies, and this object is attained by coating over the inside of +the furnace with a kind of plaster, composed of materials that are bad +conductors of heat.</p> + +<p>Carbon, combined with a small quantity of iron, forms a compound +called plumbago, or black-lead, of which pencils are made. This +substance, agreeably to the nomenclature, is <i>a carburet of +iron</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>Why, then, is it called black-lead?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is an ancient name given to it by ignorant people, from its +shining metallic appearance; but it is certainly a most improper name +for it, as there is not a particle of lead in the composition. +<span class="pagenum">305</span> +<a name="conver1.page305" id="conver1.page305"> </a> +There is only one mine of this mineral, which is in Cumberland. It is +supposed to approach as nearly to pure carbon as the best prepared +charcoal does, as it contains only five parts of iron, unadulterated by +any other foreign ingredients. There is another carburet of iron, in +which the iron, though united only to an extremely small proportion of +carbon, acquires very remarkable properties; this is steel.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Really; and yet steel is much harder than iron?</p> + +<p class="speaker">MRS. B.</p> + +<p>But carbon is not ductile like iron, and therefore may render the +steel more brittle, and prevent its bending so easily. Whether it is +that the carbon, by introducing itself into the pores of the iron, and, +by filling them, makes the metal both harder and heavier; or whether +this change depends upon some chemical cause, I cannot pretend to +decide. But there is a subsequent operation, by which the hardness of +steel is very much increased, which simply consists in heating the steel +till it is red-hot, and then plunging it into cold water.</p> + +<p>Carbon, besides the combination just mentioned, enters into the +composition of a vast number of natural productions, such, for instance, +as all +<span class="pagenum">306</span> +<a name="conver1.page306" id="conver1.page306"> </a> +the various kinds of oils, which result from the combination of carbon, +hydrogen, and caloric, in various proportions.</p> + +<p class="speaker">EMILY.</p> + +<p>I thought that carbon, hydrogen, and caloric, formed carbonated +hydrogen gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is the case when a small portion of carbonic acid gas is held in +solution by hydrogen gas. Different proportions of the same principles, +together with the circumstances of their union, produce very different +combinations; of this you will see innumerable examples. Besides, we are +not now talking of gases, but of carbon and hydrogen, combined only with +a quantity of caloric sufficient to bring them to the consistency of oil +or fat.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But oil and fat are not of the same consistence?</p> + +<p class="speaker">MRS. B.</p> + +<p>Fat is only congealed oil; or oil, melted fat. The one requires a +little more heat to maintain it in a fluid state than the other. Have +you never observed the fat of meat turned to oil by the caloric it has +imbibed from the fire?</p> + +<span class="pagenum">307</span> +<a name="conver1.page307" id="conver1.page307"> </a> +<p class="speaker">EMILY.</p> + +<p>Yet oils in general, as salad-oil, and lamp-oil, do not turn to fat +when cold?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not at the common temperature of the atmosphere, because they retain +too much caloric to congeal at that temperature; but if exposed to a +sufficient degree of cold, their latent heat is extricated, and they +become solid fat substances. Have you never seen salad oil frozen in +winter?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes; but it appears to me in that state very different from animal +fat.</p> + +<p class="speaker">MRS. B.</p> + +<p>The essential constituent parts of either vegetable or animal oils +are the same, carbon and hydrogen; their variety arises from the +different proportions of these substances, and from other accessory +ingredients that may be mixed with them. The oil of a whale, and the oil +of roses, are, in their essential constituent parts, the same; but the +one is impregnated with the offensive particles of animal matter, the +other with the delicate perfume of a flower.</p> + +<p>The difference of <i>fixed oils</i>, and <i>volatile</i> or +<i>essential oils</i>, consists also in the various proportions of +carbon and hydrogen. Fixed oils are those which +<span class="pagenum">308</span> +<a name="conver1.page308" id="conver1.page308"> </a> +will not evaporate without being decomposed; this is the case with all +common oils, which contain a greater proportion of carbon than the +essential oils. The essential oils (which comprehend the whole class of +essences and perfumes) are lighter; they contain more equal proportions +of carbon and hydrogen, and are volatilized or evaporated without being +decomposed.</p> + +<p class="speaker">EMILY.</p> + +<p>When you say that one kind of oil will evaporate, and the other be +decomposed, you mean, I suppose, by the application of heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not necessarily; for there are oils that will evaporate slowly at the +common temperature of the atmosphere; but for a more rapid +volatilization, or for their decomposition, the assistance of heat is +required.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I shall now remember, I think, that fat and oil are really the same +substances, both consisting of carbon and hydrogen; that in fixed oils +the carbon preponderates, and heat produces a decomposition; while, in +essential oils, the proportion of hydrogen is greater, and heat produces +a volatilization only.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose the reason why oil burns so well in +<span class="pagenum">309</span> +<a name="conver1.page309" id="conver1.page309"> </a> +lamps is because its two constituents are so combustible?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; the combustion of oil is just the same as that of a +candle; if tallow, it is only oil in a concrete state; if wax, or +spermaceti, its chief chemical ingredients are still hydrogen and +carbon.</p> + +<p class="speaker">EMILY.</p> + +<p>I wonder, then, there should be so great a difference between tallow +and wax?</p> + +<p class="speaker">MRS. B.</p> + +<p>I must again repeat, that the same substances, in different +proportions, produce results that have sometimes scarcely any +resemblance to each other. But this is rather a general remark that I +wish to impress upon your minds, than one which is applicable to the +present case; for tallow and wax are far from being very dissimilar; the +chief difference consists in the wax being a purer compound of carbon +and hydrogen than the tallow, which retains more of the gross particles +of animal matter. The combustion of a candle, and that of a lamp, both +produce water and carbonic acid gas. Can you tell me how these are +formed?</p> + +<p class="speaker">EMILY.</p> + +<p>Let me reflect . . . . Both the candle and lamp +<span class="pagenum">310</span> +<a name="conver1.page310" id="conver1.page310"> </a> +burn by means of fixed oil—this is decomposed as the combustion +goes on; and the constituent parts of the oil being thus separated, the +carbon unites to a portion of oxygen from the atmosphere to form +carbonic acid gas, whilst the hydrogen combines with another portion of +oxygen, and forms with it water.—The products, therefore, of the +combustion of oils are water and carbonic acid gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But we see neither water nor carbonic acid produced by the combustion +of a candle.</p> + +<p class="speaker">MRS. B.</p> + +<p>The carbonic acid gas, you know, is invisible, and the water being in +a state of vapour, is so likewise. Emily is perfectly correct in her +explanation, and I am very much pleased with it.</p> + +<p>All the vegetable acids consist of various proportions of carbon and +hydrogen, acidified by oxygen. Gums, sugar, and starch, are likewise +composed of these ingredients; but, as the oxygen which they contain is +not sufficient to convert them into acids, they are classed with the +oxyds, and called vegetable oxyds.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am very much delighted with all these new +<span class="pagenum">311</span> +<a name="conver1.page311" id="conver1.page311"> </a> +ideas; but, at the same time, I cannot help being apprehensive that +I may forget many of them.</p> + +<p class="speaker">MRS. B.</p> + +<p>I would advise you to take notes, or, what would answer better still, +to write down, after every lesson, as much of it as you can recollect. +And, in order to give you a little assistance, I shall lend you the +heads or index, which I occasionally consult for the sake of preserving +some method and arrangement in these conversations. Unless you follow +some such plan, you cannot expect to retain nearly all that you learn, +how great soever be the impression it may make on you at first.</p> + +<p class="speaker">EMILY.</p> + +<p>I will certainly follow your advice.—Hitherto I have found that +I recollected pretty well what you have taught us; but the history of +carbon is a more extensive subject than any of the simple bodies we have +yet examined.</p> + +<p class="speaker">MRS. B.</p> + +<p>I have little more to say on carbon at present; but hereafter you +will see that it performs a considerable part in most chemical +operations.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is, I suppose, owing to its entering into +<span class="pagenum">312</span> +<a name="conver1.page312" id="conver1.page312"> </a> +the composition of so great a variety of substances?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; it is the basis, you have seen, of all vegetable matter; +and you will find that it is very essential to the process of +animalization. But in the mineral kingdom also, particularly in its form +of carbonic acid, we shall often discover it combined with a great +variety of substances.</p> + +<p>In chemical operations, carbon is particularly useful, from its very +great attraction for oxygen, as it will absorb this substance from many +oxygenated or burnt bodies, and thus deoxygenate, or <i>unburn</i> them, +and restore them to their original combustible state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not understand how a body can be <i>unburnt</i>, and restored to +its original state. This piece of tinder, for instance, that has been +burnt, if by any means the oxygen were extracted from it, would not be +restored to its former state of linen; for its texture is destroyed by +burning, and that must be the case with all organized or manufactured +substances, as you observed in a former conversation.</p> + +<p class="speaker">MRS. B.</p> + +<p>A compound body is decomposed by combustion in a way which generally +precludes the possibility +<span class="pagenum">313</span> +<a name="conver1.page313" id="conver1.page313"> </a> +of restoring it to its former state; the oxygen, for instance, does not +become fixed in the tinder, but it combines with its volatile parts, and +flies off in the shape of gas, or watery vapour. You see, therefore, how +vain it would be to attempt the recomposition of such bodies. But, with +regard to simple bodies, or at least bodies whose component parts are +not disturbed by the process of oxygenation or deoxygenation, it is +often possible to restore them, after combustion, to their original +state.—The metals, for instance, undergo no other alteration by +combustion than a combination with oxygen; therefore, when the oxygen is +taken from them, they return to their pure metallic state. But I shall +say nothing further of this at present, as the metals will furnish ample +subject for another morning; and they are the class of simple bodies +that come next under consideration.</p> + + + + +<span class="pagenum">314</span> +<a name="conver1.page314" id="conver1.page314"> </a> +<h4><a name="convX" id="convX">CONVERSATION X.</a><br> +<span class="subhead">ON METALS.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">T</span>he</span> <span class="smallroman">METALS</span>, which we are now to examine, are bodies of a +very different nature from those which we have hitherto considered. They +do not, like the bases of gases, elude the immediate observation of our +senses; for they are the most brilliant, the most ponderous, and the +most palpable substances in nature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I doubt, however, whether the metals will appear to us so +interesting, and give us so much entertainment as those mysterious +elements which conceal themselves from our view. Besides, they cannot +afford so much novelty; they are bodies with which we are already so +well acquainted.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are not aware, my dear, of the interesting discoveries which were +a few years ago made by Sir H. Davy respecting this class of bodies. By +the aid of the Voltaic battery, he has obtained from +<span class="pagenum">315</span> +<a name="conver1.page315" id="conver1.page315"> </a> +a variety of substances, metals before unknown, the properties of +which are equally new and curious. We shall begin, however, by noticing +those metals with which you profess to be so well acquainted. But the +acquaintance, you will soon perceive, is but very superficial; and I +trust that you will find both novelty and entertainment in considering +the metals in a chemical point of view. To treat of this subject fully, +would require a whole course of lectures; for metals form of themselves +a most important branch of practical chemistry. We must, therefore, +confine ourselves to a general view of them. These bodies are seldom +found naturally in their metallic form: they are generally more or less +oxygenated or combined with sulphur, earths, or acids, and are often +blended with each other. They are found buried in the bowels of the +earth in most parts of the world, but chiefly in mountainous districts, +where the surface of the globe has suffered from the earthquakes, +volcanos, and other convulsions of nature. They are spread in strata or +beds, called veins, and these veins are composed of a certain quantity +of metal, combined with various earthy substances, with which they form +minerals of different nature and appearance, which are called +<i>ores</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I now feel quite at home, for my father has +<span class="pagenum">316</span> +<a name="conver1.page316" id="conver1.page316"> </a> +a lead-mine in Yorkshire, and I have heard a great deal about veins +of ore, and of the <i>roasting</i> and <i>smelting</i> of the lead; but, +I confess, that I do not understand in what these operations +consist.</p> + +<p class="speaker">MRS. B.</p> + +<p>Roasting is the process by which the volatile parts of the ore are +evaporated; smelting, that by which the pure metal is afterwards +separated from the earthy remains of the ore. This is done by throwing +the whole into a furnace, and mixing with it certain substances that +will combine with the earthy parts and other foreign ingredients of the +ore; the metal being the heaviest, falls to the bottom, and runs out by +proper openings in its pure metallic state.</p> + +<p class="speaker">EMILY.</p> + +<p>You told us in a preceding lesson that metals had a great affinity +for oxygen. Do they not, therefore, combine with oxygen, when strongly +heated in the furnace, and run out in the state of oxyds?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; for the scoriæ, or oxyd, which soon forms on the surface of the +fused metal, when it is oxydable, prevents the air from having any +further influence on the mass; so that neither combustion nor +oxygenation can take place.</p> + +<span class="pagenum">317</span> +<a name="conver1.page317" id="conver1.page317"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Are all the metals equally combustible?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; their attraction for oxygen varies extremely. There are some that +will combine with it only at a very high temperature, or by the +assistance of acids; whilst there are others that oxydate spontaneously +and with great rapidity, even at the lowest temperature; such is in +particular manganese, which scarcely ever exists in the metallic state, +as it immediately absorbs oxygen on being exposed to the air, and +crumbles to an oxyd in the course of a few hours.</p> + +<p class="speaker">EMILY.</p> + +<p>Is not that the oxyd from which you extracted the oxygen gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is: so that, you see, this metal attracts oxygen at a low +temperature, and parts with it when strongly heated.</p> + +<p class="speaker">EMILY.</p> + +<p>Is there any other metal that oxydates at the temperature of the +atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>They all do, more or less, excepting gold, silver, and platina.</p> + +<span class="pagenum">318</span> +<a name="conver1.page318" id="conver1.page318"> </a> +<p>Copper, lead, and iron, oxydate slowly in the air, and cover +themselves with a sort of rust, a process which depends on the +gradual conversion of the surface into an oxyd. This rusty surface +preserves the interior metal from oxydation, as it prevents the air from +coming in contact with it. Strictly speaking, however, the word rust +applies only to the oxyd, which forms on the surface of iron, when +exposed to air and moisture, which oxyd appears to be united with a +small portion of carbonic acid.</p> + +<p class="speaker">EMILY.</p> + +<p>When metals oxydate from the atmosphere without an elevation of +temperature, some light and heat, I suppose, must be disengaged, +though not in sufficient quantities to be sensible.</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; and, indeed, it is not surprising that in this case the +light and heat should not be sensible, when you consider how extremely +slow, and, indeed, how imperfectly, most metals oxydate by mere exposure +to the atmosphere. For the quantity of oxygen with which metals are +capable of combining, generally depends upon their temperature; and the +absorption stops at various points of oxydation, according to the degree +to which their temperature is raised.</p> + +<span class="pagenum">319</span> +<a name="conver1.page319" id="conver1.page319"> </a> +<p class="speaker">EMILY.</p> + +<p>That seems very natural; for the greater the quantity of caloric +introduced into a metal, the more will its positive electricity be +exalted, and consequently the stronger will be its affinity for +oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly. When the metal oxygenates with sufficient rapidity for +light and heat to become sensible, combustion actually takes place. But +this happens only at very high temperatures, and the product is +nevertheless an oxyd; for though, as I have just said, metals will +combine with different proportions of oxygen, yet with the exception of +only five of them, they are not susceptible of acidification.</p> + +<p>Metals change colour during the different degrees of oxydation which +they undergo. Lead, when heated in contact with the atmosphere, first +becomes grey; if its temperature be then raised, it turns yellow, and a +still stronger heat changes it to red. Iron becomes successively a +green, brown, and white oxyd. Copper changes from brown to blue, and +lastly green.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray, is the white lead with which houses are painted prepared by +oxydating lead?</p> + +<span class="pagenum">320</span> +<a name="conver1.page320" id="conver1.page320"> </a> +<p class="speaker">MRS. B.</p> + +<p>Not merely by oxydating, but by being also united with carbonic acid. +It is a carbonat of lead. The mere oxyd of lead is called red lead. +Litharge is another oxyd of lead, containing less oxygen. Almost all the +metallic oxyds are used as paints. The various sorts of ochres consist +chiefly of iron more or less oxydated. And it is a remarkable +circumstance, that if you burn metals rapidly, the light or flame they +emit during combustion partakes of the colours which the oxyd +successively assumes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How is that accounted for, Mrs. B.? For light, you know, does not +proceed from the burning body, but from the decomposition of the oxygen +gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>The correspondence of the colour of the light with that of the oxyd +which emits it, is, in all probability, owing to some particles of the +metal which are volatilised and carried off by the caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is then a sort of metallic gas.</p> + +<p class="speaker">EMILY.</p> + +<p>Why is it reckoned so unwholesome to breathe the air of a place in +which metals are melting?</p> + +<span class="pagenum">321</span> +<a name="conver1.page321" id="conver1.page321"> </a> +<p class="speaker">MRS. B.</p> + +<p>Perhaps the notion is too generally entertained. But it is true with +respect to lead, and some other noxious metals, because, unless care be +taken, the particles of the oxyd which are volatilised by the heat are +inhaled in with the breath, and may produce dangerous effects.</p> + +<p>I must show you some instances of the combustion of metals; it would +require the heat of a furnace to make them burn in the common air, but +if we supply them with a stream of oxygen gas, we may easily +accomplish it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But it will still, I suppose, be necessary in some degree to raise +their temperature?</p> + +<p class="speaker">MRS. B.</p> + +<p>This, as you shall see, is very easily done, particularly if the +experiment be tried upon a small scale.—I begin by lighting +this piece of charcoal with the candle, and then increase the rapidity +<ins class="mycorr" title="text reads ‘of of’">of</ins> its +combustion by blowing upon it with a blow-pipe. (<a class="smallcaps" +href="#plateXII">Plate XII.</a> fig. 1.)</p> + +<p class="figname"> +<a name="plateXII" id="plateXII">Plate XII.</a></p> + +<p class="illustration"> +<img src="images/plate12_thumb.png" width="336" height="507" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. Igniting charcoal with a taper & blow-pipe.<br> +Fig. 2. Combustion of metals by means of a blow-pipe conveying a +stream of oxygen gas from a gas holder.</p> + +<p class="figlink"> +<a href="images/plate12_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">EMILY.</p> + +<p>That I do not understand; for it is not every kind of air, but merely +oxygen gas, that produces combustion. Now you said that in breathing we +<span class="pagenum">322</span> +<a name="conver1.page322" id="conver1.page322"> </a> +inspired, but did not expire oxygen gas. Why, therefore, should the air +which you breathe through the blow-pipe promote the combustion of the +charcoal?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the air, which has but once passed through the lungs, is yet +but little altered, a small portion only of its oxygen being +destroyed; so that a great deal more is gained by increasing the +rapidity of the current, by means of the blow-pipe, than is lost in +consequence of the air passing once through the lungs, as you shall +see—</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, indeed, it makes the charcoal burn much brighter.</p> + +<p class="speaker">MRS. B.</p> + +<p>Whilst it is red-hot, I shall drop some iron filings on it, and +supply them with a current of oxygen gas, by means of this apparatus, +(<a class="smallcaps" href="#plateXII">Plate XII.</a> fig 2.) which +consists simply of a closed tin cylindrical vessel, full of oxygen gas, +with two apertures and stop-cocks, by one of which a stream of water is +thrown into the vessel through a long funnel, whilst by the other the +gas is forced out through a blow-pipe adapted to it, as the water gains +admittance.—Now that I pour water into the funnel, you may hear +the gas issuing from the +<span class="pagenum">323</span> +<a name="conver1.page323" id="conver1.page323"> </a> +blow-pipe—I bring the charcoal close to the current, and drop the +filings upon it—</p> + +<p class="speaker">CAROLINE.</p> + +<p>They emit much the same vivid light as the combustion of the iron +wire in oxygen gas.</p> + +<p class="speaker">MRS. B.</p> + +<p>The process is, in fact, the same; there is only some difference in +the mode of conducting it. Let us burn some tin in the same +manner—you see that it is equally combustible.—Let us now +try some copper—</p> + +<p class="speaker">CAROLINE.</p> + +<p>This burns with a greenish flame; it is, I suppose, owing to the +colour of the oxyd?</p> + +<p class="speaker">EMILY.</p> + +<p>Pray, shall we not also burn some gold?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is not in our power, at least in this way. Gold, silver, and +platina, are incapable of being oxydated by the greatest heat that we +can produce by the common method. It is from this circumstance, that +they have been called perfect metals. Even these, however, have an +affinity for oxygen; but their oxydation or combustion can be performed +only by means of acids or by electricity. +<span class="pagenum">324</span> +<a name="conver1.page324" id="conver1.page324"> </a> +The spark given out by the Voltaic battery produces at the point of +contact a greater degree of heat than any other process; and it is at +this very high temperature only that the affinity of these metals for +oxygen will enable them to act on each other.</p> + +<p>I am sorry that I cannot show you the combustion of the perfect +metals by this process, but it requires a considerable Voltaic battery. +You will see these experiments performed in the most perfect manner, +when you attend the chemical lectures of the Royal Institution. But in +the mean time I can, without difficulty, show you an ingenious apparatus +lately contrived for the purpose of producing intense heats, the power +of which nearly equals that of the largest Voltaic batteries. It simply +consists, you see, in a strong box, made of iron or copper, (<a class="smallcaps" href="#plateXb">Plate X.</a> fig. 2.) to which may be +adapted this air-syringe or condensing-pump, and a stop-cock terminating +in a small orifice similar to that of a blow-pipe. By working the +condensing syringe, up and down in this manner, a quantity of air +is accumulated in the vessel, which may be increased to almost any +extent; so that if we now turn the stop-cock, the condensed air will +rush out, forming a jet of considerable force; and if we place the flame +of a lamp in the current, you will see how violently the flame is driven +in that direction.</p> + +<p class="figname"> +<a name="plateXb" id="plateXb">Plate X.</a></p> + +<p class="illustration"> +<img src="images/plate10b_thumb.png" width="378" height="184" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 2. A. the reservoir of condensed air. +B. the condensing Syringe. +C. the bladder for Oxygen. +D. the moveable jet.</p> + +<p class="figlink"> +<a href="images/plate10_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="mynote"> +This part of the Plate was printed sideways to fit alongside the +illustration of the miner’s lamp, added for this edition.</p> + +<span class="pagenum">325</span> +<a name="conver1.page325" id="conver1.page325"> </a> +<p class="speaker">CAROLINE.</p> + +<p>It seems to be exactly the same effect as that of a blow-pipe worked +by the mouth, only much stronger.</p> + +<p class="speaker">EMILY.</p> + +<p>Yes; and this new instrument has this additional advantage, that it +does not fatigue the mouth and lungs like the common blow-pipe, and +requires no art in blowing.</p> + +<p class="speaker">MRS. B.</p> + +<p>Unquestionably; but yet this blow-pipe would be of very limited +utility, if its energy and power could not be greatly increased by some +other contrivance. Can you imagine any mode of producing such an +effect?</p> + +<p class="speaker">EMILY.</p> + +<p>Could not the reservoir be charged with pure oxygen, instead of +common air, as in the case of the gas-holder?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; and this is precisely the contrivance I allude to. The +vessel need only be supplied with air from a bladder full of oxygen, +instead of the air of the room, and this, you see, may be easily done by +screwing the bladder on the upper part of the syringe, so that in +working the syringe the oxygen gas is forced from the bladder into the +condensing vessel.</p> + +<span class="pagenum">326</span> +<a name="conver1.page326" id="conver1.page326"> </a> +<p class="speaker">CAROLINE.</p> + +<p>With the aid of this small apparatus, therefore, we could obtain the +same effects as those we have just produced with the gas-holder, by +means of a column of water forcing the gas out of it?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and much more conveniently so. But there is a mode of using this +apparatus by which more powerful effects still may be obtained. It +consists in condensing in the reservoir, not oxygen alone, but a mixture +of oxygen and hydrogen in the exact proportion in which they unite to +produce water; and then kindling the jet formed by the mixed gases. The +heat disengaged by this combustion, without the help of any lamp, is +probably the most intense known; and various effects are said to have +been obtained from it which exceed all expectation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But why should we not try this experiment?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because it is not exempt from danger; the combustion (notwithstanding +various contrivances which have been resorted to with a view to prevent +accident) being apt to penetrate into the inside of the vessel, and to +produce a dangerous and violent +<span class="pagenum">327</span> +<a name="conver1.page327" id="conver1.page327"> </a> +explosion.—We shall, therefore, now proceed in our subject.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think you said the oxyds of metals could be restored to their +metallic state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; this is called <i>reviving</i> a metal. Metals are in general +capable of being revived by charcoal, when heated red hot, charcoal +having a greater attraction for oxygen than the metals. You need only, +therefore, decompose, or unburn the oxyd, by depriving it of its oxygen, +and the metal will be restored to its pure state.</p> + +<p class="speaker">EMILY.</p> + +<p>But will the carbon, by this operation, be burnt, and be converted +into carbonic acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly. There are other combustible substances to which metals at +a high temperature will part with their oxygen. They will also yield it +to each other, according to their several degrees of attraction for it; +and if the oxygen goes into a more dense state in the metal which it +enters, than it existed in that which it quits, a proportional +disengagement of caloric will take place.</p> + +<span class="pagenum">328</span> +<a name="conver1.page328" id="conver1.page328"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And cannot the oxyds of gold, silver, and platina, which are formed +by means of acids or of the electric fluid, be restored to their +metallic state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, they may; and the intervention of a combustible body is not +required; heat alone will take the oxygen from them, convert it into a +gas, and revive the metal.</p> + +<p class="speaker">EMILY.</p> + +<p>You said that rust was an oxyd of iron; how is it, then, that water, +or merely dampness, produces it, which, you know, it very frequently +does on steel grates, or any iron instruments?</p> + +<p class="speaker">MRS. B.</p> + +<p>In that case the metal decomposes the water, or dampness (which is +nothing but water in a state of vapour), and obtains the oxygen +from it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I thought that it was necessary to bring metals to a very high +temperature to enable them to decompose water.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is so, if it is required that the process should be performed +rapidly, and if any considerable quantity is to be decomposed. Rust, you +knew, +<span class="pagenum">329</span> +<a name="conver1.page329" id="conver1.page329"> </a> +is sometimes months in forming, and then it is only the surface of the +metal that is oxydated.</p> + +<p class="speaker">EMILY.</p> + +<p>Metals, then, that do not rust, are incapable of spontaneous +oxydation, either by air or water?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and this is the case with the perfect metals, which, on that +account, preserve their metallic lustre so well.</p> + +<p class="speaker">EMILY.</p> + +<p>Are all metals capable of decomposing water, provided their +temperature be sufficiently raised?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; a certain degree of attraction is requisite, besides the +assistance of heat. Water, you recollect, is composed of oxygen and +hydrogen; and, unless the affinity of the metal for oxygen be stronger +than that of hydrogen, it is in vain that we raise its temperature, for +it cannot take the oxygen from the hydrogen. Iron, zinc, tin, and +antimony, have a stronger affinity for oxygen than hydrogen has, +therefore these four metals are capable of decomposing water. But +hydrogen having an advantage over all the other metals with respect to +its affinity for oxygen, it not only withholds its oxygen from them, but +is even capable, +<span class="pagenum">330</span> +<a name="conver1.page330" id="conver1.page330"> </a> +under certain circumstances, of taking the oxygen from the oxyds of +these metals.</p> + +<p class="speaker">EMILY.</p> + +<p>I confess that I do not quite understand why hydrogen can take oxygen +from those metals that do not decompose water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now I think I do perfectly. Lead, for instance, will not decompose +water, because it has not so strong an attraction for oxygen as hydrogen +has. Well, then, suppose the lead to be in a state of oxyd; hydrogen +will take the oxygen from the lead, and unite with it to form water, +because hydrogen has a stronger attraction for oxygen, than oxygen has +for lead; and it is the same with all the other metals which do not +decompose water.</p> + +<p class="speaker">EMILY.</p> + +<p>I understand your explanation, Caroline, very well; and I imagine +that it is because lead cannot decompose water that it is so much +employed for pipes for conveying that fluid.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; lead is, on that account, particularly appropriate to such +purposes; whilst, on the contrary, this metal, if it was oxydable by +water, +<span class="pagenum">331</span> +<a name="conver1.page331" id="conver1.page331"> </a> +would impart to it very noxious qualities, as all oxyds of lead are more +or less pernicious.</p> + +<p>But, with regard to the oxydation of metals, the most powerful mode +of effecting it is by means of acids. These, you know, contain a much +greater proportion of oxygen than either air or water; and will, most of +them, easily yield it to metals. Thus, you recollect, the zinc plates of +the Voltaic battery are oxydated by the acid and water, much more +effectually than by water alone.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And I have often observed that if I drop vinegar, lemon, or any acid +on the blade of a knife, or on a pair of <ins class="correction" title="unchanged">scissars</ins>, it will immediately produce a spot of +rust.</p> + +<p class="speaker">EMILY.</p> + +<p>Metals have, then, three ways of obtaining oxygen; from the +atmosphere, from water, and from acids.</p> + +<p class="speaker">MRS. B.</p> + +<p>The two first you have already witnessed, and I shall now show you +how metals take the oxygen from an acid. This bottle contains nitric +acid; I shall pour some of it over this piece of copper-leaf +. . . . . . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>Oh, what a disagreeable smell!</p> + +<span class="pagenum">332</span> +<a name="conver1.page332" id="conver1.page332"> </a> +<p class="speaker">EMILY.</p> + +<p>And what is it that produces the effervescency and that thick yellow +vapour?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is the acid, which being abandoned by the greatest part of its +oxygen, is converted into a weaker acid, which escapes in the form of +gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And whence proceeds this heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>Indeed, Caroline, I think you might now be able to answer that +question yourself.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Perhaps it is that the oxygen enters into the metal in a more solid +state than it existed in the acid, in consequence of which caloric is +disengaged.</p> + +<p class="speaker">MRS. B.</p> + +<p>If the combination of the oxygen and the metal results from the union +of their opposite electricities, of course caloric must be given +out.</p> + +<p class="speaker">EMILY.</p> + +<p>The effervescence is over; therefore I suppose that the metal is now +oxydated.</p> + +<span class="pagenum">333</span> +<a name="conver1.page333" id="conver1.page333"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes. But there is another important connection between metals and +acids, with which I must now make you acquainted. Metals, when in the +state of oxyds, are capable of being dissolved by acids. In this +operation they enter into a chemical combination with the acid, and form +an entirely new compound.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what difference is there between the <i>oxydation</i> and the +<i>dissolution</i> of the metal by an acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>In the first case, the metal merely combines with a portion of oxygen +taken from the acid, which is thus partly deoxygenated, as in the +instance you have just seen; in the second case, the metal, after being +previously oxydated, is actually dissolved in the acid, and enters into +a chemical combination with it, without producing any further +decomposition or effervescence.—This complete combination of an +oxyd and an acid forms a peculiar and important class of compound +salts.</p> + +<p class="speaker">EMILY.</p> + +<p>The difference between an oxyd and a compound salt, therefore, is +very obvious: the one consists of a metal and oxygen; the other of an +oxyd and an acid.</p> + +<span class="pagenum">334</span> +<a name="conver1.page334" id="conver1.page334"> </a> +<p class="speaker">MRS. B.</p> + +<p>Very well: and you will be careful to remember that the metals are +incapable of entering into this combination with acids, unless they are +previously oxydated; therefore, whenever you bring a metal in contact +with an acid, it will be first oxydated and afterwards dissolved, +provided that there be a sufficient quantity of acid for both +operations.</p> + +<p>There are some metals, however, whose solution is more easily +accomplished, by diluting the acid in water; and the metal will, in this +case, be oxydated, not by the acid, but by the water, which it will +decompose. But in proportion as the oxygen of the water oxydates the +surface of the metal, the acid combines with it, washes it off, and +leaves a fresh surface for the oxygen to act upon: then other coats of +oxyd are successively formed, and rapidly dissolved by the acid, which +continues combining with the new-formed surfaces of oxyd till the whole +of the metal is dissolved. During this process the hydrogen gas of the +water is disengaged, and flies off with effervescence.</p> + +<p class="speaker">EMILY.</p> + +<p>Was not this the manner in which the sulphuric acid assisted the iron +filings in decomposing water?</p> + +<span class="pagenum">335</span> +<a name="conver1.page335" id="conver1.page335"> </a> +<p class="speaker">MRS. B.</p> + +<p>Exactly; and it is thus that several metals, which are incapable +alone of decomposing water, are enabled to do it by the assistance of an +acid, which, by continually washing off the covering of oxyd, as it is +formed, prepares a fresh surface of metal to act upon the water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The acid here seems to act a part not very different from that of a +scrubbing-brush.—But pray would not this be a good method of +cleaning metallic utensils?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; on some occasions a weak acid, as vinegar, is used for cleaning +copper. Iron plates, too, are freed from the rust on their surface by +diluted muriatic acid, previous to their being covered with tin. You +must remember, however, that in this mode of cleaning metals the acid +should be quickly afterwards wiped off, otherwise it would produce fresh +oxyd.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Let us watch the dissolution of the copper in the nitric acid; for I +am very impatient to see the salt that is to result from it. The mixture +is now of a beautiful blue colour; but there is no appearance +<span class="pagenum">336</span> +<a name="conver1.page336" id="conver1.page336"> </a> +of the formation of a salt; it seems to be a tedious operation.</p> + +<p class="speaker">MRS. B.</p> + +<p>The crystallisation of the salt requires some length of time to be +completed; if, however, you are so impatient, I can easily show you +a metallic salt already formed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But that would not satisfy my curiosity half so well as one of our +own manufacturing.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is one of our own preparing that I mean to show you. When we +decomposed water a few days since, by the oxydation of iron filings +through the assistance of sulphuric acid, in what did the process +consist?</p> + +<p class="speaker">CAROLINE.</p> + +<p>In proportion as the water yielded its oxygen to the iron, the acid +combined with the new-formed oxyd, and the hydrogen escaped alone.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well; the result, therefore, was a compound salt, formed by the +combination of sulphuric acid with oxyd of iron. It still remains in +<span class="pagenum">337</span> +<a name="conver1.page337" id="conver1.page337"> </a> +the vessel in which the experiment was performed. Fetch it, and we shall +examine it.</p> + +<p class="speaker">EMILY.</p> + +<p>What a variety of processes the decomposition of water, by a metal +and an acid, implies; 1st, the decomposition of the water; 2dly, the +oxydation of the metal; and 3dly, the formation of a compound salt.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Here it is, Mrs. B.—What beautiful green crystals! But we do +not perceive any crystals in the solution of copper in nitrous acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the salt is now suspended in the water which the nitrous acid +contains, and will remain so till it is deposited in consequence of rest +and cooling.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised that a body so opake as iron can be converted into +such transparent crystals.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is the union with the acid that produces the transparency; for if +the pure metal were melted, and afterwards permitted to cool and +crystallise, it would be found just as opake as before.</p> + +<span class="pagenum">338</span> +<a name="conver1.page338" id="conver1.page338"> </a> +<p class="speaker">EMILY.</p> + +<p>I do not understand the exact meaning of <i>crystallisation</i>?</p> + +<p class="speaker">MRS. B.</p> + +<p>You recollect that when a solid body is dissolved either by water or +caloric it is not decomposed; but that its integrant parts are only +suspended in the solvent. When the solution is made in water, the +integrant particles of the body will, on the water being evaporated, +again unite into a solid mass by the force of their mutual attraction. +But when the body is dissolved by caloric alone, nothing more is +necessary, in order to make its particles reunite, than to reduce its +temperature. And, in general, if the solvent, whether water or caloric, +be slowly separated by evaporation or by cooling, and care taken that +the particles be not agitated during their reunion, they will arrange +themselves in regular masses, each individual substance assuming a +peculiar form or arrangement; and this is what is called +crystallisation.</p> + +<p class="speaker">EMILY.</p> + +<p>Crystallisation, therefore, is simply the reunion of the particles of +a solid body that has been dissolved in a fluid.</p> + +<span class="pagenum">339</span> +<a name="conver1.page339" id="conver1.page339"> </a> +<p class="speaker">MRS. B.</p> + +<p>That is a very good definition of it. But I must not forget to +observe, that <i>heat</i> and <i>water</i> may unite their solvent +powers; and, in this case, crystallisation may be hastened by cooling, +as well as by evaporating the liquid<ins class="correction" title="text has ?">. </ins></p> + +<p class="speaker">CAROLINE.</p> + +<p>But if the body dissolved is of a volatile nature, will it not +evaporate with the fluid?</p> + +<p class="speaker">MRS. B.</p> + +<p>A crystallised body held in solution only by water is scarcely ever +so volatile as the fluid itself, and care must be taken to manage the +heat so that it may be sufficient to evaporate the water only.</p> + +<p>I should not omit also to mention that bodies, in crystallising from +their watery solution, always retain a small portion of water, which +remains confined in the crystal in a solid form, and does not reappear +unless the body loses its crystalline state. This is called the <i>water +of crystallisation</i>. But you must observe, that whilst a body may be +separated from its solution in water or caloric simply by cooling or by +evaporation, an acid can be taken from a metal with which it is combined +only by stronger affinities, which produce a decomposition.</p> + +<span class="pagenum">340</span> +<a name="conver1.page340" id="conver1.page340"> </a> +<p class="speaker">EMILY.</p> + +<p>Are the perfect metals susceptible of being dissolved and converted +into compound salts by acids?</p> + +<p class="speaker">MRS. B.</p> + +<p>Gold is acted upon by only one acid, the <i>oxygenated muriatic</i>, +a very remarkable acid, which, when in its most concentrated state, +dissolves gold or any other metal, by burning them rapidly.</p> + +<p>Gold can, it is true, be dissolved likewise by a mixture of two +acids, commonly called <i>aqua regia</i>; but this mixed solvent derives +that property from containing the peculiar acid which I have just +mentioned. Platina is also acted upon by this acid only; silver is +dissolved by nitric acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think you said that some of the metals might be so strongly +oxydated as to become acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>There are five metals, arsenic, molybdena, chrome, tungsten, and +columbium, which are susceptible of combining with a sufficient quantity +of oxygen to be converted into acids.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Acids are connected with metals in such a variety of ways, that I am +afraid of some confusion in remembering +<span class="pagenum">341</span> +<a name="conver1.page341" id="conver1.page341"> </a> +them.—In the first place, acids will yield their oxygen to metals. +Secondly, they will combine with them in their state of oxyds, to form +compound salts; and lastly, several of the metals are themselves +susceptible of acidification.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well; but though metals have so great an affinity for acids, it +is not with that class of bodies alone that they will combine. They are +most of them, in their simple state, capable of uniting with sulphur, +with phosphorus, with carbon, and with each other; these combinations, +according to the nomenclature which was explained to you on a former +occasion, are called <i>sulphurets</i>, <i>phosphorets</i>, +<i>carburets</i>, &c.</p> + +<p>The metallic phosphorets offer nothing very remarkable. The +sulphurets form the peculiar kind of mineral called <i>pyrites</i>, from +which certain kinds of mineral waters, as those of Harrogate, derive +their chief chemical properties. In this combination, the sulphur, +together with the iron, have so strong an attraction for oxygen, that +they obtain it both from the air and from water, and by condensing it in +a solid form, produce the heat which raises the temperature of the water +in such a remarkable degree.</p> + +<p class="speaker">EMILY.</p> + +<p>But if pyrites obtain oxygen from water, that +<span class="pagenum">342</span> +<a name="conver1.page342" id="conver1.page342"> </a> +water must suffer a decomposition, and hydrogen gas be evolved.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is actually the case in the hot springs alluded to, which give +out an extremely fetid gas, composed of hydrogen impregnated with +sulphur.</p> + +<p class="speaker">CAROLINE.</p> + +<p>If I recollect right, steel and plumbago, which you mentioned in the +last lesson, are both carburets of iron?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and they are the only carburets of much consequence.</p> + +<p>A curious combination of metals has lately very much attracted the +attention of the scientific world: I mean the meteoric stones that +fall from the atmosphere. They consist principally of native or pure +iron, which is never found in that state in the bowels of the earth; and +contain also a small quantity of nickel and chrome, a combination +likewise new in the mineral kingdom.</p> + +<p>These circumstances have led many scientific persons to believe that +those substances have fallen from the moon, or some other planet, while +others are of opinion either that they are formed in the atmosphere, or +are projected into it by some unknown volcano on the surface of our +globe.</p> + +<span class="pagenum">343</span> +<a name="conver1.page343" id="conver1.page343"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I have heard much of these stones, but I believe many people are of +opinion that they are formed on the surface of the earth, and laugh at +their pretended celestial origin.</p> + +<p class="speaker">MRS. B.</p> + +<p>The fact of their falling is so well ascertained, that I think no +person who has at all investigated the subject, can now entertain any +doubt of it. Specimens of these stones have been discovered in all parts +of the world, and to each of them some tradition or story of its fall +has been found connected. And as the analysis of all those specimens +affords precisely the same results, there is strong reason to conjecture +that they all proceed from the same source. It is to Mr. Howard that +philosophers are indebted for having first analysed these stones, and +directed their attention to this interesting subject.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But pray, Mrs. B., how can solid masses of iron and nickel be formed +from the atmosphere, which consists of the two airs, nitrogen and +oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>I really do not see how they could, and think it much more probable +that they fall from the moon.—But we must not suffer this +digression to take up too much of our time.</p> + +<span class="pagenum">344</span> +<a name="conver1.page344" id="conver1.page344"> </a> +<p>The combinations of metals with each other are called alloys; thus +brass is an alloy of copper and zinc; bronze, of copper and +tin, &c.</p> + +<p class="speaker">EMILY.</p> + +<p>And is not pewter also a combination of metal?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is. The pewter made in this country is mostly composed of tin, +with a very small proportion of zinc and lead.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Block-tin is a kind of pewter, I believe?</p> + +<p class="speaker">MRS. B.</p> + +<p>Properly speaking, block-tin means tin in blocks, or square massive +ingots; but in the sense in which it is used by ignorant workmen, it is +iron plated with tin, which renders it more durable, as tin will not so +easily rust. Tin alone, however, would be too soft a metal to be worked +for common use, and all tin-vessels and utensils are in fact made of +plates of iron, thinly coated with tin, which prevents the iron from +rusting.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Say rather <i>oxydating</i>, Mrs. B.—Rust is a word that should +be exploded in chemistry.</p> + +<span class="pagenum">345</span> +<a name="conver1.page345" id="conver1.page345"> </a> +<p class="speaker">MRS. B.</p> + +<p>Take care, however, not to introduce the word oxydate, instead of +rust, in general conversation; for you would probably not be understood, +and you might be suspected of affectation.</p> + +<p>Metals differ very much in their affinity for each other; some will +not unite at all, others readily combine together, and on this property +of metals the art of <i>soldering</i> depends.</p> + +<p class="speaker">EMILY.</p> + +<p>What is soldering?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is joining two pieces of metal together, by a more fusible metal +interposed between them. Thus tin is a solder for lead; brass, gold, or +silver, are solder for iron, &c.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And is not <i>plating</i> metals something of the same nature?</p> + +<p class="speaker">MRS. B.</p> + +<p>In the operation of plating, two metals are united, one being covered +with the other, but without the intervention of a third; iron or copper +may thus be covered with gold or silver.</p> + +<span class="pagenum">346</span> +<a name="conver1.page346" id="conver1.page346"> </a> +<p class="speaker">EMILY.</p> + +<p>Mercury appears to me of a very different nature from the other +metals.</p> + +<p class="speaker">MRS. B.</p> + +<p>One of its greatest peculiarities is, that it retains a fluid state +at the temperature of the atmosphere. All metals are fusible at +different degrees of heat, and they have likewise each the property of +freezing or becoming solid at a certain fixed temperature. Mercury +congeals only at seventy-two degrees below the freezing point.</p> + +<p class="speaker">EMILY.</p> + +<p>That is to say, that in order to freeze, it requires a temperature of +seventy-two degrees colder than that at which water freezes.</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But is the temperature of the atmosphere ever so low as that?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, often in Siberia; but happily never in this part of the globe. +Here, however, mercury may be congealed by artificial cold; I mean +such intense cold as can be produced by some chemical +<span class="pagenum">347</span> +<a name="conver1.page347" id="conver1.page347"> </a> +mixtures, or by the rapid evaporation of ether under the air-pump.<a +class="tag" name="tag20" id="tag20" href="#note20">*</a></p> + +<p class="speaker">CAROLINE.</p> + +<p>And can mercury be made to boil and evaporate?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, like any other liquid; only it requires a much greater degree of +heat. At the temperature of six hundred degrees, it begins to boil and +evaporate like water.</p> + +<p>Mercury combines with gold, silver, tin, and with several other +metals; and, if mixed with any of them in a sufficient proportion, it +penetrates the solid metal, softens it, loses its own fluidity, and +forms an <i>amalgam</i>, which is the name given to the combination of +any metal with mercury, forming a substance more or less solid, +according as the mercury or the other metal predominates.</p> + +<p class="speaker">EMILY.</p> + +<p>In the list of metals there are some whose names I have never before +heard mentioned.</p> + +<p class="speaker">MRS. B.</p> + +<p>Besides those which Sir H. Davy has obtained, there are several that +have been recently discovered, +<span class="pagenum">348</span> +<a name="conver1.page348" id="conver1.page348"> </a> +whose properties are yet but little known, as for instance, titanium, +which was discovered by the Rev. Mr. Gregor, in the tin-mines of +Cornwall; columbium or tantalium, which has lately been discovered by +Mr. Hatchett; and osmium, iridium, palladium, and rhodium, all of which +Dr. Wollaston and Mr. Tennant found mixed in minute quantities with +crude platina, and the distinct existence of which they proved by +curious and delicate experiments.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Arsenic has been mentioned amongst the metals<ins class="mycorr" +title="text has ,">. </ins>I had no notion that it belonged to +that class of bodies, for I had never seen it but as a powder, and never +thought of it but as a most deadly poison.</p> + +<p class="speaker">MRS. B.</p> + +<p>In its pure metallic state, I believe, it is not so poisonous; but it +has such a great affinity for oxygen, that it absorbs it from the +atmosphere at its natural temperature: you have seen it, therefore, only +in its state of oxyd, when, from its combination with oxygen, it has +acquired its very poisonous properties.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it possible that oxygen can impart poisonous qualities? That +valuable substance which produces +<span class="pagenum">349</span> +<a name="conver1.page349" id="conver1.page349"> </a> +light and fire, and which all bodies in nature are so eager to +obtain?</p> + +<p class="speaker">MRS. B.</p> + +<p>Most of the metallic oxyds are poisonous, and derive this property +from their union with oxygen. The white lead, so much used in paint, +owes its pernicious effects to oxygen. In general, oxygen, in a concrete +state, appears to be particularly destructive in its effects on flesh or +any animal matter; and those oxyds are most caustic that have an acrid +burning taste, which proceeds from the metal having but a slight +affinity for oxygen, and therefore easily yielding it to the flesh, +which it corrodes and destroys.</p> + +<p class="speaker">EMILY.</p> + +<p>What is the meaning of the word <i>caustic</i>, which you have just +used?</p> + +<p class="speaker">MRS. B.</p> + +<p>It expresses that property which some bodies possess, of +disorganizing and destroying animal matter, by operating a kind of +combustion, or at least a chemical decomposition. You must often have +heard of caustic used to burn warts, or other animal excrescences; most +of these bodies owe their destructive power to the oxygen with which +they are combined. The common caustic, called +<span class="pagenum">350</span> +<a name="conver1.page350" id="conver1.page350"> </a> +<i>lunar caustic</i>, is a compound formed by the union of nitric acid +and silver; and it is supposed to owe its caustic qualities to the +oxygen contained in the nitric acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, pray, are not acids still more caustic than oxyds, as they +contain a greater proportion of oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Some of the acids are; but the caustic property of a body depends not +only upon the quantity of oxygen which it contains, but also upon its +slight affinity for that principle, and the consequent facility with +which it yields it.</p> + +<p class="speaker">EMILY.</p> + +<p>Is not this destructive property of oxygen accounted for?</p> + +<p class="speaker">MRS. B.</p> + +<p>It proceeds probably from the strong attraction of oxygen for +hydrogen; for if the one rapidly absorb the other from the animal fibre, +a disorganisation of the substance must ensue.</p> + +<p class="speaker">EMILY.</p> + +<p>Caustics are, then, very properly said to burn the flesh, since the +combination of oxygen and hydrogen is an actual combustion.</p> + +<span class="pagenum">351</span> +<a name="conver1.page351" id="conver1.page351"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Now, I think, this effect would be more properly termed an oxydation, +as there is no disengagement of light and heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>But there really is a sensation of heat produced by the action of +caustics.</p> + +<p class="speaker">EMILY.</p> + +<p>If oxygen is so caustic, why does not that which is contained in the +atmosphere burn us?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because it is in a gaseous state, and has a greater attraction for +its electricity than for the hydrogen of our bodies. Besides, should the +air be slightly caustic, we are in a great measure sheltered from its +effects by the skin; you know how much a wound, however trifling, smarts +on being exposed to it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is a curious idea, however, that we should live in a slow fire. +But, if the air was caustic, would it not have an acrid taste?</p> + +<p class="speaker">MRS. B.</p> + +<p>It possibly may have such a taste; though in so +<span class="pagenum">352</span> +<a name="conver1.page352" id="conver1.page352"> </a> +slight a degree, that custom has rendered it insensible.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And why is not water caustic? When I dip my hand into water, though +cold, it ought to burn me from the caustic nature of its oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your hand does not decompose the water; the oxygen in that state is +much better supplied with hydrogen than it would be by animal matter, +and if its causticity depend on its affinity for that principle, it will +be very far from quitting its state of water to act upon your hand. You +must not forget that oxyds are caustic in proportion as the oxygen +adheres slightly to them.</p> + +<p class="speaker">EMILY.</p> + +<p>Since the oxyd of arsenic is poisonous, its acid, I suppose, is +fully as much so?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; it is one of the strongest poisons in nature.</p> + +<p class="speaker">EMILY.</p> + +<p>There is a poison called <i>verdigris</i>, which forms on brass and +copper when not kept very clean; and this, I have heard, is an +objection to these +<span class="pagenum">353</span> +<a name="conver1.page353" id="conver1.page353"> </a> +metals being made into kitchen utensils. Is this poison likewise +occasioned by oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is produced by the intervention of oxygen; for verdigris is a +compound salt formed by the union of vinegar and copper; it is of a +beautiful green colour, and much used in painting.</p> + +<p class="speaker">EMILY.</p> + +<p>But, I believe, verdigris is often formed on copper when no vinegar +has been in contact with it.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not real verdigris, but compound salts, somewhat resembling it, may +be produced by the action of any acid on copper.</p> + +<p>The solution of copper in nitric acid, if evaporated, affords a salt +which produces an effect on tin that will surprise you, and I have +prepared some from the solution we made before, that I might show it to +you. I shall first sprinkle some water on this piece of tin-foil, +and then some of the salt.—Now observe that I fold it up suddenly, +and press it into one lump.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a prodigious vapour issues from it—and sparks of fire I +declare!</p> + +<span class="pagenum">354</span> +<a name="conver1.page354" id="conver1.page354"> </a> +<p class="speaker">MRS. B.</p> + +<p>I thought it would surprise you. The effect, however, I dare say +you could account for, since it is merely the consequence of the oxygen +of the salt rapidly entering into a closer combination with the tin.</p> + +<p>There is also a beautiful green salt too curious to be omitted; it is +produced by the combination of cobalt with muriatic acid, which has the +singular property of forming what is called <i>sympathetic ink</i>. +Characters written with this solution are invisible when cold, but when +a gentle heat is applied, they assume a fine bluish green colour.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think one might draw very curious landscapes with the assistance of +this ink; I would first make a water-colour drawing of a +winter-scene, in which the trees should be leafless, and the grass +scarcely green: I would then trace all the verdure with the +invisible ink, and whenever I chose to create spring, I should hold +it before the fire, and its warmth would cover the landscape with a rich +verdure.</p> + +<p class="speaker">MRS. B.</p> + +<p>That will be a very amusing experiment, and I advise you by all means +to try it.</p> + +<p class="mynote"> +Several cobalt compounds, including the cobalt chloride described here, +are still in use as invisible (“sympathetic”) inks. They are safe if +used appropriately.</p> + +<p>Before we part, I must introduce to your acquaintance the curious +metals which Sir H. Davy +<span class="pagenum">355</span> +<a name="conver1.page355" id="conver1.page355"> </a> +has recently discovered. The history of these extraordinary bodies is +yet so much in its infancy, that I shall confine myself to a very short +account of them; it is more important to point out to you the vast, and +apparently inexhaustible, field of research which has been thrown open +to our view by Sir H. Davy’s memorable discoveries, than to enter into a +minute account of particular bodies or experiments.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But I have heard that these discoveries, however splendid and +extraordinary, are not very likely to prove of any great benefit to the +world, as they are rather objects of curiosity than of use.</p> + +<p class="speaker">MRS. B.</p> + +<p>Such may be the illiberal conclusions of the ignorant and +narrow-minded; but those who can duly estimate the advantages of +enlarging the sphere of science, must be convinced that the acquisition +of every new fact, however unconnected it may at first appear with +practical utility, must ultimately prove beneficial to mankind. But +these remarks are scarcely applicable to the present subject; for some +of the new metals have already proved eminently useful as chemical +agents, and are likely soon to be employed in the arts. For the +enumeration of these metals, I must refer you to our list of simple +bodies; they are derived from the alkalies, the +<span class="pagenum">356</span> +<a name="conver1.page356" id="conver1.page356"> </a> +earths, and three of the acids, all of which had been hitherto +considered as undecompoundable or simple bodies.</p> + +<p>When Sir H. Davy first turned his attention to the effects of the +Voltaic battery, he tried its power on a variety of compound bodies, and +gradually brought to light a number of new and interesting facts, which +led the way to more important discoveries. It would be highly +interesting to trace his steps in this new department of science, but it +would lead us too far from our principal object. A general view of +his most remarkable discoveries is all that I can aim at, or that you +could, at present, understand.</p> + +<p>The facility with which compound bodies yielded to the Voltaic +electricity, induced him to make trial of its effects on substances +hitherto considered as simple, but which he suspected of being compound, +and his researches were soon crowned with the most complete success.</p> + +<p>The body which he first submitted to the Voltaic battery, and which +had never yet been decomposed, was one of the fixed alkalies, called +potash. This substance gave out an elastic fluid at the positive wire, +which was ascertained to be oxygen, and at the negative wire, small +globules of a very high metallic lustre, very similar in appearance to +mercury; thus proving that potash, which had hitherto been considered as +a simple incombustible body, +<span class="pagenum">357</span> +<a name="conver1.page357" id="conver1.page357"> </a> +was in fact a metallic oxyd; and that its incombustibility proceeded +from its being already combined with oxygen.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose the wires used in this experiment were of platina, as they +were when you decomposed water; for if of iron, the oxygen would have +combined with the wire, instead of appearing in the form of gas.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly: the metal, however, would equally have been disengaged. +Sir H. Davy has distinguished this new substance by the name of <span +class="smallroman">POTASSIUM</span>, which is derived from that of the +alkali, from which it is procured. I have some small pieces of it +in this phial, but you have already seen it, as it is the metal which we +burnt in contact with sulphur.</p> + +<p class="speaker">EMILY.</p> + +<p>What is the liquid in which you keep it?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is naptha, a bituminous liquid, with which I shall hereafter make +you acquainted. It is almost the only fluid in which potassium can be +preserved, as it contains no oxygen, and this metal has so powerful an +attraction for oxygen, that it will not only absorb it from the air, but +likewise from water, or any body whatever that contains it.</p> + +<span class="pagenum">358</span> +<a name="conver1.page358" id="conver1.page358"> </a> +<p class="speaker">EMILY.</p> + +<p>This, then, is one of the bodies that oxydates spontaneously without +the application of heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and it has this remarkable peculiarity that it attracts oxygen +much more rapidly from water than from air; so that when thrown into +water, however cold, it actually bursts into flame. I shall now +throw a small piece, about the size of a pin’s head, on this drop of +water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It instantaneously exploded, producing a little flash of light! this +is, indeed, a most curious substance!</p> + +<p class="speaker">MRS. B.</p> + +<p>By its combustion it is reconverted into potash; and as potash is now +decidedly a compound body, I shall not enter into any of its +properties till we have completed our review of the simple bodies; but +we may here make a few observations on its basis, potassium. If this +substance is left in contact with air, it rapidly returns to the state +of potash, with a disengagement of heat, but without any flash of +light.</p> + +<p class="speaker">EMILY.</p> + +<p>But is it not very <ins class="mycorr" title="text reads ‘singulr’">singular</ins> +that it should burn better in water than in air?</p> + +<span class="pagenum">359</span> +<a name="conver1.page359" id="conver1.page359"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I do not think so: for if the attraction of potassium for oxygen is +so strong that it finds no more difficulty in separating it from the +hydrogen in water, than in absorbing it from the air, it will no doubt +be more amply and rapidly supplied by water than by air.</p> + +<p class="speaker">MRS. B.</p> + +<p>That cannot, however, be precisely the reason, for when potassium is +introduced under water, without contact of air, the combustion is not so +rapid, and indeed, in that case, there is no luminous appearance; but a +violent action takes place, much heat is excited, the potash is +regenerated, and hydrogen gas is evolved.</p> + +<p>Potassium is so eminently combustible, that instead of requiring, +like other metals, an elevation of temperature, it will burn rapidly in +contact with water, even below the freezing point. This you may witness +by throwing a piece on this lump of ice.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It again exploded with flame, and has made a deep hole in the +ice.</p> + +<p class="speaker">MRS. B.</p> + +<p>This hole contains a solution of potash; for the alkali being +extremely soluble, disappears in the +<span class="pagenum">360</span> +<a name="conver1.page360" id="conver1.page360"> </a> +water at the instant it is produced. Its presence, however, may be +easily ascertained, alkalies having the property of changing paper, +stained with turmeric, to a red colour; if you dip one end of this slip +of paper into the hole in the ice you will see it change colour, and the +same, if you wet it with the drop of water in which the first piece of +potassium was burnt.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It has indeed changed the paper from yellow to red.</p> + +<p class="speaker">MRS. B.</p> + +<p>This metal will burn likewise in carbonic acid gas, a gas that +had always been supposed incapable of supporting combustion, as we were +unacquainted with any substance that had a greater attraction for oxygen +than carbon. Potassium, however, readily decomposes this gas, by +absorbing its oxygen, as I shall show you. This retort is filled with +carbonic acid gas.—I will put a small piece of potassium in +it; but for this combustion a slight elevation of temperature is +required, for which purpose I shall hold the retort over the lamp.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now it has taken fire, and burns with violence! It has burst the +retort.</p> + +<span class="pagenum">361</span> +<a name="conver1.page361" id="conver1.page361"> </a> +<p class="speaker">MRS. B.</p> + +<p>Here is the piece of regenerated potash; can you tell me why it is +become so black?</p> + +<p class="speaker">EMILY.</p> + +<p>No doubt it is blackened by the carbon, which, when its oxygen +entered into combination with the potassium, was deposited on its +surface.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are right. This metal is perfectly fluid at the temperature of +one hundred degrees; at fifty degrees it is solid, but soft and +malleable; at thirty-two degrees it is hard and brittle, and its +fracture exhibits an appearance of confused crystallization. It is +scarcely more than half as heavy as water; its specific gravity being +about six when water is reckoned at ten; so that this metal is actually +lighter than any known fluid, even than ether.</p> + +<p>Potassium combines with sulphur and phosphorus, forming sulphurets +and phosphurets; it likewise forms alloys with several metals, and +amalgamates with mercury.</p> + +<p class="speaker">EMILY.</p> + +<p>But can a sufficient quantity of potassium be obtained, by means of +the Voltaic battery, to admit of all its properties and relations to +other bodies being satisfactorily ascertained?</p> + +<span class="pagenum">362</span> +<a name="conver1.page362" id="conver1.page362"> </a> +<p class="speaker">MRS. B.</p> + +<p>Not easily; but I must not neglect to inform you that a method of +obtaining this metal in considerable quantities has since been +discovered. Two eminent French chemists, Thenard and <ins class="correction" title="name generally hyphenated as ‘Gay-Lussac’">Gay +Lussac</ins>, stimulated by the triumph which Sir H. Davy had obtained, +attempted to separate potassium from its combination with oxygen, by +common chemical means, and without the aid of electricity. They caused +red hot potash in a state of fusion to filter through iron turnings in +an iron tube, heated to whiteness. Their experiment was crowned with the +most complete success; more potassium was obtained by this single +operation, that could have been collected in many weeks by the most +diligent use of the Voltaic battery.</p> + +<p class="speaker">EMILY.</p> + +<p>In this experiment, I suppose, the oxygen quitted its combination +with the potassium to unite with the iron turnings?</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so; and the potassium was thus obtained in its simple state. +From that time it has become a most convenient and powerful instrument +of deoxygenation in chemical experiments. This important improvement, +engrafted on Sir H. Davy’s previous discoveries, served but to add to +his glory, since the facts which he had established, +<span class="pagenum">363</span> +<a name="conver1.page363" id="conver1.page363"> </a> +when possessed of only a few atoms of this curious substance, and the +accuracy of his analytical statements, were all confirmed when an +opportunity occurred of repeating his experiments upon this substance, +which can now be obtained in unlimited quantities.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a satisfaction Sir H. Davy must have felt, when by an effort of +genius he succeeded in bringing to light and actually giving existence, +to these curious bodies, which without him might perhaps have ever +remained concealed from our view!</p> + +<p class="speaker">MRS. B.</p> + +<p>The next substance which Sir H. Davy submitted to the influence of +the Voltaic battery was <i>Soda</i>, the other fixed alkali, which +yielded to the same powers of decomposition; from this alkali too, +a metallic substance was obtained, very analogous in its properties +to that which had been discovered in potash; Sir H. Davy has called it +<span class="smallroman">SODIUM</span>. It is rather heavier than +potassium, though considerably lighter than water; it is not so easily +fusible as potassium.</p> + +<p>Encouraged by these extraordinary results, Sir H. Davy next performed +a series of beautiful experiments on <i>Ammonia</i>, or the volatile +alkali, which, from analogy, he was led to suspect might also contain +oxygen. This he soon ascertained to be the +<span class="pagenum">364</span> +<a name="conver1.page364" id="conver1.page364"> </a> +fact, but he has not yet succeeded in obtaining the basis of ammonia in +a separate state; it is from analogy, and from the power which the +volatile alkali has, in its gaseous form, to oxydate iron, and also from +the amalgams which can be obtained from ammonia by various processes, +that the proofs of that alkali being also a metallic oxyd are +deduced.</p> + +<p>Thus, then, the three alkalies, two of which had always been +considered as simple bodies, have now lost all claim to that title, and +I have accordingly classed the alkalies amongst the compounds, whose +properties we shall treat of in a future conversation.</p> + +<p class="speaker">EMILY.</p> + +<p>What are the other newly discovered metals which you have alluded to +in your list of simple bodies?