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diff --git a/38246-h/38246-h.htm b/38246-h/38246-h.htm new file mode 100644 index 0000000..dbfaeed --- /dev/null +++ b/38246-h/38246-h.htm @@ -0,0 +1,9041 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /> +<title>The Project Gutenberg eBook of Heroes of Science, by M. M. Pattison Muir</title> + <style type="text/css"> + + p { margin-top: .75em; + text-align: justify; + margin-bottom: .75em; + } + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; + } + hr { width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; + } + + table {margin-left: auto; margin-right: auto;} + + body{margin-left: 10%; + margin-right: 10%; + } + + .pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: smaller; + text-align: right; + } /* page numbers */ + + .tocnum {position: absolute; top: auto; right: 10%;} + .blockquot{margin-left: 5%; margin-right: 10%;} + + .center {text-align: center;} + .right {text-align: right;} + .smcap {font-variant: small-caps;} + + .caption {font-weight: bold;} + + .figcenter {margin: auto; text-align: center;} + + .figleft {float: left; clear: left; margin-left: 0; margin-bottom: 1em; margin-top: + 1em; margin-right: 1em; padding: 0; text-align: center;} + + .figright {float: right; clear: right; margin-left: 1em; margin-bottom: 1em; + margin-top: 1em; margin-right: 0; padding: 0; text-align: center;} + + .footnotes {border: dashed 1px;} + .footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + .footnote .label {position: absolute; right: 84%; text-align: right;} + .fnanchor {vertical-align: super; font-size: .8em; text-decoration: none;} + + .poem {margin-left:10%; margin-right:10%; text-align: left;} + .poem br {display: none;} + .poem .stanza {margin: 1em 0em 1em 0em;} + .poem span.i0 {display: block; margin-left: 0em; padding-left: 3em; text-indent: -3em;} + .poem span.i2 {display: block; margin-left: 1em; padding-left: 3em; text-indent: -3em;} + .poem span.i4 {display: block; margin-left: 2em; padding-left: 3em; text-indent: -3em;} + .poem span.i1 {display: block; margin-left: 0em; padding-left: 3em; text-indent: -3em;} + .poem span.i10 {display: block; margin-left: 5em; padding-left: 3em; text-indent: -3em;} + .poem span.i14 {display: block; margin-left: 7em; padding-left: 3em; text-indent: -3em;} + .poem span.i17 {display: block; margin-left: 8em; padding-left: 3em; text-indent: -3em;} + .poem span.i3 {display: block; margin-left: 2em; padding-left: 3em; text-indent: -3em;} + .poem span.i8 {display: block; margin-left: 4em; padding-left: 3em; text-indent: -3em;} + + hr.full { width: 100%; + margin-top: 3em; + margin-bottom: 0em; + margin-left: auto; + margin-right: auto; + height: 4px; + border-width: 4px 0 0 0; /* remove all borders except the top one */ + border-style: solid; + border-color: #000000; + clear: both; } + pre {font-size: 85%;} + </style> +</head> +<body> +<h1>The Project Gutenberg eBook, Heroes of Science, by M. M. Pattison Muir</h1> +<pre> +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 <a href = "http://www.gutenberg.org">www.gutenberg.org</a></pre> +<p>Title: Heroes of Science</p> +<p> Chemists</p> +<p>Author: M. M. Pattison Muir</p> +<p>Release Date: December 7, 2011 [eBook #38246]</p> +<p>Language: English</p> +<p>Character set encoding: ISO-8859-1</p> +<p>***START OF THE PROJECT GUTENBERG EBOOK HEROES OF SCIENCE***</p> +<p> </p> +<h3>E-text prepared by<br /> + Albert László, P. G. Máté, Josephine Paolucci,<br /> + and the Online Distributed Proofreading Team<br /> + (http://www.pgdp.net)</h3> +<p> </p> +<hr class="full" /> +<p> </p> +<p> </p> +<p> </p> + +<h1>HEROES OF SCIENCE.</h1> + +<h2>CHEMISTS</h2> + +<h3>BY</h3> + +<h2>M. M. PATTISON MUIR, M.A., F.R.S.E.,</h2> + +<h4>FELLOW, AND PRÆLECTOR IN CHEMISTRY, OF GONVILLE AND CAIUS COLLEGE, +CAMBRIDGE.</h4> + +<p class="center"> +PUBLISHED UNDER THE DIRECTION OF THE COMMITTEE<br /> +OF GENERAL LITERATURE AND EDUCATION APPOINTED BY THE<br /> +SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE.<br /> +<br /><br /><br /><br /><br /> +LONDON:<br /> +<br /> +SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE,<br /> +NORTHUMBERLAND AVENUE, CHARING CROSS;<br /> +<br /> +43, QUEEN VICTORIA STREET, E.C.;<br /> +26, ST. GEORGE'S PLACE, HYDE PARK CORNER, S.W.<br /> +<br /> +BRIGHTON: <span class="smcap">135, north street</span>.<br /> +<br /> +<span class="smcap">New York</span>: E. & J. B. YOUNG & CO.<br /> +1883.<br /><br /> +</p> + + +<div class="blockquot"><p>"The discoveries of great men never leave us; they are +immortal; they contain those eternal truths which +survive the shock of empires, outlive the struggles of +rival creeds, and witness the decay of successive +religions."—<span class="smcap">Buckle.</span></p> + +<p>"He who studies Nature has continually the exquisite +pleasure of discerning or half discerning and divining +laws; regularities glimmer through an appearance of +confusion, analogies between phenomena of a different +order suggest themselves and set the imagination in +motion; the mind is haunted with the sense of a vast +unity not yet discoverable or nameable. There is food +for contemplation which never runs short; you gaze at +an object which is always growing clearer, and yet +always, in the very act of growing clearer, presenting +new mysteries."—<span class="smcap">The author of "Ecce Homo."</span></p> + +<p>"Je länger ich lebe, desto mehr verlern' ich das +Gelernte, nämlich die Systeme."—<span class="smcap">Jean Paul Richter.</span></p></div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p> + + +<div class="figcenter" style="width: 500px;"> +<img src="images/pref.jpg" width="500" height="100" alt="" title="" /> +</div> + +<h2>PREFACE.</h2> + + +<p>I have endeavoured in this book to keep to the lines laid down for me by +the Publication Committee of the Society, viz. "to exhibit, by selected +biographies, the progress of chemistry from the beginning of the inductive +method until the present time." The progress of chemistry has been made the +central theme; around this I have tried to group short accounts of the +lives of those who have most assisted this progress by their labours.</p> + +<p>This method of treatment, if properly conducted, exhibits the advances made +in science as intimately connected with the lives and characters of those +who studied it, and also impresses on the reader the continuity of the +progress of natural knowledge.<span class='pagenum'><a name="Page_iv" id="Page_iv">[Pg iv]</a></span></p> + +<p>The lives of a few chemists have been written; of others there are, +however, only scanty notices to be found. The materials for this book have +been collected chiefly from the following works:—</p> + +<div class="blockquot"><p>Kopp's "Geschichte der Chemie."</p> + +<p>Thomson's "History of Chemistry."</p> + +<p>Ladenburg's "Entwickelungsgeschichte der Chemie."</p> + +<p>Wurtz's "History of the Atomic Theory."</p> + +<p>Watts's "Dictionary of Chemistry."</p> + +<p>Whewell's "History of the Inductive Sciences."</p> + +<p>Rodwell's "Birth of Chemistry;" "Inquiry into the +Hermetic Mystery and Alchemy" (London, 1850); "Popular +Treatises on Science written during the Middle Ages," +edited for the Historical Society of Science by Thomas +Wright, M.A. (London, 1841); "Ripley Reviv'd; or, An +Exposition upon Sir George Ripley's Hermetico-Poetical +Works," by Eirenæus Philalethes (London, 1678); "Tripus +Aureus, hoc est Tres Tractates Chymici Selectissimi" +(Frankfurt, 1618).</p> + +<p>"Alchemy;" article in "Encyclopædia Britannica."</p> + +<p>Boyle's "Sceptical Chymist."</p> + +<p>"Biographie Universelle;" for notices of Berzelius and +Lavoisier.</p> + +<p>"English Cyclopædia;" for notices of Black, Berzelius +and Lavoisier.</p> + +<p>Black's "Lectures," with Memoir: edited by Dr. +Robinson.</p> + +<p>Priestley's "Memoirs:" written partly by himself.</p> + +<p>Priestley's works on "Air," etc.</p> + +<p>Lavoisier's "Œuvres."</p> + +<p>Dalton's "Life," by Dr. Henry; "Life," by Dr. R. Angus +Smith; "New System of Chemical Philosophy."</p> + +<p>Davy's "Collected Works;" with Life, by his brother; +"Life," by Dr. Paris.<span class='pagenum'><a name="Page_v" id="Page_v">[Pg v]</a></span></p> + +<p>Berzelius's "Lehrbuch," and various dissertations.</p> + +<p>Wöhler's "Jugenderinnerungen eines Chemikers."</p> + +<p>Graham's "Collected Memoirs."</p> + +<p>Sketch of Graham's life, in Chemical Society's Journal.</p> + +<p>"Life-Work of Liebig," by A. W. Hofmann.</p> + +<p>"Dumas," by A. W. Hofmann.</p> + +<p>Various dissertations by Liebig and Dumas in <i>Annalen</i>, +and elsewhere.</p></div> + +<p>My warmest thanks are due to my friend, Mr. Francis Rye, for the great +assistance he has given me in correcting the proof-sheets.</p> + +<p class="right"> +M. M. PATTISON MUIR.<br /> +<br /> +<span class="smcap">Cambridge</span>, <i>April, 1883</i>.<br /> +</p> + + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_vi" id="Page_vi">[Pg vi]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/cont.jpg" width="500" height="97" alt="" title="" /> +</div> + +<h2>CONTENTS.</h2> + + +<p><span class="tocnum">PAGE</span><br /><br /></p> + +<p><span class="smcap">Introductory</span> <span class="tocnum"><a href='#Page_1'>1</a></span></p> + + +<h4>CHAPTER I.</h4> + +<p>ALCHEMY: AND THE DAWN OF CHEMISTRY.</p> + +<div class="blockquot"><p>Beginnings of natural knowledge—Chemistry in the +Middle Ages—Alchemy—The phlogistic theory <span class="tocnum"><a href='#Page_5'>5</a></span></p></div> + + +<h4>CHAPTER II.</h4> + +<p>ESTABLISHMENT OF CHEMISTRY AS A SCIENCE—PERIOD OF BLACK, PRIESTLEY AND +LAVOISIER.</p> + +<div class="blockquot"><p>Introduction of accurate measurements into +chemistry—Black's researches on alkalis and on fixed +air—His conception of heat—Priestley's experiments on +airs—His discovery of oxygen—Lavoisier, the founder +of the science of chemistry—He clearly establishes a +connection between composition and properties of bodies <span class="tocnum"><a href='#Page_30'>30</a></span></p></div> + + +<h4>CHAPTER III.</h4> + +<p>ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL SCIENCE—PERIOD OF DALTON.</p> + +<div class="blockquot"><p>Dalton's training in physical science—He revives and +renders quantitative the atomic theory—The term "atom" +is applied by him to elements and compounds alike—His +rules for chemical synthesis <span class="tocnum"><a href='#Page_106'>106</a></span></p></div><p><span class='pagenum'><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p> + + +<h4>CHAPTER IV.</h4> + +<p>ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL SCIENCE +(<i>continued</i>)—PERIOD OF DAVY AND BERZELIUS.</p> + +<div class="blockquot"><p>Electro-chemistry—The dualistic theory developed by +Berzelius—Davy's work on acids, alkalis, and salts—He +proves chlorine to be an element—His discovery of the +safety-lamp <span class="tocnum"><a href='#Page_155'>155</a></span></p></div> + + +<h4>CHAPTER V.</h4> + +<p>THE WORK OF GRAHAM.</p> + +<div class="blockquot"><p>Graham traces the movements of molecules—He +distinguishes between colloids and +cystalloids—Dialysis <span class="tocnum"><a href='#Page_232'>232</a></span></p></div> + + +<h4>CHAPTER VI.</h4> + +<p>RISE AND PROGRESS OF ORGANIC CHEMISTRY—PERIOD OF LIEBIG AND DUMAS.</p> + +<div class="blockquot"><p>The barrier between inorganic and organic chemistry +begins to be broken down—Wöhler prepares urea—Dumas +opposes the dualistic system of Berzelius—Liebig's +conception of compound radicles—His work in animal and +agricultural chemistry <span class="tocnum"><a href='#Page_252'>252</a></span></p></div> + + +<h4>CHAPTER VII.</h4> + +<p>MODERN CHEMISTRY.</p> + +<div class="blockquot"><p>The relations between composition and properties of +bodies are developed and rendered more +definite—Physical methods are more largely made use of +in chemistry—Spectroscopic analysis <span class="tocnum"><a href='#Page_294'>294</a></span></p></div> + + +<h4>CHAPTER VIII.</h4> + +<div class="blockquot"><p>SUMMARY AND CONCLUSION <span class="tocnum"><a href='#Page_316'>316</a></span></p></div><p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>HEROES OF SCIENCE.</h2> + + + +<hr style="width: 65%;" /> + + +<div class="figcenter" style="width: 500px;"> +<img src="images/intro.jpg" width="500" height="102" alt="" title="" /> +</div> + +<h2>INTRODUCTORY.</h2> + + +<p>As we trace the development of any branch of natural knowledge we find that +there has been a gradual progress from vague and fanciful to accurate and +definite views of Nature. We find that as man's conceptions of natural +phenomena become more accurate they also for a time become more limited, +but that this limitation is necessary in order that facts may be correctly +classified, and so there may be laid the basis for generalizations which, +being definite, shall also be capable of expansion.</p> + +<p>At first Nature is strange; she is full of wonderful and fearful +appearances. Man is overwhelmed by the sudden and apparently irregular +outbreaks of storms, by the capricious freaks of thunder and lightning, by +the awful and unannounced devastations of the volcano or the earthquake; he +believes himself to be surrounded by an invisible array of<span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span> beings more +powerful than himself, but, like himself, changeable in their moods and +easily provoked to anger. After a time he begins to find that it is +possible to trace points of connection between some of the appearances +which had so overpowered or perplexed him.</p> + +<p>The huntsman observes that certain kinds of plants always grow where the +game which he pursues is chiefly to be found; from the appearance of the +sky at morning and evening the fisherman is able to tell whether there will +follow weather suitable for him to set out in his fishing-boat; the tiller +of the ground begins to feel sure that if he sow the seed in the well-dug +soil and water it in proper seasons he will certainly reap the harvest in +due time. And thus man comes to believe that natural events follow each +other in a fixed order; there arises a conscious reference on his part of +certain effects to certain definite causes. Accurate knowledge has begun.</p> + +<p>As knowledge of natural appearances advances there comes a time when men +devote themselves chiefly to a careful study of some one class of facts; +they try to consider that part of Nature with which they are mostly +concerned as separate from all other parts of Nature. Thus the various +branches of natural knowledge begin to have each a distinct existence. +These branches get more and more subdivided, each division is more +accurately studied, and so a great number of facts is accumulated in many +classes. Then we usually<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span> find that a master mind arises, who shows the +connection which exists between the different parts of each division of +natural knowledge, who takes a wide, far-reaching view of the whole range +of the province of knowledge which he studies, and who, at the same time, +is able to hold in his vision all the important details of each branch of +which that province is composed.</p> + +<p>And thus we again get wide views of Nature. But these are very different +from the vague, dim and hesitating notions in which natural knowledge had +its beginnings. In this later time men see that Nature is both simple and +complex; that she is more wonderful than their fathers dreamed, but that +through all the complexity there runs a definite purpose; that the +apparently separate facts are bound together by definite laws, and that to +discover this purpose and these laws is possible for man.</p> + +<p>As we trace this progress in the various branches of natural knowledge we +are struck with the fact that each important advance is generally +accomplished by one or two leading men; we find that it becomes possible to +group the history of each period round a few central figures; and we also +learn that the character of the work done by each of these men of note is +dependent on the nature and training of the individual man.</p> + +<p>It will be my endeavour in the following pages to give an account of the +advance of chemical science, grouping the facts in each stage of progress<span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span> +round the figures of one or two men who were prominent in that period.</p> + +<p>For the purposes of this book it will be necessary that I should sketch +only the most important periods in the story of chemical progress, and that +in each of these I should fill in the prominent points alone.</p> + +<p>I shall therefore select three periods in the progress of this science, and +try to give an account of the main work done in each of these. And the +periods will be:—</p> + +<p>I. The period wherein, chiefly by the work of Black, Priestley and +Lavoisier, the aim of chemical science was defined and the essential +characters of the phenomena to be studied were clearly stated.</p> + +<p>II. The period during which, chiefly by the labours of Dalton, Berzelius +and Davy, the great central propositions of the science were laid down and +were developed into a definite theory. As belonging in great extent to this +period, although chronologically later, I shall also consider the work of +Graham.</p> + +<p>III. The period when, chiefly owing to advances made in organic chemistry, +broader and more far-reaching systems of classification were introduced, +and the propositions laid down in the preceding period were modified and +strengthened. The workers in this period were very numerous; I shall +chiefly consider these two—Liebig and Dumas.</p> + +<p>I shall conclude with a brief sketch of some of the important advances of +chemical science in more recent times, and a summary of the characteristics +of each of the three periods.</p> + + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap1.jpg" width="500" height="99" alt="" title="" /> +</div> + +<h2>CHAPTER I.</h2> + +<h3>ALCHEMY: AND THE DAWN OF CHEMISTRY.</h3> + + +<p>Early chemistry was not a science. The ancient chemists dealt chiefly with +what we should now call chemical manufactures; they made glass, cleaned +leather, dyed cloth purple and other colours, extracted metals from their +ores, and made alloys of metals. No well-founded explanations of these +processes could be expected either from men who simply used the recipes of +their predecessors, or from philosophers who studied natural science, not +by the help of accurate experiments, but by the unaided light of their own +minds.</p> + +<p>At somewhat later times chemistry assumed a very important place in the +general schemes propounded by philosophers.</p> + +<p>Change is vividly impressed on all man's surroundings: the endeavour to +find some resting-place amidst the chaos of circumstances, some unchanging +substance beneath the ever-changing<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span> appearances of things, has always held +a prominent place with those who study the phenomena of the world which +surrounds them. In the third and fourth centuries of our era much attention +was given to the art which professed to explain the changes of Nature. +Religion, philosophy, and what we should now call natural science, were at +that time closely intermingled; the scheme of things which then, and for +several centuries after that time, exerted a powerful influence over the +minds of many thinkers was largely based on the conception of a fundamental +unity underlying and regulating the observed dissimilarities of the +universe.</p> + +<p>Thus, in the <i>Emerald Table of Hermes</i>, which was held in much repute in +the Middle Ages, we read—</p> + +<p>"True, without error, certain and most true: that which is above is as that +which is below, and that which is below is as that which is above, for +performing the miracles of the <i>One Thing</i>; and as all things were from +one, by the mediation of one, so all things arose from this one thing by +adaptation: the father of it is the Sun, the mother of it is the Moon, the +wind carried it in its belly, the nurse of it is the Earth. This is the +father of all perfection, the consummation of the whole world."</p> + +<p>And again, in a later writing we have laid down the basis of the art of +alchemy in the proposition that "there abides in nature a certain pure +matter,<span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span> which, being discovered and brought by art to perfection, converts +to itself proportionally all imperfect bodies that it touches."</p> + +<p>To discover this fundamental principle, this <i>One Thing</i>, became the object +of all research. Earth and the heavens were supposed to be bound together +by the all-pervading presence of the One Thing; he who should attain to a +knowledge of this precious essence would possess all wisdom. To the vision +of those who pursued the quest for the One Thing the whole universe was +filled by one ever-working spirit, concealed now by this, now by that veil +of sense, ever escaping identification in any concrete form, yet certainly +capable of being apprehended by the diligent searcher.</p> + +<p>Analogy was the chief guide in this search. If it were granted that all +natural appearances were manifestations of the activity of one essential +principle, then the vaguest and most far-fetched analogies between the +phenomena of nature might, if properly followed up, lead to the +apprehension of this hidden but everywhere present essence.</p> + +<p>The history of alchemy teaches, in the most striking manner, the dangers +which beset this method of pursuing the study of Nature; this history +teaches us that analogies, unless founded on carefully and accurately +determined facts, are generally utterly misleading in natural science.</p> + +<p>Let us consider the nature of the experimental evidence which an alchemist +of the fourth or fifth century could produce in favour of his statement<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span> +that transmutation of one kind of matter into another is of constant +occurrence in Nature.</p> + +<p>The alchemist heated a quantity of water in an open glass vessel; the water +slowly disappeared, and when it was all gone there remained in the vessel a +small quantity of a white earthy solid substance. What could this +experiment teach save that water was changed into earth and air? The +alchemist then plunged a piece of red-hot iron into water placed under a +bell-shaped glass vessel; some of the water seemed to be changed into air, +and a candle, when brought into the bell, caused the air therein to take +fire. Therefore, concluded the experimenter, water is proved to be +changeable into fire.</p> + +<p>A piece of lead was then strongly heated in the air; it lost its lustre and +became changed into a reddish-white powder, very unlike lead in its +properties; this powder was then heated in a convenient vessel with a +little wheat, whereupon the lead was again produced. Therefore, said the +alchemist, lead is destroyed by fire, but it can be reproduced from its +ashes by the help of heat and a few grains of corn.</p> + +<p>The experimenter would now proceed to heat a quantity of a mineral +containing lead in an open vessel made of pulverized bones; the lead slowly +disappeared, and at the close of the experiment a button of silver +remained. Might he not triumphantly assert that he had transmuted lead into +silver?<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span></p> + +<p>In order that the doctrine of the transmutation of metals might rest on yet +surer evidence, the alchemist placed a piece of copper in spirits of nitre +(nitric acid); the metal disappeared; into the green liquid thus produced +he then placed a piece of iron; the copper again made its appearance, while +the iron was removed. He might now well say that if lead was thus +demonstrably changed into silver, and copper into iron, it was, to say the +least, extremely probable that any metal might be changed into any other +provided the proper means for producing the change could be discovered.</p> + +<p>But the experimental alchemist had a yet stranger transmutation wherewith +to convince the most sceptical. He poured mercury in a fine stream on to +melted sulphur; at once the mercury and the sulphur disappeared, and in +their place was found a solid substance black as the raven's wing. He then +heated this black substance in a closed vessel, when it also disappeared, +and in its place there was found, deposited on the cooler part of the +vessel, a brilliantly red-coloured solid. This experiment taught lessons +alike to the alchemist, the philosopher, and the moralist of these times. +The alchemist learned that to change one kind of matter into another was an +easy task: the philosopher learned that the prevalence of change or +transmutation is one of the laws of Nature: and the moralist learned that +evil is not wholly evil, but contains also some germs of good; for was not +the raven-black substance emblematical of the evil,<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> and the red-coloured +matter of the good principle of things?<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></p> + +<p>On such experimental evidence as this the building of alchemy was reared. A +close relationship was believed to prevail through the whole phenomena of +Nature. What more natural then than to regard the changes which occur among +the forms of matter on this earth as intimately connected with the changes +which occur among the heavenly bodies?</p> + +<p>Man has ever been overawed by the majesty of the stars; yet he has not +failed to notice that the movements of these bodies are apparently +capricious. The moon has always been to him a type of mutability; only in +the sun has he seemed to find a settled resting-point. Now, when we +remember that in the alchemical scheme of things the material earth and +material heavens, the intellectual, the moral, and the spiritual world were +regarded as one great whole, the parts of which were continuously acting +and reacting on each other, we cannot wonder that the alchemist should +regard special phenomena which he observed in his laboratory, or special +forms of matter which he examined, as being more directly than other +phenomena or other forms of matter, under the influence of the heavenly +bodies. This connection became gradually more apparent to the student of +alchemy,<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span> until at last it was fixed in the language and the symbols which +he employed.</p> + +<p>Thus the sun (Sol) was represented by a circle, which likewise became the +symbol for gold, as being the most perfect metal. The moon (Luna) was ever +changing; she was represented by a half-circle, which also symbolized the +pale metal silver.</p> + +<p>Copper and iron were regarded as belonging to the same class of metals as +gold, but their less perfect nature was denoted by the sign + or ↑. Tin and lead belonged to the lunar class, but like copper +they were supposed to be imperfect metals. Mercury was at once solar and +lunar in its properties.</p> + +<p>These suppositions were summed up in such alchemical symbols as are +represented below—</p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/i_019.jpg" width="500" height="376" alt="" title="" /> +</div><p><span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span></p> + +<p>Many of the alchemical names remain to the present time; thus in pharmacy +the name "lunar caustic" is applied to silver nitrate, and the symptoms +indicative of lead-poisoning are grouped together under the designation of +"saturnine cholic."</p> + +<p>But as the times advanced the older and nobler conception of alchemy became +degraded.</p> + +<p>If it be true, the later alchemists urged, that all things suffer change, +but that a changeless essence or principle underlies all changing things, +and that the presence of more or less of this essence confers on each form +of matter its special properties, it follows that he who can possess +himself of this principle will be able to transmute any metal into any +other; he will be able to change any metal into gold.</p> + +<p>Now, as the possession of gold has always carried with it the means of +living luxuriously, it is easy to understand how, when this practical +aspect of alchemy had taken firm root in men's minds, the pursuit of the +art became for all, except a few lofty and noble spirits, synonymous with +the pursuit of wealth. So that we shall not, I think, much err if we +describe the chemistry of the later Middle Ages as an effort to accumulate +facts on which might be founded the art of making gold. In one respect this +was an advance. In the early days of alchemy there had been too much +trusting to the mental powers for the manufacture of natural facts: +chemists now actually worked in laboratories;<span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span> and very hard did many of +these alchemists work.</p> + +<p>Paracelsus says of the alchemists, "They are not given to idleness, nor go +in a proud habit, or plush and velvet garments, often showing their rings +upon their fingers, or wearing swords with silver hilts by their sides, or +fine and gay gloves upon their hands; but diligently follow their labours, +sweating whole days and nights by their furnaces. They do not spend their +time abroad for recreation, but take delight in their laboratory. They put +their fingers amongst coals, into clay and filth, not into gold rings. They +are sooty and black like smiths and miners, and do not pride themselves +upon clean and beautiful faces." By thus "taking delight in their +laboratories" the later alchemists gathered together many facts; but their +work centred round one idea, viz. that metals might all be changed into +gold, and this idea was the result rather of intellectual guessing than of +reasoning on established facts of Nature.</p> + +<p>One of the most famous alchemists of the Middle Ages was born at +Einsiedeln, in Switzerland, in 1493. His name, when paraphrased into Greek, +became Paracelsus. This man, some of whose remarks have just been quoted, +acquired great fame as a medical practitioner, and also as a lecturer on +medicine: he travelled throughout the greater part of Europe, and is +supposed to have been taught the use of several new medicines by the +Arabian physicians whom he met in Spain. With an over-weening<span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span> sense of his +own powers, with an ardent and intemperate disposition, revolting against +all authority in medicine or science, Paracelsus yet did a good work in +calling men to the study of Nature as the only means whereby natural +science could be advanced.</p> + +<p>"Alchemy has but one aim and object," Paracelsus taught: "to extract the +quintessence of things, and to prepare arcana and elixirs which may serve +to restore to man the health and soundness he has lost." He taught that the +visible universe is but an outer shell or covering, that there is a spirit +ever at work underneath this veil of phenomena; but that all is not active: +"to separate the active function (the spirit) of this outside shell from +the passive" was, he said, the proper province of alchemy.</p> + +<p>Paracelsus strongly insisted on the importance of the changes which occur +when a substance burns, and in doing this he prepared the way for Stahl and +the phlogistic chemists.</p> + +<p>However we may admire the general conceptions underlying the work of the +earlier alchemists, we must admit that the method of study which they +adopted could lead to very few results of lasting value; and I think we may +add that, however humble the speculations of these older thinkers might +appear, this humility was for the most part only apparent.</p> + +<p>These men were encompassed (as we are) by unexplained appearances: they +were every moment<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span> reminded that man is not "the measure of all things;" +and by not peering too anxiously into the mysteries around them, by drawing +vague conclusions from partially examined appearances, they seemed at once +to admit their own powerlessness and the greatness of Nature. But I think +we shall find, as we proceed with our story, that this is not the true kind +of reverence, and that he is the really humble student of Nature who +refuses to overlook any fact, however small, because he feels the +tremendous significance of every part of the world of wonders which it is +his business and his happiness to explore.</p> + +<p>As examples of the kind of explanation given by alchemists of those aspects +of Nature which they professed to study, I give two quotations from +translations of the writings of Basil Valentine and Paracelsus, who +flourished in the first half of the fifteenth and sixteenth centuries +respectively.</p> + +<p>"Think most diligently about this; often bear in mind, observe and +comprehend that all minerals and metals together, in the same time, and +after the same fashion, and of one and the same principal matter, are +produced and generated. That matter is no other than a mere vapour, which +is extracted from the elementary earth by the superior stars, or by a +sidereal distillation of the macrocosm; which sidereal hot infusion, with +an airy sulphureous property, descending upon inferiors, so acts and +operates as that there is implanted, spiritually and invisibly, a certain +power and virtue<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> in those metals and minerals; which fume, moreover, +resolves in the earth into a certain water wherefrom all metals are +thenceforth generated and ripened to their perfection, and thence proceeds +this or that metal or mineral, according as one of the three principles +acquires dominion and they have much or little of sulphur and salt, or an +unequal mixture of these; whence some metals are fixed, that is, constant +or stable; and some are volatile and easily changeable, as is seen in gold, +silver, copper, iron, tin and lead."</p> + +<p>"The life of metals is a secret fatness; of salts, the spirit of aqua +fortis; of pearls, their splendour; of marcasites and antimony, a tingeing +metalline spirit; of arsenics, a mineral and coagulated poison. The life of +all men is nothing else but an astral balsam, a balsamic impression, and a +celestial invisible fire, an included air, and a tingeing spirit of salt. I +cannot name it more plainly, although it is set out by many names."</p> + +<p>When the alchemists gave directions for making the stone which was to turn +all it touched into gold, they couched them in such strange and symbolical +language as this: "After our serpent has been bound by her chain, +penetrated with the blood of our green dragon, and driven nine or ten times +through the combustible fire into the elementary air, if you do not find +her to be exceeding furious and extremely penetrating, it is a sign that +you do not hit our subject, the notion of the homogenea, or their +proportion; if this furious<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span> serpent does not come over in a cloud and turn +into our virgin milk, or argentine water, not corrosive at all and yet +insensibly and invisibly devouring everything that comes near it, it is +plainly to be seen that you err in the notion of our universal menstruum." +Or, again, what could any reasonable man make of this? "In the green lion's +bed the sun and moon are born; they are married and beget a king. The king +feeds on the lion's blood, which is the king's father and mother, who are +at the same time his brother and sister. I fear I betray the secret, which +I promised my master to conceal in dark speech from any one who knows not +how to rule the philosopher's fire."</p> + +<p>Concerning the same lion, another learned author says that "though called a +lion, it is not an animal substance, but for its transcendant force, and +the rawness of its origin, it is called the green lion." But he adds in a +moment of confidence: "This horrid beast has so many names, that unless God +direct the searcher it is impossible to distinguish him."</p> + +<p>And once more. "Take our two serpents, which are to be found everywhere on +the face of the earth: tie them in a love-knot and shut them up in the +Arabian <i>caraha</i>. This is the first labour; but the next is more difficult. +Thou must encamp against them with the fire of nature, and be sure thou +dost bring thy line round about. Circle them in and stop all avenues that +they find no relief.<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span> Continue this siege patiently, and they turn into an +ugly venomous black toad, which will be transformed to a horrible devouring +dragon, creeping and weltering in the bottom of her cave without wings. +Touch her not by any means, for there is not on earth such a vehement +transcending poison. As thou hast begun so proceed, and this dragon will +turn into a swan. Henceforth I will show thee how to fortify thy fire till +the phœnix appear: it is a red bird of a most deep colour, with a +shining fiery hue. Feed this bird with the fire of his father and the ether +of his mother: for the first is meat and the second is drink, and without +this last he attains not to his full glory. Be sure to understand this +secret," etc., etc.</p> + +<p>The alchemists spoke of twelve gates through which he who would attain to +the palace of true art must pass: these twelve gates were to be unlocked by +twelve keys, descriptions of which, couched in strange and symbolical +language, were given in alchemical treatises. Thus in "Ripley reviv'd"<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> +we read that Canon Ripley, of Bridlington, who lived in the time of Edward +IV., sang thus of the first gate, which was "Calcination:"—</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"The battle's fought, the conquest won,<br /></span> +<span class="i2">The Lyon dead reviv'd;<br /></span> +<span class="i0">The eagle's dead which did him slay,<br /></span> +<span class="i2">And both of sense depriv'd.<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span><br /></span> +<span class="i0">The showers cease, the dews which fell<br /></span> +<span class="i2">For six weeks do not rise;<br /></span> +<span class="i0">The ugly toad that did so swell<br /></span> +<span class="i2">With swelling bursts and dies."<br /></span> +</div></div> + +<p>And of the third gate, or "Conjunction," we find the Canon saying—</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"He was a king, yet dead as dead could be;<br /></span> +<span class="i10">His sister a queen,<br /></span> +<span class="i0">Who when her brother she did breathless see,<br /></span> +<span class="i10">The like was never seen,<br /></span> +<span class="i17">She cryes<br /></span> +<span class="i14">Until her eyes<br /></span> +<span class="i0">With over-weeping were waxed dim—<br /></span> +<span class="i10">So long till her tears<br /></span> +<span class="i10">Reach'd up to her ears:<br /></span> +<span class="i0">The queen sunk, but the king did swim."