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are the metals of the earths which became next the object of Sir +H. Davy’s researches; these bodies had never yet been decomposed, though +they were strongly suspected not only of being compounds, but of being +metallic oxyds. From the circumstance of their incombustibility it was +conjectured, with some plausibility, that they might possibly be bodies +that had been already burnt.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And metals, when oxydated, become, to all appearance, a kind of +earthy substance.</p> + +<span class="pagenum">365</span> +<a name="conver1.page365" id="conver1.page365"> </a> +<p class="speaker">MRS. B.</p> + +<p>They have, besides, several features of resemblance with metallic +oxyds; Sir H. Davy had therefore great reason to be sanguine in his +expectations of decomposing them, and he was not disappointed. He could +not, however, succeed in obtaining the basis of the earths in a pure +separate state; but metallic alloys were formed with other metals, which +sufficiently proved the existence of the metallic basis of the +earths.</p> + +<p>The last class of new metallic bodies which Sir H. Davy discovered +was obtained from the three undecompounded acids, the boracic, the +fluoric, and the muriatic acids; but as you are entirely unacquainted +with these bodies, I shall reserve the account of their +decomposition till we come to treat of their properties as acids.</p> + +<p>Thus in the course of two years, by the unparalleled exertions of a +single individual, chemical science has assumed a new aspect. Bodies +have been brought to light which the human eye never before beheld, and +which might have remained eternally concealed under their impenetrable +disguise.</p> + +<p>It is impossible at the present period to appreciate to their full +extent the consequences which science or the arts may derive from these +discoveries; we may, however, anticipate the most important results.</p> + +<span class="pagenum">366</span> +<a name="conver1.page366" id="conver1.page366"> </a> +<p>In chemical analysis we are now in possession of more energetic +agents of decomposition than were ever before known.</p> + +<p>In geology new views are opened, which will probably operate a +revolution in that obscure and difficult science. It is already proved +that all the earths, and, in fact, the solid surface of this globe, are +metallic bodies mineralized by oxygen, and as our planet has been +calculated to be considerably more dense upon the whole than on the +surface, it is reasonable to suppose that the interior part is composed +of a metallic mass, the surface of which only has been mineralized by +the atmosphere.</p> + +<p>The eruptions of volcanos, those stupendous problems of nature, admit +now of an easy explanation. For if the bowels of the earth are the grand +recess of these newly discovered inflammable bodies, whenever water +penetrates into them, combustions and explosions must take place; and it +is remarkable that the lava which is thrown out, is the very kind of +substance which might be expected to result from these combustions.</p> + +<p>I must now take my leave of you; we have had a very long conversation +to-day, and I hope you will be able to recollect what you have learnt. +At our next interview we shall enter on a new subject.</p> + +<p class="footnote"> +<a name="note20" id="note20" href="#tag20">*</a> +By a process analogous to that described, <a href="#page155">page +155</a>. of this volume.</p> + +<h5>END OF THE FIRST VOLUME.</h5> + +</div> <!-- end div maintext --> + +<h6>Printed by A. Strahan,<br> +Printers-Street, London.</h6> + +<hr><hr> + +<h1 class="two">CONVERSATIONS</h1> +<h1 class="seven">ON</h1> +<h1 class="one extended">CHEMISTRY;</h1> +<h1 class="seven">IN WHICH</h1> +<h1 class="three">THE ELEMENTS OF THAT SCIENCE</h1> +<h1 class="seven">ARE</h1> +<h1 class="five"><i>FAMILIARLY EXPLAINED</i></h1> +<h1 class="seven">AND</h1> +<h1 class="five">ILLUSTRATED BY EXPERIMENTS.</h1> + +<hr class="fat"> +<hr class="thin"> + +<h1 class="six">IN TWO VOLUMES.</h1> + +<hr class="thin"> +<hr class="fat"> + +<h1 class="six"><i>The Fifth Edition, revised, corrected, and +considerably enlarged.</i><br> + </h1> + +<h1 class="four">VOL. II.</h1> +<h1 class="five">ON COMPOUND BODIES.</h1> + +<p class="illustration"> +<img src="images/dec_line.png" width="91" height="8" +alt="----"> +</p> + +<h1 class="five"><i>LONDON:</i></h1> +<h1 class="six">PRINTED FOR LONGMAN, HURST, REES, ORME, AND BROWN,<br> +PATERNOSTER-ROW.</h1> +<h1 class="five">1817.</h1> + +<p> <br> </p> + +<span class="pagenum">v</span> + +<h3 class="three"><a name="contents2" id="contents2"> +CONTENTS</a></h3> +<h3 class="seven">OF</h3> +<h3 class="four"><i>THE SECOND VOLUME</i>.</h3> + +<hr class="fat"> +<hr class="thin"> + +<h3 class="five">ON COMPOUND BODIES.</h3> + +<hr class="thin"> +<hr class="fat"> + +<table class="toc" summary="table of contents"> +<tr> +<td class="chapnum"><a href="#convXIII"> +CONVERSATION XIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname bottom">ON THE ATTRACTION OF COMPOSITION.</td> +<td class="number">Page<br> +1</td> +</tr> +<tr> +<td><p><span class="firstword"><span class="firstletter">O</span>f</span> the laws which regulate the Phenomena of +the Attraction of Composition.—1. It takes place only between +Bodies of a different Nature.—2. Between the most minute +Particles only.—3. Between 2, 3, 4, or more Bodies.—Of +Compound or Neutral Salts.—4. Produces a Change of +Temperature.—5. The Properties which characterise Bodies in +their separate State, destroyed by Combination.—6. The Force +of Attraction estimated by that which is required by the Separation of +the Constituents.—7. Bodies have amongst themselves different +Degrees of Attraction.—Of simple elective and double elective +Attractions.—Of quiescent and divellent Forces.—Law of +definite Proportions.—Decomposition of Salts by Voltaic +Electricity.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"> +<span class="pagenum">vi</span> +<a href="#convXIV"> +CONVERSATION XIV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ALKALIES.</td> +<td class="number">19</td> +</tr> +<tr> +<td><p>Of the Composition and general Properties of the +Alkalies.—Of Potash.—Manner of preparing +it.—Pearlash.—Soap.—Carbonat of Potash.—Chemical +Nomenclature.—Solution of Potash.—Of Glass.—Of Nitrat +of Potash or Saltpetre.—Effect of Alkalies on Vegetable +Colours.—Of Soda.—Of Ammonia or Volatile +Alkali.—Muriat of Ammonia.—Ammoniacal Gas.—Composition +of Ammonia.—Hartshorn <ins class="mycorr" title="text reads ‘ad’">and</ins> Sal Volatile.—Combustion of Ammoniacal +Gas.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXV"> +CONVERSATION XV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON EARTHS.</td> +<td class="number">44</td> +</tr> +<tr> +<td><p>Composition of the Earths.—Of their +Incombustibility.—Form the Basis of all Minerals.—Their +Alkaline Properties.—Silex; its Properties and Uses in the +Arts.—Alumine; its Uses in Pottery, &c.—Alkaline +Earths.—Barytes.—Lime; its extensive chemical Properties and +Uses in the Arts.—Magnesia.—Strontian.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXVI"> +CONVERSATION XVI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ACIDS.</td> +<td class="number">69</td> +</tr> +<tr> +<td><p>Nomenclature of the Acids.—Of the Classification of +Acids.—1st Class—Acids of simple and known Radicals, or +Mineral Acids.—2d Class—Acids of double Radicals, or +Vegetable Acids.—3d Class—Acids of triple Radicals or +Animal Acids.—Of the Decomposition of Acids of the 1st Class by +Combustible bodies.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"> +<span class="pagenum">vii</span> +<a href="#convXVII"> +CONVERSATION XVII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname long"><p>OF THE SULPHURIC AND PHOSPHORIC ACIDS: +OR, THE COMBINATIONS OF OXYGEN WITH SULPHUR AND WITH PHOSPHORUS; AND OF +THE SULPHATS AND PHOSPHATS.</p></td> +<td class="number">80</td> +</tr> +<tr> +<td><p>Of the Sulphuric Acid.—Combustion of Animal or Vegetable +Bodies by this Acid.—Method of preparing it.—The Sulphurous +Acid obtained in the Form of Gas.—May be obtained from Sulphuric +Acid.—May be reduced to Sulphur.—Is absorbable by +Water.—Destroys Vegetable Colours.—Oxyd of Sulphur.—Of +Salts in general.—Sulphats.—Sulphat of Potash, or Sal +Polychrest.—Cold produced by the melting of Salts.—Sulphat +of Soda, or Glauber’s Salt.—Heat evolved during the Formation of +Salts.—Crystallisation of Salts.—Water of +Crystallisation.—Efflorescence and Deliquescence of +Salts.—Sulphat of Lime, Gypsum or Plaister of Paris.—Sulphat +of Magnesia.—Sulphat of Alumine, or Alum.—Sulphat of +Iron.—Of Ink.—Of the Phosphoric and Phosphorous +Acids.—Phosphorus obtained from Bones.—Phosphat of +Lime.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXVIII"> +CONVERSATION XVIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname long"><p>OF THE NITRIC AND CARBONIC ACIDS: OR THE +COMBINATION OF OXYGEN WITH NITROGEN AND WITH CARBON; AND OF THE NITRATS +AND CARBONATS.</p></td> +<td class="number">100</td> +</tr> +<tr> +<td><p>Nitrogen susceptible of various Degrees of +Acidification.—Of the Nitric Acid.—Its Nature and +Composition discovered by Mr. Cavendish.—Obtained from Nitrat +of Potash.—Aqua Fortis.—Nitric Acid may be converted +<span class="pagenum">viii</span> +into Nitrous Acid.—Nitric Oxyd Gas.—Its Conversion into +Nitrous Acid Gas.—Used as an Eudiometrical Test.—Gaseous +Oxyd of Nitrogen, or exhilarating Gas, obtained from Nitrat of +Ammonia.—Its singular Effects on being +respired.—Nitrats.—Of Nitrat of Potash, Nitre or +Saltpetre.—Of Gunpowder.—Causes of +Detonation.—Decomposition of +Nitre.—Deflagration.—Nitrat of Ammonia.—Nitrat of +Silver.—Of the Carbonic Acid.—Formed by the Combustion of +Carbon.—Constitutes a component Part of the +Atmosphere.—Exhaled in some Caverns.—Grotto del +Cane.—Great Weight of this Gas.—Produced from calcareous +Stones by Sulphuric Acid.—Deleterious Effects of this Gas when +respired.—Sources which keep up a Supply of this Gas in the +Atmosphere.—Its Effects on Vegetation.—Of the Carbonats of +Lime; Marble, Chalk, Shells, Spars, and calcareous Stones.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXIX"> +CONVERSATION XIX.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED +MURIATIC ACIDS; AND ON MURIATS.</td> +<td class="number">131</td> +</tr> +<tr> +<td><p>On the Boracic Acid.—Its Decomposition by Sir H. +Davy.—Its Basis Boracium.—Its Recomposition.—Its Uses +in the Arts.—Borax or Borat of Soda.—Of the Fluoric +Acid.—Obtained from Fluor; corrodes Siliceous Earth; its supposed +Composition.—Fluorine; its supposed Basis.—Of the Muriatic +Acid.—Obtained from Muriats.—Its gaseous Form.—Is +absorbable by Water.—Its Decomposition.—Is susceptible of a +stronger Degree of Oxygenation.—Oxygenated Muriatic +Acid.—Its gaseous Form and other Properties.—Combustion of +Bodies in this Gas.—It dissolves Gold.—Composition +<span class="pagenum">ix</span> +of Aqua Regia.—Oxygenated Muriatic Acid destroys all +Colours.—Sir H. Davy’s Theory of the Nature of Muriatic and +Oxymuriatic Acid.—Chlorine.—Used for Bleaching and for +Fumigations.—Its offensive Smell, +&c.—Muriats.—Muriat of Soda, or common +Salt.—Muriat of Ammonia.—Oxygenated Muriat of +Potash.—Detonates with Sulphur, Phosphorus, +&c.—Experiment of burning Phosphorus under Water by means of +this Salt and of Sulphuric Acid.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXX"> +CONVERSATION XX.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE NATURE AND COMPOSITION OF VEGETABLES.</td> +<td class="number">162</td> +</tr> +<tr> +<td><p>Of organised Bodies.—Of the Functions of +Vegetables.—Of the Elements of Vegetables.—Of the Materials +of Vegetables.—Analysis of Vegetables.—Of +Sap.—Mucilage, or Gum.—Sugar.—Manna, and +Honey.—Gluten.—Vegetable Oils.—Fixed Oils, Linseed, +Nut, and Olive Oils.—Volatile Oils, forming Essences and +Perfumes.—Camphor.—Resins and Varnishes.—Pitch, Tar, +Copal, Mastic, &c.—Gum Resins.—Myrrh, Assafœtida, +&c.—Caoutchouc, or Gum Elastic.—Extractive colouring +Matter; its Use in the Arts of Dyeing and Painting.—Tannin; its +Use in the Art of preparing Leather.—Woody Fibre.—Vegetable +Acids.—The Alkalies and Salts contained in Vegetables.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXXI"> +CONVERSATION XXI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE DECOMPOSITION OF VEGETABLES.</td> +<td class="number">202</td> +</tr> +<tr> +<td><p>Of Fermentation in general.—Of the Saccharine Fermentation, +the Product of which is Sugar.—Of the Vinous Fermentation, the +Product of which is Wine. +<span class="pagenum">x</span> +—Alcohol, or Spirit of Wine.—Analysis of Wine by +Distillation.—Of Brandy, Rum, Arrack, Gin, &c.—Tartrit +of Potash, or Cream of Tartar.—Liqueurs.—Chemical Properties +of Alcohol.—Its Combustion.—Of Ether.—Of the Acetous +Fermentation, the Product of which is Vinegar.—Fermentation of +Bread.—Of the Putrid Fermentation, which reduces Vegetables to +their Elements.—Spontaneous Succession of these +Fermentations.—Of Vegetables said to be petrified.—Of +Bitumens: Naphtha, Asphaltum, Jet, Coal, Succin, or Yellow +Amber.—Of Fossil Wood, Peat, and Turf.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXXII"> +CONVERSATION XXII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">HISTORY OF VEGETATION.</td> +<td class="number">243</td> +</tr> +<tr> +<td><p>Connexion between the Vegetable and Animal Kingdoms.—Of +Manures.—Of Agriculture.—Inexhaustible Sources of Materials +for the Purposes of Agriculture.—Of sowing Seed.—Germination +of the Seed.—Function of the Leaves of Plants.—Effects of +Light and Air on Vegetation.—Effects of Water on +Vegetation.—Effects of Vegetation on the +Atmosphere.—Formation of Vegetable Materials by the Organs of +Plants.—Vegetable Heat.—Of the Organs of Plants.—Of +the Bark, consisting of Epidermis, Parenchyma, and Cortical +Layers.—Of Alburnum, or Wood.—Leaves, Flowers, and +Seeds.—Effects of the Season on Vegetation.—Vegetation of +Evergreens in Winter.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXXIII"> +CONVERSATION XXIII.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE COMPOSITION OF ANIMALS.</td> +<td class="number">276</td> +</tr> +<tr> +<td><p>Elements of Animals.—Of the principal Materials of Animals, +viz.—Gelatine, Albumen, Fibrine, Mucus. +<span class="pagenum">xi</span> +—Of Animal Acids.—Of Animal Colours, Prussian Blue, Carmine, +and Ivory Black.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXXIV"> +CONVERSATION XXIV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON THE ANIMAL ECONOMY.</td> +<td class="number">297</td> +</tr> +<tr> +<td><p>Of the principal Animal Organs.—Of Bones, Teeth, Horns, +Ligaments, and Cartilage.—Of the Muscles, constituting the Organs +of Motion.—Of the Vascular System, for the Conveyance of +Fluids.—Of the Glands, for the Secretion of Fluids.—Of the +Nerves, constituting the Organs of Sensation.—Of the Cellular +Substance which connects the several Organs.—Of the Skin.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXXV"> +CONVERSATION XXV.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ANIMALISATION, NUTRITION, AND +RESPIRATION.</td> +<td class="number">314</td> +</tr> +<tr> +<td><p>Digestion.—Solvent Power of the Gastric +Juice.—Formation of a Chyle.—Its Assimilation, or Conversion +into Blood.—Of Respiration.—Mechanical Process of +Respiration.—Chemical Process of Respiration.—Of the +Circulation of the Blood.—Of the Functions of the Arteries, the +Veins, and the Heart.—Of the Lungs.—Effects of Respiration +on the Blood.</p></td> +<td></td> +</tr> + +<tr> +<td class="chapnum"><a href="#convXXVI"> +CONVERSATION XXVI.</a></td> +<td></td> +</tr> +<tr> +<td class="chapname">ON ANIMAL HEAT; AND OF VARIOUS ANIMAL +PRODUCTS.</td> +<td class="number">336</td> +</tr> +<tr> +<td><p>Of the Analogy of Combustion and Respiration.—Animal Heat +evolved in the Lungs.—Animal Heat evolved in the +Circulation.—Heat produced by Fever.—Perspiration. +<span class="pagenum">xii</span> +—Heat produced by Exercise.—Equal Temperature of Animals at +all Seasons.—Power of the Animal Body to resist the Effects of +Heat.—Cold produced by Perspiration.—Respiration of Fish and +of Birds.—Effects of Respiration on Muscular Strength.—Of +several Animal Products, viz. Milk, Butter, and Cheese; Spermaceti; +Ambergris; Wax; Lac; Silk; Musk; Civet; Castor.—Of the putrid +Fermentation.—Conclusion.</p></td> +<td></td> +</tr> +</table> + +<div class="page"> + +<h2 class="two">CONVERSATIONS</h2> + +<h2 class="seven">ON</h2> + +<h2 class="one extended">CHEMISTRY.</h2> + +</div> + +<hr class="thin"> +<hr class="fat"> + +<div class="maintext"> + +<a name="conver2.page1" id="conver2.page1"> </a> + +<h4><a name="convXIII" id="convXIII">CONVERSATION XIII.</a><br> +<span class="subhead">ON THE ATTRACTION OF COMPOSITION.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">H</span>aving</span> completed our examination of the +simple or elementary bodies, we are now to proceed to those of a +compound nature; but before we enter on this extensive subject, it will +be necessary to make you acquainted with the principal laws by which +chemical combinations are governed.</p> + +<p>You recollect, I hope, what we formerly said of the nature of the +attraction of composition, or chemical attraction, or affinity, as it is +also called?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, I think perfectly; it is the attraction that +<span class="pagenum">2</span> +<a name="conver2.page2" id="conver2.page2"> </a> +subsists between bodies of a different nature, which occasions them to +combine and form a compound, when they come in contact, and, according +to Sir H. Davy’s opinion, this effect is produced by the attraction of +the opposite electricities, which prevail in bodies of different +kinds.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well; your definition comprehends the first law of chemical +attraction, which is, that <i>it takes place only between bodies of a +different nature</i>; as, for instance, between an acid and an alkali; +between oxygen and a metal, &c.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That we understand of course; for the attraction between particles of +a similar nature is that of aggregation, or cohesion, which is +independent of any chemical power.</p> + +<p class="speaker">MRS. B.</p> + +<p>The 2d law of chemical attraction is, that <i>it takes place only +between the most minute particles of bodies</i>; therefore, the more you +divide the particles of the bodies to be combined, the more readily they +act upon each other.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is again a circumstance which we might +<span class="pagenum">3</span> +<a name="conver2.page3" id="conver2.page3"> </a> +have supposed, for the finer the particles of the two substances are, +the more easily and perfectly they will come in contact with each other, +which must greatly facilitate their union. It was for this purpose, you +said, that you used iron filings, in preference to wires or pieces of +iron, for the decomposition of water.</p> + +<p class="speaker">MRS. B.</p> + +<p>It was once supposed that no mechanical power could divide bodies +into particles sufficiently minute for them to act on each other; and +that, in order to produce the extreme division requisite for a chemical +action, one, if not both of the bodies, should be in a fluid state. +There are, however, a few instances in which two solid bodies, very +finely pulverized, exert a chemical action on one another; but such +exceptions to the general rule are very rare indeed.</p> + +<p class="speaker">EMILY.</p> + +<p>In all the combinations that we have hitherto seen, one of the +constituents has, I believe, been either liquid or aëriform. In +combustions, for instance, the oxygen is taken from the atmosphere, in +which it existed in the state of gas; and whenever we have seen acids +combine with metals or with alkalies, they were either in a liquid or an +aëriform state.</p> + +<span class="pagenum">4</span> +<a name="conver2.page4" id="conver2.page4"> </a> +<p class="speaker">MRS. B.</p> + +<p>The 3d law of chemical attraction is, that <i>it can take place +between two, three, four, or even a greater number of bodies</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Oxyds and acids are bodies composed of two constituents; but I +recollect no instance of the combination of a greater number of +principles.</p> + +<p class="speaker">MRS. B.</p> + +<p>The compound salts, formed by the union of the metals with acids, are +composed of three principles. And there are salts formed by the +combination of the alkalies with the earths which are of a similar +description.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Are they of the same kind as the metallic salts?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; they are very analogous in their nature, although different in +many of their properties.</p> + +<p>A methodical nomenclature, similar to that of the acids, has been +adopted for the compound salts. Each individual salt derives its name +from its constituent parts, so that every name implies a knowledge of +the composition of the salt.</p> + +<p>The three alkalies, the alkaline earths, and the +<span class="pagenum">5</span> +<a name="conver2.page5" id="conver2.page5"> </a> +metals, are called <i>salifiable bases</i> or <i>radicals</i>; and the +acids, <i>salifying principles</i>. The name of each salt is composed +both of that of the acid and the salifiable base; and it terminates in +<i>at</i> or <i>it</i>, according to the degree of the oxygenation of +the acid. Thus, for instance, all those salts which are formed by the +combination of the sulphuric acid with any of the salifiable bases are +called <i>sulphats</i>, and the name of the radical is added for the +specific distinction of the salt; if it be potash, it will compose a +<i>sulphat of potash</i>; if ammonia, <i>sulphat of +ammonia</i>, &c.</p> + +<p class="speaker">EMILY.</p> + +<p>The crystals which we obtained from the combination of iron and +sulphuric acid were therefore <i>sulphat of iron</i>?</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely; and those which we prepared by dissolving copper in nitric +acid, <i>nitrat of copper</i>, and so on.—But this is not all; if +the salt be formed by that class of acids which ends in <i>ous</i>, +(which you know indicates a less degree of oxygenation,) the termination +of the name of the salt will be in <i>it</i>, as <i>sulphit of +potash</i>, <i>sulphit of ammonia</i>, &c.</p> + +<p class="speaker">EMILY.</p> + +<p>There must be an immense number of compound +<span class="pagenum">6</span> +<a name="conver2.page6" id="conver2.page6"> </a> +salts, since there is so great a variety of salifiable radicals, as well +as of salifying principles.</p> + +<p class="speaker">MRS. B.</p> + +<p>Their real number cannot be ascertained, since it increases every +day. But we must not proceed further in the investigation of the +compound salts, until we have completed the examination of the nature of +the ingredients of which they are composed.</p> + +<p>The 4th law of chemical attraction is, that <i>a change of +temperature always takes place at the moment of combination</i>. This +arises from the extrication of the two electricities in the form of +caloric, which takes place when bodies unite; and also sometimes in part +from a change of capacity of the bodies for heat, which always takes +place when the combination is attended with an increase of density, but +more especially when the compound passes from the liquid to the solid +form. I shall now show you a striking instance of a change of +temperature from chemical union, merely by pouring some nitrous acid on +this small quantity of oil of turpentine—the oil will instantly +combine with the oxygen of the acid, and produce a considerable change +of temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a blaze! The temperature of the oil and +<span class="pagenum">7</span> +<a name="conver2.page7" id="conver2.page7"> </a> +the acid must be greatly raised, indeed, to produce such a violent +combustion.</p> + +<p class="speaker">MRS. B.</p> + +<p>There is, however, a peculiarity in this combustion, which is, that +the oxygen, instead of being derived from the atmosphere alone, is +principally supplied by the acid itself.</p> + +<p class="speaker">EMILY.</p> + +<p>And are not all combustions instances of the change of temperature +produced by the chemical combination of two bodies?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; when oxygen loses its gaseous form, in order to combine +with a solid body, it becomes condensed, and the caloric evolved +produces the elevation of temperature. The specific gravity of bodies is +at the same time altered by chemical combination; for in consequence of +a change of capacity for heat, a change of density must be +produced.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That was the case with the sulphuric acid and water, which, by being +mixed together, gave out a great deal of heat, and increased in +density.</p> + +<span class="pagenum">8</span> +<a name="conver2.page8" id="conver2.page8"> </a> +<p class="speaker">MRS. B.</p> + +<p>The 5th law of chemical attraction is, that <i>the properties which +characterise bodies, when separate, are altered or destroyed by their +combination</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Certainly; what, for instance, can be so different from water as the +hydrogen and oxygen gases?</p> + +<p class="speaker">EMILY.</p> + +<p>Or what more unlike sulphat of iron than iron or sulphuric acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Every chemical combination is an illustration of this rule. But let +us proceed—</p> + +<p>The 6th law is, that <i>the force of chemical affinity between the +constituents of a body is estimated by that which is required for their +separation</i>. This force is not always proportional to the facility +with which bodies unite; for manganese, for instance, which, you know, +is so much disposed to unite with oxygen that it is never found in a +metallic state, yields it more easily than any other metal.</p> + +<p class="speaker">EMILY.</p> + +<p>But, Mrs. B., you speak of estimating the force of attraction between +bodies, by the force required +<span class="pagenum">9</span> +<a name="conver2.page9" id="conver2.page9"> </a> +to separate them; how can you measure these forces?</p> + +<p class="speaker">MRS. B.</p> + +<p>They cannot be precisely measured, but they are comparatively +ascertained by experiment, and can be represented by numbers which +express the relative degrees of attraction.</p> + +<p>The 7th law is, that <i>bodies have amongst themselves different +degrees of attraction</i>. Upon this law, (which you may have discovered +yourselves long since,) the whole science of chemistry depends; for it +is by means of the various degrees of affinity which bodies have for +each other, that all the chemical compositions and decompositions are +effected. Every chemical fact or experiment is an instance of the same +kind; and whenever the decomposition of a body is performed by the +addition of any single new substance, it is said to be effected by +<i>simple elective attractions</i>. But it often happens that no simple +substance will decompose a body, and that, in order to effect this, you +must offer to the compound a body which is itself composed of two, or +sometimes three principles, which would not, each separately, perform +the decomposition. In this case there are two new compounds formed in +consequence of a reciprocal decomposition and recomposition. All +instances of this kind are called <i>double elective +attractions</i>.</p> + +<span class="pagenum">10</span> +<a name="conver2.page10" id="conver2.page10"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I confess I do not understand this clearly.</p> + +<p class="speaker">MRS. B.</p> + +<p>You will easily comprehend it by the assistance of this diagram, in +which the reciprocal forces of attraction are represented by +numbers:</p> + +<p class="illustration"> +<img src="images/diagram.png" width="376" height="369" +alt="see endnote for text version"> +</p> + +<p>We here suppose that we are to decompose sulphat of soda; that is, to +separate the acid from +<span class="pagenum">11</span> +<a name="conver2.page11" id="conver2.page11"> </a> +the alkali; if, for this purpose, we add some lime, in order to make it +combine with the acid, we shall fail in our attempt, because the soda +and the sulphuric acid attract each other by a force which is superior, +and (by way of supposition) is represented by the number 8; while +the lime tends to unite with this acid by an affinity equal only to the +number 6. It is plain, therefore, that the sulphat of soda will not +be decomposed, since a force equal to 8 cannot be overcome by a force +equal only to 6.</p> + +<p class="speaker">CAROLINE.</p> + +<p>So far, this appears very clear.</p> + +<p class="illustration"> +<img src="images/diagram1.png" width="233" height="263" +alt="part of larger diagram"> + +<img src="images/diagram2.png" width="233" height="266" +alt="part of larger diagram"> +</p> + +<p class="speaker">MRS. B.</p> + +<p>If, on the other hand, we endeavour to decompose this salt by nitric +acid, which tends to combine with soda, we shall be equally +unsuccessful, as nitric acid tends to unite with the alkali by a force +equal only to 7.</p> + +<p>In neither of these cases of simple elective attraction, therefore, +can we accomplish our purpose. But let us previously combine together +the lime and nitric acid, so as to form a nitrat of lime, +a compound salt, the constituents of which are united by a power +equal to 4. If then we present this compound to the sulphat of soda, +a decomposition will ensue, because the sum of the forces +<span class="pagenum">12</span> +<a name="conver2.page12" id="conver2.page12"> </a> +which tend to preserve the two salts in their actual state is not equal +to that of the forces which tend to decompose them, and to form new +combinations. The nitric acid, therefore, will combine with the soda, +and the sulphuric acid with the lime.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I understand you now very well. This double effect takes place +because the numbers 8 and 4, which represent the degrees of attraction +of the constituents of the two original salts, make a sum less than the +numbers 7 and 6, which represent the degrees of attraction of the two +new compounds that will in consequence be formed.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely so.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what is the meaning of <i>quiescent</i> and <i>divellent</i> +forces, which are written in the diagram?</p> + +<p class="speaker">MRS. B.</p> + +<p>Quiescent forces are those which tend to preserve compounds in a +state of rest, or such as they actually are: divellent forces, those +which tend to destroy that state of combination, and to form new +compounds.</p> + +<p>These are the principal circumstances relative to the doctrine of +chemical attractions, which +<span class="pagenum">13</span> +<a name="conver2.page13" id="conver2.page13"> </a> +have been laid down as rules by modern chemists; a few others might +be mentioned respecting the same theory, but of less importance, and +such as would take us too far from our plan. I should, however, not +omit to mention that Mr. Berthollet, a celebrated French chemist, +has questioned the uniform operation of elective attraction, and has +advanced the opinion, that, in chemical combinations, the changes which +take place depend not only upon the affinities, but also, in some +degree, on the respective quantities of the substances concerned, on the +heat applied during the process, and some other circumstances.</p> + +<p class="speaker">CAROLINE.</p> + +<p>In that case, I suppose, there would hardly be two compounds exactly +similar, though composed of the same materials?</p> + +<p class="speaker">MRS. B.</p> + +<p>On the contrary, it is found that a remarkable uniformity prevails, +as to proportions, between the ingredients of bodies of similar +composition. Thus water, as you may recollect to have seen in a former +conversation, is composed of two volumes of hydrogen gas to one of +oxygen, and this is always found to be precisely the proportion of its +constituents, from whatever source the water be derived. The same +uniformity prevails with regard to the various salts; the acid and +alkali, in +<span class="pagenum">14</span> +<a name="conver2.page14" id="conver2.page14"> </a> +each kind of salt, being always found to combine in the same +proportions. Sometimes, it is true, the same acid, and the same alkali, +are capable of making two distinct kinds of salts; but in all these +cases it is found that one of the salts contains just twice, or in some +instances, thrice as much acid, or alkali, as the other.</p> + +<p class="speaker">EMILY.</p> + +<p>If the proportions in which bodies combine are so constant and so +well defined, how can Mr. Berthollet’s remark be reconciled with this +uniform system of combination?</p> + +<p class="speaker">MRS. B.</p> + +<p>Great as that philosopher’s authority is in chemistry, it is now +generally supposed that his doubts on this subject were in a great +degree groundless, and that the exceptions he has observed in the laws +of definite proportions, have been only apparent, and may be accounted +for consistently with those laws.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, Mrs. B., can you decompose a salt by means of electricity, in +the same way as we decompose water?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; and I am glad this question occurred to you, because it +gives me an opportunity +<span class="pagenum">15</span> +<a name="conver2.page15" id="conver2.page15"> </a> +of showing you some very interesting experiments on the subject.</p> + +<p>If we dissolve a quantity, however small, of any salt in a glass of +water, and if we plunge into it the extremities of the wires which +proceed from the two ends of the Voltaic battery, the salt will be +gradually decomposed, the acid being attracted by the positive, and the +alkali by the negative wire.</p> + +<p class="speaker">EMILY.</p> + +<p>But how can you render that decomposition perceptible<ins class="correction" title="text has .">? </ins></p> + +<p class="speaker">MRS. B.</p> + +<p>By placing in contact with the extremities of each wire, in the +solution, pieces of paper stained with certain vegetable colours, which +are altered by the contact of an acid or an alkali. Thus this blue +vegetable preparation called litmus becomes red when touched by an acid; +and the juice of violets becomes green by the contact of an alkali.</p> + +<p>But the experiment can be made in a much more distinct manner, by +receiving the extremities of the wires into two different vessels, so +that the alkali shall appear in one vessel and the acid in the +other.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But then the Voltaic circle will not be completed; how can any effect +be produced?</p> + +<span class="pagenum">16</span> +<a name="conver2.page16" id="conver2.page16"> </a> +<p class="speaker">MRS. B.</p> + +<p>You are right; I ought to have added that the two vessels must be +connected together by some interposed substance capable of conducting +electricity. A piece of moistened cotton-wick answers this purpose +very well. You see that the cotton (<a class="smallcaps" href="#plateXIII">Plate XIII.</a> fig. 2. c.) has one end immersed +in one glass and the other end in the other, so as to establish a +communication between any fluids contained in them. We shall now put +into each of the glasses a little glauber salt, or sulphat of soda, +(which consists of an acid and an alkali,) and then we shall fill the +glasses with water, which will dissolve the salt. Let us now connect the +glasses by means of the wires (e, d,) with the two ends of the +battery, thus . . . .</p> + +<p class="figname"> +<a name="plateXIII" id="plateXIII">Plate XIII.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. II.</span> page 16.</p> + +<p class="illustration"> +<img src="images/plate13b_thumb.png" width="394" height="429" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 2. 3 & 4. Instances of Chemical decomposition by the +Voltaic Battery.</p> + +<p class="figlink"> +<a href="images/plate13_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>The wires are already giving out small bubbles; is this owing to the +decomposition of the salt?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; these are bubbles produced by the decomposition of the water, as +you saw in a former experiment. In order to render the separation of the +acid from the alkali visible, I pour into the glass (a), which +is connected with the positive wire, a few drops of a solution of +litmus, +<span class="pagenum">17</span> +<a name="conver2.page17" id="conver2.page17"> </a> +which the least quantity of acid turns red; and into the other +glass (b), which is connected with the negative wire, I pour a +few drops of the juice of violets . . . .</p> + +<p class="speaker">EMILY.</p> + +<p>The blue solution is already turning red all round the wire.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And the violet solution is beginning to turn green. This is indeed +very singular!</p> + +<p class="speaker">MRS. B.</p> + +<p>You will be still more astonished when we vary the experiment in this +manner:—These three glasses (fig. 3. f, g, h,) are, as +in the former instance, connected together by wetted cotton, but the +middle one alone contains a saline solution, the two others containing +only distilled water, coloured as before by vegetable infusions. Yet, on +making the connection with the battery, the alkali will appear in the +negative glass (h), and the acid in the positive glass (f), +though neither of them contained any saline matter.</p> + +<p class="speaker">EMILY.</p> + +<p>So that the acid and alkali must be conveyed right and left from the +central glass, into the +<span class="pagenum">18</span> +<a name="conver2.page18" id="conver2.page18"> </a> +other glasses, by means of the connecting moistened cotton?</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so; and you may render the experiment still more striking, by +putting into the central glass (k, fig. 3.) an alkaline +solution, the glauber salt being placed into the negative +glass (l), and the positive glass (i) containing only water. The +acid will be attracted by the positive wire (m), and will actually +appear in the vessel (i), after passing through the alkaline +solution (k), without combining with it, although, you know, acids +and alkalies are so much disposed to combine.—But this +conversation has already much exceeded our usual limits, and we cannot +enlarge more upon this interesting subject at present.</p> + + + + +<span class="pagenum">19</span> +<a name="conver2.page19" id="conver2.page19"> </a> +<h4><a name="convXIV" id="convXIV">CONVERSATION XIV.</a><br> +<span class="subhead">ON ALKALIES.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">H</span>aving</span> now given you some idea of the laws +by which chemical attractions are governed, we may proceed to the +examination of bodies which are formed in consequence of these +attractions.</p> + +<p>The first class of compounds that present themselves to our notice, +in our gradual ascent to the most complicated combinations, are bodies +composed of only two principles. The sulphurets, phosphurets, carburets, +&c. are of this description; but the most numerous and important of +these compounds are the combinations of oxygen with the various simple +substances with which it has a tendency to unite. Of these you have +already acquired some knowledge, but it will be necessary to enter into +further particulars respecting the nature and properties of those most +deserving our notice. Of this class are the <span class="smallroman">ALKALIES</span> +<span class="pagenum">20</span> +<a name="conver2.page20" id="conver2.page20"> </a> +and the <span class="smallroman">EARTHS</span>, which we shall +successively examine.</p> + +<p>We shall first take a view of the alkalies, of which there are three, +viz. <span class="smallroman">POTASH</span>, <span class="smallroman">SODA</span>, and <span class="smallroman">AMMONIA</span>. +The two first are called <i>fixed alkalies</i>, because they exist in a +solid form at the temperature of the atmosphere, and require a great +heat to be volatilised. They consist, as you already know, of metallic +bases combined with oxygen. In potash, the proportions are about +eighty-six parts of potassium to fourteen of oxygen; and in soda, +seventy-seven parts of sodium to twenty-three of oxygen. The third +alkali, ammonia, has been distinguished by the name of <i>volatile +alkali</i>, because its natural form is that of gas. Its composition is +of a more complicated nature, of which we shall speak hereafter.</p> + +<p>Some of the earths bear so strong a resemblance in their properties +to the alkalies, that it is difficult to know under which head to place +them. The celebrated French chemist, Fourcroy, has classed two of them +(barytes and strontites) with the alkalies; but as lime and magnesia +have almost an equal title to that rank, I think it better not to +separate them, and therefore have adopted the common method of classing +them with the earths, and of distinguishing them by the name of +<i>alkaline earths</i>.</p> + +<p>The general properties of alkalies are, <ins class="mycorr" title="text reads ‘on’">an</ins> acrid +<span class="pagenum">21</span> +<a name="conver2.page21" id="conver2.page21"> </a> +burning taste, a pungent smell, and a caustic action on the skin +and flesh.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I wonder they should be caustic, Mrs. B., since they contain so +little oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>Whatever substance has an affinity for any one of the constituents of +animal matter, sufficiently powerful to decompose it, is entitled to the +appellation of caustic. The alkalies, in their pure state, have a very +strong attraction for water, for hydrogen, and for carbon, which, you +know, are the constituent principles of oil, and it is chiefly by +absorbing these substances from animal matter that they effect its +decomposition; for, when diluted with a sufficient quantity of water, or +combined with any oily substance, they lose their causticity.</p> + +<p>But, to return to the general properties of alkalies—they +change, as we have already seen, the colour of syrup of violets, and +other blue vegetable infusions, to green; and have, in general, +a very great tendency to unite with acids, although the respective +qualities of these two classes of bodies form a remarkable contrast.</p> + +<p>We shall examine the result of the combination of acids and alkalies +more particularly hereafter. +<span class="pagenum">22</span> +<a name="conver2.page22" id="conver2.page22"> </a> +It will be sufficient at present to inform you, that whenever acids are +brought in contact with alkalies, or alkaline earths, they unite with a +remarkable eagerness, and form compounds perfectly different from either +of their constituents; these bodies are called <i>neutral</i> or +<i>compound salts</i>.</p> + +<p>The dry white powder which you see in this phial is pure caustic +<span class="smallroman">POTASH</span>; it is very difficult to +preserve it in this state, as it attracts, with extreme avidity, the +moisture from the atmosphere, and if the air were not perfectly +excluded, it would, in a very short time, be actually melted.</p> + +<p class="speaker">EMILY.</p> + +<p>It is then, I suppose, always found in a liquid state?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; it exists in nature in a great variety of forms and combinations, +but is never found in its pure separate state; it is combined with +carbonic acid, with which it exists in every part of the vegetable +kingdom, and is most commonly obtained from the ashes of vegetables, +which are the residue that remains after all the other parts have been +volatilised by combustion.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But you once said, that after all the volatile +<span class="pagenum">23</span> +<a name="conver2.page23" id="conver2.page23"> </a> +parts of a vegetable were evaporated, the substance that remained was +charcoal?</p> + +<p class="speaker">MRS. B.</p> + +<p>I am surprised that you should still confound the processes of +volatilisation and combustion. In order to procure charcoal, we +evaporate such parts as can be reduced to vapour by the operation of +heat alone; but when we <i>burn</i> the vegetable, we burn the carbon +also, and convert it into carbonic acid gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is true; I hope I shall make no more mistakes in my favourite +theory of combustion.</p> + +<p class="speaker">MRS. B.</p> + +<p>Potash derives its name from the <i>pots</i> in which the vegetables, +from which it was obtained, used formerly to be burnt; the alkali +remained mixed with the ashes at the bottom, and was thence called +potash.</p> + +<p class="speaker">EMILY.</p> + +<p>The ashes of a wood-fire, then, are potash, since they are vegetable +ashes?</p> + +<p class="speaker">MRS. B.</p> + +<p>They always contain more or less potash, but are very far from +consisting of that substance alone, as they are a mixture of various +earths and salts +<span class="pagenum">24</span> +<a name="conver2.page24" id="conver2.page24"> </a> +which remain after the combustion of vegetables, and from which it is +not easy to separate the alkali in its pure form. The process by which +potash is obtained, even in the imperfect state in which it is used in +the arts, is much more complicated than simple combustion. It was once +deemed impossible to separate it entirely from all foreign substances, +and it is only in chemical laboratories that it is to be met with in the +state of purity in which you find it in this phial. Wood-ashes are, +however, valuable for the alkali which they contain, and are used for +some purposes without any further preparation. Purified in a certain +degree, they make what is commonly called <i>pearlash</i>, which is of +great efficacy in taking out grease, in washing linen, &c.; for +potash combines readily with oil or fat, with which it forms a compound +well known to you under the name of <i>soap</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Really! Then I should think it would be better to wash all linen with +pearlash than with soap, as, in the latter case, the alkali being +already combined with oil, must be less efficacious in extracting +grease.</p> + +<p class="speaker">MRS. B.</p> + +<p>Its effect would be too powerful on fine linen, and would injure its +texture; pearlash is therefore only used for that which is of a strong +coarse +<span class="pagenum">25</span> +<a name="conver2.page25" id="conver2.page25"> </a> +kind. For the same reason you cannot wash your hands with plain potash; +but, when mixed with oil in the form of soap, it is soft as well as +cleansing, and is therefore much better adapted to the purpose.</p> + +<p>Caustic potash, as we already observed, acts on the skin, and animal +fibre, in virtue of its attraction for water and oil, and converts all +animal matter into a kind of saponaceous jelly.</p> + +<p class="speaker">EMILY.</p> + +<p>Are vegetables the only source from which potash can be derived?</p> + +<p class="speaker">MRS. B.</p> + +<p>No: for though far most abundant in vegetables, it is by no means +confined to that class of bodies, being found also on the surface of the +earth, mixed with various minerals, especially with earths and stones, +whence it is supposed to be conveyed into vegetables by the roots of the +plant. It is also met with, though in very small quantities, in some +animal substances. The most common state of potash is that of +<i>carbonat</i>; I suppose you understand what that is?</p> + +<p class="speaker">EMILY.</p> + +<p>I believe so; though I do not recollect that you ever mentioned the +word before. If I am not mistaken, +<span class="pagenum">26</span> +<a name="conver2.page26" id="conver2.page26"> </a> +it must be a compound salt, formed by the union of carbonic acid with +potash.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very true; you see how admirably the nomenclature of modern chemistry +is adapted to assist the memory; when you hear the name of a compound, +you necessarily learn what are its constituent parts; and when you are +acquainted with these constituents, you can immediately name the +compound which they form.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, how were bodies arranged and distinguished before this +nomenclature was introduced?</p> + +<p class="speaker">MRS. B.</p> + +<p>Chemistry was then a much more difficult study; for every substance +had an arbitrary name, which it derived either from the person who +discovered it, as <i>Glauber’s salts</i> for instance; or from some +other circumstance relative to it, though quite unconnected with its +real nature, as potash.</p> + +<p>These names have been retained for some of the simple bodies; for as +this class is not numerous, and therefore can easily be remembered, it +has not been thought necessary to change them.</p> + +<p class="speaker">EMILY.</p> + +<p>Yet I think it would have rendered the new nomenclature more complete +to have methodised +<span class="pagenum">27</span> +<a name="conver2.page27" id="conver2.page27"> </a> +the names of the elementary, as well as of the compound bodies, though +it could not have been done in the same manner. But the names of the +simple substances might have indicated their nature, or, at least, some +of their principal properties; and if, like the acids and compound +salts, all the simple bodies had a similar termination, they would have +been immediately known as such. So complete and regular a nomenclature +would, I think, have given a clearer and more comprehensive view of +chemistry than the present, which is a medley of the old and new +terms.</p> + +<p class="speaker">MRS. B.</p> + +<p>But you are not aware of the difficulty of introducing into science +an entire set of new terms; it obliges all the teachers and professors +to go to school again, and if some of the old names, that are least +exceptionable, were not left as an introduction to the new ones, few +people would have had industry and perseverance enough to submit to the +study of a completely new language; and the inferior classes of artists, +who can only act from habit and routine, would, at least for a time, +have felt material inconvenience from a total change of their habitual +terms. From these considerations, Lavoisier and his colleagues, who +invented the new nomenclature, thought it most prudent to leave a few +links of the old chain, in +<span class="pagenum">28</span> +<a name="conver2.page28" id="conver2.page28"> </a> +order to connect it with the new one. Besides, you may easily conceive +the inconvenience which might arise from giving a regular nomenclature +to substances, the simple nature of which is always uncertain; for the +new names might, perhaps, have proved to have been founded in error. +And, indeed, cautious as the inventors of the modern chemical language +have been, it has already been found necessary to modify it in many +respects. In those few cases, however, in which new terms have been +adopted to designate simple bodies, these names have been so contrived +as to indicate one of the chief properties of the body in question; this +is the case with oxygen, which, as I explained to you, signifies +generator of acids; and hydrogen generator of water. If all the +elementary bodies had a similar termination, as you propose, it would be +necessary to change the name of any that might hereafter be found of a +compound nature, which would be very inconvenient in this age of +discovery.</p> + +<p>But to return to the alkalies.—We shall now try to melt some of +this caustic potash in a little water, as a circumstance occurs during +its solution very worthy of observation.—Do you feel the heat that +is produced?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes, I do; but is not this directly contrary to +<span class="pagenum">29</span> +<a name="conver2.page29" id="conver2.page29"> </a> +our theory of latent heat, according to which <ins class="correction" +title="‘t’ invisible">heat</ins> is disengaged when fluids become +solid, and cold produced when solids are melted?</p> + +<p class="speaker">MRS. B.</p> + +<p>The latter is really the case in all solutions; and if the solution +of caustic alkalies seems to make an exception to the rule, it does not, +I believe, form any solid objection to the theory. The matter may +be explained thus: When water first comes in contact with the potash, it +produces an effect similar to the slaking of lime, that is, the water is +solidified in combining with the potash, and thus loses its latent heat; +this is the heat that you now feel, and which is, therefore, produced +not by the melting of the solid, but by the solidification of the fluid. +But when there is more water than the potash can absorb and solidify, +the latter then yields to the solvent power of the water; and if we do +not perceive the cold produced by its melting, it is because it is +counterbalanced by the heat previously disengaged.<a class="tag" name="tag21" id="tag21" href="#note21">*</a></p> + +<p>A very remarkable property of potash is the +<span class="pagenum">30</span> +<a name="conver2.page30" id="conver2.page30"> </a> +formation of glass by its fusion with siliceous earth. You are not yet +acquainted with this last substance, further than its being in the list +of simple bodies. It is sufficient, for the present, that you should +know that sand and flint are chiefly composed of it; alone, it is +infusible, but mixed with potash, it melts when exposed to the heat of a +furnace, combines with the alkali, and runs into glass.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Who would ever have supposed that the same substance which converts +transparent oil into such an opake body as soap, should transform that +opake substance, sand, into transparent glass!</p> + +<p class="speaker">MRS. B.</p> + +<p>The transparency, or opacity of bodies, does not, I conceive, +depend so much upon their intimate nature, as upon the arrangement of +their particles: we cannot have a more striking instance of this, than +is afforded by the different states of carbon, which, though it commonly +appears in the form of a black opake body, sometimes assumes the most +dazzling transparent form in nature, that of diamond, which, you +recollect, is carbon, and which, in all probability, derives its +beautiful transparency from the peculiar arrangement of its particles +during their crystallisation.</p> + +<span class="pagenum">31</span> +<a name="conver2.page31" id="conver2.page31"> </a> +<p class="speaker">EMILY.</p> + +<p>I never should have supposed that the formation of glass was so +simple a process as you describe it.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is by no means an easy operation to make perfect glass; for if the +sand, or flint, from which the siliceous earth is obtained, be mixed +with any metallic particles, or other substance, which cannot be +vitrified, the glass will be discoloured, or defaced, by opake +specks.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That, I suppose, is the reason why objects so often appear irregular +and shapeless through a common glass-window.</p> + +<p class="speaker">MRS. B.</p> + +<p>This species of imperfection proceeds, I believe, from another cause. +It is extremely difficult to prevent the lower part of the vessels, in +which the materials of glass are fused, from containing a more dense +vitreous matter than the upper, on account of the heavier ingredients +falling to the bottom. When this happens, it occasions the appearance of +veins or waves in the glass, from the difference of density in its +several parts, which produces an irregular refraction of the rays of +light that pass through it.</p> + +<span class="pagenum">32</span> +<a name="conver2.page32" id="conver2.page32"> </a> +<p>Another species of imperfection sometimes arises from the fusion not +being continued for a length of time sufficient to combine the two +ingredients completely, or from the due proportion of potash and silex +(which are as two to one) not being carefully observed; the glass, in +those cases, will be liable to alteration from the action of the air, of +salts, and especially of acids, which will effect its decomposition by +combining with the potash, and forming compound salts.</p> + +<p class="speaker">EMILY.</p> + +<p>What an extremely useful substance potash is!</p> + +<p class="speaker">MRS. B.</p> + +<p>Besides the great importance of potash in the manufactures of glass +and soap, it is of very considerable utility in many of the other arts, +and in its combinations with several acids, particularly the nitric, +with which it forms saltpetre.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Then saltpetre must be a <i>nitrat of potash</i>? But we are not yet +acquainted with the nitric acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall therefore defer entering into the particulars of these +combinations till we come to a general review of the compound salts. In +order +<span class="pagenum">33</span> +<a name="conver2.page33" id="conver2.page33"> </a> +to avoid confusion, it will be better at present to confine ourselves to +the alkalies.</p> + +<p class="speaker">EMILY.</p> + +<p>Cannot you show us the change of colour which you said the alkalies +produced on blue vegetable infusions?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; very easily. I shall dip a piece of white paper into this syrup +of violets, which, you see, is of a deep blue, and dyes the paper of the +same colour.—As soon as it is dry, we shall dip it into a solution +of potash, which, though itself colourless, will turn the paper +green—</p> + +<p class="speaker">CAROLINE.</p> + +<p>So it has, indeed! And do the other alkalies produce a similar +effect?</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly the same.—We may now proceed to <span class="smallroman">SODA</span>, which, however important, will detain us but a +very short time; as in all its general properties it very strongly +resembles potash; indeed, so great is their similitude, that they have +been long confounded, and they can now scarcely be distinguished, except +by the difference of the salts which they form with acids.</p> + +<p>The great source of this alkali is the sea, where, +<span class="pagenum">34</span> +<a name="conver2.page34" id="conver2.page34"> </a> +combined with a peculiar acid, it forms the salt with which the waters +of the ocean are so strongly impregnated.</p> + +<p class="speaker">EMILY.</p> + +<p>Is not that the common table salt?</p> + +<p class="speaker">MRS. B.</p> + +<p>The very same; but again we must postpone entering into the +particulars of this interesting combination, till we treat of the +neutral salts. Soda may be obtained from common salt; but the easiest +and most usual method of procuring it is by the combustion of marine +plants, an operation perfectly analogous to that by which potash is +obtained from vegetables.</p> + +<p class="speaker">EMILY.</p> + +<p>From what does soda derive its name?</p> + +<p class="speaker">MRS. B.</p> + +<p>From a plant called by us <i>soda</i>, and by the Arabs <i>kali</i>, +which affords it in great abundance. Kali has, indeed, given its name to +the alkalies in general.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Does soda form glass and soap in the same manner as potash?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, it does; it is of equal importance in the +<span class="pagenum">35</span> +<a name="conver2.page35" id="conver2.page35"> </a> +arts, and is even preferred to potash for some purposes; but you will +not be able to distinguish their properties till we examine the compound +salts which they form with acids; we must therefore leave soda for the +present, and proceed to <span class="smallroman">AMMONIA</span>, or +the <span class="smallroman">VOLATILE ALKALI</span>.</p> + +<p class="speaker">EMILY.</p> + +<p>I long to hear something of this alkali; is it not of the same nature +as hartshorn?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, it is, as you will see by-and-bye. This alkali is seldom found +in nature in its pure state; it is most commonly extracted from a +compound salt, called <i>sal ammoniac</i>, which was formerly imported +from <i>Ammonia</i>, a region of Libya, from which both these salts +and the alkali derive their names. The crystals contained in this bottle +are specimens of this salt, which consists of a combination of ammonia +and muriatic acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Then it should be called <i>muriat of ammonia</i>; for though I am +ignorant what muriatic acid is, yet I know that its combination with +ammonia cannot but be so called; and I am surprised to see sal ammoniac +inscribed on the label.</p> + +<span class="pagenum">36</span> +<a name="conver2.page36" id="conver2.page36"> </a> +<p class="speaker">MRS. B.</p> + +<p>That is the name by which it has been so long known, that the modern +chemists have not yet succeeded in banishing it altogether; and it is +still sold under that name by druggists, though by scientific chemists +it is more properly called muriat of ammonia.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Both the popular and the common name should be inscribed on +labels—this would soon introduce the new nomenclature.</p> + +<p class="speaker">EMILY.</p> + +<p>By what means can the ammonia be separated from the muriatic +acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>By chemical attractions; but this operation is too complicated for +you to understand, till you are better acquainted with the agency of +affinities.</p> + +<p class="speaker">EMILY.</p> + +<p>And when extracted from the salt, what kind of substance is +ammonia?</p> + +<p class="speaker">MRS. B.</p> + +<p>Its natural form, at the temperature of the atmosphere, when free +from combination, is that of gas; and in this state it is called +<i>ammoniacal gas</i>. +<span class="pagenum">37</span> +<a name="conver2.page37" id="conver2.page37"> </a> +But it mixes very readily with water, and can be thus obtained in a +liquid form.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You said that ammonia was more complicated in its composition than +the other alkalies; pray of what principles does it consist?</p> + +<p class="speaker">MRS. B.</p> + +<p>It was discovered a few years since, by Berthollet, a celebrated +French chemist, that it consisted of about one part of hydrogen to four +parts of nitrogen. Having heated ammoniacal gas under a receiver, by +causing the electrical spark to pass repeatedly through it, he found +that it increased considerably in bulk, lost all its alkaline +properties, and was actually converted into hydrogen and nitrogen gases; +and from the latest and most accurate experiments, the proportions +appear to be, one volume of nitrogen gas to three of <ins class="mycorr" title="text reads ‘oxygen’">hydrogen</ins> gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Ammonia, therefore, has not, like the two other alkalies, +a metallic basis?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is believed it has, though it is extremely difficult to reconcile +that idea with what I have just stated of its chemical nature. But the +fact is, that +<span class="pagenum">38</span> +<a name="conver2.page38" id="conver2.page38"> </a> +although this supposed metallic basis of ammonia has never been obtained +distinct and separate, yet both Professor Berzelius, of Stockholm, and +Sir H. Davy, have succeeded in forming a combination of mercury with the +basis of ammonia, which has so much the appearance of an amalgam, that +it strongly corroborates the idea of ammonia having a metallic basis.<a +class="tag" name="tag22" id="tag22" href="#note22">*</a> But +these theoretical points are full of difficulties and doubts, and it +would be useless to dwell any longer upon them.</p> + +<p>Let us therefore return to the properties of volatile alkali. +Ammoniacal gas is considerably lighter than oxygen gas, and only about +half the weight of atmospherical air. It possesses most of the +properties of the fixed alkalies; but cannot be of so much use in the +arts on account of its volatile nature. It is, therefore, never employed +in the manufacture of glass, but it forms soap with oils equally as well +as potash and soda; it resembles them likewise in its strong attraction +for water; for which reason it can be collected in a receiver over +mercury only.</p> + +<span class="pagenum">39</span> +<a name="conver2.page39" id="conver2.page39"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I do not understand this?</p> + +<p class="speaker">MRS. B.</p> + +<p>Do you recollect the method which we used to collect gases in a +glass-receiver over water?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Perfectly.</p> + +<p class="speaker">MRS. B.</p> + +<p>Ammoniacal gas has so strong a tendency to unite with water, that, +instead of passing through that fluid, it would be instantaneously +absorbed by it. We can therefore neither use water for that purpose, nor +any other liquid of which water is a component part; so that, in order +to collect this gas, we are obliged to have recourse to mercury, +(a liquid which has no action upon it,) and a mercurial bath is +used instead of a water bath, such as we employed on former occasions. +Water impregnated with this gas is nothing more than the fluid which you +mentioned at the beginning of the conversation—hartshorn; it is +the ammoniacal gas escaping from the water which gives it so powerful a +smell.</p> + +<p class="speaker">EMILY.</p> + +<p>But there is no appearance of effervescence in hartshorn.</p> + +<span class="pagenum">40</span> +<a name="conver2.page40" id="conver2.page40"> </a> +<p class="speaker">MRS. B.</p> + +<p>Because the particles of gas that rise from the water are too subtle +and minute for their effect to be visible.</p> + +<p>Water diminishes in density, by being impregnated with ammoniacal +gas; and this augmentation of bulk increases its capacity for +caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>In making hartshorn, then, or impregnating water with ammonia, heat +must be absorbed, and cold produced?</p> + +<p class="speaker">MRS. B.</p> + +<p>That effect would take place if it was not counteracted by another +circumstance; the gas is liquefied by incorporating with the water, and +gives out its latent heat. The condensation of the gas more than +counterbalances the expansion of the water; therefore, upon the whole, +heat is produced.—But if you dissolve ammoniacal gas with ice or +snow, cold is produced.—Can you account for that?</p> + +<p class="speaker">EMILY.</p> + +<p>The gas, in being condensed into a liquid, must give out heat; and, +on the other hand, the snow or ice, in being rarefied into a liquid, +must absorb heat; so that, between the opposite effects, I should +have supposed the original temperature would have been preserved.</p> + +<span class="pagenum">41</span> +<a name="conver2.page41" id="conver2.page41"> </a> +<p class="speaker">MRS. B.</p> + +<p>But you have forgotten to take into the account the rarefaction of +the water (or melted ice) by the impregnation of the gas; and this is +the cause of the cold which is ultimately produced.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is the <i>sal volatile</i> (the smell of which so strongly resembles +hartshorn) likewise a preparation of ammonia?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is carbonat of ammonia dissolved in water; and which, in its +concrete state, is commonly called salts of hartshorn. Ammonia is +caustic, like the fixed alkalies, as you may judge by the pungent +effects of hartshorn, which cannot be taken internally, nor applied to +delicate external parts, without being plentifully diluted with +water.—Oil and acids are very excellent antidotes for alkaline +poisons; can you guess why?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Perhaps, because the oil combines with the alkali, and forms soap, +and thus destroys its caustic properties; and the acid converts it into +a compound salt, which, I suppose, is not so pernicious as caustic +alkali.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely so.</p> + +<span class="pagenum">42</span> +<a name="conver2.page42" id="conver2.page42"> </a> +<p>Ammoniacal gas, if it be mixed with atmospherical air, and a burning +taper repeatedly plunged into it, will burn with a large flame of a +peculiar yellow colour.</p> + +<p class="speaker">EMILY.</p> + +<p>But pray tell me, can ammonia be procured from this Lybian salt +only?</p> + +<p class="speaker">MRS. B.</p> + +<p>So far from it, that it is contained in, and may be extracted from, +all animal substances whatever. Hydrogen and nitrogen are two of the +chief constituents of animal matter; it is therefore not surprising that +they should occasionally meet and combine in those proportions that +compose ammonia. But this alkali is more frequently generated by the +spontaneous decomposition of animal substances; the hydrogen and +nitrogen gases that arise from putrefied bodies combine, and form the +volatile alkali.</p> + +<p>Muriat of ammonia, instead of being exclusively brought from Lybia, +as it originally was, is now chiefly prepared in Europe, by chemical +processes. Ammonia, although principally extracted from this salt, can +also be produced by a great variety of other substances. The horns of +cattle, especially those of deer, yield it in abundance, and it is from +this circumstance that a solution of ammonia in water has been called +hartshorn. It may likewise +<span class="pagenum">43</span> +<a name="conver2.page43" id="conver2.page43"> </a> +be procured from wool, flesh, and bones; in a word, any animal substance +whatever yields it by decomposition.</p> + +<p>We shall now lay aside the alkalies, however important the subject +may be, till we treat of their combination with acids. The next time we +meet we shall examine the earths.</p> + +<div class="footnote"> + +<p><a name="note21" id="note21" href="#tag21">*</a> +This defence of the general theory, however plausible, is liable to some +obvious objections. The phenomenon might perhaps be better accounted for +by supposing that a solution of alkali in water has less capacity for +heat than either water or alkali in their separate state.</p> + +<p><a name="note22" id="note22" href="#tag22">*</a> +This amalgam is easily obtained, by placing a globule of mercury upon a +piece of muriat, or carbonat of ammonia, and electrifying this globule +by the Voltaic battery. The globule instantly begins to expand to three +or four times its former size, and becomes much less fluid, though +without losing its metallic lustre, a change which is ascribed to +the metallic basis of ammonia uniting with the mercury. This is an +extremely curious experiment.</p> + +</div> + + +<span class="pagenum">44</span> +<a name="conver2.page44" id="conver2.page44"> </a> +<h4><a name="convXV" id="convXV">CONVERSATION XV.</a><br> +<span class="subhead">ON EARTHS.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">T</span>he</span> <span class="smallroman">EARTHS</span>, which we are to-day to examine, are nine in +number:</p> + +<div class="list space"> +<p><span class="smallroman">SILEX</span>,</p> +<p><span class="smallroman">ALUMINE</span>,</p> +<p><span class="smallroman">BARYTES</span>,</p> +<p><span class="smallroman">LIME</span>,</p> +<p><span class="smallroman">MAGNESIA</span>,</p> +<p><span class="smallroman">STRONTITES</span>,</p> +<p><span class="smallroman">YTTRIA</span>,</p> +<p><span class="smallroman">GLUCINA</span>,</p> +<p><span class="smallroman">ZIRCONIA</span>.</p> +</div> + +<p>The last three are of late discovery; their properties are but +imperfectly known; and, as they have not yet been applied to use, it +will be unnecessary to enter into any particulars respecting them; we +shall confine our remarks, therefore, to the first five. They are +composed, as you have already learnt, of a metallic basis combined with +oxygen; and, from this circumstance, are incombustible.</p> + +<span class="pagenum">45</span> +<a name="conver2.page45" id="conver2.page45"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Yet I have seen turf burnt in the country, and it makes an excellent +fire; the earth becomes red hot, and produces a very great quantity of +heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not the earth that burns, my dear, but the roots, grass, and +other remnants of vegetables that are intermixed with it. The caloric, +which is produced by the combustion of these substances, makes the earth +red hot, and this being a bad conductor of heat, retains its caloric a +long time; but were you to examine it when cooled, you would find that +it had not absorbed one particle of oxygen, nor suffered any alteration +from the fire. Earth is, however, from the circumstance just mentioned, +an excellent radiator of heat, and owes its utility, when mixed with +fuel, solely to that property. It is in this point of view that Count +Rumford has recommended balls of incombustible substances to be arranged +in fire-places, and mixed with the coals, by which means the caloric +disengaged by the combustion of the latter is more perfectly reflected +into the room, and an expense of fuel is saved.</p> + +<p class="speaker">EMILY.</p> + +<p>I expected that the list of earths would be much more considerable. +When I think of the great +<span class="pagenum">46</span> +<a name="conver2.page46" id="conver2.page46"> </a> +variety of soils, I am astonished that there is not a greater +number of earths to form them.</p> + +<p class="speaker">MRS. B.</p> + +<p>You might, indeed, almost confine that number to four; for barytes, +strontites, and the others of late discovery, act but so small a part in +this great theatre, that they cannot be reckoned as essential to the +general formation of the globe. And you must not confine your idea of +earths to the formation of soil; for rock, marble, chalk, slate, sand, +flint, and all kinds of stones, from the precious jewels to the +commonest pebbles; in a word, all the immense variety of mineral +products, may be referred to some of these earths, either in a simple +state, or combined the one with the other, or blended with other +ingredients.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Precious stones composed of earth! That seems very difficult to +conceive.</p> + +<p class="speaker">EMILY.</p> + +<p>Is it more extraordinary than that the most precious of all jewels, +diamond, should be composed of carbon? But diamond forms an exception, +Mrs. B.; for, though a stone, it is not composed of earth.</p> + +<span class="pagenum">47</span> +<a name="conver2.page47" id="conver2.page47"> </a> +<p class="speaker">MRS. B.</p> + +<p>I did not specify the exception, as I knew you were so well +acquainted with it. Besides, I would call a diamond a mineral +rather than a stone, as the latter term always implies the presence of +some earth.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I cannot conceive how such coarse materials can be converted into +such beautiful productions.</p> + +<p class="speaker">MRS. B.</p> + +<p>We are very far from understanding all the secret resources of +nature; but I do not think the spontaneous formation of the crystals, +which we call precious stones, one of the most difficult phenomena to +comprehend.</p> + +<p>By the slow and regular work of ages, perhaps of hundreds of ages, +these earths may be gradually dissolved by water, and as gradually +deposited by their solvent in the undisturbed process of +crystallisation. The regular arrangement of their particles, during +their reunion in a solid mass, gives them that brilliancy, transparency, +and beauty, for which they are so much admired; and renders them in +appearance so totally different from their rude and primitive +ingredients.</p> + +<span class="pagenum">48</span> +<a name="conver2.page48" id="conver2.page48"> </a> +<p class="speaker">CAROLINE.</p> + +<p>But how does it happen that they are spontaneously dissolved, and +afterwards crystallised?</p> + +<p class="speaker">MRS. B.</p> + +<p>The scarcity of many kinds of crystals, as rubies, emeralds, topazes, +&c. shows that their formation is not an operation very easily +carried on in nature. But cannot you imagine that when water, holding in +solution some particles of earth, filters through the crevices of hills +or mountains, and at length dribbles into some cavern, each successive +drop may be slowly evaporated, leaving behind it the particle of earth +which it held in solution? You know that crystallisation is more regular +and perfect, in proportion as the evaporation of the solvent is slow and +uniform; nature, therefore, who knows no limit of time, has, in all +works of this kind, an infinite advantage over any artist who attempts +to imitate such productions.</p> + +<p class="speaker">EMILY.</p> + +<p>I can now conceive that the arrangement of the particles of earth, +during crystallisation, may be such as to occasion transparency, by +admitting a free passage to the rays of light; but I cannot understand +why crystallised earths should assume such beautiful colours as most of +them do. Sapphire, +<span class="pagenum">49</span> +<a name="conver2.page49" id="conver2.page49"> </a> +for instance, is of a celestial blue; ruby, a deep red; topaz, +a brilliant yellow?</p> + +<p class="speaker">MRS. B.</p> + +<p>Nothing is more simple than to suppose that the arrangement of their +particles is such, as to transmit some of the coloured rays of light, +and to reflect others, in which case the stone must appear of the colour +of the rays which it reflects. But besides, it frequently happens that +the colour of a stone is owing to a mixture of some metallic matter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, are the different kinds of precious stones each composed of one +individual earth, or are they formed of a combination of several +earths?