<br /></span> +</div></div> + +<p>In some books these gates and keys are symbolically represented in +drawings, <i>e.g.</i> in a pamphlet by Paracelsus, called "Tripus Aureus, hoc +est Tres Tractates chymici selectissimi." (Frankfurt, 1618.)</p> + +<p>It is evident that a method of studying Nature which resulted in such dim +and hazy explanations as these was eminently fitted to produce many who +pretended to possess secrets by the use of which they could bring about +startling results beyond the power of ordinary men; and, at the same time, +the almost universal acceptance of such statements as those I have quoted +implied the existence in men generally of a wondrous readiness to believe +anything and everything. Granted that a man<span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span> by "sweating whole days and +nights by his furnaces" can acquire knowledge which gives him great power +over his fellows, it necessarily follows that many will be found ready to +undergo these days and nights of toil. And when we find that this supposed +knowledge is hidden under a mask of strange and mystical signs and +language, we may confidently assert that there will be many who learn to +repeat these strange terms and use these mystical signs without attempting +to penetrate to the truths which lie behind—without, indeed, believing +that the mystical machinery which they use has any real meaning at all.</p> + +<p>We find, as a matter of fact, that the age of the alchemists produced many +deceivers, who, by mumbling incantations and performing a few tricks, which +any common conjuror would now despise, were able to make crowds of men +believe that they possessed a supernatural power to control natural +actions, and, under this belief, to make them part with their money and +their substance.</p> + +<p>One respectable physician of the Hague, who entertained a peripatetic +alchemist, complains that the man entered his "best-furnished room without +wiping his shoes, although they were full of snow and dirt." However, the +physician was rewarded, as the stranger gave him, "out of his philosophical +commiseration, as much as a turnip seed in size" of the much-wished-for +stone of wisdom.</p> + +<p>That the alchemist of popular belief was a man who used a jargon of strange +and high-sounding<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span> words, that he might the better deceive those whom he +pretended to help, is evident from the literature of the sixteenth and +seventeenth centuries.</p> + +<p>In the play of the "Alchymist" Ben Jonson draws the character of Subtle as +that of a complete scoundrel, whose aim is to get money from the pockets of +those who are stupid enough to trust him, and who never hesitates to use +the basest means for this end. From the speeches of Subtle we may learn the +kind of jargon employed by the men who pretended that they could cure +diseases and change all baser metals into gold.</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"<i>Subtle.</i> Name the vexations and the martyrizations of metals in the work.<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Face.</i> Sir, putrefaction,<br /></span> +<span class="i0">Solution, ablution, sublimation,<br /></span> +<span class="i0">Cohobation, calcination, ceration, and<br /></span> +<span class="i0">Fixation.<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Sub.</i> And when comes vivification?<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Face.</i> After mortification.<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Sub.</i> What's cohobation?<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Face.</i> 'Tis the pouring on<br /></span> +<span class="i0">Your aqua regis, and then drawing him off,<br /></span> +<span class="i0">To the trine circle of the seven spheres.<br /></span> +</div></div> + +<hr style='width: 25%;' /> + +<div class="poem"><div class="stanza"> +<span class="i0"><i>Sub.</i> And what's your mercury?<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Face.</i> A very fugitive; he will be gone, sir.<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Sub.</i> How know you him?<br /></span> +</div><div class="stanza"> +<span class="i0"><i>Pace.</i> By his viscosity,<br /></span> +<span class="i0">His oleosity, and his suscitability."<br /></span> +</div></div> + +<p>Even in the fourteenth century, Chaucer (in the "Canon's Yeoman's Tale") +depicts the alchemist as a mere cunning knave. A priest is prevailed<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span> on to +give the alchemist money, and is told that he will be shown the change of +base metal into gold. The alchemist busies himself with preparations, and +sends the priest to fetch coals.</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"And whil he besy was, this feendly wrecche,<br /></span> +<span class="i0">This false chanoun (the foule feende him fecche)<br /></span> +<span class="i0">Out of his bosom took a bechen cole<br /></span> +<span class="i0">In which ful subtilly was maad an hole,<br /></span> +<span class="i0">And therein put was of silver lymayle<br /></span> +<span class="i0">An unce, and stopped was withoute fayle<br /></span> +<span class="i0">The hole with wex, to keep the lymayle in.<br /></span> +<span class="i0">And understondith, that this false gyn<br /></span> +<span class="i0">Was not maad there, but it was maad before."<br /></span> +</div></div> + +<p>This "false gyn" having been put in the crucible and burned with the rest +of the ingredients, duly let out its "silver lymayle" (filings), which +appeared in the shape of a small button of silver, and so accomplished the +"false chanoun's" end of deceiving his victim.</p> + +<p>The alchemists accumulated many facts: they gained not a little knowledge +concerning the appearances of Nature, but they were dominated by a single +idea. Living in the midst of an extremely complex order of things, +surrounded by a strange and apparently capricious succession of phenomena, +they were convinced that the human intelligence, directed and aided by the +teachings of the Church, would guide them through the labyrinth. And so +they entered on the study of Nature with preconceived notions and foregone +conclusions: enthusiastic and determined to know although many of them +were, they nevertheless<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> failed because they refused to tread the only path +which leads to true advances in natural science—the path of unprejudiced +accurate experiment, and of careful reasoning on experimentally determined +facts.</p> + +<p>And even when they had become convinced that their aims were visionary, +they could not break free from the vicious system which bound them.</p> + +<div class="poem"><div class="stanza"> +<span class="i10">"... I am broken and trained<br /></span> +<span class="i0">To my old habits: they are part of me.<br /></span> +<span class="i0">I know, and none so well, my darling ends<br /></span> +<span class="i0">Are proved impossible: no less, no less,<br /></span> +<span class="i0">Even now what humours me, fond fool, as when<br /></span> +<span class="i0">Their faint ghosts sit with me and flatter me,<br /></span> +<span class="i0">And send me back content to my dull round."<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a><br /></span> +</div></div> + +<p>One of the most commonly occurring and most noticeable changes in the +properties of matter is that which proceeds when a piece of wood, or a +candle, or a quantity of oil burns. The solid wood, or candle, or the +liquid oil slowly disappears, and this disappearance is attended with the +visible formation of flame. Even the heavy fixed metals, tin or lead, may +be caused to burn; light is produced, a part of the metal seems to +disappear, and a white (or reddish) solid, very different from the original +metal, remains. The process of burning presents all those peculiarities +which are fitted to strike an observer of the changes of Nature; that is, +which are fitted to strike a chemist—for chemistry has<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span> always been +recognized as having for its object to explain the changes which matter +undergoes. The chemists of the seventeenth and eighteenth centuries were +chiefly occupied in trying to explain this process of burning or +combustion.</p> + +<p>Van Helmont (1577-1644), who was a physician and chemist of Brussels, +clearly distinguished between common air and other "airs" or gases produced +in different ways. Robert Hooke (1635-1703), one of the original Fellows of +the Royal Society, in the "Micographia, or Philosophical Description of +Minute Bodies," published in 1665, concluded from the results of numerous +experiments that there exists in common air a peculiar kind of gas, similar +to, or perhaps identical with the gas or air which is got by heating +saltpetre; and he further supposed that when a solid burns, it is dissolved +by (or we should now say, it is converted into a gas by combining with) +this peculiar constituent of the air.</p> + +<p>John Mayow (1645-1679), a physician of Oxford, experimented on the basis of +facts established by Hooke. He showed that when a substance, <i>e.g.</i> a +candle, burns in air, the volume of air is thereby lessened. To that +portion of the air which had <i>dissolved</i> the burned substance he gave the +name of <i>nitre-air</i>, and he argued that this air exists in condensed form +in nitre, because sulphur burns when heated with nitre in absence of common +air. Mayow added the most important fact—a fact which was forgotten by +many later experimenters—that the solid substance obtained by burning a +metal<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span> in air weighs more than the metal itself did before burning. He +explained this increase in weight by saying that the burning metal absorbs +particles of "nitre-air" from the atmosphere. Thus Hooke and Mayow had +really established the fact that common air consists of more than one +definite kind of matter—in other words, that common air is not an element; +but until recent times the term "element" or "elementary principle" was +used without any definite meaning. When we say that the ancients and the +alchemists recognized four elements—earth, air, fire, and water—we do not +attach to the word "element" the same definite meaning as when we now say, +"Iron is an element."</p> + +<p>From earth, air, fire and water other substances were obtained; or it might +be possible to resolve other substances into one or more of these four. But +even to such a word as "substance" or "matter" no very definite meaning +could be attached. Although, therefore, the facts set forth by Hooke and +Mayow might now justify the assertion that air is not an element, they did +not, in the year 1670, necessarily convey this meaning to men's minds. The +distinction between element and compound was much more clearly laid down by +the Hon. Robert Boyle (1627-1691), whose chemical work was wonderfully +accurate and thorough, and whose writings are characterized by acute +scientific reasoning. We shall again return to these terms "element" and +"compound."</p> + +<p>But the visible and striking phenomenon in most processes of burning is the +production of light and<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> sometimes of flame. The importance of the fact +that the burned substance (when a solid) weighs more than the unburned +substance was overshadowed by the apparent importance of the outward part +of the process, which could scarcely be passed over by any observer. There +appears to be an outrush of <i>something</i> from the burning substance. There +<i>is</i> an outrush of something, said Becher and Stahl, and this something is +the "principle of fire." The principle of fire, they said, is of a very +subtle nature; its particles, which are always in very rapid motion, can +penetrate any substance, however dense. When metals burn—the argument +continued—they lose this principle of fire; when the burned metal—or +<i>calx</i> as it was usually called—is heated with charcoal it regains this +"principle," and so the metal is re-formed from the calx.</p> + +<p>Thus arose the famous theory of <i>phlogiston</i> (from Greek, = "burned"), +which served as a central nucleus round which all chemical facts were +grouped for nearly a hundred years.</p> + +<p>John Joachim Becher was born at Speyer in 1635, and died in 1682; in his +chemical works, the most important of which is the "Physica Subterranea," +he retained the alchemical notion that the metals are composed of three +"principles"—the nitrifiable, the combustible, and the mercurial—and +taught that during calcination the combustible and mercurial principles are +expelled, while the nitrifiable remains in the calx.<span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span></p> + +<p>George Ernest Stahl—born at Anspach in 1660, and died at Berlin in +1734—had regard chiefly to the principles which escape during the +calcination of metals, and simplifying, and at the same rendering more +definite the idea of Becher, he conceived and enunciated the theory of +phlogiston.</p> + +<p>But if <i>something</i> (name it "phlogiston" or call it by any other name you +please) is lost by a metal when the metal is burned, how is it that the +loss of this thing is attended with an increase in the weight of the matter +which loses it? Either the theory of phlogiston must be abandoned, or the +properties of the <i>thing</i> called phlogiston must be very different from +those of any known kind of matter.</p> + +<p>Stahl replied, phlogiston is a "principle of levity;" the presence of +phlogiston in a substance causes that substance to weigh less than it did +before it received this phlogiston.</p> + +<p>In criticizing this strange statement, we must remember that in the middle +of the seventeenth century philosophers in general were not firmly +convinced of the truth that the essential character of matter is that it +possesses weight, nor of the truth that it is impossible to destroy or to +create any quantity of matter however small. It was not until the +experimental work of Lavoisier became generally known that chemists were +convinced of these truths. Nevertheless, the opponents of the Stahlian +doctrine were justified in asking for further explanations—in demanding +that some other facts<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span> analogous to this supposed fact, viz. that a +substance can weigh less than nothing, should be experimentally +established.</p> + +<p>The phlogistic theory however maintained its ground; we shall find that it +had a distinct element of truth in it, but we shall also find that it did +harm to scientific advance. This theory was a wide and sweeping +generalization from a few facts; it certainly gave a central idea around +which some facts might be grouped, and it was not very difficult, by +slightly cutting down here and slightly adding there, to bring many new +discoveries within the general theory.</p> + +<p>We now know that in order to explain the process of combustion much more +accurate knowledge was required than the chemists of the seventeenth +century possessed; but we ought to be thankful to these chemists, and +notably to Stahl, that they did not hesitate to found a generalization on +the knowledge they had. Almost everything propounded in natural science has +been modified as man's knowledge of nature has become wider and more +accurate; but it is because the scientific student of nature uses the +generalizations of to-day as stepping-stones to the better theories of +to-morrow, that science grows "from more to more."</p> + +<p>Looking at the state of chemistry about the middle of the eighteenth +century, we find that the experiments, and especially the measurements, of +Hooke and Mayow had laid a firm basis of fact<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span> concerning the process of +combustion, but that the phlogistic theory, which appeared to contradict +these facts, was supreme; that the existence of airs, or gases, different +from common air was established, but that the properties of these airs were +very slightly and very inaccurately known; that Boyle had distinguished +element from compound and had given definite meanings to these terms, but +that nevertheless the older and vaguer expression, "elementary principle," +was generally used; and lastly, that very few measurements of the masses of +the different kinds of matter taking part in chemical changes had yet been +made.</p> + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> I have borrowed these illustrations of the alchemical, +experimental method from M. Hoefer's "Histoire de la Chimie," quoted in the +"Encyclopædia Brittanica," art. "Alchemy."</p></div> + +<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> "Ripley reviv'd: or an exposition upon Sir George Ripley's +Hermetico-poetical works," by Eirenæus Philalethes. London, 1678.</p></div> + +<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> Browning's "Paracelsus."</p></div> +</div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap2.jpg" width="500" height="99" alt="" title="" /> +</div> + +<h2>CHAPTER II.</h2> + +<h3>ESTABLISHMENT OF CHEMISTRY AS A SCIENCE —PERIOD OF BLACK, PRIESTLEY AND LAVOISIER.</h3> + + +<h4><i>Joseph Black</i>, 1728-1799. <i>Joseph, Priestley</i>, 1733-1804. <i>Antoine Laurent Lavoisier</i>, 1743-1794.</h4> + +<p>During this period of advance, which may be broadly stated as comprising +the last half of the eighteenth century, the aim and scope of chemical +science were clearly indicated by the labours of Black, Priestley and +Lavoisier. The work of these men dealt chiefly with the process of +combustion. Black and Priestley finally proved the existence of airs or +gases different from common air, and Lavoisier applied these discoveries to +give a clear explanation of what happens when a substance burns.</p> + +<hr style='width: 45%;' /> + +<p><span class="smcap">Joseph Black</span> was born near Bordeaux in the year 1728. His father was of +Scottish family, but a native of Belfast; his mother was the daughter of +Mr. Gordon, of Hilhead in Aberdeenshire. We<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> are told by Dr. Robison, in +his preface to Black's Lectures, that John Black, the father of Joseph, was +a man "of most amiable manners, candid and liberal in his sentiments, and +of no common information."</p> + +<p>At the age of twelve Black was sent home to a school at Belfast; after +spending six years there he went to the University of Glasgow in the year +1746. Little is known of his progress at school or at the university, but +judging from his father's letters, which his son preserved, he seems to +have devoted himself to study. While at Glasgow he was attracted to the +pursuit of physical science, and chose medicine as a profession. Becoming a +pupil of Dr. Cullen, he was much impressed with the importance of chemical +knowledge to the student of medicine. Dr. Cullen appears to have been one +of the first to take large and philosophical views of the scope of chemical +science, and to attempt to raise chemistry from the rank of a useful art to +that of a branch of natural philosophy. Such a man must have been attracted +by the young student, whose work was already at once accurate in detail and +wide in general scope.</p> + +<p>In the notes of work kept by Black at this time are displayed those +qualities of methodical arrangement, perseverance and thoroughness which +are so prominent in his published investigations and lectures. In one place +we find, says his biographer, many disjointed facts and records of diverse +observations, but the next time he refers<span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span> to the same subjects we +generally have analogous facts noted and some conclusions drawn—we have +the beginnings of knowledge. Having once entered on an investigation Black +works it out steadily until he gets definite results.</p> + +<p>His earlier notes are concerned chiefly with heat and cold; about 1752 he +begins to make references to the subject of "fixed air."</p> + +<p>About 1750 Black went to Edinburgh University to complete his medical +studies, and here he was again fortunate in finding a really scientific +student occupying the chair of natural philosophy.</p> + +<p>The attention of medical men was directed at this time to the action of +limewater as a remedy for stone in the bladder. All the medicines which +were of any avail in mitigating the pain attendant on this disease more or +less resembled the "caustic ley of the soap-boilers" (or as we should now +call it caustic potash or soda). These caustic medicines were mostly +prepared by the action of quicklime on some other substance, and quicklime +was generally supposed to derive its caustic, or corrosive properties from +the fire which was used in changing ordinary limestone into quicklime.</p> + +<p>When quicklime was heated with "fixed alkalis" (<i>i.e.</i> with potassium or +sodium carbonate), it changed these substances into caustic bodies which +had a corrosive action on animal matter; hence it was concluded that the +quicklime had derived a "power"—or some said had derived "igneous +matter"—from the fire, and had communicated this<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span> to the fixed alkalis, +which thereby acquired the property of corroding animal matter.</p> + +<p>Black thought that he might be able to lay hold of this "igneous matter" +supposed to be taken by the limestone from the fire; but he found that +limestone loses weight when changed into quicklime. He then dissolved +limestone (or chalk) in spirits of salt (hydrochloric acid), and compared +the loss of weight undergone by the chalk in this process with the loss +suffered by an equal quantity of chalk when strongly heated. This +investigation led Black to a fuller study of the action of heat on chalk +and on "mild magnesia" (or as we now say, magnesium carbonate).</p> + +<p>In order that his experiments might be complete and his conclusions well +established, he delayed taking the degree of Doctor of Medicine for three +years. He graduated as M. D. in 1755, and presented his thesis on "Magnesia +Alba, Quicklime and other Alkaline Substances," which contained the results +of what is probably the first accurately quantitative examination of a +chemical action which we possess.</p> + +<p>Black prepared mild magnesia (magnesium carbonate) by boiling together +solutions of Epsom salts (magnesium sulphate) and fixed alkali (potassium +carbonate). He showed that when mild magnesia is heated—</p> + +<p>1. It is much decreased in bulk.</p> + +<p>2. It loses weight (twelve parts become five, according to Black).</p> + +<p>3. It does not precipitate lime from solutions<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> of that substance in acids +(Black had already shown that mild magnesia does precipitate lime).</p> + +<p>He then strongly heated a weighed quantity of mild magnesia in a retort +connected with a receiver; a few drops of water were obtained in the +receiver, but the magnesia lost six or seven times as much weight as the +weight of the water produced. Black then recalls the experiments of Hales, +wherein airs other than common air had been prepared, and concludes that +the loss of weight noticed when mild magnesia is calcined is probably due +to expulsion, by the heat, of some kind of air. Dissolving some of his mild +magnesia in acid he noticed that effervescence occurred, and from this he +concluded that the same air which, according to his hypothesis, is expelled +by heat, is also driven out from the mild magnesia by the action of acid. +He then proceeded to test this hypothesis. One hundred and twenty grains of +mild magnesia were strongly calcined; the calcined matter, amounting to +seventy grains, was dissolved in dilute oil of vitriol, and this solution +was mixed with common fixed alkali (potassium carbonate). The solid which +was thus produced was collected, washed and weighed; it amounted to a +trifle less than one hundred and twenty grains, and possessed all the +properties—detailed by Black—of the original mild magnesia. But this is +exactly the result which ought to have occurred according to his +hypothesis.</p> + +<p>The next step in the investigation was to collect the peculiar air which +Black had proved to be<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> evolved during the calcination of mild magnesia. To +this substance he gave the name of "fixed air," because it was fixed or +held by magnesia. Black established the existence of this air in the +expired breath of animals, and also showed that it was present in the air +evolved during vinous fermentation. He demonstrated several of its +properties; among these, the fact that animals die when placed in this air. +An air with similar properties was obtained by calcining chalk. Black held +that the chemical changes which occur when chalk is calcined are exactly +analogous to those which he had proved to take place when magnesia is +strongly heated. Chalk ought therefore to lose weight when calcined; the +residue ought to neutralize an acid without evolution of any gas, and the +quantity of acid thus neutralized ought to be the same as would be +neutralized by the uncalcined chalk; lastly, it ought to be possible to +recover the uncalcined chalk by adding a fixed alkali to a solution of the +calcined chalk or quicklime.</p> + +<p>The actual results which Black obtained were as follows:—</p> + +<p>One hundred and twenty grains of chalk were dissolved in dilute muriatic +(hydrochloric) acid; 421 grains of the acid were needed to neutralize the +chalk, and 48 grains of fixed air were evolved. One hundred and twenty +grains of the same specimen of chalk were strongly calcined, and then +dissolved in dilute muriatic acid; 414 grains<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span> of the acid were required to +neutralize the calcined chalk. The difference between 421 and 414 is very +slight; considering the state of practical chemistry at Black's time, we +may well agree with him that he was justified in the conclusion that equal +weights of calcined and of uncalcined chalk neutralize the same amount of +acid. One hundred and twenty grains of the same specimen of chalk were +again strongly heated; the calcined chalk, amounting to 68 grains, was +digested with a solution of fixed alkali in water. The substance thus +obtained, when washed and dried, weighed 118 grains, and had all the +properties of ordinary chalk. Therefore, said Black, it is possible to +recover the whole of the chalk originally present before calcination, by +adding a fixed alkali to the calcined chalk or quicklime.</p> + +<p>At this time it was known that water dissolves quicklime, but it was +generally held that only about one-fourth (or perhaps a little more) of any +specimen of quicklime could be dissolved by water, however much water was +employed. Black's researches had led him to regard quicklime as a +homogeneous chemical compound; he concluded that as water undoubtedly +dissolves quicklime to some extent, any specimen of this substance, +provided it be pure, must be wholly soluble in water. Carefully conducted +experiments proved that Black's conclusion was correct. Black had thus +proved that quicklime is a definite substance, with certain fixed +properties which characterize it and mark it off<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> from all other +substances; that by absorbing, or combining with another definite substance +(fixed air), quicklime is changed into a third substance, namely chalk, +which is also characterized by properties as definite and marked as those +of quicklime or fixed air.</p> + +<p>Black, quite as much as the alchemists, recognized the fact that change is +continually proceeding in Nature; but he clearly established the +all-important conclusion that these natural changes proceed in definite +order, and that it is possible by careful experiment and just reasoning to +acquire a knowledge of this order. He began the great work of showing that, +as in other branches of natural science, so also in chemistry, which is +pre-eminently the study of the changes of Nature, "the only distinct +meaning of that word" (natural) "is <i>stated</i>, <i>fixed</i>, or <i>settled</i>" +(Butler's "Analogy," published 1736).</p> + +<p>This research by Black is a model of what scientific work ought to be. He +begins with a few observations of some natural phenomenon; these he +supplements by careful experiments, and thus establishes a sure basis of +fact; he then builds on this basis a general hypothesis, which he proceeds +to test by deducing from it certain necessary conclusions, and proving, or +disproving, these by an appeal to Nature. This is the scientific method; it +is common sense made accurate.</p> + +<p>Very shortly after the publication of the thesis on magnesia and quicklime, +a vacancy occurred<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span> in the chemical chair in Glasgow University, and Black +was appointed Professor of Anatomy and Lecturer on Chemistry. As he did not +feel fully qualified to lecture on anatomy, he made an arrangement to +exchange subjects with the Professor of Medicine, and from this time he +delivered lectures on chemistry and on "The Institutes of Medicine."</p> + +<p>Black devoted a great deal of care and time to the teaching duties of his +chair. His chemical experimental researches were not much advanced after +this time; but he delivered courses of lectures in which new light was +thrown on the whole range of chemical science.</p> + +<p>In the years between 1759 and 1763 Black examined the phenomena of heat and +cold, and gave an explanation, founded on accurate experiments, of the +thermal changes which accompany the melting of solids and the vaporization +of liquids.</p> + +<p>If pieces of wood, lead and ice be taken by the hand from a box in which +they have been kept cold, the wood feels cold to the touch, the lead feels +colder than the wood, and the ice feels colder than the lead; hence it was +concluded that the hand receives cold from the wood, more cold from the +lead, and most cold from the ice.</p> + +<p>Black however showed that the wood really takes away heat from the hand, +but that as the wood soon gets warmed, the process stops before long; that +the lead, not being so quickly warmed as the wood, takes away more heat +from the hand than<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> the wood does, and that the ice takes away more heat +than either wood or lead.</p> + +<p>Black thought that the heat which is taken by melting ice from a warm body +remains in the water which is produced; as soon as winter came he proceeded +to test this supposition by comparing the times required to melt one pound +of ice and to raise the temperature of one pound of water through one +degree, the source of heat being the same in each case. He also compared +the time required to lower the temperature of one pound of water through +one degree with that required to freeze one pound of ice-cold water. He +found that in order to melt one pound of ice without raising its +temperature, as much heat had to be added to the ice as sufficed to raise +the temperature of one pound of water through about 140 degrees of +Fahrenheit's thermometer. But this heat which has been added to the ice to +convert it into water is not indicated by the thermometer. Black called +this "<i>latent heat</i>."</p> + +<p>The experimental data and the complete theory of latent heat were contained +in a paper read by Black to a private society which met in the University +of Glasgow, on April 23, 1762; but it appears that Black was accustomed to +teach the theory in his ordinary lectures before this date.</p> + +<p>The theory of latent heat ought also to explain the phenomena noticed when +liquid water is changed into steam. Black applied his theory generally to +this change, but did not fully work out the details and actually measure +the quantity of heat which is<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> absorbed by water at the boiling point +before it is wholly converted into steam at the same temperature, until +some years later when he had the assistance of his pupil and friend James +Watt.</p> + +<p>Taking a survey of the phenomena of Nature, Black insisted on the +importance of these experimentally established facts—that before ice melts +it must absorb a large quantity of heat, and before water is vaporized it +must absorb another large quantity of heat, which amounts of heat are +restored to surrounding substances when water vapour again becomes liquid +water and when liquid water is congealed to ice. He allows his imagination +to picture the effects of these properties of water in modifying and +ameliorating the climates of tropical and of Northern countries. In his +lectures he says, "Here we can also trace another magnificent train of +changes which are nicely accommodated to the wants of the inhabitants of +this globe. In the equatorial regions, the oppressive heat of the sun is +prevented from a destructive accumulation by copious evaporation. The +waters, stored with their vaporific heat, are then carried aloft into the +atmosphere till the rarest of the vapour reaches the very cold regions of +the air, which immediately forms a small portion of it into a fleecy cloud. +This also further tempers the scorching heat by its opacity, performing the +acceptable office of a screen. From thence the clouds are carried to the +inland countries, to form the sources in the mountains which are to supply +the numberless streams that water the<span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span> fields. And by the steady operation +of causes, which are tolerably uniform, the greater part of the vapours +passes on to the circumpolar regions, there to descend in rains and dews; +and by this beneficent conversion into rain by the cold of those regions, +each particle of steam gives up the heat which was latent in it. This is +immediately diffused, and softens the rigour of those less comfortable +climates."</p> + +<p>In the year 1766 Black was appointed Professor of Chemistry in the +University of Edinburgh, in which position he remained till his death in +1799. During these thirty-three years he devoted himself chiefly to +teaching and to encouraging the advance of chemical science. He was +especially careful in the preparation of his elementary lectures, being +persuaded that it was of the utmost importance that his pupils should be +well grounded in the principles of chemistry.</p> + +<p>His health had never been robust, and as he grew old he was obliged to use +great care in his diet; his simple and methodical character and habits made +it easy for him to live on the plainest food, and to take meals and +exercise at stated times and in fixed quantities.</p> + +<p>Black's life closed, as was fitting, in a quiet and honoured old age. He +had many friends, but lived pretty much alone—he was never married.</p> + +<p>On the 26th of November 1799, "being at table with his usual fare, some +bread, a few prunes and a measured quantity of milk diluted with water,<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span> +and having the cup in his hand when the last stroke of his pulse was to be +given, he had set it down on his knees, which were joined together, and +kept it steady with his hand, in the manner of a person perfectly at ease; +and in this attitude he expired, without spilling a drop, and without a +writhe in his countenance, as if an experiment had been required to show to +his friends the facility with which he departed."</p> + +<p>Black was characterized by "moderation and sobriety of thought;" he had a +great sense of the fitness of things—of what is called by the older +writers "propriety." But he was by no means a dull companion; he enjoyed +general society, and was able to bear a part in any kind of conversation. A +thorough student of Nature, he none the less did not wish to devote his +whole time to laboratory work or to the labours of study; indeed he seems +to have preferred the society of well-cultivated men and women to that of +specialists in his own or other branches of natural science. But with his +true scientific peers he doubtless appeared at his best. Among his more +intimate friends were the famous political economist Adam Smith, and the no +less celebrated philosopher David Hume. Dr. Hutton, one of the earliest +workers in geology, was a particular friend of Black; his friendship with +James Watt began when Watt was a student in his class, and continued during +his life.</p> + +<p>With such men as his friends, and engaged in the study of Nature—that +boundless subject which<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> one can never know to the full, but which one can +always know a little more year by year—Black's life could not but be +happy. His example and his teaching animated his students; he was what a +university professor ought to be, a student among students, but yet a +teacher among pupils. His work gained for him a place in the first rank of +men of science; his clearness of mind, his moderation, his gentleness, his +readiness to accept the views of others provided these views were well +established on a basis of experimentally determined facts, fitted him to be +the centre of a circle of scientific students who looked on him as at once +their teacher and their friend.</p> + +<p>As a lecturer Black was eminently successful. He endeavoured to make all +his lectures plain and intelligible; he enlivened them by many experiments +designed simply to illustrate the special point which he had in view. He +abhorred ostentatious display and trickiness in a teacher.</p> + +<p>Black was strongly opposed to the use of hypotheses in science. Dr. Robison +(the editor of his lectures) tells that when a student in Edinburgh he met +Black, who became interested in him from hearing him speak somewhat +enthusiastically in favour of one of the lecturers in the university. Black +impressed on him the necessity of steady experimental work in natural +science, gave him a copy of Newton's "Optics" as a model after which +scientific work ought to be conducted, and advised him "to reject, even +without examination,<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span> any hypothetical explanation, as a mere waste of time +and ingenuity." But, when we examine Black's own work, we see that by +"hypothetical explanations" he meant vague guesses. He himself made free +use of scientific (<i>i.e.</i> of exact) hypotheses; indeed the history of +science tells us that without hypotheses advance is impossible. Black +taught by his own researches that science is not an array of facts, but +that the object of the student of Nature is to explain facts. But the +method generally in vogue before the time of Black was to gather together a +few facts, or what seemed to be facts, and on these to raise a vast +superstructure of "vain imaginings." Naturalists had scarcely yet learned +that Nature is very complex, and that guessing and reasoning on guesses, +with here and there an observation added, was not the method by which +progress was to be made in learning the lessons written in this complex +book of Nature.</p> + +<p>In place of this loose and slipshod method Black insisted that the student +must endeavour to form a clear mental image of every phenomenon which he +studied. Such an image could be obtained only by beginning with detailed +observation and experiment. From a number of definite mental images the +student must put together a picture of the whole natural phenomenon under +examination; perceiving that something was wanted here, or that the picture +was overcrowded there, he must again go to Nature and gain fresh facts, or +sometimes prove that what had been accepted as facts had no<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> real +existence, and so at length he would arrive at a true representation of the +whole process.</p> + +<p>So anxious was Black to define clearly what he knew and professed to teach, +that he preferred to call his lectures "On the Effects of Heat and +Mixtures," rather than to announce them as "A Systematic Course on +Chemistry."</p> + +<p>His introductory lecture on "Heat in General" is very admirable; the +following quotation will serve to show the clearness of his style and the +methodical but yet eminently suggestive manner of his teaching:—</p> + + +<p><i>"Of Heat in General.</i></p> + +<p>"That this extensive subject may be treated in a profitable manner, I +propose—</p> + +<p>"First. To ascertain what I mean by the word <i>heat</i> in these lectures.</p> + +<p>"Secondly. To explain the meaning of the term <i>cold</i>, and ascertain the +real difference between heat and cold.</p> + +<p>"Thirdly. To mention some of the attempts which have been made to discover +the nature of heat, or to form an idea of what may be the immediate cause +of it.</p> + +<p>"Fourthly and lastly. I shall begin to describe sensible effects produced +by heat on the bodies to which it is communicated.</p> + +<p>"Any person who reflects on the ideas which we annex to the word <i>heat</i> +will perceive that this word<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span> is used for two meanings, or to express two +different things. It either means a sensation excited in our organs, or a +certain quality, affection, or condition of the bodies around us, by which +they excite in us that sensation. The word is used in the first sense when +we say, we feel heat; in the second, when we say, there is heat in the fire +or in a hot stone. There cannot be a sensation of heat in the fire, or in +the hot stone, but the matter of the fire, or of the stone, is in a state +or condition by which it excites in us the sensation of heat.</p> + +<p>"Now, in beginning to treat of heat and its effects, I propose to use the +word in this second sense only; or as expressing that state, condition, or +quality of matter by which it excites in us the sensation of heat. This +idea of heat will be modified a little and extended as we proceed, but the +meaning of the word will continue at bottom the same, and the reason of the +modification will be easily perceived."</p> + +<p>Black's manner of dealing with the phenomenon of combustion illustrates the +clearness of the conceptions which he formed of natural phenomena, and +shows moreover the thoroughly unbiased nature of his mind. As soon as he +had convinced himself that the balance of evidence was in favour of the new +(antiphlogistic) theory, he gave up those doctrines in which he had been +trained, and accepted the teaching of the French chemists; but he did +not—as some with less well-balanced minds might do—regard the new theory +as a final statement, but rather as one stage nearer the complete<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> +explanation which future experiments and future reasoning would serve to +establish.</p> + +<p>In his lectures on combustion Black first of all establishes the facts, +that when a body is burned it is changed into a kind (or kinds) of matter +which is no longer inflammable; that the presence of air is needed for +combustion to proceed; that the substance must be heated "to a certain +degree" before combustion or inflammation begins; that this degree of heat +(or we should now say this degree of temperature) differs for each +combustible substance; that the supply of air must be renewed if the +burning is to continue; and that the process of burning produces a change +in the quality of the air supplied to the burning body.</p> + +<p>He then states the phlogistic interpretation of these phenomena: that +combustion is caused by the outrush from the burning body of a something +called the <i>principle of fire</i>, or <i>phlogiston</i>.</p> + +<p>Black then proceeds to demonstrate certain other facts:—When the +substances produced by burning phosphorus or sulphur are heated with carbon +(charcoal) the original phosphorus or sulphur is reproduced. This +reproduction is due, according to the phlogistic chemists, to the giving +back, by carbon, of the phlogiston which had escaped during the burning. +Hence carbon contains much phlogiston. But as a similar reproduction of +phosphorus or sulphur, from the substances obtained by burning these +bodies, can be accomplished by the use of substances other than carbon,<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span> it +is evident that these other substances also contain much phlogiston, and, +moreover, that the phlogiston contained in all these substances is one and +the same <i>principle</i>. What then, he asks, is this "principle" which can so +escape, and be so restored by the action of various substances? He then +proceeds as follows:—</p> + +<p>"But when we inquire further, and endeavour to learn what notion was formed +of the nature of this principle, and what qualities it was supposed to have +in its separate state, we find this part of the subject very obscure and +unsatisfactory, and the opinions very unsettled.</p> + +<p>"The elder chemists, and the alchemists, considered sulphur as the +universal inflammable principle, or at least they chose to call the +inflammable part of all bodies, that are more or less inflammable, by the +name of their sulphur.... The famous German chemist Becher was, I believe, +the first who rejected the notion of sulphur being the principle of +inflammability in bodies.... His notion of the nature of the pure principle +of inflammability was afterwards more fully explained and supported by +Professor Stahl, who, agreeably to the doctrine of Becher, represented the +principle of inflammability as a dry substance, or of an earthy nature, the +particles of which were exquisitely subtile, and were much disposed to be +agitated and set in motion with inconceivable velocity.... The opinion of +Becher and Stahl concerning this <i>terra secunda</i>, or <i>terra inflammabilis</i>, +or <i>phlogiston</i>,<span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span> was that the atoms of it are, more than all others, +disposed to be affected with an excessively swift whirling motion (<i>motus +vorticillaris</i>). The particles of other elementary substances are likewise +liable to be affected with the same sort of motion, but not so liable as +those of <i>terra secunda</i>; and when the particles of any body are agitated +with this sort of motion, the body exhibits the phenomena of heat, or +ignition, or inflammation according to the violence and rapidity of the +motion.... Becher and Stahl, therefore, did not suppose that heat depended +on the abundance of a peculiar matter, such as the matter of heat or fire +is now supposed to be, but on a peculiar motion of the particles of +matter....</p> + +<p>"This very crude opinion of the earthy nature of the principle of +inflammability appears to have been deduced from a quality of many of the +inflammable substances, by which they resist the action of water as a +solvent. The greater number of the earthy substances are little, or not at +all, soluble in water.... And when Becher and Stahl found those compounds, +which they supposed contained phlogiston in the largest quantity, to be +insoluble in water, although the other matter, with which the phlogiston +was supposed to be united, was, in its separate state, exceedingly soluble +in that fluid, they concluded that <i>a dry nature, or an incapability to be +combined with water</i>, was an eminent quality of their phlogiston; and this +was what they meant by calling it an earth or earthy substance....<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span> But +these authors supposed, at the same time, that the particles of this dry +and earthy phlogiston were much disposed to be excessively agitated with a +whirling motion; which whirling motion, exerted in all directions from the +bodies in which phlogiston is contained, produced the phenomena of +inflammation. This appears to have been the notion formed by Becher and +Stahl, concerning the nature of the principle of inflammability, or the +phlogiston; a notion which seems the least entitled to the name of +explanation of anything we can think of. I presume that few persons can +form any clear conception of this whirling motion, or, if they can, are +able to explain to themselves how it produces, or can produce, anything +like the phenomena of heat or fire."</p> + +<p>Black then gives a clear account of the experiments of Priestley and +Lavoisier (see pp. 58, 59, and 87-89), which established the presence, in +common air, of a peculiar kind of gas which is especially concerned in the +processes of combustion; he emphasizes the fact that a substance increases +in weight when it is burned; and he gives a simple and clear statement of +that explanation of combustion which is now accepted by all, and which does +not require that the existence of any principle of fire should be assumed.</p> + +<p>It is important to note that Black clearly connects the <i>physical</i> fact +that heat is absorbed, or evolved, by a substance during combustion, with +the <i>chemical</i> changes which are brought about in the properties of the +substance burned. He concludes<span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span> with an admirable contrast between the +phlogistic theory and the theory of Lavoisier, which shows how wide, and at +the same time how definite, his conceptions were. Black never speaks +contemptuously of a theory which he opposes.</p> + +<p>"According to this theory" (<i>i.e.</i> the theory of Lavoisier), "the +inflammable bodies, sulphur for example, or phosphorus, are simple +substances. The acid into which they are changed by inflammation is a +compound. The chemists, on the contrary" (<i>i.e.</i> the followers of Stahl), +"consider the inflammable bodies as compounds, and the uninflammable matter +as more simple. In the common theory the heat and light are supposed to +emanate from, or to be furnished by, the burning body. But, in Mr. +Lavoisier's theory, both are held to be furnished by the air, of which they +are held to be constituent parts, or ingredients, while in its state of +fire-supporting air."</p> + +<p>Black was not a brilliant discoverer, but an eminently sound and at the +same time imaginative worker; whatever he did he did well, but he did not +exhaust any field of inquiry. Many of the facts established by him have +served as the basis of important work done by those who came after him. The +number of new facts added by Black to the data of chemistry was not large; +but by his lectures—which are original dissertations of the highest +value—he did splendid service in advancing the science of chemistry. Black +possessed that which has generally distinguished great men<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span> of science, a +marked honesty of character; and to this he added comprehensiveness of +mental vision: he saw beyond the limits of the facts which formed the +foundations of chemical science in his day. He was not a fact-collector, +but a philosopher.</p> + +<hr style='width: 45%;' /> + +<p><span class="smcap">Joseph Priestley</span>, the son of Jonas Priestley, "a maker and dresser of +woollen cloth," was born at Fieldhead, near Leeds, in the year 1733. His +mother, who was the daughter of a farmer near Wakefield, died when he was +seven years old. From that time he was brought up by a sister of his +father, who was possessed of considerable private means.</p> + +<p>Priestley's surroundings in his young days were decidedly religious, and +evidently gave a tone to his whole after life. We shall find that +Priestley's work as a man of science can scarcely be separated from his +theological and metaphysical work. His cast of mind was decidedly +metaphysical; he was altogether different from Black, who, as we have seen, +was a typical student of natural phenomena.</p> + +<p>The house of Priestley's aunt was a resort for all the Dissenting ministers +of that part of the county. She herself was strictly Calvinistic in her +theological views, but not wholly illiberal.</p> + +<p>Priestley's early schooling was chiefly devoted to learning languages; he +acquired a fair knowledge of Latin, a little Greek, and somewhat later he +learned the elements of Hebrew. At one time he thought of going into trade, +and therefore, as he<span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span> tells us in his "Memoirs," he acquired some knowledge +of French, Italian and High Dutch. With the help of a friend, a Dissenting +minister, he learned something of geometry, mathematics and natural +philosophy, and also got some smattering of the Chaldee and Syriac tongues.</p> + +<p>At the age of nineteen Priestley went to an "academy" at Daventry. The +intellectual atmosphere here seems to have been suitable to the rapid +development of Priestley's mind. Great freedom of discussion was allowed; +even during the teachers' lectures the students were permitted "to ask +whatever questions and to make whatever remarks" they pleased; and they did +it, Priestley says, "with the greatest, but without any offensive, +freedom."</p> + +<p>The students were required to read and to give an account of the more +important arguments for and against the questions discussed in the +teachers' lectures. Theological disputations appear to have been the +favourite topics on which the students exercised their ingenuity among +themselves. Priestley tells us that he "saw reason to embrace what is +generally called the heterodox side of almost every question."</p> + +<p>Leaving this academy, Priestley went, in 1755, as assistant to the +Dissenting minister at Needham, in Suffolk. Here he remained for three +years, living on a salary of about £30 a year, and getting more and more +into bad odour because of his peculiar theological views.<span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span></p> + +<p>From Needham he moved to Nantwich, in Cheshire, where he was more +comfortable, and, having plenty of work to do, he had little time for +abstruse speculations. School work engaged most of his time at Nantwich; he +also began to collect a few scientific instruments, such as an electrical +machine and an air-pump. These he taught his scholars to use and to keep in +good order. He gave lectures on natural phenomena, and encouraged his +scholars to make experiments and sometimes to exhibit their experiments +before their parents and friends. He thus extended the reputation of his +school and implanted in his scholars a love of natural knowledge.</p> + +<p>In the year 1761 Priestley removed to Warrington, to act as tutor in a +newly established academy, where he taught languages—a somewhat wide +subject, as it included lectures on "The Theory of Languages," on "Oratory +and Criticism," and on "The History, Laws, and Constitution of England." He +says, "It was my province to teach elocution, and also logic and Hebrew. +The first of these I retained, but after a year or two I exchanged the two +last articles with Dr. Aikin for the civil law, and one year I gave a +course of lectures on anatomy."</p> + +<p>During his stay at Warrington, which lasted until 1767, Priestley married a +daughter of Mr. Isaac Wilkinson, an ironmaster of Wrexham, in Wales. He +describes his wife as "a woman of an excellent understanding much improved +by reading, of great<span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span> fortitude and strength of mind, and of a temper in +the highest degree affectionate and generous, feeling strongly for others +and little for herself, also greatly excelling in everything relating to +household affairs."</p> + +<p>About this time Priestley met Dr. Franklin more than once in London. His +conversation seems to have incited Priestley to a further study of natural +philosophy. He began to examine electrical phenomena, and this led to his +writing and publishing a "History of Electricity," in the course of which +he found it necessary to make new experiments. The publication of the +results of these experiments brought him more into notice among scientific +men, and led to his election as a Fellow of the Royal Society, and to his +obtaining the degree of LL.D. from the University of Edinburgh. In the year +1767 Priestley removed to Leeds, where he spent six years as minister of +Millhill Chapel.</p> + +<p>He was able to give freer expression to his theological views in Leeds than +could be done in smaller places, such as Needham and Nantwich. During this +time he wrote and published many theological and metaphysical treatises. +But, what is of more importance to us, he happened to live near a brewery. +Now, the accidental circumstances, as we call them, of Priestley's life +were frequently of the greatest importance in their effects on his +scientific work. Black had established the existence and leading properties +of fixed air about twelve or thirteen years before the time when Priestley +came<span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span> to live near the brewery in Leeds. He had shown that this fixed air +is produced during alcoholic fermentation. Priestley knowing this used to +collect the fixed air which came off from the vats in the neighbouring +brewery, and amuse himself with observing its properties. But removing from +this part of the town his supplies of fixed air were stopped. As however he +had become interested in working with airs, he began to make fixed air for +himself from chalk, and in order to collect this air he devised a very +simple piece of apparatus which has played a most important part in the +later development of the chemistry of gases, or pneumatic chemistry. +Priestley's <i>pneumatic trough</i> is at this day to be found in every +laboratory; it is extremely simple and extremely perfect. A dish of glass, +or earthenware, or wood is partly filled with water; a shelf runs across +the dish at a little distance beneath the surface of the water; a +wide-mouthed bottle is filled with water and placed, mouth downwards, over +a hole in this shelf. The gas which is to be collected in this bottle is +generated in a suitable vessel, from which a piece of glass or metal tubing +passes under the shelf and stops just where the hole is made. The gas which +comes from the apparatus bubbles up into the bottle, drives out the water, +and fills the bottle. When the bottle is full of gas, it is moved to one +side along the shelf, and another bottle filled with water is put in its +place. As the mouth of each bottle is under water there is no connection +between the gas inside and the<span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span> air outside the bottle; the gas may +therefore be kept in the bottle until the experimenter wants it. (See Fig. +1. which is reduced from the cut in Priestley's "Air.")</p> + +<div class="figcenter" style="width: 498px;"> +<img src="images/fig1.jpg" width="498" height="413" alt="Fig. 1." title="" /> +<span class="caption">Fig. 1.</span> +</div> + +<p>Priestley tells us that at this time he knew very little chemistry, but he +thinks that this was a good thing, else he might not have been led to make +so many new discoveries as he did afterwards make.</p> + +<p>Experimenting with fixed air, he found that water could be caused to +dissolve some of the gas. In 1772 he published a pamphlet on the method of<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span> +impregnating water with fixed air; this solution of fixed air in water was +employed medicinally, and from this time we date the manufacture of +artificial mineral waters.</p> + +<p>The next six years of Priestley's life (1773-1779) are very important in +the history of chemistry; it was during these years that much of his best +work on various airs was performed. During this time he lived as a kind of +literary companion (nominally as librarian) with the Earl of Shelburne +(afterwards Marquis of Lansdowne.) His wife and family—he had now three +children—lived at Calne, in Wiltshire, near Lord Shelburne's seat of +Bowood. Priestley spent most of the summer months with his family, and the +greater part of each winter with Lord Shelburne at his London residence; +during this time he also travelled in Holland and Germany, and visited +Paris in 1774.</p> + +<p>In a paper published in November 1772, Priestley says that he examined a +specimen of air which he had extracted from saltpetre above a year before +this date. This air "had by some means or other become noxious, but," he +supposed, "had been restored to its former wholesome state, so as to +effervesce with nitrous air" (in modern language, to combine with nitric +oxide) "and to admit a candle to burn in it, in consequence of agitation +with water." He tells us, in his "Observations on Air" (1779), that at this +time he was altogether in the dark as to the nature of this air obtained +from saltpetre. In August 1774, he was amusing himself<span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span> by observing the +action of heat on various substances—"without any particular view," he +says, "except that of extracting air from a variety of substances by means +of a burning lens in quicksilver, which was then a new process with me, and +which I was very proud of"—when he obtained from <i>red precipitate</i> (oxide +of mercury) an air in which a candle burned with a "remarkably vigorous +flame." The production of this peculiar air "surprised me more than I can +well express;" "I was utterly at a loss how to account for it." At first he +thought that the specimen of <i>red precipitate</i> from which the air had been +obtained was not a proper preparation, but getting fresh specimens of this +salt, he found that they all yielded the same kind of air. Having satisfied +himself by experiment that this peculiar air had "all the properties of +common air, only in much greater perfection," he gave to it the name of +<i>dephlogisticated air</i>. Later experiments taught him that the same air +might be obtained from red lead, from manganese oxide, etc., by the action +of heat, and from various other salts by the action of acids.</p> + +<p>Priestley evidently regards the new "dephlogisticated air" simply as very +pure ordinary air; indeed, he seems to look on all airs, or gases, as +easily changeable one into the other. He always interprets his experimental +results by the help of the theory of phlogiston. One would indeed think +from Priestley's papers that the existence of this substance phlogiston was +an unquestioned and unquestionable<span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span> fact. Thus, he says in the preface to +his "Experiments on Air:" "If any opinion in all the modern doctrine +concerning air be well founded, it is certainly this, that nitrous air is +highly charged with phlogiston, and that from this quality only it renders +pure air noxious.... If I have completely ascertained anything at all +relating to air it is this." Priestley thought that "very pure air" would +take away phlogiston from some metals without the help of heat or any acid, +and thus cause these metals to rust. He therefore placed some clean iron +nails in <i>dephlogisticated air</i> standing over mercury; after three months +he noticed that about one-tenth of the air in the vessel had disappeared, +and he concluded, although no rust appeared, that the dephlogisticated air +had as a fact withdrawn phlogiston from the iron nails. This is the kind of +reasoning which Black described to his pupils as "mere waste of time and +ingenuity." The experiment with the nails was made in 1779; at this time, +therefore, Priestley had no conception as to what his <i>dephlogisticated +air</i> really was.</p> + +<p>Trying a great many experiments, and finding that the new air was obtained +by the action of acids on earthy substances, Priestley was inclined to +regard this air, and if this then all other airs, as made up of an acid (or +acids) and an earthy substance. We now know how completely erroneous this +conclusion was, but we must remember that in Priestley's time chemical +substances were generally regarded as of no very definite or fixed +composition;<span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span> that almost any substance, it was supposed, might be changed +into almost any other; that no clear meaning was attached to the word +"element;" and that few, if any, careful measurements of the quantities of +different kinds of matter taking part in chemical actions had yet been +made.</p> + +<p>But at the same time we cannot forget that the books of Hooke and Mayow had +been published years before this time, and that twenty years before +Priestley began his work on airs, Black had published his exact, scientific +investigation on fixed air.</p> + +<p>Although we may agree with Priestley that, had he made himself acquainted +with what others had done before he began his own experiments, he might not +have made so many new discoveries as he did, yet one cannot but think that +his discoveries, although fewer, would have been more accurate.</p> + +<p>We are told by Priestley that, when he was in Paris in 1774, he exhibited +the method of obtaining dephlogisticated air from <i>red precipitate</i> to +Lavoisier and other French chemists. We shall see hereafter what important +results to science followed from this visit to Lavoisier.</p> + +<p>Let us shortly review Priestley's answer to the question, "What happens +when a substance burns in air?"</p> + +<p>Beginning to make chemical experiments when he had no knowledge of +chemistry, and being an extremely rapid worker and thinker, he naturally +adopted the prevalent theory, and as naturally<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span> interpreted the facts which +he discovered in accordance with this theory.</p> + +<p>When a substance burns, phlogiston, it was said, rushes out of it. But why +does rapid burning only take place in air? Because, said Priestley, air has +a great affinity for phlogiston, and draws it out of the burning substance. +What then becomes of this phlogiston? we next inquire. The answer is, +obviously it remains in the air around the burning body, and this is proved +by the fact that this air soon becomes incapable of supporting the process +of burning, it becomes phlogisticated. Now, if phlogisticated air cannot +support combustion, the greater the quantity of phlogiston in air, the less +will it support burning; but we know that if a substance is burnt in a +closed tube containing air, the air which remains when the burning is quite +finished at once extinguishes a lighted candle. Priestley also proved that +an air can be obtained by heating <i>red precipitate</i>, characterized by its +power of supporting combustion with great vigour. What is this but common +air completely deprived of phlogiston? It is dephlogisticated air. Now, if +common air draws phlogiston out of substances, surely this dephlogisticated +air will even more readily do the same. That it really does this Priestley +thought he had proved by his experiment with clean iron nails (see p. 60).</p> + +<p>Water was regarded as a substance which, like air, readily combined with +phlogiston; but Priestley thought that a candle burned less vigorously in +dephlogisticated air which had been shaken with<span class='pagenum'><a name="Page_63" id="Page_63">[Pg 63]</a></span> water than in the same air +before this treatment; hence he concluded that phlogiston had been taken +from the water.</p> + +<p>After Cavendish had discovered (or rather rediscovered) hydrogen, and had +established the fact that this air is extremely inflammable, most chemists +began to regard this gas as pure or nearly pure phlogiston, or, at least, +as a substance very highly charged with phlogiston. "Now," said Priestley, +"when a metal burns phlogiston rushes out of it; if I restore this +phlogiston to the metallic calx, I shall convert it back into the metal." +He then showed by experiment that when calx of iron is heated with +hydrogen, the hydrogen disappears and the metal iron is produced.</p> + +<p>He seemed, therefore, to have a large experimental basis for his answer to +the question, "What happens when a substance burns?" But at a later time it +was proved that iron was also produced by heating the calx of iron with +carbon. The antiphlogistic chemists regarded fixed air as composed of +carbon and dephlogisticated air; the phlogisteans said it was a substance +highly charged with phlogiston. The antiphlogistic school said that calx of +iron is composed of iron and dephlogisticated air; the phlogisteans said it +was iron deprived of its phlogiston. Here was surely an opportunity for a +crucial experiment: when calx of iron is heated with carbon, and iron is +produced, there must either be a production of fixed air (which is a +non-inflammable gas, and forms a white solid substance<span class='pagenum'><a name="Page_64" id="Page_64">[Pg 64]</a></span> when brought into +contact with limewater), or there must be an outrush of phlogiston from the +carbon. The experiment was tried: a gas was produced which had no action on +limewater and which was very inflammable; what could this be but +phlogiston, already recognized by this very property of extreme +inflammability? Thus the phlogisteans appeared to triumph. But if we +examine these experiments made by Priestley with the light thrown on them +by subsequent research, we find that they bear the interpretation which he +put on them only because they were not accurate; thus, two gases are +inflammable, but it by no means follows that these gases are one and the +same. We must have more accurate knowledge of the properties of these +gases.</p> + +<p>The air around a burning body, such as iron, after a time loses the power +of supporting combustion; but this is merely a qualitative fact. Accurately +to trace the change in the properties of this air, it is absolutely +necessary that exact measurements should be made; when this is done, we +find that the volume of air diminishes during the combustion, that the +burning body gains weight, and that this gain in weight is just equal to +the loss in weight undergone by the air. When the inflammable gas produced +by heating calx of iron with carbon was carefully and <i>quantitatively</i> +analyzed, it was found to consist of carbon and oxygen (dephlogisticated +air), but to contain these substances in a proportion different from that +in<span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span> which they existed in fixed air. It was a new kind of air or gas; it +was <i>not</i> hydrogen.</p> + +<p>This account of Priestley's experiments and conclusions regarding +combustion shows how easy it is in natural science to interpret +experimental results, especially when these results are not very accurate, +in accordance with a favourite theory; and it also illustrates one of the +lessons so emphatically taught by all scientific study, viz. the necessity +of suspending one's judgment until accurate measurements have been made, +and the great wisdom of then judging cautiously.</p> + +<p>About 1779 Priestley left Lord Shelburne, and went as minister of a chapel +to Birmingham, where he remained until 1791.</p> + +<p>During his stay in Birmingham, Priestley had a considerable amount of +pecuniary help from his friends. He had from Lord Shelburne, according to +an agreement made when he entered his service, an annuity of £150 a year +for life; some of his friends raised a sum of money annually for him, in +order that he might be able to prosecute his researches without the +necessity of taking pupils. During the ten years or so after he settled in +Birmingham, Priestley did a great deal of chemical work, and made many +discoveries, almost entirely in the field of pneumatic chemistry.</p> + +<p>Besides the discovery of dephlogisticated air (or oxygen) which has been +already described, Priestley discovered and gave some account of the +properties of <i>nitrous air</i> (nitric acid), <i>vitriolic acid<span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span> air</i> (sulphur +dioxide), <i>muriatic acid air</i> (hydrochloric acid), and <i>alkaline air</i> +(ammonia), etc.</p> + +<p>In the course of his researches on the last-named air he showed, that when +a succession of electric sparks is passed through this gas a great increase +in the volume of the gas occurs. This fact was further examined at a later +time by Berthollet, who, by measuring the increase in volume undergone by a +measured quantity of ammonia gas, and determining the nature of the gases +produced by the passage of the electric sparks, proved that ammonia is a +compound of hydrogen and nitrogen, and that three volumes of the former gas +combine with one volume of the latter to produce two volumes of ammonia +gas.</p> + +<p>Priestley's experiments on "inflammable air"—or hydrogen—are important +and interesting. The existence of this substance as a definite kind of air +had been proved by the accurate researches of Cavendish in 1766. Priestley +drew attention to many actions in which this inflammable air is produced, +chiefly to those which take place between acids and metals. He showed that +inflammable air is not decomposed by electric sparks; but he thought that +it was decomposed by long-continued heating in closed tubes made of +lead-glass. Priestley regarded inflammable air as an air containing much +phlogiston. He found that tubes of lead-glass, filled with this air, were +blackened when strongly heated for a long time, and he explained this by +saying that the lead in the glass had a great<span class='pagenum'><a name="Page_67" id="Page_67">[Pg 67]</a></span> affinity for phlogiston, and +drew it out of the inflammable air.</p> + +<p>When inflammable air burns in a closed vessel containing common air, the +latter after a time loses its property of supporting combustion. Priestley +gave what appeared to be a fairly good explanation of this fact, when he +said that the inflammable air parted with phlogiston, which, becoming mixed +with the ordinary air in the vessel, rendered it unable to support the +burning of a candle. He gave a few measurements in support of this +explanation; but we now know that the method of analysis which he employed +was quite untrustworthy.</p> + +<p>Thinking that by measuring the extent to which the <i>phlogistication</i> (we +would now say the <i>deoxidation</i>) of common air was carried by mixing +measured quantities of common and inflammable airs and exploding this +mixture, he might be able to determine the amount of phlogiston in a given +volume of inflammable air, he mixed the two airs in glass tubes, through +the sides of which he had cemented two pieces of wire, sealed the tubes, +and exploded the mixture by passing electric sparks from wire to wire. The +residual air now contained, according to Priestley, more phlogiston, and +therefore relatively less dephlogisticated air than before the explosion. +He made various measurements of the quantities of dephlogisticated air in +the tubes, but without getting any constant results. He noticed that after +the explosions the insides of the tubes were covered with moisture. At a +later<span class='pagenum'><a name="Page_68" id="Page_68">[Pg 68]</a></span> time he exploded a mixture of dephlogisticated and inflammable airs +(oxygen and hydrogen) in a copper globe, and recorded the fact that after +the explosion the globe contained a little water. Priestley was here +apparently on the eve of a great discovery. "In looking for one thing," +says Priestley, "I have generally found another, and sometimes a thing of +much more value than that which I was in quest of." Had he performed the +experiment of exploding dephlogisticated and inflammable airs with more +care, and had he made sure that the airs used were quite dry before the +explosion, he would probably have found a thing of indeed much more value +than that of which he was in quest; he would probably have discovered the +compound nature of water—a discovery which was made by Cavendish three or +four years after these experiments described by Priestley.</p> + +<p>Some very curious observations were made by Priestley regarding the colour +of the gas obtained by heating "spirit of nitre" (<i>i.e.</i> nitric acid). He +showed that a yellow gas or air is obtained by heating colourless liquid +spirit of nitre in a sealed glass tube, and that as the heating is +continued the colour of the gas gets darker, until it is finally very dark +orange red. These experiments have found an explanation only in quite +recent times.</p> + +<p>Another discovery made by Priestley while in Birmingham, viz. that an acid +is formed when electric sparks are passed through ordinary air for some +time, led, in the hands of Cavendish—an experimenter<span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span> who was as careful +and deliberate as Priestley was rapid and careless—to the demonstration of +the composition of nitric acid.</p> + +<p>Many observations were made by Priestley on the effects of various airs on +growing plants and living animals; indeed, one of his customary methods of +testing different airs was to put a mouse into each and watch the effects +of the air on its breathing. He grew sprigs of mint in common air, in +dephlogisticated air (oxygen), and in phlogisticated air (nitrogen, but +probably not pure); the sprig in the last-named air grew best, while that +in the dephlogisticated air soon appeared sickly. He also showed that air +which has been rendered "noxious" by the burning of a candle in it, or by +respiration or putrefaction, could be restored to its original state by the +action of growing plants. He thought that the air was in the first instance +rendered noxious by being impregnated with phlogiston, and that the plant +restored the air by removing this phlogiston. Thus Priestley distinctly +showed that (to use his own words) "it is very probable that the injury +which is continually done to the atmosphere by the respiration of such a +number of animals as breathe it, and the putrefaction of such vast masses, +both of vegetable and animal substances, exposed to it, is, in part at +least, repaired by the vegetable creation." But from want of quantitative +experiments he failed to give any just explanation of the process whereby +this "reparation" is accomplished.