</p> + +<p class="speaker">MRS. B.</p> + +<p>A great variety of materials enters into the composition of most of +them; not only several earths, but sometimes salts and metals. The +earths, however, in their simple state, frequently form very beautiful +crystals; and, indeed, it is in that state only that they can be +obtained perfectly pure.</p> + +<p class="speaker">EMILY.</p> + +<p>Is not the Derbyshire spar produced by the crystallisation of earths, +in the way you have just +<span class="pagenum">50</span> +<a name="conver2.page50" id="conver2.page50"> </a> +explained? I have been in some of the subterraneous caverns where +it is found, which are similar to those you have described.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but this spar is a very imperfect specimen of crystallisation; +it consists of a variety of ingredients confusedly blended together, as +you may judge by its opacity, and by the various colours and appearances +which it exhibits.</p> + +<p>But, in examining the earths in their most perfect and agreeable +form, we must not lose sight of that state in which they are commonly +found, and which, if less pleasing to the eye, is far more interesting +by its utility.</p> + +<p>All the earths are more or less endowed with alkaline properties; but +there are four, barytes, magnesia, lime, and strontites, which are +called <i>alkaline earths</i>, because they possess those qualities in +so great a degree, as to entitle them, in most respects, to the rank of +alkalies. They combine and form compound salts with acids, in the same +way as alkalies; they are, like them, susceptible of a considerable +degree of causticity, and are acted upon in a similar manner by chemical +tests.—The remaining earths, silex and alumine, with one or two +others of late discovery, are in some degree more earthy, that is to +say, they possess more completely the properties common to all the +earths, which +<span class="pagenum">51</span> +<a name="conver2.page51" id="conver2.page51"> </a> +are, insipidity, dryness, unalterableness in the fire, +infusibility, &c.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet, did you not tell us that silex, or siliceous earth, when mixed +with an alkali, was fusible, and run into glass?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, my dear; but the characteristic properties of earths, which I +have mentioned, are to be considered as belonging to them in a state of +purity only; a state in which they are very seldom to be met with +in nature.—Besides these general properties, each earth has its +own specific characters, by which it is distinguished from any other +substance.—Let us therefore review them separately.</p> + +<p class="space"> +<span class="smallcaps">Silex</span>, or <span class="smallroman">SILICA</span>, abounds in flint, sand, sandstone, agate, +jasper, &c.; it forms the basis of many precious stones, and +particularly of those which strike fire with steel. It is rough to the +touch, scratches and wears away metals; it is acted upon by no acid but +the fluoric, and is not soluble in water by any known process; but +nature certainly dissolves it by means with which we are unacquainted, +and thus produces a variety of siliceous crystals, and amongst these +<i>rock crystal</i>, +<span class="pagenum">52</span> +<a name="conver2.page52" id="conver2.page52"> </a> +which is the purest specimen of this earth. Silex appears to have been +intended by Providence to form the solid basis of the globe, to serve as +a foundation for the original mountains, and give them that hardness and +durability which has enabled them to resist the various revolutions +which the surface of the earth has successively undergone. From these +mountains siliceous rocks have, during the course of ages, been +gradually detached by torrents of water, and brought down in fragments; +these, in the violence and rapidity of their descent, are sometimes +crumbled to sand, and in this state form the beds of rivers and of the +sea, chiefly composed of siliceous materials. Sometimes the fragments +are broken without being pulverised by their fall, and assume the form +of pebbles, which gradually become rounded and polished.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is the true colour of silex, which forms such a variety of +different coloured substances? Sand is brown, flint is nearly black, and +precious stones are of all colours.</p> + +<p class="speaker">MRS. B.</p> + +<p>Pure silex, such as is found only in the chemist’s laboratory, is +perfectly white, and the various colours which it assumes, in the +different substances +<span class="pagenum">53</span> +<a name="conver2.page53" id="conver2.page53"> </a> +you have just mentioned, proceed from the different ingredients with +which it is mixed in them.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I wonder that silex is not more valuable, since it forms the basis of +so many precious stones.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must not forget that the value we set upon precious stones +depends in a great measure upon the scarcity with which nature affords +them; for, were those productions either common or perfectly imitable by +art, they would no longer, notwithstanding their beauty, be so highly +esteemed. But the real value of siliceous earth, in many of the most +useful arts, is very extensive. Mixed with clay, it forms the basis of +all the various kinds of earthen ware, from the most common utensils to +the most refined ornaments.</p> + +<p class="speaker">EMILY.</p> + +<p>And we must recollect its importance in the formation of glass with +potash.</p> + +<p class="speaker">MRS. B.</p> + +<p>Nor should we omit to mention, likewise, many other important uses of +silex, such as being the chief ingredient of some of the most durable +cements, of mortar, &c.</p> + +<span class="pagenum">54</span> +<a name="conver2.page54" id="conver2.page54"> </a> +<p>I said before, that siliceous earth combined with no acid but the +fluoric; it is for this reason that glass is liable to be attacked by +that acid only, which, from its strong affinity for silex, forces that +substance from its combination with the potash, and thus destroys the +glass.</p> + +<p>We will now hasten to proceed to the other earths, for I am rather +apprehensive of your growing weary of this part of our subject.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The history of the earths is not quite so entertaining as that of the +simple substances.</p> + +<p class="speaker">MRS. B.</p> + +<p>Perhaps not; but it is absolutely indispensable that you should know +something of them; for they form the basis of so many <ins class="mycorr" title="text reads ‘interesing’">interesting</ins> and +important compounds, that their total omission would throw great +obscurity on our general outline of chemical science. We shall, however, +review them in as cursory a manner as the subject can admit of.</p> + +<p class="space"> +<span class="smallcaps">Alumine</span> derives its name from a +compound salt called <i>alum</i>, of which it forms the basis.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But it ought to be just the contrary, Mrs. B.; +<span class="pagenum">55</span> +<a name="conver2.page55" id="conver2.page55"> </a> +the simple body should give, instead of taking, its name from the +compound.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is true; but as the compound salt was known long before its +basis was discovered, it was very natural that when the earth was at +length separated from the acid, it should derive its name from the +compound from which it was obtained. However, to remove your scruples, +we will call the salt according to the new nomenclature, <i>sulphat of +alumine</i>. From this combination, alumine may be obtained in its pure +state; it is then soft to the touch, makes a paste with water, and +hardens in the fire. In nature, it is found chiefly in clay, which +contains a considerable proportion of this earth; it is very abundant in +fuller’s earth, slate, and a variety of other mineral productions. There +is indeed scarcely any mineral substance more useful to mankind than +alumine. In the state of clay, it forms large strata of the earth, gives +consistency to the soil of valleys, and of all low and damp spots, such +as swamps and marshes. The beds of lakes, ponds, and springs, are almost +entirely of clay; instead of allowing of the filtration of water, as +sand does, it forms an impenetrable bottom, and by this means water is +accumulated in the caverns of the earth, producing +<span class="pagenum">56</span> +<a name="conver2.page56" id="conver2.page56"> </a> +those reservoirs whence springs issue, and spout out at the surface.</p> + +<p class="speaker">EMILY.</p> + +<p>I always thought that these subterraneous reservoirs of water were +bedded by some hard stone, or rock, which the water could not +penetrate.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is not the case; for in the course of time water would +penetrate, or wear away silex, or any other kind of stone, while it is +effectually stopped by clay, or alumine.</p> + +<p>The solid compact soils, such as are fit for corn, owe their +consistence in a great measure to alumine; this earth is therefore used +to improve sandy or chalky soils, which do not retain a sufficient +quantity of water for the purpose of vegetation.</p> + +<p>Alumine is the most essential ingredient in all potteries. It enters +into the composition of brick, as well as that of the finest porcelain; +the addition of silex and water hardens it, renders it susceptible of a +degree of vitrification, and makes it perfectly fit for its various +purposes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I can scarcely conceive that brick and china should be made of the +same materials.</p> + +<span class="pagenum">57</span> +<a name="conver2.page57" id="conver2.page57"> </a> +<p class="speaker">MRS. B.</p> + +<p>Brick consists almost entirely of baked clay; but a certain +proportion of silex is essential to the formation of earthen or stone +ware. In common potteries sand is used for that purpose; a more +pure silex is, I believe, necessary for the composition of +porcelain, as well as a finer kind of clay; and these materials are, no +doubt, more carefully prepared, and curiously wrought, in the one case +than in the other. Porcelain owes its beautiful semitransparency to a +commencement of vitrification.</p> + +<p class="speaker">EMILY.</p> + +<p>But the commonest earthen-ware, though not transparent, is covered +with a kind of glazing.</p> + +<p class="speaker">MRS. B.</p> + +<p>That precaution is equally necessary for use as for beauty, as the +ware would be liable to be spoiled and corroded by a variety of +substances, if not covered with a coating of this kind. In porcelain it +consists of enamel, which is a fine white opake glass, formed of +metallic oxyds, sand, salts, and such other materials as are susceptible +of vitrification. The glazing of common earthen-ware is made chiefly of +oxyd of lead, or sometimes merely of salt, which, when thinly spread +over earthen vessels, will, at a certain heat, run into opake glass.</p> + +<span class="pagenum">58</span> +<a name="conver2.page58" id="conver2.page58"> </a> +<p class="speaker"><ins class="mycorr" title="speaker name missing: supplied from other editions">CAROLINE.</ins></p> + +<p>And of what nature are the colours which are used for painting +porcelain<ins class="mycorr" title="text has .">? </ins></p> + +<p class="speaker">MRS. B.</p> + +<p>They are all composed of metallic oxyds, so that these colours, +instead of receiving injury from the application of fire, are +strengthened and developed by its action, which causes them to undergo +different degrees of oxydation.</p> + +<p>Alumine and silex are not only often combined by art, but they have +in nature a very strong tendency to unite, and are found combined, in +different proportions, in various gems and other minerals. Indeed, many +of the precious stones, such as ruby, oriental sapphire, amethyst, +&c. consist chiefly of alumine.</p> + + +<p class="space"> +We may now proceed to the alkaline earths, I shall say but a few +words on <span class="smallroman">BARYTES</span>, as it is hardly ever +used, except in chemical laboratories. It is remarkable for its great +weight, and its strong alkaline properties, such as destroying animal +substances, turning green some blue vegetable colours, and showing a +powerful attraction for acids; this last property it possesses to such a +degree, particularly with regard to the sulphuric acid, that it will +always detect its presence in any substance or combination whatever, by +immediately uniting with it, and forming a sulphat of barytes. This +<span class="pagenum">59</span> +<a name="conver2.page59" id="conver2.page59"> </a> +renders it a very valuable chemical test. It is found pretty abundantly +in nature in the state of carbonat, from which the pure earth can be +easily separated.</p> + + +<p class="space"> +The next earth we have to consider is <span class="smallroman">LIME</span>. This is a substance of too great and general +importance to be passed over so slightly as the last.</p> + +<p>Lime is strongly alkaline. In nature it is not met with in its simple +state, as its affinity for water and carbonic acid is so great, that it +is always found combined with these substances, with which it forms the +common lime-stone; but it is separated in the kiln from these +ingredients, which are volatilised whenever a sufficient degree of heat +is applied.</p> + +<p class="speaker">EMILY.</p> + +<p>Pure lime, then, is nothing but lime-stone, which has been deprived, +in the kiln, of its water and carbonic acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely: in this state it is called <i>quick-lime</i>, and it is so +caustic, that it is capable of decomposing the dead bodies of animals +very rapidly, without their undergoing the process of +putrefaction.—I have here some quick lime, which is kept +carefully corked up in a bottle to prevent the access +<span class="pagenum">60</span> +<a name="conver2.page60" id="conver2.page60"> </a> +of air; for were it at all exposed to the atmosphere, it would absorb +both moisture and carbonic acid gas from it, and be soon slaked. Here is +also some lime-stone—we shall pour a little water on each, and +observe the effects that result from it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How the quick-lime hisses! It is become excessively hot!—It +swells, and now it bursts and crumbles to powder, while the water +appears to produce no kind of alteration on the lime-stone.</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the lime-stone is already saturated with water, whilst the +quick-lime, which has been deprived of it in the kiln, combines with it +with very great avidity, and produces this prodigious disengagement of +heat, the cause of which I formerly explained to you; do you +recollect it?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes; you said that the heat did not proceed from the lime, but from +the water which was <i>solidified</i>, and thus parted with its heat of +liquidity.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well. If we continue to add successive quantities of water to +the lime after being slaked +<span class="pagenum">61</span> +<a name="conver2.page61" id="conver2.page61"> </a> +and crumbled as you see, it will then gradually be diffused in the +water, till it will at length be dissolved in it, and entirely +disappear; but for this purpose it requires no less than 700 times its +weight of water. This solution is called <i>lime-water</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How very small, then, is the proportion of lime dissolved!</p> + +<p class="speaker">MRS. B.</p> + +<p>Barytes is still of more difficult solution; it dissolves only in 900 +times its weight of water: but it is much more soluble in the state of +crystals. The liquid contained in this bottle is lime-water; it is often +used as a medicine, chiefly, I believe, for the purpose of +combining with, and neutralising, the superabundant acid which it meets +with in the stomach.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised that it is so perfectly clear; it does not at all +partake of the whiteness of the lime.</p> + +<p class="speaker">MRS. B.</p> + +<p>Have you forgotten that, in solutions, the solid body is so minutely +subdivided by the fluid as to become invisible, and therefore will not +in the least degree impair the transparency of the solvent?</p> + +<span class="pagenum">62</span> +<a name="conver2.page62" id="conver2.page62"> </a> +<p>I said that the attraction of lime for carbonic acid was so strong, +that it would absorb it from the atmosphere. We may see this effect by +exposing a glass of lime-water to the air; the lime will then separate +from the water, combine with the carbonic acid, and re-appear on the +surface in the form of a white film, which is carbonat of lime, commonly +called <i>chalk</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Chalk is, then, a compound salt! I never should have supposed +that those immense beds of chalk, that we see in many parts of the +country, were a salt.—Now, the white film begins to appear on the +surface of the water; but it is far from resembling hard solid +chalk.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is owing to its state of extreme division; in a little time it +will collect into a more compact mass, and subside at the bottom of the +glass.</p> + +<p>If you breathe into lime-water, the carbonic acid, which is mixed +with the air that you expire, will produce the same effect. It is an +experiment very easily made;—I shall pour some lime-water +into this glass tube, and, by breathing repeatedly into it, you will +soon perceive a precipitation of chalk—</p> + +<span class="pagenum">63</span> +<a name="conver2.page63" id="conver2.page63"> </a> +<p class="speaker">EMILY.</p> + +<p>I see already a small white cloud formed.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is composed of minute particles of chalk; at present it floats in +the water, but it will soon subside.</p> + +<p>Carbonat of lime, or chalk, you see, is insoluble in water, since the +lime which was dissolved re-appears when converted into chalk; but you +must take notice of a very singular circumstance, which is, that chalk +is soluble in water impregnated with carbonic acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is very curious, indeed, that carbonic acid gas should render lime +soluble in one instance, and insoluble in the other!</p> + +<p class="speaker">MRS. B.</p> + +<p>I have here a bottle of Seltzer water, which, you know, is strongly +impregnated with carbonic acid:—let us pour a little of it into a +glass of lime-water. You see that it immediately forms a precipitation +of carbonat of lime?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, a white cloud appears.</p> + +<span class="pagenum">64</span> +<a name="conver2.page64" id="conver2.page64"> </a> +<p class="speaker">MRS. B.</p> + +<p>I shall now pour an additional quantity of the Seltzer water into the +lime-water—</p> + +<p class="speaker">EMILY.</p> + +<p>How singular! The cloud is re-dissolved, and the liquid is again +transparent.</p> + +<p class="speaker">MRS. B.</p> + +<p>All the mystery depends upon this circumstance, that carbonat of lime +is soluble in carbonic acid, whilst it is insoluble in water; the first +quantity of carbonic acid, therefore, which I introduce into the +lime-water, was employed in forming the carbonat of lime, which remained +visible, until an additional quantity of carbonic acid dissolved it. +Thus, you see, when the lime and carbonic acid are in proper proportions +to form chalk, the white cloud appears, but when the acid predominates, +the chalk is no sooner formed than it is dissolved.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is now the case; but let us try whether a further addition of +lime-water will again precipitate the chalk.</p> + +<p class="speaker">EMILY.</p> + +<p>It does, indeed! The cloud re-appears, because, +<span class="pagenum">65</span> +<a name="conver2.page65" id="conver2.page65"> </a> +I suppose, there is now no more of the carbonic acid than is +necessary to form chalk; and, in order to dissolve the chalk, +a superabundance of acid is required.</p> + +<p class="speaker">MRS. B.</p> + +<p>We have, I think, carried this experiment far enough; every +repetition would but exhibit the same appearances.</p> + +<p>Lime combines with most of the acids, to which the carbonic (as being +the weakest) readily yields it; but these combinations we shall have an +opportunity of noticing more particularly hereafter. It unites with +phosphorus, and with sulphur, in their simple state; in short, of all +the earths, lime is that which nature employs most frequently, and most +abundantly, in its innumerable combinations. It is the basis of all +calcareous earths and stones; we find it likewise in the animal and the +vegetable creations.</p> + +<p class="speaker">EMILY.</p> + +<p>And in the arts is not lime of very great utility?</p> + +<p class="speaker">MRS. B.</p> + +<p>Scarcely any substance more so; you know that it is a most essential +requisite in building, as it constitutes the basis of all cements, such +as mortar, stucco, plaister, &c.</p> + +<span class="pagenum">66</span> +<a name="conver2.page66" id="conver2.page66"> </a> +<p>Lime is also of infinite importance in agriculture; it lightens and +warms soils that are too cold, and compact, in consequence of too great +a proportion of clay.—But it would be endless to enumerate the +various purposes for which it is employed; and you know enough of it to +form some idea of its importance; we shall, therefore, now proceed to +the third alkaline earth, <span class="smallroman">MAGNESIA</span>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am already pretty well acquainted with that earth; it is a +medicine.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is in the state of carbonat that magnesia is usually employed +medicinally; it then differs but little in appearance from its simple +form, which is that of a very fine light white powder. It dissolves in +2000 times its weight of water, but forms with acids extremely soluble +salts. It has not so great an attraction for acids as lime, and +consequently yields them to the latter. It is found in a great variety +of mineral combinations, such as slate, mica, amianthus, and more +particularly in a certain lime stone, which has lately been discovered +by Mr. Tennant to contain it in very great quantities. It does not +attract and solidify water, like lime: but when mixed with water and +exposed to the atmosphere, it slowly absorbs +<span class="pagenum">67</span> +<a name="conver2.page67" id="conver2.page67"> </a> +carbonic acid from the latter, and thus loses its causticity. Its chief +use in medicine is, like that of lime, derived from its readiness to +combine with, and neutralise, the acid which it meets with in the +stomach.</p> + +<p class="speaker">EMILY.</p> + +<p>Yet, you said that it was taken in the state of carbonat, in which +case it has already combined with an acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but the carbonic is the last of all the acids in the order of +affinities; it will therefore yield the magnesia to any of the others. +It is, however, frequently taken in its caustic state as a remedy for +flatulence. Combined with sulphuric acid, magnesia forms another and +more powerful medicine, commonly called <i>Epsom salt</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And properly, <i>sulphat of magnesia</i>, I suppose? Pray why +was it ever called Epsom salt?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because there is a spring in the neighbourhood of Epsom which +contains this salt in great abundance.</p> + +<p>The last alkaline earth which we have to mention is <span class="smallroman">STRONTIAN</span>, or <span class="smallroman">STRONTITES</span>, discovered by +<span class="pagenum">68</span> +<a name="conver2.page68" id="conver2.page68"> </a> +Dr. Hope a few years ago. It so strongly resembles barytes in its +properties, and is so sparingly found in nature, and of so little use in +the arts, that it will not be necessary to enter into any particulars +respecting it. One of the remarkable characteristic properties of +strontites is, that its salts, when dissolved in spirit of wine, tinge +the flame of a deep red, or blood colour.</p> + + + + +<span class="pagenum">69</span> +<a name="conver2.page69" id="conver2.page69"> </a> +<h4><a name="convXVI" id="convXVI">CONVERSATION XVI.</a><br> +<span class="subhead">ON ACIDS.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> may now proceed to the acids. Of the +metallic oxyds, you have already acquired some general notions. This +subject, though highly interesting in its details, is not of sufficient +importance to our concise view of chemistry, to be particularly treated +of; but it is absolutely necessary that you should be better acquainted +with the acids, and likewise with their combinations with the alkalies, +which form the triple compounds called <span class="smallroman">NEUTRAL SALTS</span>.</p> + +<p>The class of acids is characterised by very distinct properties. They +all change blue vegetable infusions to a red colour: they are all more +or less sour to the taste; and have a general tendency to combine with +the earths, alkalies, and metallic oxyds.</p> + +<p>You have, I believe, a clear idea of the nomenclature by which +the base (or radical) of the acid, and the various degrees of +acidification, are expressed?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, I think so; the acid is distinguished by the +<span class="pagenum">70</span> +<a name="conver2.page70" id="conver2.page70"> </a> +name of its base, and its degree of oxydation, that is, the quantity of +oxygen it contains, by the termination of that name in <i>ous</i> or +<i>ic</i>; thus sulphure<i>ous</i> acid is that formed by the smallest +proportion of oxygen combined with sulphur; sulphur<i>ic</i> acid that +which results from the combination of sulphur with the greatest quantity +of oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>A still greater latitude may, in many cases, be allowed to the +proportions of oxygen than can be combined with <ins class="mycorr" +title="text reads ‘acidificiable’">acidifiable</ins> radicals; for +several of these radicals are susceptible of uniting with a quantity of +oxygen so small as to be insufficient to give them the properties of +acids; in these cases, therefore, they are converted into oxyds. Such is +sulphur, which by exposure to the atmosphere with a degree of heat +inadequate to produce inflammation, absorbs a small proportion of +oxygen, which colours it red or brown. This, therefore, is the first +degree of oxygenation of sulphur; the 2d converts it into +sulphur<i>ous</i> acid; the 3d into the sulphur<i>ic</i> acid; and +4thly, if it was found capable of combining with a still larger +proportion of oxygen, it would then be termed <i>super-oxygenated +sulphuric acid</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>Are these various degrees of oxygenation common to all the acids?</p> + +<span class="pagenum">71</span> +<a name="conver2.page71" id="conver2.page71"> </a> +<p class="speaker">MRS. B.</p> + +<p>No; they vary much in this respect: some are susceptible of only one +degree of oxygenation; others, of two, or three; there are but very few +that will admit of more.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The modern nomenclature must be of immense advantage in pointing out +so easily the nature of the acids, and their various degrees of +oxygenation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Till lately many of the acids had not been decomposed; but analogy +afforded so strong a proof of their compound nature, that I never could +reconcile myself to classing them with the simple bodies, though this +division has been adopted by several chemical writers. At present there +are only the muriatic and the fluoric acids, which have not had their +bases distinctly separated.</p> + +<p class="speaker">CAROLINE.</p> + +<p>We have heard of a great variety of acids; pray how many are there in +all?</p> + +<p class="speaker">MRS. B.</p> + +<p>I believe there are reckoned at present thirty-four, and their number +is constantly increasing, as the science improves; but the most +important, +<span class="pagenum">72</span> +<a name="conver2.page72" id="conver2.page72"> </a> +and those to which we shall almost entirely confine our attention, are +but few. I shall, however, give you a general view of the whole; +and then we shall more particularly examine those that are the most +essential.</p> + +<p>This class of bodies was formerly divided into mineral, vegetable, +and animal acids, according to the substances from which they were +commonly obtained.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That, I should think, must have been an excellent arrangement; why +was it altered?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because in many cases it produced confusion. In which class, for +instance, would you place carbonic acid?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now I see the difficulty. I should be at a loss where to place it, as +you have told us that it exists in the animal, vegetable, and mineral +kingdoms.</p> + +<p class="speaker">EMILY.</p> + +<p>There would be the same objection with respect to phosphoric acid, +which, though obtained chiefly from bones, can also, you said, be found +in small quantities in stones, and likewise in some plants.</p> + +<p class="speaker">MRS. B.</p> + +<p>You see, therefore, the propriety of changing +<span class="pagenum">73</span> +<a name="conver2.page73" id="conver2.page73"> </a> +this mode of classification. These objections do not exist in the +present nomenclature; for the composition and nature of each individual +acid is in some degree pointed out, instead of the class of bodies from +which it is extracted; and, with regard to the more general division of +acids, they are classed under these three heads:</p> + +<p>First, Acids of known or supposed simple bases, which are formed by +the union of these bases with oxygen. They are the following:</p> + +<table class="list inline" summary="list of substances"> +<tr> +<td>The</td><td><i>Sulphuric</i></td> +<td class="middle" rowspan="10"> +<img src="images/bracket_tall.gif" height="100%" +alt="}"> +</td> +<td class="middle" rowspan="10"> +<p>Acids, of known and simple bases.</p></td> +</tr> +<tr> +<td></td><td><i>Carbonic</i></td> +</tr> +<tr> +<td></td><td><i>Nitric</i></td> +</tr> +<tr> +<td></td><td><i>Phosphoric</i></td> +</tr> +<tr> +<td></td><td><i>Arsenical</i></td> +</tr> +<tr> +<td></td><td><i>Tungstenic</i></td> +</tr> +<tr> +<td></td><td><i>Molybdenic</i></td> +</tr> +<tr> +<td></td><td><i>Boracic</i></td> +</tr> +<tr> +<td></td><td><i>Fluoric</i></td> +</tr> +<tr> +<td></td><td><i>Muriatic</i></td> +</tr> +</table> + +<p>This class comprehends the most anciently known and most important +acids. The sulphuric, nitric, and muriatic were formerly, and are still +frequently, called <i>mineral acids</i>.</p> + +<p>2dly, Acids that have double or binary radicals, and which +consequently consist of triple combinations. These are the vegetable +acids, whose common radical is a compound of hydrogen and carbon.</p> + +<span class="pagenum">74</span> +<a name="conver2.page74" id="conver2.page74"> </a> +<p class="speaker">CAROLINE.</p> + +<p>But if the basis of all the vegetable acids be the same, it should +form but one acid; it may indeed combine with different proportions of +oxygen, but the nature of the acid must be the same.</p> + +<p class="speaker">MRS. B.</p> + +<p>The only difference that exists in the basis of vegetable acids, is +the various proportions of hydrogen and carbon from which they are +severally composed. But this is enough to produce a number of acids +apparently very dissimilar. That they do not, however, differ +essentially, is proved by their susceptibility of being converted into +each other, by the addition or subtraction of a portion of hydrogen or +of carbon. The names of these acids are,</p> + +<table class="list inline" summary="list of substances"> +<tr> +<td>The</td><td><i>Acetic</i></td> +<td class="middle" rowspan="11"> +<img src="images/bracket_tall.gif" height="100%" +alt="}"> +</td> +<td class="middle" rowspan="11"> +<p>Acids, of double bases, being of vegetable origin.</p></td> +</tr> +<tr> +<td></td><td><i>Oxalic</i></td> +</tr> +<tr> +<td></td><td><i>Tartarous</i></td> +</tr> +<tr> +<td></td><td><i>Citric</i></td> +</tr> +<tr> +<td></td><td><i>Malic</i></td> +</tr> +<tr> +<td></td><td><i>Gallic</i></td> +</tr> +<tr> +<td></td><td><i>Mucous</i></td> +</tr> +<tr> +<td></td><td><i>Benzoic</i></td> +</tr> +<tr> +<td></td><td><i>Succinic</i></td> +</tr> +<tr> +<td></td><td><i>Camphoric</i></td> +</tr> +<tr> +<td></td><td><i>Suberic</i></td> +</tr> +</table> + +<span class="pagenum">75</span> +<a name="conver2.page75" id="conver2.page75"> </a> +<p>The 3d class of acids consists of those which have triple radicals, +and are therefore of a still more compound nature. This class +comprehends the animal acids, which are,</p> + +<table class="list inline" summary="list of substances"> +<tr> +<td>The</td><td><i>Lactic</i></td> +<td class="middle" rowspan="7"> +<img src="images/bracket_tall.gif" height="100%" +alt="}"> +</td> +<td class="middle" rowspan="7"> +<p>Acids, of triple bases, or animal acids.</p></td> +</tr> +<tr> +<td></td><td><i>Prussic</i></td> +</tr> +<tr> +<td></td><td><i>Formic</i></td> +</tr> +<tr> +<td></td><td><i>Bombic</i></td> +</tr> +<tr> +<td></td><td><i>Sebacic</i></td> +</tr> +<tr> +<td></td><td><i>Zoonic</i></td> +</tr> +<tr> +<td></td><td><i>Lithic</i></td> +</tr> +</table> + +<p>I have given you this summary account or enumeration of the acids, as +you may find it more satisfactory to have at once an outline or a +general notion of the extent of the subject; but we shall now confine +ourselves to the first class, which requires our more immediate +attention; and defer the few remarks which we shall have to make on the +others, till we treat of the chemistry of the animal and vegetable +kingdoms.</p> + +<p>The acids of simple and known radicals are all capable of being +decomposed by combustible bodies, to which they yield their oxygen. If, +for instance, I pour a drop of sulphuric acid on this piece of +iron, it will produce a spot of rust, you know what that is?</p> + +<span class="pagenum">76</span> +<a name="conver2.page76" id="conver2.page76"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Yes; it is an oxyd, formed by the oxygen of the acid combining with +the iron.</p> + +<p class="speaker">MRS. B.</p> + +<p>In this case you see the sulphur deposits the oxygen by which it was +acidified on the metal. And again, if we pour some acid on a compound +combustible substance, (we shall try it on this piece of wood,) it will +combine with one or more of the constituents of that substance, and +occasion a decomposition.</p> + +<p class="speaker">EMILY.</p> + +<p>It has changed the colour of the wood to black. How is that?</p> + +<p class="speaker">MRS. B.</p> + +<p>The oxygen deposited by the acid has burnt it; you know that wood in +burning becomes black before it is reduced to ashes. Whether it derives +the oxygen which burns it from the atmosphere, or from any other source, +the chemical effect on the wood is the same. In the case of real +combustion, wood becomes black, because it is reduced to the state of +charcoal by the evaporation of its other constituents. But can you tell +me the reason why wood turns black when burnt by the application of an +acid?</p> + +<span class="pagenum">77</span> +<a name="conver2.page77" id="conver2.page77"> </a> +<p class="speaker">CAROLINE.</p> + +<p>First, tell me what are the ingredients of wood?</p> + +<p class="speaker">MRS. B.</p> + +<p>Hydrogen and carbon are the chief constituents of wood, as of all +other vegetable substances.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Well, then, I suppose that the oxygen of the acid combines with the +hydrogen of the wood, to form water; and that the carbon of the wood, +remaining alone, appears of its usual black colour.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well indeed, my dear; that is certainly the most plausible +explanation.</p> + +<p class="speaker">EMILY.</p> + +<p>Would not this be a good method of making charcoal?</p> + +<p class="speaker">MRS. B.</p> + +<p>It would be an extremely expensive, and, I believe, very +imperfect method; for the action of the acid on the wood, and the heat +produced by it, are far from sufficient to deprive the wood of all its +evaporable parts.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What is the reason that vinegar, lemon, and the acid of fruits, do +not produce this effect on wood?</p> + +<span class="pagenum">78</span> +<a name="conver2.page78" id="conver2.page78"> </a> +<p class="speaker">MRS. B.</p> + +<p>They are vegetable acids, whose bases are composed of hydrogen and +carbon; the oxygen, therefore, will not be disposed to quit this +radical, where it is already united with hydrogen. The strongest of +these may, perhaps, yield a little of their oxygen to the wood, and +produce a stain upon it; but the carbon will not be sufficiently +uncovered to assume its black colour. Indeed, the several mineral acids +themselves possess this power of <ins class="mycorr" title="text reads ‘charing’">charring</ins> wood in very different degrees.</p> + +<p class="speaker">EMILY.</p> + +<p>Cannot vegetable acids be decomposed, by any combustibles?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; because their radical is composed of two substances which have a +greater attraction for oxygen than any known body.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And are those strong acids, which burn and decompose wood, capable of +producing similar effects on the skin and flesh of animals?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; all the mineral acids, and one of them more especially, possess +powerful caustic qualities. They actually corrode and destroy the +<span class="pagenum">79</span> +<a name="conver2.page79" id="conver2.page79"> </a> +skin and flesh; but they do not produce upon these exactly the same +alteration they do on wood, probably because there is a great proportion +of nitrogen and other substances in animal matter, which prevents the +separation of carbon from being so conspicuous.</p> + + + + +<span class="pagenum">80</span> +<a name="conver2.page80" id="conver2.page80"> </a> +<h4><a name="convXVII" id="convXVII">CONVERSATION XVII.</a></h4> + +<h4 class="subhead"> +OF THE SULPHURIC AND PHOSPHORIC ACIDS; OR THE COMBINATIONS OF OXYGEN +WITH SULPHUR AND PHOSPHORUS; AND OF THE SULPHATS AND PHOSPHATS.</h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">I</span>n</span> addition to the general survey which we +have taken of acids, I think you will find it interesting to +examine individually a few of the most important of them, and likewise +some of their principal combinations with the alkalies, alkaline earths, +and metals. The first of the acids, in point of importance, is the <span +class="smallroman">SULPHURIC</span>, formerly called <i>oil of +vitriol</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have known it a long time by that name, but had no idea that it was +the same fluid as sulphuric acid. What resemblance or connection can +there be between oil of vitriol and this acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Vitriol is the common name for sulphat of iron, a salt which is +formed by the combination of sulphuric acid and iron; the sulphuric acid +was formerly +<span class="pagenum">81</span> +<a name="conver2.page81" id="conver2.page81"> </a> +obtained by distillation from this salt, and it very naturally received +its name from the substance which afforded it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But it is still usually called oil of vitriol?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; a sufficient length of time has not yet elapsed, since the +invention of the new nomenclature, for it to be generally disseminated; +but, as it is adopted by all scientific chemists, there is every reason +to suppose that it will gradually become universal. When I received this +bottle from the chemists, <i>oil of vitriol</i> was inscribed on the +label; but, as I knew you were very punctilious in regard to the +nomenclature, I changed it, and substituted the words <i>sulphuric +acid</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>This acid has neither colour nor smell, but it appears much thicker +than water.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is nearly twice as heavy as water, and has, you see, an oily +consistence.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And it is probably from this circumstance that +<span class="pagenum">82</span> +<a name="conver2.page82" id="conver2.page82"> </a> +it has been called an oil, for it can have no real claim to that name, +as it does not contain either hydrogen or carbon, which are the +essential constituents of oil.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; and therefore it would be the more absurd to retain a name +which owed its origin to such a mistaken analogy.</p> + +<p>Sulphuric acid, in its purest state, would probably be a concrete +substance, but its attraction for water is such, that it is impossible +to obtain that acid perfectly free from it; it is, therefore, always +seen in a liquid form, such as you here find it. One of the most +striking properties of sulphuric acid is that of evolving a considerable +quantity of heat when mixed with water; this I have already shown +you.</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, I recollect it; but what was the degree of heat produced by that +mixture?</p> + +<p class="speaker">MRS. B.</p> + +<p>The thermometer may be raised by it to 300 degrees, which is +considerably above the temperature of boiling water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Then water might be made to boil in that mixture?</p> + +<span class="pagenum">83</span> +<a name="conver2.page83" id="conver2.page83"> </a> +<p class="speaker">MRS. B.</p> + +<p>Nothing more easy, provided that you employ sufficient quantities of +acid and of water, and in the due proportions. The greatest heat is +produced by a mixture of one part of water to four of the acid: we shall +make a mixture of these proportions, and immerse in it this thin glass +tube, which is full of water.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The vessel feels extremely hot, but the water does not boil yet.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must allow some time for the heat to penetrate the tube, and +raise the temperature of the water to the boiling point—</p> + +<p class="speaker">CAROLINE.</p> + +<p>Now it boils—and with increasing violence.</p> + +<p class="speaker">MRS. B.</p> + +<p>But it will not continue boiling long; for the mixture gives out heat +only while the particles of the water and the acid are mutually +penetrating each other: as soon as the new arrangement of those +particles is effected, the mixture will gradually cool, and the water +return to its former temperature.</p> + +<p>You have seen the manner in which sulphuric +<span class="pagenum">84</span> +<a name="conver2.page84" id="conver2.page84"> </a> +acid decomposes all combustible substances, whether animal, vegetable, +or mineral, and burns them by means of its oxygen?</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have very unintentionally repeated the experiment on my gown, by +letting a drop of the acid fall upon it, and it has made a stain, which, +I suppose, will never wash out.</p> + +<p class="speaker">MRS. B.</p> + +<p>No, certainly; for before you can put it into water, the spot will +become a hole, as the acid has literally burnt the muslin.</p> + +<p class="speaker">CAROLINE.</p> + +<p>So it has, indeed! Well, I will fasten the stopper, and put the +bottle away, for it is a dangerous substance.—Oh, now I have done +worse still, for I have spilt some on my hand!</p> + +<p class="speaker">MRS. B.</p> + +<p>It is then burned, as well as your gown, for you know that oxygen +destroys animal as well as vegetable matters; and, as far as the +decomposition of the skin of your finger is effected, there is no +remedy; but by washing it immediately in water, you will dilute the +acid, and prevent any further injury.</p> + +<span class="pagenum">85</span> +<a name="conver2.page85" id="conver2.page85"> </a> +<p class="speaker">CAROLINE.</p> + +<p>It feels extremely hot, I assure you.</p> + +<p class="speaker">MRS. B.</p> + +<p>You have now learned, by experience, how cautiously this acid must be +used. You will soon become acquainted with another acid, the nitric, +which, though it produces less heat on the skin, destroys it still +quicker, and makes upon it an indelible stain. You should never handle +any substances of this kind, without previously dipping your fingers in +water, which will weaken their caustic effects. But, since you will not +repeat the experiment, I must put in the stopper, for the acid +attracts the moisture from the atmosphere, which would destroy its +strength and purity.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray, how can sulphuric acid be extracted from sulphat of iron by +distillation?</p> + +<p class="speaker">MRS. B.</p> + +<p>The process of distillation, you know, consists in separating +substances from one another by means of their different degrees of +volatility, and by the introduction of a new chemical agent, caloric. +Thus, if sulphat of iron be exposed in a retort to a proper degree of +heat, it will be decomposed, and the sulphuric acid will be +volatilised.</p> + +<span class="pagenum">86</span> +<a name="conver2.page86" id="conver2.page86"> </a> +<p class="speaker">EMILY.</p> + +<p>But now that the process of forming acids by the combustion of their +radicals is known, why should not this method be used for making +sulphuric acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>This is actually done in most manufactures; but the usual method of +preparing sulphuric acid does not consist in burning the sulphur in +oxygen gas (as we formerly did by the way of experiment), but in heating +it together with another substance, nitre, which yields oxygen in +sufficient abundance to render the combustion in common air rapid and +complete.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This substance, then, answers the same purpose as oxygen gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly. In manufactures the combustion is performed in a leaden +chamber, with water at the bottom, to receive the vapour and assist its +condensation. The combustion is, however, never so perfect but that a +quantity of <i>sulphureous</i> acid is formed at the same time; for you +recollect that the sulphureous acid, according to the chemical +nomenclature, differs from the sulphuric only by containing less +oxygen.</p> + +<p>From its own powerful properties, and from the various combinations +into which it enters, sulphuric +<span class="pagenum">87</span> +<a name="conver2.page87" id="conver2.page87"> </a> +acid is of great importance in many of the arts.</p> + +<p>It is used also in medicine in a state of great dilution; for were it +taken internally, in a concentrated state, it would prove a most +dangerous poison.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am sure it would burn the throat and stomach.</p> + +<p class="speaker">MRS. B.</p> + +<p>Can you think of any thing that would prove an antidote to this +poison?</p> + +<p class="speaker">CAROLINE.</p> + +<p>A large draught of water to dilute it.</p> + +<p class="speaker">MRS. B.</p> + +<p>That would certainly weaken the caustic power of the acid, but it +would increase the heat to an intolerable degree. Do you recollect +nothing that would destroy its deleterious properties more +effectually?</p> + +<p class="speaker">EMILY.</p> + +<p>An alkali might, by combining with it; but, then, a pure alkali +is itself a poison, on account of its causticity.</p> + +<p class="speaker">MRS. B.</p> + +<p>There is no necessity that the alkali should be +<span class="pagenum">88</span> +<a name="conver2.page88" id="conver2.page88"> </a> +caustic. Soap, in which it is combined with oil; or magnesia, either in +the state of carbonat, or mixed with water, would prove the best +antidotes.</p> + +<p class="speaker">EMILY.</p> + +<p>In those cases then, I suppose, the potash and the magnesia would +quit their combinations to form salts with the sulphuric acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely.</p> + +<p>We may now make a few observations on the sulphure<i>ous</i> acid, +which we have found to be the product of sulphur slowly and imperfectly +burnt. This acid is distinguished by its pungent smell, and its gaseous +form.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Its aëriform state is, I suppose, owing to the smaller proportion of +oxygen, which renders it lighter than sulphur<i>ic</i> acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Probably; for by adding oxygen to the weaker acid, it may be +converted into the stronger kind. But this change of state may also be +connected with a change of affinity with regard to caloric.</p> + +<p class="speaker">EMILY.</p> + +<p>And may sulphureous acid be obtained from sulphuric acid by a +diminution of oxygen?</p> + +<span class="pagenum">89</span> +<a name="conver2.page89" id="conver2.page89"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes; it can be done by bringing any combustible substance in contact +with the acid. This decomposition is most easily performed by some of +the metals; these absorb a portion of the oxygen from the sulphuric +acid, which is thus converted into the sulphureous, and flies off in its +gaseous form.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And cannot the sulphureous acid itself be decomposed and reduced to +sulphur?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; if this gas be heated in contact with charcoal, the oxygen of +the gas will combine with it, and the pure sulphur is regenerated.</p> + +<p>Sulphureous acid is readily absorbed by water; and in this liquid +state it is found particularly useful in bleaching linen and woollen +cloths, and is much used in manufactures for those purposes. I can +show you its effect in destroying colours, by taking out vegetable +stains—I think I see a spot on your gown, Emily, on which we may +try the experiment.</p> + +<p class="speaker">EMILY.</p> + +<p>It is the stain of mulberries; but I shall be almost afraid of +exposing my gown to the experiment, after seeing the effect which the +sulphuric acid produced on that of Caroline—</p> + +<span class="pagenum">90</span> +<a name="conver2.page90" id="conver2.page90"> </a> +<p class="speaker">MRS. B.</p> + +<p>There is no such danger from the sulphureous; but the experiment must +be made with great caution, for, during the formation of sulphureous +acid by combustion, there is always some sulphuric produced.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But where is your sulphureous acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>We may easily prepare some ourselves, simply by burning a match; we +must first wet the stain with water, and now hold it in this way, at a +little distance, over the lighted match: the vapour that arises from it +is sulphureous acid, and the stain, you see, gradually disappears.</p> + +<p class="speaker">EMILY.</p> + +<p>I have frequently taken out stains by this means, without +understanding the nature of the process. But why is it necessary to wet +the stain before it is exposed to the acid fumes?</p> + +<p class="speaker">MRS. B.</p> + +<p>The moisture attracts and absorbs the sulphureous acid; and it serves +likewise to dilute any particles of sulphuric acid which might injure +the linen.</p> + +<p>Sulphur is susceptible of a third combination +<span class="pagenum">91</span> +<a name="conver2.page91" id="conver2.page91"> </a> +with oxygen, in which the proportion of the latter is too small to +render the sulphur acid. It acquires this slight oxygenation by mere +exposure to the atmosphere, without any elevation of temperature: in +this case, the sulphur does not change its natural form, but is only +discoloured, being changed to red or brown; and in this state it is an +oxyd of sulphur.</p> + +<p>Before we take leave of the sulphuric acid, we shall say a few words +of its principal combinations. It unites with all the alkalies, alkaline +earths and metals, to form compound salts.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, give me leave to interrupt you for a moment: you have never +mentioned any other salts than the compound or neutral salts; is there +no other kind?</p> + +<p class="speaker">MRS. B.</p> + +<p>The term <i>salt</i> has been used, from time immemorial, as a kind +of general name for any substance that has savour, odour, is soluble in +water, and crystallisable, whether it be of an acid, an alkaline, or +compound nature; but the compound salts alone retain that appellation in +modern chemistry.</p> + +<p>The most important of the salts, formed by the combinations of the +sulphuric acid, are, first, <i>sulphat of potash</i>, formerly called +<i>sal polychrest</i>: this +<span class="pagenum">92</span> +<a name="conver2.page92" id="conver2.page92"> </a> +is a very bitter salt, much used in medicine; it is found in the ashes +of most vegetables, but it may be prepared artificially by the immediate +combination of sulphuric acid and potash. This salt is easily soluble in +boiling water. Solubility is, indeed, a property common to all +salts; and they always produce cold in melting.</p> + +<p class="speaker">EMILY.</p> + +<p>That must be owing to the caloric which they absorb in passing from a +solid to a fluid form.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is, certainly, the most probable explanation.</p> + +<p><i>Sulphat of soda</i>, commonly called Glauber’s salt, is another +medicinal salt, which is still more bitter than the preceding. We must +prepare some of these compounds, that you may observe the phenomena +which take place during their formation. We need only pour some +sulphuric acid over the soda which I have put into this glass.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What an amazing heat is disengaged!—I thought you said that +cold was produced by the melting of salts?</p> + +<p class="speaker">MRS. B.</p> + +<p>But you must observe that we are now <i>making</i>, +<span class="pagenum">93</span> +<a name="conver2.page93" id="conver2.page93"> </a> +not <i>melting</i> a salt. Heat is disengaged during the formation of +compound salts, and a faint light is also emitted, which may sometimes +be perceived in the dark.</p> + +<p class="speaker">EMILY.</p> + +<p>And is this heat and light produced by the union of the opposite +electricities of the alkali and the acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>No doubt it is, if that theory be true.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The union of an acid and an alkali is then an actual combustion?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not precisely, though there is certainly much analogy in these +processes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Will this sulphat of soda become solid?</p> + +<p class="speaker">MRS. B.</p> + +<p>We have not, I suppose, mixed the acid and the alkali in the exact +proportions that are required for the formation of the salt, otherwise +the mixture would have been almost immediately changed to a solid mass; +but, in order to obtain it in crystals, as you see it in this bottle, it +would be necessary first to dilute it with water, and afterwards +<span class="pagenum">94</span> +<a name="conver2.page94" id="conver2.page94"> </a> +to evaporate the water, during which operation the salt would gradually +crystallise.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But of what use is the addition of water, if it is afterwards to be +evaporated?</p> + +<p class="speaker">MRS. B.</p> + +<p>When suspended in water, the acid and the alkali are more at liberty +to act on each other, their union is more complete, and the salt assumes +the regular form of crystals during the slow evaporation of its +solvent.</p> + +<p>Sulphat of soda liquefies by heat, and effloresces in the air.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is the meaning of the word <i>effloresces</i>? I do +not recollect your having mentioned it before.</p> + +<p class="speaker">MRS. B.</p> + +<p>A salt is said to effloresce when it loses its water of +crystallisation on being exposed to the atmosphere, and is thus +gradually converted into a dry powder: you may observe that these +crystals of sulphat of soda are far from possessing the transparency +which belongs to their crystalline state; they are covered with a white +powder, occasioned by their having been exposed to the atmosphere, which +has deprived their surface of its lustre, by +<span class="pagenum">95</span> +<a name="conver2.page95" id="conver2.page95"> </a> +absorbing its water of crystallisation. Salts are, in general, either +<i>efflorescent</i> or <i>deliquescent</i>: this latter property is +precisely the reverse of the former; that is to say, deliquescent salts +absorb water from the atmosphere, and are moistened and gradually melted +by it. Muriat of lime is an instance of great deliquescence.</p> + +<p class="speaker">EMILY.</p> + +<p>But are there no salts that have the same degree of attraction for +water as the atmosphere, and that will consequently not be affected +by it?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; there are many such salts, as, for instance, common salt, +sulphat of magnesia, and a variety of others.</p> + +<p><i>Sulphat of lime</i> is very frequently met with in nature, and +constitutes the well-known substance called <i>gypsum</i>, or <i>plaster +of Paris</i>.</p> + +<p><i>Sulphat of magnesia</i>, commonly called <i>Epsom salt</i>, is +another very bitter medicine, which is obtained from sea-water and from +several springs, or may be prepared by the direct combination of its +ingredients.</p> + +<p>We have formerly mentioned <i>sulphat of alumine</i> as constituting +the common <i>alum</i>; it is found in nature chiefly in the +neighbourhood of volcanos, and is particularly useful in the arts, from +its +<span class="pagenum">96</span> +<a name="conver2.page96" id="conver2.page96"> </a> +strong astringent qualities. It is chiefly employed by dyers and +calico-printers, to fix colours; and is used also in the manufacture of +some kinds of leather.</p> + +<p>Sulphuric acid combines also with the metals.</p> + +<p class="speaker">CAROLINE.</p> + +<p>One of these combinations, <i>sulphat of iron</i>, we are already +well acquainted with.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is the most important metallic salt formed by sulphuric acid, +and the only one that we shall here notice. It is of great use in the +arts; and, in medicine, it affords a very valuable tonic: it is of this +salt that most of those preparations called <i>steel medicines</i> are +composed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But does any carbon enter into these compositions to form steel?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not an atom: they are, therefore, very improperly called steel: but +it is the vulgar appellation, and medical men themselves often comply +with the general custom.</p> + +<p>Sulphat of iron may be prepared, as you have seen, by dissolving iron +in sulphuric acid; but it +<span class="pagenum">97</span> +<a name="conver2.page97" id="conver2.page97"> </a> +is generally obtained from the natural production called <i>Pyrites</i>, +which being a sulphuret of iron, requires only exposure to the +atmosphere to be oxydated, in order to form the salt; this, therefore, +is much the most easy way of procuring it on a large scale.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised to find that both acids and compound salts are +generally obtained from their various combinations, rather than from the +immediate union of their ingredients.</p> + +<p class="speaker">MRS. B.</p> + +<p>Were the simple bodies always at hand, their combinations would +naturally be the most convenient method of forming compounds; but you +must consider that, in most instances, there is great difficulty and +expense in obtaining the simple ingredients from their combinations; it +is, therefore, often more expedient to procure compounds from the +decomposition of other compounds. But, to return to the sulphat of +iron.—There is a certain vegetable acid called <i>Gallic acid</i>, +which has the remarkable property of precipitating this salt +black—I shall pour a few drops of the gallic acid into this +solution of sulphat of iron—</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is become as black as ink!</p> + +<span class="pagenum">98</span> +<a name="conver2.page98" id="conver2.page98"> </a> +<p class="speaker">MRS. B.</p> + +<p>And it is ink in reality. Common writing ink is a precipitate of +sulphat of iron by gallic acid; the black colour is owing to the +formation of gallat of iron, which being insoluble, remains suspended in +the fluid.</p> + +<p>This acid has also the property of altering the colour of iron in its +metallic state. You may frequently see its effect on the blade of a +knife, that has been used to cut certain kinds of fruits.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; and that is, perhaps, the reason that a silver knife is +preferred to cut fruits; the gallic acid, I suppose, does not act +upon silver.—Is this acid found in all fruits?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is contained, more or less, in the rind of most fruits and roots, +especially the radish, which, if scraped with a steel or iron knife, has +its bright red colour changed to a deep purple, the knife being at the +same time blackened. But the vegetable substance in which the gallic +acid most abounds is <i>nutgall</i>, a kind of excrescence that +grows on oaks, and from which the acid is commonly obtained for its +various purposes.</p> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<span class="pagenum">99</span> +<a name="conver2.page99" id="conver2.page99"> </a> + +<p class="speaker">MRS. B.</p> + +<p>We now come to the <span class="smallroman">PHOSPHORIC</span> and +<span class="smallroman">PHOSPHOROUS ACIDS</span>. In treating of +phosphorus, you have seen how these acids may be obtained from it by +combustion?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes; but I should be much surprised if it was the usual method of +obtaining them, since it is so very difficult to procure phosphorus in +its pure state.</p> + +<p class="speaker">MRS. B.</p> + +<p>You are right, my dear; the phosphoric acid, for general purposes, is +extracted from bones, in which it is contained in the state of phosphat +of lime; from this salt the phosphoric acid is separated by means of the +sulphuric, which combines with the lime. In its pure state, phosphoric +acid is either liquid or solid, according to its degree of +concentration.</p> + +<p>Among the salts formed by this acid, <i>phosphat of lime</i> is the +only one that affords much interest; and this, we have already observed, +constitutes the basis of all bones. It is also found in very small +quantities in some vegetables.</p> + + + + +<span class="pagenum">100</span> +<a name="conver2.page100" id="conver2.page100"> </a> +<h4><a name="convXVIII" id="convXVIII">CONVERSATION XVIII.</a></h4> + +<h4 class="subhead"> +OF THE NITRIC AND CARBONIC ACIDS: OR THE COMBINATIONS OF OXYGEN WITH +NITROGEN AND CARBON; AND OF THE NITRATS AND CARBONATS.</h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">I</span> +am</span> almost afraid of introducing the subject of the <span class="smallroman">NITRIC ACID</span>, as I am sure that I shall be blamed by +Caroline for not having made her acquainted with it before.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Why so, Mrs. B.?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because you have long known its radical, which is nitrogen or azote; +and in treating of that element, I did not even hint that it was +the basis of an acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And what could be your reason for not <ins class="mycorr" title="text reads ‘mention-/this’ at line break">mentioning this</ins> acid +sooner?</p> + +<p class="speaker">MRS. B.</p> + +<p>I do not know whether you will think the reason +<span class="pagenum">101</span> +<a name="conver2.page101" id="conver2.page101"> </a> +sufficiently good to acquit me; but the omission, I assure you, did +not proceed from negligence. You may recollect that nitrogen was one of +the first simple bodies which we examined; you were then ignorant of the +theory of combustion, which I believe was, for the first time, mentioned +in that lesson; and therefore it would have been in vain, at that time, +to have attempted to explain the nature and formation of acids.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I wonder, however, that it never occurred to us to enquire whether +nitrogen could be acidified; for, as we knew it was classed among the +combustible bodies, it was natural to suppose that it might produce an +acid.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is not a necessary consequence; for it might combine with oxygen +only in the degree requisite to form an oxyd. But you will find that +nitrogen is susceptible of various degrees of oxygenation, some of which +convert it merely into an oxyd, and others give it all the acid +properties.</p> + +<p>The acids, resulting from the combination of oxygen and nitrogen, are +called the <span class="smallroman">NITROUS</span> and <span class="smallroman">NITRIC</span> acids. We will begin with the <span class="smallroman">NITRIC</span>, in which nitrogen is in the highest state of +oxygenation. This acid naturally exists in the form of +<span class="pagenum">102</span> +<a name="conver2.page102" id="conver2.page102"> </a> +gas; but is so very soluble in water, and has so great an affinity for +it, that one grain of water will absorb and condense ten grains of acid +gas, and form the limpid fluid which you see in this bottle.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a strong offensive smell it has!</p> + +<p class="speaker">MRS. B.</p> + +<p>This acid contains a greater abundance of oxygen than any other, but +it retains it with very little force.</p> + +<p class="speaker">EMILY.</p> + +<p>Then it must be a powerful caustic, both from the facility with which +it parts with its oxygen, and the quantity which it affords?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well, Emily; both cause and effect are exactly such as you +describe: nitric acid burns and destroys all kinds of organised matter. +It even sets fire to some of the most combustible substances.—We +shall pour a little of it over this piece of dry warm charcoal—you +see it inflames it immediately; it would do the same with oil of +turpentine, phosphorus, and several other very combustible bodies. This +shows you how easily this acid is decomposed by combustible bodies, +<span class="pagenum">103</span> +<a name="conver2.page103" id="conver2.page103"> </a> +since these effects must depend upon the absorption of its oxygen.</p> + +<p>Nitric acid has been used in the arts from time immemorial, but it is +only within these twenty-five years that its chemical nature has been +ascertained. The celebrated Mr. Cavendish discovered that it consisted +of about 10 parts of nitrogen and 25 of oxygen.<a class="tag" name="tag23" id="tag23" href="#note23">*</a> These principles, in their +gaseous state, combine at a high temperature; and this may be effected +by repeatedly passing the electrical spark through a mixture of the two +gases.</p> + +<p class="speaker">EMILY.</p> + +<p>The nitrogen and oxygen gases, of which the atmosphere is composed, +do not combine, I suppose, because their temperature is not +sufficiently elevated?</p> + +<p class="speaker">CAROLINE.</p> + +<p>But in a thunder-storm, when the lightning repeatedly passes through +them, may it not produce nitric acid? We should be in a strange +situation, if a violent storm should at once convert the atmosphere into +nitric acid.</p> + +<p class="speaker">MRS. B.</p> + +<p>There is no danger of it, my dear; the lightning can affect but a +very small portion of the atmosphere, +<span class="pagenum">104</span> +<a name="conver2.page104" id="conver2.page104"> </a> +and though it were occasionally to produce a little nitric acid, yet +this never could happen to such an extent as to be perceivable.</p> + +<p class="speaker">EMILY.</p> + +<p>But how could the nitric acid be known, and used, before the method +of combining its constituents was discovered?</p> + +<p class="speaker">MRS. B.</p> + +<p>Before that period the nitric acid was obtained, and it is indeed +still extracted, for the common purposes of art, from the compound salt +which it forms with potash, commonly called <i>nitre</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Why is it so called? Pray, Mrs. B., let these old unmeaning names be +entirely given up, by us at least; and let us call this salt <i>nitrat +of potash</i>.</p> + +<p class="speaker">MRS. B.</p> + +<p>With all my heart; but it is necessary that I should, at least, +mention the old names, and more especially those which are yet in common +use; otherwise, when you meet with them, you would not be able to +understand their meaning.</p> + +<p class="speaker">EMILY.</p> + +<p>And how is the acid obtained from this salt?</p> + +<span class="pagenum">105</span> +<a name="conver2.page105" id="conver2.page105"> </a> +<p class="speaker">MRS. B.</p> + +<p>By the intervention of sulphuric acid, which combines with the +potash, and sets the nitric acid at liberty. This I can easily show you, +by mixing some nitrat of potash and sulphuric acid in this retort, and +heating it over a lamp; the nitric acid will come over in the form of +vapour, which we shall collect in a glass bell. This acid, diluted in +water, is commonly called <i>aqua fortis</i>, if Caroline will allow me +to mention that name.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have often heard that aqua fortis will dissolve almost all metals; +it is no doubt because it yields its oxygen so easily.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and from this powerful solvent property, it derived the name of +aqua fortis, or strong water. Do you not recollect that we oxydated, and +afterwards dissolved, some copper in this acid?</p> + +<p class="speaker">EMILY.</p> + +<p>If I remember right, the nitrat of copper was the first instance you +gave us of a compound salt.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Can the nitric acid be completely decomposed and converted into +nitrogen and oxygen?</p> + +<span class="pagenum">106</span> +<a name="conver2.page106" id="conver2.page106"> </a> +<p class="speaker">EMILY.</p> + +<p>That cannot be the case, Caroline; since the acid can be decomposed +only by the combination of its constituents with other bodies.</p> + +<p class="speaker">MRS. B.</p> + +<p>True; but caloric is sufficient for this purpose. By making the acid +pass through a red hot porcelain tube, it is decomposed; the nitrogen +and oxygen regain the caloric which they had lost in combining, and are +thus both restored to their gaseous state.</p> + +<p>The nitric acid may also be partly decomposed, and is by this means +converted into <span class="smallroman">NITROUS ACID</span>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This conversion must be easily effected, as the oxygen is so slightly +combined with the nitrogen.</p> + +<p class="speaker">MRS. B.</p> + +<p>The partial decomposition of nitric acid is readily effected by most +metals; but it is sufficient to expose the nitric acid to a very strong +light to make it give out oxygen gas, and thus be converted into nitrous +acid. Of this acid there are various degrees, according to the +proportions of oxygen which it contains; the strongest, and that into +which the nitric is first converted, is of a yellow colour, as you see +in this bottle.</p> + +<span class="pagenum">107</span> +<a name="conver2.page107" id="conver2.page107"> </a> +<p class="speaker">CAROLINE.</p> + +<p>How it fumes when the stopper is taken out!</p> + +<p class="speaker">MRS. B.</p> + +<p>The acid exists naturally in a gaseous state, and is here so strongly +concentrated in water, that it is constantly escaping.</p> + +<p>Here is another bottle of nitrous acid, which, you see, is of an +orange red; this acid is weaker, the nitrogen being combined with a +smaller quantity of oxygen; and with a still less proportion of oxygen +it is an olive-green colour, as it appears in this third bottle. In +short, the weaker the acid, the deeper is its colour.</p> + +<p>Nitrous acid acts still more powerfully on some inflammable +substances than the nitric.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised at that, as it contains less oxygen.</p> + +<p class="speaker">MRS. B.</p> + +<p>But, on the other hand, it parts with its oxygen much more readily: +you may recollect that we once inflamed oil with this acid.</p> + +<p>The next combinations of nitrogen and oxygen form only oxyds of +nitrogen, the first of which is commonly called <i>nitrous air</i>; or +more properly <i>nitric oxyd gas</i>. This may be obtained from nitric +acid, by exposing the latter to the action of metals, +<span class="pagenum">108</span> +<a name="conver2.page108" id="conver2.page108"> </a> +as in dissolving them it does not yield the whole of its oxygen, but +retains a portion of this principle sufficient to convert it into this +peculiar gas, a specimen of which I have prepared, and preserved +within this inverted glass bell.</p> + +<p class="speaker">EMILY.</p> + +<p>It is a perfectly invisible elastic fluid.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and it may be kept any length of time in this manner over water, +as it is not, like the nitric and nitrous acids, absorbable by it. It is +rather heavier than atmospherical air, and is incapable of supporting +either combustion or respiration. I am going to incline the glass +gently on one side, so as to let some of the gas escape—</p> + +<p class="speaker">EMILY.</p> + +<p>How very curious!—It produces orange fumes like the nitrous +acid! that is the more extraordinary, as the gas within the glass is +perfectly invisible.</p> + +<p class="speaker">MRS. B.</p> + +<p>It would give me much pleasure if you could make out the reason of +this curious change without requiring any further explanation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It seems, by the colour and smell, as if it were +<span class="pagenum">109</span> +<a name="conver2.page109" id="conver2.page109"> </a> +converted into nitrous acid gas: yet that cannot be, unless it combines +with more oxygen; and how can it obtain oxygen the very instant it +escapes from the glass?</p> + +<p class="speaker">EMILY.</p> + +<p>From the atmosphere, no doubt. Is it not so, Mrs. B.?</p> + +<p class="speaker">MRS. B.</p> + +<p>You have guessed it; as soon as it comes in contact with the +atmosphere, it absorbs from it the additional quantity of oxygen +necessary to convert it into nitrous acid gas. And, if I now remove the +bottle entirely from the water, so as to bring at once the whole of the +gas into contact with the atmosphere, this conversion will appear still +more striking—</p> + +<p class="speaker">EMILY.</p> + +<p>Look, Caroline, the whole capacity of the bottle is instantly tinged +of an orange colour!</p> + +<p class="speaker">MRS. B.</p> + +<p>Thus, you see, it is the most easy process imaginable to convert +<i>nitrous oxyd gas</i> into <i>nitrous acid gas</i>. The property of +attracting oxygen from the atmosphere, without any elevation of +temperature, has occasioned this gaseous oxyd being used as a test for +ascertaining the degree +<span class="pagenum">110</span> +<a name="conver2.page110" id="conver2.page110"> </a> +of purity of the atmosphere. I am going to show you how it is +applied to this purpose.—You see this graduated glass tube, which +is closed at one end, (<a class="smallcaps" href="#plateXb">Plate X.</a> Fig. 2.)—I first +fill it with water, and then introduce a certain measure of nitrous gas, +which, not being absorbable by water, passes through it, and occupies +the upper part of the tube. I must now add rather above two-thirds +of oxygen gas, which will just be sufficient to convert the nitrous oxyd +gas into nitrous acid gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>So it has!—I saw it turn of an orange colour; but it +immediately afterwards disappeared entirely, and the water, you see, has +risen, and almost filled the tube.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is because the acid gas is absorbable by water, and in +proportion as the gas impregnates the water, the latter rises in the +tube. When the oxygen gas is very pure, and the required proportion of +nitrous oxyd gas very exact, the whole is absorbed by the water; but if +any other gas be mixed with the oxygen, instead of combining with the +nitrous oxygen, it will remain and occupy the upper part of the tube; +or, if the gases be not in the due proportion, there will be a residue +of that which predominates.—Before we leave this +<span class="pagenum">111</span> +<a name="conver2.page111" id="conver2.page111"> </a> +subject, I must not forget to remark that nitrous acid may be +formed by dissolving nitrous oxyd gas in nitric acid. This solution may +be effected simply by making bubbles of nitrous oxyd gas pass through +nitric acid.</p> + +<p class="speaker">EMILY.</p> + +<p>That is to say, that nitrogen at its highest degree of oxygenation, +being mixed with nitrogen at its lowest degree of oxygenation, will +produce a kind of intermediate substance, which is nitrous acid.</p> + +<p class="speaker">MRS. B.</p> + +<p>You have stated the fact with great precision.—There are +various other methods of preparing nitrous oxyd, and of obtaining it +from compound bodies; but it is not necessary to enter into these +particulars. It remains for me only to mention another curious +modification of oxygenated nitrogen, which has been distinguished by the +name of <i>gaseous oxyd of nitrogen</i>. It is but lately that this gas +has been accurately examined, and its properties have been investigated +chiefly by Sir H. Davy. It has obtained also the name of +<i>exhilarating</i> gas, from the very singular property which that +gentleman has discovered in it, of elevating the animal spirits, when +inhaled into the lungs, to a degree sometimes resembling delirium or +intoxication.</p> + +<span class="pagenum">112</span> +<a name="conver2.page112" id="conver2.page112"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Is it respirable, then?</p> + +<p class="speaker">MRS. B.</p> + +<p>It can scarcely be called respirable, as it would not support life +for any length of time; but it may be breathed for a few moments without +any other effects, than the singular exhilaration of spirits I have just +mentioned. It affects different people, however, in a very different +manner. Some become violent, even outrageous: others experience a +languor, attended with faintness; but most agree in opinion, that the +sensations it excites are extremely pleasant.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think I should like to try it—how do you breathe it?</p> + +<p class="speaker">MRS. B.</p> + +<p>By collecting the gas in a bladder, to which a short tube with a +stop-cock is adapted; this is applied to the mouth with one hand, whilst +the nostrils are kept closed with the other, that the common air may +have no access. You then alternately inspire, and expire the gas, till +you perceive its effects. But I cannot consent to your making the +experiment; for the nerves are sometimes unpleasantly affected by it, +and I would not run any risk of that kind.</p> + +<span class="pagenum">113</span> +<a name="conver2.page113" id="conver2.page113"> </a> +<p class="speaker">EMILY.</p> + +<p>I should like, at least, to see somebody breathe it; but pray by what +means is this curious gas obtained?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is procured from <i>nitrat of ammonia</i>, an artificial salt +which yields this gas on the application of a gentle heat. I have +put some of the salt into a retort, and by the aid of a lamp the gas +will be extricated.—</p> + +<p class="speaker">CAROLINE.</p> + +<p>Bubbles of air begin to escape through the neck of the retort into +the water apparatus; will you not collect them?</p> + +<p class="speaker">MRS. B.</p> + +<p>The gas that first comes over need not be preserved, as it consists +of little more than the common air that was in the retort; besides, +there is always in this experiment a quantity of watery vapour which +must come away before the nitrous oxyd appears.</p> + +<p class="speaker">EMILY.</p> + +<p>Watery vapour! Whence does that proceed? There is no water in nitrat +of ammonia?</p> + +<p class="speaker">MRS. B.</p> + +<p>You must recollect that there is in every salt a quantity of water of +crystallisation, which may +<span class="pagenum">114</span> +<a name="conver2.page114" id="conver2.page114"> </a> +be evaporated by heat alone. But, besides this, water is actually +generated in this experiment, as you will see presently. First tell me, +what are the constituent parts of nitrat of ammonia?</p> + +<p class="speaker">EMILY.</p> + +<p>Ammonia, and nitric acid: this salt, therefore, contains three +different elements, nitrogen and hydrogen, which produce the ammonia; +and oxygen, which, with nitrogen, forms the acid.</p> + +<p class="speaker">MRS. B.</p> + +<p>Well then, in this process the ammonia is decomposed; the hydrogen +quits the nitrogen to combine with some of the oxygen of the nitric +acid, and forms with it the watery vapour which is now coming over. When +that is effected, what will you expect to find?</p> + +<p class="speaker">EMILY.</p> + +<p>Nitrous acid instead of nitric acid, and nitrogen instead of +ammonia.</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so; and the nitrous acid and nitrogen combine, and form the +gaseous oxyd of nitrogen, in which the proportion of oxygen is 37 parts +to 63 of nitrogen.</p> + +<p>You may have observed, that for a little while +<span class="pagenum">115</span> +<a name="conver2.page115" id="conver2.page115"> </a> +no bubbles of air have come over, and we have perceived only a stream of +vapour condensing as it issued into the water.—Now bubbles of air +again make their appearance, and I imagine that by this time all the +watery vapour is come away, and that we may begin to collect the gas. We +may try whether it is pure, by filling a phial with it, and plunging a +taper into it—yes, it will do now, for the taper burns brighter +than in the common air, and with a greenish flame.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how is that? I thought no gas would support combustion but oxygen +or chlorine.</p> + +<p class="speaker">MRS. B.</p> + +<p>Or any gas that contains oxygen, and is ready to yield it, which is +the case with this in a considerable degree; it is not, therefore, +surprising that it should accelerate the combustion of the taper.</p> + +<p>You see that the gas is now produced in great abundance; we shall +collect a large quantity of it, and I dare say that we shall find some +of the family who will be curious to make the experiment of respiring +it. Whilst this process is going on, we may take a general survey of the +most important combinations of the nitric and nitrous acids with the +alkalies.</p> + +<span class="pagenum">116</span> +<a name="conver2.page116" id="conver2.page116"> </a> +<p>The first of these is <i>nitrat of potash</i>, commonly called +<i>nitre</i> or <i>saltpetre</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is not that the salt with which gunpowder is made?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes. Gunpowder is a mixture of five parts of nitre to one of sulphur, +and one of charcoal.—Nitre from its great proportion of oxygen, +and from the facility with which it yields it, is the basis of most +detonating compositions.</p> + +<p class="speaker">EMILY.</p> + +<p>But what is the cause of the violent detonation of gunpowder when set +fire to?</p> + +<p class="speaker">MRS. B.</p> + +<p>Detonation may proceed from two causes; the sudden formation or +destruction of an elastic fluid. In the first case, when either a solid +or liquid is instantaneously converted into an elastic fluid, the +prodigious and sudden expansion of the body strikes the air with great +violence, and this concussion produces the sound called detonation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That I comprehend very well; but how can a similar effect be produced +by the destruction of a gas?</p> + +<span class="pagenum">117</span> +<a name="conver2.page117" id="conver2.page117"> </a> +<p class="speaker">MRS. B.</p> + +<p>A gas can be destroyed only by condensing it to a liquid or solid +state; when this takes place suddenly, the gas, in assuming a new and +more compact form, produces a vacuum, into which the surrounding air +rushes with great impetuosity; and it is by that rapid and violent +motion that the sound is produced. In all detonations, therefore, gases +are either suddenly formed, or destroyed. In that of gunpowder, can you +tell me which of these two circumstances takes place?</p> + +<p class="speaker">EMILY.</p> + +<p>As gunpowder is a solid, it must, of course, produce the gases in its +detonation; but how, I cannot tell.</p> + +<p class="speaker">MRS. B.</p> + +<p>The constituents of gunpowder, when heated to a certain degree, enter +into a number of new combinations, and are instantaneously converted +into a variety of gases, the sudden expansion of which gives rise to the +detonation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And in what instance does the destruction or condensation of gases +produce detonation?</p> + +<p class="speaker">MRS. B.</p> + +<p>I can give you one with which you are well +<span class="pagenum">118</span> +<a name="conver2.page118" id="conver2.page118"> </a> +acquainted; the sudden combination of the oxygen and hydrogen gases.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; I recollect perfectly that hydrogen detonates with oxygen when +the two gases are converted into water.</p> + +<p class="speaker">MRS. B.</p> + +<p>But let us return to the nitrat of potash.—This salt is +decomposed when exposed to heat, and mixed with any combustible body, +such as carbon, sulphur, or metals, these substances oxydating rapidly +at the expense of the nitrat. I must show you an instance of +this.—I expose to the fire some of the salt in a small iron +ladle, and, when it is sufficiently heated, add to it some powdered +charcoal; this will attract the oxygen from the salt, and be converted +into carbonic acid.—</p> + +<p class="speaker">EMILY.</p> + +<p>But what occasions that crackling noise, and those vivid flashes that +accompany it?</p> + +<p class="speaker">MRS. B.</p> + +<p>The rapidity with which the carbonic acid gas is formed occasions a +succession of small detonations, which, together with the emission of +flame, is called <i>deflagration</i>.</p> + +<p><i>Nitrat of ammonia</i> we have already noticed, +<span class="pagenum">119</span> +<a name="conver2.page119" id="conver2.page119"> </a> +on account of the gaseous oxyd of nitrogen which is obtained +from it.</p> + +<p><i>Nitrat of silver</i> is the lunar caustic, so remarkable for its +property of destroying animal fibre, for which purpose it is often used +by surgeons.—We have said so much on a former occasion, on the +mode in which caustics act on animal matter, that I shall not detain you +any longer on this subject.</p> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p>We now come to the <span class="smallroman">CARBONIC ACID</span>, +which we have already had many opportunities of noticing. You recollect +that this acid may be formed by the combustion of carbon, whether in its +imperfect state of charcoal, or in its purest form of diamond. And it is +not necessary, for this purpose, to burn the carbon in oxygen gas, as we +did in the preceding lecture; for you need only light a piece of +charcoal and suspend it under a receiver on the water bath. The charcoal +will soon be extinguished, and the air in the receiver will be found +mixed with carbonic acid. The process, however, is much more expeditious +if the combustion be performed in pure oxygen gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how can you separate the carbonic acid, +<span class="pagenum">120</span> +<a name="conver2.page120" id="conver2.page120"> </a> +obtained in this manner, from the air with which it is mixed?</p> + +<p class="speaker">MRS. B.</p> + +<p>The readiest mode is to introduce under the receiver a quantity of +caustic lime, or caustic alkali, which soon attracts the whole of the +carbonic acid to form a carbonat.—The alkali is found increased in +weight, and the volume of the air is diminished by a quantity equal to +that of the carbonic acid which was mixed with it.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray is there no method of obtaining pure carbon from carbonic +acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>For a long time it was supposed that carbonic acid was not +decompoundable; but Mr. Tennant discovered, a few years ago, that +this acid may be decomposed by burning phosphorus in a closed vessel +with carbonat of soda or carbonat of lime: the phosphorus absorbs the +oxygen from the carbonat, whilst the carbon is separated in the form of +a black powder. This decomposition, however, is not effected simply by +the attraction of the phosphorus for oxygen, since it is weaker than +that of charcoal; but the attraction of the alkali of lime for the +phosphoric acid, unites its power at the same time.</p> + +<span class="pagenum">121</span> +<a name="conver2.page121" id="conver2.page121"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Cannot we make that experiment?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not easily; it requires being performed with extreme nicety, in order +to obtain any sensible quantity of carbon, and the experiment is much +too delicate for me to attempt it. But there can be no doubt of the +accuracy of Mr. Tennant’s results; and all chemists now agree, that one +hundred parts of carbonic acid gas consists of about twenty-eight parts +of carbon to seventy-two of oxygen gas. But if you recollect, we +decomposed carbonic acid gas the other day by burning potassium +in it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True, so we did; and found the carbon precipitated on the regenerated +potash.</p> + +<p class="speaker">MRS. B.</p> + +<p>Carbonic acid gas is found very abundantly in nature; it is supposed +to form about one thousandth part of the atmosphere, and is constantly +produced by the respiration of animals; it exists in a great variety of +combinations, and is exhaled from many natural decompositions. It is +contained in a state of great purity in certain caves, such as the +<i>Grotto del Cane</i>, near Naples.</p> + +<span class="pagenum">122</span> +<a name="conver2.page122" id="conver2.page122"> </a> +<p class="speaker">EMILY.</p> + +<p>I recollect having read an account of that grotto, and of the cruel +experiments made on the poor dogs, to gratify the curiosity of +strangers. But I understood that the vapour exhaled by this cave was +called <i>fixed air</i>.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is the name by which carbonic acid was known before its chemical +composition was discovered.—This gas is more destructive of life +than any other; and if the poor animals that are submitted to its +effects are not plunged into cold water as soon as they become +senseless, they do not recover. It extinguishes flame instantaneously. +I have collected some in this glass, which I will pour over the +candle.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This is extremely singular—it seems to extinguish it as it were +by enchantment, as the gas is invisible. I never should have +imagined that gas could have been poured like a liquid.</p> + +<p class="speaker">MRS. B.</p> + +<p>It can be done with carbonic acid only, as no other gas is +sufficiently heavy to be susceptible of being poured out in the +atmospherical air without mixing with it.</p> + +<span class="pagenum">123</span> +<a name="conver2.page123" id="conver2.page123"> </a> +<p class="speaker">EMILY.</p> + +<p>Pray by what means did you obtain this gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>I procured it from marble. Carbonic acid gas has so strong an +attraction for all the alkalies and alkaline earths, that these are +always found in nature in the state of carbonats. Combined with lime, +this acid forms chalk, which may be considered as the basis of all kinds +of marbles, and calcareous stones. From these substances carbonic acid +is easily separated, as it adheres so slightly to its combinations, that +the carbonats are all decomposable by any of the other acids. I can +easily show you how I obtained this gas; I poured some diluted +sulphuric acid over pulverised marble in this bottle (the same which we +used the other day to prepare hydrogen gas), and the gas escaped through +the tube connected with it; the operation still continues, as you may +easily perceive—</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, it does; there is a great fermentation in the glass vessel. What +singular commotion is excited by the sulphuric acid taking possession of +the lime, and driving out the carbonic acid!</p> + +<p class="speaker">CAROLINE.</p> + +<p>But did the carbonic acid exist in a gaseous state in the marble?</p> + +<span class="pagenum">124</span> +<a name="conver2.page124" id="conver2.page124"> </a> +<p class="speaker">MRS. B.</p> + +<p>Certainly not; the acid, when in a state of combination, is capable +of existing in a solid form.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Whence, then, does it obtain the caloric necessary to convert it into +gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>It may be supplied in this case from the mixture of sulphuric acid +and water, which produces an evolution of heat, even greater than is +required for the purpose; since, as you may perceive by touching the +glass vessel, a considerable quantity of the caloric disengaged +becomes sensible. But a supply of caloric may be obtained also from a +diminution of capacity for heat, occasioned by the new combination which +takes place; and, indeed, this must be the case when other acids are +employed for the disengagement of carbonic acid gas, which do not, like +the sulphuric, produce heat on being mixed with water. Carbonic acid may +likewise be disengaged from its combinations by heat alone, which +restores it to its gaseous state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It appears to me very extraordinary that the same gas, which is +produced by the burning of wood and coals, should exist also in such +bodies +<span class="pagenum">125</span> +<a name="conver2.page125" id="conver2.page125"> </a> +as marble, and chalk, which are incombustible substances.</p> + +<p class="speaker">MRS. B.</p> + +<p>I will not answer that objection, Caroline, because I think I can put +you in a way of doing it yourself. Is carbonic acid combustible?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Why, no—because it is a body that has been already burnt; it is +carbon only, and not the acid, that is combustible.</p> + +<p class="speaker">MRS. B.</p> + +<p>Well, and what inference do you draw from this?</p> + +<p class="speaker">CAROLINE.</p> + +<p>That carbonic acid cannot render the bodies with which it is united +combustible; but that simple carbon does, and that it is in this +elementary state that it exists in wood, coals, and a great variety of +other combustible bodies.—Indeed, Mrs. B., you are very +ungenerous; you are not satisfied with convincing me that my objections +are frivolous, but you oblige me to prove them so myself.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must confess, however, that I make ample amends for the detection +of error, when I enable +<span class="pagenum">126</span> +<a name="conver2.page126" id="conver2.page126"> </a> +you to discover the truth. <ins class="correction" title="all commas in original">You, +understand, now,</ins> I hope, that carbonic acid +is equally produced by the decomposition of chalk, or by the combustion +of charcoal. These processes are certainly of a very different nature; +in the first case the acid is already formed, and requires nothing more +than heat to restore it to its gaseous state; whilst, in the latter, the +acid is actually made by the process of combustion.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I understand it now perfectly. But I have just been thinking of +another difficulty, which, I hope, you will excuse my not being +able to remove myself. How does the immense quantity of calcareous +earth, which is spread all over the globe, obtain the carbonic acid with +which it is combined?</p> + +<p class="speaker">MRS. B.</p> + +<p>The question is, indeed, not very easy to answer; but I conceive that +the general carbonisation of calcareous matter may have been the effect +of a general combustion, occasioned by some revolution of our globe, and +producing an immense supply of carbonic acid, with which the calcareous +matter became impregnated; or that this may have been effected by a +gradual absorption of carbonic acid from the atmosphere.—But this +would lead us to discussions which we cannot indulge +<span class="pagenum">127</span> +<a name="conver2.page127" id="conver2.page127"> </a> +in, without deviating too much from our subject.</p> + +<p class="speaker">EMILY.</p> + +<p>How does it happen that we do not perceive the pernicious effects of +the carbonic acid which is floating in the atmosphere?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because of the state of very great dilution in which it exists there. +But can you tell me, Emily, what are the sources which keep the +atmosphere constantly supplied with this acid?</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose the combustion of wood, coals, and other substances, that +contain carbon.</p> + +<p class="speaker">MRS. B.</p> + +<p>And also the breath of animals.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The breath of animals! I thought you said that this gas was not at +all respirable, but on the contrary, extremely poisonous.</p> + +<p class="speaker">MRS. B.</p> + +<p>So it is; but although animals cannot breathe in carbonic acid gas, +yet, in the process of respiration, they have the power of forming this +gas in +<span class="pagenum">128</span> +<a name="conver2.page128" id="conver2.page128"> </a> +their lungs; so that the air which we <i>expire</i>, or reject from the +lungs, always contains a certain proportion of carbonic acid, which is +much greater than that which is commonly found in the atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what is it that renders carbonic acid such a deadly poison?</p> + +<p class="speaker">MRS. B.</p> + +<p>The manner in which this gas destroys life, seems to be merely by +preventing the access of respirable air; for carbonic acid gas, unless +very much diluted with common air, does not penetrate into the lungs, as +the windpipe actually contracts and refuses it admittance.—But we +must dismiss this subject at present, as we shall have an opportunity of +treating of respiration much more fully, when we come to the chemical +functions of animals.</p> + +<p class="speaker">EMILY.</p> + +<p>Is carbonic acid as destructive to the life of vegetables as it is to +that of animals?</p> + +<p class="speaker">MRS. B.</p> + +<p>If a vegetable be completely immersed in it, I believe it +generally proves fatal to it; but mixed in certain proportions with +atmospherical air, it is, on the contrary, very favourable to +vegetation.</p> + +<span class="pagenum">129</span> +<a name="conver2.page129" id="conver2.page129"> </a> +<p>You remember, I suppose, our mentioning the mineral waters, both +natural and artificial, which contain carbonic acid gas?</p> + +<p class="speaker">CAROLINE.</p> + +<p>You mean the Seltzer water?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is one of those which are the most used; there are, however, +a variety of others into which carbonic acid enters as an +ingredient: all these waters are usually distinguished by the name of +<i>acidulous</i> or <i>gaseous mineral waters</i>.</p> + +<p>The class of salts called <i>carbonats</i> is the most numerous in +nature; we must pass over them in a very cursory manner, as the subject +is far too extensive for us to enter on it in detail. The state of +carbonat is the natural state of a vast number of minerals, and +particularly of the alkalies and alkaline earths, as they have so great +an attraction for the carbonic acid, that they are almost always found +combined with it; and you may recollect that it is only by separating +them from this acid, that they acquire that causticity and those +striking qualities which I have formerly described. All marbles, chalks, +shells, calcareous spars, and lime-stones of every description, are +neutral salts, in which <i>lime</i>, their common basis, has lost all +its characteristic properties.</p> + +<span class="pagenum">130</span> +<a name="conver2.page130" id="conver2.page130"> </a> +<p class="speaker">EMILY.</p> + +<p>But if all these various substances are formed by the union of lime +with carbonic acid, whence arises their diversity of form and +appearance?</p> + +<p class="speaker">MRS. B.</p> + +<p>Both from the different proportions of their component parts, and +from a variety of foreign ingredients which may be occasionally blended +with them: the veins and colours of marbles, for instance, proceed from +a mixture of metallic substances; silex and alumine also frequently +enter into these combinations. The various carbonats, therefore, that I +have enumerated, cannot be considered as pure unadulterated neutral +salts, although they certainly belong to that class of bodies.</p> + +<p class="footnote"> +<a name="note23" id="note23" href="#tag23">*</a> +The proportion stated by Sir H. Davy, in his Chemical Researches, is as +1 to <ins class="correction" title="text reads ‘2,389’">2.389</ins>.</p> + + +<span class="pagenum">131</span> +<a name="conver2.page131" id="conver2.page131"> </a> +<h4><a name="convXIX" id="convXIX">CONVERSATION XIX.</a></h4> + +<h4 class="subhead"> +ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MURIATIC ACIDS; AND ON +MURIATS.—ON IODINE AND IODIC ACID.</h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> now come to the three remaining acids +with simple bases, the compound nature of which, though long suspected, +has been but recently proved. The chief of these is the muriatic; but I +shall first describe the two others, as their bases have been obtained +more distinctly than that of the muriatic acid.</p> + +<p>You may recollect I mentioned the <span class="smallroman">BORACIC +ACID</span>. This is found very sparingly in some parts of Europe, but +for the use of manufactures we have always received it from the remote +country of Thibet, where it is found in some lakes, combined with soda. +It is easily separated from the soda by sulphuric acid, and appears in +the form of shining scales, as you see here.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am glad to meet with an acid which we need +<span class="pagenum">132</span> +<a name="conver2.page132" id="conver2.page132"> </a> +not be afraid to touch; for I perceive, from your keeping it in a piece +of paper, that it is more innocent than our late acquaintance, the +sulphuric and nitric acids.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; but being more inert, you will not find its properties so +interesting. However, its decomposition, and the brilliant spectacle it +affords when its basis again unites with oxygen, atones for its want of +other striking qualities.</p> + +<p>Sir H. Davy succeeded in decomposing the boracic acid, (which had +till then been considered as undecompoundable,) by various methods. On +exposing this acid to the Voltaic battery, the positive wire gave out +oxygen, and on the negative wire was deposited a black substance, in +appearance resembling charcoal. This was the basis of the acid, which +Sir H. Davy has called <i>Boracium</i>, or <i>Boron</i>.</p> + +<p>The same substance was obtained in more considerable quantities, by +exposing the acid to a great heat in an iron gun-barrel.</p> + +<p>A third method of decomposing the boracic acid consisted in burning +potassium in contact with it in vacuo. The potassium attracts the oxygen +from the acid, and leaves its basis in a separate state.</p> + +<p>The recomposition of this acid I shall show +<span class="pagenum">133</span> +<a name="conver2.page133" id="conver2.page133"> </a> +you, by burning some of its basis, which you see here, in a retort full +of oxygen gas. The heat of a candle is all that is required for this +combustion.—</p> + +<p class="speaker">EMILY.</p> + +<p>The light is astonishingly brilliant, and what beautiful sparks it +throws out!</p> + +<p class="speaker">MRS. B.</p> + +<p>The result of this combustion is the boracic acid, the nature of +which, you see, is proved both by analytic and synthetic means. Its +basis has not, it is true, a metallic appearance; but it makes very +hard alloys with other metals.</p> + +<p class="speaker">EMILY.</p> + +<p>But pray, Mrs. B., for what purpose is the boracic acid used in +manufactures?</p> + +<p class="speaker">MRS. B.</p> + +<p>Its principal use is in conjunction with soda, that is, in the state +of <i>borat of soda</i>, which in the arts is commonly called borax. +This salt has a peculiar power of dissolving metallic oxyds, and of +promoting the fusion of substances capable of being melted; it is +accordingly employed in various metallic arts; it is used, for example, +to remove the oxyd from the surface of metals, and +<span class="pagenum">134</span> +<a name="conver2.page134" id="conver2.page134"> </a> +is often employed in the assaying of metallic ores.</p> + + +<p class="space"> +Let us now proceed to the <span class="smallroman">FLUORIC +ACID</span>. This acid is obtained from a substance which is found +frequently in mines, and particularly in those of Derbyshire, called +<i>fluor</i>, a name which it acquired from the circumstance of its +being used to render the ores of metals more fluid when heated.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray is not this the Derbyshire spar, of which so many ornaments are +made?</p> + +<p class="speaker">MRS. B.</p> + +<p>The same; but though it has long been employed for a variety of +purposes, its nature was unknown until Scheele, the great Swedish +chemist, discovered that it consisted of lime united with a peculiar +acid, which obtained the name of <i>fluoric acid</i>. It is easily +separated from the lime by the sulphuric acid, and unless condensed in +water, ascends in the form of gas. A very peculiar property of this +acid is its union with siliceous earths, which I have already mentioned. +If the distillation of this acid is performed in glass vessels, they are +corroded, and the siliceous part of the glass comes over, united with +the gas; if water +<span class="pagenum">135</span> +<a name="conver2.page135" id="conver2.page135"> </a> +is then admitted, part of the silex is deposited, as you may observe in +this jar.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I see white flakes forming on the surface of the water; is that +silex?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes it is. This power of corroding glass has been used for engraving, +or rather etching, upon it. The glass is first covered with a coat of +wax, through which the figures to be engraved are to be scratched with a +pin; then pouring the fluoric acid over the wax, it corrodes the glass +where the scratches have been made.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I should like to have a bottle of this acid, to make engravings.</p> + +<p class="speaker">MRS. B.</p> + +<p>But you could not have it in a <i>glass</i> bottle, for in that case +the acid would be saturated with silex, and incapable of executing an +engraving; the same thing would happen were the acid kept in vessels of +porcelain or earthen-ware; this acid must therefore be both prepared and +preserved in vessels of silver.</p> + +<span class="pagenum">136</span> +<a name="conver2.page136" id="conver2.page136"> </a> +<p>If it be distilled from fluor spar and vitriolic acid, in silver or +leaden vessels, the receiver being kept very cold during the +distillation, it assumes the form of a dense fluid, and in that state is +the most intensely corrosive substance known. This seems to be the acid +combined with a little water. It may be called <i>hydro-fluoric +acid</i>; and Sir H. Davy has been led, from some late experiments on +the subject, to consider <i>pure</i> fluoric acid as a compound of a +certain unknown principle, which he calls <i>fluorine</i>, with +hydrogen.</p> + +<p>Sir H. Davy has also attempted to decompose the fluoric acid by +burning potassium in contact with it; but he has not yet been able by +this or any other method, to obtain its basis in a distinct separate +state.</p> + + +<p class="space"> +We shall conclude our account of the acids with that of the <span class="smallroman">MURIATIC ACID</span>, which is perhaps the most curious +and interesting of all of them. It is found in nature combined with +soda, lime, and magnesia. <i>Muriat of soda</i> is the common sea-salt, +and from this substance the acid is usually disengaged by means of the +sulphuric acid. The natural state of the muriatic acid is that of an +invisible permanent gas, at the common temperature of the atmosphere; +but it has a remarkably strong attraction for water, and assumes +<span class="pagenum">137</span> +<a name="conver2.page137" id="conver2.page137"> </a> +the form of a whitish cloud whenever it meets any moisture to combine +with. This acid is remarkable for its peculiar and very pungent smell, +and possesses, in a powerful degree, most of the acid properties. Here +is a bottle containing muriatic acid in a liquid state.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And how is it liquefied?</p> + +<p class="speaker">MRS. B.</p> + +<p>By impregnating water with it; its strong attraction for water makes +it very easy to obtain it in a liquid form. Now, if I open the phial, +you may observe a kind of vapour rising from it, which is muriatic acid +gas, of itself invisible, but made apparent by combining with the +moisture of the atmosphere.</p> + +<p class="speaker">EMILY.</p> + +<p>Have you not any of the pure muriatic acid gas?</p> + +<p class="speaker">MRS. B.</p> + +<p>This jar is full of that acid in its gaseous state—it is +inverted over mercury instead of water, because, being absorbable by +water, this gas cannot be confined by it.—I shall now raise +the jar a little on one side, and suffer some of the gas to +<span class="pagenum">138</span> +<a name="conver2.page138" id="conver2.page138"> </a> +escape.—You see that it immediately becomes visible in the form of +a cloud.</p> + +<p class="speaker">EMILY.</p> + +<p>It must be, no doubt, from its uniting with the moisture of the +atmosphere, that it is converted into this dewy vapour.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; and for the same reason, that is to say, its extreme +eagerness to unite with water, this gas will cause snow to melt as +rapidly as an intense fire.</p> + +<p>This acid proved much more refractory when Sir H. Davy attempted to +decompose it than the other two undecompounded acids. It is singular +that potassium will burn in muriatic acid, and be converted into potash, +without decomposing the acid, and the result of this combustion is a +<i>muriat of potash</i>; for the potash, as soon as it is regenerated, +combines with the muriatic acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how can the potash be regenerated if the muriatic acid does not +oxydate the potassium?</p> + +<p class="speaker">MRS. B.</p> + +<p>The potassium, in this process, obtains oxygen from the moisture with +which the muriatic acid is +<span class="pagenum">139</span> +<a name="conver2.page139" id="conver2.page139"> </a> +always combined, and accordingly hydrogen, resulting from the +decomposition of the moisture, is invariably evolved.</p> + +<p class="speaker">EMILY.</p> + +<p>But why not make these experiments with dry muriatic acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Dry acids cannot be acted on by the Voltaic battery, because acids +are non-conductors of electricity, unless moistened. In the course of a +number of experiments which Sir H. Davy made upon acids in a state of +dryness, he observed that the presence of water appeared always +necessary to develop the acid properties, so that acids are not even +capable of reddening vegetable blues if they have been carefully +deprived of moisture. This remarkable circumstance led him to suspect, +that water, instead of oxygen, may be the acidifying principle; but this +he threw out rather as a conjecture than as an established point.</p> + +<p>Sir H. Davy obtained very curious results from burning potassium in a +mixture of phosphorus and muriatic acid, and also of sulphur and +muriatic acid; the latter detonates with great violence. All his +experiments, however, failed in presenting to his view the basis of the +muriatic acid, of which he was in search; and he was at last induced to +<span class="pagenum">140</span> +<a name="conver2.page140" id="conver2.page140"> </a> +form an opinion respecting the nature of this acid, which I shall +presently explain.</p> + +<p class="speaker">EMILY.</p> + +<p>Is this acid susceptible of different degrees of oxygenation?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, for though we cannot deoxygenate this acid, yet we may add +oxygen to it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Why, then, is not the least degree of oxygenation of the acid called +the <i>muriatous</i>, and the higher degree the <i>muriatic</i> +acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because, instead of becoming, like other acids, more dense, and more +acid by an addition of oxygen, it is rendered on the contrary more +volatile, more pungent, but less acid, and less absorbable by water. +These circumstances, therefore, seem to indicate the propriety of making +an exception to the nomenclature. The highest degree of oxygenation of +this acid has been distinguished by the additional epithet of +<i>oxygenated</i>, or, for the sake of brevity, <i>oxy</i>, so that it +is called the <i>oxygenated</i>, or <i>oxy-muriatic acid</i>. This +likewise exists in a gaseous form, at the temperature of the atmosphere; +it is also susceptible of being absorbed +<span class="pagenum">141</span> +<a name="conver2.page141" id="conver2.page141"> </a> +by water, and can be congealed, or solidified, by a certain degree of +cold.</p> + +<p class="speaker">EMILY.</p> + +<p>And how do you obtain the oxy-muriatic acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>In various ways; but it may be most conveniently obtained by +distilling liquid muriatic acid over oxyd of manganese, which supplies +the acid with the additional oxygen. One part of the acid being put into +a retort, with two parts of the oxyd of manganese, and the heat of a +lamp applied, the gas is soon disengaged, and may be received over +water, as it is but sparingly absorbed by it.—I have +collected some in this jar—</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is not invisible, like the generality of gases; for it is of a +yellowish colour.</p> + +<p class="speaker">MRS. B.</p> + +<p>The muriatic acid extinguishes flame, whilst, on the contrary, the +oxy-muriatic makes the flame larger, and gives it a dark red colour. Can +you account for this difference in the two acids?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, I think so; the muriatic acid will not supply +<span class="pagenum">142</span> +<a name="conver2.page142" id="conver2.page142"> </a> +the flame with the oxygen necessary for its support; but when this acid +is further oxygenated, it will part with its additional quantity of +oxygen, and in this way support combustion.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is exactly the case; indeed the oxygen added to the muriatic +acid, adheres so slightly to it, that it is separated by mere exposure +to the sun’s rays. This acid is decomposed also by combustible bodies, +many of which it burns, and actually inflames, without any previous +increase of temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>That is extraordinary, indeed! I hope you mean to indulge us with +some of these experiments?</p> + +<p class="speaker">MRS. B.</p> + +<p>I have prepared several glass jars of oxy-muriatic acid gas for that +purpose. In the first we shall introduce some Dutch gold leaf.—Do +you observe that it takes fire?</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, indeed it does—how wonderful it is! It became immediately +red hot, but was soon smothered in a thick vapour.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a disagreeable smell!</p> + +<span class="pagenum">143</span> +<a name="conver2.page143" id="conver2.page143"> </a> +<p class="speaker">MRS. B.</p> + +<p>We shall try the same experiment with phosphorus in another jar of +this acid.—You had better keep your handkerchief to your nose when +I open it—now let us drop into it this little piece of +phosphorus—</p> + +<p class="speaker">CAROLINE.</p> + +<p>It burns really; and almost as brilliantly as in oxygen gas! But, +what is most extraordinary, these combustions take place without the +metal or phosphorus being previously lighted, or even in the least +heated.</p> + +<p class="speaker">MRS. B.</p> + +<p>All these curious effects are owing to the very great facility with +which this acid yields oxygen to such bodies as are strongly disposed to +combine with it. It appears extraordinary indeed to see bodies, and +metals in particular, melted down and inflamed, by a gas without any +increase of temperature, either of the gas, or of the combustible. The +phenomenon, however, is, you see, well accounted for.</p> + +<p class="speaker">EMILY.</p> + +<p>Why did you burn a piece of Dutch gold leaf rather than a piece of +any other metal?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because, in the first place, it is a composition +<span class="pagenum">144</span> +<a name="conver2.page144" id="conver2.page144"> </a> +of metals (consisting chiefly of copper) which burns readily; and I use +a thin metallic leaf in preference to a lump of metal, because it offers +to the action of the gas but a small quantity of matter under a large +surface. Filings, or shavings, would answer the purpose nearly as well; +but a lump of metal, though the surface would oxydate with great +rapidity, would not take fire. Pure gold is not inflamed by oxy-muriatic +acid gas, but it is rapidly oxydated, and dissolved by it; indeed, this +acid is the only one that will dissolve gold.</p> + +<p class="speaker">EMILY.</p> + +<p>This, I suppose, is what is commonly called <i>aqua regia</i>, which +you know is the only thing that will act upon gold.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is not exactly the case either; for aqua regia is composed of a +mixture of muriatic acid and nitric acid.—But, in fact, the result +of this mixture is the formation of oxy-muriatic acid, as the muriatic +acid oxygenates itself at the expence of the nitric; this mixture, +therefore, though it bears the name of <i>nitro-muriatic acid</i>, acts +on gold merely in virtue of the oxy-muriatic acid which it contains.</p> + +<p>Sulphur, volatile oils, and many other substances, will burn in the +same manner in oxy-muriatic +<span class="pagenum">145</span> +<a name="conver2.page145" id="conver2.page145"> </a> +acid gas; but I have not prepared a sufficient quantity of it, to show +you the combustion of all these bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>There are several jars of the gas yet remaining.</p> + +<p class="speaker">MRS. B.</p> + +<p>We must reserve these for future experiments. The oxy-muriatic acid +does not, like other acids, redden the blue vegetable colours; but it +totally destroys any colour, and turns all vegetables perfectly white. +Let us collect some vegetable substances to put into this glass, which +is full of gas.</p> + +<p class="speaker">EMILY.</p> + +<p>Here is a sprig of myrtle—</p> + +<p class="speaker">CAROLINE.</p> + +<p>And here some coloured paper—</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall also put in this piece of scarlet riband, and a +rose—</p> + +<p class="speaker">EMILY.</p> + +<p>Their colours begin to fade immediately! But how does the gas produce +this effect?</p> + +<p class="speaker">MRS. B.</p> + +<p>The oxygen combines with the colouring matter of these substances, +and destroys it; that is to +<span class="pagenum">146</span> +<a name="conver2.page146" id="conver2.page146"> </a> +say, destroys the property which these colours had of reflecting only +one kind of rays, and renders them capable of reflecting them all, +which, you know, will make them appear white. Old prints may be cleaned +by this acid, for the paper will be whitened without injury to the +impression, as printer’s ink is made of materials (oil and lamp black) +which are not acted upon by acids.</p> + +<p>This property of the oxy-muriatic acid has lately been employed in +manufactures in a variety of bleaching processes; but for these purposes +the gas must be dissolved in water, as the acid is thus rendered much +milder and less powerful in its effects; for, in a gaseous state, it +would destroy the texture, as well as the colour of the substance +submitted to its action.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Look at the things which we put into the gas; they have now entirely +lost their colour!</p> + +<p class="speaker">MRS. B.</p> + +<p>The effect of the acid is almost completed; and, if we were to +examine the quantity that remains, we should find it to consist chiefly +of muriatic acid.</p> + +<p>The oxy-muriatic acid has been used to purify the air in fever +hospitals and prisons, as it burns and destroys putrid effluvia of every +kind. The +<span class="pagenum">147</span> +<a name="conver2.page147" id="conver2.page147"> </a> +infection of the small-pox is likewise destroyed by this gas, and matter +that has been submitted to its influence will no longer generate that +disorder.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Indeed, I think the remedy must be nearly as bad as the disease; the +oxy-muriatic acid has such a dreadfully suffocating smell.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is certainly extremely offensive; but by keeping the mouth shut, +and wetting the nostrils with liquid ammonia, in order to neutralize the +vapour as it reaches the nose, its prejudicial effects may be in some +degree prevented. At any rate, however, this mode of disinfection can +hardly be used in places that are inhabited. And as the vapour of nitric +acid, which is scarcely less efficacious for this purpose, is not at all +prejudicial, it is usually preferred on such occasions.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You have not told us yet what is Sir H. Davy’s new opinion respecting +the nature of muriatic acid, to which you alluded a few minutes ago?</p> + +<p class="speaker">MRS. B.</p> + +<p>True; I avoided noticing it then, because you could not have +understood it without some previous +<span class="pagenum">148</span> +<a name="conver2.page148" id="conver2.page148"> </a> +knowledge of the oxy-muriatic acid, which I have but just introduced to +your acquaintance.</p> + +<p>Sir H. Davy’s idea is that muriatic acid, instead of being a +compound, consisting of an unknown basis and oxygen, is formed by the +union of oxy-muriatic gas with hydrogen.</p> + +<p class="speaker">EMILY.</p> + +<p>Have you not told us just now that oxy-muriatic gas was itself a +compound of muriatic acid and oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but according to Sir H. Davy’s hypothesis, oxy-muriatic gas is +considered as a simple body, which contains no oxygen—as a +substance of its own kind, which has a great analogy to oxygen in most +of its properties, though in others it differs entirely from +it.—According to this view of the subject, the name of +<i>oxy-muriatic acid</i> can no longer be proper, and therefore Sir H. +Davy has adopted that of <i>chlorine</i>, or <i>chlorine gas</i>, +a name which is simply expressive of its greenish colour; and in +compliance with that philosopher’s theory, we have placed chlorine in +our table among the simple bodies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what was Sir H. Davy’s reason for adopting an opinion so contrary +to that which had hitherto prevailed?</p> + +<span class="pagenum">149</span> +<a name="conver2.page149" id="conver2.page149"> </a> +<p class="speaker">MRS. B.</p> + +<p>There are many circumstances which are favourable to the new +doctrine; but the clearest and simplest fact in its support is, that if +hydrogen gas and oxy-muriatic gas be mixed together, both these gases +disappear, and muriatic acid gas is formed.</p> + +<p class="speaker">EMILY.</p> + +<p>That seems to be a complete proof; is it not considered as perfectly +conclusive?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not so decisive as it appears at first sight; because it is argued by +those who still incline to the old doctrine, that muriatic acid gas, +however dry it may be, always contains a certain quantity of water, +which is supposed essential to its formation. So that, in the experiment +just mentioned, this water is supplied by the union of the hydrogen gas +with the oxygen of the oxy-muriatic acid; and therefore the mixture +resolves itself into the base of muriatic acid and water, that is, +muriatic acid gas.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I think the old theory must be the true one; for otherwise how could +you explain the formation of oxy-muriatic gas, from a mixture of +muriatic acid and oxyd of manganese?</p> + +<span class="pagenum">150</span> +<a name="conver2.page150" id="conver2.page150"> </a> +<p class="speaker">MRS. B.</p> + +<p>Very easily; you need only suppose that in this process the muriatic +acid is decomposed; its hydrogen unites with the oxygen of the manganese +to form water, and the chlorine appears in its separate state.</p> + +<p class="speaker">EMILY.</p> + +<p>But how can you explain the various combustions which take place in +oxy-muriatic gas, if you consider it as containing no oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>We need only suppose that combustion is the result of intense +chemical action; so that chlorine, like oxygen, in combining with +bodies, forms compounds which have less capacity for caloric than their +constituent principles, and, therefore, caloric is evolved at the moment +of their combination.</p> + +<p class="speaker">EMILY.</p> + +<p>If, then, we may explain every thing by either theory, to which of +the two shall we give the preference?</p> + +<p class="speaker">MRS. B.</p> + +<p>It will, perhaps, be better to wait for more positive proofs, if such +can be obtained, before we decide positively upon the subject. The new +doctrine has certainly gained ground very rapidly, and may be considered +as nearly established; but several +<span class="pagenum">151</span> +<a name="conver2.page151" id="conver2.page151"> </a> +competent judges still refuse their assent to it, and until that theory +is very generally adopted, it may be as well for us still occasionally +to use the language to which chemists have long been +accustomed.—But let us proceed to the examination of salts formed +by muriatic acid.</p> + +<p>Among the compound salts formed by muriatic acid, the <i>muriat of +soda</i>, or common salt, is the most interesting.<a class="tag" name="tag24" id="tag24" href="#note24">*</a> The uses and properties of +this salt are too well known to require much comment. Besides the +pleasant flavour it imparts to the food, it is very wholesome, when not +used to excess, as it assists the process of digestion.</p> + +<p>Sea-water is the great source from which muriat of soda is extracted +by evaporation. But it is also found in large solid masses in the bowels +of the earth, in England, and in many other parts of the world.</p> + +<p class="speaker">EMILY.</p> + +<p>I thought that salts, when solid, were always in the state of +crystals; but the common table-salt is in the form of a coarse white +powder.</p> + +<span class="pagenum">152</span> +<a name="conver2.page152" id="conver2.page152"> </a> +<p class="speaker">MRS. B.</p> + +<p>Crystallisation depends, as you may recollect, on the slow and +regular reunion of particles dissolved in a fluid; common sea-salt is +only in a state of imperfect crystallisation, because the process by +which it is prepared is not favourable to the formation of regular +crystals. But if you dissolve it, and afterwards evaporate the water +slowly, you will obtain a regular crystallisation.</p> + +<p><i>Muriat of ammonia</i> is another combination of this acid, which +we have already mentioned as the principal source from which ammonia is +derived.</p> + +<p>I can at once show you the formation of this salt by the immediate +combination of muriatic acid with ammonia.—These two glass jars +contain, the one muriatic acid gas, the other ammoniacal gas, both of +which are perfectly invisible—now, if I mix them together, you see +they immediately form an opake white cloud, like smoke.—If a +thermometer was placed in the jar in which these gases are mixed, you +would perceive that some heat is at the same time produced.</p> + +<p class="speaker">EMILY.</p> + +<p>The effects of chemical combinations are, indeed, +wonderful!—How extraordinary it is that two invisible bodies +should become visible by their union!</p> + +<span class="pagenum">153</span> +<a name="conver2.page153" id="conver2.page153"> </a> +<p class="speaker">MRS. B.</p> + +<p>This strikes you with astonishment, because it is a phenomenon which +nature seldom exhibits to our view; but the most common of her +operations are as wonderful, and it is their frequency only that +prevents our regarding them with equal admiration. What would be more +surprising, for instance, than combustion, were it not rendered so +familiar by custom?</p> + +<p class="speaker">EMILY.</p> + +<p>That is true.—But pray, Mrs. B., is this white cloud the salt +that produces ammonia? How different it is from the solid muriat of +ammonia which you once showed us!</p> + +<p class="speaker">MRS. B.</p> + +<p>It is the same substance which first appears in the state of vapour, +but will soon be condensed by cooling against the sides of the jar, in +the form of very minute crystals.</p> + +<p>We may now proceed to the <i>oxy-muriats</i>. In this class of salts +the <i>oxy-muriat of potash</i> is the most worthy of our attention, for +its striking properties. The acid, in this state of combination, +contains a still greater proportion of oxygen than when alone.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how can the oxy-muriatic acid acquire an increase of oxygen by +combining with potash?</p> + +<span class="pagenum">154</span> +<a name="conver2.page154" id="conver2.page154"> </a> +<p class="speaker">MRS. B.</p> + +<p>It does not really acquire an additional quantity of oxygen, but it +loses some of the muriatic acid, which produces the same effect, as the +acid which remains is proportionably super-oxygenated.<a class="tag" +name="tag25" id="tag25" href="#note25">*</a></p> + +<p>If this salt be mixed, and merely rubbed together with sulphur, +phosphorus, charcoal, or indeed any other combustible, it explodes +strongly.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Like gun-powder, I suppose, it is suddenly converted into elastic +fluids?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but with this remarkable difference, that no increase of +temperature, any further than is produced by gentle friction, is +required in this instance. Can you tell me what gases are generated by +the detonation of this salt with charcoal?</p> + +<p class="speaker">EMILY.</p> + +<p>Let me consider . . . . . The oxy-muriatic acid parts with its excess +of oxygen to the charcoal, by which means it is converted into muriatic +acid gas; whilst the charcoal, being burnt by the oxygen, is +<span class="pagenum">155</span> +<a name="conver2.page155" id="conver2.page155"> </a> +changed to carbonic acid gas.—What becomes of the potash I cannot +tell.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is a fixed product which remains in the vessel.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But since the potash does not enter into the new combinations, +I do not understand of what use it is in this operation. Would not +the oxy-muriatic acid and the charcoal produce the same effect +without it?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; because there would not be that very great concentration of +oxygen which the combination with the potash produces, as I have just +explained.</p> + +<p>I mean to show you this experiment, but I would advise you not to +repeat it alone; for if care be not taken to mix only very small +quantities at a time, the detonation will be extremely violent, and may +be attended with dangerous effects. You see I mix an exceedingly small +quantity of the salt with a little powdered charcoal, in this Wedgwood +mortar, and rub them together with the pestle—</p> + +<p class="speaker">CAROLINE.</p> + +<p>Heavens! How can such a loud explosion be produced by so small a +quantity of matter?</p> + +<span class="pagenum">156</span> +<a name="conver2.page156" id="conver2.page156"> </a> +<p class="speaker">MRS. B.</p> + +<p>You must consider that an extremely small quantity of solid substance +may produce a very great volume of gases; and it is the sudden evolution +of these which occasions the sound.</p> + +<p class="speaker">EMILY.</p> + +<p>Would not oxy-muriat of potash make stronger gunpowder than nitrat of +potash?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but the preparation, as well as the use of this salt, is +attended with so much danger, that it is never employed for that +purpose.</p> + +<p class="speaker">CAROLINE.</p> + +<p>There is no cause to regret it, I think; for the common gunpowder is +quite sufficiently destructive.</p> + +<p class="speaker">MRS. B.</p> + +<p>I can show you a very curious experiment with this salt; but it must +again be on condition that you will never attempt to repeat it by +yourselves. I throw a small piece of phosphorus into this glass of +water; then a little oxy-muriat of potash; and, lastly, I pour in +(by means of this funnel, so as to bring it in contact with the two +other ingredients at the bottom of the glass) a small quantity of +sulphuric acid—</p> + +<span class="pagenum">157</span> +<a name="conver2.page157" id="conver2.page157"> </a> +<p class="speaker">CAROLINE.</p> + +<p>This is, indeed, a beautiful experiment! The phosphorus takes fire +and burns from the bottom of the water.</p> + +<p class="speaker">EMILY.</p> + +<p>How wonderful it is to see flame bursting out under water, and rising +through it! Pray, how is this accounted for?</p> + +<p class="speaker">MRS. B.</p> + +<p>Cannot you find it out, Caroline?</p> + +<p class="speaker">EMILY.</p> + +<p>Stop—I think I can explain it. Is it not because the sulphuric +acid decomposes the salt by combining with the potash, so as to liberate +the oxy-muriatic acid gas by which the phosphoric is set on fire?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well, Emily; and with a little more reflection you would have +discovered another concurring circumstance, which is, that an increase +of temperature is produced by the mixture of the sulphuric acid and +water, which assists in promoting the combustion of the phosphorus.</p> + + +<p class="space"> +I must, before we part, introduce to your acquaintance the +newly-discovered substance <span class="smallroman">IODINE</span>, +which you may recollect we placed next to oxygen and chlorine in our +table of simple bodies.</p> + +<span class="pagenum">158</span> +<a name="conver2.page158" id="conver2.page158"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Is this also a body capable of maintaining combustion like oxygen and +chlorine?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is; and although it does not so generally disengage light and heat +from inflammable bodies, as oxygen and chlorine do, yet it is capable of +combining with most of them; and sometimes, as in the instance of +potassium and phosphorus, the combination is attended with an actual +appearance of light and heat.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But what sort of a substance is iodine: what is its form, and +colour?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a very singular body, in many respects. At the ordinary +temperature of the atmosphere, it commonly appears in the form of +blueish black crystalline scales, such as you see in this tube.</p> + +<p class="speaker">CAROLINE.</p> + +<p>They shine like black lead, and some of the scales have the shape of +lozenges.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is actually the form which the crystals of iodine often assume. +But if we heat them gently, +<span class="pagenum">159</span> +<a name="conver2.page159" id="conver2.page159"> </a> +by holding the tube over the flame of a candle, see what a change takes +place in them.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How curious! They seem to melt, and the tube immediately fills with a +beautiful violet vapour. But look, Mrs. B., the same scales are now +appearing at the other end of the tube.</p> + +<p class="speaker">MRS. B.</p> + +<p>This is in fact a sublimation of iodine, from one part of the tube to +another; but with this remarkable peculiarity, that, while in the +gaseous state, iodine assumes that bright violet colour, which, as you +may already perceive, it loses as the tube cools, and the substance +resumes its usual solid form.—It is from the violet colour of the +gas that iodine has obtained its name.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how is this curious substance obtained?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is found in the ley of ashes of sea-weeds, after the soda has been +separated by crystallisation; and it is disengaged by means of sulphuric +acid, which expels it from the alkaline ley in the form of a violet gas, +which may be collected and condensed in the way you have just +<span class="pagenum">160</span> +<a name="conver2.page160" id="conver2.page160"> </a> +seen.—This interesting discovery was made in the year 1812, by M. +Courtois, a manufacturer of saltpetre at Paris.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And pray, Mrs. B., what is the proof of iodine being a simple +body?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is considered as a simple body, both because it is not capable of +being resolved into other ingredients; and because it is itself capable +of combining with other bodies, in a manner analogous to oxygen and +chlorine. The most curious of these combinations is that which it forms +with hydrogen gas, the result of which is a peculiar gaseous acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Just as chlorine and hydrogen gas form muriatic acid? In this respect +chlorine and iodine seem to bear a strong analogy to each other.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is indeed the case; so that if the theory of the constitution of +either of these two bodies be true, it must be true also in regard to +the other; if erroneous in the one, the theory must fall in both.</p> + +<span class="pagenum">161</span> +<a name="conver2.page161" id="conver2.page161"> </a> +<p>But it is now time to conclude; we have examined such of the acids +and salts as I conceived would appear to you most +interesting.—I shall not enter into any particulars +respecting the metallic acids, as they offer nothing sufficiently +striking for our present purpose.</p> + +<div class="footnote"> + +<p><a name="note24" id="note24" href="#tag24">*</a> +According to Sir H. Davy’s views of the nature of the muriatic and +oxy-muriatic acids, dry muriat of soda is a compound of sodium and +chlorine, for it may be formed by the direct combination of oxy-muriatic +gas and sodium. In his opinion, therefore, what we commonly call muriat +of soda contains neither soda nor muriatic acid.</p> + +<p><a name="note25" id="note25" href="#tag25">*</a> +According to Sir H. Davy’s new views, just explained, oxy-muriat of +potash is a compound of chlorine with oxyd of potassium.</p> + +</div> + + +<span class="pagenum">162</span> +<a name="conver2.page162" id="conver2.page162"> </a> +<h4><a name="convXX" id="convXX">CONVERSATION XX.</a><br> +<span class="subhead">ON THE NATURE AND COMPOSITION OF +VEGETABLES.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> have hitherto treated only of the +simplest combinations of elements, such as alkalies, earths, acids, +compound salts, stones, &c.; all of which belong to the mineral +kingdom. It is time now to turn our attention to a more complicated +class of compounds, that of <span class="smallroman">ORGANISED +BODIES</span>, which will furnish us with a new source of instruction +and amusement.</p> + +<p class="speaker">EMILY.</p> + +<p>By organised bodies, I suppose, you mean the vegetable and animal +creation? I have, however, but a very vague idea of the word +<i>organisation</i>, and I have often wished to know more precisely what +it means.</p> + +<span class="pagenum">163</span> +<a name="conver2.page163" id="conver2.page163"> </a> +<p class="speaker">MRS. B.</p> + +<p>Organised bodies are such as are endowed by nature with various +parts, peculiarly constructed and adapted to perform certain functions +connected with life. Thus you may observe, that mineral compounds are +formed by the simple effect of mechanical or chemical attraction, and +may appear to some to be in a great measure the productions of chance; +whilst organised bodies bear the most striking and impressive marks of +design, and are eminently distinguished by that unknown principle, +called <i>life</i>, from which the various organs derive the power of +exercising their respective functions.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But in what manner does life enable these organs to perform their +several functions?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is a mystery which, I fear, is enveloped in such profound +darkness that there is very little hope of our ever being able to unfold +it. We must content ourselves with examining the effects of this +principle; as for the cause, we have been able only to give it a name, +without attaching any other meaning to it than the vague and +unsatisfactory idea of au unknown agent.</p> + +<span class="pagenum">164</span> +<a name="conver2.page164" id="conver2.page164"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And yet I think I can form a very clear idea of life.</p> + +<p class="speaker">MRS. B.</p> + +<p>Pray let me hear how you would define it?</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is perhaps more easy to conceive than to express—let me +consider—Is not life the power which enables both the animal and +the vegetable creation to perform the various functions which nature has +assigned to them?</p> + +<p class="speaker">MRS. B.</p> + +<p>I have nothing to object to your definition; but you will allow me to +observe, that you have only mentioned the effects which the unknown +cause produces, without giving us any notion of the cause itself.</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, Caroline, you have told us what life <i>does</i>, but you have +not told us what it <i>is</i>.</p> + +<p class="speaker">MRS. B.</p> + +<p>We may study its operations, but we should puzzle ourselves to no +purpose by attempting to form an idea of its real nature.</p> + +<p>We shall begin with examining its effects in the +<span class="pagenum">165</span> +<a name="conver2.page165" id="conver2.page165"> </a> +vegetable world, which constitutes the simplest class of organised +bodies; these we shall find distinguished from the mineral creation, not +only by their more complicated nature, but by the power which they +possess within themselves, of forming new chemical arrangements of their +constituent parts, by means of appropriate organs. Thus, though all +vegetables are ultimately composed of hydrogen, carbon, and oxygen, +(with a few other occasional ingredients,) they separate and combine +these principles by their various organs, in a thousand ways, and form, +with them, different kinds of juices and solid parts, which exist ready +made in vegetables, and may, therefore, be considered as their immediate +materials.</p> + +<p>These are:</p> + +<div class="list space"> +<p><i>Sap</i>,</p> +<p><i>Mucilage</i>,</p> +<p><i>Sugar</i>,</p> +<p><i>Fecula</i>,</p> +<p><i>Gluten</i>,</p> +<p><i>Fixed Oil</i>,</p> +<p><i>Volatile Oil</i>,</p> +<p><i>Camphor</i>,</p> +<p><i>Resins</i>,</p> +<p><i>Gum Resins</i>,</p> +<p><i>Balsams</i>,</p> +<p><i>Caoutchouc</i>,</p> +<p><i>Extractive colouring Matter</i>,</p> +<p><i>Tannin</i>,</p> +<p><i>Woody Fibre</i>,</p> +<p><i>Vegetable Acids</i>, <i>&c.</i></p> +</div> + +<p class="speaker">CAROLINE.</p> + +<p>What a long list of names! I did not suppose +<span class="pagenum">166</span> +<a name="conver2.page166" id="conver2.page166"> </a> +that a vegetable was composed of half so many ingredients.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must not imagine that every one of these materials is formed in +each individual plant. I only mean to say, that they are all +derived exclusively from the vegetable kingdom.</p> + +<p class="speaker">EMILY.</p> + +<p>But does each particular part of the plant, such as the root, the +bark, the stem, the seeds, the leaves, consist of one of these +ingredients only, or of several of them combined together?</p> + +<p class="speaker">MRS. B.</p> + +<p>I believe there is no part of a plant which can be said to consist +solely of any one particular ingredient; a certain number of +vegetable materials must always be combined for the formation of any +particular part, (of a seed for instance,) and these combinations are +carried on by sets of vessels, or minute organs, which select from other +parts, and bring together, the several principles required for the +development and growth of those particular parts which they are intended +to form and to maintain.</p> + +<p class="speaker">EMILY.</p> + +<p>And are not these combinations always regulated by the laws of +chemical attraction?</p> + +<span class="pagenum">167</span> +<a name="conver2.page167" id="conver2.page167"> </a> +<p class="speaker">MRS. B.</p> + +<p>No doubt; the organs of plants cannot force principles to combine +that have no attraction for each other; nor can they compel superior +attractions to yield to those of inferior power; they probably act +rather mechanically, by bringing into contact such principles, and in +such proportions, as will, by their chemical combination, form the +various vegetable products.</p> + +<p class="speaker">CAROLINE.</p> + +<p>We may then consider each of these organs as a curiously constructed +apparatus, adapted for the performance of a variety of chemical +processes.</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so. As long as the plant lives and thrives, the carbon, +hydrogen, and oxygen, (the chief constituents of its immediate +materials,) are so balanced and connected together, that they are not +susceptible of entering into other combinations; but no sooner does +death take place, than this state of equilibrium is destroyed, and new +combinations produced.</p> + +<p class="speaker">EMILY.</p> + +<p>But why should death destroy it; for these principles must remain in +the same proportions, and consequently, I should suppose, in the +same order of attractions?</p> + +<span class="pagenum">168</span> +<a name="conver2.page168" id="conver2.page168"> </a> +<p class="speaker">MRS. B.</p> + +<p>You must remember, that in the vegetable, as well as in the animal +kingdom, it is by the principle of <i>life</i> that the organs are +enabled to act; when deprived of that agent or stimulus, their power +ceases, and an order of attractions succeeds similar to that which would +take place in mineral or unorganised matter.</p> + +<p class="speaker">EMILY.</p> + +<p>It is this new order of attractions, I suppose, that destroys the +organisation of the plant after death; for if the same combinations +still continued to prevail, the plant would always remain in the state +in which it died?</p> + +<p class="speaker">MRS. B.</p> + +<p>And that, you know, is never the case; plants may be partially +preserved for some time after death, by drying; but in the natural +course of events they all return to the state of simple elements; +a wise and admirable dispensation of Providence, by which dead +plants are rendered fit to enrich the soil, and become subservient to +the nourishment of living vegetables.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But we are talking of the dissolution of plants, before we have +examined them in their living state.</p> + +<span class="pagenum">169</span> +<a name="conver2.page169" id="conver2.page169"> </a> +<p class="speaker">MRS. B.</p> + +<p>That is true, my dear. But I wished to give you a general idea of the +nature of vegetation, before we entered into particulars. Besides, it is +not so irrelevant as you suppose to talk of vegetables in their dead +state, since we cannot analyse them without destroying life; and it is +only by hastening to submit them to examination, immediately after they +have ceased to live, that we can anticipate their natural decomposition. +There are two kinds of analysis of which vegetables are susceptible; +first, that which separates them into their immediate materials, such as +sap, resin, mucilage, &c.; secondly, that which decomposes them into +their primitive elements, as carbon, hydrogen, and oxygen.</p> + +<p class="speaker">EMILY.</p> + +<p>Is there not a third kind of analysis of plants, which consists in +separating their various parts, as the stem, the leaves, and the several +organs of the flower?</p> + +<p class="speaker">MRS. B.</p> + +<p>That, my dear, is rather the department of the botanist; we shall +consider these different parts of plants only, as the organs by which +the various secretions or separations are performed; but we must first +examine the nature of these secretions.</p> + +<span class="pagenum">170</span> +<a name="conver2.page170" id="conver2.page170"> </a> +<p>The <i>sap</i> is the principal material of vegetables, since it +contains the ingredients that nourish every part of the plant. The basis +of this juice, which the roots suck up from the soil, is water; this +holds in solution the various other ingredients required by the several +parts of the plant, which are gradually secreted from the sap by the +different organs appropriated to that purpose, as it passes them in +circulating through the plant.</p> + + +<p class="space"> +<i>Mucus</i>, or <i>mucilage</i>, is a vegetable substance, which, like +all the others, is secreted from the sap; when in excess, it exudes from +trees in the form of gum.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is that the gum so frequently used instead of paste or glue?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is; almost all fruit-trees yield some sort of gum, but that most +commonly used in the arts is obtained from a species of acacia-tree in +Arabia, and is called <i>gum arabic</i>; it forms the chief nourishment +of the natives of those parts, who obtain it in great quantities from +incisions which they make in the trees.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I did not know that gum was eatable.</p> + +<span class="pagenum">171</span> +<a name="conver2.page171" id="conver2.page171"> </a> +<p class="speaker">MRS. B.</p> + +<p>There is an account of a whole ship’s company being saved from +starving by feeding on the cargo, which was gum senegal. I should +not, however, imagine, that it would be either a pleasant or a +particularly eligible diet to those who have not, from their birth, been +accustomed to it. It is, however, frequently taken medicinally, and +considered as very nourishing. Several kinds of vegetable acids may be +obtained, by particular processes, from gum or mucilage, the principal +of which is called the <i>mucous acid</i>.</p> + + +<p class="space"> +<i>Sugar</i> is not found in its simple state in plants, but is always +mixed with gum, sap, or other ingredients; this saccharine matter is to +be met with in every vegetable, but abounds most in roots, fruits, and +particularly in the sugar-cane.</p> + +<p class="speaker">EMILY.</p> + +<p>If all vegetables contain sugar, why is it extracted exclusively from +the sugar-cane?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because it is both most abundant in that plant, and most easily +obtained from it. Besides, the sugars produced by other vegetables +differ a little in their nature.</p> + +<span class="pagenum">172</span> +<a name="conver2.page172" id="conver2.page172"> </a> +<p>During the late troubles in the West-Indies, when Europe was but +imperfectly supplied with sugar, several attempts were made to extract +it from other vegetables, and very good sugar was obtained from parsnips +and from carrots; but the process was too expensive to carry this +enterprize to any extent.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I should think that sugar might be more easily obtained from sweet +fruits, such as figs, dates, &c.</p> + +<p class="speaker">MRS. B.</p> + +<p>Probably; but it would be still more expensive, from the high price +of those fruits.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray, in what manner is sugar obtained from the sugar-cane?</p> + +<p class="speaker">MRS. B.</p> + +<p>The juice of this plant is first expressed by passing it between two +cylinders of iron. It is then boiled with lime-water, which makes a +thick scum rise to the surface. The clarified liquor is let off below +and evaporated to a very small quantity, after which it is suffered to +crystallise by standing in a vessel, the bottom of which is perforated +<span class="pagenum">173</span> +<a name="conver2.page173" id="conver2.page173"> </a> +with holes, that are imperfectly stopped, in order that the syrup may +drain off. The sugar obtained by this process is a coarse brown powder, +commonly called raw or moist sugar; it undergoes another operation to be +refined and converted into loaf sugar. For this purpose it is dissolved +in water, and afterwards purified by an animal fluid called albumen. +White of eggs chiefly consist of this fluid, which is also one of the +constituent parts of blood; and consequently eggs, or bullocks’ blood, +are commonly used for this purpose.