<span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span></p> + +<p>During his stay in Birmingham, Priestley was busily engaged, as was his +wont during life, in writing metaphysical and theological treatises and +pamphlets.</p> + +<p>At this time the minds of men in England were much excited by the events of +the French Revolution, then being enacted before them. Priestley and some +of his friends were known to sympathize with the French people in this +great struggle, as they had been on the side of the Americans in the War of +Independence. Priestley's political opinions had, in fact, always been more +advanced than the average opinion of his age; by some he was regarded as a +dangerous character. But if we read what he lays down as a fundamental +proposition in the "Essay on the First Principles of Civil Government" +(1768), we cannot surely find anything very startling.</p> + +<p>"It must be understood, whether it be expressed or not, that all people +live in society for their mutual advantage; so that the good and happiness +of the members, that is the majority of the members of any state, is the +great standard by which everything relating to that state must be finally +determined. And though it may be supposed that a body of people may be +bound by a voluntary resignation of all their rights to a single person, or +to a few, it can never be supposed that the resignation is obligatory on +their posterity, because it is manifestly contrary to the good of the whole +that it should be so."<span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span></p> + +<p>Priestley proposed many political reforms, but he was decidedly of opinion +that these ought to be brought about gradually. He was in favour of +abolishing all religious State establishments, and was a declared enemy to +the Church of England. His controversies with the clergy of Birmingham +helped to stir up a section of public opinion against him, and to bring +about the condemnation of his writings in many parts of the country; he was +also unfortunate in making an enemy of Mr. Burke, who spoke against him and +his writings in the House of Commons.</p> + +<p>In the year 1791, the day of the anniversary of the taking of the Bastille +was celebrated by some of Priestley's friends in Birmingham. On that day a +senseless mob, raising the cry of "Church and King," caused a riot in the +town. Finding that they were not checked by those in authority, they after +a time attacked and burned Dr. Priestley's meeting-house, and then +destroyed his dwelling-house, and the houses of several other Dissenters in +the town. One of his sons barely escaped with his life. He himself found it +necessary to leave Birmingham for London, as he considered his life to be +in danger. Many of his manuscripts, his library, and much of his apparatus +were destroyed, and his house was burned.</p> + +<p>A congregation at Hackney had the courage at this time to invite Priestley +to become their minister. Here he remained for about three years, +ministering to the congregation, and pursuing his<span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span> chemical and other +experiments with the help of apparatus and books which had been supplied by +his friends, and by the expenditure of part of the sum, too small to cover +his losses, given him by Government in consideration of the damage done to +his property in the riots at Birmingham.</p> + +<p>But finding himself more and more isolated and lonely, especially after the +departure of his three sons to America, which occurred during these years, +he at last resolved to follow them, and spend the remainder of his days in +the New World. Although Priestley had been very badly treated by a +considerable section of the English people, yet he left his native country +"without any resentment or ill will." "When the time for reflection," he +says, "shall come, my countrymen will, I am confident, do me more justice." +He left England in 1795, and settled at Northumberland, in Pennsylvania, +about a hundred and thirty miles north-west of Philadelphia. By the help of +his friends in England he was enabled to build a house and establish a +laboratory and a library; an income was also secured sufficient to maintain +him in moderate comfort.</p> + +<p>The chair of chemistry in the University of Philadelphia was offered to +him, and he was also invited to the charge of a Unitarian chapel in New +York; but he preferred to remain quietly at work in his laboratory and +library, rather than again to enter into the noisy battle of life. In +America he published several writings. Of his chemical<span class='pagenum'><a name="Page_73" id="Page_73">[Pg 73]</a></span> discoveries made +after leaving England, the most important was that an inflammable gas is +obtained by heating metallic calces with carbon. The production of this gas +was regarded by Priestley as an indisputable proof of the justness of the +theory of phlogiston (see pp. 63, 64).</p> + +<p>His health began to give way about 1801; gradually his strength declined, +and in February 1804, the end came quietly and peacefully.</p> + +<p>A list of the books and pamphlets published by Priestley on theological, +metaphysical, philological, historical, educational and scientific subjects +would fill several pages of this book. His industry was immense. To +accomplish the vast amount of work which he did required the most careful +outlay of time. In his "Memoirs," partly written by himself, he tells us +that he inherited from his parents "a happy temperament of body and mind;" +his father especially was always in good spirits, and "could have been +happy in a workhouse." His paternal ancestors had, as a race, been healthy +and long-lived. He was not himself robust as a youth, yet he was always +able to study: "I have never found myself," he says, "less disposed or less +qualified for mental exertion of any kind at one time of the day more than +another; but all seasons have been equal to me, early or late, before +dinner or after."</p> + +<p>His peculiar evenness of disposition enabled him quickly to recover from +the effects of any unpleasant occurrence; indeed, he assures us that "the +most perfect satisfaction" often came a day<span class='pagenum'><a name="Page_74" id="Page_74">[Pg 74]</a></span> or two after "an event that +afflicted me the most, and without any change having taken place in the +state of things."</p> + +<p>Another circumstance which tended to make life easy to him was his fixed +resolution, that in any controversy in which he might be engaged, he would +frankly acknowledge every mistake he perceived himself to have fallen into.</p> + +<p>Priestley's scientific work is marked by rapidity of execution. The +different parts do not hang together well; we are presented with a +brilliant series of discoveries, but we do not see the connecting strings +of thought. We are not then astonished when he tells us that sometimes he +forgot that he had made this or that experiment, and repeated what he had +done weeks before. He says that he could not work in a hurry, and that he +was therefore always methodical; but he adds that he sometimes blamed +himself for "doing to-day what had better have been put off until +to-morrow."</p> + +<p>Many of his most startling discoveries were the results of chance +operations, "not of themes worked out and applied." He was led to the +discovery of oxygen, he says, by a succession of extraordinary accidents. +But that he was able to take advantage of the chance observations, and from +these to advance to definite facts, constitutes the essential difference +between him and ordinary plodding investigators. Although he rarely, if +ever, saw all the bearings of his own discoveries, although none of his +experiments was accurately<span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span> worked out to its conclusion, yet he did see, +rapidly and as it appeared almost at one glance, something of their +meanings, and this something was enough to urge him on to fresh +experimental work.</p> + +<p>Although we now condemn Priestley's theories as quite erroneous, yet we +must admire his undaunted devotion to experiment. He was a true student of +science in one essential point, viz. Nature was for him the first and the +last court of appeal. He theorized and speculated much, he experimented +rapidly and not accurately, but he was ever appealing to natural facts; and +in doing this he could not but lay some foundation which should remain. The +facts discovered by him are amongst the very corner-stones on which the +building of chemical science was afterwards raised.</p> + +<p>So enthusiastic was Priestley in the prosecution of his experiments, that +when he began, he tells us, "I spent all the money I could possibly raise, +carried on by my ardour in philosophical investigation, and entirely +regardless of consequences, except so far as never to contract any debts." +He seems all through his life to have been perfectly free from anxiety +about money affairs.</p> + +<p>Priestley's manner of work shows how kindly and genial he was. He trained +himself to talk and think and write with his family by the fireside; +"nothing but reading aloud, or speaking without interruption," was an +obstruction to his work.</p> + +<p>Priestley was just the man who was wanted in<span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span> the early days of chemical +science. By the vast number, variety and novelty of his experimental +results, he astonished scientific men—he forcibly drew attention to the +science in which he laboured so hard; by the brilliancy of some of his +experiments he obliged chemists to admit that a new field of research was +opened before them, and the instruments for the prosecution of this +research were placed in their hands; and even by the unsatisfactoriness of +his reasoning he drew attention to the difficulties and contradictions of +the theories which then prevailed in chemistry.</p> + +<p>That the work of Priestley should bear full fruit it was necessary that a +greater than he should interpret it, and should render definite that which +Priestley had but vaguely shown to exist.</p> + +<p>The man who did this, and who in doing it really established chemistry as a +science, was Lavoisier.</p> + +<p>But before considering the work of Lavoisier, I should like to point out +that many of the physical characters of common air had been clearly +established in the later years of the seventeenth century by the Honourable +Robert Boyle. In the "Sceptical Chymist," published in 1661, Mr. Boyle had +established the fact that air is a material substance possessed of weight, +that this air presses on the surface of all things, and that by removing +part of the air in an enclosed space the pressure within that space is +diminished. He had demonstrated that the boiling point of water is +dependent<span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span> on the pressure of the air on the surface of the water. Having +boiled some water "a pretty while, that by the heat it might be freed from +the latitant air," he placed the vessel containing the hot water within the +receiver of an arrangement which he had invented for sucking air out of an +enclosed space; as soon as he began to suck out air from this receiver, the +water boiled "as if it had stood over a very quick fire.... Once, when the +air had been drawn out, the liquor did, upon a single exsuction, boil so +long with prodigiously vast bubbles, that the effervescence lasted almost +as long as was requisite for the rehearsing of a <i>Pater noster</i>." Boyle had +gone further than the qualitative fact that the volume of an enclosed +quantity of air alters with changes in the pressure to which that air is +subjected; he had shown by simple and accurate experiments that "the volume +varies inversely as the pressure." He had established the generalization of +so much importance in physical science now known as <i>Boyle's law</i>.</p> + +<p>The work of the Honourable Henry Cavendish will be considered in some +detail in the book on "The Physicists" belonging to this series, but I must +here briefly allude to the results of his experiments on air published in +the <i>Philosophical Transactions</i> for 1784 and 1785.</p> + +<p>Cavendish held the ordinary view that when a metal burns in air, the air is +thereby phlogisticated; but why is it, he asked, that the volume of air is +decreased by this process? It was very<span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span> generally said that fixed air was +produced during the calcination of metals, and was absorbed by the calx. +But Cavendish instituted a series of experiments which proved that no fixed +air could be obtained from metallic calces. In 1766 inflammable air +(hydrogen) was discovered by Cavendish; he now proved that when this air is +exploded with dephlogisticated air (oxygen), water is produced. He showed +that when these two airs are mixed in about the proportion of two volumes +of hydrogen to one volume of oxygen, the greater part, if not the whole of +the airs is condensed into water by the action of the electric spark. He +then proceeded to prove by experiments that when common air is exploded +with inflammable air water is likewise produced, and phlogisticated air +(<i>i.e.</i> nitrogen) remains.</p> + +<p>Priestley and Cavendish had thus distinctly established the existence of +three kinds of air, viz. dephlogisticated air, phlogisticated air, and +inflammable air. Cavendish had shown that when the last named is exploded +with common air water is produced (which is composed of dephlogisticated +and inflammable airs), and phlogisticated air remains. Common air had thus +been proved to consist of these two—phlogisticated and dephlogisticated +airs (nitrogen and oxygen). Applying these results to the phenomenon of the +calcination of metals, Cavendish gave reasons for thinking that the metals +act towards common air in a manner analogous to that in which inflammable<span class='pagenum'><a name="Page_79" id="Page_79">[Pg 79]</a></span> +air acts—that they withdraw dephlogisticated and leave phlogisticated air; +but, as he was a supporter of the phlogistic theory, he rather preferred to +say that the burning metals withdraw dephlogisticated air and phlogisticate +that which remains; in other words, while admitting that a metal in the +process of burning gains dephlogisticated air, he still thought that the +metal also loses <i>something</i>; viz. phlogiston.</p> + +<p>That Cavendish in 1783-84 had proved air to consist of two distinct gases, +and water to be produced by the union of two gases, must be remembered as +we proceed with the story of the discoveries of Lavoisier.</p> + + +<p><span class="smcap">Antoine Laurent Lavoisier</span>, born in Paris in 1743, was the son of a wealthy +merchant, who, judging from his friendship with many of the men of science +of that day, was probably of a scientific bent of mind, and who certainly +showed that he was a man of sense by giving his son the best education +which he could obtain. After studying in the Mazarin College, Lavoisier +entered on a course of training in physical, astronomical, botanical and +chemical science. The effects of this training in the accurate methods of +physics are apparent in the chemical researches of Lavoisier.</p> + +<p>At the age of twenty-one Lavoisier wrote a memoir which gained the prize +offered by the French Government for the best and most economical method of +lighting the streets of a large city.<span class='pagenum'><a name="Page_80" id="Page_80">[Pg 80]</a></span> While making experiments, the +results of which were detailed in this paper, Lavoisier lived for six weeks +in rooms lighted only by artificial light, in order that his eyesight might +become accustomed to small differences in the intensities of light from +various sources. When he was twenty-five years old Lavoisier was elected a +member of the Academy of Sciences. During the next six years (1768-1774) he +published various papers, some on chemical, some on geological, and some on +mathematical subjects. Indeed at this time, although an ardent cultivator +of natural science, he appears to have been undecided as to which branch of +science he should devote his strength.</p> + +<p>The accuracy and thoroughness of Lavoisier's work, and the acuteness of his +reasoning powers, are admirably illustrated in two papers, published in the +Memoirs of the Academy for 1770, on the alleged conversion of water into +earth.</p> + +<p>When water is boiled for a long time in a glass vessel a considerable +quantity of white siliceous earth is found in the vessel. This apparent +conversion or transmutation of water into earthy matter was quite in +keeping with the doctrines which had been handed down from the times of the +alchemists; the experiment was generally regarded as conclusively proving +the possibility of changing water into earth. Lavoisier found that after +heating water for a hundred and one days in a closed <i>and weighed</i> glass +vessel, there was no change in the total weight of the vessel and its<span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span> +contents; when he poured out the water and evaporated it to dryness, he +obtained 20.4 grains of solid earthy matter; but he also found, what had +been before overlooked, that the glass vessel had lost weight. The actual +loss amounted to 17.4 grains. The difference between this and the weight of +the earthy matter in the water, viz. three grains, was set down (and as we +now know justly set down) by Lavoisier to errors of experiment. Lavoisier +therefore concluded that water, when boiled, is not changed into earth, but +that a portion of the earthy matter of which glass is composed is dissolved +by the water. This conclusion was afterwards confirmed by the Swedish +chemist <i>Scheele</i>, who proved that the composition of the earthy matter +found in the water is identical with that of some of the constituents of +glass.</p> + +<p>By this experiment Lavoisier proved the old alchemical notion of +transmutation to be erroneous; he showed that water is not transmuted into +earth, but that each of these substances is possessed of definite +properties which belong to it and to it only. He established the +all-important generalization—which subsequent research has more amply +confirmed, until it is to-day accepted as the very foundation of every +branch of physical science—that in no process of change is there any +alteration in the total mass of matter taking part in that change. The +glass vessel in which Lavoisier boiled water for so many days lost weight; +but<span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span> the matter lost by the glass was found dissolved in the water.</p> + +<p>We know that this generalization holds good in all chemical changes. Solid +sulphur may be converted into liquid oil of vitriol, but it is only by the +sulphur combining with other kinds of matter; the weight of oil of vitriol +produced is always exactly equal to the sum of the weights of the sulphur, +hydrogen and oxygen which have combined to form it. The colourless gases, +hydrogen and oxygen, combine, and the limpid liquid water is the result; +but the weight of the water produced is equal to the sum of the weights of +hydrogen and oxygen which combined together. It is impossible to overrate +the importance of the principle of the <i>conservation of mass</i>, first +definitely established by Lavoisier.</p> + +<p>Some time about the year 1770 Lavoisier turned his attention seriously to +chemical phenomena. In 1774 he published a volume entitled "Essays Physical +and Chemical," wherein he gave an historical account of all that had been +done on the subject of airs from the time of Paracelsus to the year 1774, +and added an account of his own experiments, in which he had established +the facts that a metal in burning absorbs air, and that when the metallic +calx is reduced to metal by heating with charcoal, an air is produced of +the same nature as the fixed air of Dr. Black.</p> + +<p>In November 1772 Lavoisier deposited a sealed note in the hands of the +Secretary to the Academy<span class='pagenum'><a name="Page_83" id="Page_83">[Pg 83]</a></span> of Sciences. This note was opened on the 1st of +May 1773, and found to run as follows<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a>:—</p> + +<div class="blockquot"><p>"About eight days ago I discovered that sulphur in +burning, far from losing, augments in weight; that is +to say, that from one pound of sulphur much more than +one pound of vitriolic acid is obtained, without +reckoning the humidity of the air. Phosphorus presents +the same phenomenon. This augmentation of weight arises +from a great quantity of air which becomes fixed during +the combustion, and which combines with the vapours.</p> + +<p>"This discovery, confirmed by experiments which I +regard as decisive, led me to think that what is +observed in the combustion of sulphur and phosphorus +might likewise take place with respect to all the +bodies which augment in weight by combustion and +calcination; and I was persuaded that the augmentation +of weight in the calces of metals proceeded from the +same cause. The experiment fully confirmed my +conjectures.</p> + +<p>"I operated the reduction of litharge in closed vessels +with Hale's apparatus, and I observed that at the +moment of the passage of the calx into the metallic +state, there was a disengagement of air in considerable +quantity, and that this air formed a volume at least +one thousand times greater than that of the litharge +employed.</p> + +<p>"As this discovery appears to me one of the most +interesting which has been made since Stahl, I<span class='pagenum'><a name="Page_84" id="Page_84">[Pg 84]</a></span> thought +it expedient to secure to myself the property, by +depositing the present note in the hands of the +Secretary of the Academy, to remain secret till the +period when I shall publish my experiments.</p> + +<p class="right"> +"<span class="smcap">Lavoisier.</span><br /> +</p> + +<p>"Paris, 11th November 1772."</p></div> + +<p>In his paper "On the Calcination of Tin in Closed Vessels, and on the Cause +of Increase of Weight acquired by the Metal during this Process" (published +in 1774), we see and admire Lavoisier's manner of working. A weighed +quantity (about half a pound) of tin was heated to melting in a glass +retort, the beak of which was drawn out to a very small opening; the air +within the retort having expanded, the opening was closed by melting the +glass before the blowpipe. The weight of retort and tin was now noted; the +tin was again heated to its melting point, and kept at this temperature as +long as the process of calcination appeared to proceed; the retort and its +contents were then allowed to cool and again weighed. No change was caused +by the heating process in the total weight of the whole apparatus. The end +of the retort beak was now broken off; air rushed in with a hissing sound. +The retort and contents were again weighed, and the increase over the +weight at the moment of sealing the retort was noted. The calcined tin in +the retort was now collected and weighed. It was found that the increase in +the weight of the tin was equal to the weight of the air<span class='pagenum'><a name="Page_85" id="Page_85">[Pg 85]</a></span> which rushed into +the retort. Hence Lavoisier concluded that the calcination of tin was +accompanied by an absorption of air, and that the difference between the +weights of the tin and the calx of tin was equal to the weight of air +absorbed; but he states that probably only a part of the air had combined +with the tin, and that hence air is not a simple substance, but is composed +of two or more constituents.</p> + +<p>Between the date of this publication and that of Lavoisier's next paper on +combustion we know that Priestley visited Paris. In his last work, "The +Doctrine of Phlogiston established" (published in 1800), Priestley says, +"Having made the discovery of dephlogisticated air some time before I was +in Paris in 1774, I mentioned it at the table of Mr. Lavoisier, when most +of the philosophical people in the city were present; saying that it was a +kind of air in which a candle burned much better than in common air, but I +had not then given it any name. At this all the company, and Mr. and Mrs. +Lavoisier as much as any, expressed great surprise. I told them that I had +got it from <i>precipitatum per se</i>, and also from <i>red lead</i>."</p> + +<p>In 1775 Lavoisier's paper, "On the Nature of the Principle which combines +with the Metals during their Calcination, and which augments their Weight," +was read before the Academy. The preparation and properties of an air +obtained, in November 1774, from <i>red precipitate</i> are described, but +Priestley's name is not mentioned. It seems<span class='pagenum'><a name="Page_86" id="Page_86">[Pg 86]</a></span> probable, however, that +Lavoisier learned the existence and the mode of preparation of this air +from Priestley;<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> but we have seen that even in 1779 Priestley was quite +in the dark as to the true nature of the air discovered by him (p. 60).</p> + +<p>In papers published in the next three or four years Lavoisier gradually +defined and more thoroughly explained the phenomenon of combustion. He +burned phosphorus in a confined volume of air, and found that about +one-fourth of the air disappeared, that the residual portion of air was +unable to support combustion or to sustain animal life, that the phosphorus +was converted into a white substance deposited on the sides of the vessel +in which the experiment was performed, and that for each grain of +phosphorus used about two and a half grains of this white solid were +obtained. He further described the properties of the substance produced by +burning phosphorus, gave it the name of <i>phosphoric acid</i>, and described +some of the substances formed by combining it with various bases.</p> + +<p>The burning of candles in air was about this time studied by Lavoisier. He +regarded his experiments as proving that the air which remained after +burning a candle, and in which animal life could not be sustained, was +really present before the burning; that common air consisted of about +one-fourth part of dephlogisticated air and three-fourths<span class='pagenum'><a name="Page_87" id="Page_87">[Pg 87]</a></span> of <i>azotic air</i> +(<i>i.e.</i> air incapable of sustaining life); and that the burning candle +simply combined with, and so removed the former of these, and at the same +time produced more or less fixed air.</p> + +<p>In his treatise on chemistry Lavoisier describes more fully his proof that +the calcination of a metal consists in the removal, by the metal, of +dephlogisticated air (or oxygen) from the atmosphere, and that the metallic +calx is simply a compound of metal and oxygen. The experiments are strictly +quantitative and are thoroughly conclusive. He placed four ounces of pure +mercury in a glass balloon, the neck of which dipped beneath the surface of +mercury in a glass dish, and then passed a little way up into a jar +containing fifty cubic inches of air, and standing in the mercury in the +dish. There was thus free communication between the air in the balloon and +that in the glass jar, but no communication between the air inside and that +outside the whole apparatus. The mercury in the balloon was heated nearly +to its boiling point for twelve days, during which time red-coloured specks +gradually formed on the surface of the metal; at the end of this time it +was found that the air in the glass jar measured between forty-two and +forty-three cubic inches. The red specks when collected amounted to +forty-five grains; they were heated in a very small retort connected with a +graduated glass cylinder containing mercury. Between seven and eight cubic +inches of pure dephlogisticated air<span class='pagenum'><a name="Page_88" id="Page_88">[Pg 88]</a></span> (oxygen) were obtained in this +cylinder, and forty-one and a half grains of metallic mercury remained when +the decomposition of the red substance was completed.</p> + +<p>The conclusion drawn by Lavoisier from these experiments was that mercury, +when heated nearly to boiling in contact with air, withdraws oxygen from +the air and combines with this gas to form <i>red precipitate</i>, and that when +the red precipitate which has been thus formed is strongly heated, it parts +with the whole of its oxygen, and is changed back again into metallic +mercury.</p> + +<p>Lavoisier had now (1777-78) proved that the calces of mercury, tin and lead +are compounds of these metals with oxygen; and that the oxygen is obtained +from the atmosphere when the metal burns. But the phlogistic chemistry was +not yet overthrown. We have seen that the upholders of phlogiston believed +that in the inflammable air of Cavendish they had at last succeeded in +obtaining the long-sought-for phlogiston. Now they triumphantly asked, Why, +when metals dissolve in diluted vitriolic or muriatic acid with evolution +of inflammable air, are calces of these metals produced? And they answered +as triumphantly, Because these metals lose phlogiston by this process, and +we know that a calx is a metal deprived of its phlogiston.</p> + +<p>Lavoisier contented himself with observing that a metallic calx always +weighed more than the metal from which it was produced; and that as<span class='pagenum'><a name="Page_89" id="Page_89">[Pg 89]</a></span> +inflammable air, although much lighter than common air, was distinctly +possessed of weight, it was not possible that a metallic calx could be +metal deprived of inflammable air. He had given a simple explanation of the +process of calcination, and had proved, by accurate experiments, that this +explanation was certainly true in some cases. Although all the known facts +about solution of metals in acids could not as yet be brought within his +explanation, yet none of these facts was absolutely contradictory of that +explanation. He was content to wait for further knowledge. And to gain this +further knowledge he set about devising and performing new experiments. The +upholders of the theory of phlogiston laid considerable stress on the fact +that metals are produced by heating metallic calces in inflammable air; the +air is absorbed, they said, and so the metal is reproduced. It was +obviously of the utmost importance that Lavoisier should learn more about +this inflammable air, and especially that he should know exactly what +happened when this air was burned. He therefore prepared to burn a large +quantity of inflammable air, arranging the experiment so that he should be +able to collect and examine the product of this burning, whatever should be +the nature of that product. But at this time the news was brought to Paris +that Cavendish had obtained water by burning mixtures of inflammable and +dephlogisticated airs. This must have been a most exciting announcement to<span class='pagenum'><a name="Page_90" id="Page_90">[Pg 90]</a></span> +Lavoisier; he saw how much depended on the accuracy of this statement, and +as a true student of Nature, he at once set about to prove or disprove it. +On the 24th of June 1783, in the presence of the King and several +notabilities (including Sir Charles Blagden, Secretary of the Royal +Society, who had told Lavoisier of the experiments of Cavendish), Lavoisier +and Laplace burned inflammable and dephlogisticated airs, and obtained +water. As the result of these experiments they determined that one volume +of dephlogisticated air combines with 1.91 volumes of inflammable air to +form water.</p> + +<p>A little later Lavoisier completed the proof of the composition of water by +showing that when steam is passed through a tube containing iron filings +kept red hot, inflammable air is evolved and calx of iron remains in the +tube.</p> + +<p>Lavoisier could now explain the conversion of a metallic calx into metal by +the action of inflammable air; this air decomposes the calx—that is, the +metallic oxide—combines with its oxygen to form water, and so the metal is +produced.</p> + +<p>When a metal is dissolved in diluted vitriolic or muriatic acid a calx is +formed, because, according to Lavoisier, the water present is decomposed by +the metal, inflammable air is evolved, and the dephlogisticated air of the +water combines with the metal forming a calx, which then dissolves in the +acid.</p> + +<p>Lavoisier now studied the properties of the compounds produced by burning +phosphorus, sulphur<span class='pagenum'><a name="Page_91" id="Page_91">[Pg 91]</a></span> and carbon in dephlogisticated air. He found that +solutions of these compounds in water had a more or less sour taste and +turned certain blue colouring matters red; but these were the properties +regarded as especially belonging to acids. These products of combustion in +dephlogisticated air were therefore acids; but as phosphorus, carbon and +sulphur were not themselves acids, the acid character of the substances +obtained by burning these bodies in dephlogisticated air must be due to the +presence in them of this air. Hence Lavoisier concluded that this air is +the substance the presence of which in a compound confers acid properties +on that compound. This view of the action of dephlogisticated air he +perpetuated in the name "oxygen" (from Greek, = <i>acid-producer</i>), which he +gave to dephlogisticated air, and by which name this gas has ever since +been known.</p> + +<p>Priestley was of opinion that the atmosphere is rendered noxious by the +breathing of animals, because it is thereby much phlogisticated, and he +thought that his experiments rendered it very probable that plants are able +to purify this noxious air by taking away phlogiston from it (see p. 69). +But Lavoisier was now able to give a much more definite account of the +effects on the atmosphere of animal and vegetable life. He had already +shown that ordinary air contains oxygen and azote (nitrogen), and that the +former is alone concerned in the process of combustion. He was now able to +show that animals during respiration draw in air into their lungs: that<span class='pagenum'><a name="Page_92" id="Page_92">[Pg 92]</a></span> a +portion of the oxygen is there combined with carbon to form carbonic acid +gas (as the fixed air of Black was now generally called), which is again +expired along with unaltered azote. Respiration was thus proved to be a +process chemically analogous to that of calcination.</p> + +<p>Thus, about the year 1784-85, the theory of phlogiston appeared to be quite +overthrown. The arguments of its upholders, after this time, were not +founded on facts; they consisted of fanciful interpretations of crudely +performed experiments. Cavendish was the only opponent to be dreaded by the +supporters of the new chemistry. But we have seen that although Cavendish +retained the language of the phlogistic theory (see pp. 78, 79) as in his +opinion equally applicable to the facts of combustion with that of the new +or Lavoisierian theory, he nevertheless practically admitted the essential +point of the latter, viz. that calces are compounds of metal and oxygen (or +dephlogisticated air). Although Cavendish was the first to show that water +is produced when the two gases hydrogen and oxygen are exploded together, +it would yet appear that he did not fully grasp the fact that water is a +compound of these two gases; it was left to Lavoisier to give a clear +statement of this all-important fact, and thus to remove the last prop from +under the now tottering, but once stately edifice built by Stahl and his +successors.</p> + +<p>The explanation given by Lavoisier of combustion was to a great extent +based on a conception<span class='pagenum'><a name="Page_93" id="Page_93">[Pg 93]</a></span> of element and compound very different from that of +the older chemists. In the "Sceptical Chymist" (1661) Boyle had argued +strongly against the doctrine of the four "elementary principles," earth, +air, fire and water, as held by the "vulgar chymists." The existence of +these principles, or some of them, in every compound substance was firmly +held by most chemists in Boyle's time. They argued thus: when a piece of +green wood bums, the existence in the wood of the principle of fire is made +evident by the flame, of the principle of air by the smoke which ascends, +of that of water by the hissing and boiling sound, and of the principle of +earth by the ashes which remain when the burning is finished.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a></p> + +<p>Boyle combated the inference that because a flame is visible round the +burning wood, and a light air or smoke ascends from it, <i>therefore</i> these +principles were contained in the wood before combustion began. He tried to +prove by experiments that one substance may be obtained from another in +which the first substance did not already exist; thus, he heated water for +a year in a closed glass vessel, and obtained solid particles heavier than, +and as he supposed formed from, the water. We have already<span class='pagenum'><a name="Page_94" id="Page_94">[Pg 94]</a></span> learned the +true interpretation of this experiment from the work of Lavoisier. Boyle +grew various vegetables in water only, and thought that he had thus changed +water into solid vegetable matter. He tells travellers' tales of the growth +of pieces of iron and other metals in the earth or while kept in +underground cellars.</p> + +<p>We now know how erroneous in most points this reasoning was, but we must +admit that Boyle established one point most satisfactorily, viz. that +because earth, or air, or fire, or water is obtained by heating or +otherwise decomposing a substance, it does not necessarily follow that the +earth, or air, or fire, or water existed as such in the original substance. +He overthrew the doctrine of elementary principles held by the "vulgar +chymists." Defining elements as "certain primitive and simple bodies which, +not being made of any other bodies, or of one another, are the ingredients +of which all those called perfectly mixt bodies are immediately compounded, +and into which they are ultimately resolved," Boyle admitted the <i>possible</i> +existence, but thought that the facts known at his time did not warrant the +assertion of the <i>certain</i> existence, of such "elements." The work of Hooke +and Mayow on combustion tended to strengthen this definition of "element" +given by Boyle.</p> + +<p>Black, as we have seen, clearly proved that certain chemical substances +were possessed of definite and unvarying composition and properties; and +Lavoisier, indirectly by his explanation of combustion,<span class='pagenum'><a name="Page_95" id="Page_95">[Pg 95]</a></span> and directly in +his "Treatise on Chemistry", laid down the definition of "element" which is +now universally adopted.</p> + +<p>An element is a substance from which no simpler forms of matter—that is, +no forms of matter each weighing less than the original substance—have <i>as +yet</i> been obtained.