</p> + +<p>The albuminous fluid being diffused through the syrup, combines with +all the solid impurities contained in it, and rises with them to the +surface, where it forms a thick scum; the clear liquor is then again +evaporated to a proper consistence, and poured into moulds, in which, by +a confused crystallisation, it forms loaf-sugar. But an additional +process is required to whiten it; to this effect the mould is inverted, +and its open base is covered with clay, through which water is made to +pass; the water slowly trickling through the sugar, combines with and +carries off the colouring matter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am very glad to hear that the blood that is used to purify sugar +does not remain in it; it would be a disgusting idea. I have heard +of some +<span class="pagenum">174</span> +<a name="conver2.page174" id="conver2.page174"> </a> +improvements by the late Mr. Howard, in the process of refining sugar. +Pray what are they?</p> + +<p class="speaker">MRS. B.</p> + +<p>It would be much too long to give you an account of the process in +detail. But the principal improvement relates to the mode of evaporating +the syrup, in order to bring it to the consistency of sugar. Instead of +boiling the syrup in a large copper, over a strong fire, Mr. Howard +carries off the water by means of a large air-pump, in a way similar to +that used in Mr. Leslie’s experiment for freezing water by evaporation; +that is, the syrup being exposed to a vacuum, the water evaporates +quickly, with no greater heat than that of a little steam, which is +introduced round the boiler. The air-pump is of course of large +dimensions, and is worked by a steam engine. A great saving is thus +obtained, and a striking instance afforded of the power of science in +suggesting useful economical improvements.</p> + +<p class="speaker">EMILY.</p> + +<p>And pray how is sugar-candy and barley-sugar prepared?</p> + +<p class="speaker">MRS. B.</p> + +<p>Candied sugar is nothing more than the regular crystals, obtained by +slow evaporation from a solution of sugar. Barley-sugar is sugar melted +by +<span class="pagenum">175</span> +<a name="conver2.page175" id="conver2.page175"> </a> +heat, and afterwards cooled in moulds of a spiral form.</p> + +<p>Sugar may be decomposed by a red heat, and, like all other vegetable +substances, resolved into carbonic acid and hydrogen. The formation and +the decomposition of sugar afford many very interesting particulars, +which we shall fully examine, after having gone through the other +materials of vegetables. We shall find that there is reason to suppose +that sugar is not, like the other materials, secreted from the sap by +appropriate organs; but that it is formed by a peculiar process with +which you are not yet acquainted.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, is not honey of the same nature as sugar?</p> + +<p class="speaker">MRS. B.</p> + +<p>Honey is a mixture of saccharine matter and gum.</p> + +<p class="speaker">EMILY.</p> + +<p>I thought that honey was in some measure an animal substance, as it +is prepared by the bees.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is rather collected by them from flowers, and conveyed to their +store-houses, the hives. It is the wax only that undergoes a real +alteration in +<span class="pagenum">176</span> +<a name="conver2.page176" id="conver2.page176"> </a> +the body of the bee, and is thence converted into an animal +substance.</p> + +<p>Manna is another kind of sugar, which is united with a nauseous +extractive matter, to which it owes its peculiar taste and colour. It +exudes like gum from various trees in hot climates, some of which have +their leaves glazed by it.</p> + +<p>The next of the vegetable materials is <i>fecula</i>; this is the +general name given to the farinaceous substance contained in all seeds, +and in some roots, as the potatoe, parsnip, &c. It is intended by +nature for the first aliment of the young vegetable; but that of one +particular grain is become a favourite and most common food of a large +part of mankind.</p> + +<p class="speaker">EMILY.</p> + +<p>You allude, I suppose, to bread, which is made of wheat-flower?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes. The fecula of wheat contains also another vegetable substance +which seems peculiar to that seed, or at least has not as yet been +obtained from any other. This is <i>gluten</i>, which is of a sticky, +ropy, elastic nature; and it is supposed to be owing to the viscous +qualities of this substance, that wheat-flour forms a much better paste +than any other.</p> + +<span class="pagenum">177</span> +<a name="conver2.page177" id="conver2.page177"> </a> +<p class="speaker">EMILY.</p> + +<p>Gluten, by your description, must be very like gum?</p> + +<p class="speaker">MRS. B.</p> + +<p>In their sticky nature they certainly have some resemblance; but +gluten is essentially different from gum in other points, and especially +in its being insoluble in water, whilst gum, you know, is extremely +soluble.</p> + +<p>The <i>oils</i> contained in vegetables all consist of hydrogen and +carbon in various proportions. They are of two kinds, <i>fixed</i> and +<i>volatile</i>, both of which we formerly mentioned. Do you remember in +what the difference between fixed and volatile oil consists?</p> + +<p class="speaker">EMILY.</p> + +<p>If I recollect rightly, the former are decomposed by heat, whilst the +latter are merely volatilised by it.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well. Fixed oil is contained only in the seeds of plants, +excepting in the olive, in which it is produced in, and expressed from, +the fruit. We have already observed that seeds contain also fecula; +these two substances, united with a little mucilage, form the white +substance contained in the seeds or kernels of plants, and is destined +for the nourishment of the young plant, to which the seed gives birth. +The milk of almonds, which is +<span class="pagenum">178</span> +<a name="conver2.page178" id="conver2.page178"> </a> +expressed from the seed of that name, is composed of these three +substances.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray, of what nature is the linseed oil which is used in +painting?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a fixed oil, obtained from the seed of flax. Nut oil, which is +frequently used for the same purpose, is expressed from walnuts.</p> + +<p>Olive oil is that which is best adapted to culinary purposes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And what are the oils used for burning?</p> + +<p class="speaker">MRS. B.</p> + +<p>Animal oils most commonly; but the preference given to them is owing +to their being less expensive; for vegetable oils burn equally well, and +are more pleasant, as their smell is not offensive.</p> + +<p class="speaker">EMILY.</p> + +<p>Since oil is so good a combustible, what is the reason that lamps so +frequently require trimming?</p> + +<p class="speaker">MRS. B.</p> + +<p>This sometimes proceeds from the construction of the lamp, which may +not be sufficiently favourable to a perfect combustion; but there is +<span class="pagenum">179</span> +<a name="conver2.page179" id="conver2.page179"> </a> +certainly a defect in the nature of oil itself, which renders it +necessary for the best-constructed lamps to be occasionally trimmed. +This defect arises from a portion of mucilage which it is extremely +difficult to separate from the oil, and which being a bad combustible, +gathers round the wick, and thus impedes its combustion, and +consequently dims the light.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But will not oils burn without a wick?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not unless their temperature be elevated to five or six hundred +degrees; the wick answers this purpose, as I think I once before +explained to you. The oil rises between the fibres of the cotton by +capillary attraction, and the heat of the burning wick volatilises it, +and brings it successively to the temperature at which it is +combustible.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose the explanation which you have given with regard to the +necessity of trimming lamps, applies also to candles, which so often +require snuffing?</p> + +<p class="speaker">MRS. B.</p> + +<p>I believe it does; at least, in some degree. But besides the +circumstance just explained, the common +<span class="pagenum">180</span> +<a name="conver2.page180" id="conver2.page180"> </a> +sorts of oils are not very highly combustible, so that the heat produced +by a candle, which is a coarse kind of animal oil, being insufficient to +volatilise them completely, a quantity of soot is gradually +deposited on the wick, which dims the light, and retards the +combustion.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Wax candles then contain no incombustible matter, since they do not +require snuffing?</p> + +<p class="speaker">MRS. B.</p> + +<p>Wax is a much better combustible than tallow, but still not perfectly +so, since it likewise contains some particles that are unfit for +burning; but when these gather round the wick, (which in a wax light is +comparatively small,) they weigh it down on one side, and fall off +together with the burnt part of the wick.</p> + +<p class="speaker">CAROLINE.</p> + +<p>As oils are such good combustibles, I wonder that they should require +so great an elevation of temperature before they begin to burn?</p> + +<p class="speaker">MRS. B.</p> + +<p>Though fixed oils will not enter into actual combustion below the +temperature of about four hundred degrees, yet they will slowly absorb +oxygen +<span class="pagenum">181</span> +<a name="conver2.page181" id="conver2.page181"> </a> +at the common temperature of the atmosphere. Hence arises a variety of +changes in oils which modify their properties and uses in the arts.</p> + +<p>If oil simply absorbs, and combines with oxygen, it thickens and +changes to a kind of wax. This change is observed to take place on the +external parts of certain vegetables, even during their life. But it +happens in many instances that the oil does not retain all the oxygen +which it attracts, but that part of it combines with, or burns, the +hydrogen of the oil, thus forming a quantity of water, which gradually +goes off by evaporation. In this case the alteration of the oil consists +not only in the addition of a certain quantity of oxygen, but in the +diminution of the hydrogen. These oils are distinguished by the name of +<i>drying oils</i>. Linseed, poppy, and nut-oils, are of this +description.</p> + +<p class="speaker">EMILY.</p> + +<p>I am well acquainted with drying oils, as I continually use them in +painting. But I do not understand why the acquisition of oxygen on one +hand, and a loss of hydrogen on the other, should render them +drying?</p> + +<p class="speaker">MRS. B.</p> + +<p>This, I conceive, may arise from two reasons; either from the oxygen +which is added being less +<span class="pagenum">182</span> +<a name="conver2.page182" id="conver2.page182"> </a> +favourable to the state of fluidity than the hydrogen, which is +subtracted; or from this additional quantity of oxygen giving rise to +new combinations, in consequence of which the most fluid parts of the +oil are liberated and volatilised.</p> + +<p>For the purpose of painting, the drying quality of oil is further +increased by adding a quantity of oxyd of lead to it, by which means it +is more rapidly oxygenated.</p> + +<p>The rancidity of oil is likewise owing to their oxygenation. In this +case a new order of attraction takes place, from which a peculiar acid +is formed, called the <i>sebacic acid</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Since the nature and composition of oil is so well known, pray could +not oil be actually <i>made</i>, by combining its principles?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is by no means a necessary consequence; for there are +innumerable varieties of compound bodies which we can decompose, +although we are unable to reunite their ingredients. This, however, is +not the case with oil, as it has very lately been discovered, that it is +possible to form oil, by a peculiar process, from the action of +oxygenated muriatic acid gas on hydro-carbonate.</p> + +<span class="pagenum">183</span> +<a name="conver2.page183" id="conver2.page183"> </a> +<p>We now pass to the <i>volatile</i> or <i>essential oils</i>. These +form the basis of all the vegetable perfumes, and are contained, more or +less, in every part of the plant excepting the seed; they are, at least, +never found in that part of the seed which contains the embrio +plant.</p> + +<p class="speaker">EMILY.</p> + +<p>The smell of flowers, then, proceeds from volatile oil?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; but this oil is often most abundant in the rind of fruits, +as in oranges, lemons, &c. from which it may be extracted by +the slightest pressure; it is found also in the leaves of plants, and +even in the wood.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it not very plentiful in the leaves of mint, and of thyme, and all +the sweet-smelling herbs?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, remarkably so; and in geranium leaves also, which have a much +more powerful odour than the flowers.</p> + +<p>The perfume of sandal fans is an instance of its existence in wood. +In short, all vegetable odours or perfumes are produced by the +evaporation of particles of these volatile oils.</p> + +<span class="pagenum">184</span> +<a name="conver2.page184" id="conver2.page184"> </a> +<p class="speaker">EMILY.</p> + +<p>They are, I suppose, very light, and of very thin consistence, since +they are so volatile?</p> + +<p class="speaker">MRS. B.</p> + +<p>They vary very much in this respect, some of them being as thick as +butter, whilst others are as fluid as water. In order to be prepared for +perfumes, or essences, these oils are first properly purified, and then +either distilled with spirit of wine, as in the case with lavender +water, or simply mixed with a large proportion of water, as is often +done with regard to peppermint. Frequently, also, these odoriferous +waters are prepared merely by soaking the plants in water, and +distilling. The water then comes over impregnated with the volatile +oil.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Such waters are frequently used to take spots of grease out of cloth, +or silk; how do they produce that effect?</p> + +<p class="speaker">MRS. B.</p> + +<p>By combining with the substance that forms these stains; for volatile +oils, and likewise the spirit in which they are distilled, will dissolve +wax, tallow, spermaceti, and resins; if, therefore, the spot proceeds +from any of these substances, it +<span class="pagenum">185</span> +<a name="conver2.page185" id="conver2.page185"> </a> +will remove it. Insects of every kind have a great aversion to perfumes, +so that volatile oils are employed with success in museums for the +preservation of stuffed birds and other species of animals.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray does not the powerful smell of camphor proceed from a volatile +oil?</p> + +<p class="speaker">MRS. B.</p> + +<p><i>Camphor</i> seems to be a substance of its own kind, remarkable by +many peculiarities. But if not exactly of the same nature as volatile +oil, it is at least very analogous to it. It is obtained chiefly from +the camphor-tree, a species of laurel which grows in China, and in +the Indian isles, from the stem and roots of which it is extracted. +Small quantities have also been distilled from thyme, sage, and other +aromatic plants; and it is deposited in pretty large quantities by some +volatile oils after long standing. It is extremely volatile and +inflammable. It is insoluble in water, but is soluble in oils, in which +state, as well as in its solid form, it is frequently applied to +medicinal purposes. Amongst the particular properties of camphor, there +is one too singular to be passed over in silence. If you take a small +piece of camphor, and place it on the surface of a bason of pure water, +it will immediately begin to move round +<span class="pagenum">186</span> +<a name="conver2.page186" id="conver2.page186"> </a> +and round with great rapidity; but if you pour into the bason a single +drop of any odoriferous fluid, it will instantly put a stop to this +motion. You can at any time try this very simple experiment; but you +must not expect that I shall be able to account for this phenomenon, as +nothing satisfactory has yet been advanced for its explanation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is very singular indeed; and I will certainly try the experiment. +Pray what are <i>resins</i>, which you just now mentioned?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are volatile oils, that have been acted on, and peculiarly +modified, by oxygen.</p> + +<p class="speaker">CAROLINE.</p> + +<p>They are, therefore, oxygenated volatile oils?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not exactly; for the process does not appear to consist so much in +the oxygenation of the oil, as in the combustion of a portion of its +hydrogen, and a small portion of its carbon. For when resins are +artificially made by the combination of volatile oils with oxygen, the +vessel in which the process is performed is bedewed with water, and the +air included within is loaded with carbonic acid.</p> + +<span class="pagenum">187</span> +<a name="conver2.page187" id="conver2.page187"> </a> +<p class="speaker">EMILY.</p> + +<p>This process must be, in some respects, similar to that for preparing +drying oils?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and it is by this operation that both of them acquire a greater +degree of consistence. Pitch, tar, and turpentine, are the most common +resins; they exude from the pine and fir trees. Copal, mastic, and +frankincense, are also of this class of vegetable substances.</p> + +<p class="speaker">EMILY.</p> + +<p>Is it of these resins that the mastic and copal varnishes, so much +used in painting, are made?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes. Dissolved either in oil, or in alcohol, resins form varnishes. +From these solutions they may be precipitated by water, in which they +are insoluble. This I can easily show you.—If you will pour some +water into this glass of mastic varnish, it will combine with the +alcohol in which the resin is dissolved, and the latter will be +precipitated in the form of a white cloud—</p> + +<p class="speaker">EMILY.</p> + +<p>It is so. And yet how is it that pictures or +<span class="pagenum">188</span> +<a name="conver2.page188" id="conver2.page188"> </a> +drawings, varnished with this solution, may safely be washed with +water?</p> + +<p class="speaker">MRS. B.</p> + +<p>As the varnish dries, the alcohol evaporates, and the dry varnish or +resin which remains, not being soluble in water, will not be acted on +by it.</p> + +<p>There is a class of compound resins called <i>gum-resins</i>, which +are precisely what their name denotes, that is to say, resins combined +with mucilage. Myrrh and assafœtida are of this description.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it possible that a substance of so disagreeable a smell as +assafœtida can be formed from a volatile oil?</p> + +<p class="speaker">MRS. B.</p> + +<p>The odour of volatile oils is by no means always grateful. Onions and +garlic derive their smell from volatile oils, as well as roses and +lavender.</p> + +<p>There is still another form under which volatile oils present +themselves, which is that of <i>balsams</i>. These consist of resinous +juices combined with a peculiar acid, called the benzoic acid. Balsams +appear to have been originally volatile oils, the oxygenation of which +has converted one part into a resin, and the other part into an acid, +which, +<span class="pagenum">189</span> +<a name="conver2.page189" id="conver2.page189"> </a> +combined together, form a balsam; such are the balsams of Peru, +Tolu, &c.</p> + + +<p class="space"> +We shall now take leave of the oils and their various modifications, and +proceed to the next vegetable substance, which is <i>caoutchouc</i>. +This is a white milky glutinous fluid, which acquires consistence, and +blackens in drying, in which state it forms the substance with which you +are so well acquainted, under the name of gum-elastic.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am surprised to hear that gum-elastic was ever white, or ever +fluid! And from what vegetable is it procured?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is obtained from two or three different species of trees, in the +East-Indies, and South-America, by making incisions in the stem. The +juice is collected as it trickles from these incisions, and moulds of +clay, in the form of little bottles of gum-elastic, are dipped into it. +A layer of this juice adheres to the clay and dries on it; and +several layers are successively added by repeating this till the bottle +is of sufficient thickness. It is then beaten to break down the clay, +which is easily shaken out. The natives of the countries where this +substance is produced sometimes make shoes and boots of it by a similar +process, and +<span class="pagenum">190</span> +<a name="conver2.page190" id="conver2.page190"> </a> +they are said to be extremely pleasant and serviceable, both from their +elasticity, and their being water-proof.</p> + + +<p class="space"> +The substance which comes next in our enumeration of the immediate +ingredients of vegetables, is <i>extractive matter</i>. This is a term, +which, in a general sense, may be applied to any substance extracted +from vegetables; but it is more particularly understood to relate to the +extractive <i>colouring matter</i> of plants. A great variety of +colours are prepared from the vegetable kingdom, both for the purposes +of painting and of dying; all the colours called <i>lakes</i> are of +this description; but they are less durable than mineral colours, for, +by long exposure to the atmosphere, they either darken or turn +yellow.</p> + +<p class="speaker">EMILY.</p> + +<p>I know that in painting, the lakes are reckoned far less durable +colours than the ochres; but what is the reason of it?</p> + +<p class="speaker">MRS. B.</p> + +<p>The change which takes place in vegetable colours is owing chiefly to +the oxygen of the atmosphere slowly burning their hydrogen, and leaving, +in some measure, the blackness of the carbon exposed. +<span class="pagenum">191</span> +<a name="conver2.page191" id="conver2.page191"> </a> +Such change cannot take place in ochre, which is altogether a mineral +substance.</p> + +<p>Vegetable colours have a stronger affinity for animal than for +vegetable substances, and this is supposed to be owing to a small +quantity of nitrogen which they contain. Thus, silk and worsted will +take a much finer vegetable dye than linen and cotton.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Dying, then, is quite a chemical process?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly. The condition required to form a good dye is, that the +colouring matter should be precipitated, or fixed, on the substance to +be dyed, and should form a compound not soluble in the liquids to which +it will probably be exposed. Thus, for instance, printed or dyed linens +or cottons must be able to resist the action of soap and water, to which +they must necessarily be subject in washing; and woollens and silks +should withstand the action of grease and acids, to which they may +accidentally be exposed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if linen and cotton have not a sufficient affinity for colouring +matter, how are they made to resist the action of washing, which they +always do when they are well printed?</p> + +<span class="pagenum">192</span> +<a name="conver2.page192" id="conver2.page192"> </a> +<p class="speaker">MRS. B.</p> + +<p>When the substance to be dyed has either no affinity for the +colouring matter, or not sufficient power to retain it, the combination +is effected, or strengthened, by the intervention of a third substance, +called a <i>mordant</i>, or basis. The mordant must have a strong +affinity both for the colouring matter and the substance to be dyed, by +which means it causes them to combine and adhere together.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And what are the substances that perform the office of thus +reconciling the two adverse parties?</p> + +<p class="speaker">MRS. B.</p> + +<p>The most common mordant is sulphat of alumine, or alum. Oxyds of tin +and iron, in the state of compound salts, are likewise used for that +purpose.</p> + +<p><i>Tannin</i> is another vegetable ingredient of great importance in +the arts. It is obtained chiefly from the bark of trees; but it is found +also in nut-galls, and in some other vegetables.</p> + +<p class="speaker">EMILY.</p> + +<p>Is that the substance commonly called <i>tan</i>, which is used in +hot-houses?</p> + +<span class="pagenum">193</span> +<a name="conver2.page193" id="conver2.page193"> </a> +<p class="speaker">MRS. B.</p> + +<p>Tan is the prepared bark in which the peculiar substance, tannin, is +contained. But the use of tan in hot-houses is of much less importance +than in the operation of <i>tanning</i>, by which skin is converted into +leather.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray, how is this operation performed?</p> + +<p class="speaker">MRS. B.</p> + +<p>Various methods are employed for this purpose, which all consist in +exposing skin to the action of tannin, or of substances containing this +principle, in sufficient quantities, and disposed to yield it to the +skin. The most usual way is to infuse coarsely powdered oak bark in +water, and to keep the skin immersed in this infusion for a certain +length of time. During this process, which is slow and gradual, the skin +is found to have increased in weight, and to have acquired a +considerable tenacity and impermeability to water. This effect may be +much accelerated by using strong saturations of the tanning principle +(which can be extracted from bark), instead of employing the bark +itself. But this quick mode of preparation does not appear to make +equally good leather.</p> + +<p>Tannin is contained in a great variety of +<span class="pagenum">194</span> +<a name="conver2.page194" id="conver2.page194"> </a> +astringent vegetable substances, as galls, the rose-tree, and wine; but +it is nowhere so plentiful as in bark. All these substances yield it to +water, from which it may be precipitated by a solution of isinglass, or +glue, with which it strongly unites and forms an insoluble compound. +Hence its valuable property of combining with skin (which consists +chiefly of glue), and of enabling it to resist the action of water.</p> + +<p class="speaker">EMILY.</p> + +<p>Might we not see that effect by pouring a little melted isinglass +into a glass of wine, which you say contains tannin?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes. I have prepared a solution of isinglass for that very +purpose.—Do you observe the thick muddy precipitate?—That is +the tannin combined with the isinglass.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This precipitate must then be of the same nature as leather?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is composed of the same ingredients; but the organisation and +texture of the skin being wanting, it has neither the consistence nor +the tenacity of leather.</p> + +<span class="pagenum">195</span> +<a name="conver2.page195" id="conver2.page195"> </a> +<p class="speaker">CAROLINE.</p> + +<p>One might suppose that men who drink large quantities of red wine +stand a chance of having the coats of their stomachs converted into +leather, since tannin has so strong an affinity for skin.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not impossible but that the coats of their stomachs may be, in +some measure, tanned, or hardened by the constant use of this liquor; +but you must remember that where a number of other chemical agents are +concerned, and, above all, where life exists, no certain chemical +inference can be drawn.</p> + +<p>I must not dismiss this subject, without mentioning a recent +discovery of Mr. Hatchett, which relates to it. This gentleman found +that a substance very similar to tannin, possessing all its leading +properties, and actually capable of tanning leather, may be produced by +exposing carbon, or any substance containing carbonaceous matter, +whether vegetable, animal, or mineral, to the action of nitric acid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And is not this discovery very likely to be of use to +manufactures?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is very doubtful, because tannin, thus artificially +<span class="pagenum">196</span> +<a name="conver2.page196" id="conver2.page196"> </a> +prepared, must probably always be more expensive than that which is +obtained from bark. But the fact is extremely curious, as it affords one +of those very rare instances of chemistry being able to imitate the +proximate principles of organised bodies.</p> + + +<p class="space"> +The last of the vegetable materials is <i>woody fibre</i>; it is the +hardest part of plants. The chief source from which this substance is +derived is wood, but it is also contained, more or less, in every solid +part of that plant. It forms a kind of skeleton of the part to which it +belongs, and retains its shape after all the other materials have +disappeared. It consists chiefly of carbon, united with a small +proportion of salts, and the other constituents common to all +vegetables.</p> + +<p class="speaker">EMILY.</p> + +<p>It is of woody fibre, then, that the common charcoal is made?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes. Charcoal, as you may recollect, is obtained from wood, by the +separation of all its evaporable parts.</p> + +<p>Before we take leave of the vegetable materials, it will be proper, +at least, to enumerate the several vegetable acids which we either have +had, or may +<span class="pagenum">197</span> +<a name="conver2.page197" id="conver2.page197"> </a> +have occasion to mention. I believe I formerly told you that their +basis, or radical, was uniformly composed of hydrogen and carbon, and +that their difference consisted only in the various proportions of +oxygen which they contained.</p> + + +<p class="space"> +The following are the names of the vegetable acids:</p> + +<table class="list inline" summary="list of substances"> +<tr> +<td>The</td><td><i>Mucous Acid</i>,</td> +<td><p>obtained from gum or mucilage;</p></td> +</tr> +<tr> +<td></td><td><i>Suberic</i></td> +<td>from cork;</td> +</tr> +<tr> +<td></td><td><i>Camphoric</i></td> +<td>from camphor;</td> +</tr> +<tr> +<td></td><td><i>Benzoic</i></td> +<td>from balsams;</td> +</tr> +<tr> +<td></td><td><i>Gallic</i></td> +<td>from galls, bark, &c.</td> +</tr> +<tr> +<td></td><td><i>Malic</i></td> +<td>from ripe fruits;</td> +</tr> +<tr> +<td></td><td><i>Citric</i></td> +<td>from lemon juice;</td> +</tr> +<tr> +<td></td><td><i>Oxalic</i></td> +<td>from sorrel;</td> +</tr> +<tr> +<td></td><td><i>Succinic</i></td> +<td>from amber;</td> +</tr> +<tr> +<td></td><td><i>Tartarous</i></td> +<td>from tartrit of potash:</td> +</tr> +<tr> +<td></td><td><i>Acetic</i></td> +<td>from vinegar.</td> +</tr> +</table> + +<p>They are all decomposable by heat, soluble in water, and turn +vegetable blue colours red. The <i>succinic</i>, the <i>tartarous</i>, +and the <i>acetous acids</i>, are the products of the decomposition of +vegetables<ins class="mycorr" title="text has ,">; </ins>we shall, +therefore, reserve their examination for a future period.</p> + +<p>The <i>oxalic acid</i>, distilled from sorrel, is the highest term of +vegetable acidification; for, if +<span class="pagenum">198</span> +<a name="conver2.page198" id="conver2.page198"> </a> +more oxygen be added to it, it loses its vegetable nature, and is +resolved into carbonic acid and water; therefore, though all the other +acids may be converted into the oxalic by an addition of oxygen, the +oxalic itself is not susceptible of a further degree of oxygenation; nor +can it be made, by any chemical processes, to return to a state of lower +acidification.</p> + +<p class="space"> +To conclude this subject, I have only to add a few words on the +<i>gallic acid</i>. . . . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is not this the same acid before mentioned, which forms ink, by +precipitating sulphat of iron from its solution?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes. Though it is usually extracted from galls, on account of its +being most abundant in that vegetable substance, it may also be obtained +from a great variety of plants. It constitutes what is called the +<i>astringent principle</i> of vegetables; it is generally combined with +tannin, and you will find that an infusion of tea, coffee, bark, +red-wine, or any vegetable substance that contains the astringent +principle, will make a black precipitate with a solution of sulphat of +iron.</p> + +<span class="pagenum">199</span> +<a name="conver2.page199" id="conver2.page199"> </a> +<p class="speaker">CAROLINE.</p> + +<p>But pray what are galls?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are excrescences which grow on the bark of young oaks, and are +occasioned by an insect which wounds the bark of trees, and lays its +eggs in the aperture. The lacerated vessels of the tree then discharge +their contents, and form an excrescence, which affords a defensive +covering for these eggs. The insect, when come to life, first feeds on +this excrescence, and some time afterward eats its way out, as it +appears from a hole which is formed in all gall-nuts that no longer +contain an insect. It is in hot climates only that strongly astringent +gall-nuts are found; those which are used for the purpose of making ink +are brought from Aleppo.</p> + +<p class="speaker">EMILY.</p> + +<p>But are not the oak-apples, which grow on the leaves of the oak in +this country, of a similar nature?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; only they are an inferior species of galls, containing less of +the astringent principle, and therefore less applicable to useful +purposes.</p> + +<span class="pagenum">200</span> +<a name="conver2.page200" id="conver2.page200"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Are the vegetable acids never found but in their pure uncombined +state?</p> + +<p class="speaker">MRS. B.</p> + +<p>By no means; on the contrary, they are frequently met with in the +state of compound salts; these, however, are in general not fully +saturated with the salifiable bases, so that the acid predominates; and, +in this state, they are called <i>acidulous</i> salts. Of this kind is +the salt called cream of tartar.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is not the salt of lemon, commonly used to take out ink-spots and +stains, of this nature?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; that salt consists of the oxalic acid, combined with a little +potash. It is found in that state in sorrel.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And pray how does it take out ink-spots?</p> + +<p class="speaker">MRS. B.</p> + +<p>By uniting with the iron, and rendering it soluble in water.</p> + + +<p class="space"> +Besides the vegetable materials which we have enumerated, a variety +of other substances, common +<span class="pagenum">201</span> +<a name="conver2.page201" id="conver2.page201"> </a> +to the three kingdoms, are found in vegetables, such as potash, which +was formerly supposed to belong exclusively to plants, and was, in +consequence, called the vegetable alkali.</p> + +<p>Sulphur, phosphorus, earths, and a variety of metallic oxyds, are +also found in vegetables, but only in small quantities. And we meet +sometimes with neutral salts, formed by the combination of these +ingredients.</p> + + + + +<span class="pagenum">202</span> +<a name="conver2.page202" id="conver2.page202"> </a> +<h4><a name="convXXI" id="convXXI">CONVERSATION XXI.</a><br> +<span class="subhead">ON THE DECOMPOSITION OF VEGETABLES.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">CAROLINE.</p> + +<p><span class="firstword"><span class="firstletter">T</span>he</span> account which you have given us, +Mrs. B., of the materials of vegetables, is, doubtless, very +instructive; but it does not completely satisfy my curiosity. +I wish to know how plants obtain the principles from which their +various materials are formed; by what means these are converted into +vegetable matter, and how they are connected with the life of the +plant?</p> + +<p class="speaker">MRS. B.</p> + +<p>This implies nothing less than a complete history of the chemistry +and physiology of vegetation, subjects on which we have yet but very +imperfect notions. Still I hope that I shall be able, in some measure, +to satisfy your curiosity. But, in order to render the subject more +intelligible, I must first +<span class="pagenum">203</span> +<a name="conver2.page203" id="conver2.page203"> </a> +make you acquainted with the various changes which vegetables undergo, +when the vital power no longer enables them to resist the common laws of +chemical attraction.</p> + +<p>The composition of vegetables being more complicated than that of +minerals, the former more readily undergo chemical changes than the +latter: for the greater the variety of attractions, the more easily is +the equilibrium destroyed, and a new order of combinations +introduced.</p> + +<p class="speaker">EMILY.</p> + +<p>I am surprised that vegetables should be so easily susceptible of +decomposition; for the preservation of the vegetable kingdom is +certainly far more important than that of minerals.</p> + +<p class="speaker">MRS. B.</p> + +<p>You must consider, on the other hand, how much more easily the former +is renewed than the latter. The decomposition of the vegetable takes +place only after the death of the plant, which, in the common course of +nature, happens when it has yielded fruit and seeds to propagate its +species. If, instead of thus finishing its career, each plant was to +retain its form and vegetable state, it would become an useless burden +to the earth and its inhabitants. When vegetables, therefore, cease to +be productive, they cease to live, and nature +<span class="pagenum">204</span> +<a name="conver2.page204" id="conver2.page204"> </a> +then begins her process of decomposition, in order to resolve them into +their chemical constituents, hydrogen, carbon, and oxygen; those simple +and primitive ingredients, which she keeps in store for all her +combinations.</p> + +<p class="speaker">EMILY.</p> + +<p>But since no system of combination can be destroyed, except by the +establishment of another order of attractions, how can the decomposition +of vegetables reduce them to their simple elements?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a very long process, during which a variety of new combinations +are successively established and successively destroyed: but, in each of +these changes, the ingredients of vegetable matter tend to unite in a +more simple order of compounds, till they are at length brought to their +elementary state, or, at least, to their most simple order of +combinations. Thus you will find that vegetables are in the end almost +entirely reduced to water and carbonic acid; the hydrogen and carbon +dividing the oxygen between them, so as to form with it these two +substances. But the variety of intermediate combinations that take place +during the several stages of the decomposition of vegetables, present us +with a new set of compounds, well worthy of our examination.</p> + +<span class="pagenum">205</span> +<a name="conver2.page205" id="conver2.page205"> </a> +<p class="speaker">CAROLINE.</p> + +<p>How is it possible that vegetables, while putrefying, should produce +any thing worthy of observation?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are susceptible of undergoing certain changes before they arrive +at the state of putrefaction, which is the final term of decomposition; +and of these changes we avail ourselves for particular and important +purposes. But, in order to make you understand this subject, which is of +considerable importance, I must explain it more in detail.</p> + +<p>The decomposition of vegetables is always attended by a violent +internal motion, produced by the disunion of one order of particles, and +the combination of another. This is called <span class="smallroman">FERMENTATION</span>. There are several periods at which +this process stops, so that a state of rest appears to be restored, and +the new order of compounds fairly established. But, unless means be used +to secure these new combinations in their actual state, their duration +will be but transient, and a new fermentation will take place, by which +the compound last formed will be <ins class="mycorr" title="text reads ‘detroyed’">destroyed</ins>; +and another, and less complex order, will succeed.</p> + +<p class="speaker">EMILY.</p> + +<p>The fermentations, then, appear to be only the +<span class="pagenum">206</span> +<a name="conver2.page206" id="conver2.page206"> </a> +successive steps by which a vegetable descends to its final +dissolution.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely so. Your definition is perfectly correct.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And how many fermentations, or new arrangements, does a vegetable +undergo before it is reduced to its simple ingredients?</p> + +<p class="speaker">MRS. B.</p> + +<p>Chemists do not exactly agree in this point; but there are, +I think, four distinct fermentations, or periods, at which the +decomposition of vegetable matter stops and changes its course. But +every kind of vegetable matter is not equally susceptible of undergoing +all these fermentations.</p> + +<p>There are likewise several circumstances required to produce +fermentation. Water and a certain degree of heat are both essential to +this process, in order to separate the particles, and thus weaken their +force of cohesion, that the new chemical affinities may be brought into +action.</p> + +<p class="speaker">CAROLINE.</p> + +<p>In frozen climates, then, how can the spontaneous decomposition of +vegetables take place?</p> + +<span class="pagenum">207</span> +<a name="conver2.page207" id="conver2.page207"> </a> +<p class="speaker">MRS. B.</p> + +<p>It certainly cannot; and, accordingly, we find scarcely any vestiges +of vegetation where a constant frost prevails.</p> + +<p class="speaker">CAROLINE.</p> + +<p>One would imagine that, on the contrary, such spots would be covered +with vegetables; for, since they cannot be decomposed, their number must +always increase.</p> + +<p class="speaker">MRS. B.</p> + +<p>But, my dear, heat and water are quite as essential to the formation +of vegetables, as they are to their decomposition. Besides, it is from +the dead vegetables, reduced to their elementary principles, that the +rising generation is supplied with sustenance. No young plant, +therefore, can grow unless its predecessors contribute both to its +formation and support; and these not only furnish the seed from which +the new plant springs, but likewise the food by which it is +nourished.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Under the torrid zone, therefore, where water is never frozen, and +the heat is very great, both the processes of vegetation and of +fermentation must, I suppose, be extremely rapid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not so much as you imagine: for in such climates +<span class="pagenum">208</span> +<a name="conver2.page208" id="conver2.page208"> </a> +<ins class="mycorr" title="missing ‘a’?">great</ins> part of the +water which it requires for these processes is in an aëriform state, +which is scarcely more conducive either to the growth or formation of +vegetables than that of ice. In those latitudes, therefore, it is only +in low damp situations, sheltered by woods from the sun’s rays, that the +smaller tribes of vegetables can grow and thrive during the dry season, +as dead vegetables seldom retain water enough to produce fermentation, +but are, on the contrary, soon dried up by the heat of the sun, which +enables them to resist that process; so that it is not till the fall of +the autumnal rains (which are very violent in such climates), that +spontaneous fermentation can take place.</p> + +<p>The several fermentations derive their names from their principal +products. The first is called the <i>saccharine fermentation</i>, +because its product is <i>sugar</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But sugar, you have told us, is found in all vegetables; it cannot, +therefore, be the product of their decomposition.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is true that this fermentation is not confined to the +decomposition of vegetables, as it continually takes place during their +life; and, indeed, this circumstance has, till lately, prevented it from +<span class="pagenum">209</span> +<a name="conver2.page209" id="conver2.page209"> </a> +being considered as one of the fermentations. But the process appears so +analogous to the other fermentations, and the formation of sugar, +whether in living or dead vegetable matter is so evidently a new +compound, proceeding from the destruction of the previous order of +combinations, and essential to the subsequent fermentations, that it is +now, I believe, generally esteemed the first step, or necessary +preliminary, to decomposition, if not an actual commencement of that +process.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I recollect your hinting to us that sugar was supposed not to be +secreted from the sap, in the same manner as mucilage, fecula, oil, and +the other ingredients of vegetables.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is rather from these materials, than from the sap itself, that +sugar is formed; and it is developed at particular periods, as you may +observe in fruits, which become sweet in ripening, sometimes even after +they have been gathered. Life, therefore, is not essential to the +formation of sugar, whilst on the contrary, mucilage, fecula, and the +other vegetable materials that are secreted from the sap by appropriate +organs, whose powers immediately depend on the vital principle, cannot +be +<span class="pagenum">210</span> +<a name="conver2.page210" id="conver2.page210"> </a> +produced but during the existence of that principle.</p> + +<p class="speaker">EMILY.</p> + +<p>The ripening of fruits is, then, their first step to destruction, as +well as their last towards perfection?</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly.—A process analogous to the saccharine fermentation +takes place also during the cooking of certain vegetables. This is the +case with parsnips, carrots, potatoes, &c. in which sweetness is +developed by heat and moisture; and we know that if we carried the +process a little farther, a more complete decomposition would +ensue. The same process takes place also in seeds previous to their +sprouting.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How do you reconcile this to your theory, Mrs. B.? Can you +suppose that a decomposition is the necessary precursor of life?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is indeed the case. The materials of the seed must be +decomposed, and the seed disorganized, before a plant can sprout from +it. Seeds, besides the embrio plant, contain (as we have already +observed) fecula, oil, and a little mucilage. These substances are +destined for the nourishment of the future plant; but they undergo some +change +<span class="pagenum">211</span> +<a name="conver2.page211" id="conver2.page211"> </a> +before they can be fit for this function. The seeds, when buried in the +earth, with a certain degree of moisture and of temperature, absorb +water, which dilates them, separates their particles, and introduces a +new order of attractions, of which sugar is the product. The substance +of the seed is thus softened, sweetened, and converted into a sort of +white milky pulp, fit for the nourishment of the embrio plant.</p> + +<p>The saccharine fermentation of seeds is artificially produced, for +the purpose of making <i>malt</i>, by the following +process:—A quantity of barley is first soaked in water for +two or three days: the water being afterwards drained off, the grain +heats spontaneously, swells, bursts, sweetens, shows a disposition to +germinate, and actually sprouts to the length of an inch, when the +process is stopped by putting it into a kiln, where it is well dried at +a gentle heat. In this state it is crisp and friable, and constitutes +the substance called <i>malt</i>, which is the principal ingredient of +beer.</p> + +<p class="speaker">EMILY.</p> + +<p>But I hope you will tell us how malt is made into beer?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; but I must first explain to you the nature of the second +fermentation, which is essential +<span class="pagenum">212</span> +<a name="conver2.page212" id="conver2.page212"> </a> +to that operation. This is called the <i>vinous fermentation</i>, +because its product is <i>wine</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>How very different the decomposition of vegetables is from what I had +imagined! The products of their disorganisation appear almost superior +to those which they yield during their state of life and perfection.</p> + +<p class="speaker">MRS. B.</p> + +<p>And do you not, at the same time, admire the beautiful economy of +Nature, which, whether she creates, or whether she destroys, directs all +her operations to some useful and benevolent purpose?—It appears +that the saccharine fermentation is extremely favourable, if not +absolutely essential, as a previous step, to the vinous fermentation; so +that if sugar be not developed during the life of the plant, the +saccharine fermentation must be artificially produced before the vinous +fermentation can take place. This is the case with barley, which does +not yield any sugar until it is made into malt; and it is in that state +only that it is susceptible of undergoing the vinous fermentation by +which it is converted into beer.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if the product of the vinous fermentation +<span class="pagenum">213</span> +<a name="conver2.page213" id="conver2.page213"> </a> +is always wine, beer cannot have undergone that process, for beer is +certainly not wine.</p> + +<p class="speaker">MRS. B.</p> + +<p>Chemically speaking, beer may be considered as the wine of grain. For +it is the product of the fermentation of malt, just as wine is that of +the fermentation of grapes, or other fruits.</p> + +<p>The consequence of the vinous fermentation is the decomposition of +the saccharine matter, and the formation of a spirituous liquor from the +constituents of the sugar. But, in order to promote this fermentation, +not only water and a certain degree of heat are necessary, but also some +other vegetable ingredients, besides the sugar, as fecula, mucilage, +acids, salts, extractive matter, &c. all of which seem to contribute +to this process; and give to the liquor its peculiar taste.</p> + +<p class="speaker">EMILY.</p> + +<p>It is, perhaps, for this reason that wine is not obtained from the +fermentation of pure sugar; but that fruits are chosen for that purpose, +as they contain not only sugar, but likewise the other vegetable +ingredients which promote the vinous fermentation, and give the peculiar +flavour.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly. And you must observe also, that +<span class="pagenum">214</span> +<a name="conver2.page214" id="conver2.page214"> </a> +the relative quantity of sugar is not the only circumstance to be +considered in the choice of vegetable juices for the formation of wine; +otherwise the sugar-cane would be best adapted for that purpose. It is +rather the manner and proportion in which the sugar is mixed with other +vegetable ingredients that influences the production and qualities of +wine. And it is found that the juice of the grape not only yields the +most considerable proportion of wine, but that it likewise affords it of +the most grateful flavour.</p> + +<p class="speaker">EMILY.</p> + +<p>I have seen a vintage in Switzerland, and I do not recollect that +heat was applied, or water added, to produce the fermentation of the +grapes.</p> + +<p class="speaker">MRS. B.</p> + +<p>The common temperature of the atmosphere in the cellars in which the +juice of the grape is fermented is sufficiently warm for this purpose; +and as the juice contains an ample supply of water, there is no occasion +for any addition of it. But when fermentation is produced in dry malt, +a quantity of water must necessarily be added.</p> + +<p class="speaker">EMILY.</p> + +<p>But what are precisely the changes that happen during the vinous +fermentation?</p> + +<span class="pagenum">215</span> +<a name="conver2.page215" id="conver2.page215"> </a> +<p class="speaker">MRS. B.</p> + +<p>The sugar is decomposed, and its constituents are recombined into two +new substances; the one a peculiar liquid substance, called +<i>alcohol</i> or <i>spirit of wine</i>, which remains in the fluid; the +other, carbonic acid gas, which escapes during the fermentation. Wine, +therefore, as I before observed, in a general point of view, may be +considered as a liquid of which alcohol constitutes the essential part. +And the varieties of strength and flavour of the different kinds of wine +are to be attributed to the different qualities of the fruits from which +they are obtained, independently of the sugar.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am astonished to hear that so powerful a liquid as spirit of wine +should be obtained from so mild a substance as sugar.</p> + +<p class="speaker">MRS. B.</p> + +<p>Can you tell me in what the principal difference consists between +alcohol and sugar?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Let me reflect . . . . . Sugar consists of carbon, hydrogen, and +oxygen. If carbonic acid be subtracted from it, during the formation of +alcohol, the latter will contain less carbon and oxygen +<span class="pagenum">216</span> +<a name="conver2.page216" id="conver2.page216"> </a> +than sugar does; therefore hydrogen must be the prevailing principle of +alcohol.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is exactly so. And this very large proportion of hydrogen accounts +for the lightness and combustible property of alcohol, and of spirits in +general, all of which consist of alcohol variously modified.</p> + +<p class="speaker">EMILY.</p> + +<p>And can sugar be recomposed from the combination of alcohol and +carbonic acid?</p> + +<p class="speaker">MRS. B.</p> + +<p>Chemists have never been able to succeed in effecting this; but from +analogy, I should suppose such a recomposition possible. Let us now +observe more particularly the phenomena that take place during the +vinous fermentation. At the commencement of this process, heat is +evolved, and the liquor swells considerably from the formation of the +carbonic acid, which is disengaged in such prodigious quantities as +would be fatal to any person who should unawares inspire it; an accident +which has sometimes happened. If the fermentation be stopped by putting +the liquor into barrels, before the whole of the carbonic acid is +evolved, the wine is brisk, like Champagne, +<span class="pagenum">217</span> +<a name="conver2.page217" id="conver2.page217"> </a> +from the carbonic acid imprisoned in it, and it tastes sweet, like +cyder, from the sugar not being completely decomposed.</p> + +<p class="speaker">EMILY.</p> + +<p>But I do not understand why heat should be evolved during this +operation. For, as there is a considerable formation of gas, in which a +proportionable quantity of heat must become insensible, I should +have imagined that cold, rather than heat, would have been produced.</p> + +<p class="speaker">MRS. B.</p> + +<p>It appears so on first consideration; but you must recollect that +fermentation is a complicated chemical process; and that, during the +decompositions and recompositions attending it, a quantity of +chemical heat may be disengaged, sufficient both to develope the gas, +and to effect an increase of temperature. When the fermentation is +completed, the liquid cools and subsides, the effervescence ceases, and +the thick, sweet, sticky juice of the fruit is converted into a clear, +transparent, spirituous liquor, called wine.</p> + +<p class="speaker">EMILY.</p> + +<p>How much I regret not having been acquainted with the nature of the +vinous fermentation, when I had an opportunity of seeing the +process!</p> + +<span class="pagenum">218</span> +<a name="conver2.page218" id="conver2.page218"> </a> +<p class="speaker">MRS. B.</p> + +<p>You have an easy method of satisfying yourself in that respect by +observing the process of brewing, which, in every essential +circumstance, is similar to that of making wine, and is really a very +curious chemical operation.</p> + +<p>Although we cannot actually make wine at this moment, it will be easy +to show you the mode of analyzing it. This is done by distillation. When +wine of any kind is submitted to this operation, it is found to contain +brandy, water, tartar, extractive colouring matter, and some vegetable +acids. I have put a little port wine into this alembic of glass (<a +class="smallcaps" href="#plateXIV">Plate XIV.</a> Fig. 1.), and +on placing the lamp under it, you will soon see the spirit and water +successively come over—</p> + +<p class="figname"> +<a name="plateXIV" id="plateXIV">Plate XIV.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. II.</span> p. 213.</p> + +<p class="illustration"> +<img src="images/plate14_thumb.png" width="578" height="310" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1. A Alembic. +B Lamp. +C Wine glass.<br> + +Fig. 2. Alcohol blowpipe. +D the Lamp. +E the vessel in which the Alcohol is boiling. +F a safety valve. +G the inflamed jet or steam of alcohol directed towards a glass +tube H.</p> + +<p class="figlink"> +<a href="images/plate14_large.jpg" target="_blank">Larger +view</a></p> + +<p class="speaker">EMILY.</p> + +<p>But you do not mention alcohol amongst the <i>products</i> of the +distillation of wine; and yet that is its most essential ingredient?</p> + +<p class="speaker">MRS. B.</p> + +<p>The alcohol is contained in the brandy which is now coming over, and +dropping from the still. Brandy is nothing more than a mixture of +alcohol and water; and in order to obtain the alcohol pure, we must +again distil it from brandy.</p> + +<span class="pagenum">219</span> +<a name="conver2.page219" id="conver2.page219"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I have just taken a drop on my finger; it tastes like strong brandy, +but it is without colour, whilst brandy is of a deep yellow.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not so naturally; in its pure state brandy is colourless, and +it obtains the yellow tint you observe, by extracting the colouring +matter from the new oaken casks in which it is kept. But if it does not +acquire the usual tinge in this way, it is the custom to colour the +brandy used in this country artificially, with a little burnt sugar, in +order to give it the appearance of having been long kept.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And is rum also distilled from wine?</p> + +<p class="speaker">MRS. B.</p> + +<p>By no means; it is distilled from the sugar-cane, a plant which +contains so great a quantity of sugar, that it yields more alcohol than +almost any other vegetable. After the juice of the cane has been pressed +out for making sugar, what still remains in the bruised cane is +extracted by water, and this watery solution of sugar is fermented, and +produces rum.</p> + +<span class="pagenum">220</span> +<a name="conver2.page220" id="conver2.page220"> </a> +<p>The spirituous liquor called <i>arack</i> is in a similar manner +distilled from the product of the vinous fermentation of rice.</p> + +<p class="speaker">EMILY.</p> + +<p>But rice has no sweetness; does it contain any sugar?</p> + +<p class="speaker">MRS. B.</p> + +<p>Like barley and most other seeds, it is insipid until it has +undergone the saccharine fermentation; and this, you must recollect, is +always a previous step to the vinous fermentation in those vegetables in +which sugar is not already formed. Brandy may in the same manner be +obtained from malt.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You mean from beer, I suppose; for the malt must have previously +undergone the vinous fermentation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Beer is not precisely the product of the vinous fermentation of malt. +For hops are a necessary ingredient for the formation of that liquor; +whilst brandy is distilled from pure fermented malt. But brandy might, +no doubt, be distilled from beer as well as from any other liquor that +has undergone the vinous fermentation; for since the basis of brandy is +alcohol, it may be obtained from any liquid that contains that +spirituous substance.</p> + +<span class="pagenum">221</span> +<a name="conver2.page221" id="conver2.page221"> </a> +<p class="speaker">EMILY.</p> + +<p>And pray, from what vegetable is the favourite spirit of the lower +orders of people, gin, extracted?</p> + +<p class="speaker">MRS. B.</p> + +<p>The spirit (which is the same in all fermented liquors) may be +obtained from any kind of grain; but the peculiar flavour which +distinguishes gin is that of juniper berries, which are distilled +together with the grain—</p> + +<p>I think the brandy contained in the wine which we are distilling +must, by this time, be all come over. Yes—taste the liquid that is +now dropping from the alembic—</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is perfectly insipid, like water.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is water, which, as I was telling you, is the second product of +wine, and comes over after all the spirit, which is the lightest part, +is distilled.—The tartar and extractive colouring matter we shall +find in a solid form at the bottom of the alembic.</p> + +<p class="speaker">EMILY.</p> + +<p>They look very like the lees of wine.</p> + +<p class="speaker">MRS. B.</p> + +<p>And in many respects they are of a similar nature; +<span class="pagenum">222</span> +<a name="conver2.page222" id="conver2.page222"> </a> +for lees of wine consist chiefly of tartrit of potash; a salt which +exists in the juice of the grape, and in many other vegetables, and is +developed only by the vinous fermentation. During this operation it is +precipitated, and deposits itself on the internal surface of the cask in +which the wine is contained. It is much used in medicine, and in various +arts, particularly dying, under the name of <i>cream of tartar</i>, and +it is from this salt that the tartarous acid is obtained.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the medicinal cream of tartar is in appearance quite different +from these dark-coloured dregs; it is perfectly colourless.</p> + +<p class="speaker">MRS. B.</p> + +<p>Because it consists of the pure salts only, in its crystallised form; +whilst in the instance before us it is mixed with the deep-coloured +extractive matter, and other foreign ingredients.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray cannot we now obtain pure alcohol from the brandy which we have +distilled?</p> + +<p class="speaker">MRS. B.</p> + +<p>We might; but the process would be tedious: for in order to obtain +alcohol perfectly free from +<span class="pagenum">223</span> +<a name="conver2.page223" id="conver2.page223"> </a> +water, it is necessary to distil, or, as the distillers call it, +<i>rectify</i> it several times. You must therefore allow me to produce +a bottle of alcohol that has been thus purified. This is a very +important ingredient, which has many striking properties, besides its +forming the basis of all spirituous liquors.</p> + +<p class="speaker">EMILY.</p> + +<p>It is alcohol, I suppose, that produces intoxication?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; but the stimulus and momentary energy it gives to the +system, and the intoxication it occasions when taken in excess, are +circumstances not yet accounted for.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I thought that it produced these effects by increasing the rapidity +of the circulation of the blood; for drinking wine or spirits, +I have heard, always quickens the pulse.</p> + +<p class="speaker">MRS. B.</p> + +<p>No doubt; the spirit, by stimulating the nerves, increases the action +of the muscles; and the heart, which is one of the strongest muscular +organs, beats with augmented vigour, and propels the blood with +accelerated quickness. After such a +<span class="pagenum">224</span> +<a name="conver2.page224" id="conver2.page224"> </a> +strong excitation the frame naturally suffers a proportional degree of +depression, so that a state of debility and <ins class="mycorr" title="text reads ‘langour’">languor</ins> is the invariable consequence of +intoxication. But though these circumstances are well ascertained, they +are far from explaining why alcohol should produce such effects.</p> + +<p class="speaker">EMILY.</p> + +<p>Liqueurs are the only kind of spirits which I think pleasant. Pray of +what do they consist?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are composed of alcohol, sweetened with syrup, and flavoured +with volatile oil.</p> + +<p>The different kinds of odoriferous spirituous waters are likewise +solutions of volatile oil in alcohol, as lavender water, eau de +Cologne, &c.</p> + +<p>The chemical properties of alcohol are important and numerous. It is +one of the most powerful chemical agents, and is particularly useful in +dissolving a variety of substances, which are soluble neither by water +nor heat.</p> + +<p class="speaker">EMILY.</p> + +<p>We have seen it dissolve copal and mastic to form varnishes; and +these resins are certainly not soluble in water, since water +precipitates them from their solution in alcohol.</p> + +<span class="pagenum">225</span> +<a name="conver2.page225" id="conver2.page225"> </a> +<p class="speaker">MRS. B.</p> + +<p>I am happy to find that you recollect these circumstances so well. +The same experiment affords also an instance of another property of +alcohol,—its tendency to unite with water; for the resin is +precipitated in consequence of losing the alcohol, which abandons it +from its preference for water. It is attended also, as you may +recollect, with the same peculiar circumstance of a disengagement of +heat and consequent diminution of bulk, which we have supposed to be +produced by a mechanical penetration of particles by which latent heat +is forced out.</p> + +<p>Alcohol unites thus readily not only with resins and with water, but +with oils and balsams; these compounds form the extensive class of +elixirs, tinctures, quintessences, &c.</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose that alcohol must be highly combustible, since it contains +so large a proportion of hydrogen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Extremely so; and it will burn at a very moderate temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have often seen both brandy and spirit of +<span class="pagenum">226</span> +<a name="conver2.page226" id="conver2.page226"> </a> +wine burnt; they produce a great deal of flame, but not a proportional +quantity of heat, and no smoke whatever.</p> + +<p class="speaker">MRS. B.</p> + +<p>The last circumstance arises from their combustion being complete; +and the disproportion between the flame and heat shows you that these +are by no means synonymous.</p> + +<p>The great quantity of flame proceeds from the combustion of the +hydrogen to which, you know, that manner of burning is +peculiar.—Have you not remarked also that brandy and alcohol will +burn without a wick?—They take fire at so low a temperature, that +this assistance is not required to concentrate the heat and volatilise +the fluid.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I have sometimes seen brandy burnt by merely heating it in a +spoon.</p> + +<p class="speaker">MRS. B.</p> + +<p>The rapidity of the combustion of alcohol may, however, be +prodigiously increased by first volatilising it. An ingenious instrument +has been constructed on this principle to answer the purpose of a +blow-pipe, which may be used for melting glass, or other chemical +purposes. It consists of a small metallic vessel (<a class="smallcaps" +href="#plateXIV">Plate <ins class="mycorr" +title="text reads ‘XIII’">XIV</ins>.</a> Fig. 2.), of a +<span class="pagenum">227</span> +<a name="conver2.page227" id="conver2.page227"> </a> +spherical shape, which contains the alcohol, and is heated by the lamp +beneath it; as soon as the alcohol is volatilised, it passes through the +spout of the vessel, and issues just above the wick of the lamp, which +immediately sets fire to the stream of vapour, as I shall show +you—</p> + +<p class="speaker">EMILY.</p> + +<p>With what amazing violence it burns! The flame of alcohol, in the +state of vapour, is, I fancy, much hotter than when the spirit is +merely burnt in a spoon?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; because in this way the combustion goes on much quicker, and, of +course, the heat is proportionally increased.—Observe its effect +on this small glass tube, the middle of which I present to the extremity +of the flame, where the heat is greatest.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The glass, in that spot, is become red hot, and bends from its own +weight.</p> + +<p class="speaker">MRS. B.</p> + +<p>I have now drawn it asunder, and am going to blow a ball at one of +the heated ends; but I must previously close it up, and flatten it with +this little metallic instrument, otherwise the breath would +<span class="pagenum">228</span> +<a name="conver2.page228" id="conver2.page228"> </a> +pass through the tube without dilating any part of it.—Now, +Caroline, will you blow strongly into the tube whilst the closed end is +red hot.</p> + +<p class="speaker">EMILY.</p> + +<p>You blowed too hard; for the ball suddenly dilated to a great size, +and then burst in pieces.</p> + +<p class="speaker">MRS. B.</p> + +<p>You will be more expert another time; but I must caution you, should +you ever use this blow-pipe, to be very careful that the combustion of +the alcohol does not go on with too great violence, for I have seen the +flame sometimes dart out with such force as to reach the opposite wall +of the room, and set the paint on fire. There is, however, no danger of +the vessel bursting, as it is provided with a safety tube, which affords +an additional vent for the vapour of alcohol when required.</p> + +<p>The products of the combustion of alcohol consist in a great +proportion of water, and a small quantity of carbonic acid. There is no +smoke or fixed remains whatever.—How do you account for that, +Emily?</p> + +<p class="speaker">EMILY.</p> + +<p>I suppose that the oxygen which the alcohol absorbs in burning, +converts its hydrogen into water +<span class="pagenum">229</span> +<a name="conver2.page229" id="conver2.page229"> </a> +and its carbon into carbonic acid gas, and thus it is completely +consumed.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very well.—<i>Ether</i>, the lightest of all fluids, and with +which you are well acquainted, is obtained from alcohol, of which it +forms the lightest and most volatile part.</p> + +<p class="speaker">EMILY.</p> + +<p>Ether, then, is to alcohol, what alcohol is to brandy?</p> + +<p class="speaker">MRS. B.</p> + +<p>No: there is an essential difference. In order to obtain alcohol from +brandy, you need only deprive the latter of its water; but for the +formation of ether, the alcohol must be decomposed, and one of its +constituents partly subtracted. I leave you to guess which of them +it is—</p> + +<p class="speaker">EMILY.</p> + +<p>It cannot be hydrogen, as ether is more volatile than alcohol, and +hydrogen is the lightest of all its ingredients: nor do I suppose that +it can be oxygen, as alcohol contains so small a proportion of that +principle; it is, therefore, most probably, carbon, a diminution of +which would not fail to render the new compound more volatile.</p> + +<span class="pagenum">230</span> +<a name="conver2.page230" id="conver2.page230"> </a> +<p class="speaker">MRS. B.</p> + +<p>You are perfectly right. The formation of ether consists simply in +subtracting from the alcohol a certain proportion of carbon; this is +effected by the action of the sulphuric, nitric, or muriatic acids, on +alcohol. The acid and carbon remain at the bottom of the vessel, whilst +the decarbonised alcohol flies off in the form of a condensable vapour, +which is ether.</p> + +<p>Ether is the most inflammable of all fluids, and burns at so <ins +class="mycorr" title="error for ‘low’?">slow</ins> a temperature +that the heat evolved during its combustion is more than is required for +its support, so that a quantity of ether is volatilised, which takes +fire, and gradually increases the violence of the combustion.</p> + + +<p class="space"> +Sir Humphry Davy has lately discovered a very singular fact respecting +the vapour of ether. If a few drops of ether be poured into a +wine-glass, and a fine platina wire, heated almost to redness, be held +suspended in the glass, close to the surface of the ether, the wire soon +becomes intensely red-hot, and remains so for any length of time. We may +easily try the experiment. . . . .</p> + +<p class="speaker">CAROLINE.</p> + +<p>How very curious! The wire is almost white hot, and a pungent smell +rises from the glass. Pray how is this accounted for?</p> + +<span class="pagenum">231</span> +<a name="conver2.page231" id="conver2.page231"> </a> +<p class="speaker">MRS. B.</p> + +<p>This is owing to a very peculiar property of the vapour of ether, and +indeed of many other combustible gaseous bodies. At a certain +temperature lower than that of ignition, these vapours undergo a slow +and imperfect combustion, which does not give rise, in any sensible +degree, to the phenomena of light and flame, and yet extricates a +quantity of caloric sufficient to react upon the wire and make it +red-hot, and the wire in its turn keeps up the effect as long as the +emission of vapour continues.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But why should not an iron or silver wire produce the same +effect?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because either iron or silver, being much better conductors of heat +than platina, the heat is carried off too fast by those metals to allow +the accumulation of caloric necessary to produce the effect in +question.</p> + + +<p class="space"> +Ether is so light that it evaporates at the common temperature of the +atmosphere; it is therefore necessary to keep it confined by a well +ground glass stopper. No degree of cold known has ever +frozen it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it not often taken medicinally?</p> + +<span class="pagenum">232</span> +<a name="conver2.page232" id="conver2.page232"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes; it is one of the most effectual antispasmodic medicines, and the +quickness of its effects, as such, probably depends on its being +instantly converted into vapour by the heat of the stomach, through the +intervention of which it acts on the nervous system. But the frequent +use of ether, like that of spirituous liquors, becomes prejudicial, and, +if taken to excess, it produces effects similar to those of +intoxication.</p> + +<p>We may now take our leave of the vinous fermentation, of which, +I hope, you have acquired a clear idea; as well as of the several +products that are derived from it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Though this process appears, at first sight, so much complicated, it +may, I think, be summed up in a few words, as it consists in the +conversion of sugar and fermentable bodies into alcohol and carbonic +acid, which give rise both to the formation of wine, and of all kinds of +spirituous liquors.</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall now proceed to the <i>acetous fermentation</i>, which is +thus called, because it converts wine into vinegar, by the formation of +the acetous acid, which is the basis or radical of vinegar.</p> + +<span class="pagenum">233</span> +<a name="conver2.page233" id="conver2.page233"> </a> +<p class="speaker">CAROLINE.</p> + +<p>But is not the acidifying principle of the acetous acid the same as +that of all other acids, oxygen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly; and on that account the contact of air is essential to +this fermentation, as it affords the necessary supply of oxygen. +Vinegar, in order to obtain pure acetous acid from it, must be distilled +and rectified by certain processes.</p> + +<p class="speaker">EMILY.</p> + +<p>But pray, Mrs. B., is not the acetous acid frequently formed without +this fermentation taking place? Is it not, for instance, contained in +acid fruits, and in every substance that becomes sour?</p> + +<p class="speaker">MRS. B.</p> + +<p>No, not in fruits; you confound it with the citric, the malic, the +oxalic, and other vegetable acids, to which living vegetables owe their +acidity. But whenever a vegetable substance turns sour, after it has +ceased to live, the acetous acid is developed by means of the acetous +fermentation, in which the substance advances a step towards its final +decomposition.</p> + +<p>Amongst the various instances of acetous fermentation, that of bread +is usually classed.</p> + +<span class="pagenum">234</span> +<a name="conver2.page234" id="conver2.page234"> </a> +<p class="speaker">CAROLINE.</p> + +<p>But the fermentation of bread is produced by yeast; how does that +effect it?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is found by experience that any substance that has already +undergone a fermentation, will readily excite it in one that is +susceptible of that process. If, for instance, you mix a little vinegar +with wine, that is intended to be acidified, it will absorb oxygen more +rapidly, and the process be completed much sooner, than if left to +ferment spontaneously. Thus yeast, which is a product of the +fermentation of beer, is used to excite and accelerate the fermentation +of malt, which is to be converted into beer, as well as that of paste +which is to be made into bread.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if bread undergoes the acetous fermentation, why is it not +sour?</p> + +<p class="speaker">MRS. B.</p> + +<p>It acquires a certain savour which corrects the heavy insipidity of +flour, and may be reckoned a first degree of acidification; or if the +process were carried further, the bread would become decidedly acid.</p> + +<p>There are, however, some chemists who do not +<span class="pagenum">235</span> +<a name="conver2.page235" id="conver2.page235"> </a> +consider the fermentation of bread as being of the acetous kind, but +suppose that it is a process of fermentation peculiar to that +substance.</p> + +<p>The <i>putrid fermentation</i> is the final operation of Nature, and +her last step towards reducing organised bodies to their simplest +combinations. All vegetables spontaneously undergo this fermentation +after death, provided there be a sufficient degree of heat and moisture, +together with access of air; for it is well known that dead plants may +be preserved by drying, or by the total exclusion of air.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But do dead plants undergo the other fermentation previous to this +last; or do they immediately suffer the putrid fermentation?</p> + +<p class="speaker">MRS. B.</p> + +<p>That depends on a variety of circumstances, such as the degrees of +temperature and of moisture, the nature of the plant itself, &c. But +if you were carefully to follow and examine the decomposition of plants +from their death to their final dissolution, you would generally find a +sweetness developed in the seeds, and a spirituous flavour in the fruits +(which have undergone the saccharine fermentation), previous to the +total disorganisation and separation of the parts.</p> + +<span class="pagenum">236</span> +<a name="conver2.page236" id="conver2.page236"> </a> +<p class="speaker">EMILY.</p> + +<p>I have sometimes remarked a kind of spirituous taste in fruits that +were over ripe, especially oranges; and this was just before they became +rotten.</p> + +<p class="speaker">MRS. B.</p> + +<p>It was then the vinous fermentation which had succeeded the +saccharine, and had you followed up these changes attentively, you would +probably have found the spirituous taste followed by acidity, previous +to the fruit passing to the state of putrefaction.</p> + +<p>When the leaves fall from the trees in autumn, they do not (if there +is no great moisture in the atmosphere) immediately undergo a +decomposition, but are first dried and withered; as soon, however, as +the rain sets in, fermentation commences, their gaseous products are +imperceptibly evolved into the atmosphere, and their fixed remains mixed +with their kindred earth.</p> + +<p>Wood, when exposed to moisture, also undergoes the putrid +fermentation and becomes rotten.</p> + +<p class="speaker">EMILY.</p> + +<p>But I have heard that the <i>dry rot</i>, which is so liable to +destroy the beams of houses, is prevented by a current of air; and yet +you said that air was essential to the putrid fermentation?</p> + +<span class="pagenum">237</span> +<a name="conver2.page237" id="conver2.page237"> </a> +<p class="speaker">MRS. B.</p> + +<p>True; but it must not be in such a proportion to the moisture as to +dissolve the latter, and this is generally the case when the rotting of +wood is prevented or stopped by the free access of air. What is commonly +called dry rot, however, is not I believe a true process of +putrefaction. It is supposed to depend on a peculiar kind of vegetation, +which, by feeding on the wood, gradually destroys it.</p> + +<p>Straw and all other kinds of vegetable matter undergo the putrid +fermentation more rapidly when mixed with animal matter. Much heat is +evolved during this process, and a variety of volatile products are +disengaged, as carbonic acid and hydrogen gas, the latter of which is +frequently either sulphurated or phosphorated.—When all these +gases have been evolved, the fixed products, consisting of carbon, +salts, potash, &c. form a kind of vegetable earth, which makes very +fine manure, as it is composed of those elements which form the +immediate materials of plants.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray are not vegetables sometimes preserved from decomposition by +petrification? I have seen very curious specimens of petrified +vegetables, in which state they perfectly preserve their form +<span class="pagenum">238</span> +<a name="conver2.page238" id="conver2.page238"> </a> +and organisation, though in appearance they are changed to stone.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is a kind of metamorphosis, which, now that you are tolerably +well versed in the history of mineral and vegetable substances, +I leave to your judgment to explain. Do you imagine that vegetables +can be converted into stone?</p> + +<p class="speaker">EMILY.</p> + +<p>No, certainly; but they might perhaps be changed to a substance in +appearance resembling stone.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is not so, however, with the substances that are called petrified +vegetables; for these are really stone, and generally of the hardest +kind, consisting chiefly of silex. The case is this: when a vegetable is +buried under water, or in wet earth, it is slowly and gradually +decomposed. As each successive particle of the vegetable is destroyed, +its place is supplied by a particle of siliceous earth, conveyed thither +by the water. In the course of time the vegetable is entirely destroyed, +but the silex has completely replaced it, having assumed its form and +apparent texture, as if the vegetable itself were changed to stone.</p> + +<span class="pagenum">239</span> +<a name="conver2.page239" id="conver2.page239"> </a> +<p class="speaker">CAROLINE.</p> + +<p>That is very curious! and I suppose that petrified animal substances +are of the same nature?</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely. It is equally impossible for either animal or vegetable +substances to be converted into stone. They may be reduced, as we find +they are, by decomposition, to their constituent elements, but cannot be +changed to elements, which do not enter into their composition.</p> + +<p>There are, however, circumstances which frequently prevent the +regular and final decomposition of vegetables; as, for instance, when +they are buried either in the sea, or in the earth, where they cannot +undergo the putrid fermentation for want of air. In these cases they are +subject to a peculiar change, by which they are converted into a new +class of compounds, called <i>bitumens</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>These are substances I never heard of before.</p> + +<p class="speaker">MRS. B.</p> + +<p>You will find, however, that some of them are very familiar to you. +Bitumens are vegetables so far decomposed as to retain no organic +appearance; but their origin is easily detected by their oily nature, +their combustibility, the products of +<span class="pagenum">240</span> +<a name="conver2.page240" id="conver2.page240"> </a> +their analysis, and the impressions of the forms of leaves, grains, +fibres of wood, and even of animals, which they frequently bear.</p> + +<p>They are sometimes of an oily liquid consistence, as the substance +called <i>naptha</i>, in which we preserved potassium; it is a fine +transparent colourless fluid, that issues out of clays in some parts of +Persia. But more frequently bitumens are solid, as <i>asphaltum</i>, +a smooth, hard, brittle substance, which easily melts, and forms, +in its liquid state, a beautiful dark brown colour for oil +painting. <i>Jet</i>, which is of a still harder texture, is a peculiar +bitumen, susceptible of so fine a polish, that it is used for many +ornamental purposes.</p> + + +<p class="space"> +<i>Coal</i> is also a bituminous substance, to the composition of which +both the mineral and animal kingdoms seem to concur. This most useful +mineral appears to consist chiefly of vegetable matter, mixed with the +remains of marine animals and marine salts, and occasionally containing +a quantity of sulphuret of iron, commonly called pyrites.</p> + +<p class="speaker">EMILY.</p> + +<p>It is, I suppose, the earthly, the metallic, and the saline parts of +coals, that compose the cinders or fixed products of their combustion; +whilst the +<span class="pagenum">241</span> +<a name="conver2.page241" id="conver2.page241"> </a> +hydrogen and carbon, which they derive from vegetables, constitute their +volatile products.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray is not <i>coke</i>, (which I have heard is much used in some +manufactures,) also a bituminous substance?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; it is a kind of fuel artificially prepared from coals. It +consists of coals reduced to a substance analogous to charcoal, by the +evaporation of their bituminous parts. Coke, therefore, is composed of +carbon, with some earthy and saline ingredients.</p> + +<p><i>Succin</i>, or <i>yellow amber</i>, is a bitumen which the +ancients called <i>electrum</i>, from whence the word electricity is +derived, as that substance is peculiarly, and was once supposed to be +exclusively, electric. It is found either deeply buried in the bowels of +the earth, or floating on the sea, and is supposed to be a resinous body +which has been acted on by sulphuric acid, as its analysis shows it to +consist of ah oil and an acid. The oil is called <i>oil of amber</i>, +the acid the <i>succinic</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>That oil I have sometimes used in painting, as it is reckoned to +change less than the other kinds of oils.</p> + +<span class="pagenum">242</span> +<a name="conver2.page242" id="conver2.page242"> </a> +<p class="speaker">MRS. B.</p> + +<p>The last class of vegetable substances that have changed their nature +are <i>fossil-wood</i>, <i>peat</i>, and <i>turf</i>. These are composed +of wood and roots of shrubs, that are partly decomposed by being exposed +to moisture under ground, and yet, in some measure, preserve their form +and organic appearance. The peat, or black earth of the moors, retains +but few vestiges of the roots to which it owes its richness and +combustibility, these substances being in the course of time reduced to +the state of vegetable earth. But in turf the roots of plants are still +discernible, and it equally answers the purpose of fuel. It is the +combustible used by the poor in <ins class="correction" title="not an error (heath-y)">heathy</ins> countries, which supply it +abundantly.</p> + +<p>It is too late this morning to enter upon the history of vegetation. +We shall reserve this subject, therefore, for our next interview, when I +expect that it will furnish us with ample matter for another +conversation.</p> + + + + +<span class="pagenum">243</span> +<a name="conver2.page243" id="conver2.page243"> </a> +<h4><a name="convXXII" id="convXXII">CONVERSATION XXII.</a><br> +<span class="subhead">HISTORY OF VEGETATION.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">T</span>he</span> <span class="smallroman">VEGETABLE +KINGDOM</span> may be considered as the link which unites the mineral +and animal creation into one common chain of beings; for it is through +the means of vegetation alone that mineral substances are introduced +into the animal system, since, generally speaking, it is from vegetables +that all animals ultimately derive their sustenance.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not understand that; the human species subsists as much on +animal as on vegetable food, and there are some carnivorous animals that +will eat only animal food.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is true; but you do not consider that those that live on animal +food, derive their sustenance equally, though not so immediately, from +<span class="pagenum">244</span> +<a name="conver2.page244" id="conver2.page244"> </a> +vegetables. The meat that we eat is formed from the herbs of the field, +and the prey of carnivorous animals proceeds, either directly or +indirectly, from the same source. It is, therefore, through this channel +that the simple elements become a part of the animal frame. We should in +vain attempt to derive nourishment from carbon, hydrogen, and oxygen, +either in their separate state, or combined in the mineral kingdom; for +it is only by being united in the form of vegetable combination, that +they become capable of conveying nourishment.</p> + +<p class="speaker">EMILY.</p> + +<p>Vegetation, then, seems to be the method which Nature employs to +prepare the food of animals?</p> + +<p class="speaker">MRS. B.</p> + +<p>That is certainly its principal object. The vegetable creation does +not exhibit more wisdom in that admirable system of organisation, by +which it is enabled to answer its own immediate ends of preservation, +nutrition, and propagation, than in its grand and ultimate object of +forming those arrangements and combinations of principles, which are so +well adapted for the nourishment of animals.</p> + +<p class="speaker">EMILY.</p> + +<p>But I am very curious to know whence vegetables +<span class="pagenum">245</span> +<a name="conver2.page245" id="conver2.page245"> </a> +obtain those principles which form their immediate materials?</p> + +<p class="speaker">MRS. B.</p> + +<p>This is a point on which we are yet so much in the dark, that I +cannot hope fully to satisfy your curiosity; but what little I know on +this subject, I will endeavour to explain to you.</p> + +<p>The soil, which, at first view, appears to be the aliment of +vegetables, is found, on a closer investigation, to be little more than +the channel through which they receive their nourishment; so that it is +very possible to rear plants without any earth or soil.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Of that we have an instance in the hyacinth and other bulbous roots, +which will grow and blossom beautifully in glasses of water. But I +confess I should think it would be difficult to rear trees in a similar +manner.</p> + +<p class="speaker">MRS. B.</p> + +<p>No doubt it would, as it is the burying of the roots in the earth +that supports the stem of the tree. But this office, besides that of +affording a vehicle for food, is far the most important part which the +earthy portion of the soil performs in the process of vegetation; for we +can discover, by +<span class="pagenum">246</span> +<a name="conver2.page246" id="conver2.page246"> </a> +analysis, but an extremely small proportion of earth in vegetable +compounds.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if earths do not afford nourishment, why is it necessary to be so +attentive to the preparation of the soil?</p> + +<p class="speaker">MRS. B.</p> + +<p>In order to impart to it those qualities which render it a proper +vehicle for the food of the plant. Water is the chief nourishment of +vegetables; if, therefore, the soil be too sandy, it will not retain a +quantity of water sufficient to supply the roots of the plants. If, on +the contrary, it abound too much with clay, the water will lodge in such +quantities as to threaten a decomposition of the roots. Calcareous soils +are, upon the whole, the most favourable to the growth of plants: soils +are, therefore, usually improved by chalk, which, you may recollect, is +a carbonat of lime. Different vegetables, however, require different +kinds of soils. Thus rice demands a moist retentive soil; potatoes a +soft sandy soil; wheat a firm and rich soil. Forest trees grow better in +fine sand than in a stiff clay; and a light ferruginous soil is best +suited to fruit-trees.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But pray what is the use of manuring the soil?</p> + +<span class="pagenum">247</span> +<a name="conver2.page247" id="conver2.page247"> </a> +<p class="speaker">MRS. B.</p> + +<p>Manure consists of all kinds of substances, whether of vegetable or +animal origin, which have undergone the putrid fermentation, and are +consequently decomposed, or nearly so, into their elementary principles. +And it is requisite that these vegetable matters should be in a state of +decay, or approaching decomposition. The addition of calcareous earth, +in the state of chalk or lime, is beneficial to such soils, as it +accelerates the dissolution of vegetable bodies. Now, I ask you, +what is the utility of supplying the soil with these decomposed +substances?</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is, I suppose, in order to furnish vegetables with the principles +which enter into their composition. For manures not only contain carbon, +hydrogen, and oxygen, but by their decomposition supply the soil with +these principles in their elementary form.</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; and it is for this reason that the finest crops are +produced in fields that were formerly covered with woods, because their +soil is composed of a rich mould, a kind of vegetable earth, which +abounds in those principles.</p> + +<p class="speaker">EMILY.</p> + +<p>This accounts for the plentifulness of the crops +<span class="pagenum">248</span> +<a name="conver2.page248" id="conver2.page248"> </a> +produced in America, where the country was but a few years since covered +with wood.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how is it that animal substances are reckoned to produce the best +manure? Does it not appear much more natural that the decomposed +elements of vegetables should be the most appropriate to the formation +of new vegetables?</p> + +<p class="speaker">MRS. B.</p> + +<p>The addition of a much greater proportion of nitrogen, which +constitutes the chief difference between animal and vegetable matter, +renders the composition of the former more complicated, and consequently +more favourable to decomposition. The use of animal substances is +chiefly to give the first impulse to the fermentation of the vegetable +ingredients that enter into the composition of manures. The manure of a +farm-yard is of that description; but there is scarcely any substance +susceptible of undergoing the putrid fermentation that will not make +good manure. The heat produced by the fermentation of manure is another +circumstance which is extremely favourable to vegetation; yet this heat +would be too great if the manure was laid on the ground during the +height of fermentation; it is used in this state only for hot-beds, to +produce melons, cucumbers, +<span class="pagenum">249</span> +<a name="conver2.page249" id="conver2.page249"> </a> +and such vegetables as require a very high temperature.</p> + +<p class="speaker">CAROLINE.</p> + +<p>A difficulty has just occurred to me which I do not know how to +remove. Since all organised bodies are, in the common course of nature, +ultimately reduced to their elementary state, they must necessarily in +that state enrich the soil, and afford food for vegetation. How is it, +then, that agriculture, which cannot increase the quantity of those +elements that are required to manure the earth, can increase its produce +so wonderfully as is found to be the case in all cultivated +countries?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is by suffering none of these decaying bodies to be dissipated, +but in applying them duly to the soil. It is by a judicious preparation +of the soil, which consists in fitting it either for the general +purposes of vegetation, or for that of the particular seed which is to +be sown. Thus, if the soil be too wet, it may be drained; if too loose +and sandy, it may be rendered more consistent and retentive of water by +the addition of clay or loam; it may be enriched by chalk, or any kind +of calcareous earth. On soils thus improved, manures will act with +double efficacy, and if attention be paid to spread them on the ground +at a proper season of the year, to mix them with +<span class="pagenum">250</span> +<a name="conver2.page250" id="conver2.page250"> </a> +the soil so that they may be generally diffused through it, to destroy +the weeds which might appropriate these nutritive principles to their +own use, to remove the stones which would impede the growth of the +plant, &c. we may obtain a produce an hundred fold more abundant +than the earth would spontaneously supply.</p> + +<p class="speaker">EMILY.</p> + +<p>We have a very striking instance of this in the scanty produce of +uncultivated commons, compared to the rich crops of meadows which are +occasionally manured.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, Mrs. B., though experience daily proves the advantage of +cultivation, there is still a difficulty which I cannot get over. +A certain quantity of elementary principles exist in nature, which +it is not in the power of man either to augment or diminish. Of these +principles you have taught us that both the animal and vegetable +creation are composed. Now the more of them is taken up by the vegetable +kingdom, the less, it would seem, will remain for animals; and, +therefore, the more populous the earth becomes, the less it will +produce.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your reasoning is very plausible; but experience +<span class="pagenum">251</span> +<a name="conver2.page251" id="conver2.page251"> </a> +every where contradicts the inference you would draw from it; for we +find that the animal and vegetable kingdoms, instead of thriving, as you +would suppose, at each other’s expense, always increase and multiply +together. For you should recollect that animals can derive the elements +of which they are formed only through the medium of vegetables. And you +must allow that your conclusion would be valid only if every particle of +the several principles that could possibly be spared from other purposes +were employed in the animal and vegetable creations. Now we have reason +to believe that a much greater proportion of these principles than is +required for such purposes remains either in an elementary state, or +engaged in a less useful mode of combination in the mineral kingdom. +Possessed of such immense resources as the atmosphere and the waters +afford us, for oxygen, hydrogen, and carbon, so far from being in danger +of working up all our simple materials, we cannot suppose that we shall +ever bring agriculture to such a degree of perfection as to require the +whole of what these resources could supply.</p> + +<p>Nature, however, in thus furnishing us with an inexhaustible stock of +raw materials, leaves it in some measure to the ingenuity of man to +appropriate them to its own purposes. But, like a kind parent, she +stimulates him to exertion, by setting +<span class="pagenum">252</span> +<a name="conver2.page252" id="conver2.page252"> </a> +the example and pointing out the way. For it is on the operations of +nature that all the improvements of art are founded. The art of +agriculture consists, therefore, in discovering the readiest method of +obtaining the several principles, either from their grand sources, air +and water, or from the decomposition of organised bodies; and in +appropriating them in the best manner to the purposes of vegetation.</p> + +<p class="speaker">EMILY.</p> + +<p>But, among the sources of nutritive principles, I am surprised +that you do not mention the earth itself, as it contains abundance of +coals, which are chiefly composed of carbon.</p> + +<p class="speaker">MRS. B.</p> + +<p>Though coals abound in carbon, they cannot, on account of their +hardness and impermeable texture, be immediately subservient to the +purposes of vegetation.</p> + +<p class="speaker">EMILY.</p> + +<p>No; but by their combustion carbonic acid is produced; and this +entering into various combinations on the surface of the earth, may, +perhaps, assist in promoting vegetation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Probably it may in some degree; but at any +<span class="pagenum">253</span> +<a name="conver2.page253" id="conver2.page253"> </a> +rate the quantity of nourishment which vegetables may derive from that +source can be but very trifling, and must entirely depend on local +circumstances.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Perhaps the smoky atmosphere of London is the cause of vegetation +being so forward and so rich in its vicinity?</p> + +<p class="speaker">MRS. B.</p> + +<p>I rather believe that this circumstance proceeds from the very ample +supply of manure, assisted, perhaps, by the warmth and shelter which the +town affords. Far from attributing any good to the smoky atmosphere of +London, I confess I like to anticipate the time when we shall have +made such progress in the art of managing combustion, that every +particle of carbon will be consumed, and the smoke destroyed at the +moment of its production. We may then expect to have the satisfaction of +seeing the atmosphere of London as clear as that of the +country.—But to return to our subject: I hope that you are +now convinced that we shall not easily experience a deficiency of +nutritive elements to fertilise the earth, and that, provided we are but +industrious in applying them to the best advantage by improving the art +of agriculture, no limits can be assigned to the fruits that we may +expect to reap from our labours.</p> + +<span class="pagenum">254</span> +<a name="conver2.page254" id="conver2.page254"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Yes; I am perfectly satisfied in that respect, and I can assure you +that I feel already much more interested in the progress and improvement +of agriculture.</p> + +<p class="speaker">EMILY.</p> + +<p>I have frequently thought that the culture of the land was not +considered as a concern of sufficient importance. Manufactures always +take the lead; and health and innocence are frequently sacrificed to the +prospect of a more profitable employment. It has often grieved me to see +the poor manufacturers crowded together in close rooms, and confined for +the whole day to the most uniform and sedentary employment, instead of +being engaged in that innocent and salutary kind of labour, which Nature +seems to have assigned to man for the immediate acquirement of comfort, +and for the preservation of his existence. I am sure that you agree +with me in thinking so, Mrs. B.?</p> + +<p class="speaker">MRS. B.</p> + +<p>I am entirely of your opinion, my dear, in regard to the importance +of agriculture; but as the conveniences of life, which we are all +enjoying, are not derived merely from the soil, I am far from +wishing to depreciate manufactures. Besides, as the labour of one man is +sufficient to produce food for several, those whose industry is not +<span class="pagenum">255</span> +<a name="conver2.page255" id="conver2.page255"> </a> +required in tillage must do something in return for the food that is +provided for them. They exchange, consequently, the accommodations for +the necessaries of life. Thus the carpenter and the weaver lodge and +clothe the peasant, who supplies them with their daily bread. The +greater stock of provisions, therefore, which the husbandman produces, +the greater is the quantity of accommodation which the artificer +prepares. Such are the happy effects which naturally result from +civilised society. It would be wiser, therefore, to endeavour to improve +the situation of those who are engaged in manufactures, than to indulge +in vain declamations on the hardships to which they are too frequently +exposed.</p> + +<p>But we must not yet take our leave of the subject of agriculture; we +have prepared the soil, it remains for us now to sow the seed. In this +operation we must be careful not to bury it too deep in the ground, as +the access of air is absolutely necessary to its germination; the earth +must, therefore, lie loose and light over it, in order that the air may +penetrate. Hence the use of ploughing and digging, harrowing and raking, +&c. A certain degree of heat and moisture, such as usually +takes place in the spring, is likewise necessary.</p> + +<p class="speaker">CAROLINE.</p> + +<p>One would imagine you were going to describe +<span class="pagenum">256</span> +<a name="conver2.page256" id="conver2.page256"> </a> +the decomposition of an old plant, rather than the formation of a new +one; for you have enumerated all the requisites of fermentation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Do you forget, my dear, that the young plant derives its existence +from the destruction of the seed, and that it is actually by the +saccharine fermentation that the latter is decomposed?</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; I wonder that I did not recollect that. The temperature and +moisture required for the germination of the seed is then employed in +producing the saccharine fermentation within it?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly. But, in order to understand the nature of germination, you +should be acquainted with the different parts of which the seed is +composed. The external covering or envelope contains, besides the germ +of the future plant, the substance which is to constitute its first +nourishment; this substance, which is called the <i>parenchyma</i>, +consists of fecula, mucilage, and oil, as we formerly observed.</p> + +<p>The seed is generally divided into two compartments, called +<i>lobes</i>, or <i>cotyledons</i>, as is exemplified by this bean (<a +class="smallcaps" href="#plateXV">Plate XV.</a> +Fig. 1.)—the dark-coloured +<span class="pagenum">257</span> +<a name="conver2.page257" id="conver2.page257"> </a> +kind of string which divides the lobes is called the <i>radicle</i>, as +it forms the root of the plant, and it is from a contiguous substance, +called <i>plumula</i>, which is enclosed within the lobes, that the stem +arises. The figure and size of the seed depend very much upon the +cotyledons; these vary in number in different seeds; some have only one, +as wheat, oats, barley, and all the grasses; some have three, others +six. But most seeds, as, for instance, all the varieties of beans, have +two cotyledons. When the seed is buried in the earth, at any temperature +above 40 degrees, it imbibes water, which softens and swells the lobes; +it then absorbs oxygen, which combines with some of its carbon, and is +returned in the form of carbonic acid. This loss of carbon increases the +comparative proportion of hydrogen and oxygen in the seed, and excites +the saccharine fermentation, by which the parenchymatous matter is +converted into a kind of sweet emulsion. In this form it is carried into +the radicle by vessels appropriated to that purpose; and in the mean +time, the fermentation having caused the seed to burst, the cotyledons +are rent asunder, the radicle strikes into the ground and becomes the +root of the plant, and hence the fermented liquid is conveyed to the +plumula, whose vessels have been previously distended by the heat of the +fermentation. The plumula being thus swelled, as it were, by the +<span class="pagenum">258</span> +<a name="conver2.page258" id="conver2.page258"> </a> +emulsive fluid, raises itself and springs up to the surface of the +earth, bearing with it the cotyledons, which, as soon as they come in +contact with the air, spread themselves, and are transformed into +leaves.—If we go into the garden, we shall probably find some +seeds in the state which I have described—</p> + +<p class="figname"> +<a name="plateXV" id="plateXV">Plate XV.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. II.</span> p. 250</p> + +<p class="illustration"> +<img src="images/plate15a_thumb.png" width="473" height="364" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 1 & 2. +A.B Cotyledons. +C Envelope. +D Radicle.<br> +Fig. 3. +A.B Cotyledons. +C Plumula. +D Radicle.<br> +Fig. 4. +A.B. Cotyledons. +C Plumula. +D Radicle.</p> + +<p class="figlink"> +<a href="images/plate15_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">EMILY.</p> + +<p>Here are some lupines that are just making their appearance above +ground.</p> + +<p class="speaker">MRS. B.</p> + +<p>We shall take up several of them to observe their different degrees +of progress in vegetation. Here is one that has but recently burst its +envelope—do you see the little radicle striking downwards? (<a +class="smallcaps" href="#plateXV">Plate XV.</a> Fig. 2.) In +this the plumula is not yet visible. But here is another in a greater +state of forwardness—the plumula, or stem, has risen out of the +ground, and the cotyledons are converted into seed leaves. (<a class="smallcaps" href="#plateXV">Plate XV.</a> Fig. 3.)</p> + +<p class="speaker">CAROLINE.</p> + +<p>These leaves are very thick and clumsy, and unlike the other leaves, +which I perceive are just beginning to appear.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because they retain the remains of the parenchyma, +<span class="pagenum">259</span> +<a name="conver2.page259" id="conver2.page259"> </a> +with which they still continue to nourish the young plant, as it has not +yet sufficient roots and strength to provide for its sustenance from the +soil.—But, in this third lupine (<a class="smallcaps" href="#plateXV">Plate <ins class="mycorr" title="text reads ‘XIV’">XV</ins>.</a> Fig. 4.), the radicle had sunk deep into the +earth, and sent out several shoots, each of which is furnished with a +mouth to suck up nourishment from the soil; the function of the original +leaves, therefore, being no longer required, they are gradually +decaying, and the plumula is become a regular stem, shooting out small +branches, and spreading its foliage.</p> + +<p class="speaker">EMILY.</p> + +<p>There seems to be a very striking analogy between a seed and an egg; +both require an elevation of temperature to be brought to life; both at +first supply with aliment the organised being which they produce; and as +soon as this has attained sufficient strength to procure its own +nourishment, the egg-shell breaks, whilst in the plant the seed-leaves +fall off.</p> + +<p class="speaker">MRS. B.</p> + +<p>There is certainly some resemblance between these processes; and when +you become acquainted with animal chemistry, you will frequently be +struck with its analogy to that of the vegetable kingdom.</p> + +<span class="pagenum">260</span> +<a name="conver2.page260" id="conver2.page260"> </a> +<p>As soon as the young plant feeds from the soil, it requires the +assistance of leaves, which are the organs by which it throws off its +super-abundant fluid; this secretion is much more plentiful in the +vegetable than in the animal creation, and the great extent of surface +of the foliage of plants is admirably calculated for carrying it on in +sufficient quantities. This transpired fluid consists of little more +than water. The sap, by this process, is converted into a liquid of +greater consistence, which is fit to be assimilated to its several +parts.</p> + +<p class="speaker">EMILY.</p> + +<p>Vegetation, then, must be essentially injured by destroying the +leaves of the plant?</p> + +<p class="speaker">MRS. B.</p> + +<p>Undoubtedly; it not only diminishes the transpiration, but also the +absorption by the roots; for the quantity of sap absorbed is always in +proportion to the quantity of fluid thrown off by transpiration. You +see, therefore, the necessity that a young plant should unfold its +leaves as soon as it begins to derive its nourishment from the soil; +and, accordingly, you will find that those lupines which have dropped +their seed-leaves, and are no longer fed by the parenchyma, have spread +their foliage, in order to perform the office just described.</p> + +<span class="pagenum">261</span> +<a name="conver2.page261" id="conver2.page261"> </a> +<p>But I should inform you that this function of transpiration seems to +be confined to the upper surface of the leaves, whilst, on the contrary, +the lower surface, which is more rough and uneven, and furnished with a +kind of hair or down, is destined to absorb moisture, or such other +ingredients as the plant derives from the atmosphere.</p> + +<p>As soon as a young plant makes its appearance above ground, light, as +well as air, becomes necessary to its preservation. Light is essential +to the development of the colours, and to the thriving of the plant. You +may have often observed what a predilection vegetables have for the +light. If you make any plants grow in a room, they all spread their +leaves, and extend their branches towards the windows.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And many plants close up their flowers as soon as it is dark.</p> + +<p class="speaker">EMILY.</p> + +<p>But may not this be owing to the cold and dampness of the evening +air?</p> + +<p class="speaker">MRS. B.</p> + +<p>That does not appear to be the case; for in a course of curious +experiments, made by Mr. Senebier, of Geneva, on plants which he reared +by +<span class="pagenum">262</span> +<a name="conver2.page262" id="conver2.page262"> </a> +lamp-light, he found that the flowers closed their petals whenever the +lamps were extinguished.</p> + +<p class="speaker">EMILY.</p> + +<p>But pray, why is air essential to vegetation, plants do not breathe +it like animals?</p> + +<p class="speaker">MRS. B.</p> + +<p>At least not in the same manner; but they certainly derive some +principles from the atmosphere, and yield others to it. Indeed, it is +chiefly owing to the action of the atmosphere and the vegetable kingdom +on each other, that the air continues always fit for respiration. But +you will understand this better when I have explained the effect of +water on plants.</p> + +<p>I have said that water forms the chief nourishment of plants; it is +the basis not only of the sap, but of all the vegetable juices. Water is +the vehicle which carries into the plant the various salts and other +ingredients required for the formation and support of the vegetable +system. Nor is this all; part of the water itself is decomposed by the +organs of the plant; the hydrogen becomes a constituent part of oil, of +extract, of colouring matter, &c. whilst a portion of the oxygen +enters into the formation of mucilage, of fecula, of sugar, and of +vegetable acids. But the greater part of the oxygen, proceeding from the +decomposition +<span class="pagenum">263</span> +<a name="conver2.page263" id="conver2.page263"> </a> +of the water, is converted into a gaseous state by the caloric +disengaged from the hydrogen during its condensation in the formation of +the vegetable materials. In this state the oxygen is transpired by the +leaves of plants when exposed to the sun’s rays. Thus you find that the +decomposition of water, by the organs of the plant, is not only a means +of supplying it with its chief ingredient, hydrogen, but at the same +time of replenishing the atmosphere with oxygen, a principle which +requires continual renovation, to make up for the great consumption of +it occasioned by the numerous oxygenations, combustions, and +respirations, that are constantly taking place on the surface of the +globe.</p> + +<p class="speaker">EMILY.</p> + +<p>What a striking instance of the harmony of nature.</p> + +<p class="speaker">MRS. B.</p> + +<p>And how admirable the design of Providence, who makes every different +part of the creation thus contribute to the support and renovation of +each other!</p> + +<p>But the intercourse of the vegetable and animal kingdoms through the +medium of the atmosphere extends still further. Animals, in breathing, +not only consume the oxygen of the air, but load it with carbonic acid, +which, if accumulated in the atmosphere, would, in a short time, render +it +<span class="pagenum">264</span> +<a name="conver2.page264" id="conver2.page264"> </a> +totally unfit for respiration. Here the vegetable kingdom again +interferes; it attracts and decomposes the carbonic acid, retains the +carbon for its own purposes, and returns the oxygen for ours.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How interesting this is! I do not know a more beautiful illustration +of the wisdom which is displayed in the laws of nature.</p> + +<p class="speaker">MRS. B.</p> + +<p>Faint and imperfect as are the ideas which our limited perceptions +enable us to form of divine wisdom, still they cannot fail to inspire us +with awe and admiration. What, then, would be our feelings, were the +complete system of nature at once displayed before us! So magnificent a +scene would probably be too great for our limited and imperfect +comprehension, and it is no doubt among the wise dispensations of +Providence, to veil the splendour of a glory with which we should be +overpowered. But it is well suited to the nature of a rational being to +explore, step by step, the works of the creation, to endeavour to +connect them into harmonious systems; and, in a word, to trace in the +chain of beings, the kindred ties and benevolent design which unites its +various links, and secure its preservation.</p> + +<span class="pagenum">265</span> +<a name="conver2.page265" id="conver2.page265"> </a> + +<p class="speaker">CAROLINE.</p> + +<p>But of what nature are the organs of plants which are endued with +such wonderful powers?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are so minute that their structure, as well as the mode in which +they perform their functions, generally elude our examination; but we +may consider them as so many vessels or <ins class="mycorr" title="Latin plural form">apparatus</ins> appropriated to perform, with the +assistance of the principle of life, certain chemical processes, by +means of which these vegetable compounds are generated. We may, however, +trace the tannin, resins, gum, mucilage, and some other vegetable +materials, in the organised arrangement of plants, in which they form +the bark, the wood, the leaves, flowers, and seeds.</p> + +<p>The <i>bark</i> is composed of the <i>epidermis</i>, the +<i>parenchyma</i>, and the <i>cortical layers</i>.</p> + +<p>The epidermis is the external covering of the plant. It is a thin +transparent membrane, consisting of a number of slender fibres, crossing +each other, and forming a kind of net-work. When of a white glossy +nature, as in several species of trees, in the stems of corn and of +seeds, it is composed of a thin coating of siliceous earth, which +accounts for the strength and hardness of those long and slender stems. +Sir H. Davy was led to the discovery of the siliceous nature of the +epidermis of +<span class="pagenum">266</span> +<a name="conver2.page266" id="conver2.page266"> </a> +such plants, by observing the singular phenomenon of sparks of fire +emitted by the collision of ratan canes with which two boys were +fighting in a dark room. On analysing the epidermis of the cane, he +found it to be almost entirely siliceous.</p> + +<p class="speaker">CAROLINE.</p> + +<p>With iron then, a cane, I suppose, will strike fire very +easily?</p> + +<p class="speaker">MRS. B.</p> + +<p>I understand that it will.—In ever-greens the epidermis is +mostly resinous, and in some few plants is formed of wax. The resin, +from its want of affinity for water, tends to preserve the plant from +the destructive effects of violent rains, severe climates, or inclement +seasons, to which this species of vegetables is peculiarly exposed.</p> + +<p class="speaker">EMILY.</p> + +<p>Resin must preserve wood just like a varnish, as it is the essential +ingredient of varnishes?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and by this means it prevents likewise all unnecessary +expenditure of moisture.</p> + +<p>The parenchyma is immediately beneath the epidermis; it is that green +rind which appears when you strip a branch of any tree or shrub of +<span class="pagenum">267</span> +<a name="conver2.page267" id="conver2.page267"> </a> +its external coat of bark. The parenchyma is not confined to the stem or +branches, but extends over every part of the plant. It forms the green +matter of the leaves, and is composed of tubes filled with a peculiar +juice.</p> + +<p>The cortical layers are immediately in contact with the wood; they +abound with tannin and gallic acid, and consist of small vessels through +which the sap descends after being elaborated in the leaves. The +cortical layers are annually renewed, the old bark being converted into +wood.</p> + +<p class="speaker">EMILY.</p> + +<p>But through what vessels does the sap ascend?</p> + +<p class="speaker">MRS. B.</p> + +<p>That function is performed by the tubes of the alburnum, or wood, +which is immediately beneath the cortical layers. The wood is composed +of woody fibre, mucilage, and resin. The fibres are disposed in two +ways; some of them longitudinally, and these form what is called the +silver grain of the wood. The others, which are concentric, are called +the spurious grain. These last are disposed in layers, from the number +of which the age of the tree may be computed, a new one being +produced annually by the conversion of the bark into wood. The oldest, +and consequently most internal part of the alburnum, is called +<span class="pagenum">268</span> +<a name="conver2.page268" id="conver2.page268"> </a> +heart-wood; it appears to be dead, at least no vital functions are +discernible in it. It is through the tubes of the living alburnum that +the sap rises. These, therefore, spread into the leaves, and there +communicate with the extremities of the vessels of the cortical layers, +into which they pour their contents.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Of what use, then, are the tubes of the parenchyma, since neither the +ascending nor descending sap passes through them?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are supposed to perform the important function of secreting from +the sap the peculiar juices from which the plant more immediately +derives its nourishment. These juices are very conspicuous, as the +vessels which contain them are much larger than those through which the +sap circulates. The peculiar juices of plants differ much in their +nature, not only in different species of vegetables, but frequently in +different parts of the same individual plant: they are sometimes +saccharine, as in the sugar-cane, sometimes resinous, as in firs and +evergreens, sometimes of a milky appearance, as in the laurel.</p> + +<p class="speaker">EMILY.</p> + +<p>I have often observed, that in breaking a young +<span class="pagenum">269</span> +<a name="conver2.page269" id="conver2.page269"> </a> +shoot, or in bruising a leaf of laurel, a milky juice will ooze out +in great abundance.</p> + +<p class="speaker">MRS. B.</p> + +<p>And it is by making incisions in the bark that pitch, tar, and +turpentine are obtained from fir-trees. The durability of this species +of wood is chiefly owing to the resinous nature of its peculiar juices. +The volatile oils have, in a great measure, the same preservative +effects, as they defend the parts, with which they are connected, from +the attack of insects. This tribe seems to have as great an aversion to +perfumes, as the human species have delight in them. They scarcely ever +attack any odoriferous parts of plants, and it is not uncommon to see +every leaf of a tree destroyed by a blight, whilst the blossoms remain +untouched. Cedar, sandal, and all aromatic woods, are on this account of +great durability.</p> + +<p class="speaker">EMILY.</p> + +<p>But the wood of the oak, which is so much esteemed for its +durability, has, I believe, no smell. Does it derive this quality +from its hardness alone?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not entirely; for the <ins class="mycorr" title="common variant spelling">chesnut</ins>, +though considerably harder and firmer than the +oak, is not so lasting. The durability of the oak is, I believe, +<span class="pagenum">270</span> +<a name="conver2.page270" id="conver2.page270"> </a> +in a great measure owing to its having very little heart-wood, the +alburnum preserving its vital functions longer than in other trees.</p> + +<p class="speaker">CAROLINE.</p> + +<p>If incisions are made into the alburnum and cortical layers, may not +the ascending and descending sap be procured in the same manner as the +peculiar juice is from the vessels of the parenchyma?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but in order to obtain specimens of these fluids, in any +quantity, the experiment must be made in the spring, when the sap +circulates with the greatest energy. For this purpose a small bent glass +tube should be introduced into the incision, through which the sap may +flow without mixing with any of the other juices of the tree. From the +bark the sap will flow much more plentifully than from the wood, as the +ascending sap is much more liquid, more abundant, and more rapid in its +motion than that which descends; for the latter having been deprived by +the operation of the leaves of a considerable part of its moisture, +contains a much greater proportion of solid matter, which retards its +motion. It does not appear that there is any excess of descending sap, +as none ever exudes from the roots of plants; this process, therefore, +seems to be carried on only in +<span class="pagenum">271</span> +<a name="conver2.page271" id="conver2.page271"> </a> +proportion to the wants of the plant, and the sap descends no further, +and in no greater quantity, than is required to nourish the several +organs. Therefore, though the sap rises and descends in the plant, it +does not appear to undergo a real circulation.</p> + +<p>The last of the organs of plants is the <i>flower</i>, or +<i>blossom</i>, which produces the <i>fruits</i> and <i>seed</i>. These +may be considered as the ultimate purpose of nature in the vegetable +creation. From fruits and seeds animals derive both a plentiful source +of immediate nourishment, and an ample provision for the reproduction of +the same means of subsistence.</p> + +<p>The seed which forms the final product of mature plants, we have +already examined as constituting the first rudiments of future +vegetation.</p> + +<p>These are the principal organs of vegetation, by means of which the +several chemical processes which are carried on during the life of the +plant are performed.</p> + +<p class="speaker">EMILY.</p> + +<p>But how are the several principles which enter into the composition +of vegetables so combined by the organs of the plant as to be converted +into vegetable matter?</p> + +<p class="speaker">MRS. B.</p> + +<p>By chemical processes, no doubt; but the apparatus in which they are +performed is so extremely +<span class="pagenum">272</span> +<a name="conver2.page272" id="conver2.page272"> </a> +minute as completely to elude our examination. We can form an opinion, +therefore, only by the result of these operations. The sap is evidently +composed of water, absorbed by the roots, and holding in solution the +various principles which it derives from the soil. From the roots the +sap ascends through the tubes of the alburnum into the stem, and thence +branches out to every extremity of the plant. Together with the sap +circulates a certain quantity of carbonic acid, which is gradually +disengaged from the former by the internal heat of the plant.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What! have vegetables a peculiar heat, analogous to animal heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a circumstance that has long been suspected; but late +experiments have decided beyond a doubt that vegetable heat is +considerably above that of unorganised matter in winter, and below it in +summer. The wood of a tree is about sixty degrees, when the thermometer +is seventy or eighty degrees. And the bark, though so much exposed, is +seldom below forty in winter.</p> + +<p>It is from the sap, after it has been elaborated by the leaves, that +vegetables derive their nourishment; in its progress through the plant +from the +<span class="pagenum">273</span> +<a name="conver2.page273" id="conver2.page273"> </a> +leaves to the roots, it deposits in the several sets of vessels with +which it communicates, the materials on which the growth and nourishment +of each plant depends. It is thus that the various peculiar juices, +saccharine, oily, mucous, acid, and colouring, are formed; as also the +more solid parts, fecula, woody fibre, tannin, resins, concrete salts; +in a word, all the immediate materials of vegetables, as well as the +organised parts of plants, which latter, besides the power of secreting +these from the sap for the general purpose of the plant, have also that +of applying them to their own particular nourishment.</p> + +<p class="speaker">EMILY.</p> + +<p>But why should the process of vegetation take place only at one +season of the year, whilst a total inaction prevails during the +other?</p> + +<p class="speaker">MRS. B.</p> + +<p>Heat is such an important chemical agent, that its effect, as such, +might perhaps alone account for the impulse which the spring gives to +vegetation. But, in order to explain the mechanism of that operation, it +has been supposed that the warmth of the spring dilates the vessels of +plants, and produces a kind of vacuum, into which the sap (which had +remained in a state of inaction in the trunk during the winter) rises: +this is followed by the +<span class="pagenum">274</span> +<a name="conver2.page274" id="conver2.page274"> </a> +ascent of the sap contained in the roots, and room is thus made for +fresh sap, which the roots, in their turn, pump up from the soil. This +process goes on till the plant blossoms and bears fruit, which +terminates its summer career: but when the cold weather sets in, the +fibres and vessels contract, the leaves wither, and are no longer able +to perform their office of transpiration; and, as this secretion stops, +the roots cease to absorb sap from the soil. If the plant be an annual, +its life then terminates; if not, it remains in a state of torpid +inaction during the winter; or the only internal motion that takes place +is that of a small quantity of resinous juice, which slowly rises from +the stem into the branches, and enlarges their buds during the +winter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet, in evergreens, vegetation must continue throughout the year.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but in winter it goes on in a very imperfect manner, compared to +the vegetation of spring and summer.</p> + +<p>We have dwelt much longer on the history of vegetable chemistry than +I had intended; but we have at length, I think, brought the subject +to a conclusion.</p> + +<span class="pagenum">275</span> +<a name="conver2.page275" id="conver2.page275"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I rather wonder that you did not reserve the account of the +fermentations for the conclusion; for the decomposition of vegetables +naturally follows their death, and can hardly, it seems, be introduced +with so much propriety at any other period.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is difficult to determine at what point precisely it may be most +eligible to enter on the history of vegetation; every part of the +subject is so closely connected, and forms such an uninterrupted chain, +that it is by no means easy to divide it. Had I begun with the +germination of the seed, which, at first view, seems to be the most +proper arrangement, I could not have explained the nature and +fermentation of the seed, or have described the changes which manure +must undergo, in order to yield the vegetable elements. To understand +the nature of germination, it is necessary, I think, previously to +decompose the parent plant, in order to become acquainted with the +materials required for that purpose. I hope, therefore, that, upon +second consideration, you will find that the order which I have adopted, +though apparently less correct, is in fact the best calculated for the +elucidation of the subject.</p> + + + + +<span class="pagenum">276</span> +<a name="conver2.page276" id="conver2.page276"> </a> +<h4><a name="convXXIII" id="convXXIII">CONVERSATION XXIII.</a><br> +<span class="subhead">ON THE COMPOSITION OF ANIMALS.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> are now come to the last branch of +chemistry, which comprehends the most complicated order of compound +beings. This is the animal creation, the history of which cannot but +excite the highest degree of curiosity and interest, though we often +fail in attempting to explain the laws by which it is governed.</p> + +<p class="speaker">EMILY.</p> + +<p>But since all animals ultimately derive their nourishment from +vegetables, the chemistry of this order of beings must consist merely in +the conversion of vegetable into animal matter.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very true; but the manner in which this is effected is, in a great +measure, concealed from our observation. This process is called +<i>animalisation</i>, +<span class="pagenum">277</span> +<a name="conver2.page277" id="conver2.page277"> </a> +and is performed by peculiar organs. The difference of the animal and +vegetable kingdoms does not however depend merely on a different +arrangement of combinations. A new principle abounds in the animal +kingdom, which is but rarely and in very small quantities found in +vegetables; this is nitrogen. There is likewise in animal substances a +greater and more constant proportion of phosphoric acid, and other +saline matters. But these are not essential to the formation of animal +matter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Animal compounds contain, then, four fundamental principles; oxygen, +hydrogen, carbon, and nitrogen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; and these form the immediate materials of animals, which are +<i>gelatine</i>, <i>albumen</i>, and <i>fibrine</i>.</p> + +<p class="speaker">EMILY.</p> + +<p>Are those all? I am surprised that animals should be composed of +fewer kinds of materials than vegetables; for they appear much more +complicated in their organisation.</p> + +<p class="speaker">MRS. B.</p> + +<p>Their organisation is certainly more perfect and intricate, and the +ingredients that occasionally +<span class="pagenum">278</span> +<a name="conver2.page278" id="conver2.page278"> </a> +enter into their composition are more numerous. But notwithstanding the +wonderful variety observable in the texture of the animal organs, we +find that the original compounds, from which all the varieties of animal +matter are derived, may be reduced to the three heads just mentioned. +Animal substances being the most complicated of all natural compounds, +are most easily susceptible of decomposition, as the scale of +attractions increases in proportion to the number of constituent +principles. Their analysis is, however, both difficult and imperfect; +for as they cannot be examined in their living state, and are liable to +alteration immediately after death, it is probable that, when submitted +to the investigation of a chemist, they are always more or less altered +in their combinations and properties, from what they were, whilst they +made part of the living animal.</p> + +<p class="speaker">EMILY.</p> + +<p>The mere diminution of temperature, which they experience by the +privation of animal heat, must, I should suppose, be sufficient to +derange the order of attractions that existed during life.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is one of the causes, no doubt: but there are many other +circumstances which prevent us from studying the nature of living animal +substances. +<span class="pagenum">279</span> +<a name="conver2.page279" id="conver2.page279"> </a> +We must therefore, in a considerable degree, confine our researches to +the phenomena of these compounds in their inanimate state.</p> + +<p>These three kinds of animal matter, gelatine, albumen, and fibrine, +form the basis of all the various parts of the animal system; either +solid, as the <i>skin</i>, <i>flesh</i>, <i>nerves</i>, +<i>membranes</i>, <i>cartilages</i>, and <i>bones</i>; or fluid, as +<i>blood</i>, <i>chyle</i>, <i>milk</i>, <i>mucus</i>, the +<i>gastric</i> and <i>pancreatic juices</i>, <i>bile</i>, +<i>perspiration</i>, <i>saliva</i>, <i>tears</i>, &c.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it not surprising that so great a variety of substances, and so +different in their nature, should yet all arise from so few materials, +and from the same original elements?</p> + +<p class="speaker">MRS. B.</p> + +<p>The difference in the nature of various bodies depends, as I have +often observed to you, rather on their state of combination, than on the +materials of which they are composed. Thus, in considering the chemical +nature of the creation in a general point of view, we observe that it is +throughout composed of a very small number of elements. But when we +divide it into the three kingdoms, we find that, in the mineral, the +combinations seem to result from the union of elements casually brought +together; whilst in the +<span class="pagenum">280</span> +<a name="conver2.page280" id="conver2.page280"> </a> +vegetable and animal kingdoms, the attractions are peculiarly and +regularly produced by appropriate organs, whose action depends on the +vital principle. And we may further observe, that by means of certain +spontaneous changes and decompositions, the elements of one kind of +matter become subservient to the reproduction of another; so that the +three kingdoms are intimately connected, and constantly contributing to +the preservation of each other.</p> + +<p class="speaker">EMILY.</p> + +<p>There is, however, one very considerable class of elements, which +seems to be confined to the mineral kingdom: I mean metals.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not entirely; they are found, though in very minute quantities, both +in the vegetable and animal kingdoms. A small portion of earths and +sulphur enters also into the composition of organised bodies. +Phosphorus, however, is almost entirely confined to the animal kingdom; +and nitrogen, but with few exceptions, is extremely scarce in +vegetables.</p> + +<p>Let us now proceed to examine the nature of the three principal +materials of the animal system.</p> + +<p><i>Gelatine</i>, or <i>jelly</i>, is the chief ingredient of skin, +<span class="pagenum">281</span> +<a name="conver2.page281" id="conver2.page281"> </a> +and of all the membranous parts of animals. It may be obtained from +these substances, by means of boiling water, under the forms of glue, +size, isinglass, and transparent jelly.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But these are of a very different nature; they cannot therefore be +all pure gelatine.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not entirely, but very nearly so. Glue is extracted from the skin of +animals. Size is obtained either from skin in its natural state, or from +leather. Isinglass is gelatine procured from a particular species of +fish; it is, you know, of this substance that the finest jelly is made, +and this is done by merely dissolving the isinglass in boiling water, +and allowing the solution to congeal.</p> + +<p class="speaker">EMILY.</p> + +<p>The wine, lemon, and spices, are, I suppose, added only to flavour +the jelly?</p> + +<p class="speaker">MRS. B.</p> + +<p>Exactly so.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But jelly is often made of hartshorn shavings, and of calves’ feet; +do these substances contain gelatine?</p> + +<span class="pagenum">282</span> +<a name="conver2.page282" id="conver2.page282"> </a> +<p class="speaker">MRS. B.</p> + +<p>Yes. Gelatine may be obtained from almost any animal substance, as it +enters more or less into the composition of all of them. The process for +obtaining it is extremely simple, as it consists merely in boiling the +substance that contains it with water. The gelatine dissolves in water, +and may be attained of any degree of consistence or strength, by +evaporating this solution. Bones in particular produce it very +plentifully, as they consist of phosphat of lime combined or cemented by +gelatine. Horns, which are a species of bone, will yield abundance of +gelatine. The horns of the hart are reckoned to produce gelatine of the +finest quality; they are reduced to the state of shavings in order that +the jelly may be more easily extracted by the water. It is of hartshorn +shavings that the jellies for invalids are usually made, as they are of +very easy digestion.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It appears singular that hartshorn, which yields such a powerful +ingredient as ammonia, should at the same time produce so mild and +insipid a substance as jelly?</p> + +<p class="speaker">MRS. B.</p> + +<p>And (what is more surprising) it is from the gelatine of bones that +ammonia is produced. You +<span class="pagenum">283</span> +<a name="conver2.page283" id="conver2.page283"> </a> +must observe, however, that the processes by which these two substances +are obtained from bones are very different. By the simple action of +water and heat, the gelatine is separated; but in order to procure the +ammonia, or what is commonly called hartshorn, the bones must be +distilled, by which means the gelatine is decomposed, and hydrogen and +nitrogen combined in the form of ammonia. So that the first operation is +a mere separation of ingredients, whilst the second requires a chemical +decomposition.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But when jelly is made from hartshorn shavings, what becomes of the +phosphat of lime which constitutes the other part of bones?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is easily separated by straining. But the jelly is afterwards more +perfectly purified, and rendered transparent, by adding white of egg, +which being coagulated by heat, rises to the surface along with any +impurities.</p> + +<p class="speaker">EMILY.</p> + +<p>I wonder that bones are not used by the common people to make jelly; +a great deal of wholesome nourishment, might, I should +suppose, be procured from them, though the jelly would perhaps +<span class="pagenum">284</span> +<a name="conver2.page284" id="conver2.page284"> </a> +not be quite so good as if made from hartshorn shavings?</p> + +<p class="speaker">MRS. B.</p> + +<p>There is a prejudice among the poor against a species of food that is +usually thrown to the dogs; and as we cannot expect them to enter into +chemical considerations, it is in some degree excusable. Besides, it +requires a prodigious quantity of fuel to dissolve bones and obtain the +gelatine from them.</p> + +<p>The solution of bones in water is greatly promoted by an accumulation +of heat. This may be effected by means of an extremely strong metallic +vessel, called <i>Papin’s digester</i>, in which the bones and water are +enclosed, without any possibility of the steam making its escape. +A heat can thus be applied much superior to that of boiling water; +and bones, by this means, are completely reduced to a pulp. But the +process still consumes too much fuel to be generally adopted among the +lower classes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And why should not a manufacture be established for grinding or +macerating bones, or at least for reducing them to the state of +shavings, when I suppose they would dissolve as readily as hartshorn +shavings?</p> + +<span class="pagenum">285</span> +<a name="conver2.page285" id="conver2.page285"> </a> +<p class="speaker">MRS. B.</p> + +<p>They could not be collected clean for such a purpose, but they are +not lost, as they are used for making hartshorn and sal ammoniac; and +such is the superior science and industry of this country, that we now +send sal ammoniac to the Levant, though it originally came to us from +Egypt.</p> + +<p class="speaker">EMILY.</p> + +<p>When jelly is made of isinglass, does it leave no sediment?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; nor does it so much require clarifying, as it consists almost +entirely of pure <ins class="mycorr" title="text reads ‘gelantine’">gelatine</ins>, +and any foreign matter that is mixed with +it, is thrown off during the boiling in the form of scum.—These +are processes which you may see performed in great perfection in the +culinary laboratory, by that very able and most useful chemist the +cook.</p> + +<p class="speaker">CAROLINE.</p> + +<p>To what an immense variety of purposes chemistry is subservient!</p> + +<p class="speaker">EMILY.</p> + +<p>It appears, in that respect, to have an advantage over most other +arts and sciences; for these, very often, have a tendency to confine the +imagination +<span class="pagenum">286</span> +<a name="conver2.page286" id="conver2.page286"> </a> +to their own particular object, whilst the pursuit of chemistry is so +extensive and diversified, that it inspires a general curiosity, and a +desire of enquiring into the nature of every object.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I suppose that soup is likewise composed of gelatine; for, when cold, +it often assumes the consistence of jelly?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not entirely; for though soups generally contain a quantity of +gelatine, the most essential ingredient is a mucous or extractive +matter, a peculiar animal substance, very soluble in water, which +has a strong taste, and is more nourishing than gelatine. The various +kinds of portable soup consist of this extractive matter in a dry state, +which, in order to be made into soup, requires only to be dissolved in +water.</p> + +<p>Gelatine, in its solid state, is a semiductile transparent substance, +without either taste or smell.—When exposed to heat, in contact +with air and water, it first swells, then fuses, and finally burns. You +may have seen the first part of this operation performed in the +carpenter’s glue-pot.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But you said that gelatine had no smell, and glue has a very +disagreeable one.</p> + +<span class="pagenum">287</span> +<a name="conver2.page287" id="conver2.page287"> </a> +<p class="speaker">MRS. B.</p> + +<p>Glue is not pure gelatine; as it is not designed for eating, it is +prepared without attending to the state of the ingredients, which are +more or less contaminated by particles that have become putrid.</p> + +<p>Gelatine may be precipitated from its solution in water by +alcohol.—We shall try this experiment with a glass of warm +jelly.—You see that the gelatine subsides by the union of the +alcohol and the water.</p> + +<p class="speaker">EMILY.</p> + +<p>How is it, then, that jelly is flavoured with wine, without producing +any precipitation?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because the alcohol contained in wine is already combined with water, +and other ingredients, and is therefore not at liberty to act upon the +jelly as when in its separate state. Gelatine is soluble both in acids +and in alkalies; the former, you know, are frequently used to season +jellies.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Among the combinations of gelatine we must not forget one which you +formerly mentioned; that with tannin, to form leather.</p> + +<span class="pagenum">288</span> +<a name="conver2.page288" id="conver2.page288"> </a> +<p class="speaker">MRS. B.</p> + +<p>True; but you must observe that leather can be produced only by +gelatine in a membranous state; for though pure gelatine and tannin will +produce a substance chemically similar to leather, yet the texture of +the skin is requisite to make it answer the useful purposes of that +substance.</p> + +<p>The next animal substance we are to examine is <i>albumen</i>; this, +although constituting a part of most of the animal compounds, is +frequently found insulated in the animal system; the white of egg, for +instance, consists almost entirely of albumen; the substance that +composes the nerves, the serum, or white part of the blood, and the +curds of milk, are little else than albumen variously modified.</p> + +<p>In its most simple state, albumen appears in the form of a +transparent viscous fluid, possessed of no distinct taste or smell; it +coagulates at the low temperature of 165 degrees, and, when once +solidified, it will never return to its fluid state.</p> + +<p>Sulphuric acid and alcohol are each of them capable of coagulating +albumen in the same manner as heat, as I am going to show you.</p> + +<p class="speaker">EMILY.</p> + +<p>Exactly so.—Pray, Mrs. B., what kind of action +<span class="pagenum">289</span> +<a name="conver2.page289" id="conver2.page289"> </a> +is there between albumen and silver? I have sometimes observed, +that if the spoon with which I eat an egg happens to be wetted, it +becomes tarnished.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because the white of egg (and, indeed, albumen in general) +contains a little sulphur, which, at the temperature of an egg just +boiled, will decompose the drop of water that wets the spoon, and +produce sulphurated hydrogen gas, which has the property of tarnishing +silver.</p> + +<p>We may now proceed to <i>fibrine</i>. This is an insipid and +inodorous substance, having somewhat the appearance of fine white +threads adhering together; it is the essential constituent of muscles or +flesh, in which it is mixed with and softened by gelatine. It is +insoluble both in water and alcohol, but sulphuric acid converts it into +a substance very analogous to gelatine.</p> + + +<p class="space"> +These are the essential and general ingredients of animal matter; but +there are other substances, which, though not peculiar to the animal +system, usually enter into its composition, such as oils, acids, +salts, &c.</p> + +<p><i>Animal oil</i> is the chief constituent of fat; it is contained in +abundance in the cream of milk, whence it is obtained in the form of +butter.</p> + +<span class="pagenum">290</span> +<a name="conver2.page290" id="conver2.page290"> </a> +<p class="speaker">EMILY.</p> + +<p>Is animal oil the same in its composition as vegetable oils?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not the same, but very analogous. The chief difference is that animal +oil contains nitrogen, a principle which seldom enters into the +composition of vegetable oils, and never in so large a proportion.</p> + +<p>There are a few animal acids, that is to say, acids peculiar to +animal matter, from which they are almost exclusively obtained.</p> + +<p>The animal acids have triple bases of hydrogen, carbon, and nitrogen. +Some of them are found native in animal matter; others are produced +during its decomposition.</p> + +<p>Those that we find ready formed are:</p> + +<p>The <i>bombic acid</i>, which is obtained from silk-worms.</p> + +<p>The <i>formic acid</i>, from ants.</p> + +<p>The <i>lactic acid</i>, from the whey of milk.</p> + +<p>The <i>sebacic</i>, from oil or fat.</p> + +<p>Those produced during the decomposition of animal substances by heat, +are the <i>prussic</i> and <i>zoonic</i> acids. This last is produced by +the roasting of meat, and gives it a brisk flavour.</p> + +<span class="pagenum">291</span> +<a name="conver2.page291" id="conver2.page291"> </a> +<p class="speaker">CAROLINE.</p> + +<p>The class of animal acids is not very extensive?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; nor are they, generally speaking, of great importance. The +<i>prussic acid</i> is, I think, the only one sufficiently +interesting to require any further comment. It can be formed by any +artificial process, without the presence of any animal matter; and it +may likewise be obtained from a variety of vegetables, particularly +those of the narcotic kind, such as poppies, laurel, &c. But it is +commonly obtained from blood, by strongly heating that substance with +caustic potash; the alkali attracts the acid from the blood, and forms +with it a <i>prussiat of potash</i>. From this state of combination the +prussic acid can be obtained pure by means of other substances which +have the power of separating it from the alkali.</p> + +<p class="speaker">EMILY.</p> + +<p>But if this acid does not exist ready formed in blood, how can the +alkali attract it from it?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is the triple basis only of this acid that exists in the blood; +and this is developed and brought to the state of acid, during the +combustion. The +<span class="pagenum">292</span> +<a name="conver2.page292" id="conver2.page292"> </a> +acid therefore is first formed, and it afterwards combines with the +potash.</p> + +<p class="speaker">EMILY.</p> + +<p>Now I comprehend it. But how can the prussic acid be artificially +made?</p> + +<p class="speaker">MRS. B.</p> + +<p>By passing ammoniacal gas over red-hot charcoal; and hence we learn +that the constituents of this acid are hydrogen, nitrogen, and carbon. +The two first are derived from the volatile alkali, the last from the +combustion of the charcoal.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But this does not accord with the system of oxygen being the +principle of acidity.</p> + +<p class="speaker">MRS. B.</p> + +<p>The colouring matter of prussian blue is called an acid, because it +unites with alkalies and metals, and not from any other characteristic +properties of acids; perhaps the name is not strictly appropriate. But +this circumstance, together with some others of the same kind, has +induced several chemists to think that oxygen may not be the exclusive +generator of acids. Sir H. Davy, I have already informed you, was +led by his experiments +<span class="pagenum">293</span> +<a name="conver2.page293" id="conver2.page293"> </a> +on dry acids to suspect that water might be essential to acidity. And it +is the opinion of some chemists that acidity may possibly depend rather +on the arrangement than on the presence of any particular principles. +But we have not yet done with the prussic acid. It has a strong affinity +for metallic oxyds, and precipitates the solutions of iron in acids of a +blue colour. This is the prussian blue, or prussiat of iron, so much +used in the arts, and with which I think you must be acquainted.</p> + +<p class="speaker">EMILY.</p> + +<p>Yes, I am; it is much used in painting, both in oil and in water +colours; but it is not reckoned a permanent oil-colour.</p> + +<p class="speaker">MRS. B.