</p> + +<p>In the decade 1774-1784 chemical science was thus established on a sure +foundation by Lavoisier. Like most great builders, whether of physical or +mental structures, he used the materials gathered by those who came before +him, but the merit of arranging these materials into a well-laid +foundation, on which the future building might firmly rest, is due to him +alone.</p> + +<p>The value of Lavoisier's work now began to be recognized by his +fellow-chemists in France. In 1785 Berthollet, one of the most rising of +the younger French chemists, declared himself a convert to the views of +Lavoisier on combustion. Fourcroy, another member of the Academy, soon +followed the example of Berthollet. Fourcroy, knowing the weakness of his +countrymen, saw that if the new views could be made to appear as especially +the views of Frenchmen, the victory would be won; he therefore gave to the +theory of Lavoisier the name "<i>La chimie Française</i>". Although this name +was obviously unfair to Lavoisier, it nevertheless caused the +antiphlogistic theory to be identified with the French chemists, and +succeeded in impressing the French public generally with the<span class='pagenum'><a name="Page_96" id="Page_96">[Pg 96]</a></span> idea that to +hold to the old theory was to be a traitor to the glory of one's country. +M. de Morveau, who held a prominent place both in politics and science, was +invited to Paris, and before long was persuaded to embrace the new theory. +This conversion—for "the whole matter was managed as if it had been a +political intrigue rather than a philosophical inquiry"—was of great +importance to Lavoisier and his friends. M. de Morveau was editor of the +chemical part of the "Encyclopédie Méthodique;" in that part of this work +which had appeared before 1784 De Morveau had skilfully opposed the +opinions of Lavoisier, but in the second part of the work he introduced an +advertisement announcing the change in his opinions on the subject of +combustion, and giving his reasons for this change.</p> + +<p>The importance of having a definite language in every science is apparent +at each step of advance. Lavoisier found great difficulty in making his +opinions clear because he was obliged to use a language which had been +introduced by the phlogistic chemists, and which bore the impress of that +theory on most of its terms. About the years 1785-1787, Lavoisier, +Berthollet, Fourcroy and De Morveau drew up a new system of chemical +nomenclature. The fundamental principles of that system have remained as +those of every nomenclature since proposed. They are briefly these:—</p> + +<p>An element is a substance from which no form of matter simpler than itself +has as yet been obtained.<span class='pagenum'><a name="Page_97" id="Page_97">[Pg 97]</a></span></p> + +<p>Every substance is to be regarded as an element until it is proved to be +otherwise.</p> + +<p>The name of every compound is to tell of what elements the substance is +composed, and it is to express as far as possible the relative amounts of +the elements which go to form the compound.</p> + +<p>Thus the compounds of oxygen with any other element were called oxides, +<i>e.g.</i> iron oxide, mercury oxide, tin oxide, etc. When two oxides of iron +came to be known, one containing more oxygen relatively to the amount of +iron present than the other, that with the greater quantity of oxygen was +called iron peroxide, and that with the smaller quantity iron protoxide.</p> + +<p>We now generally prefer to use the name of the element other than oxygen in +adjectival form, and to indicate the relatively smaller or greater quantity +of oxygen present by modifications in the termination of this adjective. +Thus iron protoxide is now generally known as ferr<i>ous</i> oxide, and iron +peroxide as ferr<i>ic</i> oxide. But the principles laid down by the four French +chemists in 1785-1787 remain as the groundwork of our present system of +nomenclature.</p> + +<p>The antiphlogistic theory was soon adopted by all French chemists of note. +We have already seen that Black, with his usual candour and openness to +conviction, adopted and taught this theory, and we are assured by Dr. +Thomas Thomson that when he attended Black's classes, nine years after the +publication of the French system of nomenclature, that<span class='pagenum'><a name="Page_98" id="Page_98">[Pg 98]</a></span> system was in +general use among the chemical students of the university. The older theory +was naturally upheld by the countrymen of the distinguished Stahl after it +had been given up in France. In the year 1792 Klaproth, who was then +Professor of Chemistry in Berlin, proposed to the Berlin Academy of +Sciences to repeat the more important experiments on which the Lavoisierian +theory rested, before the Academy. His offer was accepted, and from that +time most of the Berlin chemists declared themselves in favour of the new +theory.</p> + +<p>By the close of last century the teaching of Lavoisier regarding combustion +found almost universal assent among chemists. But this teaching carried +with it, as necessary parts, the fundamental distinction between element +and compound; the denial of the existence of "principles" or "essences;" +the recognition of the study of actually occurring reactions between +substances as the basis on which all true chemical knowledge was to be +built; and the full acknowledgment of the fact that matter is neither +created nor destroyed, but only changed as to its form, in any chemical +reaction.</p> + +<p>Of Lavoisier's other work I can only mention the paper on "Specific Heats" +contributed by Laplace and Lavoisier to the Memoirs of the Academy for +1780. In this paper is described the ice calorimeter, whereby the amount of +heat given out by a substance in cooling from one definite temperature to +another is determined, by measuring the amount<span class='pagenum'><a name="Page_99" id="Page_99">[Pg 99]</a></span> of ice converted into water +by the heated substance in cooling through the stated interval of +temperature. The specific heats of various substances, <i>e.g.</i> iron, glass, +mercury, quicklime, etc., were determined by the help of this instrument.</p> + +<p>As we read the record of work done by Lavoisier during the years between +1774 and 1794—work which must have involved a great amount of concentrated +thought as well as the expenditure of much time—we find it hard to realize +that the most tremendous political and social revolution which the modern +world has seen was raging around him during this time.</p> + +<p>In the earlier days of the French Revolution, and in the time immediately +preceding that movement, many minds had been stirred to see the importance +of the study of Nature; but it was impossible that natural science should +continue to flourish when the tyrant Robespierre had begun the Reign of +Terror.</p> + +<p>The roll of those who perished during this time contains no more +illustrious name than that of Antoine Laurent Lavoisier. In the year 1794 +Lavoisier, who had for some time acted as a <i>fermier-général</i> under the +Government, was accused of mixing with the tobacco "water and other +ingredients hurtful to the health of the citizens." On this pretext he and +some of his colleagues were condemned to death. For some days Lavoisier +found a hiding-place among his friends, but hearing that his colleagues had +been arrested, he delivered<span class='pagenum'><a name="Page_100" id="Page_100">[Pg 100]</a></span> himself up to the authorities, only asking +that the death sentence should not be executed until he had completed the +research in which he was engaged; "not" that he was "unwilling to part with +life," but because he thought the results would be "for the good of +humanity."</p> + +<p>"The Republic has no need of chemists; the course of justice cannot be +suspended," was the reply.</p> + +<p>On the 8th of May 1794, the guillotine did its work; and in his fifty-first +year Lavoisier "joined the majority." To the honour of the Academy of which +he was so illustrious a member it is recorded that a deputation of his +fellow-workers in science, braving the wrath of Robespierre, penetrated to +the dungeons of the prison and placed a wreath on the grave of their +comrade.</p> + +<hr style='width: 45%;' /> + +<p>The period of the infancy of chemical science which I have now briefly +described is broadly contemporaneous with the second half of the eighteenth +century.</p> + +<p>At this time the minds of men were greatly stirred. Opinions and beliefs +consecrated by the assent of generations of men were questioned or denied; +the pretensions of civil and ecclesiastical authorities were withstood; +assertions however strongly made, and by whatever authority supported, were +met by demands for reasons. In France this revolt against mere authority +was especially marked. Led by the great thinker<span class='pagenum'><a name="Page_101" id="Page_101">[Pg 101]</a></span> Voltaire, the French +philosophers attacked the generally accepted views in moral, theological +and historical matters. A little later they began to turn with eager +attention and hope to the facts of external Nature. Physical science was +cultivated with wonderful vigour and with surprising success.</p> + +<p>In the sciences of heat and light we have at this time the all-important +works of Fourier, Prévost and Fresnel; in geology and natural history we +have Buffon and Cuvier; the name of Bichat marks the beginning of +biological science, and chemistry takes rank as a science only from the +time of Lavoisier.</p> + +<p>From the philosophers an interest in natural science spread through the +mass of the people. About the year 1870 the lecture-rooms of the great +teachers of chemistry, astronomy, electricity, and even anatomy were +crowded with ladies and gentlemen of fashion in the French capital. A +similar state of matters was noticeable in this country. Dr. Black's +lecture theatre was filled by an audience which comprised many young men of +good position. To know something of chemistry became an essential part of +the training of all who desired to be liberally educated.</p> + +<p>The secrets of Nature were now rapidly explored; astonishing advances were +made, and as a matter of course much opposition was raised.</p> + +<p>In this active, inquiring atmosphere the young science of chemistry grew +towards maturity.</p> + +<p>Priestley, ever seeking for new facts, announcing<span class='pagenum'><a name="Page_102" id="Page_102">[Pg 102]</a></span> discovery after +discovery, attacking popular belief in most matters, yet satisfied to +interpret his scientific discoveries in terms of the hypothesis with which +he was most familiar, was the pioneer of the advancing science. He may be +compared to the advance-guard sent forward by the explorers of a new +country with orders to clear a way for the main body: his work was not to +level the rough parts of the way, or to fill in the miry places with +well-laid metal, but rather rapidly to make a road as far into the heart of +the country as possible.</p> + +<p>And we have seen how well he did the work. In his discovery of various +kinds of airs, notably of oxygen, he laid the basis of the great +generalizations of Lavoisier, and, what was perhaps of even more +importance, he introduced a new method into chemistry. He showed the +existence of a new and unexplored region. Before his time, Hooke and Mayow +had proved the existence of more than one kind of air, but the chemistry of +gases arose with the discoveries of Priestley.</p> + +<p>Although Black's chief research, on fixed air and on latent heat, was +completed fifteen or twenty years before Priestley's discovery of oxygen, +yet the kind of work done by Black, and its influence on chemical science, +mark him as coming after Priestley in order of development. We have seen +that the work of Black was characterized by thoroughness and +suggestiveness. The largeness of scope, the breadth of view, of this great +philosopher are best illustrated in his discourses on<span class='pagenum'><a name="Page_103" id="Page_103">[Pg 103]</a></span> heat; he there leads +us with him in his survey of the domain of Nature, and although he tells us +that hypotheses are a "mere waste of time," we find that it is by the +strength of his imagination that he commands assent. But he never allows +the imagination to degenerate into fanciful guesses; he vigorously tests +the fundamental facts of his theory, and then he uses the imagination in +developing the necessary consequences of these facts.</p> + +<p>To Black we owe not only the first rigorously accurate chemical +investigation, but also the establishment of just ideas concerning the +nature of heat.</p> + +<p>But Lavoisier came before us as a greater than either Priestley or Black. +To great accuracy and great breadth of view he added wonderful power of +generalizing; with these, aided by marked mental activity and, on the +whole, favourable external circumstances, he was able finally to overthrow +the loose opinions regarding combustion and elementary principles which +prevailed before his time, and so to establish chemistry as one of the +natural sciences.</p> + +<p>At the close of the first period of advance we find that the sphere of +chemistry has been defined; that the object of the science has been laid +down, as being to find an explanation of the remarkable changes noticed in +the properties of bodies; that as a first step towards the wished-for +explanation, all material substances have been divided by the chemist into +elements and compounds; that an element has been defined as any kind of +matter<span class='pagenum'><a name="Page_104" id="Page_104">[Pg 104]</a></span> from a given weight of which no simpler forms of matter—that is, +no kinds of matter each weighing less than the original matter—have as yet +been obtained; that the great principle of the indestructibility of matter +has been established, viz. that however the properties of matter may be +altered, yet the total mass (or quantity) remains unchanged; and lastly, we +find that an explanation of one important class of chemical changes—those +changes which occur when substances burn—has been found.</p> + +<p>And we have also learned that the method by which these results were +obtained was this—to go to Nature, to observe and experiment accurately, +to consider carefully the results of these experiments, and so to form a +general hypothesis; by the use of the mental powers, and notably by the use +of the imagination, to develop the necessary deductions from this +hypothesis; and finally, to try these deductions by again inquiring from +Nature "whether these things were so."</p> + +<p>Before the time which we have been considering the paths of chemical +science had scarcely yet been trodden. Each discovery was full of promise, +each advance displayed the possibility of further progress; the atmosphere +was filled as with "a mighty rushing wind" ready to sweep away the old +order of things. The age was an age of doubt and of freedom from the +trammels of authority; it was a time eminently suited for making advances +in natural knowledge.<span class='pagenum'><a name="Page_105" id="Page_105">[Pg 105]</a></span></p> + +<p>In the unceasing activity of Priestley and Lavoisier we may trace the +influence of the restlessness of the age; but in the quietness and strength +of the best work of these men, and notably in the work of Black; in the +calmness with which Priestley bore his misfortunes at Birmingham; in the +noble words of Lavoisier, "I am not unwilling to part with life, but I ask +time to finish my experiments, because the results will, I believe, be for +the good of humanity"—we see the truth of the assertion made by one who +was himself a faithful student of Nature—</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"Nature never did betray<br /></span> +<span class="i3">The heart that loved her."<br /></span> +</div></div> + + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> The translation is taken from Thomson's "History of +Chemistry."</p></div> + +<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> Nevertheless, in other places Lavoisier most readily +acknowledges the merits of Priestley.</p></div> + +<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> A similar method of reasoning was employed so far back as the +tenth century: thus, in an Anglo-Saxon "Manual of Astronomy" we read, +"There is no corporeal thing which has not in it the four elements, that +is, air and fire, earth and water.... Take a stick and rub it on something, +it becomes hot directly with the fire which lurks in it; burn one end, then +goeth the moisture out at the other end with the smoke."</p></div> +</div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_106" id="Page_106">[Pg 106]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap3.jpg" width="500" height="115" alt="" title="" /> +</div> + +<h2>CHAPTER III.</h2> + +<h3>ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL SCIENCE—PERIOD OF DALTON.</h3> + + +<h4><i>John Dalton</i>, 1766-1844.</h4> + +<p>The progress of chemical knowledge became so rapid in the early years of +the present century, that although I have in this chapter called the time +immediately succeeding that of Lavoisier "the period of John Dalton," and +although I shall attempt to describe the advances made by this philosopher +without considering those of his contemporaries Davy and Berzelius, yet I +must insist on the facts that this arrangement is made purely for the sake +of convenience, and that many of the discoveries of Davy, Berzelius and +others came in order of time before, or followed close upon the publication +of Dalton's atomic theory.</p> + +<p>Nevertheless, as the work of these men belongs in its essence to the modern +period, and as the promulgation of the atomic theory by Dalton<span class='pagenum'><a name="Page_107" id="Page_107">[Pg 107]</a></span> marks the +beginning of this period, it seems better that we should have a clear +conception of what was done by this chemist before proceeding to consider +the advances made by his contemporaries and successors.</p> + + +<p><span class="smcap">John Dalton</span>, the second of three children of Joseph and Deborah Dalton, was +born at Eaglesfield, a village near Cockermouth, in Cumberland, on the 5th +of September 1766. One of the first meeting-houses established by the +Society of Friends is to be found in Eaglesfield.</p> + +<p>The Dalton family had been settled for several generations on a small +copyhold estate in this village. The first of them to join the Friends was +the grandfather of John Dalton; his descendants remained faithful adherents +of this society.</p> + +<p>Dalton attended the village schools of Eaglesfield and the neighbourhood +until he was eleven years old, by which time, in addition to learning +reading, writing and arithmetic, he had "gone through a course of +mensuration, surveying, navigation, etc." At the age of ten his taste for +measurements and calculations began to be remarked by those around him; +this taste was encouraged by Mr. Robinson, a relative of Dalton, who +recognizing the indomitable perseverance of the boy appears to have taken +some care about this time in directing his mathematical studies.</p> + +<p>At the early age of twelve Dalton affixed to the door of his father's house +a large sheet of paper<span class='pagenum'><a name="Page_108" id="Page_108">[Pg 108]</a></span> whereon he announced that he had opened a school +for youth of both sexes; also that "paper, pens and ink" were sold within. +The boy-teacher had little authority over his pupils, who challenged their +master to fight in the graveyard, and broke the windows of the room into +which they had been locked till their tasks should be learned.</p> + +<p>When he was fifteen years old Dalton removed to Kendal, where he continued +for eleven or twelve years, at first as assistant-master, and then, along +with his elder brother Jonathan, as principal of a boarding school for +boys.</p> + +<p>It was announced by the brothers that in this school "youth will be +carefully instructed in English, Latin, Greek and French; also writing, +arithmetic, merchants' accounts and the mathematics." The school was not +very successful. Both brothers were hard, inflexible, and ungainly in their +habits, and neither was fitted to become a successful teacher of boys: of +the two, John had the gentler disposition, and was preferred by the boys; +"besides, his mind was so occupied by mathematics that their faults escaped +his notice."</p> + +<p>During this time Dalton employed his leisure in learning Latin, Greek and +French, and in pursuing his studies in mathematics and natural philosophy. +He became a frequent contributor to the <i>Gentlemen's Diary</i>, a paper which +received problems of various kinds—chiefly mathematical—and presented +prizes for their successful solution.</p> + +<p>Besides setting and answering mathematical<span class='pagenum'><a name="Page_109" id="Page_109">[Pg 109]</a></span> problems in this journal, and +also in the <i>Ladies' Diary</i>, Dalton sometimes ventured into the wider +fields of mental phenomena. It seems strange to read that, even at the age +of twenty-six, Dalton should occupy his leisure time composing answers to +such queries as these:—</p> + +<p>"Whether, to a generous mind, is the conferring or receiving an obligation, +the greater pleasure?"</p> + +<p>"Is it possible for a person of sensibility and virtue, who has once felt +the passion of love in the fullest extent that the human heart is capable +of receiving it (being by death or some other circumstance for ever +deprived of the object of its wishes), ever to feel an equal passion for +any other object?"</p> + +<p>In his answer to the second of these queries, Dalton carefully framed two +hypotheses, and as carefully drew conclusions from each. The question in +the <i>Diary</i> was by "Mira;" if "Mira" were a "rapturous maiden" she would +not derive much comfort from the cold and mathematical answer by "Mr. John +Dalton of Kendal."</p> + +<p>At Kendal Dalton made the acquaintance of Mr. Gough, who was about eight +years older than Dalton, and had been blind from the age of two. Mr. Gough, +we are assured by Dalton, was "a perfect master of the Latin, Greek and +French tongues;" he understood "well all the different branches of +mathematics;" there was "no branch of natural philosophy but what he was +well acquainted with;" he knew "by the touch, taste and smell, almost<span class='pagenum'><a name="Page_110" id="Page_110">[Pg 110]</a></span> +every plant within twenty miles of Kendal." To the friendship of this +remarkable man Dalton owed much; with his help he acquired a fair knowledge +of the classical languages, and he it was who set Dalton the example of +keeping a regular record of weather observations.</p> + +<p>On the 24th of March 1787 Dalton made his first entry in a book which he +entitled "Observations on the Weather, etc.;" the last entry in this book +he made fifty-seven years later on the evening preceding his death. The +importance of Dalton's meteorological observations, as leading him to the +conception of the atomic theory, will be noticed as we proceed.</p> + +<p>In the year 1793 Dalton, who was now twenty-seven years of age, was invited +to Manchester to become tutor in the mathematical and natural philosophy +department of a college recently established by influential Dissenters in +that town. Eighty pounds for the session of ten months was guaranteed him; +and he was provided with "rooms and commons" in the college at a charge of +£27 10<i>s.</i> per session.</p> + +<p>He held this appointment for six years, when he retired, and continuing to +live in Manchester devoted himself to researches in natural philosophy, +gaining a living by giving private lessons in mathematics and physical +science at a charge of 2<i>s.</i> 6<i>d.</i> per hour, or 1<i>s.</i> 6<i>d.</i> each if more +than two pupils attended at the same time.</p> + +<p>Dalton was elected a Fellow of the Literary<span class='pagenum'><a name="Page_111" id="Page_111">[Pg 111]</a></span> and Philosophical Society of +Manchester in the year 1794; and from the time of his retiring from the +tutorship of Manchester New College till the close of his life he spent a +great part of his time in a room in the society's house in George Street, +in studying and teaching. The fifty years thus spent are marked by few +outward events. The history of Dalton's life from this time is the history +of the development of his intellect, and the record of his scientific +discoveries.</p> + +<p>On one occasion during Dalton's stay at Kendal, as he was about to make a +visit to his native village, he bethought himself that the present of a +pair of silken hose would be acceptable to his mother. He accordingly +purchased a pair marked "newest fashion;" but his mother's remark, "Thou +hast brought me a pair of grand hose, John; but what made thee fancy so +light a colour? I can never show myself at meeting in them," rather +disconcerted him, as to his eyes the hose were of the orthodox drab colour. +His mother insisted that the stockings were "as red as a cherry." John's +brother upheld the "drab" side of the dispute; so the neighbours were +called in, and gave their decision that the hose were "varra fine stuff, +but uncommon scarlety."</p> + +<p>From this time Dalton made observations on the peculiarities of his own +vision and that of others, and in his first paper read before the Literary +and Philosophical Society in 1794, he described these peculiarities. He +says, "Since the year 1790 the<span class='pagenum'><a name="Page_112" id="Page_112">[Pg 112]</a></span> occasional study of botany obliged me to +attend more to colour than before. With respect to colours that were white, +yellow, or green, I readily assented to the appropriate term; blue, purple, +pink and crimson appeared rather less distinguishable, being, according to +my idea, all referable to blue. I have often seriously asked a person +whether a flower was blue or pink, but was generally considered to be in +jest." Dalton's colour-blindness was amusingly illustrated at a later time, +when having been created D.C.L. by the University of Oxford he continued to +wear the red robes of his degree for some days; and when his attention was +drawn to the somewhat strange phenomenon, even in a university town, of an +elderly gentleman in the dress of a Quaker perambulating the town day after +day in a scarlet robe, he remarked that to him the gown appeared to be of +the same colour as the green trees.</p> + +<p>Dalton's work during the next six or eight years dealt chiefly with +problems suggested by his meteorological observations; he published a +volume on "Meteorological Observations and Essays," chiefly occupied with +descriptions of the instruments employed, more especially of the +thermometer and barometer, and an instrument for determining the dew-point +of air. By this time he had established the existence of a connection of +some kind between magnetism and the aurora, and had thus laid the +foundations of a most important branch of meteorology.<span class='pagenum'><a name="Page_113" id="Page_113">[Pg 113]</a></span></p> + +<p>In 1799, in a note to a paper on rain and dew, he begins his work on +aqueous vapour in the atmosphere by proving that water vapour exists as +such in the air. This paper is quickly followed by another on the +conducting power of water for heat.</p> + +<p>A very important paper was published in 1801, on the "Constitution of Mixed +Gases, etc.," wherein Dalton asserted that the total pressure of a mixture +of two gases on the walls of the containing vessel is equal to the sum of +the pressures of each gas; in other words, that if one gas is removed the +pressure now exerted by the remaining gas is exactly the same as was +exerted by that gas in the original mixture. In a paper published much +later (1826), when his views and experiments on this subject were matured, +he writes: "It appears to me as completely demonstrated as any physical +principle, that whenever two or more ... gases or vapours ... are put +together, either into a limited or unlimited space, they will finally be +arranged each as if it occupied the whole space, and the others were not +present; the nature of the fluids and gravitation being the only +efficacious agents."</p> + +<p>This conclusion was followed out and extended in a paper published in 1803, +on the absorption of gases by water and other liquids, wherein he states +that the amount of each gas <i>mechanically dissolved</i> by a liquid from a +mixture of gases depends only on the quantity of <i>that</i> gas in the mixture, +the other gases exerting no influence in this respect.</p> + +<p>Dalton now considered the variation in the<span class='pagenum'><a name="Page_114" id="Page_114">[Pg 114]</a></span> pressures of various gases +caused by increasing or decreasing temperature, and then proceeded to +discuss the relations which exist between the volumes of gases and the +temperature at which these volumes are measured. He concluded that "all +elastic fluids" under the same pressure expand equally by heat: and he adds +the very important remark, "It seems, therefore, that general laws +respecting the absolute quantity and the nature of heat are more likely to +be derived from the study of elastic fluids than of other substances"—a +remark the profound truth of which has been emphasized by each step in the +advances made in our conception of the nature of heat since the time of +Dalton.</p> + +<p>In these papers on the "Constitution of Mixed Gases" Dalton also describes +and illustrates a method whereby the actual amount of water vapour in a +given bulk of atmospheric air may be found from a knowledge of the +dew-point of that air, that is, the temperature at which the deposition of +water in the liquid form begins. The introduction of this method for +finding the humidity of air marks an important advance in the history of +meteorology.</p> + +<p>In this series of papers published within the first three years of the +present century Dalton evidently had before his mind's eye a picture of a +gas as a quantity of matter built up of small but independent particles; he +constantly speaks of pressures between the small particles of elastic<span class='pagenum'><a name="Page_115" id="Page_115">[Pg 115]</a></span> +fluids, of these particles as repelling each other, etc. In his "New +System" he says, "A vessel full of any pure elastic fluid presents to the +imagination a picture like one full of small shot."</p> + +<p>It is very important to notice that Dalton makes use of this conception of +small particles to explain purely physical experiments and operations. +Although we know that during these years he was thinking much of "chemical +combinations," yet we find that it was his observations on the weather +which led him to the conception—a purely physical conception—of each +chemically distinct gas as being built up of a vast number of small, +equally heavy particles. A consideration of these papers by Dalton on the +constitution of mixed gases shows us the method which he pursued in his +investigations. "The progress of philosophical knowledge," he says, "is +advanced by the discovery of new and important facts; but much more when +these facts lead to the establishment of general laws." Dalton always +strove to attain to general laws. The facts which he describes are +frequently inaccurate; he was singularly deficient in manipulation, and he +cannot claim a high place as a careful experimenter. He was however able to +draw general conclusions of wide applicability. He seems sometimes to have +stated a generalization in definite form before he had obtained any +experimental verification of it.</p> + +<p>In the year 1802 Dalton conducted an examination of air from various +localities, and concluded<span class='pagenum'><a name="Page_116" id="Page_116">[Pg 116]</a></span> that one hundred volumes of air are composed of +twenty-one volumes of oxygen and seventy-nine volumes of nitrogen. This +appears to have been his first piece of purely chemical work. But in the +next year he again returns to physical phenomena. In the paper already +referred to, on the absorption of gases by water and other liquids, +published in this year, he had stated that "All gases that enter into water +and other liquids by means of pressure, and are wholly disengaged again by +the removal of that pressure, are <i>mechanically</i> mixed with the liquid, and +not <i>chemically</i> combined with it." But if this be so, why, he asked, does +not water mechanically dissolve the same bulk of every kind of gas? The +answer which he gives to this question is found at the close of the paper; +to the student of chemistry it is very important:—</p> + +<p>"This question I have duly considered, and though I am not yet able to +satisfy myself completely, I am nearly persuaded that the circumstance +depends upon the weight and number of the ultimate particles of the several +gases, those whose particles are lightest and single being least +absorbable, and the others more, accordingly as they increase in weight and +complexity. An inquiry into the relative weights of the ultimate particles +of bodies is a subject, as far as I know, entirely new. I have lately been +prosecuting this inquiry with remarkable success. The principle cannot be +entered upon in this paper; but I shall just subjoin the results, as far as +they appear to be<span class='pagenum'><a name="Page_117" id="Page_117">[Pg 117]</a></span> ascertained by my experiments." Then follows a "<i>Table +of the relative weights of the ultimate particles of gaseous and other +bodies.</i>" The following numbers, among others, are given:—</p> + +<div class='center'> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align='left'>Hydrogen</td><td align='left'>1</td><td align='left'> </td><td align='left'>Sulphur</td><td align='left'>14·4</td></tr> +<tr><td align='left'>Oxygen</td><td align='left'>5·5</td><td align='left'> </td><td align='left'>Alcohol</td><td align='left'>15·1</td></tr> +<tr><td align='left'>Azote</td><td align='left'>4·2</td><td align='left'> </td><td align='left'>Nitrous oxide</td><td align='left'>13·7</td></tr> +<tr><td align='left'>Phosphorus</td><td align='left'>7·2</td><td align='left'> </td><td align='left'>Ether</td><td align='left'> 9·6</td></tr> +</table></div> + + +<p>Here is the beginning of the atomic theory; and yet Dalton's strictly +chemical experimental work lies in the future. The scope of the theory is +defined in that sentence—"<i>An inquiry into the relative weights of the +ultimate particles of bodies.</i>" His paper on mixed gases is illustrated by +a plate,<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> which shows how vividly Dalton at this time pictured to himself +a quantity of gas as composed of many little particles, and how clearly he +recognized the necessity of regarding all the particles of each elementary +gas as alike, but as differing from those of every other elementary gas.</p> + +<p>In 1804 Dalton was invited to deliver a course of lectures in the Royal +Institution of London, on heat, mixed gases and similar subjects. In these +lectures he expounded his views on the constitution of gases, on absorption +of gases by liquids, etc. These views drew much attention in this and other +<span class='pagenum'><a name="Page_118" id="Page_118">[Pg 118]</a></span>countries. "They are busy with them," he writes in 1804, "at London, +Edinburgh, Paris and in various parts of Germany, some maintaining one side +and some another. The truth will surely out at last."</p> + +<div class="figcenter" style="width: 245px;"> +<img src="images/fig2.jpg" width="245" height="650" alt="Fig. 2" title="" /> +<span class="caption">Fig. 2</span> +</div> + +<p>Dalton's love of numerical calculations is noticeable in a trivial +circumstance which he mentions in a letter from London to his brother. He +tried to count the number of coaches which he met in going to the Friends' +morning meeting: this he assures his brother he "effected with tolerable +precision. The number was one hundred and four."</p> + +<p>During vacation time Dalton usually made a walking excursion in the Lake +district. He was extremely<span class='pagenum'><a name="Page_119" id="Page_119">[Pg 119]</a></span> fond of mountain scenery, but generally +combined the pursuit of science with that of pleasure; he carried his +meteorological instruments with him, determined the dew-point at various +altitudes, and measured mountain heights by the aid of his barometer. +Sometimes however he refused to have anything to do with science. A +companion in one of these excursions says that he was "like a schoolboy +enjoying a holiday, mocking the cuckoos, putting up and chasing the hares, +stopping from time to time to point out some beautiful view, or loitering +to chat with passing pedestrians."</p> + +<p>This side of Dalton's nature was not often apparent. In him the quiet, +hard-working student generally appeared prominently marked; but on the +half-holiday which he allowed himself on each Thursday afternoon, in order +to enjoy the society of a few friends and to engage in his favourite +amusement of a game at bowls, he laid aside something of the quietness, +regularity and decorum which usually characterized him. "When it came to +his turn to bowl he threw his whole soul into the game,... and it was not a +little amusing to spectators to see him running after the ball across the +green, stooping down as if talking to it, and waving his hands from one +side to the other exactly as he wished the line of the ball to be, and +manifesting the most intense interest in its coming near to the point at +which he aimed."</p> + +<p>From the year 1803-4 Dalton becomes more and more a worker in chemistry. +The establishment<span class='pagenum'><a name="Page_120" id="Page_120">[Pg 120]</a></span> of the atomic theory now engaged most of his time and +attention. The results of his investigation of "the primary laws which seem +to obtain in regard to heat and to chemical combinations" appeared in his +"New System of Chemical Philosophy," Part I. of which, "On Heat, on the +Constitution of Bodies and on Chemical Synthesis," was published in 1808.</p> + +<p>We have now arrived at the time when Dalton's inquiry into the "relative +weights of the ultimate particles of bodies" was in his opinion +sufficiently advanced for presentation to the scientific world; but I think +we shall do better to postpone our consideration of this great inquiry +until we have completed our review of the chief events in the life of +Dalton, other than this the greatest event of all.</p> + +<p>Dalton did not look for rewards—he desired only the just fame of one who +sought for natural truths; but after the publication of the "New System" +rewards began to come to him. In 1817 he was elected a corresponding member +of the French Academy of Sciences.