</p> + +<p>That defect arises, I believe, in general, from its being badly +prepared, which is the case when the iron is not so fully oxydated as to +form a red oxyd. For a solution of green oxyd of iron (in which the +metal is more slightly oxydated), makes only a pale green, or even a +white precipitate, with prussiat of potash; and this gradually changes +to blue by being exposed to the air, as I can immediately show you.</p> + +<span class="pagenum">294</span> +<a name="conver2.page294" id="conver2.page294"> </a> +<p class="speaker">CAROLINE.</p> + +<p>It already begins to assume a pale blue colour. But how does the air +produce this change?</p> + +<p class="speaker">MRS. B.</p> + +<p>By oxydating the iron more perfectly. If we pour some nitrous acid on +it, the prussian blue colour will be immediately produced, as the acid +will yield its oxygen to the precipitate, and fully saturate it with +this principle, as you shall see.</p> + +<p class="speaker">CAROLINE.</p> + +<p>It is very curious to see a colour change so instantaneously.</p> + +<p class="speaker">MRS. B.</p> + +<p>Hence you perceive that prussian blue cannot be a permanent colour, +unless prepared with red oxyd of iron, since by exposure to the +atmosphere it gradually darkens, and in a short time is no longer in +harmony with the other colours of the painting.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But it can never become darker, by exposure to the atmosphere, than +the true prussian blue, in which the oxyd is perfectly saturated?</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly not. But in painting, the artist not +<span class="pagenum">295</span> +<a name="conver2.page295" id="conver2.page295"> </a> +reckoning upon partial alterations in his colours, gives his blue tints +that particular shade which harmonises with the rest of the picture. If, +afterwards, those tints become darker, the harmony of the colouring must +necessarily be destroyed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, of what nature is the paint called <i>carmine</i>?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is an animal colour prepared from <i>cochineal</i>, an insect, the +infusion of which produces a very beautiful red.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Whilst we are on the subject of colours, I should like to learn +what <i>ivory black</i> is?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is a carbonaceous substance obtained by the combustion of ivory. +A more common species of black is obtained from the burning of +bone.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But during the combustion of ivory or bone, the carbon, I should +have imagined, must be converted into carbonic acid gas, instead of this +black substance?</p> + +<span class="pagenum">296</span> +<a name="conver2.page296" id="conver2.page296"> </a> +<p class="speaker">MRS. B.</p> + +<p>In this, as in most combustions, a considerable part of the carbon is +simply volatilised by the heat, and again obtained concrete on cooling. +This colour, therefore, may be called the soot produced by the burning +of ivory or bone.</p> + + + + +<span class="pagenum">297</span> +<a name="conver2.page297" id="conver2.page297"> </a> +<h4><a name="convXXIV" id="convXXIV">CONVERSATION XXIV.</a><br> +<span class="subhead">ON THE ANIMAL ECONOMY.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> have now acquired some idea of the +various materials that compose the animal system; but if you are curious +to know in what manner these substances are formed by the animal organs, +from vegetable, as well as from animal substances, it will be necessary +to have some previous knowledge of the nature and functions of these +organs, without which it is impossible to form any distinct idea of the +process of <i>animalisation</i> and <i>nutrition</i>.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I do not exactly understand the meaning of the word +animalisation?</p> + +<p class="speaker">MRS. B.</p> + +<p>Animalisation is the process by which the food +<span class="pagenum">298</span> +<a name="conver2.page298" id="conver2.page298"> </a> +is <i>assimilated</i>, that is to say, converted into animal matter; and +nutrition is that by which the food thus assimilated is rendered +subservient to the purposes of nourishing and maintaining the animal +system.</p> + +<p class="speaker">EMILY.</p> + +<p>This, I am sure, must be the most interesting of all the branches of +chemistry!</p> + +<p class="speaker">CAROLINE.</p> + +<p>So I think; particularly as I expect that we shall hear something of +the nature of respiration, and of the circulation of the blood?</p> + +<p class="speaker">MRS. B.</p> + +<p>These functions undoubtedly occupy a most important place in the +history of the animal economy.—But I must previously give you a +very short account of the principal organs by which the various +operations of the animal system are performed. These are:</p> + +<table class="list" summary="list of organs"> +<tr> +<td>The</td><td><i>Bones</i>;</td> +</tr> +<tr> +<td></td><td><i>Muscles</i>,</td> +</tr> +<tr> +<td></td><td><i>Blood vessels</i>,</td> +</tr> +<tr> +<td></td><td><i>Lymphatic vessels</i>,</td> +</tr> +<tr> +<td></td><td><i>Glands</i>, and</td> +</tr> +<tr> +<td></td><td><i>Nerves</i>.</td> +</tr> +</table> + +<span class="pagenum">299</span> +<a name="conver2.page299" id="conver2.page299"> </a> +<p>The <i>bones</i> are the most solid part of the animal frame, and in +a great measure determine its form and dimensions. You recollect, +I suppose, what are the ingredients which enter into their +composition?</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yes; phosphat of lime, cemented by gelatine.</p> + +<p class="speaker">MRS. B.</p> + +<p>During the earliest period of animal life, they consist almost +entirely of gelatinous membrane having the form of the bones, but of a +loose spongy texture, the cells or cavities of which are destined to be +filled with phosphat of lime; it is the gradual acquisition of this salt +which gives to the bones their subsequent hardness and durability. +Infants first receive it from their mother’s milk, and afterwards derive +it from all animal and from most vegetable food, especially farinaceous +substances, such as wheat-flour, which contain it in sensible +quantities. A portion of the phosphat, after the bones of the +infant have been sufficiently expanded and solidified, is deposited in +the teeth, which consist at first only of a gelatinous membrane or case, +fitted for the reception of this salt; and which, after acquiring +hardness within the gum, gradually protrude from it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>How very curious this is; and how ingeniously +<span class="pagenum">300</span> +<a name="conver2.page300" id="conver2.page300"> </a> +nature has first provided for the solidification of such bones as are +immediately wanted, and afterwards for the formation of the teeth, which +would not only be useless, but detrimental in infancy!</p> + +<p class="speaker">MRS. B.</p> + +<p>In quadrupeds the phosphat of lime is deposited likewise in their +horns, and in the hair or wool with which they are generally +clothed.</p> + +<p>In birds it serves also to harden the beaks and the quills of their +feathers.</p> + +<p>When animals are arrived at a state of maturity, and their bones have +acquired a sufficient degree of solidity, the phosphat of lime which is +taken with the food is seldom assimilated, excepting when the female +nourishes her young; it is then all secreted into the milk, as a +provision for the tender bones of the nursling.</p> + +<p class="speaker">EMILY.</p> + +<p>So that whatever becomes superfluous to one being, is immediately +wanted by another; and the child acquires strength precisely by the +species of nourishment which is no longer necessary to the mother. +Nature is, indeed, an admirable economist!</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, Mrs. B., does not the disease in the bones +<span class="pagenum">301</span> +<a name="conver2.page301" id="conver2.page301"> </a> +of children, called the rickets, proceed from a deficiency of phosphat +of lime?</p> + +<p class="speaker">MRS. B.</p> + +<p>I have heard that this disease may arise from two causes; it is +sometimes occasioned by the growth of the muscles being too rapid in +proportion to that of the bones. In this case the weight of the flesh is +greater than the bones can support, and presses upon them so as to +produce a swelling of the joints, which is the great indication of the +rickets. The other cause of this disorder is supposed to be an imperfect +digestion and assimilation of the food, attended with an excess of acid, +which counteracts the formation of phosphat of lime. In both instances, +therefore, care should be taken to alter the child’s diet, not merely by +increasing the quantity of aliment containing phosphat of lime, but also +by avoiding all food that is apt to turn acid on the stomach, and to +produce indigestion. But the best preservative against complaints of +this kind is, no doubt, good nursing: when a child has plenty of air and +exercise, the digestion and assimilation will be properly performed, no +acid will be produced to interrupt these functions, and the muscles and +bones will grow together in just proportions.</p> + +<span class="pagenum">302</span> +<a name="conver2.page302" id="conver2.page302"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I have often heard the rickets attributed to bad nursing, but I never +could have guessed what connection there was between exercise and the +formation of the bones.</p> + +<p class="speaker">MRS. B.</p> + +<p>Exercise is generally beneficial to all the animal functions. If man +is destined to labour for his subsistence, the bread which he earns is +scarcely more essential to his health and preservation than the +exertions by which he obtains it. Those whom the gifts of fortune have +placed above the necessity of bodily labour are compelled to take +exercise in some mode or other, and when they cannot convert it into an +amusement, they must submit to it as a task, or their health will soon +experience the effects of their indolence.</p> + +<p class="speaker">EMILY.</p> + +<p>That will never be my case: for exercise, unless it becomes fatigue, +always gives me pleasure; and, so far from being a task, is to me a +source of daily enjoyment. I often think what a blessing it is, +that exercise, which is so conducive to health, should be so delightful; +whilst fatigue, which is rather hurtful, instead of pleasure, occasions +painful sensations. So that fatigue, no doubt, was +<span class="pagenum">303</span> +<a name="conver2.page303" id="conver2.page303"> </a> +intended to moderate our bodily exertions, as satiety puts a limit to +our appetites.</p> + +<p class="speaker">MRS. B.</p> + +<p>Certainly.—But let us not deviate too far from our +subject.—The bones are connected together by ligaments, which +consist of a white thick flexible substance, adhering to their +extremities, so far as to secure the joints firmly, though without +impeding their motion. And the joints are moreover covered by a solid, +smooth, elastic, white substance, called <i>cartilage</i>, the use of +which is to allow, by its smoothness and elasticity, the bones to slide +easily over one another, so that the joints may perform their office +without difficulty or detriment.</p> + +<p>Over the bones the <i>muscles</i> are placed; they consist of bundles +of fibres which terminate in a kind of string, or ligament, by which +they are fastened to the bones. The muscles are the organs of motion; by +their power of dilatation and contraction they put into action the +bones, which act as levers, in all the motions of the body, and form the +solid support of its various parts. The muscles are of various degrees +of strength or consistence in different species of animals. The +mammiferous tribe, or those that suckle their young, seem in this +respect to occupy an intermediate place between birds and cold-blooded +animals, such as reptiles and fishes.</p> + +<span class="pagenum">304</span> +<a name="conver2.page304" id="conver2.page304"> </a> +<p class="speaker">EMILY.</p> + +<p>The different degrees of firmness and solidity in the muscles of +these several species of animals proceed, I imagine, from the +different nature of the food on which they subsist?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; that is not supposed to be the case: for the human species, who +are of the mammiferous tribe, live on more substantial food than birds, +and yet the latter exceed them in muscular strength. We shall hereafter +attempt to account for this difference; but let us now proceed in the +examination of the animal functions.</p> + +<p>The next class of organs is that of the <i>vessels</i> of the body, +the office of which is to convey the various fluids throughout the +frame. These vessels are innumerable. The most considerable of them are +those through which the blood circulates, which are of two kinds: the +<i>arteries</i>, which convey it from the heart to the extremities of +the body, and the <i>veins</i>, which bring it back into the heart.</p> + +<p>Besides these, there are a numerous set of small transparent vessels, +destined to absorb and convey different fluids into the blood; they are +generally called the <i>absorbent</i> or <i>lymphatic</i> vessels: but +it is to a portion of them only that the function of conveying into the +blood the fluid called <i>lymph</i> is assigned.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is the nature of that fluid?</p> + +<span class="pagenum">305</span> +<a name="conver2.page305" id="conver2.page305"> </a> +<p class="speaker">MRS. B.</p> + +<p>The nature and use of the lymph have, I believe, never been perfectly +ascertained; but it is supposed to consist of matter that has been +previously animalised, and which, after answering the purpose for which +it was intended, must, in regular rotation, make way for the fresh +supplies produced by nourishment. The lymphatic vessels pump up this +fluid from every part of the system, and convey it into the veins to be +mixed with the blood which runs through them, and which is commonly +called venous blood.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But does it not again enter into the animal system through that +channel?</p> + +<p class="speaker">MRS. B.</p> + +<p>Not entirely; for the venous blood does not return into the +circulation until it has undergone a peculiar change, in which it throws +off whatever is become useless.</p> + +<p>Another set of absorbent vessels pump up the <i>chyle</i> from the +stomach and intestines, and convey it, after many circumvolutions, into +the great vein near the heart.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray what is chyle?</p> + +<span class="pagenum">306</span> +<a name="conver2.page306" id="conver2.page306"> </a> +<p class="speaker">MRS. B.</p> + +<p>It is the substance into which food is converted by digestion.</p> + +<p class="speaker">CAROLINE.</p> + +<p>One set of the absorbent vessels, then, is employed in bringing away +the old materials that are no longer fit for use; whilst the other set +is busy in conveying into the blood the new materials that are to +replace them.</p> + +<p class="speaker">EMILY.</p> + +<p>What a great variety of ingredients must enter into the composition +of the blood?</p> + +<p class="speaker">MRS. B.</p> + +<p>You must observe that there is also a great variety of substances to +be secreted from it. We may compare the blood to a general receptacle or +storehouse for all kinds of commodities, which are afterwards fashioned, +arranged, and disposed of as circumstances require.</p> + +<p>There is another set of absorbent vessels in females which is +destined to secrete milk for the nourishment of the young.</p> + +<p class="speaker">EMILY.</p> + +<p>Pray is not milk very analogous in its composition to blood; for, +since the nursling derives its nourishment from that source only, it +must contain +<span class="pagenum">307</span> +<a name="conver2.page307" id="conver2.page307"> </a> +every principle which the animal system requires?</p> + +<p class="speaker">MRS. B.</p> + +<p>Very true. Milk is found, by its analysis, to contain the principal +materials of animal matter, albumen, oil, and phosphat of lime; so that +the suckling has but little trouble to digest and assimilate this +nourishment. But we shall examine the composition of milk more fully +afterwards.</p> + +<p>In many parts of the body numbers of small vessels are collected +together in little bundles called <i>glands</i>, from a Latin word +meaning acorn, on account of the resemblance which some of them bear in +shape to that fruit. The function of the glands is to <i>secrete</i>, or +separate certain matters from the blood.</p> + +<p>The secretions are not only mechanical, but chemical separations from +the blood; for the substances thus formed, though contained in the +blood, are not ready combined in that fluid. The secretions are of two +kinds, those which form peculiar animal fluids, as bile, tears, saliva, +&c.; and those which produce the general materials of the animal +system, for the purpose of recruiting and nourishing the several organs +of the body; such as albumen, gelatine, and fibrine; the latter may be +distinguished by the name of <i>nutritive secretions</i>.</p> + +<span class="pagenum">308</span> +<a name="conver2.page308" id="conver2.page308"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I am quite astonished to hear that all the secretions should be +derived from the blood.</p> + +<p class="speaker">EMILY.</p> + +<p>I thought that the bile was produced by the liver?</p> + +<p class="speaker">MRS. B.</p> + +<p>So it is; but the liver is nothing more than a very large gland, +which secretes the bile from the blood.</p> + +<p>The last of the animal organs which we have mentioned are the +<i>nerves</i>; these are the vehicles of sensation, every other part of +the body being, of itself, totally insensible.</p> + +<p class="speaker">CAROLINE.</p> + +<p>They must then be spread through every part of the frame, for we are +every where susceptible of feeling.</p> + +<p class="speaker">EMILY.</p> + +<p>Excepting the nails and the hair.</p> + +<p class="speaker">MRS. B.</p> + +<p>And those are almost the only parts in which nerves cannot be +discovered. The common source of all the nerves is the brain; thence +they descend, some of them through different holes of the skull, but the +greatest part through the back bone, +<span class="pagenum">309</span> +<a name="conver2.page309" id="conver2.page309"> </a> +and extend themselves by innumerable ramifications throughout the whole +body. They spread themselves over the muscles, penetrate the glands, +wind round the vascular system, and even pierce into the interior of the +bones. It is most probably through them that the communication is +carried on between the mind and the other parts of the body; but in what +manner they are acted on by the mind, and made to re-act on the body, is +still a profound secret. Many hypotheses have been formed on this very +obscure subject, but they are all equally improbable, and it would be +useless for us to waste our time in conjectures on an enquiry, which, in +all probability, is beyond the reach of human capacity.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But you have not mentioned those particular nerves that form the +senses of hearing, seeing, smelling, and tasting?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are considered as being of the same nature as those which are +dispersed over every part of the body, and constitute the general sense +of feeling. The different sensations which they produce arise from their +peculiar situation and connection with the several organs of taste, +smell, and hearing.</p> + +<span class="pagenum">310</span> +<a name="conver2.page310" id="conver2.page310"> </a> +<p class="speaker">EMILY.</p> + +<p>But these senses appear totally different from that of feeling?</p> + +<p class="speaker">MRS. B.</p> + +<p>They are all of them sensations, but variously modified according to +the nature of the different organs in which the nerves are situated. +For, as we have formerly observed, it is by contact only that the nerves +are affected. Thus odoriferous particles must strike upon the nerves of +the nose, in order to excite the sense of smelling; in the same manner +that taste is produced by the particular substance coming in contact +with the nerves of the palate. It is thus also that the sensation of +sound is produced by the concussion of the air striking against the +auditory nerve; and sight is the effect of the light falling upon the +optic nerve. These various senses, therefore, are affected only by the +actual contact of particles of matter, in the same manner as that of +feeling.</p> + +<p>The different organs of the animal body, though easily separated and +perfectly distinct, are loosely connected together by a kind of spongy +substance, in texture somewhat resembling net-work, called the cellular +membrane; and the whole is covered by the skin.</p> + +<p>The <i>skin</i>, as well as the bark of vegetables, is formed of +three coats. The external one is called the <i>cuticle</i> or +<i>epidermis</i>; the second, which is +<span class="pagenum">311</span> +<a name="conver2.page311" id="conver2.page311"> </a> +called the <i>mucous membrane</i>, is of a thin soft texture, and +consists of a mucous substance, which in negroes is black, and is the +cause of their skin appearing of that colour.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is then the external skin of negroes white like ours?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; but as the cuticle is transparent, as well as porous, the +blackness of the mucous membrane is visible through it. The extremities +of the nerves are spread over this skin, so that the sensation of +feeling is transmitted through the cuticle. The internal covering of the +muscles, which is properly the skin, is the thickest, the toughest, and +most resisting of the whole; it is this membrane which is so essential +in the arts, by forming leather when combined with tannin.</p> + +<p>The skin which covers the animal body, as well as those membranes +that form the coats of the vessels, consists almost exclusively of +gelatine; and is capable of being converted into glue, size, or +jelly.</p> + +<p>The cavities between the muscles and the skin are usually filled with +fat, which lodges in the cells of the membranous net before mentioned, +and gives to the external form (especially in the +<span class="pagenum">312</span> +<a name="conver2.page312" id="conver2.page312"> </a> +human figure) that roundness, smoothness, and softness, so essential to +beauty.</p> + +<p class="speaker">EMILY.</p> + +<p>And the skin itself is, I think, a very ornamental part of the +human frame, both from the fineness of its texture, and the variety and +delicacy of its tints.</p> + +<p class="speaker">MRS. B.</p> + +<p>This variety and harmonious graduation of colours, proceed, not so +much from the skin itself, as from the internal organs which transmit +their several colours through it, these being only softened and blended +by the colour of the skin, which is uniformly of a yellowish white.</p> + +<p>Thus modified, the darkness of the veins appears of a pale blue +colour, and the floridness of the arteries is changed to a delicate +pink. In the most transparent parts, the skin exhibits the bloom of the +rose, whilst where it is more opake its own colour predominates; and at +the joints, where the bones are most prominent, their whiteness is often +discernible. In a word, every part of the human frame seems to +contribute to its external grace; and this not merely by producing a +pleasing variety of tints, but by a peculiar kind of beauty which +belongs to each individual part. Thus it is to the solidity and +arrangement of the bones that the human figure owes the grandeur of its +stature, +<span class="pagenum">313</span> +<a name="conver2.page313" id="conver2.page313"> </a> +and its firm and dignified deportment. The muscles delineate the form, +and stamp it with energy and grace; and the soft substance which is +spread over them smooths their ruggedness, and gives to the contours the +gentle undulations of the line of beauty. Every organ of sense is a +peculiar and separate ornament; and the skin, which polishes the +surface, and gives it that charm of colouring so inimitable by art, +finally conspires to render the whole the fairest work of the +creation.</p> + +<p>But now that we have seen in what manner the animal frame is formed, +let us observe how it provides for its support, and how the several +organs, which form so complete a whole, are nourished and +maintained.</p> + +<p>This will lead us to a more particular explanation of the internal +organs: here we shall not meet with so much apparent beauty, because +these parts were not intended by nature to be exhibited to view; but the +beauty of design, in the internal organisation of the animal frame, is, +if possible, still more remarkable than that of the external parts.</p> + +<p>We shall defer this subject till our next interview.</p> + + + + +<span class="pagenum">314</span> +<a name="conver2.page314" id="conver2.page314"> </a> +<h4><a name="convXXV" id="convXXV">CONVERSATION XXV.</a><br> +<span class="subhead">ON ANIMALISATION, NUTRITION, AND +RESPIRATION.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">MRS. B.</p> + +<p><span class="firstword"><span class="firstletter">W</span>e</span> have now learnt of what materials the +animal system is composed, and have formed some idea of the nature of +its organisation. In order to complete the subject, it remains for us to +examine in what manner it is nourished and supported.</p> + +<p>Vegetables, we have observed, obtain their nourishment from various +substances, either in their elementary state, or in a very simple state +of combination; as carbon, water, and salts, which they pump up from the +soil; and carbonic acid and oxygen, which they absorb from the +atmosphere.</p> + +<p>Animals, on the contrary, feed on substances of the most complicated +kind; for they derive their sustenance, some from the animal creation, +others from the vegetable kingdom, and some from both.</p> + +<span class="pagenum">315</span> +<a name="conver2.page315" id="conver2.page315"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And there is one species of animals, which, not satisfied with +enjoying either kind of food in its simple state, has invented the art +of combining them together in a thousand ways, and of rendering even the +mineral kingdom subservient to its refinements.</p> + +<p class="speaker">EMILY.</p> + +<p>Nor is this all; for our delicacies are collected from the various +climates of the earth, so that the four quarters of the globe are often +obliged to contribute to the preparation of our simplest dishes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the very complicated substances which constitute the nourishment +of animals, do not, I suppose, enter into their system in their +actual state of combination?</p> + +<p class="speaker">MRS. B.</p> + +<p>So far from it, that they not only undergo a new arrangement of their +parts, but a selection is made of such as are most proper for the +nourishment of the body, and those only enter into the system, and are +animalised.</p> + +<p class="speaker">EMILY.</p> + +<p>And by what organs is this process performed?</p> + +<p class="speaker">MRS. B.</p> + +<p>Chiefly by the stomach, which is the organ of +<span class="pagenum">316</span> +<a name="conver2.page316" id="conver2.page316"> </a> +digestion, and the prime regulator of the animal frame.</p> + +<p><i>Digestion</i> is the first step towards nutrition. It consists in +reducing into one homogeneous mass the various substances that are taken +as nourishment; it is performed by first chewing and mixing the solid +aliment with the saliva, which reduces it to a soft mass, in which state +it is conveyed into the stomach, where it is more completely dissolved +by the <i>gastric juice</i>.</p> + +<p>This fluid (which is secreted into the stomach by appropriate glands) +is so powerful a solvent that scarcely any substances will resist its +action.</p> + +<p class="speaker">EMILY.</p> + +<p>The coats of the stomach, however, cannot be attacked by it, +otherwise we should be in danger of having them destroyed when the +stomach was empty.</p> + +<p class="speaker">MRS. B.</p> + +<p>They are probably not subject to its action; as long, at least, as +life continues. But it appears, that when the gastric juice has no +foreign substance to act upon, it is capable of occasioning a degree of +irritation in the coats of the stomach, which produces the sensation of +hunger. The gastric juice, together with the heat and muscular action of +the stomach, converts the aliment into an uniform pulpy mass called +chyme. This passes +<span class="pagenum">317</span> +<a name="conver2.page317" id="conver2.page317"> </a> +into the intestines, where it meets with the bile and some other fluids, +by the agency of which, and by the operation of other causes hitherto +unknown, the chyme is changed into chyle, a much thinner substance, +somewhat resembling milk, which is pumped by immense numbers of small +absorbent vessels spread over the internal surface of the intestines. +These, after many circumvolutions, gradually meet and unite into large +branches, till they at length collect the chyle into one vessel, which +pours its contents into the great vein near the heart, by which means +the food, thus prepared, enters into the circulation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But I do not yet clearly understand how the blood, thus formed, +nourishes the body and supplies all the secretions?</p> + +<p class="speaker">MRS. B.</p> + +<p>Before this can be explained to you, you must first allow me to +complete the formation of the blood. The chyle may, indeed, be +considered as forming the chief ingredient of blood; but this fluid is +not perfect until it has passed through the lungs, and undergone +(together with the blood that has already circulated) certain necessary +changes that are effected by <span class="smallroman">RESPIRATION</span>.</p> + +<span class="pagenum">318</span> +<a name="conver2.page318" id="conver2.page318"> </a> +<p class="speaker">CAROLINE.</p> + +<p>I am very glad that you are going to explain the nature of +respiration: I have often longed to understand it, for though we +talk incessantly of <i>breathing</i>, I never knew precisely what +purpose it answered.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is indeed one of the most interesting processes imaginable; but, +in order to understand this function well, it will be necessary to enter +into some previous explanations. Tell me, Emily,—what do you +understand by respiration?</p> + +<p class="speaker">EMILY.</p> + +<p>Respiration, I conceive, consists simply in alternately +<i>inspiring</i> air into the lungs, and <i>expiring</i> it from +them.</p> + +<p class="speaker">MRS. B.</p> + +<p>Your answer will do very well as a general definition. But, in order +to form a tolerably clear notion of the various phenomena of +respiration, there are many circumstances to be taken into +consideration.</p> + +<p>In the first place, there are two things to be distinguished in +respiration, the <i>mechanical</i> and the <i>chemical</i> part of the +process.</p> + +<p>The mechanism of breathing depends on the alternate expansions and +contractions of the chest, in which the lungs are contained. When the +<span class="pagenum">319</span> +<a name="conver2.page319" id="conver2.page319"> </a> +chest dilates, the cavity is enlarged, and the air rushes in at the +mouth, to fill up the vacuum formed by this dilatation; when it +contracts, the cavity is diminished, and the air forced out again.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I thought that it was the lungs that contracted and expanded in +breathing?</p> + +<p class="speaker">MRS. B.</p> + +<p>They do likewise; but their action is only the consequence of that of +the chest. The lungs, together with the heart and largest blood vessels, +in a manner fill up the cavity of the chest; they could not, therefore, +dilate if the chest did not previously expand; and, on the other hand, +when the chest contracts, it compresses the lungs and forces the air out +of them.</p> + +<p class="speaker">CAROLINE.</p> + +<p>The lungs, then, are like bellows, and the chest is the power that +works them.</p> + +<p class="speaker">MRS. B.</p> + +<p>Precisely so. Here is a curious little figure (<a class="smallcaps" +href="#plateXVb">Plate XV.</a> Fig. 5.), that will assist me in +explaining the mechanism of breathing.</p> + + +<p class="figname"> +<a name="plateXVb" id="plateXVb">Plate XV.</a></p> + +<p class="figpage"> +<span class="smallcaps">Vol. II.</span> p. 250</p> + +<p class="illustration"> +<img src="images/plate15b_thumb.png" width="324" height="360" +alt="see text and caption"> +</p> + +<p class="caption"> +Fig. 5. A.A Glass Bell. +B Bladder representing the lungs. +C Bladder representing the Diaphragm.</p> + +<p class="figlink"> +<a href="images/plate15_large.jpg" target="_blank">Larger view</a> +(complete Plate)</p> + +<p class="speaker">CAROLINE.</p> + +<p>What a droll figure! a little head fixed upon a glass bell, with a +bladder tied over the bottom of it!</p> + +<span class="pagenum">320</span> +<a name="conver2.page320" id="conver2.page320"> </a> +<p class="speaker">MRS. B.</p> + +<p>You must observe that there is another bladder within the glass, the +neck of which communicates with the mouth of the figure—this +represents the lungs contained within the chest; the other bladder, +which you see is tied loose, represents a muscular membrane, called the +<i>diaphragm</i>, which separates the chest from the lower part of the +body. By the chest, therefore, I mean that large cavity in the +upper part of the body contained within the ribs, the neck, and the +diaphragm; this membrane is muscular, and capable of contraction and +dilatation. The contraction may be imitated by drawing the bladder tight +over the bottom of the receiver, when the air in the bladder, which +represents the lungs, will be forced out through the mouth of the +figure—</p> + +<p class="speaker">EMILY.</p> + +<p>See, Caroline, how it blows the flame of the candle in breathing!</p> + +<p class="speaker">MRS. B.</p> + +<p>By letting the bladder loose again, we imitate the dilatation of the +diaphragm, and the cavity of the chest being enlarged, the lungs expand, +and the air rushes in to fill them.</p> + +<p class="speaker">EMILY.</p> + +<p>This figure, I think, gives a very clear idea of the process of +breathing.</p> + +<span class="pagenum">321</span> +<a name="conver2.page321" id="conver2.page321"> </a> +<p class="speaker">MRS. B.</p> + +<p>It illustrates tolerably well the action of the lungs and diaphragm; +but those are not the only powers that are concerned in enlarging or +diminishing the cavity of the chest; the ribs are also possessed of a +muscular motion for the same purpose; they are alternately drawn in, +edgeways, to assist the contraction, and stretched out, like the hoops +of a barrel, to contribute to the dilatation of the chest.</p> + +<p class="speaker">EMILY.</p> + +<p>I always supposed that the elevation and depression of the ribs were +the consequence, not the cause of breathing.</p> + +<p class="speaker">MRS. B.</p> + +<p>It is exactly the reverse. The muscular action of the <ins class="mycorr" title="text reads ‘diaphram’">diaphragm</ins>, together with +that of the ribs, are the <i>causes</i> of the contraction and expansion +of the chest; and the air rushing into, and being expelled from the +lungs, are only <i>consequences</i> of those actions.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I confess that I thought the act of breathing began by opening the +mouth for the air to rush in, and that it was the air alone, which, by +alternately rushing in and out, occasioned the dilatations and +contractions of the lungs and chest.</p> + +<span class="pagenum">322</span> +<a name="conver2.page322" id="conver2.page322"> </a> +<p class="speaker">MRS. B.</p> + +<p>Try the experiment of merely opening your mouth; the air will not +rush in, till by an interior muscular action you produce a +vacuum—yes, just so, your diaphragm is now dilated, and the ribs +expanded. But you will not be able to keep them long in that state. Your +lungs and chest are already resuming their former state, and expelling +the air with which they had just been filled. This mechanism goes on +more or less rapidly, but, in general, a person at rest and in +health will breathe between fifteen and twenty-five times in a +minute.</p> + +<p>We may now proceed to the chemical effects of respiration; but, for +this purpose, it is necessary that you should previously have some +notion of the <i>circulation</i> of the blood. Tell me, Caroline, what +do you understand by the circulation of the blood?</p> + +<p class="speaker">CAROLINE.</p> + +<p>I am delighted that you come to that subject, for it is one that has +long excited my curiosity. But I cannot conceive how it is connected +with respiration. The idea I have of the circulation is, that the blood +runs from the heart through the veins all over the body, and back again +to the heart.</p> + +<p class="speaker">MRS. B.</p> + +<p>I could hardly have expected a better definition +<span class="pagenum">323</span> +<a name="conver2.page323" id="conver2.page323"> </a> +from you; it is, however, not quite correct, for you do not distinguish +the <i>arteries</i> from the <i>veins</i>, which, as we have already +observed, are two distinct sets of vessels, each having its own peculiar +functions. The arteries convey the blood from the heart to the +extremities of the body; and the veins bring it back into the heart.</p> + +<p>This sketch will give you an idea of the manner in which some of the +principal veins and arteries of the human body branch out of the heart, +which may be considered as a common centre to both sets of vessels. The +heart is a kind of strong elastic bag, or muscular cavity, which +possesses a power of dilating and contracting itself, for the purposes +of alternately receiving and expelling the blood, in order to carry on +the process of circulation.</p> + +<p class="speaker">EMILY.</p> + +<p>Why are the arteries in this drawing painted red, and the veins +purple?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is to point out the difference of the colour of the blood in these +two sets of vessels.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But if it is the same blood that flows from the arteries into the +veins, how can its colour be changed?</p> + +<span class="pagenum">324</span> +<a name="conver2.page324" id="conver2.page324"> </a> +<p class="speaker">MRS. B.</p> + +<p>This change arises from various circumstances. In the first place, +during its passage through the arteries, the blood undergoes a +considerable alteration, some of its constituent parts being gradually +separated from it for the purpose of nourishing the body, and of +supplying the various secretions. The consequence of this is, that the +florid arterial colour of the blood changes by degrees to a deep purple, +which is its constant colour in the veins. On the other hand, the blood +is recruited during its return through the veins by the fresh chyle, or +imperfect blood, which has been produced by food; and it receives also +lymph from the absorbent vessels, as we have before mentioned. In +consequence of these several changes, the blood returns to the heart in +a state very different from that in which it left it. It is loaded with +a greater proportion of hydrogen and carbon, and is no longer fit for +the nourishment of the body, or other purposes of circulation.</p> + +<p class="speaker">EMILY.</p> + +<p>And in this state does it mix in the heart with the pure florid blood +that runs into the arteries?</p> + +<p class="speaker">MRS. B.</p> + +<p>No. The heart is divided into two cavities or compartitions, called +the <i>right</i> and <i>left ventricles</i>. +<span class="pagenum">325</span> +<a name="conver2.page325" id="conver2.page325"> </a> +The left ventricle is the receptacle for the pure arterial blood +previous to its circulation; whilst the venous, or impure blood, which +returns to the heart after having circulated, is received into the right +ventricle, previous to its purification, which I shall presently +explain.</p> + +<p class="speaker">CAROLINE.</p> + +<p>For my part, I always thought that the same blood circulated again +and again through the body, without undergoing any change.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yet you must have supposed that the blood circulated for some +purpose?</p> + +<p class="speaker">CAROLINE.</p> + +<p>I knew that it was indispensable to life; but had no idea of its real +functions.</p> + +<p class="speaker">MRS. B.</p> + +<p>But now that you understand that the blood conveys nourishment to +every part of the body, and supplies the various secretions, you must be +sensible that it cannot constantly answer these objects without being +proportionally renovated and purified.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But does not the chyle answer this purpose?</p> + +<span class="pagenum">326</span> +<a name="conver2.page326" id="conver2.page326"> </a> +<p class="speaker">MRS. B.</p> + +<p>Only in part. It renovates the nutritive principles of the blood, but +does not relieve it from the superabundance of water and carbon with +which it is encumbered.</p> + +<p class="speaker">EMILY.</p> + +<p>How, then, is this effected?</p> + +<p class="speaker">MRS. B.</p> + +<p>By <span class="smallroman">RESPIRATION</span>. This is one of the +grand mysteries which modern chemistry has disclosed. When the venous +blood enters the right ventricle of the heart, it contracts by its +muscular power, and throws the blood through a large vessel into the +lungs, which are contiguous, and through which it circulates by millions +of small ramifications. Here it comes in contact with the air which we +breathe. The action of the air on the blood in the lungs is, indeed, +concealed, from our immediate observation; but we are able to form a +tolerably accurate judgment of it from the changes which it effects not +only in the blood, but also on the air expired.</p> + +<p>The air, after passing through the lungs, is found to contain all the +nitrogen inspired, but to have lost part of its oxygen, and to have +acquired a portion of watery vapour and of carbonic acid gas. Hence it +is inferred, that when the air comes +<span class="pagenum">327</span> +<a name="conver2.page327" id="conver2.page327"> </a> +in contact with the venous blood in the lungs, the oxygen attracts from +it the superabundant quantity of carbon with which it has impregnated +itself during the circulation, and converts it into carbonic acid. This +gaseous acid, together with the redundant moisture from the lungs<a +class="tag" name="tag26" id="tag26" href="#note26">*</a>, being +then expired, the blood is restored to its former purity, that is, to +the state of arterial blood, and is thus again enabled to perform its +various functions.</p> + +<p class="speaker">CAROLINE.</p> + +<p>This is truly wonderful! Of all that we have yet learned, I do +not recollect any thing that has appeared to me so curious and +interesting. I almost believe that I should like to study anatomy +now, though I have hitherto had so disgusting an idea of it. Pray, to +whom are we indebted for these beautiful discoveries?</p> + +<p class="speaker">MRS. B.</p> + +<p>Priestley and Crawford, in this country, and Lavoisier, in France, +are the principal inventors of the theory of respiration. Of late years +the subject has been farther illustrated and simplified by the accurate +experiments of Messrs. Allen and Pepys. But the still more important and +more +<span class="pagenum">328</span> +<a name="conver2.page328" id="conver2.page328"> </a> +admirable discovery of the circulation of the blood was made long before +by our immortal countryman Harvey.</p> + +<p class="speaker">EMILY.</p> + +<p>Indeed I never heard any thing that delighted me so much as this +theory of respiration. But I hope, Mrs. B., that you will enter a +little more into particulars before you dismiss so interesting a +subject. We left the blood in the lungs to undergo the salutary change: +but how does it thence spread to all the parts of the body?</p> + +<p class="speaker">MRS. B.</p> + +<p>After circulating through the lungs, the blood is collected into four +large vessels, by which it is conveyed into the left ventricle of the +heart, whence it is propelled to all the different parts of the body by +a large artery, which gradually ramifies into millions of small arteries +through the whole frame. From the extremities of these little +ramifications the blood is transmitted to the veins, which bring it back +to the heart and lungs, to go round again and again in the manner we +have just described. You see, therefore, that the blood actually +undergoes two circulations; the one, through the lungs, by which it is +converted into pure arterial blood; the other, or general circulation, +by which nourishment is conveyed to every part of the +<span class="pagenum">329</span> +<a name="conver2.page329" id="conver2.page329"> </a> +body; and these are both equally indispensable to the support of animal +life.</p> + +<p class="speaker">EMILY.</p> + +<p>But whence proceeds the carbon with which the blood is impregnated +when it comes into the lungs?</p> + +<p class="speaker">MRS. B.</p> + +<p>Carbon exists in a greater proportion in blood than in organised +animal matter. The blood, therefore, after supplying its various +secretions, becomes loaded with an excess of carbon, which is carried +off by respiration; and the formation of new chyle from the food affords +a constant supply of carbonaceous matter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I wonder what quantity of carbon may be expelled from the blood by +respiration in the course of 24 hours?</p> + +<p class="speaker">MRS. B.</p> + +<p>It appears by the experiments of Messrs. Allen and Pepys that about +40,000 cubic inches of carbonic acid gas are emitted from the lungs of a +healthy person, daily; which is equivalent to <i>eleven ounces</i> of +solid carbon every 24 hours.</p> + +<p class="speaker">EMILY.</p> + +<p>What an immense quantity! And pray how +<span class="pagenum">330</span> +<a name="conver2.page330" id="conver2.page330"> </a> +much of carbonic acid gas do we expel from our lungs at each +expiration?</p> + +<p class="speaker">MRS. B.</p> + +<p>The quantity of air which we take into our lungs at each inspiration, +is about 40 cubic inches, which contain a little less than 10 cubic +inches of oxygen; and of those 10 inches, one-eighth is converted into +carbonic acid gas on passing once through the lungs<a class="tag" name="tag27" id="tag27" href="#note27">*</a>, a change which is +sufficient to prevent air which has only been breathed once from +suffering a taper to burn in it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Pray, how does the air come in contact with the blood in the +lungs?</p> + +<p class="speaker">MRS. B.</p> + +<p>I cannot answer this question without entering into an explanation of +the nature and structure of the lungs. You recollect that the venous +blood, on being expelled from the right ventricle, enters the lungs to +go through what we may call the lesser circulation; the large trunk or +vessel that conveys it branches out, at its entrance into the lungs, +into an infinite number of very fine ramifications. +<span class="pagenum">331</span> +<a name="conver2.page331" id="conver2.page331"> </a> +The windpipe, which conveys the air from the mouth into the lungs, +likewise spreads out into a corresponding number of air vessels, which +follow the same course as the blood vessels, forming millions of very +minute air-cells. These two sets of vessels are so interwoven as to form +a sort of net-work, connected into a kind of spongy mass, in which every +particle of blood must necessarily come in contact with a particle of +air.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But since the blood and the air are contained in different vessels, +how can they come into contact?</p> + +<p class="speaker">MRS. B.</p> + +<p>They act on each other through the membrane which forms the coats of +these vessels; for although this membrane prevents the blood and the air +from mixing together in the lungs, yet it is no impediment to their +chemical action on each other.</p> + +<p class="speaker">EMILY.</p> + +<p>Are the lungs composed entirely of blood vessels and air vessels?</p> + +<p class="speaker">MRS. B.</p> + +<p>I believe they are, with the addition only of nerves and of a small +quantity of the cellular substance before mentioned, which connects the +whole into an uniform mass.</p> + +<span class="pagenum">332</span> +<a name="conver2.page332" id="conver2.page332"> </a> +<p class="speaker">EMILY.</p> + +<p>Pray, why are the lungs always spoken of in the plural number? Are +there more than one?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; for though they form but one organ, they really consist of two +compartments called lobes, which are enclosed in separate membranes or +bags, each occupying one side of the chest, and being in close contact +with each other, but without communicating together. This is a beautiful +provision of nature, in consequence of which, if one of the lobes be +wounded, the other performs the whole process of respiration till the +first is healed.</p> + +<p>The blood, thus completed, by the process of respiration, forms the +most complex of all animal compounds, since it contains not only the +numerous materials necessary to form the various secretions, as saliva, +tears, &c. but likewise all those that are required to nourish the +several parts of the body, as the muscles, bones, nerves, +glands, &c.</p> + +<p class="speaker">EMILY.</p> + +<p>There seems to be a singular analogy between the blood of animals and +the sap of vegetables; for each of these fluids contains the several +materials destined for the nutrition of the numerous class of bodies to +which they respectively belong.</p> + +<span class="pagenum">333</span> +<a name="conver2.page333" id="conver2.page333"> </a> +<p class="speaker">MRS. B.</p> + +<p>Nor is the production of these fluids in the animal and vegetable +systems entirely different; for the absorbent vessels, which pump up the +chyle from the stomach and intestines, may be compared to the absorbents +of the roots of plants, which suck up the nourishment from the soil. And +the analogy between the sap and the blood may be still further traced, +if we follow the latter in the course of its circulation; for, in the +living animal, we find every where organs which are possessed of a power +to secrete from the blood and appropriate to themselves the ingredients +requisite for their support.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But whence do these organs derive their respective powers?</p> + +<p class="speaker">MRS. B.</p> + +<p>From a peculiar organisation, the secret of which no one has yet been +able to unfold. But it must be ultimately by means of the vital +principle that both their mechanical and chemical powers are brought +into action.</p> + +<p>I cannot dismiss the subject of circulation without mentioning +<i>perspiration</i>, a secretion which is immediately connected +with it, and acts a most important part in the animal economy.</p> + +<span class="pagenum">334</span> +<a name="conver2.page334" id="conver2.page334"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Is not this secretion likewise made by appropriate glands?</p> + +<p class="speaker">MRS. B.</p> + +<p>No; it is performed by the extremities of the arteries, which +penetrate through the skin and terminate under the cuticle, through the +pores of which the perspiration issues. When this fluid is not secreted +in excess, it is <i>insensible</i>, because it is dissolved by the air +as it exudes from the pores; but when it is secreted faster than it can +be dissolved, it becomes <i>sensible</i>, as it assumes its liquid +state.</p> + +<p class="speaker">EMILY.</p> + +<p>This secretion bears a striking resemblance to the transpiration of +the sap of plants. They both consist of the most fluid part, and both +exude from the surface by the extremities of the vessels through which +they circulate.</p> + +<p class="speaker">MRS. B.</p> + +<p>And the analogy does not stop there; for, since it has been +ascertained that the sap returns into the roots of the plants, the +resemblance between the animal and vegetable circulation is become still +more obvious. The latter, however, is far from being complete, since, as +we observed before, it consists only in a rising and descending of +<span class="pagenum">335</span> +<a name="conver2.page335" id="conver2.page335"> </a> +the sap, whilst in animals the blood actually <i>circulates</i> through +every part of the system.</p> + +<p>We have now, I think, traced the process of nutrition, from the +introduction of the food into the stomach to its finally becoming a +constituent part of the animal frame. This will, therefore, be a fit +period to conclude our present conversation. What further remarks we +have to make on the animal economy shall be reserved for our next +interview.</p> + +<div class="footnote"> + +<p><a name="note26" id="note26" href="#tag26">*</a> +The quantity of moisture discharged by the lungs in 24 hours, may be +computed at eight or nine ounces.</p> + +<p><a name="note27" id="note27" href="#tag27">*</a> +The bulk of carbonic acid gas formed by respiration, is exactly the same +as that of the oxygen gas which disappears.</p> + +</div> + + +<span class="pagenum">336</span> +<a name="conver2.page336" id="conver2.page336"> </a> +<h4><a name="convXXVI" id="convXXVI">CONVERSATION XXVI.</a><br> +<span class="subhead">ON ANIMAL HEAT; AND ON VARIOUS ANIMAL +PRODUCTS.</span></h4> + +<p class="illustration"> +<img src="images/dec_line.png" width="99" height="8" +alt="----"> +</p> + +<p class="speaker">EMILY.</p> + +<p><span class="firstword"><span class="firstletter">S</span>ince</span> our last interview, I have been +thinking much of the theory of respiration; and I cannot help being +struck with the resemblance which it appears to bear to the process of +combustion. For in respiration, as in most cases of combustion, the air +suffers a change, and a portion of its oxygen combines with carbon, +producing carbonic acid gas.</p> + +<p class="speaker">MRS. B.</p> + +<p>I am much pleased that this idea has occurred to you: these two +processes appear so very analogous, that it has been supposed that a +kind of combustion actually takes place in the lungs; not +<span class="pagenum">337</span> +<a name="conver2.page337" id="conver2.page337"> </a> +of the blood, but of the superfluous carbon which the oxygen attracts +from it.</p> + +<p class="speaker">CAROLINE.</p> + +<p>A combustion in our lungs! that is a curious idea indeed! But, +Mrs. B., how can you call the action of the air on the blood in the +lungs combustion, when neither light nor heat are produced +by it?</p> + +<p class="speaker">EMILY.</p> + +<p>I was going to make the same objection.—Yet I do not conceive +how the oxygen can combine with the carbon, and produce carbonic acid, +without disengaging heat?</p> + +<p class="speaker">MRS. B.</p> + +<p>The fact is, that heat is disengaged.<a class="tag" name="tag28" +id="tag28" href="#note28">*</a> Whether any light be evolved, +I cannot pretend to determine; but that heat is produced in +considerable and very sensible quantities is certain, and this is the +principal, if not the only source of <span class="smallroman">ANIMAL +HEAT</span>.</p> + +<p class="speaker">EMILY.</p> + +<p>How wonderful! that the very process which purifies and elaborates +the blood, should afford an inexhaustible supply of internal heat?</p> + +<span class="pagenum">338</span> +<a name="conver2.page338" id="conver2.page338"> </a> +<p class="speaker">MRS. B.</p> + +<p>This is the theory of animal heat in its original simplicity, such +nearly as it was first proposed by Black and Lavoisier. It was equally +clear and ingenious; and was at first generally adopted. But it was +objected, on second consideration, that if the whole of the animal heat +was evolved in the lungs, it would necessarily be much less in the +extremities of the body than immediately at its source; which is not +found to be the case. This objection, however, which was by no means +frivolous, is now satisfactorily removed by the following +consideration:—Venous blood has been found by experiment to have +<i>less capacity for heat</i> than arterial blood; whence it follows +that the blood, in gradually passing from the arterial to the venous +state, during the circulation, parts with a portion of caloric, by means +of which heat is diffused through every part of the body.</p> + +<p class="speaker">EMILY.</p> + +<p>More and more admirable!</p> + +<p class="speaker">CAROLINE.</p> + +<p>The cause of animal heat was always a perfect mystery to me, and I am +delighted with its explanation.—But pray, Mrs. B., can you +tell me what is the reason of the increase of heat that takes place in a +fever?</p> + +<span class="pagenum">339</span> +<a name="conver2.page339" id="conver2.page339"> </a> +<p class="speaker">EMILY.</p> + +<p>Is it not because we then breathe quicker, and therefore more heat is +disengaged in the system?</p> + +<p class="speaker">MRS. B.</p> + +<p>That may be one reason: but I should think that the principal cause +of the heat experienced in fevers, is, that there is no vent for the +caloric which is generated in the body. One of the most considerable +secretions is the insensible perspiration; this is constantly carrying +off caloric in a latent state; but during the hot stage of a fever, the +pores are so contracted, that all perspiration ceases, and the +accumulation of caloric in the body occasions those burning sensations +which are so painful.</p> + +<p class="speaker">EMILY.</p> + +<p>This is, no doubt, the reason why the perspiration that often +succeeds the hot stage of a fever affords so much relief. If I had known +this theory of animal heat when I had a fever last summer, I think +I should have found some amusement in watching the chemical processes +that were going on within me.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But exercise likewise produces animal heat, and that must be quite in +a different manner.</p> + +<span class="pagenum">340</span> +<a name="conver2.page340" id="conver2.page340"> </a> +<p class="speaker">MRS. B.</p> + +<p>Not so much so as you think; for the more exercise you take, the more +the body is stimulated, and requires recruiting. For this purpose the +circulation of the blood is quickened, the breath proportionably +accelerated, and consequently a greater quantity of caloric evolved.</p> + +<p class="speaker">CAROLINE.</p> + +<p>True; after running very fast, I gasp for breath, my respiration is +quick and hard, and it is just then that I begin to feel hot.</p> + +<p class="speaker">EMILY.</p> + +<p>It would seem, then, that violent exercise should produce fever.</p> + +<p class="speaker">MRS. B.</p> + +<p>Not if the person is in a good state of health; for the additional +caloric is then carried off by the perspiration which succeeds.</p> + +<p class="speaker">EMILY.</p> + +<p>What admirable resources nature has provided for us! By the +production of animal heat she has enabled us to keep up the temperature +of our bodies above that of inanimate objects; and whenever this source +becomes too abundant, the excess is carried off by perspiration.</p> + +<span class="pagenum">341</span> +<a name="conver2.page341" id="conver2.page341"> </a> +<p class="speaker">MRS. B.</p> + +<p>It is by the same law of nature that we are enabled, in all climates, +and in all seasons, to preserve our bodies of an equal temperature, or +at least very nearly so.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You cannot mean to say that our bodies are of the same temperature in +summer, and in winter, in England, and in the West-Indies.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes, I do; at least if you speak of the temperature of the blood, and +the internal parts of the body; for those parts that are immediately in +contact with the atmosphere, such as the hands and face, will +occasionally get warmer, or colder, than the internal or more sheltered +parts. But if you put the bulb of a thermometer in your mouth, which is +the best way of ascertaining the real temperature of your body, you will +scarcely perceive any difference in its indication, whatever may be the +difference of temperature of the atmosphere.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And when I feel overcome by heat, I am really not hotter than when I +am shivering with cold?</p> + +<span class="pagenum">342</span> +<a name="conver2.page342" id="conver2.page342"> </a> +<p class="speaker">MRS. B.</p> + +<p>When a person in health feels very hot, whether from internal heat, +from violent exercise, or from the temperature of the atmosphere, his +body is certainly a little warmer than when he feels very cold; but this +difference is much smaller than our sensations would make us believe; +and the natural standard is soon restored by rest and by perspiration. +It is chiefly the external parts that are warmer, and I am sure that you +will be surprised to hear that the internal temperature of the body +scarcely ever descends below ninety-five or ninety-six degrees, and +seldom attains one hundred and four or one hundred and five degrees, +even in the most violent fevers.</p> + +<p class="speaker">EMILY.</p> + +<p>The greater quantity of caloric, therefore, that we receive from the +atmosphere in summer, cannot raise the temperature of our bodies beyond +certain limits, as it does that of inanimate bodies, because an excess +of caloric is carried off by perspiration.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the temperature of the atmosphere, and consequently that of +inanimate bodies, is surely never so high as that of animal heat?</p> + +<span class="pagenum">343</span> +<a name="conver2.page343" id="conver2.page343"> </a> +<p class="speaker">MRS. B.</p> + +<p>I beg your pardon. Frequently in the East and West Indies, and +sometimes in the southern parts of Europe, the atmosphere is above +ninety-eight degrees, which is the common temperature of animal heat. +Indeed, even in this country, it occasionally happens that the sun’s +rays, setting full on an object, elevate its temperature above that +point.</p> + +<p>In illustration of the power which our bodies have to resist the +effects of external heat, Sir Charles Blagden, with some other +gentlemen, made several very curious experiments. He remained for some +time in an oven heated to a temperature not much inferior to that of +boiling water, without suffering any other inconvenience than a profuse +perspiration, which he supported by drinking plentifully.</p> + +<p class="speaker">EMILY.</p> + +<p>He could scarcely consider the perspiration as an inconvenience, +since it saved him from being baked by giving vent to the excess of +caloric.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I always thought, I confess, that it was from the heat of the +perspiration that we suffered in summer.</p> + +<span class="pagenum">344</span> +<a name="conver2.page344" id="conver2.page344"> </a> +<p class="speaker">MRS. B.</p> + +<p>You now find that you are quite mistaken. Whenever evaporation takes +place, cold, you know, is produced in consequence of a quantity of +caloric being carried off in a latent state; this is the case with +perspiration, and it is in this way that it affords relief. It is on +that account also that we are so apt to <i>catch cold</i>, when in a +state of profuse perspiration. It is for the same reason that tea is +often refreshing in summer, though it appears to heat you at the moment +you drink it.</p> + +<p class="speaker">EMILY.</p> + +<p>And in winter, on the contrary, tea is pleasant on account of its +heat.</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; for we have then rather to guard against a deficiency than an +excess of caloric, and you do not find that tea will excite perspiration +in winter, unless after dancing, or any other violent exercise.</p> + +<p class="speaker">CAROLINE.</p> + +<p>What is the reason that it is dangerous to eat ice after dancing, or +to drink any thing cold when one is very hot?</p> + +<span class="pagenum">345</span> +<a name="conver2.page345" id="conver2.page345"> </a> +<p class="speaker">MRS. B.</p> + +<p>Because the loss of heat arising from the perspiration, conjointly +with the chill occasioned by the cold draught, produce more cold than +can be borne with safety, unless you continue to use the same exercise +after drinking that you did before; for the heat occasioned by the +exercise will counteract the effects of the cold drink, and the danger +will be removed. You may, however, contrary to the common notion, +consider it as a rule, that cold liquids may, at all times, be drunk +with perfect safety, however hot you may feel, provided you are not at +the moment in a state of great perspiration, and on condition that you +keep yourself in gentle exercise afterwards.</p> + +<p class="speaker">EMILY.</p> + +<p>But since we are furnished with such resources against the extremes +of heat or cold, I should have thought that all climates would have +been equally wholesome.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is true, in a certain degree, with regard to those who have been +accustomed to them from birth; for we find that the natives of those +climates, which we consider as most deleterious, are as healthy as +ourselves; and if such climates are unwholesome to those who are +habituated to a +<span class="pagenum">346</span> +<a name="conver2.page346" id="conver2.page346"> </a> +more moderate temperature, it is because the animal economy does not +easily accustom itself to considerable changes.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But pray, Mrs. B., if the circulation preserves the body of an +uniform temperature, how does it happen that animals are sometimes +frozen?</p> + +<p class="speaker">MRS. B.</p> + +<p>Because, if more heat be carried off by the atmosphere than the +circulation can supply, the cold will finally prevail, the heart will +cease to beat, and the animal will be frozen. And, likewise, if the body +remained long exposed to a degree of heat, greater than the perspiration +could carry off, it would at last lose the power of resisting its +destructive influence.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Fish, I suppose, have no animal heat, but only partake of the +temperature of the water in which they live?</p> + +<p class="speaker">EMILY.</p> + +<p>And their coldness, no doubt, proceeds from their not breathing?</p> + +<p class="speaker">MRS. B.</p> + +<p>All kinds of fish breathe more or less, though +<span class="pagenum">347</span> +<a name="conver2.page347" id="conver2.page347"> </a> +in a much smaller degree than land animals. Nor are they entirely +destitute of animal heat, though, for the same reason, they are much +colder than other creatures. They have comparatively but a very small +quantity of blood, therefore but very little oxygen is required, and a +proportionally small quantity of animal heat is generated.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But how can fish breathe under water?</p> + +<p class="speaker">MRS. B.</p> + +<p>They breathe by means of the air which is dissolved in the water, and +if you put them into water deprived of air by boiling, they are soon +suffocated.</p> + +<p>If a fish is confined in a vessel of water closed from the air, it +soon dies; and any fish put in afterwards would be killed immediately, +as all the air had been <ins class="mycorr" title="text reads +‘previouly’">previously</ins> consumed.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Are there any species of animals that breathe more than +we do?</p> + +<p class="speaker">MRS. B.</p> + +<p>Yes; birds, of all animals, breathe the greatest quantity of air in +proportion to their size; and it +<span class="pagenum">348</span> +<a name="conver2.page348" id="conver2.page348"> </a> +is to this that they are supposed to owe the peculiar firmness and +strength of their muscles, by which they are enabled to support the +violent exertion of flying.</p> + +<p>This difference between birds and fish, which may be considered as +the two extremes of the scale of muscular strength, is well worth +observing. Birds residing constantly in the atmosphere, surrounded by +oxygen, and respiring it in greater proportions than any other species +of animals, are endowed with a superior degree of muscular strength, +whilst the muscles of fish, on the contrary, are flaccid and oily; these +animals are comparatively feeble in their motions, and their temperature +is scarcely above that of the water in which they live. This is, in all +probability, owing to their imperfect respiration; the quantity of +hydrogen and carbon, that is in consequence accumulated in their bodies, +forms the oil which is so strongly characteristic of that species of +animals, and which relaxes and softens the small quantity of fibrine +which their muscles contain.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, Mrs. B., there are some species of birds that frequent both +elements, as, for instance, ducks and other water fowl. Of what nature +is the flesh of these?</p> + +<span class="pagenum">349</span> +<a name="conver2.page349" id="conver2.page349"> </a> +<p class="speaker">MRS. B.</p> + +<p>Such birds, in general, make but little use of their wings; if they +fly, it is but feebly, and only to a short distance. Their flesh, too, +partakes of the oily nature, and even in taste sometimes resembles that +of fish. This is the case not only with the various kinds of water +fowls, but with all other amphibious animals, as the otter, the +crocodile, the lizard, &c.</p> + +<p class="speaker">CAROLINE.</p> + +<p>And what is the reason that reptiles are so deficient in muscular +strength?</p> + +<p class="speaker">MRS. B.</p> + +<p>It is because they usually live under ground, and seldom come into +the atmosphere. They have imperfect, and sometimes no discernible organs +of respiration; they partake therefore of the soft oily nature of fish; +indeed, many of them are amphibious, as frogs, toads, and snakes, and +very few of them find any difficulty in remaining a length of time under +water. Whilst, on the contrary, the insect tribe, that are so strong in +proportion to their size, and alert in their motions, partake of the +nature of birds, air being their peculiar element, and their organs of +respiration being comparatively larger than in other classes of +animals.</p> + +<span class="pagenum">350</span> +<a name="conver2.page350" id="conver2.page350"> </a> +<p>I have now given you a short account of the principal animal +functions. However interesting the subject may appear to you, +a fuller investigation of it would, I fear, lead us too far +from our object.</p> + +<p class="speaker">EMILY.</p> + +<p>Yet I shall not quit it without much regret; for of all the branches +of chemistry, it is certainly the most curious and most interesting.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But, Mrs. B., I must remind you that you promised to give us +some account of the nature of <i>milk</i>.</p> + +<p class="speaker">MRS. B.</p> + +<p>True. There are several other animal productions that deserve +likewise to be mentioned. We shall begin with milk, which is certainly +the most important and the most interesting of all the animal +secretions.</p> + +<p>Milk, like all other animal substances, ultimately yields by analysis +oxygen, hydrogen, carbon, and nitrogen. These are combined in it under +the forms of albumen, gelatine, oil, and water. But milk contains, +besides, a considerable portion of phosphat of lime, the purposes +of which I have already pointed out.</p> + +<span class="pagenum">351</span> +<a name="conver2.page351" id="conver2.page351"> </a> +<p class="speaker">CAROLINE.</p> + +<p>Yes; it is this salt which serves to nourish the tender bones of the +suckling.</p> + +<p class="speaker">MRS. B.</p> + +<p>To reduce milk to its elements, would be a very complicated, as well +as useless operation; but this fluid, without any chemical assistance, +may be decomposed into three parts, <i>cream</i>, <i>curds</i>, and +<i>whey</i>. These constituents of milk have but a very slight affinity +for each other, and you find accordingly that cream separates from milk +by mere standing. It consists chiefly of oil, which being lighter than +the other parts of the milk, gradually rises to the surface. It is of +this, you know, that butter is made, which is nothing more than +oxygenated cream.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Butter, then, is somewhat analogous to the waxy substance formed by +the oxygenation of vegetable oils.</p> + +<p class="speaker">MRS. B.</p> + +<p>Very much so.</p> + +<p class="speaker">EMILY.</p> + +<p>But is the cream oxygenated by churning?</p> + +<p class="speaker">MRS. B.</p> + +<p>Its oxygenation commences previous to churning, +<span class="pagenum">352</span> +<a name="conver2.page352" id="conver2.page352"> </a> +merely by standing exposed to the atmosphere, from which it absorbs +oxygen. The process is afterwards completed by churning; the violent +motion which this operation occasions brings every particle of cream in +contact with the atmosphere, and thus facilitates its oxygenation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>But the effect of churning, I have often observed in the dairy, is to +separate the cream into two substances, butter and butter-milk.</p> + +<p class="speaker">MRS. B.</p> + +<p>That is to say, in proportion as the oily particles of the cream +become oxygenated, they separate from the other constituent parts of the +cream in the form of butter. So by churning you produce, on the one +hand, butter, or oxygenated oil; and, on the other, butter-milk, or +cream deprived of oil. But if you make butter by churning new milk +instead of cream, the butter-milk will then be exactly similar in its +properties to creamed or skimmed milk.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Yet butter-milk is very different from common skimmed milk.</p> + +<p class="speaker">MRS. B.</p> + +<p>Because you know it is customary, in order to +<span class="pagenum">353</span> +<a name="conver2.page353" id="conver2.page353"> </a> +save time and labour, to make butter from cream alone. In this case, +therefore, the butter-milk is deprived of the creamed milk, which +contains both the curd and whey. Besides, in consequence of the milk +remaining exposed to the atmosphere during the separation of the cream, +the latter becomes more or less acid, as well as the butter-milk which +it yields in churning.</p> + +<p class="speaker">EMILY.</p> + +<p>Why should not the butter be equally acidified by oxygenation?</p> + +<p class="speaker">MRS. B.</p> + +<p>Animal oil is not so easily acidified as the other ingredients of +milk. Butter, therefore, though usually made of sour cream, is not sour +itself, because the oily part of the cream had not been acidified. +Butter, however, is susceptible of becoming acid by an excess of oxygen; +it is then said to be rancid, and produces the sebacic acid, the same as +that which is obtained from fat.</p> + +<p class="speaker">EMILY.</p> + +<p>If that be the case, might not rancid butter be sweetened by mixing +with it some substance that would take the acid from it?</p> + +<p class="speaker">MRS. B.</p> + +<p>This idea has been suggested by Sir H. Davy, +<span class="pagenum">354</span> +<a name="conver2.page354" id="conver2.page354"> </a> +who supposes, that if rancid butter were well washed in an alkaline +solution, the alkali would separate the acid from the butter.</p> + +<p class="speaker">CAROLINE.</p> + +<p>You said just now that creamed milk consisted of curd and whey. Pray +how are these separated?</p> + +<p class="speaker">MRS. B.</p> + +<p>They may be separated by standing for a certain length of time +exposed to the atmosphere; but this decomposition may be almost +instantaneously effected by the chemical agency of a variety of +substances. Alkalies, rennet<a class="tag" name="tag29" id="tag29" +href="#note29">*</a>, and indeed almost all animal substances, +decompose milk by combining with the curds.</p> + +<p>Acids and spirituous liquors, on the other hand, produce a +decomposition by combining with the whey. In order, therefore, to obtain +the whey pure, rennet, or alkaline substances, must be used to attract +the curds from it.</p> + +<p>But if it be wished to obtain the curds pure, the whey must be +separated by acids, wine, or other spirituous liquors.</p> + +<span class="pagenum">355</span> +<a name="conver2.page355" id="conver2.page355"> </a> +<p class="speaker">EMILY.</p> + +<p>This is a very useful piece of information; for I find white-wine +whey, which I sometimes take when I have a cold, extremely heating; now, +if the whey were separated by means of an alkali instead of wine, it +would not produce that effect.</p> + +<p class="speaker">MRS. B.</p> + +<p>Perhaps not. But I would strenuously advise you not to place too much +reliance on your slight chemical knowledge in medical matters. I do +not know why whey is not separated from curd by rennet, or by an alkali, +for the purpose which you mention; but I strongly suspect that there +must be some good reason why the preparation by means of wine is +generally preferred. I can, however, safely point out to you a +method of obtaining whey without either alkali, rennet, or wine; it is +by substituting lemon juice, a very small quantity of which will +separate it from the curds.</p> + +<p>Whey, as an article of diet, is very wholesome, being remarkable +light of digestion. But its effect, taken medicinally, is chiefly, +I believe, to excite perspiration, by being drunk warm on going to +bed.</p> + +<p>From whey a substance may be obtained in crystals by evaporation, +called <i>sugar of milk</i>. This substance is sweet to the taste, and +in its composition is so analogous to common sugar, +<span class="pagenum">356</span> +<a name="conver2.page356" id="conver2.page356"> </a> +that it is susceptible of undergoing the vinous fermentation.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Why then is not wine, or alcohol, made from whey?</p> + +<p class="speaker">MRS. B.</p> + +<p>The quantity of sugar contained in milk is so trifling, that it can +hardly answer that purpose. I have heard of only one instance of +its being used for the production of a spirituous liquor, and this is by +the <ins class="correction" title="error for ‘Tartar’?">Tartan</ins> +Arabs; their abundance of horses, as well as their scarcity of fruits, +has introduced the fermentation of mares’ milk, by which they produce a +liquor called <i>koumiss</i>. Whey is likewise susceptible of being +acidified by combining with oxygen from the atmosphere. It then produces +the <i>lactic acid</i>, which you may recollect is mentioned amongst the +animal acids, as the acid of milk.</p> + +<p>Let us now see what are the properties of curds.</p> + +<p class="speaker">EMILY.</p> + +<p>I know that they are made into cheese; but I have heard that for that +purpose they are separated from the whey by rennet, and yet this you +have just told us is not the method of obtaining pure curds?</p> + +<p class="speaker">MRS. B.</p> + +<p>Nor are pure curds so well adapted for the formation +<span class="pagenum">357</span> +<a name="conver2.page357" id="conver2.page357"> </a> +of cheese. For the nature and flavour of the cheese depend, in a great +measure, upon the cream or oily matter which is left in the curds; so +that if every particle of cream be removed from the curds, the cheese is +scarcely eatable. Rich cheeses, such as cream and Stilton cheeses, +derive their excellence from the quantity, as well as the quality, of +the cream that enters into their composition.</p> + +<p class="speaker">CAROLINE.</p> + +<p>I had no idea that milk was such an interesting compound. In many +respects there appears to me to be a very striking analogy between milk +and the contents of an egg, both in respect to their nature and their +use. They are, each of them, composed of the various substances +necessary for the nourishment of the young animal, and equally destined +for that purpose.</p> + +<p class="speaker">MRS. B.</p> + +<p>There is, however, a very essential difference. The young animal is +formed, as well as nourished, by the contents of the egg-shell; whilst +milk serves as nutriment to the suckling, only after it is born.</p> + + +<p class="space"> +There are several peculiar animal substances which do not enter into the +general enumeration of animal compounds, and which, however, deserve to +be mentioned.</p> + +<span class="pagenum">358</span> +<a name="conver2.page358" id="conver2.page358"> </a> +<p><i>Spermaceti</i> is of this class; it is a kind of oily substance +obtained from the head of the whale, which, however, must undergo a +certain preparation before it is in a fit state to be made into candles. +It is not much more combustible than tallow, but it is pleasanter to +burn, as it is less fusible and less greasy.</p> + +<p><i>Ambergris</i> is another peculiar substance derived from a species +of whale. It is, however, seldom obtained from the animal itself, but is +generally found floating on the surface of the sea.</p> + +<p><i>Wax</i>, you know, is a concrete oil, the peculiar product of the +bee, part of the constituents of which may probably be derived from +flowers, but so prepared by the organs of the bee, and so mixed with its +own substance, as to be decidedly an animal product. Bees’ wax is +naturally of a yellow colour, but it is bleached by long exposure to the +atmosphere, or may be instantaneously whitened by the oxy-muriatic acid. +The combustion of wax is far more perfect than that of tallow, and +consequently produces a greater quantity of light and heat.</p> + +<p><i>Lac</i> is a substance very similar to wax in the manner of its +formation; it is the product of an insect, which collects its +ingredients from flowers, apparently for the purpose of protecting its +eggs from injury. It is formed into cells, fabricated with as much skill +as those of the honey-comb, +<span class="pagenum">359</span> +<a name="conver2.page359" id="conver2.page359"> </a> +but differently arranged. The principal use of lac is in the manufacture +of sealing-wax, and in making varnishes and lacquers.</p> + +<p><i>Musk</i>, <i>civet</i>, and <i>castor</i>, are other particular +productions, from different species of quadrupeds. The two first are +very powerful perfumes; the latter has a nauseous smell and taste, and +is only used medicinally.</p> + +<p class="speaker">CAROLINE.</p> + +<p>Is it from this substance that castor oil is obtained?</p> + +<p class="speaker">MRS. B.</p> + +<p>No. Far from it, for castor oil is a vegetable oil, expressed from +the seeds of a particular plant; and has not the least resemblance to +the medicinal substance obtained from the castor.</p> + +<p><i>Silk</i> is a peculiar secretion of the silk-worm, with which it +builds its nest or cocoon. This insect was originally brought to Europe +from China. Silk, in its chemical nature, is very similar to the hair +and wool of animals; whilst in the insect it is a fluid, which is +coagulated, apparently by uniting with oxygen, as soon as it comes in +contact with the air. The moth of the silk-worm ejects a liquor which +appears to contain a particular acid, called <i>bombic</i>, the +properties of which are but very little known.</p> + +<span class="pagenum">360</span> +<a name="conver2.page360" id="conver2.page360"> </a> +<p class="speaker">EMILY.</p> + +<p>Before we conclude the subject of the animal economy, shall we not +learn by what steps dead animals return to their elementary state?</p> + +<p class="speaker">MRS. B.</p> + +<p>Animal matter, although the most complicated of all natural +substances, returns to its elementary state by one single spontaneous +process, the <i>putrid fermentation</i>. By this, the albumen, fibrine, +&c. are slowly reduced to the state of oxygen, hydrogen, nitrogen, +and carbon; and thus the circle of changes through which these +principles have passed is finally completed. They first quitted their +elementary form, or their combination with unorganised matter, to enter +into the vegetable system. Hence they were transmitted to the animal +kingdom; and from this they return, again to their primitive simplicity, +soon to re-enter the sphere of organised existence.</p> + +<p>When all the circumstances necessary to produce fermentation do not +take place, animal, like vegetable matter, is liable to a partial or +imperfect decomposition, which converts it into a combustible substance +very like spermaceti. I dare say that Caroline, who is so fond of +analogies, will consider this as a kind of animal bitumen.</p> + +<span class="pagenum">361</span> +<a name="conver2.page361" id="conver2.page361"> </a> +<p class="speaker">CAROLINE.</p> + +<p>And why should I not, since the processes which produce these +substances are so similar?</p> + +<p class="speaker">MRS. B.</p> + +<p>There is, however, one considerable difference; the state of bitumen +seems permanent, whilst that of animal substances, thus imperfectly +decomposed, is only transient; and unless precautions be taken to +preserve them in that state, a total dissolution infallibly ensues. +This circumstance, of the occasional conversion of animal matter into a +kind of spermaceti, is of late discovery. A manufacture has in +consequence been established near Bristol, in which, by exposing the +carcases of horses and other animals for a length of time under water, +the muscular parts are converted into this spermaceti-like substance. +The bones afterwards undergo a different process to produce hartshorn, +or, more properly, ammonia, and phosphorus; and the skin is prepared for +leather.</p> + +<p>Thus art contrives to enlarge the sphere of useful purposes, for +which the elements were intended by nature; and the productions of the +several kingdoms are frequently arrested in their course, and variously +modified, by human skill, which compels them to contribute, under new +forms, to the necessities or luxuries of man.</p> + +<p>But all that we enjoy, whether produced by the +<span class="pagenum">362</span> +<a name="conver2.page362" id="conver2.page362"> </a> +spontaneous operations of nature, or the ingenious efforts of art, +proceed alike from the goodness of Providence.—To <span class="smallcaps">God</span> alone man owes the admirable faculties which +enable him to improve and modify the productions of nature, no less than +those productions themselves. In contemplating the works of the +creation, or studying the inventions of art<ins class="mycorr" title="text has ;">, </ins>let us, therefore, never forget the Divine Source +from which they proceed; and thus every acquisition of knowledge will +prove a lesson of piety and virtue.</p> + +<div class="footnote"> + +<p><a name="note28" id="note28" href="#tag28">*</a> +It has been calculated that the heat produced by respiration in 12 +hours, in the lungs of a healthy person, is such as would melt about 100 +pounds of ice.</p> + +<p><a name="note29" id="note29" href="#tag29">*</a> +Rennet is the name given to a watery infusion of the coats of the +stomach of a sucking calf. Its remarkable efficacy in promoting +coagulation is supposed to depend on the gastric juice with which it is +impregnated.</p> + +</div> + +<h5>END.</h5> + + +</div> <!-- end div maintext --> + + +<h6>Printed by A. Strahan,<br> +Printers-Street, London.</h6> + +<div class="endnote"> +<pre> _Diagram from Conversation XIII_ + + + <i>Original Compound</i> + Sulphat of Soda. + + Soda 8 Sulphuric Acid + + | + | <i>Quies-</i> + | + | <i>cent</i> + | + <i>Result</i> <i>Result</i> + Nitrat <i>Divellent Attractions</i> 6} 13 Sulphat + of Soda of Lime + | + | + | <i>Attrac-</i> + | + | <i>tions</i> + | + + Nitric Acid 4 Lime + -- + 12 + + <i>Original Compound</i> + Nitrat of Lime. +</pre> +</div> + +<hr><hr> + +<div class="index"> + +<span class="pagenum left">363</span> +<a name="page363" id="page363"> </a> + +<h3><a name="index" id="index">INDEX.</a></h3> + +<hr class="thin"> +<hr class="fat"> + +<div class="mynote"> +<p>Index links lead only to the top of the page, not to the exact item +referenced. Some browsers may not display page numbers correctly. If a +link seems to lead to the wrong page, the link is right and the visible +page number is wrong.</p> + +<p class="center"> +<a href="#indexA"> A </a> +<a href="#indexB"> B </a> +<a href="#indexC"> C </a> +<a href="#indexD"> D </a> +<a href="#indexE"> E </a> +<a href="#indexF"> F </a> +<a href="#indexG"> G </a> +<a href="#indexH"> H </a> +<a href="#indexI"> IJ </a> +<a href="#indexK"> K </a> +<br> +<a href="#indexL"> L </a> +<a href="#indexM"> M </a> +<a href="#indexN"> N </a> +<a href="#indexO"> O </a> +<a href="#indexP"> P </a> +<a href="#indexQ"> Q </a> +<a href="#indexR"> R </a> +<a href="#indexS"> S </a> +<a href="#indexT"> T </a> +<a href="#indexV"> V </a> +<a href="#indexU"> U </a> +<a href="#indexW"> W </a> +<a href="#indexY"> Y </a> +<a href="#indexZ"> Z </a> +</p> + +<p>U, V are alphabetized as shown. J is not separated from I.</p> +</div> + +<table summary="index"> +<tr> +<td width="50%"> +<p class="letterhead"><a name="indexA" id="indexA">A</a></p> + +<p><span class="firstword"> +<span class="firstletter">A</span>bsorbent </span>vessels, <a href="#conver2.pagepage304">ii. 304</a></p> + +<p>Absorption of caloric, <a href="#conver1.pagepage59">i. 59</a>. +<a href="#conver1.pagepage66">66</a></p> + +<p>Acetic acid, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Acetous fermentation, <a href="#conver2.pagepage232">ii. +232</a></p> + +<p>—— acid, <a href="#conver2.pagepage193">ii. 193</a>. +<a href="#conver2.pagepage232">232</a></p> + +<p>Acidulous gaseous mineral waters, <a href="#conver2.pagepage129">ii. 129</a></p> + +<p>—— salts, <a href="#conver2.pagepage200">ii. +200</a></p> + +<p>Acids, <a href="#conver1.pagepage262">i. 262</a>. <a href="#conver2.pagepage69">ii. 69</a></p> + +<p>Aeriform, <a href="#conver1.pagepage36">i. 36</a></p> + +<p>Affinity, <a href="#conver1.pagepage19">i. 19</a>. <a href="#conver2.pagepage1">ii. 1</a></p> + +<p>Agate, <a href="#conver2.pagepage51">ii. 51</a></p> + +<p>Agriculture, <a href="#conver2.pagepage252">ii. 252</a></p> + +<p>Air, <a href="#conver1.pagepage182">i. 182</a>. <a href="#conver2.pagepage262">ii. 262</a></p> + +<p>Albumen, <a href="#conver2.pagepage277">ii. 277</a>. +<a href="#conver2.pagepage288">288</a></p> + +<p>Alburnum, <a href="#conver2.pagepage267">ii. 267</a></p> + +<p>Alchemists, <a href="#conver1.pagepage4">i. 4</a></p> + +<p>Alcohol, or spirit of wine, <a href="#conver2.pagepage215">ii. 215</a>. +<a href="#conver2.pagepage222">222</a></p> + +<p>Alembic, <a href="#conver1.pagepage258">i. 258</a></p> + +<p>Alkalies, <a href="#conver2.pagepage19">ii. 19</a></p> + +<p>Alkaline earths, <a href="#conver2.pagepage50">ii. 50</a>. +<a href="#conver2.pagepage58">58</a></p> + +<p>Alloys, <a href="#conver1.pagepage344">i. 344</a></p> + +<p>Alum, or sulphat of alumine, <a href="#conver2.pagepage55">ii. 55</a>. +<a href="#conver2.pagepage95">95</a></p> + +<p>Alumine, <a href="#conver2.pagepage54">ii. 54</a></p> + +<p>Alumium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Amalgam, <a href="#conver1.pagepage347">i. 347</a></p> + +<p>Ambergris, <a href="#conver2.pagepage358">ii. 358</a></p> + +<p>Amethyst, <a href="#conver2.pagepage58">ii. 58</a></p> + +<p>Amianthus, <a href="#conver2.pagepage66">ii. 66</a></p> + +<p>Ammonia, or volatile alkali, <a href="#conver1.pagepage363">i. 363</a>. <a href="#conver2.pagepage20">ii. 20</a>. +<a href="#conver1.pagepage35">35</a></p> + +<p>Ammoniacal gas, <a href="#conver2.pagepage36">ii. 36</a></p> + +<p>Ammonium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Analysis, <a href="#conver1.pagepage287">i. 287</a></p> + +<p>—— of vegetables, <a href="#conver2.pagepage165">ii. +165</a></p> + +<p>Animals, <a href="#conver2.pagepage276">ii. 276</a></p> + +<p>Animal acids, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage290">290</a></p> + +<p>—— colours, <a href="#conver2.pagepage292">ii. +292</a></p> + +<p>—— heat, <a href="#conver2.pagepage337">ii. 337</a></p> + +<p>—— oil, <a href="#conver2.pagepage178">ii. 178</a>. +<a href="#conver2.pagepage283">283</a></p> + +<p>Animalization, <a href="#conver2.pagepage276">ii. 276</a>. +<a href="#conver2.pagepage297">297</a>. +<a href="#conver2.pagepage315">315</a></p> + +<p>Antidotes, <a href="#conver2.pagepage41">ii. 41</a>. +<a href="#conver2.pagepage87">87</a></p> + +<p>Antimony, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Aqua fortis, <a href="#conver2.pagepage105">ii. 105</a></p> + +<p>—— regia, <a href="#conver1.pagepage340">i. 340</a>. +<a href="#conver2.pagepage144">ii. 144</a></p> + +<p><ins class="mycorr" title="body text has ‘arack’">Arrack</ins>, +<a href="#conver2.pagepage220">ii. 220</a></p> + +<p>Argand’s Lamp, <a href="#conver1.pagepage208">i. 208</a></p> + +<p>Arsenic, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage340">340</a>. +<a href="#conver1.pagepage348">348</a></p> + +<p>Arteries, <a href="#conver2.pagepage304">ii. 304</a>. +<a href="#conver2.pagepage323">323</a></p> + +<p>Arterial blood, <a href="#conver2.pagepage305">ii. 305</a>. +<a href="#conver2.pagepage326">326</a>. +<a href="#conver2.pagepage338">338</a></p> + +<p>Asphaltum, <a href="#conver2.pagepage240">ii. 240</a></p> + +<p>Assafœtida, <a href="#conver2.pagepage188">ii. 188</a></p> + +<p>Assimilation, <a href="#conver2.pagepage298">ii. 298</a></p> + +<p>Astringent principle, <a href="#conver2.pagepage198">ii. +198</a></p> + +<p>Atmosphere, <a href="#conver1.pagepage90">i. 90</a>. +<a href="#conver1.pagepage181">181</a>. <a href="#conver2.pagepage262">ii. 262</a></p> + +<p>Atmospherical air, <a href="#conver1.pagepage182">i. 182</a></p> + +<p>Attraction of aggregation, or cohesion, <a href="#conver1.pagepage16">i. 16</a>. <a href="#conver2.pagepage2">ii. 2</a></p> + +<span class="pagenum left">364</span> +<a name="page364" id="page364"> </a> +<p>—— of composition, <a href="#conver1.pagepage16">i. 16</a>. <a href="#conver2.pagepage1">ii. 1</a></p> + +<p>Azot, or nitrogen, <a href="#conver1.pagepage182">i. 182</a>, +<a href="#conver2.pagepage100">ii. 100</a></p> + +<p>Azotic gas, <a href="#conver1.pagepage182">i. 182</a></p> + + +<p class="letterhead"><a name="indexB" id="indexB">B</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Balsams, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage188">188</a></p> + +<p>Balloons, <a href="#conver1.pagepage245">i. 245</a></p> + +<p>Bark, <a href="#conver2.pagepage193">ii. 193</a>. +<a href="#conver2.pagepage265">265</a></p> + +<p>Barytes, <a href="#conver2.pagepage44">ii. 44</a>. +<a href="#conver2.pagepage58">58</a>. +<a href="#conver2.pagepage61">61</a></p> + +<p>Bases of acids, <a href="#conver1.pagepage263">i. 263</a>. +<a href="#conver2.pagepage69">ii. 69</a></p> + +<p>—— gases, <a href="#conver1.pagepage183">i. 183</a></p> + +<p>—— salts, <a href="#conver2.pagepage5">ii. 5</a></p> + +<p>Beer, <a href="#conver2.pagepage212">ii. 212</a>. +<a href="#conver2.pagepage220">220</a></p> + +<p>Benzoic acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Bile, <a href="#conver2.pagepage308">ii. 308</a></p> + +<p>Birds, <a href="#conver2.pagepage347">ii. 347</a></p> + +<p>Bismuth, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Bitumens, <a href="#conver2.pagepage239">ii. 239</a></p> + +<p>Black lead, or plumbago, <a href="#conver1.pagepage304">i. 304</a></p> + +<p>Bleaching, <a href="#conver1.pagepage32">i. 32</a>. <a href="#conver2.pagepage89">ii. 89</a>. +<a href="#conver1.pagepage140">140</a>.</p> + +<p>Blow-pipe, <a href="#conver1.pagepage324">i. 324</a>. <a href="#conver2.pagepage226">ii. 226</a></p> + +<p>Blood, <a href="#conver2.pagepage306">ii. 306</a>. +<a href="#conver2.pagepage317">317</a></p> + +<p>Blood-vessels, <a href="#conver2.pagepage298">ii. 298</a></p> + +<p>Boiling water, <a href="#conver1.pagepage93">i. 93</a></p> + +<p>Bombic acid, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage290">290</a></p> + +<p>Bones, <a href="#conver2.pagepage298">ii. 298, 299</a></p> + +<p>Boracic acid, <a href="#conver1.pagepage365">i. 365</a>. <a href="#conver2.pagepage131">ii. 131</a></p> + +<p>Boracium, <a href="#conver1.pagepage13">i. 13</a>. <a href="#conver2.pagepage132">ii. 132</a></p> + +<p>Borat of soda, <a href="#conver2.pagepage133">ii. 133</a></p> + +<p>Brandy, <a href="#conver2.pagepage218">ii. 218</a></p> + +<p>Brass, <a href="#conver1.pagepage344">i. 344</a></p> + +<p>Bread, <a href="#conver2.pagepage233">ii. 233</a></p> + +<p>Bricks, <a href="#conver2.pagepage56">ii. 56</a></p> + +<p>Brittle-metals, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Bronze, <a href="#conver1.pagepage341">i. 341</a></p> + +<p>Butter, <a href="#conver2.pagepage351">ii. 351</a></p> + +<p>Butter-milk, <a href="#conver2.pagepage352">ii. 352</a></p> + + +<p class="letterhead"><a name="indexC" id="indexC">C</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Calcareous earths, <a href="#conver2.pagepage65">ii. 65</a></p> + +<p>—— stones, <a href="#conver2.pagepage123">ii. +123</a></p> + +<p>Calcium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Caloric, <a href="#conver1.pagepage12">i. 12</a>. +<a href="#conver1.pagepage33">33</a></p> + +<p>——, absorption of, <a href="#conver1.pagepage66">i. 66</a></p> + +<p>——, conductors of, <a href="#conver1.pagepage70">i. 70</a></p> + +<p>——, combined, <a href="#conver1.pagepage122">i. +122</a></p> + +<p>——, expansive power of <a href="#conver1.pagepage35">i. 35</a></p> + +<p>——, equilibrium of, <a href="#conver1.pagepage50">i. 50</a></p> + +<p>——, reflexion of, <a href="#conver1.pagepage54">i. 54</a>. +<a href="#conver1.pagepage67">67</a></p> + +<p>——, radiation of, <a href="#conver1.pagepage52">i. 52</a>. +<a href="#conver1.pagepage61">61</a></p> + +<p>——, solvent power of, <a href="#conver1.pagepage96">i. 96</a>. +<a href="#conver1.pagepage102">102</a></p> + +<p>——, capacity for, <a href="#conver1.pagepage124">i. 124</a></p> + +<p>Calorimeter, <a href="#conver1.pagepage156">i. 156</a></p> + +<p>Calx, <a href="#conver1.pagepage183">i. 183</a></p> + +<p>Camphor, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage185">185</a></p> + +<p>Camphoric acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Caoutchouc, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage189">189</a></p> + +<p>Carbonats, <a href="#conver2.pagepage25">ii. 25</a>. +<a href="#conver2.pagepage129">129</a></p> + +<p>Carbonat of ammonia, <a href="#conver2.pagepage41">ii. 41</a></p> + +<p>—— lead, <a href="#conver1.pagepage320">i. 320</a></p> + +<p>—— lime, <a href="#conver2.pagepage59">ii. 59</a>. +<a href="#conver2.pagepage130">130</a></p> + +<p>—— magnesia, <a href="#conver2.pagepage67">ii. +67</a></p> + +<p>—— potash, <a href="#conver2.pagepage25">ii. 25</a></p> + +<p>Carbonated hydrogen gas, <a href="#conver1.pagepage302">i. 302</a></p> + +<p>Carbon, <a href="#conver1.pagepage282">i. 282</a>. <a href="#conver2.pagepage329">ii. 329</a></p> + +<p>Carbonic acid, <a href="#conver1.pagepage290">i. 290</a>. +<a href="#conver1.pagepage359">359</a>. <a href="#conver2.pagepage327">ii. 327</a></p> + +<p>Carburet of iron, <a href="#conver1.pagepage304">i. 304</a>. +<a href="#conver1.pagepage342">342</a></p> + +<p>Carmine, <a href="#conver2.pagepage295">ii. 295</a></p> + +<p>Cartilage, <a href="#conver2.pagepage303">ii. 303</a></p> + +<p>Castor, <a href="#conver2.pagepage359">ii. 359</a></p> + +<p>Cellular membrane, <a href="#conver2.pagepage311">ii. 311</a></p> + +<p>Caustics, <a href="#conver1.pagepage349">i. 349</a></p> + +<p>Chalk, <a href="#conver2.pagepage62">ii. 62</a>. +<a href="#conver2.pagepage123">123</a></p> + +<p>Charcoal, <a href="#conver1.pagepage282">i. 282</a></p> + +<p>Cheese, <a href="#conver2.pagepage356">ii. 356</a></p> + +<p>Chemical attraction, <a href="#conver1.pagepage15">i. 15</a>. +<a href="#conver2.pagepage9">ii. 9</a></p> + +<p>Chemistry, <a href="#conver1.pagepage3">i. 3</a></p> + +<p>Chest, <a href="#conver2.pagepage318">ii. 318</a></p> + +<p>China, <a href="#conver2.pagepage54">ii. 54</a></p> + +<p>Chlorine, <a href="#conver1.pagepage214">i. 214</a></p> + +<p>Chrome, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage340">340</a></p> + +<p>Chyle, <a href="#conver2.pagepage305">ii. 305</a>. +<a href="#conver2.pagepage317">317</a></p> + +<p>Chyme, <a href="#conver2.pagepage316">ii. 316</a></p> + +<span class="pagenum left">365</span> +<a name="page365" id="page365"> </a> +<p>Citric acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Circulation of the blood, <a href="#conver2.pagepage322">ii. 322</a></p> + +<p>Civet, <a href="#conver2.pagepage359">ii. 359</a></p> + +<p>Clay, <a href="#conver1.pagepage48">i. 48</a>. <a href="#conver2.pagepage55">ii. 55</a></p> + +<p>Coke, <a href="#conver2.pagepage241">ii. 241</a></p> + +<p>Coal, <a href="#conver2.pagepage240">ii. 240</a>. +<a href="#conver2.pagepage252">252</a></p> + +<p>Cobalt, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Cochineal, <a href="#conver2.pagepage295">ii. 295</a></p> + +<p>Cold, <a href="#conver1.pagepage50">i. 50</a>. +<a href="#conver1.pagepage58">58</a></p> + +<p>—— from evaporation, <a href="#conver1.pagepage102"><ins class="mycorr" +title="volume number missing">i</ins>. 102</a>. +<a href="#conver1.pagepage113">113</a>. +<a href="#conver1.pagepage150">150</a></p> + +<p>Colours of metallic oxyds, <a href="#conver1.pagepage319">i. 319</a></p> + +<p>Columbium, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage340">340</a>. +<a href="#conver1.pagepage348">348</a></p> + +<p>Combined caloric, <a href="#conver1.pagepage122">i. 122</a></p> + +<p>Combustion, <a href="#conver1.pagepage190">i. 190</a></p> + +<p>——, volatile products of, <a href="#conver1.pagepage207">i. 207</a></p> + +<p>——, fixed products of, <a href="#conver1.pagepage207">i. 207</a></p> + +<p>——, of alcohol, <a href="#conver2.pagepage225">ii. +225</a></p> + +<p>——, of ammoniacal gas, <a href="#conver2.pagepage42">ii. 42</a></p> + +<p>——, of boracium, <a href="#conver2.pagepage133">ii. +133</a></p> + +<p>——, by oxymuriatic acid or chlorine, <a href="#conver2.pagepage142">ii. 142</a></p> + +<p>——, of carbon, <a href="#conver1.pagepage289">i. 289</a></p> + +<p>——, of coals, <a href="#conver1.pagepage207">i. 207</a>. +<a href="#conver1.pagepage297">297</a></p> + +<p>——, of charcoal by nitric acid, <a href="#conver2.pagepage102">ii. 102</a></p> + +<p>——, of candles, <a href="#conver1.pagepage236">i. 236</a>. +<a href="#conver1.pagepage309">309</a>. <a href="#conver2.pagepage179">ii. 179</a></p> + +<p>——, of diamonds, <a href="#conver1.pagepage292">i. 292</a></p> + +<p>——, of ether, <a href="#conver2.pagepage230">ii. +230</a></p> + +<p>——, of hydrogen, <a href="#conver1.pagepage229">i. 229</a>.</p> + +<p>——, of iron, <a href="#conver1.pagepage200">i. 200</a>. +<a href="#conver1.pagepage322">322</a></p> + +<p>——, of metals, <a href="#conver1.pagepage321">i. 321</a></p> + +<p>——, of oils, <a href="#conver1.pagepage208">i. 208</a>. <a href="#conver2.pagepage178">ii. 178</a>. +<a href="#conver1.pagepage309">309</a></p> + +<p>——, of oil of turpentine by nitrous acid, <a href="#conver2.pagepage6">ii. 6</a></p> + +<p>——, of phosphorus, <a href="#conver1.pagepage272">i. 272</a></p> + +<p>——, of sulphur, <a href="#conver1.pagepage261">i. 261</a></p> + +<p>—— of potassium, <a href="#conver1.pagepage358">i. 358</a>. <a href="#conver2.pagepage132">ii. 132</a>. +<a href="#conver1.pagepage138">138, 139</a></p> + +<p>Compound bodies, <a href="#conver1.pagepage9">i. 9</a>. <a href="#conver2.pagepage14">ii. 14</a></p> + +<p>—— or neutral salts <a href="#conver1.pagepage333">i. 333</a>. <a href="#conver2.pagepage4">ii. 4</a></p> + +<p>Conductors of heat, <a href="#conver1.pagepage71">i. 71</a></p> + +<p>——, solids, <a href="#conver1.pagepage73">i. 73</a></p> + +<p>——, fluids, <a href="#conver1.pagepage78">i. 78</a></p> + +<p>——, Count Rumford’s theory, <a href="#conver1.pagepage79">i. 79</a></p> + +<p>Constituent parts, <a href="#conver1.pagepage9">i. 9</a></p> + +<p>Copper, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage331">331</a></p> + +<p>Copal, <a href="#conver2.pagepage187">ii. 187</a>. +<a href="#conver2.pagepage224">224</a></p> + +<p>Cortical layers, <a href="#conver2.pagepage265">ii. 265</a>. +<a href="#conver2.pagepage267">267</a></p> + +<p>Cotyledons, or lobes, <a href="#conver2.pagepage256">ii. 256</a></p> + +<p>Cream, <a href="#conver2.pagepage351">ii. 351</a></p> + +<p>Cream of tartar, or tartrit of potash, <a href="#conver2.pagepage200">ii. 200</a>. +<a href="#conver2.pagepage222">222</a></p> + +<p>Cryophorus, <a href="#conver1.pagepage154">i. 154</a></p> + +<p>Crystallisation, <a href="#conver1.pagepage338">i. 338</a>. <a href="#conver2.pagepage47">ii. 47</a></p> + +<p>Cucurbit, <a href="#conver1.pagepage258">i. 258</a></p> + +<p>Culinary heat, <a href="#conver1.pagepage88">i. 88</a></p> + +<p>Curd, <a href="#conver2.pagepage351">ii. 351</a>. +<a href="#conver2.pagepage354">354</a></p> + +<p>Cuticle, or epidermis, <a href="#conver2.pagepage310">ii. +310</a></p> + + +<p class="letterhead"><a name="indexD" id="indexD">D</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Decomposition, <a href="#conver1.pagepage8">i. 8</a>. +<a href="#conver1.pagepage20">20</a></p> + +<p>—— of atmospherical air, <a href="#conver1.pagepage181">i. 181</a>. +<a href="#conver1.pagepage209">209</a></p> + +<p>—— of water by the Voltaic battery, <a href="#conver1.pagepage220">i. 220</a></p> + +<p>—— of salts by the Voltaic battery, <a href="#conver2.pagepage14">ii. 14</a></p> + +<p>—— of water by metals, <a href="#conver1.pagepage225">i. 225</a>. +<a href="#conver1.pagepage334">334</a></p> + +<p>—— —— by carbon, <a href="#conver1.pagepage301">i. 301</a></p> + +<p>—— of vegetables, <a href="#conver2.pagepage202">ii. 202</a></p> + +<p>—— of potash, <a href="#conver1.pagepage356">i. 356</a></p> + +<p>—— of soda, <a href="#conver1.pagepage56">i. 56</a></p> + +<p>—— of <ins class="mycorr" +title="text reads ‘ammonnia’">ammonia</ins>, +<a href="#conver1.pagepage363"><ins class="mycorr" title="volume number invisible">i</ins>. 363</a>. +<a href="#conver2.pagepage37">ii. 37</a></p> + +<span class="pagenum left">366</span> +<a name="page366" id="page366"> </a> +<p>—— of the boracic acid, <a href="#conver2.pagepage132">ii. 132</a></p> + +<p>—— of the fluoric acid, <a href="#conver2.pagepage136">ii. 136</a></p> + +<p>—— of the muriatic acid, <a href="#conver2.pagepage139">ii. 139</a></p> + +<p>Deflagration, <a href="#conver2.pagepage118">ii. 118</a></p> + +<p>Definite proportions, <a href="#conver2.pagepage13">ii. 13</a></p> + +<p>Deliquescence, <a href="#conver2.pagepage95">ii. 95</a></p> + +<p>Detonation, <a href="#conver1.pagepage219">i. 219</a>. <a href="#conver2.pagepage116">ii. 116</a></p> + +<p>Dew, <a href="#conver1.pagepage105">i. 105</a></p> + +<p>Diamond, <a href="#conver1.pagepage285">i. 285</a></p> + +<p>Diaphragm, <a href="#conver2.pagepage320">ii. 320</a></p> + +<p>Digestion, <a href="#conver2.pagepage316">ii. 316</a></p> + +<p>Dissolution of metals, <a href="#conver1.pagepage165">i. 165</a>. +<a href="#conver1.pagepage316">316</a>. +<a href="#conver1.pagepage333">333</a></p> + +<p>Distillation, <a href="#conver1.pagepage259">i. 259</a>. <a href="#conver2.pagepage218">ii. 218</a></p> + +<p>—— of red wine, <a href="#conver2.pagepage218">ii. +218</a></p> + +<p>Divellent forces, <a href="#conver2.pagepage12">ii. 12</a></p> + +<p>Division, <a href="#conver1.pagepage7">i. 7</a></p> + +<p>Drying oils, <a href="#conver2.pagepage181">ii. 181</a></p> + +<p>Dying, <a href="#conver2.pagepage191">ii. 191</a></p> + + +<p class="letterhead"><a name="indexE" id="indexE">E</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Earths, <a href="#conver2.pagepage44">ii. 44</a></p> + +<p>Earthen-ware, <a href="#conver2.pagepage53">ii. 53</a>. +<a href="#conver2.pagepage57">57</a></p> + +<p>Effervescence, <a href="#conver1.pagepage298">i. 298</a></p> + +<p>Efflorescence, <a href="#conver2.pagepage94">ii. 94</a></p> + +<p>Elastic fluids, <a href="#conver1.pagepage37">i. 37</a></p> + +<p>Electricity, <a href="#conver1.pagepage12">i. 12</a>. +<a href="#conver1.pagepage25">25</a>. +<a href="#conver1.pagepage160">160</a>. +<a href="#conver1.pagepage220">220</a>. <a href="#conver2.pagepage139">ii. 139</a></p> + +<p>Electric machine, <a href="#conver1.pagepage169">i. 169</a></p> + +<p>Elective attractions, <a href="#conver2.pagepage9">ii. 9</a></p> + +<p>Elementary bodies, <a href="#conver1.pagepage8">i. 8</a>. +<a href="#conver1.pagepage12">12</a></p> + +<p>Elixirs, tinctures, or quintessences, <a href="#conver2.pagepage225">ii. 225</a></p> + +<p>Enamel, <a href="#conver2.pagepage57">ii. 57</a></p> + +<p>Epidermis of vegetables, <a href="#conver2.pagepage269">ii. +269</a></p> + +<p>—— of animals, <a href="#conver2.pagepage310">ii. +310</a></p> + +<p>Epsom salts, <a href="#conver2.pagepage63">ii. 63</a>. +<a href="#conver2.pagepage95">95</a></p> + +<p>Equilibrium of caloric, <a href="#conver1.pagepage50">i. 50</a></p> + +<p>Essences, <a href="#conver1.pagepage307">i. 307</a>. <a href="#conver2.pagepage183">ii. 183</a>. +<a href="#conver1.pagepage224">224</a></p> + +<p>Essential, or volatile oils, <a href="#conver1.pagepage307">i. 307</a>. <a href="#conver2.pagepage183">ii. 183</a></p> + +<p>Ether, <a href="#conver1.pagepage111">i. 111</a>. <a href="#conver2.pagepage229">ii. 229</a></p> + +<p>Evaporation, <a href="#conver1.pagepage103">i. 103</a></p> + +<p>Evergreens, <a href="#conver2.pagepage274">ii. 274</a></p> + +<p>Eudiometer, <a href="#conver1.pagepage276">i. 276</a></p> + +<p>Expansion of caloric, <a href="#conver1.pagepage36">i. 36</a></p> + +<p>Extractive colouring matter, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage190">190</a></p> + + +<p class="letterhead"><a name="indexF" id="indexF">F</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Falling stones, <a href="#conver1.pagepage319">i. 319</a></p> + +<p>Fat, <a href="#conver1.pagepage306">i. 306</a>. <a href="#conver2.pagepage311">ii. 311</a></p> + +<p>Feathers, <a href="#conver2.pagepage300">ii. 300</a></p> + +<p>Fecula, <a href="#conver2.pagepage176">ii. 176</a></p> + +<p>Fermentation, <a href="#conver2.pagepage205">ii. 205</a></p> + +<p>Fibrine, <a href="#conver2.pagepage277">ii. 277</a>. +<a href="#conver2.pagepage289">289</a></p> + +<p>Fire, <a href="#conver1.pagepage7">i. 7</a>. +<a href="#conver1.pagepage27">27</a></p> + +<p>Fish, <a href="#conver2.pagepage346">ii. 346</a></p> + +<p>Fixed air, or carbonic acid, <a href="#conver1.pagepage290">i. 290</a>. <a href="#conver2.pagepage125">ii. 125</a></p> + +<p>—— alkalies, <a href="#conver2.pagepage20">ii. +20</a></p> + +<p>—— oils, <a href="#conver1.pagepage307">i. 307</a>. +<a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver1.pagepage177">177</a></p> + +<p>—— products of combustion, <a href="#conver1.pagepage207">i. 207</a></p> + +<p>Flame, <a href="#conver1.pagepage237">i. 237</a></p> + +<p>Flint, <a href="#conver2.pagepage30">ii. 30</a>. +<a href="#conver2.pagepage51">51</a></p> + +<p>Flower or blossom, <a href="#conver2.pagepage271">ii. 271</a></p> + +<p>Fluoric acid, <a href="#conver2.pagepage54">ii. 54</a>. +<a href="#conver2.pagepage134">134</a></p> + +<p>Fluorium, or Fluorine, <a href="#conver1.pagepage12">i. 12</a>. <a href="#conver2.pagepage136">ii. 136</a></p> + +<p>Formic acid, <a href="#conver2.pagepage290">ii. 290</a></p> + +<p>Fossil wood, <a href="#conver2.pagepage242">ii. 242</a></p> + +<p><ins class="mycorr" title="text reads ‘Francincense’">Frankincense</ins>, +<a href="#conver2.pagepage187">ii. 187</a></p> + +<p>Free or radiant caloric, or heat of temperature, <a href="#conver1.pagepage33">i. 33</a></p> + +<p>Freezing mixtures, <a href="#conver1.pagepage142">i. 142</a></p> + +<p>—— by evaporation, <a href="#conver1.pagepage104"><ins +class="mycorr" title="volume number invisible">i</ins>. 104</a>. +<a href="#conver1.pagepage150">150</a>, &c.</p> + +<p>Frost, <a href="#conver1.pagepage94">i. 94</a></p> + +<p>Fruit, <a href="#conver2.pagepage271">ii. 271</a></p> + +<p>Fuller’s earth, <a href="#conver2.pagepage55">ii. 55</a></p> + +<p>Furnace, <a href="#conver1.pagepage304">i. 304</a></p> + + +<span class="pagenum left">367</span> +<a name="page367" id="page367"> </a> +<p class="letterhead"><a name="indexG" id="indexG">G</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Galls, <a href="#conver2.pagepage199">ii. 199</a></p> + +<p>Gallat of iron, <a href="#conver2.pagepage98">ii. 98</a></p> + +<p>Gallic acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197, 198</a></p> + +<p>Galvanism, <a href="#conver1.pagepage163">i. 163</a></p> + +<p>Gas, <a href="#conver1.pagepage182">i. 182</a></p> + +<p>Gas-lights, <a href="#conver1.pagepage240">i. 240</a></p> + +<p>Gaseous oxyd of carbon, <a href="#conver1.pagepage296">i. 296</a></p> + +<p>—— nitrogen, <a href="#conver2.pagepage111">ii. +111</a></p> + +<p>Gastric juice, <a href="#conver2.pagepage316">ii. 316</a></p> + +<p>Gelatine, or jelly, <a href="#conver2.pagepage277">ii. 277</a>. +<a href="#conver2.pagepage280">280</a></p> + +<p>Germination, <a href="#conver2.pagepage256">ii. 256</a></p> + +<p>Gin, <a href="#conver2.pagepage221">ii. 221</a></p> + +<p>Glands, <a href="#conver2.pagepage298">ii. 298</a>. +<a href="#conver2.pagepage307">307</a></p> + +<p>Glass, <a href="#conver2.pagepage30">ii. 30</a></p> + +<p>Glauber’s salts, or sulphat of soda, <a href="#conver2.pagepage92">ii. 92</a></p> + +<p>Glazing, <a href="#conver2.pagepage57">ii. 57</a></p> + +<p>Glucium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Glue, <a href="#conver2.pagepage281"><ins class="mycorr" title="volume number missing">ii</ins>. 281</a>. +<a href="#conver2.pagepage287">287</a></p> + +<p>Gluten, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage177">177</a></p> + +<p>Gold, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage323">323</a></p> + +<p>Gum, <a href="#conver2.pagepage170">ii. 170</a></p> + +<p>—— arabic, <a href="#conver2.pagepage170">ii. +170</a></p> + +<p>—— elastic, or caoutchouc, <a href="#conver2.pagepage189">ii. 189</a></p> + +<p>—— resins, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage188">188</a></p> + +<p>Gunpowder, <a href="#conver2.pagepage116">ii. 116</a></p> + +<p>Gypsum, or plaister of Paris, or sulphat of lime, <a href="#conver2.pagepage95">ii. 95</a></p> + + +<p class="letterhead"><a name="indexH" id="indexH">H</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Hair, <a href="#conver2.pagepage300">ii. 300</a></p> + +<p>Harrogate water, <a href="#conver1.pagepage268">i. 268</a>. +<a href="#conver1.pagepage341">341</a></p> + +<p>Hartshorn, <a href="#conver2.pagepage35">ii. 35</a>. +<a href="#conver2.pagepage39">39</a>. +<a href="#conver2.pagepage281">281</a>. +<a href="#conver2.pagepage285">285</a></p> + +<p>Heart, <a href="#conver2.pagepage323">ii. 323</a></p> + +<p>—— wood, <a href="#conver2.pagepage268">ii. 268</a></p> + +<p>Heat, <a href="#conver1.pagepage26">i. 26</a>. +<a href="#conver1.pagepage33">33</a></p> + +<p>—— of capacity, <a href="#conver1.pagepage127">i. 127</a>. +<a href="#conver1.pagepage135">135</a></p> + +<p>—— of temperature, <a href="#conver1.pagepage33">i. 33</a></p> + +<p>Honey, <a href="#conver2.pagepage175">ii. 175</a></p> + +<p>Horns, <a href="#conver2.pagepage282">ii. 282</a>. +<a href="#conver2.pagepage300">300</a></p> + +<p>Hydro-carbonat, <a href="#conver1.pagepage241">i. 241</a>. +<a href="#conver1.pagepage303">303</a></p> + +<p>Hydrogen, <a href="#conver1.pagepage214">i. 214</a></p> + +<p>—— gas, <a href="#conver1.pagepage215">i. 215</a></p> + + +<p class="letterhead"><a name="indexI" id="indexI">IJ</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Jasper, <a href="#conver2.pagepage51">ii. 51</a></p> + +<p>Ice, <a href="#conver1.pagepage138">i. 138</a></p> + +<p>Jelly, <a href="#conver2.pagepage281">ii. 281</a></p> + +<p>Jet, <a href="#conver2.pagepage240">ii. 240</a></p> + +<p>Ignes fatui, <a href="#conver1.pagepage277">i. 277</a></p> + +<p>Ignition, <a href="#conver1.pagepage119">i. 119</a></p> + +<p>Imponderable agents, <a href="#conver1.pagepage12">i. 12</a></p> + +<p>Inflammable air, <a href="#conver1.pagepage215">i. 215</a></p> + +<p>Ink, <a href="#conver2.pagepage98">ii. 98</a>. +<a href="#conver2.pagepage199">199</a></p> + +<p>Insects, <a href="#conver2.pagepage349">ii. 349</a></p> + +<p>Integrant pans, <a href="#conver1.pagepage9">i. 9</a></p> + +<p>Iridium, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Iron, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage319">319</a>. +<a href="#conver1.pagepage328">328</a></p> + +<p>Isinglass, <a href="#conver2.pagepage194">ii. 194</a>. +<a href="#conver2.pagepage285">285</a></p> + +<p>Ivory black, <a href="#conver2.pagepage295">ii. 295</a></p> + +<p>Iodine, <a href="#conver1.pagepage214">i. 214</a>. <a href="#conver2.pagepage157">ii. 157</a></p> + + +<p class="letterhead"><a name="indexK" id="indexK">K</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Kali, <a href="#conver2.pagepage34">ii. 34</a></p> + +<p>Koumiss, <a href="#conver2.pagepage356">ii. 356</a></p> + +</td> +<td> + +<p class="letterhead"><a name="indexL" id="indexL">L</a></p> + +<p>Lac, <a href="#conver2.pagepage358">ii. 358</a></p> + +<p>Lactic acid, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage290">290</a>. +<a href="#conver2.pagepage356">356</a></p> + +<p>Lakes, colours, <a href="#conver2.pagepage190">ii. 190</a></p> + +<p>Latent heat, <a href="#conver1.pagepage133">i. 133</a></p> + +<p>Lavender water, <a href="#conver2.pagepage184">ii. 184</a>. +<a href="#conver2.pagepage224">224</a></p> + +<p>Lead, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage318">318</a>. +<a href="#conver1.pagepage330">330</a></p> + +<p>Leather, <a href="#conver2.pagepage193">ii. 193</a>. +<a href="#conver2.pagepage287">287</a></p> + +<p>Leaves, <a href="#conver2.pagepage260">ii. 260</a></p> + +<p>Life, <a href="#conver2.pagepage159">ii. 159</a>. +<a href="#conver2.pagepage168">168</a></p> + +<p>Ligaments, <a href="#conver2.pagepage303">ii. 303</a></p> + +<p>Light, <a href="#conver1.pagepage12">i. 12</a>. +<a href="#conver1.pagepage26">26</a>. <a href="#conver2.pagepage261">ii. 261</a></p> + +<p>Lightning, <a href="#conver1.pagepage248">i. 248</a></p> + +<p>Lime, <a href="#conver2.pagepage59">ii. 59</a></p> + +<p>—— water, <a href="#conver2.pagepage61">ii. 61</a></p> + +<span class="pagenum">368</span> +<a name="page368" id="page368"> </a> +<p>Limestone, <a href="#conver2.pagepage60">ii. 60</a></p> + +<p>Linseed oil, <a href="#conver2.pagepage178">ii. 178</a></p> + +<p>Liqueurs, <a href="#conver2.pagepage224">ii. 224</a></p> + +<p>Liver, <a href="#conver2.pagepage308">ii. 308</a></p> + +<p>Lobes, <a href="#conver2.pagepage256">ii. 256</a>. +<a href="#conver2.pagepage332">332</a></p> + +<p>Lunar caustic, or nitrat of silver, <a href="#conver1.pagepage350">i. 350</a>. <a href="#conver2.pagepage119">ii. 119</a></p> + +<p>Lungs, <a href="#conver2.pagepage319">ii. 319</a>. +<a href="#conver2.pagepage330">330</a></p> + +<p>Lymph, <a href="#conver2.pagepage304">ii. 304</a></p> + +<p>Lymphatic vessels, <a href="#conver2.pagepage304">ii. 304</a></p> + + +<p class="letterhead"><a name="indexM" id="indexM">M</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Magnesia, <a href="#conver2.pagepage44">ii. 44</a>. +<a href="#conver2.pagepage66">66</a></p> + +<p>Magnium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Malic acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Malt, <a href="#conver2.pagepage211">ii. 211</a></p> + +<p>Malleable metals, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Manganese, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage317">317</a></p> + +<p>Manna, <a href="#conver2.pagepage176">ii. 176</a></p> + +<p>Manure, <a href="#conver2.pagepage247">ii. 247</a></p> + +<p>Marble, <a href="#conver2.pagepage123">ii. 123</a></p> + +<p>Marine acid, or muriatic acid, <a href="#conver2.pagepage136">ii. 136</a></p> + +<p>Mastic, <a href="#conver2.pagepage187">ii. 187</a>. +<a href="#conver2.pagepage224">224</a></p> + +<p>Materials of animals, <a href="#conver2.pagepage277">ii. 277</a></p> + +<p>—— of vegetables, <a href="#conver2.pagepage165">ii. +165</a></p> + +<p>Mercury, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage346">346</a></p> + +<p>——, new mode of freezing, <a href="#conver1.pagepage155">i. 155</a>. +<a href="#conver1.pagepage347">347</a></p> + +<p>Metallic acids, <a href="#conver1.pagepage340">i. 340</a></p> + +<p>—— oxyds, <a href="#conver1.pagepage316">i. 316</a></p> + +<p>Metals, <a href="#conver1.pagepage12">i. 12</a>. +<a href="#conver1.pagepage314">314</a></p> + +<p>Meteoric stones, <a href="#conver1.pagepage342">i. 342</a></p> + +<p>Mica, <a href="#conver2.pagepage66">ii. 66</a></p> + +<p>Milk, <a href="#conver2.pagepage299">ii. 299</a>. +<a href="#conver2.pagepage306">306</a>. +<a href="#conver2.pagepage350">350</a></p> + +<p>Minerals, <a href="#conver1.pagepage315">i. 315</a>. <a href="#conver2.pagepage44">ii. 44</a>. +<a href="#conver1.pagepage158">158</a></p> + +<p>Mineral waters, <a href="#conver1.pagepage296">i. 296</a>. <a href="#conver2.pagepage129">ii. 129</a></p> + +<p>—— acids, <a href="#conver2.pagepage73">ii. 73</a></p> + +<p>Miner’s lamp, <a href="#conver1.pagepage249">i. 249</a></p> + +<p>Mixture, <a href="#conver1.pagepage99">i. 99</a></p> + +<p>Molybdena, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage340">340</a></p> + +<p>Mordant, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage192">192</a></p> + +<p>Mortar, <a href="#conver2.pagepage53">ii. 53</a>. +<a href="#conver2.pagepage65">65</a></p> + +<p>Mucilage, <a href="#conver2.pagepage170">ii. 170</a></p> + +<p>Mucous acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage171">171</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>—— membrane, <a href="#conver2.pagepage311">ii. +311</a></p> + +<p>Muriatic acid, or marine acid, <a href="#conver2.pagepage136">ii. 136</a></p> + +<p>Muriats, <a href="#conver2.pagepage151">ii. 151</a></p> + +<p>Muriat of ammonia, <a href="#conver2.pagepage35">ii. 35</a>. +<a href="#conver2.pagepage152">152</a></p> + +<p>—— lime, <a href="#conver1.pagepage100">i. 100</a></p> + +<p>—— soda, or common salt, <a href="#conver2.pagepage136">ii. 136</a>. +<a href="#conver2.pagepage151">151</a></p> + +<p>—— potash, <a href="#conver2.pagepage138">ii. +138</a></p> + +<p>Muriatium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Muscles of animals, <a href="#conver2.pagepage298">ii. 298</a>. +<a href="#conver2.pagepage303">303</a></p> + +<p>Musk, <a href="#conver2.pagepage359">ii. 359</a></p> + +<p>Myrrh, <a href="#conver2.pagepage188">ii. 188</a></p> + + +<p class="letterhead"><a name="indexN" id="indexN">N.</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Naphtha, <a href="#conver1.pagepage357">i. 357</a>. <a href="#conver2.pagepage240">ii. 240</a></p> + +<p>Negative electricity, <a href="#conver1.pagepage25">i. 25</a>. +<a href="#conver1.pagepage161">161</a>. +<a href="#conver1.pagepage185">185</a></p> + +<p>Nerves, <a href="#conver2.pagepage279">ii. 279</a>. +<a href="#conver2.pagepage298">298</a>. +<a href="#conver2.pagepage308">308</a></p> + +<p>Neutral, or compound salts, <a href="#conver1.pagepage333">i. 333</a>. <a href="#conver2.pagepage4">ii. 4</a>. +<a href="#conver1.pagepage22">22</a>. +<a href="#conver1.pagepage69">69</a></p> + +<p>Nickel, <a href="#conver1.pagepage13">i. 13</a>. +<a href="#conver1.pagepage343">343</a></p> + +<p>Nitre, or nitrat of potash, or saltpetre, <a href="#conver2.pagepage32">ii. 32</a>. +<a href="#conver2.pagepage104">104</a>. +<a href="#conver2.pagepage116">116</a></p> + +<p>Nitric acid, <a href="#conver2.pagepage100">ii. 100</a></p> + +<p>Nitrogen, or azot, <a href="#conver1.pagepage181">i. 181</a>. +<a href="#conver2.pagepage100">ii. 100</a></p> + +<p>—— gas, <a href="#conver1.pagepage182">i. 182</a>. +<a href="#conver1.pagepage211">211</a></p> + +<p>Nitro-muriatic acid, or aqua regia, <a href="#conver2.pagepage144">ii. 144</a></p> + +<p>Nitrous acid gas, <a href="#conver2.pagepage101">ii. 101</a>. +<a href="#conver2.pagepage106">106</a></p> + +<p>—— air, or nitrit oxyd gas, <a href="#conver2.pagepage107">ii. 107</a></p> + +<p>Nitrats, <a href="#conver2.pagepage116">ii. 116</a></p> + +<p>Nitrat of copper, <a href="#conver2.pagepage5">ii. 5</a></p> + +<p>—— ammonia, <a href="#conver2.pagepage113">ii. 113</a>. +<a href="#conver2.pagepage118">118</a></p> + +<p>—— potash, or nitre, or saltpetre, <a href="#conver2.pagepage32">ii. 32</a>. +<a href="#conver2.pagepage104">104</a>. +<a href="#conver2.pagepage116">116</a></p> + +<p>—— silver, or lunar caustic, <a href="#conver2.pagepage19">ii. 19</a></p> + +<p>Nomenclature of acids, <a href="#conver1.pagepage264">i. 264</a>. <a href="#conver2.pagepage69">ii. 69</a></p> + +<p>—— compound salts, <a href="#conver2.pagepage4">ii. 4</a>. +<a href="#conver2.pagepage22">22</a></p> + +<span class="pagenum">369</span> +<a name="page369" id="page369"> </a> +<p>—— other binary compounds, <a href="#conver1.pagepage278">i. 278</a></p> + +<p>Nut-galls, <a href="#conver2.pagepage98">ii. 98</a>. +<a href="#conver2.pagepage199">199</a></p> + +<p>Nut-oil, <a href="#conver2.pagepage178">ii. 178</a></p> + +<p>Nutrition, <a href="#conver2.pagepage297">ii. 297</a></p> + + +<p class="letterhead"><a name="indexO" id="indexO">O</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Ochres, <a href="#conver1.pagepage320">i. 320</a></p> + +<p>Oils, <a href="#conver1.pagepage285">i. 285</a>. <a href="#conver2.pagepage306">ii. 306</a></p> + +<p>Oil of amber, <a href="#conver2.pagepage241">ii. 241</a></p> + +<p>—— vitriol, or sulphuric acid, <a href="#conver2.pagepage80">ii. 80</a></p> + +<p>Olive oil, <a href="#conver2.pagepage178">ii. 178</a></p> + +<p>Ores, <a href="#conver1.pagepage315">i. 315</a></p> + +<p>Organized bodies, <a href="#conver2.pagepage159">ii. 159</a></p> + +<p>Organs of animals, <a href="#conver2.pagepage290">ii. 290</a>. +<a href="#conver2.pagepage310">310</a></p> + +<p>—— vegetables, <a href="#conver2.pagepage159">ii. +159</a>. +<a href="#conver2.pagepage265">265</a>. +<a href="#conver2.pagepage271">271</a></p> + +<p>Osmium, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage348">348</a></p> + +<p>Oxalic acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Oxyds, <a href="#conver1.pagepage198">i. 198</a></p> + +<p>Oxyd of manganese, <a href="#conver1.pagepage117">i. 117</a>. +<a href="#conver1.pagepage317">317</a></p> + +<p>—— iron, <a href="#conver1.pagepage204">i. 204</a>. +<a href="#conver1.pagepage319">319</a></p> + +<p>—— lead, <a href="#conver1.pagepage319">i. 319</a></p> + +<p>—— sulphur, <a href="#conver2.pagepage91">ii. +91</a></p> + +<p>Oxydation, or oxygenation, <a href="#conver1.pagepage196">i. 196</a></p> + +<p>Oxygen, <a href="#conver1.pagepage11">i. 11</a>. +<a href="#conver1.pagepage181">181</a>. +<a href="#conver1.pagepage201">201</a>. +<a href="#conver1.pagepage211">211</a></p> + +<p>—— gas, or vital air, <a href="#conver1.pagepage182">i. 182</a>. +<a href="#conver1.pagepage201">201</a></p> + +<p>Oxy-muriatic acid, <a href="#conver2.pagepage140">ii. 140</a></p> + +<p>Oxy-muriats, <a href="#conver2.pagepage153">ii. 153</a></p> + +<p>Oxy-muriat of potash, <a href="#conver2.pagepage155">ii. 155</a></p> + + +<p class="letterhead"><a name="indexP" id="indexP">P</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Palladium, <a href="#conver1.pagepage13">i. 13</a>. +<a href="#conver1.pagepage348">348</a></p> + +<p>Papin’s digester, <a href="#conver1.pagepage120">i. 120</a>. +<a href="#conver2.pagepage284">ii. 284</a></p> + +<p>Parenchyma, <a href="#conver2.pagepage256">ii. 256</a>. +<a href="#conver2.pagepage266">266</a></p> + +<p>Particles, <a href="#conver1.pagepage16">i. 16</a></p> + +<p>Pearlash, <a href="#conver2.pagepage24">ii. 24</a></p> + +<p>Peat, <a href="#conver2.pagepage242">ii. 242</a></p> + +<p>Peculiar juice of plants, <a href="#conver2.pagepage268">ii. 268</a></p> + +<p>Perfect metals, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage324">324</a></p> + +<p>Perfumes, <a href="#conver1.pagepage308">i. 308</a>. <a href="#conver2.pagepage183">ii. 183</a></p> + +<p>Perspiration, <a href="#conver2.pagepage333">ii. 333</a>. +<a href="#conver2.pagepage329">329</a></p> + +<p>Petrification, <a href="#conver2.pagepage237">ii. 237</a></p> + +<p>Pewter, <a href="#conver1.pagepage344">i. 344</a></p> + +<p>Pharmacy, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Phosphat of lime, <a href="#conver2.pagepage99">ii. 99</a>. +<a href="#conver2.pagepage299">299</a></p> + +<p>Phosphorated hydrogen gas, <a href="#conver1.pagepage277">i. 277</a></p> + +<p>Phosphorescence, <a href="#conver1.pagepage29">i. 29</a></p> + +<p>Phosphoric acid, <a href="#conver1.pagepage273">i. 273</a>. <a href="#conver2.pagepage99">ii. 99</a></p> + +<p>Phosphorous acid, <a href="#conver1.pagepage274">i. 274</a>. +<a href="#conver2.pagepage99">ii. 99</a></p> + +<p>Phosphorus, <a href="#conver1.pagepage270">i. 270</a></p> + +<p>Phosphoret of lime, <a href="#conver1.pagepage278">i. 278</a>. +<a href="#conver1.pagepage341">341</a></p> + +<p>—— sulphur, <a href="#conver1.pagepage279">i. 279</a>. +<a href="#conver1.pagepage341">341</a></p> + +<p>Pitch, <a href="#conver2.pagepage187">ii. 187</a></p> + +<p>Plaster, <a href="#conver2.pagepage65">ii. 65</a></p> + +<p>Platina, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage323">323</a></p> + +<p>Plating, <a href="#conver1.pagepage345">i. 345</a></p> + +<p>Plumbago, or black lead, <a href="#conver1.pagepage304">i. 304</a></p> + +<p>Plumula, <a href="#conver2.pagepage257">ii. 257</a></p> + +<p>Porcelain, <a href="#conver2.pagepage56">ii. 56</a></p> + +<p>Positive electricity, <a href="#conver1.pagepage25">i. 25</a>. +<a href="#conver1.pagepage161">161</a>. +<a href="#conver1.pagepage185">185</a></p> + +<p>Potassium, <a href="#conver1.pagepage13">i. 13</a>. +<a href="#conver1.pagepage357">357</a>. <a href="#conver2.pagepage15">ii. 15</a></p> + +<p>Pottery, <a href="#conver2.pagepage56">ii. 56</a></p> + +<p>Potash, <a href="#conver1.pagepage356">i. 356</a>. <a href="#conver2.pagepage22">ii. 22</a></p> + +<p>Precipitate, <a href="#conver1.pagepage22">i. 22</a></p> + +<p>Pressure of the atmosphere, <a href="#conver1.pagepage112">i. 112</a>. +<a href="#conver1.pagepage116">116</a></p> + +<p>Printer’s ink, <a href="#conver2.pagepage144">ii. 144</a></p> + +<p>Prussiat of iron, or prussian blue, <a href="#conver2.pagepage291">ii. 291</a></p> + +<p>—— potash, <a href="#conver2.pagepage291">ii. +291</a></p> + +<p>Prussic acid, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage290">290</a></p> + +<p>Putrid fermentation, <a href="#conver2.pagepage235">ii. 235</a>. +<a href="#conver2.pagepage360">360</a></p> + +<p>Pyrites, <a href="#conver1.pagepage341">i. 341</a>. <a href="#conver2.pagepage97">ii. 97</a></p> + +<p>Pyrometer, <a href="#conver1.pagepage38">i. 38</a>. +<a href="#conver1.pagepage42">42</a></p> + + +<p class="letterhead"><a name="indexQ" id="indexQ">Q</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Quick lime, <a href="#conver2.pagepage59">ii. 59</a></p> + +<p>Quiescent forces, <a href="#conver2.pagepage12">ii. 12</a></p> + + +<span class="pagenum">370</span> +<a name="page370" id="page370"> </a> +<p class="letterhead"><a name="indexR" id="indexR">R</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Radiation of caloric, <a href="#conver1.pagepage52">i. 52</a></p> + +<p>——, Prevost’s theory, <a href="#conver1.pagepage52">i. 52</a></p> + +<p>——, Pictet’s explanations, <a href="#conver1.pagepage54">i. 54</a></p> + +<p>——, Leslie’s illustrations, <a href="#conver1.pagepage61">i. 61</a></p> + +<p>Radicals, <a href="#conver2.pagepage5">ii. 5</a>. +<a href="#conver2.pagepage69">69</a></p> + +<p>Radicle; or root, <a href="#conver2.pagepage257">ii. 257</a></p> + +<p>Rain, <a href="#conver1.pagepage104">i. 104</a></p> + +<p>Rancidity, <a href="#conver2.pagepage182">ii. 182</a></p> + +<p>Rectification, <a href="#conver2.pagepage223">ii. 223</a></p> + +<p>Reflexion of caloric, <a href="#conver1.pagepage54">i. 54</a>. +<a href="#conver1.pagepage64">64</a></p> + +<p>Reptiles, <a href="#conver2.pagepage349">ii. 349</a></p> + +<p>Resins, <a href="#conver2.pagepage165">ii. 165</a>, <a href="#conver2.pagepage186">186</a>. <a href="#conver2.pagepage266">266</a></p> + +<p>Respiration, <a href="#conver2.pagepage317">ii. 317</a>. +<a href="#conver2.pagepage326">326</a></p> + +<p>Reviving of metals, <a href="#conver1.pagepage327">i. 327</a></p> + +<p>Rhodium, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage348">348</a></p> + +<p>Roasting metals, <a href="#conver1.pagepage316">i. 316</a></p> + +<p>Rock crystal, <a href="#conver2.pagepage61">ii. 61</a></p> + +<p>Ruby, <a href="#conver2.pagepage53">ii. 53</a></p> + +<p>Rum, <a href="#conver2.pagepage219">ii. 219</a></p> + +<p>Rust, <a href="#conver1.pagepage318">i. 318</a>. +<a href="#conver1.pagepage328">328</a></p> + + +<p class="letterhead"><a name="indexS" id="indexS">S</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Saccharine fermentation, <a href="#conver2.pagepage208">ii. +208</a></p> + +<p>Sal ammoniac, or muriat of ammonia, <a href="#conver2.pagepage35">ii. 35</a></p> + +<p>—— polychrest, or sulphat of potash, <a href="#conver2.pagepage91">ii. 91</a></p> + +<p>—— volatile, or carbonat of ammonia, <a href="#conver2.pagepage41">ii. 41</a></p> + +<p>Salifiable bases, <a href="#conver2.pagepage5">ii. 5</a></p> + +<p>Salifying principles, <a href="#conver2.pagepage5">ii. 5</a></p> + +<p>Saltpetre, or nitre, or nitrat of potash, <a href="#conver2.pagepage32">ii. 32</a>. +<a href="#conver2.pagepage104">104</a>. +<a href="#conver2.pagepage116">116</a></p> + +<p>Salt, <a href="#conver2.pagepage91">ii. 91</a></p> + +<p>Sand, <a href="#conver2.pagepage30">ii. 30</a>. +<a href="#conver2.pagepage51">51</a></p> + +<p>Sandstone, <a href="#conver2.pagepage51">ii. 51</a></p> + +<p>Sap of plants, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage260">260</a>. +<a href="#conver2.pagepage262">262</a>. +<a href="#conver2.pagepage270">270</a>. +<a href="#conver2.pagepage272">272</a></p> + +<p>Sapphire, <a href="#conver2.pagepage58">ii. 58</a></p> + +<p>Saturation, <a href="#conver1.pagepage101">i. 101</a>.</p> + +<p>Sapphire, <a href="#conver2.pagepage58">ii. 58</a></p> + +<p>Saturation, <a href="#conver1.pagepage101">i. 101</a></p> + +<p>Seas, temperature of, <a href="#conver1.pagepage33">i. 33</a>.</p> + +<p>Sebacic acid, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage182">182</a>. +<a href="#conver2.pagepage290">290</a>. +<a href="#conver2.pagepage353">353</a></p> + +<p>Secretions, <a href="#conver2.pagepage307">ii. 307</a></p> + +<p>Seeds of plants, <a href="#conver2.pagepage210">ii. 210</a>. +<a href="#conver2.pagepage271">271</a></p> + +<p>Seltzer water, <a href="#conver1.pagepage289">i. 289</a>. <a href="#conver2.pagepage63">ii. 63</a>. +<a href="#conver1.pagepage129">129</a></p> + +<p>Senses, <a href="#conver2.pagepage310">ii. 310</a></p> + +<p>Silex, or silica, <a href="#conver2.pagepage30">ii. 30</a>. +<a href="#conver2.pagepage51">51</a></p> + +<p>Silicium, <a href="#conver1.pagepage13">i. 13</a>.</p> + +<p>Silk, <a href="#conver2.pagepage359">ii. 359</a></p> + +<p>Silver, <a href="#conver1.pagepage321">i. 321</a></p> + +<p>Simple bodies, <a href="#conver1.pagepage10">i. 10</a>. +<a href="#conver1.pagepage12">12</a></p> + +<p>Size, <a href="#conver2.pagepage281">ii. 281</a></p> + +<p>Skin, <a href="#conver2.pagepage279">ii. 279</a>. +<a href="#conver2.pagepage310">310</a>. +<a href="#conver2.pagepage193">193</a></p> + +<p>Slakeing of lime, <a href="#conver1.pagepage147">i. 147</a>. +<a href="#conver2.pagepage56">ii. 56</a></p> + +<p>Slate, <a href="#conver2.pagepage51">ii. 51</a>. +<a href="#conver2.pagepage66">66</a></p> + +<p>Smelting metals, <a href="#conver1.pagepage316">i. 316</a></p> + +<p>Smoke <a href="#conver1.pagepage208">i. 208</a></p> + +<p>Soap, <a href="#conver2.pagepage24">ii. 24</a></p> + +<p>Soda, <a href="#conver1.pagepage363">i. 363</a>. <a href="#conver2.pagepage33">ii. 33</a></p> + +<p>—— water, <a href="#conver1.pagepage299">i. 299</a></p> + +<p>Sodium, <a href="#conver1.pagepage13">i. 13</a>. +<a href="#conver1.pagepage363">363</a></p> + +<p>Soils, <a href="#conver1.pagepage42">i. 42</a>. <a href="#conver2.pagepage245">ii. 245</a></p> + +<p>Soldering, <a href="#conver1.pagepage345">i. 345</a></p> + +<p>Solubility, <a href="#conver2.pagepage92">ii. 92</a></p> + +<p>Solution, <a href="#conver1.pagepage96">i. 96</a></p> + +<p>—— by the air, <a href="#conver1.pagepage102">i. 102</a></p> + +<p>—— of potash, <a href="#conver2.pagepage28">ii. +28</a></p> + +<p>Specific heat, <a href="#conver1.pagepage126">i. 126</a></p> + +<p>Spermaceti, <a href="#conver2.pagepage358">ii. 358</a></p> + +<p>Spirits, <a href="#conver2.pagepage313">ii. 313</a></p> + +<p>Steam, <a href="#conver1.pagepage140">i. 140</a>. +<a href="#conver1.pagepage182">182</a></p> + +<p>Steel, <a href="#conver1.pagepage305">i. 305</a></p> + +<p>Stomach, <a href="#conver2.pagepage315">ii. 315</a></p> + +<p>Stones, <a href="#conver2.pagepage46">ii. 46</a></p> + +<p>Stucco, <a href="#conver2.pagepage65">ii. 65</a></p> + +<p>Strontites, <a href="#conver2.pagepage44">ii. 44</a>. +<a href="#conver2.pagepage68">68</a></p> + +<p>Strontium, <a href="#conver1.pagepage13">i. 13</a></p> + +<p>Suberic acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Sublimation, <a href="#conver1.pagepage257">i. 257</a></p> + +<p>Succin, or yellow amber, <a href="#conver2.pagepage241">ii. 241</a></p> + +<p>Succinic acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a>. +<a href="#conver2.pagepage241">241</a></p> + +<p>Sugar, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage174">174</a>. +<a href="#conver2.pagepage208">208</a></p> + +<p>—— of milk, <a href="#conver2.pagepage355">ii. +355</a></p> + +<span class="pagenum">371</span> +<a name="page371" id="page371"> </a> +<p>Sulphats, <a href="#conver2.pagepage5">ii. 5</a>. +<a href="#conver2.pagepage91">91</a></p> + +<p>Super oxygenated sulphuric acid, <a href="#conver2.pagepage70">ii. 70</a>.</p> + +<p>Sulphat of alumine, or alum, <a href="#conver2.pagepage54">ii. 54</a>. +<a href="#conver2.pagepage95">95</a></p> + +<p>—— barytes, <a href="#conver2.pagepage58">ii. +58</a></p> + +<p>—— iron, <a href="#conver2.pagepage96">ii. 96</a></p> + +<p>—— lime, or <ins class="mycorr" +title="text reads ‘gypsum of’">gypsum, or</ins> +plaster of Paris, <a href="#conver2.pagepage95">ii. 95</a></p> + +<p>—— magnesia, or Epsom salt, <a href="#conver2.pagepage67">ii. 67</a>. +<a href="#conver2.pagepage95">95</a></p> + +<p>—— potash, or sal polychrest, <a href="#conver2.pagepage91">ii. 91</a></p> + +<p>—— soda, or Glauber’s salts, <a href="#conver2.pagepage92">ii. 92</a></p> + +<p>Sulphur, <a href="#conver1.pagepage256">i. 256</a></p> + +<p>—— flowers of, <a href="#conver1.pagepage257"><ins +class="mycorr" title="volume number missing">i</ins>. 257</a></p> + +<p>Sulphurated hydrogen gas, <a href="#conver1.pagepage165">i. 165</a>. +<a href="#conver1.pagepage268">268</a></p> + +<p>Sulphurets, <a href="#conver1.pagepage341">i. 341</a></p> + +<p>Sulphurous acid, <a href="#conver1.pagepage254">i. 254</a>. <a href="#conver2.pagepage88">ii. 88</a></p> + +<p>Sulphuric acid, <a href="#conver1.pagepage74">i. 74</a>. <a href="#conver2.pagepage265">ii. 265</a></p> + +<p>Sympathetic ink, <a href="#conver1.pagepage354">i. 354</a></p> + +<p>Synthesis, <a href="#conver1.pagepage287">i. 287</a></p> + + +<p class="letterhead"><a name="indexT" id="indexT">T</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Tan, <a href="#conver2.pagepage192">ii. 192</a></p> + +<p>Tannin, <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver2.pagepage192">192</a></p> + +<p>Tar, <a href="#conver2.pagepage187">ii. 187</a></p> + +<p>Tartarous acid, <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver2.pagepage197">197</a></p> + +<p>Tartrit of potash, <a href="#conver2.pagepage222">ii. 222</a></p> + +<p>Teeth, <a href="#conver2.pagepage300">ii. 300</a></p> + +<p>Tellurium, <a href="#conver1.pagepage14">i. 14</a></p> + +<p>Temperature, <a href="#conver1.pagepage33">i. 33</a></p> + +<p>Thaw, <a href="#conver1.pagepage158">i. 158</a></p> + +<p>Thermometers, <a href="#conver1.pagepage40">i. 40</a></p> + +<p>——, Fahrenheit’s, <a href="#conver1.pagepage42">i. +42</a></p> + +<p>——, Reaumur’s, <a href="#conver1.pagepage42">i. +42</a></p> + +<p>——, <ins class="mycorr" +title="text reads ‘Centrigade’">Centigrade</ins>, +<a href="#conver1.pagepage43">i. 43</a></p> + +<p>——, air, <a href="#conver1.pagepage44">i. 44</a></p> + +<p>——, <ins class="mycorr" +title="text reads ‘differentiial’">differential</ins>, +<a href="#conver1.pagepage46">i. 46</a></p> + +<p>Thunder, <a href="#conver1.pagepage248">i. 248</a></p> + +<p>Tin, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage344">344</a></p> + +<p>Titanium, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage348">348</a></p> + +<p>Turf, <a href="#conver2.pagepage242">ii. 242</a></p> + +<p>Turpentine, <a href="#conver2.pagepage187">ii. 187</a></p> + +<p>Transpiration of plants, <a href="#conver2.pagepage260">ii. 260</a></p> + +<p>Tungsten, <a href="#conver1.pagepage14">i. 14</a>. +<a href="#conver1.pagepage340">340</a></p> + + +<p class="letterhead"><a name="indexV" id="indexV">V</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Vapour, <a href="#conver1.pagepage36">i. 36</a>. +<a href="#conver1.pagepage49">49</a>. +<a href="#conver1.pagepage93">93</a>. +<a href="#conver1.pagepage182">182</a></p> + +<p>Vaporisation, <a href="#conver1.pagepage103">i. 103</a></p> + +<p>Varnishes, <a href="#conver2.pagepage187">ii. 187</a></p> + +<p>Vegetables, <a href="#conver2.pagepage158">ii. 158</a></p> + +<p>Vegetable acid, <a href="#conver1.pagepage310">i. 310</a>. <a href="#conver2.pagepage74">ii. 74</a>. +<a href="#conver1.pagepage197">197</a></p> + +<p>—— colours, <a href="#conver2.pagepage190">ii. +190</a></p> + +<p>—— heat, <a href="#conver2.pagepage272">ii. 272</a></p> + +<p>—— oils, <a href="#conver2.pagepage177">ii. 177</a></p> + +<p>Veins, <a href="#conver2.pagepage304">ii. 304</a>. +<a href="#conver2.pagepage323">323</a>.</p> + +<p>Venous blood, <a href="#conver2.pagepage305">ii. 305</a>. +<a href="#conver2.pagepage326">326</a>. +<a href="#conver2.pagepage338">338</a></p> + +<p>Ventricles, <a href="#conver2.pagepage324">ii. 324</a></p> + +<p>Verdigris, <a href="#conver1.pagepage352">i. 352</a></p> + +<p>Vessels, <a href="#conver2.pagepage304">ii. 304</a></p> + +<p>Vinegar, <a href="#conver2.pagepage232">ii. 232</a></p> + +<p>Vinous fermentation, <a href="#conver2.pagepage212">ii. 212</a></p> + +<p>Vital air, or oxygen gas, <a href="#conver1.pagepage182">i. 182</a></p> + +<p>Vitriol, or sulphat of iron, <a href="#conver2.pagepage81">ii. 81</a></p> + +<p>Volatile oils, <a href="#conver1.pagepage307">i. 307</a>. <a href="#conver2.pagepage165">ii. 165</a>. +<a href="#conver1.pagepage183">183</a>. +<a href="#conver1.pagepage224">224</a>. +<a href="#conver1.pagepage269">269</a></p> + +<p>—— products of combustion, <a href="#conver1.pagepage207">i. 207</a></p> + +<p>—— alkali, <a href="#conver1.pagepage363">i. 363</a>. +<a href="#conver2.pagepage20">ii. 20</a>. +<a href="#conver1.pagepage35">35</a></p> + +<p>Voltaic battery, <a href="#conver1.pagepage164">i. 164</a>. +<a href="#conver1.pagepage220">220</a>. +<a href="#conver1.pagepage356">356</a>. <a href="#conver2.pagepage15">ii. 15</a></p> + + +<p class="letterhead"><a name="indexU" id="indexU">U</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Uranium, <a href="#conver1.pagepage14">i. 14</a></p> + + +<p class="letterhead"><a name="indexW" id="indexW">W</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Water, <a href="#conver1.pagepage215">i. 215</a>. <a href="#conver2.pagepage262">ii. 262</a></p> + +<span class="pagenum">372</span> +<a name="page372" id="page372"> </a> +<p>——, decomposition of, by electricity, <a href="#conver1.pagepage200">i. 200</a>. +<a href="#conver1.pagepage225">225</a></p> + +<p>——, condensation of, <a href="#conver1.pagepage32">i. 32</a></p> + +<p>—— of the sea, <a href="#conver1.pagepage86">i. 86</a></p> + +<p>——, boiling, <a href="#conver1.pagepage93">i. +93</a></p> + +<p>——, solution by, <a href="#conver1.pagepage96">i. 96</a></p> + +<p>—— of crystallisation, <a href="#conver1.pagepage339">i. 339</a></p> + +<p>Wax, <a href="#conver1.pagepage309">i. 309</a>. <a href="#conver2.pagepage180">ii. 180</a>. +<a href="#conver1.pagepage358">358</a></p> + +<p>Whey, <a href="#conver2.pagepage351">ii. 351</a></p> + +<p>Wine, <a href="#conver2.pagepage212">ii. 212</a></p> + +<p>Wood, <a href="#conver2.pagepage267">ii. 267</a></p> + +<p>Woody fibre, <a href="#conver2.pagepage156">ii. 156</a>. +<a href="#conver2.pagepage196">196</a>. +<a href="#conver2.pagepage267">267</a></p> + +<p>Wool, <a href="#conver2.pagepage300">ii. 300</a></p> + + +<p class="letterhead"><a name="indexY" id="indexY">Y</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Yeast, <a href="#conver2.pagepage234">ii. 234</a>.</p> + +<p>Yttria, <a href="#conver2.pagepage44">ii. 44</a>.</p> + +<p>Yttrium, <a href="#conver1.pagepage13">i. 13</a>.</p> + + +<p class="letterhead"><a name="indexZ" id="indexZ">Z</a> +<a href="#index"><i>Index top</i></a></p> + +<p>Zinc, <a href="#conver2.pagepage14">ii. 14</a>. +<a href="#conver2.pagepage344">344</a></p> + +<p><ins class="mycorr" title="text reads ‘Zicornia’">Zirconia</ins>, +<a href="#conver2.pagepage44">ii. 44</a></p> + +<p><ins class="mycorr" title="text reads ‘Zicornium’">Zirconium</ins>, +<a href="#conver1.pagepage14">i. <ins class="mycorr" title="text reads ‘13’">14</ins></a>.</p> + +<p>Zoonic acid, <a href="#conver2.pagepage75">ii. 75</a>. +<a href="#conver2.pagepage220">220</a></p> +</td> +</tr> +</table> + +</div> + +<div class="endnote"> + +<h4><a name="endnotes" id="endnotes">Transcriber’s Notes</a></h4> + +<h5>Terminology</h5> + +<p>Many scientific terms used in this book are different from today’s +standard terminology. The following is not meant as a comprehensive +list.</p> + +<table summary="list of terms"> +<tr> +<td width="33%"><p>oxy-muriatic acid</p></td> +<td><p>chlorine<br> +<i>proposed as an element in 1815: see Conversation XIX</i></p></td> +</tr> +<tr> +<td><p>“columbium or tantalium”</p></td> +<td><p>niobium and tantalum<br> +<i>the two elements always occur together, and were not recognized as +separate until much later in the 19th century</i> +</p></td> +</tr> +<tr> +<td><p>phosphat of lime</p></td> +<td><p>calcium diphosphate <i>or</i> calcium<br> +<i>the element calcium was isolated in 1808, but is named only once in +this 1817 edition</i> +</p></td> +</tr> +<tr> +<td><p>glucium</p></td> +<td><p>beryllium<br> +<i>Humphry Davy’s name for the element</i></p></td> +</tr> +<tr> +<td><p>muriatic acid</p></td> +<td><p>hydrochloric acid<br> +<i>but still called “muriatic acid” for some commercial uses</i> +</p></td> +</tr> +<tr> +<td><p>muriat of lime</p></td> +<td><p>calcium chloride</p></td> +</tr> +<tr> +<td><p>oxymuriate of potash</p></td> +<td><p>potassium chlorate</p></td> +</tr> +<tr> +<td><p>muriat of soda</p></td> +<td><p>sodium chloride (table salt)</p></td> +</tr> +<tr> +<td><p>carbonic acid</p></td> +<td><p>carbon dioxide</p></td> +</tr> +</table> + +<p>Note also:</p> + +<table summary="list of terms"> +<tr> +<td width="33%"><p>simple body, fundamental principle</p></td> +<td><p>element</p></td> +</tr> +<tr> +<td><p>fecula</p></td> +<td><p>starch (usually spelled “fæcula”)</p></td> +</tr> +<tr> +<td><p>spirit of wine</p></td> +<td><p>alcohol</p></td> +</tr> +<tr> +<td><p>philosopher</p></td> +<td><p>scientist</p></td> +</tr> +<tr> +<td><p>arts</p></td> +<td><p>industry, manufacture, crafts etc. (seldom “fine arts”)</p></td> +</tr> +</table> + +<p>Some essential concepts relating to living +things—photosynthesis, microorganisms, the cell, +proteins—are either unknown or not mentioned. The atom theory had +been proposed, but not by Humphry Davy; it is not mentioned in this +book.</p> + +<p>The word “explode” is used at least once in its orginal, figurative +sense (“a word that should be exploded in chemistry”) but far more +often in its later, concrete one. The word “explosion” is always used +concretely (“an explosion, or a <i>detonation</i> as chemists commonly +call it”).</p> + + +<h5>Calculated Values:</h5> + +<p>“the point of zero, or the absolute privation of heat, must +consequently be 1260 degrees below 32 degrees”</p> + +<p class="inset"> +-1228° F. The calculation is based on wrong premises; the correct figure +is about -460° F or -273° C.</p> + +<p>“Mercury congeals only at seventy-two degrees below the freezing +point.”</p> + +<p class="inset"> +-40° F, which is also -40° C. This figure is correct, though +approximate.</p> + +<p>“The proportion stated by Sir H. Davy, in his Chemical Researches, is +as 1 to 2.389.”</p> + +<p>[ammonia] “consisted of about one part of hydrogen to four parts of +nitrogen.... and from the latest and most accurate experiments, the +proportions appear to be, one volume of nitrogen gas to three of +hydrogen gas”</p> + +<p class="inset"> +These and similar calculations involving relative weight and volume make +more sense when one knows the elements’ atomic weights. For nitric acid, +HNO<sub>3</sub>, the figures are 1:14:48, giving a proportion closer to +1:3.5. For ammonia, NH<sub>3</sub> (not 4), the figures are 14:3.</p> + +<p class="inset"> +<i>The first proportion was printed “2,389”. No other decimal numbers +occur in the text, but a comma appears once as a thousands +separator.</i></p> + +<p>“The <i>oxalic acid</i>, distilled from sorrel, is the highest term +of +vegetable acidification; for, if more oxygen be added to it, it loses +its vegetable nature, and is resolved into carbonic acid and water;”</p> + +<p class="inset"> +Oxalic acid = H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>; carbonic acid +(carbon dioxide) = CO<sub>2</sub>. +H<sub>2</sub>C<sub>2</sub>O<sub>4</sub> + O becomes H<sub>2</sub>O + +CO<sub>2</sub> + CO<sub>2</sub>.</p> + + +<h5>Chapter Numbering</h5> + +<p>The 3rd and 4th editions used the same Conversation (chapter) +numbering. The apparent disappearance of XI and XII is the result of +changes between the 4th and 5th (present text) editions:</p> + +<table summary="comparison of editions"> +<tr class="space"> +<td class="center" colspan="3"> +<b>Volume I: On Simple Bodies</b></td> +</tr> +<tr> +<td class="center">4th<br> +edn.</td> +<td class="center">5th<br> +edn.</td> +<td></td> +</tr> +<tr> +<td>I.<br> +II.<br> +III.</td> +<td>I.<br> +II.<br> +III.</td> +<td class="middle"><p><i>No change</i></p></td> +</tr> +<tr> +<td>IV.</td> +<td>IV.</td> +<td> +<p><i>4th:</i> On Specific Heat, Latent Heat, and Chemical Heat.</p> +<p><i>5th:</i> On Combined Caloric, Comprehending Specific Heat and +Latent Heat.</p> +</td> +</tr> +<tr> +<td></td> +<td>V.</td> +<td><p>On The Chemical Agencies Of Electricity.</p> +<p><i>Chapter added in 5th edition</i></p></td> +</tr> +<tr> +<td>V.</td> +<td>VI.</td> +<td><p>On Oxygen And Nitrogen.</p></td> +</tr> +<tr> +<td>VI.</td> +<td>VII.</td> +<td><p>On Hydrogen.</p> +<p><i>5th:</i> new sections on Gas lights and Miner’s Lamp</p></td> +</tr> +<tr> +<td>VII.</td> +<td>VIII.</td> +<td><p>On Sulphur And Phosphorus.</p> +<p><i>5th:</i> new section on Decomposition of Sulphur</p> +</td> +</tr> +<tr> +<td>VIII.</td> +<td>IX.</td> +<td> +<p><i>4th:</i> On Carbone.</p> +<p><i>5th:</i> On Carbon.</p> +</td> +</tr> +<tr> +<td>IX.</td> +<td>X.</td> +<td><p>On Metals.</p></td> +</tr> +<tr> +<td>X.</td> +<td></td> +<td><p>On Alkalies.</p></td> +</tr> +<tr> +<td>XI.</td> +<td></td> +<td> +<p>On Earths.</p> +<p><i>Conversations X, XI were moved to Volume II as XIV, XV.</i></p> +</td> +</tr> +<tr class="space"> +<td class="center" colspan="3"> +<b>Volume II: On Compound Bodies</b> +</td> +</tr> +<tr> +<td class="center">4th<br> +edn.</td> +<td class="center">5th<br> +edn.</td> +<td></td> +</tr> +<tr> +<td>XII.</td> +<td>XIII.</td> +<td><p>On The Attraction Of Composition.</p></td> +</tr> +<tr> +<td></td> +<td>XIV.</td> +<td><p>On Alkalies.</p></td> +</tr> +<tr> +<td></td> +<td>XV.</td> +<td> +<p>On Earths.</p> +<p><i>Conversations XIV, XV were previously X, XI in Volume I.</i></p> +</td> +</tr> +<tr> +<td>XIII.</td> +<td>XVI.</td> +<td><p><i>4th:</i> On Compound Bodies.</p> +<p><i>5th:</i> On Acids.</p> +<p><i>Most of XIII, On Compound Bodies, became XVI, On Acids. Some +introductory material was moved to XIV, On Alkalies.</i></p> +</td> +</tr> +<tr> +<td>XIV.</td> +<td>XVII.</td> +<td> +<p><i>4th:</i> On The Combinations of Oxygen with Sulphur and with +Phosphorus; and of the Sulphats And Phosphats.</p> +<p><i>5th:</i> Of the Sulphuric and Phosphoric Acids: or, The +Combinations of ....</p> +</td> +</tr> +<tr> +<td>XV.</td> +<td>XVIII.</td> +<td> +<p><i>4th:</i> On The Combination of Oxygen With Nitrogen and with +Carbone; and of The Nitrats And Carbonats.</p> +<p><i>5th:</i> Of The Nitric And Carbonic Acids: Or The Combination +...</p> +</td> +</tr> +<tr> +<td>XVI.</td> +<td>XIX.</td> +<td> +<p><i>4th:</i> On Muriatic And Oxygenated Muriatic Acids; and on +Muriats.</p> +<p><i>5th:</i> On The Boracic, Fluoric, Muriatic, and Oxygenated +Muriatic Acids; and on Muriats.</p> +</td> +</tr> +<tr> +<td>XVII.</td> +<td>XX.</td> +<td><p>On The Nature And Composition Of Vegetables.</p></td> +</tr> +<tr> +<td class="center" colspan="3"> +<i>Remainder of book: number in 4th edn. + 3 = number in 5th edn.</i> +</td> +</tr> +</table> + +<h5>Plates</h5> + +<p>Most Plates include the following text, engraved in smaller +print:</p> + +<p class="inset"> +Drawn by the Author / Engraved by Lowry / Published by Longman & +C<sup>o</sup>. Oct<sup>r</sup>. 2<sup>nd</sup>. 1809.</p> + +<p>This date corresponds to the 3rd edition. Plates V, X and +XIII—each containing material new to the 5th edition—read +only “Lowry sculp.”</p> + +<h5>Inconsistencies and variant spellings</h5> + +<p>None of these lists are meant to be inclusive. They are typical of +variations that were not marked as errors.</p> + +<p>Standard spellings throughout the book:</p> + +<div class="inset"> +<p>bason, judgment, embrio, volcanos (plural), potatoe (singular)</p> +</div> + +<p>Inconsistencies:</p> + +<div class="inset"> +<p>capitalization of “Fig.” or “fig.”</p> +<p>hyphenization of words such as “oxy-muriatic”</p> +<p>“glauber salt” and “Glauber’s salt” both occur</p> +</div> + +<p>Variant forms:</p> + +<div class="inset"> +<p>opake, opaque</p> +<p>aëriform, aeriform</p> +<p>gasses, gases</p> +<p>phosphoret, phosphuret (but always carburet)</p> +<p>Libya, Lybia</p> +<p>dy(e)ing (from “dye”)</p> +<p>nap(h)tha</p> +<p>pla(i)ster</p> +<p>slak(e)ing</p> +<p>earthen-ware, earthen ware</p> +<p>“sulphurous”, “naphtha” are used in the Contents and the Index; +“sulphureous”, “naptha” in the body text</p> +<p>forms in “-xion” (such as “connexion”) appear only in the Contents +and the Index</p> +</div> + +<p>Volume I has more archaic forms than Volume II:</p> + +<div class="inset"> +<p>“shew”, “inclose” are sometimes used instead of “show”, “enclose”</p> +<p>“carbone” with final “e” appears in one Plate caption. (In the same +plate’s header, the “e” appears to have been removed by the +engraver.)</p> +<p>“develope(ment)” is more common in Volume I, “develop(ment)” in +Volume II</p> +<p>“-ize” and “-yze” forms (for later “-ise” and “-yse”) are common in +Volume I, rare in Volume II except in the Index</p> +</div> + +<p class="space"> +The “Dr. Marcet” mentioned in a few footnotes and figure captions is the +author’s husband. Humphry Davy (“Sir H. Davy”) was knighted in 1812, +between the 3rd and 4th editions of the book.</p> + +<h5>Reminder</h5> + +<p>DO NOT TRY THIS AT HOME.</p> + + +</div> + + + + + + + + +<pre> + + + + + +End of Project Gutenberg's Conversations on Chemistry, V. 1-2, by Jane Marcet + +*** END OF THIS PROJECT GUTENBERG EBOOK CONVERSATIONS ON CHEMISTRY, V. 1-2 *** + +***** This file should be named 26908-h.htm or 26908-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/6/9/0/26908/ + +Produced by Louise Hope + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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