</p> + +<p>In 1822, when his fame as a philosophical chemist was fully established, +Dalton visited Paris. This visit gave him great pleasure. He was constantly +in the society of the great men who then so nobly represented the dignity +of natural science in France; Laplace, Cuvier, Biot, Arago, Gay-Lussac, +Milne-Edwards and others were his friends. For some time after this visit +he was more vivacious and communicative than usual, and we are told by one<span class='pagenum'><a name="Page_121" id="Page_121">[Pg 121]</a></span> +who lived in the same house as he, "We frequently bantered him with having +become half a Frenchman." Dalton especially valued the friendship of +Clementine Cuvier, daughter of the great naturalist, with whom he became +acquainted during his visit to Paris. All through life he greatly delighted +in the society of cultivated women, and his warmest friendships were with +gentlewomen. At one time, shortly after going to Manchester, he was much +taken by a widow lady who combined great personal charms with considerable +mental culture. "During my <i>captivity</i>," he writes to a friend, "which +lasted about a week, I lost my appetite, and had other symptoms of +<i>bondage</i> about me, as incoherent discourse, etc., but have now happily +regained my freedom." The society of men who like himself were actively +engaged in the investigation of natural science was also a source of much +pleasure to Dalton. Such men used to visit him in Manchester, so that in +the house of the Rev. Mr. Johns, in whose family he lived, "there were +found from time to time some of the greatest philosophers in Europe."</p> + +<p>Dalton was elected a Fellow of the Royal Society in 1822, and four years +later he became the first recipient of one of the Royal Medals, then +founded by the King (George IV.). In 1830 he was elected one of the eight +foreign Associates of the French Academy, an honour which is generally +regarded as the highest that can be bestowed on any man of science.<span class='pagenum'><a name="Page_122" id="Page_122">[Pg 122]</a></span></p> + +<p>Dalton was one of the original members of the British Association for the +Advancement of Science, and he attended most of the meetings from the first +held in York in 1831 to that held in Manchester two years before his death. +At the Oxford meeting of 1832 he was created D.C.L. by the University, and +two years later the University of Edinburgh honoured herself by enrolling +his name on the list of her doctors of law.</p> + +<p>About this time some of Dalton's scientific friends, who considered his +work of great national importance, endeavoured to obtain a pension for him +from the civil list. At the meeting of the British Association held at +Cambridge in 1833, the president, Professor Sedgwick, was able to announce +that "His Majesty, willing to manifest his attachment to science, and his +regard for a character like that of Dr. Dalton, had graciously conferred on +him, out of the funds of the civil list, a substantial mark of his royal +favour." The "substantial mark of royal favour," the announcement of which +Dalton received "with his customary quietness and simplicity of manner," +consisted of a pension of £150 <i>per annum</i>, which was increased three years +later to £300.</p> + +<p>The second part of Volume I. of his "New System" was published by Dalton in +1810, and the second volume of the same work in 1827. In 1844 a paper by +him was read before the British Association, in which he announced some +important discoveries with regard to the water in crystallizable<span class='pagenum'><a name="Page_123" id="Page_123">[Pg 123]</a></span> salts, +and thus brought a new class of facts within the range of the atomic +theory.</p> + +<p>He was seized with paralysis in 1837, but recovered to a great extent; a +second attack in 1844 however completely prostrated him. On the 16th of +July in that year he made the last entry in his book of "Observations on +the Weather"—"<i>Little rain</i>;" next morning he became insensible and +quietly passed away.</p> + +<hr style='width: 45%;' /> + +<p>It is as the founder of the chemical atomic theory that Dalton must ever be +remembered by all students of physical and chemical science.</p> + +<p>To the Greek philosophers Leucippus and Democritus (flourished about +440-400 <span class="smcap">b.c.</span>) we owe the conception that "The bodies which we see and +handle, which we can set in motion or leave at rest, which we can break in +pieces and destroy, are composed of smaller bodies, which we cannot see or +handle, which are always in motion, and which can neither be stopped, nor +broken in pieces, nor in any way destroyed or deprived of the least of +their properties" (Clerk Maxwell). The heavier among these small +indivisible bodies or atoms were regarded as always moving downwards. By +collisions between these and the lighter ascending atoms lateral movements +arose. By virtue of the natural law (as they said) that things of like +weight and shape must come to the same place, the atoms of the various +elements came together; thus larger masses of matter were formed; these +again<span class='pagenum'><a name="Page_124" id="Page_124">[Pg 124]</a></span> coalesced, and so finally worlds came into existence.</p> + +<p>This doctrine was extended by Epicurus (340-270 <span class="smcap">B.C.</span>), whose teaching is +preserved for us in the poem of Lucretius (95-52 <span class="smcap">B.C.</span>), "De Rerum Natura;" +he ascribed to the atoms the power of deviating from a straight line in +their descending motion. On this hypothesis Epicurus built a general theory +to explain all material and spiritual phenomena.</p> + +<p>The ceaseless change and decay in everything around them was doubtless one +of the causes which led men to this conception of atoms as indivisible, +indestructible substances which could never wear out and could never be +changed. But even here rest could not be found; the mind was obliged to +regard these atoms as always in motion. The dance of the dust-motes in the +sunbeam was to Lucretius the result of the more complex motion whereby the +atoms which compose that dust are agitated. In his dream as told by +Tennyson—</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"A void was made in Nature: all her bonds<br /></span> +<span class="i0">Cracked: and I saw the flaring atom-streams<br /></span> +<span class="i0">And torrents of her myriad universe,<br /></span> +<span class="i0">Ruining along the illimitable inane,<br /></span> +<span class="i0">Fly on to clash together again, and make<br /></span> +<span class="i0">Another and another frame of things<br /></span> +<span class="i0">For ever."<br /></span> +</div></div> + +<p>The central quest of the physicist, from the days of Democritus to the +present time, has been to explain the conception of "atom"—to develop more +clearly the observed properties of the things which are seen and which may +be handled as dependent<span class='pagenum'><a name="Page_125" id="Page_125">[Pg 125]</a></span> on the properties of those things which cannot be +seen, but which yet exist. For two thousand years he has been trying to +penetrate beneath the ever-changing appearances of Nature, and to find some +surer resting-place whence he may survey these shifting pictures as they +pass before his mental vision. The older atomists thought to find this +resting-place, not in the atoms themselves, but in the wide spaces which +they supposed to exist between the worlds:—</p> + +<div class="poem"><div class="stanza"> +<span class="i0">"The lucid interspace of world and world<br /></span> +<span class="i0">Where never creeps a cloud, or moves a wind,<br /></span> +<span class="i0">Nor ever falls the least white star of snow,<br /></span> +<span class="i0">Nor ever lowest roll of thunder moans,<br /></span> +<span class="i0">Nor sound of human sorrow mounts to mar<br /></span> +<span class="i0">Their sacred everlasting calm."<br /></span> +</div></div> + +<p>To the modern student of science the idea of absolute rest appears +unthinkable; but in the most recent outcome of the atomic theory—in the +vortex atoms of Helmholtz and Thomson—he thinks he perceives the very +"foundation stones of the material universe."</p> + +<p>Newton conceived the atom as a "solid, massy, hard, impenetrable, movable +particle." To the mind of D. Bernoulli the pressure exerted by a gas on the +walls of a vessel enclosing it was due to the constant bombardment of the +walls by the atoms of which the gas consisted.</p> + +<p>Atomic motion was the leading idea in the explanation of heat given by +Rumford and Davy, and now universally accepted; and, as we have seen, +Dalton was himself accustomed to regard all<span class='pagenum'><a name="Page_126" id="Page_126">[Pg 126]</a></span> "elastic fluids" (<i>i.e.</i> +gases) as consisting of vast numbers of atoms.</p> + +<p>But in the year 1802 or so, Dalton thought that by the study of chemical +combinations it would be possible to determine the relative weights of +atoms. Assume that any elementary gas is composed of small, indivisible, +equally heavy parts; assume that the weight of an atom of one element is +different from that of the atom of any other element; and, lastly, assume +that when elements combine the atom of the compound so produced is built up +of the atoms of the various elements. Make these assumptions, and it +follows that the relative weights of two or more elements which combine +together must represent the relative weights of the atoms of these +elements.</p> + +<p>We know that the fixity of composition of chemical compounds had been +established before this time, largely by the labours of Black and +Lavoisier. Fixity of composition had however been called in question by +Berthollet, who held that elements combine together in very varying +quantities; that, in fact, in place of there being two or three, or a few +definite compounds of, say, iron and oxygen, there exists a graduated +series of such bodies; and that the amount of iron which combines with +oxygen depends chiefly on such physical conditions as the temperature, the +pressure, etc., under which the chemical action occurs. But by the date of +the publication of the first part of Dalton's "New System," the long +dispute between<span class='pagenum'><a name="Page_127" id="Page_127">[Pg 127]</a></span> Berthollet and Proust regarding fixity of composition of +compounds had nearly closed in favour of the latter chemist, who strongly +upheld the affirmative side of the argument. But if Dalton's assumptions +are correct, it is evident that when two elements form more than one +compound, the quantity of element A in one of these must be a simple +multiple of the quantity in the other of these compounds; because there +must be a greater number of atoms of element A in the atom of one compound +than in that of the other compound, and an elementary atom is assumed to be +indivisible. Hence it follows that if one element be taken as a standard, +it must be possible to affix to any other element a certain number which +shall express the smallest quantity of that element which combines with one +part by weight of the standard element; and this number shall also +represent how many times the atom of the given element is heavier than the +atom of the standard element, the weight of which has been taken to be +<i>one</i>. If this element forms two compounds with the standard element, the +amount of this element in the second compound must be expressed by a simple +multiple of the number assigned to this element, because it is not +possible, according to the fundamental assumptions of the theory, to form a +compound by the combination of fractions of elementary atoms.</p> + +<p>By pondering on the facts regarding chemical combinations which had been +established by various workers previous to the year 1802, Dalton had<span class='pagenum'><a name="Page_128" id="Page_128">[Pg 128]</a></span> +apparently come to such conclusions as those now indicated.</p> + +<p>In his paper on the properties of the gases constituting the atmosphere, +read to the Manchester Society on November 12, 1802, he stated that one +hundred measures of common air would combine with thirty-six measures of +"nitrous gas" in a narrow tube to produce an oxide of nitrogen, but with +seventy-two measures of the same gas in a wide vessel to produce another +oxide of nitrogen. These facts, he says, "clearly point out the theory of +the process: the elements of oxygen may combine with a certain portion of +nitrous gas, or with twice that portion, but with no intermediate +quantity."</p> + +<p>In the concluding paragraph of his paper on absorption of gases by liquids, +read on October 21, 1803, we found (see p. 116) that he had got so far in +his inquiry into the "relative weights of the ultimate particles of bodies" +as to give a table of twenty-one such weights. About this time Dalton made +analyses of two gaseous compounds of carbon—olefiant gas and carburetted +hydrogen or marsh-gas. He found that both are compounds of carbon and +hydrogen; that in one 4.3 parts by weight of carbon are combined with one +part by weight of hydrogen, and in the other the same amount (4.3) of +carbon is combined with two parts by weight of <span class='pagenum'><a name="Page_129" id="Page_129">[Pg 129]</a></span>hydrogen.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a></p> + +<p>This was a striking confirmation of his views regarding combination in +multiple proportions, which views followed as a necessary deduction from +the atomic hypothesis. From this time he continued to develop and extend +this hypothesis, and in the year 1808 he published his "New System of +Chemical Philosophy."</p> + +<p>The first detailed account of the atomic theory was however given to the +chemical world the year before Dalton's book appeared. During a +conversation with Dalton in the autumn of 1804 Dr. Thomas Thomson learned +the fundamental points of the new theory, and in the third edition of his +"System of Chemistry," published in 1807, he gave an account of Dalton's +views regarding the composition of bodies.</p> + +<p>In the same year a paper by Thomson appeared in the <i>Philosophical +Transactions</i>, wherein it was experimentally proved that oxalic acid +combines with strontia to form two distinct compounds, one of which +contains twice as much oxalic acid as the other, the amount of strontia +being the same in both. Analyses of the oxalates of potash, published about +the same time by Wollaston, afforded another illustration of the <i>law of +multiple proportions</i>, and drew the attention of chemists to Dalton's +theory. But the new theory was opposed by several very eminent chemists, +notably by Sir Humphry Davy. In the autumn of 1807 Wollaston, Thomson and +Davy were present at the dinner of the Royal Society Club, at the Crown +and<span class='pagenum'><a name="Page_130" id="Page_130">[Pg 130]</a></span> Anchor, in the Strand. After dinner, these three chemists discussed +the new theory for an hour and a half, Wollaston and Thomson trying to +convince Davy of the truth of Dalton's theory; but "so far from being +convinced, he went away, if possible, more prejudiced against it than +ever."</p> + +<p>Soon after this Wollaston succeeded in convincing Mr. Davis Gilbert +(afterwards President of the Royal Society) of the justness of the atomic +theory, and he in turn so placed the facts and the reasoning before Davy, +that from this time he became a supporter of the new theory.</p> + +<p>In order that the atomic theory should be fruitful of results, it was now +necessary that the values of the atomic weights of many elements should be +carefully determined.</p> + +<p>Let us consider what knowledge must be acquired before the value to be +assigned to the atomic weight of an element can be found.</p> + +<p>Hydrogen was the element chosen as a standard by Dalton. He assumed that +the atom of hydrogen weighs 1; the atomic weight of any other element is +therefore a number which tells how many times the atom of that element is +heavier than the atom of hydrogen. Thus, when Dalton said the atomic weight +of oxygen is 8, he meant that the atom of oxygen is eight times heavier +than that of hydrogen. How was this number obtained?</p> + +<p>Accurate analyses of water show that in this liquid one part by weight of +hydrogen is combined with eight parts by weight of oxygen; but (it is<span class='pagenum'><a name="Page_131" id="Page_131">[Pg 131]</a></span> +said) as the atom of hydrogen weighs 1, the atom of oxygen must weigh 8. In +drawing this conclusion it is assumed that the atom, or smallest particle, +of water is built up of one atom of hydrogen and one atom of oxygen. Let it +be assumed that the atom of water contains two atoms of hydrogen and one of +oxygen, then the latter atom must weigh sixteen times as much as each atom +of hydrogen; let it be assumed that three atoms of hydrogen combine with +one atom of oxygen to form an atom of water, then the weight of the oxygen +atom must be twenty-four times that of the hydrogen atom. Any one of these +assumptions will equally satisfy the figures obtained by analyzing water +(1: 8 = 2: 16 = 3: 24). Now, had we any method whereby we could determine +how many times an atom of water is heavier than an atom of hydrogen we +should be able to determine which of the foregoing assumptions is correct, +and therefore to determine the atomic weight of oxygen. Hence, before the +atomic weight of an element can be determined, there must be found some +method for determining the atomic weights of compounds of that element. +Unless this can be done the atomic theory is of little avail in chemistry.</p> + +<p>I conceive it to be one of the signal merits of Dalton that he so clearly +lays down rules, the best which could be devised at his time, for +determining the atomic weights of compounds, or, what is the same thing, +for determining the number of elementary atoms in one atom of any +compound.<span class='pagenum'><a name="Page_132" id="Page_132">[Pg 132]</a></span> In his "New System" he says that he wishes to show the +importance of ascertaining "the relative weights of the ultimate particles +both of simple and compound bodies, the number of simple elementary +particles which constitute one compound particle, and the number of less +compound particles which enter into the formation of one more compound +particle."</p> + +<p>Considering compounds of two elements, he divides these into binary, +ternary, quaternary, etc., according as the compound atom contains two, +three, four, etc., atoms of the elements. He then proceeds thus—</p> + +<p>"The following general rules may be adopted as guides in all our +investigations respecting chemical synthesis:—</p> + +<p>"1st. When only one combination of two bodies can be obtained, it must be +presumed to be a <i>binary</i> one, unless some cause appear to the contrary.</p> + +<p>"2nd. When two combinations are observed, they must be presumed to be a +<i>binary</i> and a <i>ternary</i>.</p> + +<p>"3rd. When three combinations are obtained, we may expect one to be +<i>binary</i> and the other two <i>ternary</i>.</p> + +<p>"4th. When four combinations are observed, we should expect one <i>binary</i>, +two <i>ternary</i>, and one <i>quaternary</i>," etc.</p> + +<p>Only one compound of hydrogen and oxygen was then known; hence it was +presumed to be a binary compound, <i>i.e.</i> a compound the smallest particle +of which consisted of one atom of hydrogen<span class='pagenum'><a name="Page_133" id="Page_133">[Pg 133]</a></span> and one atom of oxygen; and +hence, from the data already given on page 130, it followed that the atomic +weight of oxygen was 8. Two compounds of carbon and oxygen were known, each +containing six parts by weight of carbon, in one case united with eight, +and in the other case with sixteen parts by weight of oxygen. From Dalton's +rules one of these was a binary, and the other a ternary compound; but as +the atomic weight of oxygen had already been determined to be 8, that +compound of carbon and oxygen containing eight of oxygen combined with six +of carbon was decided to be binary, and that containing sixteen of oxygen +(<i>i.e.</i> two atoms) to be ternary; and hence the atomic weight of carbon was +determined to be 6.</p> + +<p>In the second part of the "New System" Dalton, guided by these rules, +determined experimentally the atomic weights of a great many substances; +but this was not the kind of work suited to Dalton's genius. His analytical +determinations were generally inaccurate; nevertheless, he clearly showed +how the values of the atomic weights of elements ought to be established, +and he obtained results sufficiently accurate to confirm his general +theory. To make accurate determinations of the relative weights of +elementary atoms was one of the tasks reserved for the great Swedish +chemist Berzelius (see pp. 162-170). When we examine Dalton's rules we must +confess that they appear somewhat arbitrary. He does not give reasons for +his assertion that<span class='pagenum'><a name="Page_134" id="Page_134">[Pg 134]</a></span> "when only one combination of two bodies can be +obtained, it must be presumed to be a binary one." Why may it not be +ternary or quaternary? Why must the atom of water be built up of one atom +of hydrogen combined with one atom of oxygen? Or, when two compounds are +known containing the same pair of elements, why must one be binary and the +other ternary?</p> + +<p>Or, even assuming that this <i>must</i> be justified by facts, does it follow +that Dalton's interpretation of the atomic structure of the two oxides of +carbon is necessarily correct? These oxides contain 6 of carbon + 8 of +oxygen, and 6 of carbon + 16 of oxygen, respectively.</p> + +<p>Take the second, 6: 16 = 3: 8; assume this to be a binary compound of one +atom of oxygen (weighing 8) with one atom of carbon (weighing 3), then the +other will be a ternary compound containing one atom of oxygen (8) and two +atoms of carbon (6).</p> + +<p>Hence it appears that Dalton's rules were too arbitrary, and that they were +insufficient to determine with certainty the atomic weights of some of the +elements. Nevertheless, without some such rules as those of Dalton, no +great advances could have been made in applying the atomic theory to the +facts of chemical combination; and Dalton's rules were undoubtedly founded +on wide considerations. In the appendix to Volume II. of his "New System" +he expressly states that before the number of atoms of two elements present +in the<span class='pagenum'><a name="Page_135" id="Page_135">[Pg 135]</a></span> atom of a compound can be determined, it is necessary that many +combinations should be examined, not only of these elements with each +other, but also of each of these with other elements; and he tells us that +to gather together facts bearing on this general question of chemical +synthesis was the object of his work from the time of the promulgation of +the atomic theory.</p> + +<p>When we find that Dalton applied the term "atom" to the small particles of +compound bodies, we at once see that by atom he could not always mean "that +which cannot be cut;" he simply meant the smallest particle of a substance +which exhibits the properties of that substance.</p> + +<p>A mass of water vapour was conceived by Dalton as "like a mass of small +shot." Each shot exhibited the characteristic chemical properties of water +vapour; it differed from the large quantity of vapour only in mass; but if +one of these little pieces of shot were divided—as Dalton, of course, knew +it could be divided—smaller pieces of matter would be produced. But these +would no longer be water; they would be new kinds of matter. They are +called oxygen and hydrogen.</p> + +<p>As aids towards gaining a clear conception of the "atom" of a compound as a +definite building, Dalton made diagrammatic representations of the +hypothetical structures of some of these atoms: the following plate is +copied from the "New System:"—A represents an atom of alum; B, an atom of +nitrate of alumina; C, of barium chloride;<span class='pagenum'><a name="Page_136" id="Page_136">[Pg 136]</a></span> D, of barium nitrate; E, of +calcium chloride; F calcium nitrate; G, of calcium sulphate; H, potassium +carbonate; I, of potash; and K, an atom of soda.</p> + +<div class="figcenter" style="width: 416px;"> +<img src="images/fig3.jpg" width="416" height="650" alt="Fig. 3." title="" /> +<span class="caption">Fig. 3.</span> +</div><p><span class='pagenum'><a name="Page_137" id="Page_137">[Pg 137]</a></span></p> + +<p>But I think if we consider this application of the term "atom" to elements +and compounds alike, we shall see objections to it. When an atom of a +compound is divided the smaller particles so produced are each very +different in chemical properties from the atom which has just been divided. +We may, if we choose, assume that the atom of an element could in like +manner be divided, and that the products of this division would be +different from the elementary atoms; but such a division of an elementary +atom has not as a matter of fact been yet accomplished, unless we class +among elements substances such as potash and soda, which for many years +were universally regarded as elements, and rightly so regarded because they +had not been decomposed. In Dalton's nomenclature then, the term "atom" is +applied alike to a small particle with definite properties known to be +divisible into smaller particles, each with properties different from those +of the undivided particle, and to a small particle which, so far as our +knowledge goes, cannot be divided into any particle smaller than or +different from itself.</p> + +<p>Nevertheless, if the atomic theory was to be victorious, it was necessary +that it should be applied to elements and compounds alike. Until a clear +conception should be obtained, and expressed in accurate language, of the +differences in structure of the ultimate particles of compounds and of +elements,<span class='pagenum'><a name="Page_138" id="Page_138">[Pg 138]</a></span> it was perhaps better to apply the term "atom" to both alike.</p> + +<p>These two difficulties—(1) the difficulty of attaching to the term "atom" +a precise meaning applicable to elements and compounds alike, and (2) the +difficulty of determining the number of elementary atoms in the atom of a +given compound, and hence of determining the relative weights of elementary +atoms themselves—were for many years stumbling-blocks in the path of the +upholders of the Daltonian theory.</p> + +<p>The very great difficulty of clearly comprehending the full meaning of +Dalton's proposed theory becomes apparent when we learn that within three +years from the publication of Part I. of the "New System," facts were made +known by the French chemist Gay-Lussac, and the true interpretation of +these facts was announced by the Italian chemist Avogadro, which facts and +interpretation were sufficient to clear away both the difficulties I have +just mentioned; but that nevertheless it is only within the last ten or +fifteen years that the true meaning of the facts established by Gay-Lussac +and the interpretation given by Avogadro have been generally recognized.</p> + +<p>In 1809 Gay-Lussac, in a memoir on the combination of gaseous bodies, +proved that gases combine chemically in simple proportions by volume, and +that the volume of the product always bears a simple relation to the +volumes of the combining gases. Thus, he showed that two volumes<span class='pagenum'><a name="Page_139" id="Page_139">[Pg 139]</a></span> of +hydrogen combine with one volume of oxygen to form two volumes of water +vapour; that one volume of nitrogen combines with three volumes of hydrogen +to form two volumes of ammonia gas, and so on. Now, as elements combine +atom with atom, the weights of these combining volumes of elements must +represent the relative weights of the atoms of the same elements.</p> + +<p>In 1811 Avogadro distinguished between the ultimate particles of compounds +and elements. Let a gaseous element, A, combine with another gaseous +element, B, to form a gaseous compound, C; then Avogadro supposed that the +little particles of A and the little particles of B (Dalton's atoms) split +up, each into two or more smaller particles, and that these smaller +particles then combine together to form particles of the compound C. The +smaller particles produced by splitting a Daltonian elementary atom were +regarded by Avogadro as all identical in properties, but these very small +particles could not exist uncombined either with each other or with very +small particles of some other element. When the atom of a compound is +decomposed, Avogadro pictured this atom as splitting into smaller particles +of two or three or more different kinds, according as the compound had +contained two or three or different elements.</p> + +<p>To Avogadro's mental vision an elementary gas appeared as built up of a +great many little particles, each exhibiting in miniature all the +properties of<span class='pagenum'><a name="Page_140" id="Page_140">[Pg 140]</a></span> the gas. The gas might be heated, or cooled, or otherwise +physically altered, but each of the little particles remained intact; the +moment however that this gas was mixed with another on which it could +chemically react, these little particles split into smaller parts, but as +the smaller parts so produced could not exist in this state, they seized +hold of the corresponding very small parts of the other gas, and thus a +particle of a compound gas was produced.</p> + +<p>A compound gas was pictured by Avogadro as also built up of small +particles, each exhibiting in miniature the properties of the gas, and each +remaining undecomposed when the gas was subjected only to physical actions; +but when the gas was chemically decomposed, each little particle split, but +the very small parts thus produced, being each a particle of an elementary +substance, continued to exist, and could be recognized by the known +properties of that element.</p> + +<p>To the smallest particle of any substance (elementary or compound) which +exhibits the properties of that substance, and which cannot be split into +parts without destroying these properties, we now give the name of +<i>molecule</i>.</p> + +<p>A molecule is itself a structure. It is built up of parts; each of these +parts we now call an <i>atom</i>. The molecule of a compound is, of course, +composed of the atoms of the elements which form that compound. The +molecule may contain two or three or more unlike atoms. The molecule of an +element is<span class='pagenum'><a name="Page_141" id="Page_141">[Pg 141]</a></span> composed of the atoms of that element, and all of these atoms +are supposed to be alike. We cannot get hold of elementary atoms and +examine them, but we have a large mass of evidence in favour of the view +which regards the molecule of an element as composed of parts each weighing +less than the molecule itself.</p> + +<p>The student of physics or chemistry now believes that, were a very small +quantity of a gas (say ammonia) or a drop of a liquid (say water) magnified +to something like the size of the earth, he should see before him a vast +heap of particles of ammonia or of water, each exhibiting all the +properties by the possession of which he now distinguishes ammonia or water +from all other kinds of matter. He believes that he should see these +particles in motion, each moving rapidly from place to place, sometimes +knocking against another, sometimes traversing a considerable space without +coming into collision with any other. But the student tries to penetrate +yet further into the nature of things. To the vision of the chemist these +particles of almost inconceivable minuteness are themselves built up of +smaller particles. As there is an architecture of masses, so is there an +architecture of molecules. Hydrogen and oxygen are mixed; the chemist sees +the molecules of each in their never-ceasing dance moving here and there +among the molecules of the other, yet each molecule retaining its identity; +an electric spark is passed through the mixture, and almost instantaneously +he sees<span class='pagenum'><a name="Page_142" id="Page_142">[Pg 142]</a></span> each hydrogen molecule split into two parts, and each oxygen +molecule split into two parts, and then he sees these parts of molecules, +these atoms, combine, a pair of hydrogen atoms with an atom of oxygen, to +form compound molecules of water.</p> + +<p>Avogadro's hypothesis gave the chemist a definition of "molecule;" it also +gave him a definition of "atom."</p> + +<p>It is evident that, however many atoms of a given element there may be in +this or in that compound molecule, no compound of this element can exist +containing less than a single atom of the element in question; therefore an +atom of an element is the smallest quantity of that element in the molecule +of any compound thereof.</p> + +<p>And so we have come back to the original hypothesis of Dalton; but we have +extended and modified that hypothesis—we have distinguished two orders of +small particles, the molecule (of a compound or of an element) and the atom +(of an element). The combination of two or more elements is now regarded as +being preceded by the decomposition of the molecules of these elements into +atoms. We have defined molecule and we have defined atom, but before we can +determine the relative weights of elementary atoms we must have a means of +determining the relative weights of compound molecules. The old difficulty +still stares us in the face—how can we find the number of elementary atoms +in the molecule of a given compound?<span class='pagenum'><a name="Page_143" id="Page_143">[Pg 143]</a></span></p> + +<p>The same naturalist who enriched chemical science by the discovery of the +molecule as distinct from the atom, placed in the hands of chemists the +instrument for determining the relative weights of molecules, and thus also +the relative weights of atoms.</p> + +<p>The great generalization, usually known as <i>Avogadro's law</i>, runs thus: +"<i>Equal volumes of gases measured at the same temperature and under the +same pressure contain equal numbers of molecules.</i>"</p> + +<p>Gay-Lussac had concluded that "equal volumes of gases contain equal numbers +of atoms;" but this conclusion was rejected, and rightly rejected by +Dalton, who however at the same time refused to admit that there is a +simple relation between the combining volumes of elements. The +generalization of Avogadro has however stood the test of experiment, and is +now accepted as one of the fundamental "laws" of chemical science.</p> + +<p>Like the atomic theory itself, Avogadro's law is an outcome of physical +work and of physical reasoning. Of late years the great naturalists, +Clausius, Helmholtz, Joule, Rankine, Clerk Maxwell and Thomson have +developed the physical theory of molecules, and have shown that Avogadro's +law may be deduced as a necessary consequence from a few simple physical +assumptions. This law has thus been raised, from being a purely empirical +generalization, to the rank of a deduction from a wide, yet simple physical +theory.</p> + +<p>Now, if "equal volumes of gases contain equal<span class='pagenum'><a name="Page_144" id="Page_144">[Pg 144]</a></span> numbers of molecules," it +follows that the ratio of the densities of any two gases must also be the +ratio of the weights of the molecules which constitute these gases. Thus, a +given volume of water vapour weighs nine times more than an equal volume of +hydrogen; therefore the molecule of gaseous water is nine times heavier +than the molecule of hydrogen. One has therefore only to adopt a standard +of reference for molecular weights, and Avogadro's law gives the means of +determining the number of times any gaseous molecule is heavier than that +of the standard molecule.</p> + +<p>But consider the combination of a gaseous element with hydrogen; let us +take the case of hydrogen and chlorine, which unite to form gaseous +hydrochloric acid, and let us determine the volumes of the uniting elements +and the volume of the product. Here is a statement of the results: one +volume of hydrogen combines with one volume of chlorine to form two volumes +of hydrochloric acid. Assume any number of molecules we please in the one +volume of hydrogen—say ten—there must be, by Avogadro's law, also ten +molecules in the one volume of chlorine; but inasmuch as the volume of +hydrochloric acid produced is double that of either the hydrogen or the +chlorine which combined to form it, it follows, by the same law, that +twenty molecules of hydrochloric acid have been formed by the union of ten +molecules of hydrogen with ten molecules of chlorine. The necessary +conclusion<span class='pagenum'><a name="Page_145" id="Page_145">[Pg 145]</a></span> is that each hydrogen molecule and each chlorine molecule has +split into two parts, and that each half-molecule (or atom) of hydrogen has +combined with one half-molecule (or atom) of chlorine, to produce one +compound molecule of hydrochloric acid.</p> + +<p>Therefore we conclude that the hydrogen molecule is composed of two atoms, +and that the chlorine molecule is also composed of two atoms; and as +hydrogen is to be our standard element, we say that if the atom of hydrogen +weighs one, the molecule of the same element weighs two.</p> + +<p>It is now easy to find the <i>molecular weight</i> of any gas; it is only +necessary to find how many times heavier the given gas is than hydrogen, +the weight of the latter being taken as 2. Thus, oxygen is sixteen times +heavier than hydrogen, but 1: 16 = 2: 32, therefore the molecule of oxygen +is thirty-two times heavier than the molecule of hydrogen. Ammonia is eight +and a half times heavier than hydrogen, but 1: 8-1/2 = 2: 17, therefore the +molecule of ammonia is seventeen times heavier than the molecule of +hydrogen. This is what we more concisely express by saying "the molecular +weight of oxygen is 32," or "the molecular weight of ammonia is 17," etc., +etc.</p> + +<p>Now, we wish to determine the <i>atomic weight</i> of oxygen; that is, we wish +to find how many times the oxygen atom is heavier than the atom of +hydrogen. We make use of Avogadro's law and of the definition of "atom" +which has been deduced from it (see p. 142).<span class='pagenum'><a name="Page_146" id="Page_146">[Pg 146]</a></span></p> + +<p>We know that eight parts by weight of oxygen combine with one part by +weight of hydrogen to form water; but we do not know whether the molecule +of water contains one atom of each element, or two atoms of hydrogen and +one atom of oxygen, or some other combination of these atoms (see p. 131). +But by vaporizing water and weighing the gas so produced, we find that +water vapour is nine times heavier than hydrogen: now, 1: 9 = 2: 18, +therefore the molecular weight of water gas is 18. Analysis tells us that +eighteen parts by weight of water gas contain sixteen parts of oxygen and +two parts of hydrogen; that is to say, we now know that in the molecule of +water gas there are two atoms of hydrogen combined with sixteen parts by +weight of oxygen. We now proceed to analyze and determine the molecular +weights of as many gaseous compounds of oxygen as we can obtain. The +outcome of all is that we have as yet failed to obtain any such compound in +the molecule of which there are less than sixteen parts by weight of +oxygen. In some of these molecules there are sixteen, in some thirty-two, +in some forty-eight, in some sixty-four parts by weight of oxygen, but in +none is there less than sixteen parts by weight of this element. Therefore +we conclude that the atomic weight of oxygen is 16, because this is the +smallest amount, referred to hydrogen taken as 1, which has hitherto been +found in the molecule of any compound of oxygen.</p> + +<p>The whole of the work done since the publication<span class='pagenum'><a name="Page_147" id="Page_147">[Pg 147]</a></span> of Dalton's "New System" +has emphasized the importance of that chemist's remark, that no safe +conclusion can be drawn as to the value of the atomic weight of an element +except from a consideration of many compounds of that with other elements. +But in Avogadro's law we have a far more accurate and trustworthy method +for determining the molecular weights of compounds than any which Dalton +was able to devise by his study of chemical combinations.</p> + +<p>We have thus got a clearer conception of "atom" than was generally +possessed by chemists in the days of Dalton, and this we have gained by +introducing the further conception of "molecule" as that of a quantity of +matter different from, and yet similar to, the atom.</p> + +<p>The task now before us will for the most part consist in tracing the +further development of the fundamental conception of Dalton, the +conception, viz., of each chemical substance as built up of small parts +possessing all the properties, other than the mass, of the whole; and—what +we also owe to Dalton—the application of this conception to explain the +facts of chemical combination.</p> + +<hr style='width: 45%;' /> + +<p>The circumstances of Dalton's early life obliged him to trust largely to +his own efforts for acquiring knowledge; and his determination not to +accept facts at second hand but to acquire them for himself, is very marked +throughout the whole of his life. In the preface to the second part of the +"New System"<span class='pagenum'><a name="Page_148" id="Page_148">[Pg 148]</a></span> he says, "Having been in my progress so often misled by +taking for granted the results of others, I have determined to write as +little as possible but what I can attest by my own experience."</p> + +<p>We should not expect such a man as this to make any great use of books; one +of his friends tells us that he heard him declare on a public occasion that +he could carry his library on his back, and yet had not read half of the +books which comprised it.</p> + +<p>The love of investigation which characterized Dalton when young would +naturally be increased by this course of intellectual life. How strong this +desire to examine everything for himself became, is amusingly illustrated +by a story told by his medical adviser, Dr. Ransome. Once when Dalton was +suffering from catarrh Dr. Ransome had prescribed a James's powder, and +finding his patient much better next day, he congratulated himself and +Dalton on the good effects of the medicine. "I do not well see how that can +be," said Dalton, "as I kept the powder until I could have an opportunity +of analyzing it."</p> + +<p>As Dalton grew older he became more than ever disinclined to place much +trust in the results obtained by other naturalists, even when these men +were acknowledged to be superior to himself in manipulative and +experimental skill. Thus, as we have already learned, he could not be +brought to allow the truth of Gay-Lussac's experimentally established law +regarding gaseous combinations; he preferred to attribute Gay-Lussac's +results to<span class='pagenum'><a name="Page_149" id="Page_149">[Pg 149]</a></span> errors of experiment. "The truth is, I believe, that gases do +not unite in equal or exact measures in any one instance; when they appear +to do so it is owing to the inaccuracy of our experiments."</p> + +<p>That Dalton did not rank high as an experimenter is evident from the many +mistakes in matters of fact which are to be found in the second part of his +"New System." A marked example of his inaccuracy in purely experimental +work is to be found in the supposed proof given by him that charcoal, after +being heated to redness, does not absorb gases. He strongly heated a +quantity of charcoal, pulverized it, and placed it in a Florence flask, +which was connected by means of a stopcock with a bladder filled with +carbonic acid: after a week he found that the flask and its contents had +not sensibly increased in weight, and he concluded that no carbonic acid +had been absorbed by the charcoal. But no trustworthy result could be +obtained from an experiment in which the charcoal, having been deprived of +air by heating, was again allowed to absorb air by being pulverized in an +open vessel, and was then placed in a flask filled with air, communication +between the carbonic acid and the external air being prevented merely by a +piece of bladder, a material which is easily permeated by gases.</p> + +<p>Dalton used a method which can only lead to notable results in natural +science when employed by a really great thinker; he acquired a few facts, +and then thought out the meaning of these.<span class='pagenum'><a name="Page_150" id="Page_150">[Pg 150]</a></span> Almost at the beginning of each +investigation he tried to get hold of some definite generalization, and +<i>then</i> he proceeded to amass special facts. The object which he kept before +himself in his experimental work was to establish or to disprove this or +that hypothesis. Every experiment was conducted with a clearly conceived +aim. He was even willing to allow a large margin for errors of experiment +if he could thereby bring the results within the scope of his hypothesis.</p> + +<p>That the <i>law of multiple proportions</i> is simply a generalization of facts, +and may be stated apart from the atomic theory, is now generally admitted. +But in Dalton's mind this law seems to have arisen rather as a deduction +from the theory of atoms than to have been gained as a generalization from +experiments. He certainly always stated this law in the language of the +atomic theory. In one of his walking excursions he explained his theory to +a friend, and after expounding his views regarding atomic combinations, he +said that the examples which he had given showed the necessary existence of +the principle of multiple proportions: "Thou knowest it must be so, for no +man can split an atom." We have seen that carburetted hydrogen was one of +the compounds on the results of the analysis of which he built his atomic +theory; yet we find him saying of the constitution of this compound that +"no correct notion seems to have been formed till the atomic theory was +introduced and applied in the investigation."<span class='pagenum'><a name="Page_151" id="Page_151">[Pg 151]</a></span></p> + +<p>When Dalton was meditating on the laws of chemical combination, a French +chemist, M. Proust, published analyses of metallic oxides, which proved +that when a metal forms two oxides the amount of metal in each is a fixed +quantity—that there is a sudden jump, as it were, from one oxide to +another. We are sometimes told that from these experiments Proust would +have recognized the law of multiple proportions had his analyses only been +more accurate; but we know that Dalton's analyses were very inaccurate, and +yet he not only recognized the law of multiple proportions, but propounded +and established the atomic theory. Something more than a correct system of +keeping books and balancing accounts is wanted in natural science. Dalton's +experimental results would be the despair of a systematic analyst, but from +these Dalton's genius evolved that splendid theory which has done so much +to advance the exact investigation of natural phenomena.</p> + +<p>Probably no greater contrast could be found between methods of work, both +leading to the establishment of scientific (that is, accurate and precise) +results, than that which exists between the method of Dalton and the method +pursued by Priestley.</p> + +<p>Priestley commenced his experiments with no particular aim in view; +sometimes he wanted to amuse himself, sometimes he thought he might light +upon a discovery of importance, sometimes his curiosity incited him to +experiment. When he<span class='pagenum'><a name="Page_152" id="Page_152">[Pg 152]</a></span> got facts he made no profound generalizations; he was +content to interpret his results by the help of the prevailing theory of +his time. But each new fact only spurred him on to make fresh incursions +into the fields of Nature. Dalton thought much and deeply; his +experimentally established facts were to him symbols of unseen powers. He +used facts as Hobbes says the wise man uses words: they were his counters +only, not his money.</p> + +<p>When we ask how it was that Dalton acquired his great power of penetrating +beneath the surface of things and finding general laws, we must attribute +this power in part to the training which he gave himself in physical +science. It was from a consideration of physical facts that he gained the +conception of ultimate particles of definite weight. His method was +essentially dynamical; that is, he pictured a gas as a mass of little +particles, each of which acted on and was acted on by, other particles. The +particles were not thrown together anyhow; definite forces existed between +them. Each elementary or compound gas was pictured as a system of little +particles, and the properties of that gas were regarded as dependent on the +nature and arrangement of these particles. Such a conception as this could +only be gained by a careful and profound thinker versed in the methods of +physical and mathematical science. Thus we see that although Dalton +appeared to gain his great chemical results by a method which we are not +generally inclined to regard as the method<span class='pagenum'><a name="Page_153" id="Page_153">[Pg 153]</a></span> of natural science, yet it was +by virtue of his careful training in a branch of knowledge which deals with +facts, as well as in that science which deduces particular conclusions from +general principles, that he was able to introduce his fruitful conceptions +into the science of chemistry.</p> + +<p>To me it appears that Dalton was pre-eminently distinguished by the +possession of imagination. He formed clear mental images of the phenomena +which he studied, and these images he was able to combine and modify so +that there resulted a new image containing in itself all the essential +parts of each separate picture which he had previously formed.</p> + +<p>From his intense devotion to the pursuit of science the development of +Dalton's general character appears to have been somewhat dwarfed. Although +he possessed imagination, it was the imagination of a naturalist rather +than that of a man of broad culture. Perhaps it was a want of broad +sympathies which made him trust so implicitly in his own work and so +readily distrust the work of others, and which moreover led him astray in +so many of his purely experimental investigations.</p> + +<hr style='width: 45%;' /> + +<p>Dalton began his chemical work about six years after the death of +Lavoisier. Unlike that great philosopher he cared nothing for political +life. The friends in whose family he spent the greater part of his life in +Manchester were never able<span class='pagenum'><a name="Page_154" id="Page_154">[Pg 154]</a></span> to tell whether he was Whig or Tory. Unlike +Priestley he was content to let metaphysical and theological speculation +alone. In his quiet devotion to study he more resembled Black, and in his +method, which was more deductive than that usually employed in chemistry, +he also resembled the Edinburgh professor. Trained from his earliest days +to depend on himself, nurtured in the creedless creed of the Friends, he +entered on his life's work with few prejudices, if without much profound +knowledge of what had been done before him. By the power of his insight +into Nature and the concentration of his thought, he drew aside the curtain +which hung between the seen and the unseen; and while Herschel, sweeping +the heavens with his telescope and night by night bringing new worlds +within the sphere of knowledge, was overpowering men's minds by new +conceptions of the infinitely great, John Dalton, with like imaginative +power, was examining the architecture of the ultimate particles of matter, +and revealing the existence of law and order in the domain of the +infinitely small.</p> + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> See Fig. 2, which is copied from the original in the "New +System of Chemical Philosophy," and illustrates Dalton's conception of a +quantity of carbonic acid gas, each atom built up of one atom of carbon and +two of oxygen; of nitrous oxide gas, each atom composed of one atom of +nitrogen and one of oxygen; and of hydrogen gas, constituted of single +atoms.</p></div> + +<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> More accurate analysis has shown that there are six parts of +carbon united respectively with one and with two parts by weight of +hydrogen in these compounds.</p></div> +</div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_155" id="Page_155">[Pg 155]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap4.jpg" width="500" height="98" alt="" title="" /> +</div> + +<h2>CHAPTER IV.</h2> + +<h3>ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL SCIENCE (<i>continued</i>)—PERIOD OF DAVY AND BERZELIUS.</h3> + + +<h4><i>Humphry Davy</i>, 1778-1829. <i>Johann Jacob Berzelius</i>, 1779-1848.</h4> + +<p>We may roughly date the period of chemical advance during which the +connections between chemistry and other branches of natural knowledge were +recognized and studied, as beginning with the first year of this century, +and as continuing to our own day.</p> + +<p>The elaboration of the atomic theory was busily carried on during the +second and third decades of this century; to this the labour of the Swedish +chemist Berzelius largely contributed.</p> + +<p>That there exist many points of close connection between chemical and +electrical science was also demonstrated by the labours of the same +chemist, and by the brilliant and impressive discoveries of Sir Humphry +Davy.<span class='pagenum'><a name="Page_156" id="Page_156">[Pg 156]</a></span></p> + +<p>A system of classification of chemical elements and compounds was +established by the same great naturalists, and many inroads were made into +the domain of the chemistry of bodies of animal and vegetable origin.</p> + +<p>The work of Berzelius and Davy, characterized as it is by thoroughness, +clearness and definiteness, belongs essentially to the modern era of +chemical advance; but I think we shall better preserve the continuity of +our story if we devote a chapter to a consideration of the work of these +two renowned naturalists before entering on our review of the time +immediately preceding the present, as typical workers in which time I have +chosen Liebig and Dumas.</p> + +<p>In the last chapter we found that the foundations of the atomic theory had +been laid, and the theory itself had been applied to general problems of +chemical synthesis, by Dalton. In giving, in that chapter, a short sketch +of the modern molecular theory, and in trying to explain the meaning of the +term "molecule" as contrasted with "atom," I necessarily carried the reader +forward to a time considerably later than the first decade of this century. +We must now retrace our steps; and in perusing the account of the work of +Berzelius and Davy given in the present chapter, the reader must endeavour +to have in his mind a conception of atom analogous to the mental picture +formed by Dalton (see pp. 135, 136); he must regard the term as applicable +to element and compound alike;<span class='pagenum'><a name="Page_157" id="Page_157">[Pg 157]</a></span> he must remember that the work of which he +reads is the work of those who are striving towards a clear conception of +the atom, and who are gradually rising to a recognition of the existence of +more than one order of small particles, by the regular putting together of +which masses of matter are constituted.</p> + +<p>No materials, so far as I am aware, exist from which a life of Berzelius +can be constructed. I must therefore content myself with giving a mere +enumeration of the more salient points in his life. Of his chemical work +abundant details are fortunately to be found in his own "Lehrbuch," and in +the works and papers of himself and his contemporaries.</p> + +<hr style='width: 45%;' /> + +<p><span class="smcap">Johann Jacob Berzelius</span> was the son of the schoolmaster of Wäfersunda, a +village near Linköping, in East Gothland, Sweden. He was born in August +1779—he was born, that is, a few years after Priestley's discovery of +oxygen; at the time when Lavoisier had nearly completed his theory of +combustion; when Dalton was endeavouring to keep the unruly youth of +Eaglesfield in subjection; and when Black, having established the existence +of fixed air and the theory of latent heat, was the central figure in the +band of students who were enlarging our knowledge of Nature in the Scottish +capital.</p> + +<p>Being left an orphan at the age of nine, the young Berzelius was brought up +by his grandfather,<span class='pagenum'><a name="Page_158" id="Page_158">[Pg 158]</a></span> who appears to have been a man of education and sense. +After attending school at Linköping, he entered the University of Upsala as +a student of medicine. Here he soon began to show a taste for chemistry. It +would appear that few or no experiments were then introduced into his +lectures by the Professor of Chemistry at Upsala; little encouragement was +given to pursue chemical experiments, and so Berzelius had to trust to his +own labours for gaining an acquaintance with practical chemistry. Having +thus made considerable progress in chemistry, and being on a visit to the +mineral baths of Medevi, he seized the opportunity to make a very thorough +analysis of the waters of this place, which were renowned in Sweden for +their curative properties. The publication of this analysis marks the first +appearance of Berzelius as an author.</p> + +<p>He graduated as M.B. in 1801, and a year or two later presented his +dissertation, entitled "The Action of Galvanism on Organic Bodies," as a +thesis for the degree of Doctor of Medicine. This thesis, like that of +Black, published about half a century earlier, marks an important stage in +the history of chemistry. These and other publications made the young +doctor famous; he was called to Stockholm to be extraordinary (or +assistant) Professor of Chemistry in the medical school of that capital.</p> + +<p>Sometimes practising medicine in order to add to his limited income, but +for the most part engaged in chemical research, he remained in Stockholm +for nearly fifty years, during most of which time<span class='pagenum'><a name="Page_159" id="Page_159">[Pg 159]</a></span> the laboratory of +Berzelius in the Swedish capital was regarded as one of the magnetic poles +of the chemical world. To this point came many of the great chemists who +afterwards enriched the science by their discoveries. Wöhler, H. and G. +Rose, Magnus, Gmelin, Mitscherlich and others all studied with Berzelius. +He visited England and France, and was on terms of intimacy and in +correspondence with Davy, Dalton, Gay-Lussac, Berthollet and the other men +who at that period shed so much lustre on English and French science.</p> + +<p>It is said that Berzelius was so much pleased with the lectures of Dr. +Marcet at Guy's Hospital, that on his return from his visit to England in +1812, he introduced much more liveliness and many more experimental +illustrations into his own lectures.</p> + +<p>At the age of thirty-one, Berzelius was chosen President of the Stockholm +Academy of Sciences; a few years later he was elected a Foreign Fellow of +the Royal Society, which society bestowed on him the Copley Medal in 1836. +He was raised to the rank of a baron by the King of Sweden, being allowed +as a special privilege to retain his own name.</p> + +<p>In the year 1832 Berzelius resigned his professorship, and in the same year +he married. During the remainder of his life, he continued to receive +honours of all kinds, but he never for a moment forsook the paths of +science. After the death of Davy, in 1829, he was recognized as the +leading<span class='pagenum'><a name="Page_160" id="Page_160">[Pg 160]</a></span> European chemist of his age; but, although firm in his own +theoretical views, he was ready to test these views by appealing to Nature. +The very persistency with which he clung to a conception established on +some solid experimental basis insured that new light would be thrown on +that conception by the researches of those chemists who opposed him.</p> + +<p>Probably no chemist has added to the science so many carefully determined +facts as Berzelius; he was always at work in the laboratory, and always +worked with the greatest care. Yet the appliances at his command were what +we should now call poor, meagre, and utterly inadequate. Professor Wöhler +of Göttingen, who in the fulness of days and honours has so lately gone +from amongst us, recently gave an account of his visit to Berzelius in the +year 1823. Wöhler had taken his degree as Doctor of Medicine at Heidelberg, +and being anxious to prosecute the study of chemistry he was advised by his +friends to spend a winter in the laboratory of the Swedish professor. +Having written to Berzelius and learned that he was willing to allow him +working room in his laboratory, the young student set out for Stockholm. +After a journey to Lübeck and a few days' passage in a small +sailing-vessel, he arrived in the Swedish capital.</p> + +<p>Knocking at the door of the house pointed out as that of Berzelius, he +tells us that his heart beat hard as the door was opened by a tall man of<span class='pagenum'><a name="Page_161" id="Page_161">[Pg 161]</a></span> +florid complexion. "It was Berzelius himself," he exclaims. Scarcely +believing that he was in the very room where so many famous discoveries had +been made, he entered the laboratory. No water, no gas, no draught-places, +no ovens were to be seen; a couple of plain tables, a blowpipe, a few +shelves with bottles, a little simple apparatus, and a large water-barrel +whereat Anna, the ancient cook of the establishment, washed the laboratory +dishes, completed the furnishings of this room, famous throughout Europe +for the work which had been done in it. In the kitchen which adjoined, and +where Anna cooked, was a small furnace and a sand bath for heating +purposes.</p> + +<p>In this room many great discoveries were made. Among these we may note the +separation of the element columbium in 1815, and of selenion in 1818; the +discovery of the new earth thoria in 1828; the elucidation of the +properties of yttrium and cerium about 1820, of uranium in 1823, and of the +platinum metals in 1828; the accurate determination of the atomic weights +of the greater number of the elements; the discovery of "sulphur salts" in +1826-27, and the proof that silica is an acid, and that most of the "stony" +minerals are compounds of this acid with various bases.</p> + +<p>But we shall better learn the value of some of these discoveries by taking +a general review of the contributions to chemical science of the man who +spent most of his life at work in that room in Stockholm.<span class='pagenum'><a name="Page_162" id="Page_162">[Pg 162]</a></span></p> + +<p>The German chemist Richter, in the first or second year of this century, +had drawn attention to the fact that when two neutral compounds, such as +nitrate of potash and chloride of lime, react chemically, the substances +produced by this reaction are also neutral. All the potash combined with +nitric acid in one salt changes places with all the lime combined with +muriatic acid in the other salt; therefore, said Richter, these different +quantities of potash and lime are neutralized by the same quantity of +nitric acid; and, hence, these amounts of potash and lime are chemically +<i>equivalent</i>, because these are the amounts which perform the same +reaction, viz. neutralization of a fixed quantity of acid. If then careful +analyses were made of a number of such neutral compounds as those named, +the <i>equivalents</i> of all the commoner "bases" and "acids"<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> might be +calculated.</p> + +<p>Richter's own determinations of the equivalents of acids and bases were not +very accurate, but Berzelius was impressed with the importance of this +work. The year before the appearance of Dalton's "New System" (<i>i.e.</i> in +1807), he began to prepare and carefully analyze series of neutral salts. +As the work was proceeding he became acquainted with the theory of Dalton, +and at once saw its extreme importance. For some time Berzelius continued +to work on the lines laid down by Dalton, and to accumulate data from which +the<span class='pagenum'><a name="Page_163" id="Page_163">[Pg 163]</a></span> atomic weights of elements might be calculated; but he soon +perceived—as the founder of the theory had perceived from the very +outset—that the fundamental conception of each atom of an element as being +a distinct mass of matter weighing more or less than the atom of every +other element, and of each atom of a compound as being built up of the +atoms of the elements which compose that compound,—Berzelius, I say, +perceived that these conceptions must remain fruitless unless means were +found for determining the number of elementary atoms in each compound atom. +We have already learned the rules framed by the founder of the atomic +theory for his guidance in attempting to solve this problem. Berzelius +thought those rules insufficient and arbitrary; he therefore laid down two +general rules, on the lines of which he prosecuted his researches into +chemical synthesis.</p> + +<p>"One atom of one element combines with one, two, three, or more atoms of +another element." This is practically the same as Dalton's definitions of +binary, ternary, etc., compounds (p. 132). "Two atoms of one element +combine with three and five atoms of another element." Berzelius here +recognizes the existence of compound atoms of a more complex structure than +any of those recognized by Dalton.</p> + +<p>Berzelius further extended the conception of atom by applying it to groups +of elements formed, according to him, by the combination of various +compound atoms. To his mind every compound<span class='pagenum'><a name="Page_164" id="Page_164">[Pg 164]</a></span> atom appeared as built up of +two parts; each of these parts might be an elementary atom, or might be +itself built up of several elementary atoms, yet in the Berzelian theory +each acted as a definite whole. So far as the building up of the complex +atom went, each of the two parts into which this atom could be divided +acted as if it were a simple atom.</p> + +<p>If we suppose a patch of two shades of red colour to be laid on a smooth +surface, and alongside of this a patch of two shades of yellow colour, and +if we suppose the whole mass of colour to be viewed from a distance such +that one patch appears uniformly red and the other uniformly yellow, we +shall have a rough illustration of the Berzelian compound atom. To the +observer the whole mass of colour appears to consist of two distinct +patches of contrasted colours; but let him approach nearer, and he +perceives that what appeared to be a uniform surface of red or yellow +really consists of two patches of unlike shades of red or of yellow. The +whole mass of colour represents the compound atom; broadly it consists of +two parts—the red colour represents one of the constituent atoms, the +yellow colour represents the other constituent atom; but on closer +examination the red atom, so to speak—and likewise the yellow atom—is +found to consist of parts which are less unlike each other than the whole +red atom is unlike the whole yellow atom.</p> + +<p>We shall have to consider in more detail the reasoning whereby Berzelius +arrived at this conception<span class='pagenum'><a name="Page_165" id="Page_165">[Pg 165]</a></span> of every compound atom as a <i>dual</i> structure +(see pp. 209-212). At present I wish to notice this conception as lying at +the root of most of the work which he did in extending and applying the +Daltonian theory. I wish to insist on the fact that the atomic theory could +not advance without methods being found for determining the number of +elementary atoms in a compound atom, without clear conceptions being gained +of every compound atom as a structure, and without at least attempts being +made to learn the laws in accordance with which that structure was built. +Before the atomic weight of oxygen could be determined it was necessary +that the number of oxygen and of hydrogen atoms in the atom of water should +be known; otherwise all that could be stated was, the atomic weight of +oxygen is a simple multiple of 8. Berzelius did much to advance chemical +science by the introduction and application of a few simple rules whereby +he determined the number of elementary atoms in various compound atoms. But +as the science advanced, and as more facts came to be known, the Berzelian +rules were found to be too narrow and too arbitrary; chemists sought for +some surer and more generally applicable method than that which Berzelius +had introduced, and the imperious demand for this method at last forced +them to recognize the importance of the great generalization of the Italian +naturalist Avogadro, which they had possessed since the year 1811, but the +meaning of which they had so long failed to understand.<span class='pagenum'><a name="Page_166" id="Page_166">[Pg 166]</a></span></p> + +<p>Berzelius made one great step in the direction of recognizing Avogadro's +distinction between atom and molecule when he accepted Gay-Lussac's +generalization that "equal volumes of gases contain equal numbers of +atoms:" but he refused to apply this to other than elementary gases. The +weights of the volumes of elementary gases which combined were, for +Berzelius, also the weights of the atoms of these elements. Thus, let the +weight of one volume of hydrogen be called 1, then two volumes of hydrogen, +weighing 2, combine with one volume of oxygen, weighing 16, to form two +volumes of water vapour; therefore, said Berzelius, the atom of water +consists of two atoms of hydrogen and one atom of oxygen, and the atom of +the latter element is sixteen times heavier than the atom of the former. +Three volumes of hydrogen, weighing 3, combine with one volume of nitrogen, +weighing 14, to form two volumes of ammonia; therefore, said Berzelius, the +atom of ammonia consists of three atoms of hydrogen combined with one atom +of nitrogen, and the nitrogen atom is fourteen times heavier than the atom +of hydrogen.</p> + +<p>While Berzelius was applying these rules to the determination of the atomic +weights of the elements, and was conducting the most important series of +analyses known in the annals of the science, two great physico-chemical +discoveries were announced.</p> + +<p>In the year 1818 the "<i>law of isomorphism</i>"<span class='pagenum'><a name="Page_167" id="Page_167">[Pg 167]</a></span> was stated by Mitscherlich: +"Compounds the atoms of which contain equal numbers of elementary atoms, +similarly arranged, have the same crystalline form." As thus stated, the +law of isomorphism affirms that if two compounds crystallize in the same +form, the atoms of these compounds are built up of the same number of +elementary atoms—however different may be the nature of the elements in +the compounds—and that these elementary atoms are similarly arranged. This +statement was soon found to be too absolute, and was accordingly modified; +but to go into the history of the law of isomorphism would lead us too far +from the great main path of chemical advance, the course of which we are +seeking to trace.</p> + +<p>Berzelius at once accepted Mitscherlich's law, as an aid in his researches +on atomic weights. The help to be derived from this law may be illustrated +thus: let us assume that two compounds have been obtained exhibiting +identity of crystalline form; let it be further assumed that the number of +elementary atoms in the atom of one of these compounds is known; it +follows, by the law of isomorphism, that the number of elementary atoms in +the atom of the other is known also. Let the two compounds be <i>sulphate of +potash</i> and <i>chromate of potash</i>; let it be assumed that the atom of the +first named is known to consist of two atoms of potassium, one atom of +sulphur, and four atoms of oxygen; and that the<span class='pagenum'><a name="Page_168" id="Page_168">[Pg 168]</a></span> second substance is known +to be a compound of the elements potassium, chromium and oxygen; then the +atom of the second compound contains, by Mitscherlich's law, two atoms of +potassium, one atom of chromium and four atoms of oxygen: hence the +relative weight of the atom of chromate of potash can be determined, and +hence the relative weight of the atom of chromium can also be determined.</p> + +<p>A year after the announcement of Mitscherlich's law, the following +generalization was stated to hold good, by two French naturalists, Dulong +and Petit:—"The atoms of all solid elements have the same capacity for +heat."</p> + +<p>If the amount of heat required to raise the temperature of one grain of +water through one degree be called <i>one unit of heat</i>, then the capacity +for heat of any body other than water is the number of units of heat +required to raise the temperature of one grain of that substance through +one degree. Each chemical substance, elementary and compound, has its own +capacity for heat; but, instead of comparing the capacities for heat of +equal weights, Dulong and Petit compared the capacities for heat of weights +representing the weights of the atoms of various elements. Thus, equal +amounts of heat are required to raise, through the same interval of +temperature, fifty-six grains of iron, one hundred and eight grains of +silver, and sixty-three and a half grains of copper; but the weights of the +atoms of these three elements are in the proportion of 56:108:63-1/2.<span class='pagenum'><a name="Page_169" id="Page_169">[Pg 169]</a></span> +Dulong and Petit based their generalization on measurements of the +capacities for heat of thirteen elements; further research has shown that +their statement most probably holds good for all the solid elements. Here +then was a most important instrument put into the hands of the chemist.</p> + +<p>It is only necessary that the atomic weight of one solid element should be +certainly known, and that the amount of heat required to raise through one +degree the number of grains of that element expressed by its atomic weight +should also be known; then the number which expresses the weight, in +grains, of any other solid element which is raised through one degree by +the same amount of heat, likewise expresses the relative weight of the atom +of that element. Thus, suppose that the atomic weight of silver is known to +be 108, and suppose that six units of heat are required to raise the +temperature of one hundred and eight grains of this metal through one +degree; then suppose it is found by experiment that six units of heat +suffice to raise the temperature of two hundred and ten grains of bismuth +through one degree, it follows—according to the law of Dulong and +Petit—that 210 is the atomic weight of bismuth.</p> + +<p>The modified generalization of Gay-Lussac—"Equal volumes of <i>elementary</i> +gases contain equal numbers of atoms;" the laws of "isomorphism" and of +"atomic heat;" and the two empirical rules stated on p. 163;—these were +the guides used by<span class='pagenum'><a name="Page_170" id="Page_170">[Pg 170]</a></span> Berzelius in interpreting the analytical results which +he and his pupils obtained in that memorable series of researches, whereby +the conceptions of Dalton were shown to be applicable to a wide range of +chemical phenomena.</p> + +<p>The fixity of composition of chemical compounds has now been established; a +definite meaning has been given to the term "element;" the conception of +"atom" has been gained, but much remains to be done in the way of rendering +this conception precise; and fairly good, but not altogether satisfactory +methods have been introduced by which the relative weights of the atoms of +elements and compounds may be determined. At this time chemists are busy +preparing and describing new compounds, and many new elements are also +being discovered; the need of classification begins to be felt more and +more.</p> + +<p>In the days of Berzelius and Davy strenuous efforts were made to obtain +some generalizations by the application of which the many known elements +and compounds might be divided into groups. It was felt that a +classification might be founded on the composition of compounds, or perhaps +on the properties of the same compounds. These two general principles +served as guides in most of the researches then instituted; answers were +sought to these two questions: Of what elements is this compound composed? +and, What can this compound do; how does it react towards other bodies?<span class='pagenum'><a name="Page_171" id="Page_171">[Pg 171]</a></span></p> + +<p>Lavoisier, as we know, regarded oxygen as the characteristic element of all +<i>acids</i>. This term <i>acid</i> implies the possession, by all the substances +denoted by it, of some common property; let us shortly trace the history of +this word in chemistry.</p> + +<p>Vinegar was known to the Greeks and Romans, and the names which they gave +this substance tell us that sourness was to them its characteristic +property. They knew that vinegar effervesced when brought into contact with +chalky earths, and that it was able to dissolve many substances—witness +the story of Cleopatra's draught of the pearl dissolved in vinegar. Other +substances possessed of these properties—for instance oil of vitriol and +spirits of salt—as they became known, were classed along with vinegar; but +no attempts were made to clearly define the properties of these bodies till +comparatively recent times.</p> + +<p>The characteristics of an acid substance enumerated by Boyle are—solvent +power, which is exerted unequally on different bodies; power of turning +many vegetable blues to red, and of restoring many vegetable colours which +had been destroyed by alkalis; power of precipitating solid sulphur from +solutions of this substance in alkalis, and the power of acting on alkalis +to produce substances without the properties of either acid or alkali.</p> + +<p>But what, one may ask, is an alkali, of which mention is so often made by +Boyle?</p> + +<p>From very early times it had been noticed that the ashes which remained +when certain plants were<span class='pagenum'><a name="Page_172" id="Page_172">[Pg 172]</a></span> burned, and the liquid obtained by dissolving +those ashes in water, had great cleansing powers; that they removed oily +matter, fat and dirt from cloth and other fabrics. The fact that an aqueous +solution of these ashes affects the coloured parts of many plants was also +noticed in early times. As progress was made in chemical knowledge +observers began to contrast the properties of this plant-ash with the +properties of acids. The former had no marked taste, the latter were always +very sour; the former turned some vegetable reds to blue, the latter turned +the blues to red; a solution of plant-ash had no great solvent action on +ordinary mineral matter, whereas this matter was generally dissolved by an +acid. In the time of the alchemists, who were always seeking for the +principles or essences of things, these properties of acids were attributed +to <i>a principle of acidity</i>, while the properties of plant-ash and +substances resembling plant-ash were attributed to a <i>principle of +alkalinity</i> (from Arabic <i>alkali</i>, or <i>the ash</i>).</p> + +<p>In the seventeenth century the distinction between acid and alkali was made +the basis of a system of chemical medicine. The two principles of acidity +and alkalinity were regarded as engaged in an active and never-ending +warfare. Every disease was traced to an undue preponderance of one or other +of these principles; to keep these unruly principles in quietness became +the aim of the physician, and of course it was necessary that the physician +should be a chemist, in order that he<span class='pagenum'><a name="Page_173" id="Page_173">[Pg 173]</a></span> might know the nature and habits of +the principles which gave him so much trouble.</p> + +<p>Up to this time the term "alkali" had been applied to almost any substance +having the properties which I have just enumerated; but this group of +substances was divided by Van Helmont and his successors into <i>fixed +alkali</i> and <i>volatile alkali</i>, and fixed alkali was further subdivided into +<i>mineral alkali</i> (what we now call soda) and <i>vegetable alkali</i> (potash). +About the same time acids were likewise divided into three groups; +<i>vegetable</i>, <i>animal</i>, and <i>mineral acids</i>. To the properties by which +alkali was distinguished, viz. cleansing power and action on vegetable +colouring matters, Stahl (the founder of the phlogistic theory) added that +of combining with acids. When an acid (that is, a sour-tasting substance +which dissolves most earthy matters and turns vegetable blues to red) is +added to an alkali (that is, a substance which feels soap-like to the +touch, which does not dissolve many earthy matters, and which turns many +vegetable reds to blue) the properties of both acid and alkali disappear, +and a new substance is produced which is not characterized by the +properties of either constituent. The new substance, as a rule, is without +action on earthy matters or on vegetable colours; it is not sour, nor is it +soapy to the touch like alkali; it is <i>neutral</i>. It is <i>a salt</i>. But, +although Stahl stated that an alkali is a substance which combines with an +acid, it was not until a century later that these three—alkali, acid, +salt—were clearly distinguished.<span class='pagenum'><a name="Page_174" id="Page_174">[Pg 174]</a></span></p> + +<p>But the knowledge that a certain group of bodies are sour and dissolve +minerals, etc., and that a certain other group of bodies are nearly +tasteless and do not dissolve minerals, etc., was evidently a knowledge of +only the outlying properties of the bodies; it simply enabled a term to be +applied to a group of bodies, which term had a definite connotation.</p> + +<p><i>Why</i> are acids acid, and <i>why</i> are alkalis alkaline?</p> + +<p>Acids are acid, said Becher (latter part of seventeenth century), because +they all contain the same principle, viz. the primordial acid. This +primordial acid is more or less mixed with earthy matter in all actual +acids; it is very pure in spirits of salt.</p> + +<p>Alkalis are alkaline, said Basil Valentine (beginning of the sixteenth +century), because they contain a special kind of matter, "the matter of +fire."</p> + +<p>According to other chemists (<i>e.g.</i> J. F. Meyer, 1764), acids owe their +acidity to the presence of a sharp or biting principle got from fire.</p> + +<p>Acids, alkalis and salts <i>all</i> contain, according to Stahl (beginning of +the eighteenth century), more or less <i>primordial acid</i>. The more of this a +substance contains, the more acid it is; the less of this it contains, the +more alkaline it is.</p> + +<p>All these attempted explanations recognize that similar properties are to +be traced to similarity of composition; but the assertion of the existence +of a "primordial acid," or of "the matter of fire," although undoubtedly a +step in advance, was not sufficiently definite (unless it was supplemented<span class='pagenum'><a name="Page_175" id="Page_175">[Pg 175]</a></span> +by a distinct account of the properties of these principles) to be accepted +when chemical knowledge became accurate.</p> + +<p>The same general consideration, founded on a large accumulation of facts, +viz. that similarity of properties is due to similarity of composition, +guided Lavoisier in his work on acids. He found the "primordial acid" of +Stahl, and the "biting principle" of Meyer, in the element oxygen.</p> + +<p>I have already (p. 91) shortly traced the reasoning whereby Lavoisier +arrived at the conclusion that oxygen is <i>the acid-producer</i>; here I would +insist on the difference between his method and that of Basil Valentine, +Stahl and the older chemists. <i>They</i> carried into the domain of natural +science conceptions obtained from, and essentially belonging to the domain +of metaphysical or extra-physical speculation; <i>he</i> said that oxygen is the +acidifier, because all the compounds of this element which he actually +examined were possessed of the properties included under the name acid. We +know that Lavoisier's conclusion was erroneous, that it was not founded on +a sufficiently broad basis of facts. The conception of an acidifying +principle, although that principle was identified with a known element, was +still tainted with the vices of the alchemical school. We shall see +immediately how much harm was done by the assertion of Lavoisier, "All +acids contain oxygen."</p> + +<p>In Chapter II. (pp. 32-37) we traced the progress of knowledge regarding +alkalis from the time when<span class='pagenum'><a name="Page_176" id="Page_176">[Pg 176]</a></span> the properties of these bodies were said to be +due to the existence in them of "matter of fire," to the time when Black +had clearly distinguished and defined caustic alkali and carbonated alkali.</p> + +<p>The truly philosophical character, and at the same time the want of +enthusiasm, of Black become apparent if we contrast his work on alkali with +that of Lavoisier on acid. Black did not hamper the advance of chemistry by +finding a "principle of alkalinity;" but neither did he give a full +explanation of the fact that certain bodies are alkaline while others are +not. He set himself the problem of accurately determining the differences +in composition between burnt (or caustic) and unburnt (or mild) alkali, and +he solved the problem most successfully. He showed that the properties of +mild alkalis differ from those of caustic alkalis, because the composition +of the former differs from that of the latter; and he showed exactly +wherein this difference of composition consists, viz. in the possession or +non-possession of fixed air.</p> + +<p>Strange we may say that this discovery did not induce Black to prosecute +the study of caustic alkalis: surely he would have anticipated Davy, and +have been known as the discoverer of potassium and sodium.</p> + +<p>In the time of Stahl the name "salt" was applied, as we have learned, to +the substance produced by the union of an acid with an alkali; but the same +word was used by the alchemists with an altogether different signification. +Originally<span class='pagenum'><a name="Page_177" id="Page_177">[Pg 177]</a></span> applied to the solid matter obtained by boiling down sea-water, +and then extended to include all substances which, like this solid matter, +are very easily dissolved by water and can be recovered by boiling down +this solution, "salt" was, in the sixteenth and seventeenth centuries, the +name given to one of the hypothetical principles or elements. Many kinds of +matter were known to be easily dissolved by water; the common possession of +these properties was sought to be accounted for by saying that all these +substances contained the same principle, namely, <i>the principle of salt</i>. I +have already tried to indicate the reasoning whereby Boyle did so much to +overthrow this conception of salt. He also extended our knowledge of +special substances which are now classed as salts. The chemists who came +after Boyle gradually reverted to the older meaning of the term "salt," +adopting as the characteristics of all substances placed in this class, +ready solubility in water, fusibility, or sometimes volatility, and the +possession of a taste more or less like that of sea-salt.</p> + +<p>Substances which resembled salts in general appearance, but were insoluble +in water, and very fixed in the fire, were called "earths"; and, as was +generally done in those days, the existence of a primordial earth was +assumed, more or less of which was supposed to be present in actual earths. +This recognition of the possibility of more or less of the primordial earth +being present in actually occurring earths, of course necessitated the +existence of<span class='pagenum'><a name="Page_178" id="Page_178">[Pg 178]</a></span> various kinds of earth. The earths were gradually +distinguished from each other; lime was recognized as a substance distinct +from baryta, baryta as distinct from alumina, etc.</p> + +<p>Stahl taught that one essential property of an earth was fusibility by +fire, with production of a substance more or less like glass. This property +was possessed in a remarkable degree by quartz or silica. Hence silica was +regarded as the typical earth, until Berzelius, in 1815, proved it to be an +acid. But the earths resembled alkalis, inasmuch as they too combined with, +and so neutralized, acids.</p> + +<p>There is an alkali hidden in every earth, said some chemists.</p> + +<p>An alkali is an earth refined by the presence of acid and combustible +matter, said others.</p> + +<p>Earths thus came to be included in the term "alkali," when that term was +used in its widest acceptation. But a little later it was found that some +of the earths were thrown down in the solid form from their solutions in +acids by the addition of alkalis; this led to a threefold division, thus—</p> + + + +<div class='center'> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align='center'>Earths</td><td align='center'><—></td><td align='center'>Alkaline earths</td><td align='center'><—></td><td align='center'>Alkalis</td></tr> +<tr><td align='center'>Insoluble in water.</td><td align='center'> </td><td align='center'>Somewhat soluble in water.</td><td align='center'> </td><td align='center'>Very soluble in water.</td></tr> +</table></div> + + + +<p>The distinction at first drawn between "earth" and "alkali" was too +absolute; the intermediate group of "alkaline earths" served to bridge over +the gap between the extreme groups.</p> + +<p>"In Nature," says Wordsworth, "everything is<span class='pagenum'><a name="Page_179" id="Page_179">[Pg 179]</a></span> distinct, but nothing defined +into absolute independent singleness."</p> + +<p>At this stage of advance, then, an earth is regarded as differing from an +alkali in being insoluble, or nearly insoluble in water; in not being soapy +to the touch, and not turning vegetable reds to blue: but as resembling an +alkali, in that it combines with and neutralizes an acid; and the product +of this neutralization, whether accomplished by an alkali or by an earth, +is called a salt. To the earth or alkali, as being the foundation on which +the salt is built, by the addition of acid, the name of <i>base</i> was given by +Rouelle in 1744.</p> + +<p>But running through every conception which was formed of these +substances—acid, alkali, earth, salt—we find a tendency, sometimes +forcibly marked, sometimes feebly indicated, but always present, to +consider salt as a term of much wider acceptation than any of the others. +An acid and an alkali, or an acid and an earth, combine to form a salt; but +the salt could not have been thus produced unless the acid, the alkali and +the earth had contained in themselves some properties which, when combined, +form the properties of the salt.</p> + +<p>The acid, the alkali, the earth, each is, in a sense, a salt. The perfect +salt is produced by the coalescence of the saltness of the acid with the +saltness of the alkali. This conception finds full utterance in the names, +once in common use, of <i>sal acidum</i> for acid, <i>sal alkali</i> for alkali, and +<i>sal salsum</i> or <i>sal neutrum</i> for salt. All are salts; at one extreme<span class='pagenum'><a name="Page_180" id="Page_180">[Pg 180]</a></span> +comes that salt which is marked by properties called acid properties, at +the other extreme comes the salt distinguished by alkaline properties, and +between these, and formed by the union of these, comes the middle or +neutral salt.</p> + +<p>It is thus that the nomenclature of chemistry marks the advances made in +the science. "What's in a name?" To the historical student of science, +almost everything.</p> + +<p>We shall find how different is the meaning attached in modern chemistry to +these terms, <i>acid salt</i>, <i>alkaline salt</i>, <i>neutral salt</i>, from that which +our predecessors gave to their <i>sal acidum</i>, <i>sal alkali</i>, and <i>sal +neutrum</i>.</p> + +<p>We must note the appearance of the term <i>vitriol</i>, applied to the solid +salt-like bodies obtained from acids and characterized by a glassy lustre. +By the middle of last century the vitriols were recognized as all derived +from, or compounded of, sulphuric acid (oil of vitriol) and metals; this +led to a subdivision of the large class of neutral salts into (1) metallic +salts produced by the action of sulphuric acid on metals, and (2) neutral +salts produced by the action of earths or alkalis on acids generally.</p> + +<p>To Rouelle, a predecessor of Lavoisier, who died four years before the +discovery of oxygen, we owe many accurate and suggestive remarks and +experiments bearing on the term "salt." I have already mentioned that it +was he who applied the word "base" to the alkali or earth, or it might be +metal,<span class='pagenum'><a name="Page_181" id="Page_181">[Pg 181]</a></span> from which, by the action of acid, a salt is built up. He also +ceased to speak of an acid as <i>sal acidum</i>, or of an alkali as <i>sal +alkali</i>, and applied the term "salt" exclusively to those substances which +are produced by the action of acids on bases. When the product of such an +action was neutral—that is, had no sour taste, no soapy feeling to the +touch, no action on vegetable colours, and no action on acids or bases—he +called that product <i>a neutral salt</i>; when the product still exhibited some +of the properties of acid, <i>e.g.</i> sourness of taste, he called it <i>an acid +salt</i>; and when the product continued to exhibit some of the properties of +alkali, <i>e.g.</i> turned vegetable reds to blue, he called it <i>an alkaline +salt</i>.</p> + +<p>Rouelle also proved experimentally that an acid salt contains more +acid—relatively to the same amount of base—than a neutral salt, and that +an alkaline salt contains more base—relatively to the same amount of +acid—than a neutral salt; and he proved that this excess of acid, or of +base, is chemically united to the rest of the salt—is, in other words, an +essential part of the salt, from which it cannot be removed without +changing the properties of the whole.</p> + +<p>But we have not as yet got to know why certain qualities connoted by the +term "acid" can be affirmed to belong to a group of bodies, why certain +other, "alkaline," properties belong to another group, nor why a third +group can be distinguished from both of these by the possession of +properties which we sum up in the term "earthy." Surely<span class='pagenum'><a name="Page_182" id="Page_182">[Pg 182]</a></span> there must be some +peculiarity in the composition of these substances, common to all, by +virtue of which all are acid. The atom of an acid is surely composed of +certain elements which are never found in the atom of an alkali or an +earth; or perhaps the difference lies in the number, rather than in the +nature of the elements in the acid atoms, or even in the arrangement of the +elementary atoms in the compound atom of acid, of alkali, and of earth.</p> + +<p>I think that our knowledge of salt is now more complete than our knowledge +of either acid, alkali, or earth. We know that a salt is formed by the +union of an acid and an alkali or earth; if, then, we get to know the +composition of acids and bases (<i>i.e.</i> alkalis and earths), we shall be +well on the way towards knowing the composition of salts.</p> + +<p>And now we must resume our story where we left it at p. 176. Lavoisier had +recognized oxygen as the acidifier; Black had proved that a caustic alkali +does not contain carbonic acid.</p> + +<p>Up to this time metallic calces, and for the most part alkalis and earths +also, had been regarded as elementary substances. Lavoisier however proved +calces to be compounds of metals and oxygen; but as some of those calces +had all the properties which characterized earths, it seemed probable that +all earths are metallic oxides, and if all earths, most likely all alkalis +also. Many attempts were made to decompose earths and alkalis, and to +obtain the metal, the oxide of which the earth or<span class='pagenum'><a name="Page_183" id="Page_183">[Pg 183]</a></span> the alkali was supposed +to be. One chemist thought he had obtained a metal by heating the earth +baryta with charcoal, but from the properties of his metal we know that he +had not worked with a pure specimen of baryta, and that his supposed +metallic base of baryta was simply a little iron or other metal, previously +present in the baryta, or charcoal, or crucible which he employed.</p> + +<p>But if Lavoisier's view were correct—if all bases contained oxygen—it +followed that all salts are oxygen compounds. Acids all contain oxygen, +said Lavoisier; this was soon regarded as one of the fundamental facts of +chemistry. Earths and alkalis are probably oxides of metals; this before +long became an article of faith with all orthodox chemists. Salts are +produced by the union of acids and bases, therefore all salts contain +oxygen: the conclusion was readily adopted by almost every one.</p> + +<p>When the controversy between Lavoisier and the phlogistic chemists was at +its height, the followers of Stahl had taunted Lavoisier with being unable +to explain the production of hydrogen (or phlogiston as they thought) +during the solution of metals in acids; but when Lavoisier learned the +composition of water, he had an answer sufficient to quell these taunts. +The metal, said Lavoisier, decomposes the water which is always present +along with the acid, hydrogen is thus evolved, and the metallic calx or +oxide so produced dissolves in the acid and forms a salt. If this +explanation were correct—and there was an immense mass of evidence in its<span class='pagenum'><a name="Page_184" id="Page_184">[Pg 184]</a></span> +favour and apparently none against it—then all the salts produced by the +action of acids on metals necessarily contained oxygen.</p> + +<p>The Lavoisierian view of a salt, as a compound of a metallic oxide—or +base—with a non-metallic oxide—or acid—seemed the only explanation which +could be accepted by any reasonable chemist: in the early years of this +century it reigned supreme.</p> + +<p>But even during the lifetime of its founder this theory was opposed and +opposed by the logic of facts. In 1787 Berthollet published an account of +experiments on prussic acid,—the existence and preparation (from Prussian +blue) of which acid had been demonstrated three or four years before by the +Swedish chemist Scheele—which led him to conclude this compound to be a +true acid, but free from oxygen. In 1796 the same chemist studied the +composition and properties of sulphuretted hydrogen, and pronounced this +body to be an acid containing no oxygen.</p> + +<p>But the experiments and reasoning of Berthollet were hidden by the masses +of facts and the cogency of argument of the Lavoisierian chemists.</p> + +<p>The prevalent views regarding acids and bases were greatly strengthened by +the earlier researches of Sir Humphry Davy, in which he employed the +voltaic battery as an instrument in chemical investigation. Let us now +consider some of the electro-chemical work of this brilliant chemist.</p> + +<p>In the spring of the year 1800 the electrical battery, which had recently +been discovered by<span class='pagenum'><a name="Page_185" id="Page_185">[Pg 185]</a></span> Volta, was applied by Nicholson and Carlisle to effect +the decomposition of water. The experiments of these naturalists were +repeated and confirmed by Davy, then resident at Bristol, who followed up +this application of electricity to effect chemical changes by a series of +experiments extending from 1800 to 1806, and culminating in the Bakerian +Lecture delivered before the Royal Society in the latter year.</p> + +<p>The history of Davy's life during these years, years rich in results of the +utmost importance to chemical science, will be traced in the sequel; +meanwhile we are concerned only with the results of his chemical work.</p> + +<p>The first Bakerian Lecture of Humphry Davy, "On some Chemical Agencies of +Electricity," deserves the careful study of all who are interested in the +methods of natural science; it is a brilliant example of the +disentanglement of a complex natural problem.</p> + +<p>Volta and others had subjected water to the action of a current of +electricity, and had noticed the appearance of acid and alkali at the +oppositely electrified metallic surfaces. According to some experimenters, +the acid was nitrous, according to others, muriatic acid. One chemist +asserted the production of a new and peculiar body which he called <i>the +electric acid</i>. The alkali was generally said to be ammonia.</p> + +<p>When Davy passed an electric current through distilled water contained in +glass vessels, connected<span class='pagenum'><a name="Page_186" id="Page_186">[Pg 186]</a></span> by pieces of moist bladder, cotton fibre, or +other vegetable matters, he found that nitric and hydrochloric acids were +formed in the water surrounding the positively electrified plate or pole, +and soda around the negatively electrified pole, of the battery.</p> + +<p>When the same piece of cotton fibre was repeatedly used for making +connection between the glass vessels, and was washed each time in dilute +nitric acid, Davy found that the production of muriatic acid gradually +ceased; hence he traced the formation of this acid to the presence of the +animal or vegetable substance used in the experiments.</p> + +<p>Finding that the glass vessels were somewhat corroded, and that the greater +the amount of corrosion the greater was the amount of soda making its +appearance around the negative pole, he concluded that the soda was +probably a product of the decomposition of the glass by the electric +current; he therefore modified the experiment. He passed an electric +current through distilled water contained in small cups of agate, +previously cleaned by boiling in distilled water for several hours, and +connected by threads of the mineral asbestos, chosen as being quite free +from vegetable matter; alkali and acid were still produced. The experiment +was repeated several times with the same apparatus; acid and alkali were +still produced, but the alkali decreased each time. The only conclusion to +be drawn was that the alkali came from the water employed. Two small cups +of gold were now used<span class='pagenum'><a name="Page_187" id="Page_187">[Pg 187]</a></span> to contain the water; a very small amount of alkali +appeared at the negative pole, and a little nitric acid at the positive +pole. The quantity of acid slowly increased as the experiment continued, +whereas the quantity of alkali remained the same as after a few minutes' +action of the electric current. The production of alkali is probably due, +said Davy, to the presence in the water of some substance which is not +removed by distillation in a glass retort. By boiling down in a silver dish +a quantity of the water he had used, a very small amount of solid matter +was obtained, which after being heated was distinctly alkaline. Moreover +when a little of this solid matter was added to the water contained in the +two golden cups, there was a sudden and marked increase in the amount of +alkali formed around the negative pole. Another quantity of the water which +he had used was again distilled in a silver retort, and a little of the +distillate was subjected to electrolysis as before. No alkali appeared. A +little piece of glass was placed in the water; alkali quickly began to +form. Davy thus conclusively proved that the alkali produced during the +electrolysis (<i>i.e.</i> decomposition by the electric current) of water is not +derived from the water itself, but from mineral impurities contained in the +water, or in the vessel in which the water is placed during the experiment. +But the production of nitric acid around the positive pole was yet to be +accounted for.</p> + +<p>Before further experiments could be made it was<span class='pagenum'><a name="Page_188" id="Page_188">[Pg 188]</a></span> necessary that Davy should +form an hypothesis—that he should mentally connect the appearance of the +nitric acid with some other phenomenon sufficient to produce this +appearance; he could then devise experiments which would determine whether +the connection supposed to exist between the two phenomena really did exist +or not.</p> + +<p>Now, of the constituents of nitric acid—nitrogen, hydrogen and oxygen—all +except the first named are present in pure water; nitrogen is present in +large quantity in the ordinary atmosphere. It was only necessary to assume +that some of the hydrogen and oxygen produced during the electrolysis of +water seized on and combined with some of the nitrogen in the air which +surrounded that water, and the continual production of nitric acid during +the whole process of electrolysis was explained.</p> + +<p>But how was this assumption to be proved or disproved? Davy adopted a +method frequently made use of in scientific investigations:—remove the +assumed cause of a phenomenon; if the phenomenon ceases to be produced, the +assumed cause is probably the real cause. Davy surrounded the little gold +cups containing the water to be electrolysed with a glass jar which he +connected with an air-pump; he exhausted most of the air from the jar and +then passed the electric current through the water. Very little nitric acid +appeared. He now again took out most of the air from the glass jar, +admitted some hydrogen to supply its place, and again pumped this out. This +process he repeated<span class='pagenum'><a name="Page_189" id="Page_189">[Pg 189]</a></span> two or three times and then passed the electric +current. <i>No</i> acid appeared in the water. He admitted air into the glass +vessel; nitric acid began to be produced. Thus he proved that whenever air +was present in contact with the water being electrolysed, nitric acid made +its appearance, and when the air was wholly removed the acid ceased to be +produced. As he had previously shown that the production of this acid was +not to be traced to impurities in the water, to the nature of the vessel +used to contain the water, or to the nature of the material of which the +poles of the battery were composed, the conclusion was forced upon him that +the production of nitric acid in the water, and the presence of ordinary +air around the water invariably existed together; that if one of these +conditions was present, the other was also present—in other words, that +one was the cause of the other.</p> + +<p>The result of this exhaustive and brilliant piece of work is summed up by +Davy in these words: "It seems evident then that water, chemically pure, is +decomposed by electricity into gaseous matter alone, into oxygen and +hydrogen."</p> + +<p>From the effects of the electric current on glass, Davy argued that other +earthy compounds would probably undergo change under similar conditions. He +therefore had little cups of gypsum made, in which he placed pure water, +and passed an electric current through the liquid. Lime was formed around +the negative, and sulphuric acid around the positive pole. Using similar +apparatus, he proved<span class='pagenum'><a name="Page_190" id="Page_190">[Pg 190]</a></span> that the electric current decomposes very many +minerals into an earthy or alkaline base and an acid.</p> + +<p>Picturing to himself the little particles of a salt as being split by the +electric current each into two smaller particles, one possessed of acid and +the other of alkaline properties, Davy thought it might be possible to +intercept the progress of these smaller particles, which he saw ever +travelling towards the positive and negative poles of the battery. He +accordingly connected these small glass vessels by threads of washed +asbestos; in one of the outer vessels he placed pure water, in the other an +aqueous solution of sulphate of potash, and in the central vessel he placed +ammonia. The negative pole of the battery being immersed in the sulphate of +potash, and the positive pole in the water, it was necessary for the +particles of sulphuric acid—produced by the decomposition of the sulphate +of potash—to travel through the ammonia in the central vessel before they +could find their way to the positive pole. Now, ammonia and sulphuric acid +cannot exist in contact—they instantly combine to form sulphate of +ammonia; the sulphuric acid particles ought therefore to be arrested by the +ammonia. But the sulphuric acid made its appearance at the positive pole +just as if the central vessel had contained water. It seemed that the +mutual attraction ordinarily exerted between sulphuric acid and ammonia was +overcome by the action of the electric current. Ammonia would<span class='pagenum'><a name="Page_191" id="Page_191">[Pg 191]</a></span> generally +present an insuperable barrier to the progress of sulphuric acid, but the +electrical energy appeared to force the acid particles over this barrier; +they passed towards their goal as if nothing stood in their way.</p> + +<p>Experiments are now multiplied by Davy, and the general conclusion drawn is +that "Hydrogen, the alkaline substances, the metals and certain metallic +oxides are attracted by negatively electrified metallic surfaces, and +repelled by positively electrified metallic surfaces; and contrariwise, +that oxygen and acid substances are attracted by positively electrified +metallic surfaces, and repelled by negatively electrified metallic +surfaces; and these attractive and repulsive forces are sufficiently +energetic to destroy or suspend the usual operation of chemical +affinity."<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a></p> + +<p>To account for this apparent suspension of the ordinary chemical laws, Davy +supposes that chemical compounds are continually decomposed and re-formed +throughout the liquid which is subjected to the electrical action. Thus, in +the experiment with water, ammonia and sulphate of potash, he supposes that +the sulphuric acid and ammonia do combine in the central vessel to form +sulphate of ammonia, but that this compound is again decomposed, by the +electrical energy, into sulphuric acid—which passes on towards the +positive pole—and ammonia—which remains in the central vessel—ready<span class='pagenum'><a name="Page_192" id="Page_192">[Pg 192]</a></span> to +combine with more sulphuric acid as that comes travelling onwards from its +source in the vessel containing sulphate of potash to its goal in the +vessel containing water.</p> + +<p>The eye of the philosopher had pierced beneath the apparent stability of +the chemical systems which he studied. To his vision there appeared in +those few drops of water and ammonia and sulphate of potash a never-ceasing +conflict of contending forces; there appeared a continual shattering and +rebuilding of the particles of which the masses were composed. The whole +was at rest, the parts were in motion; the whole was constant in chemical +composition, the composition of each particle was changed a thousand times +in the minutest portion of every second. To the mind of Davy, the +electrolysis of every chemical compound was a new application of the great +law established by Newton—"To every action there is an equal and opposite +reaction."</p> + +<p>Each step made in chemical science since Davy's time has but served to +emphasize the universality of this principle of action and reaction, a +principle which has been too much overlooked in the chemical text-books, +but the importance of which recent researches are beginning to impress on +the minds of chemists.</p> + +<p>It is the privilege of the philosophic student of Nature to penetrate the +veil with which she conceals her secrets from the vulgar gaze. To him are +shown sights which "eye hath not seen," and<span class='pagenum'><a name="Page_193" id="Page_193">[Pg 193]</a></span> by him are perceived sounds +which "ear hath not heard." Each drop of water is seen by him not only to +be built up of myriads of small parts, but each particle is seen to be in +motion; many particles are being decomposed into still smaller particles of +matter, different in properties from the original particles, but as the +original particles are at the same time being reproduced, the continued +existence of the drop of water with the properties of water is to him the +result of the mutual action and reaction of contending forces. He knows +that rest and permanence are gained, not by the cessation of action, but by +the continuance of conflict; he knows that in the realm of natural +phenomena, stable equilibrium is the resultant of the action of opposite +forces, and that complete decomposition occurs only when one force becomes +too powerful or another becomes too weak.</p> + +<p>Pursuing the train of thought initiated by the experiments which I have +described, Davy entered upon a series of researches which led him to +consider every chemical substance as possessing definite electrical +relations towards every other substance. "As chemical attraction between +two bodies seems to be destroyed by giving one of them an electrical state +different from that which it naturally possessed—that is, by bringing it +into a state similar to the other—so it may be increased by exalting its +natural energy." Thus zinc, a metal easily oxidized, does not combine with +oxygen when negatively electrified, whereas silver, a metal<span class='pagenum'><a name="Page_194" id="Page_194">[Pg 194]</a></span> oxidized with +difficulty, readily combines with oxygen when positively electrified.</p> + +<p>Substances in opposite electrical states appear to combine chemically, and +the greater the electrical difference the greater the readiness with which +chemical combination is effected. Electrical energy and chemical attraction +or <i>affinity</i> are evidently closely connected; perhaps, said Davy, they are +both results of the same cause.</p> + +<p>Thus Davy arrived at the conception of a system of bodies as maintained in +equilibrium by the mutual actions and reactions of both chemical and +electrical forces; by increasing either of these a change is necessarily +produced in the other. Under certain electrical conditions the bodies will +exert no chemical action on one another, but such action may be started by +changing these electrical conditions, or, on the other hand, by changes in +the chemical relations of the bodies a change in the electrical relations +may be induced. Thus Davy found that if plates of copper and sulphur are +heated, the copper exhibits a positive and the sulphur a negative +electrical condition; that these electrical states become more marked as +temperature rises, until the melting point of sulphur is reached, when the +copper and sulphur combine together chemically and produce sulphide of +copper.</p> + +<p>When water is electrolysed, Davy looked on the oppositely electrified +metallic plates in the battery as striving to attain a state of +equilibrium; the<span class='pagenum'><a name="Page_195" id="Page_195">[Pg 195]</a></span> negatively electrified zinc strives to gain positive +electricity from the copper, which strives to gain negative electricity +from the zinc. The water he regarded as the carrier of these electricities, +the one in this direction, the other in that. In thus acting as a carrier, +the water is itself chemically decomposed, with production of hydrogen and +oxygen; but this chemical rearrangement of some of the substances which +composed the original system (of battery and water) involves a fresh +disturbance of electrical energy, and so the process proceeds until the +whole of the water is decomposed or the whole of the copper or zinc plate +is dissolved in the battery. If the water were not chemically decomposed, +Davy thought that the zinc and copper in the battery would quickly attain +the state of electrical equilibrium towards which they continually strive, +and that the current would therefore quickly cease.</p> + +<p>Davy thought that "however strong the natural electrical energies of the +elements of bodies may be, yet there is every probability of a limit to +their strength; whereas the powers of our artificial instruments seem +capable of indefinite increase." By making use of a very powerful battery, +he hoped to be able to decompose substances generally regarded as simple +bodies.</p> + +<p>Taking a wide survey of natural phenomena, he sees these two forces, which +we call chemical and electrical, everywhere at work, and by their mutual +actions upholding the material universe in equilibrium.<span class='pagenum'><a name="Page_196" id="Page_196">[Pg 196]</a></span> In the outbreaks +of volcanoes he sees the disturbance of this equilibrium by the undue +preponderance of electrical force; and in the formation of complex minerals +beneath the surface of the earth, he traces the action of those chemical +attractions which are ever ready to bring about the combination of +elements, if they are not held in check by the opposing influence of +electrical energy.</p> + +<p>We shall see how the great and philosophical conception of Davy was used by +Berzelius, and how, while undoubtedly gaining in precision, it lost much in +breadth in being made the basis of a rigid system of chemical +classification.</p> + +<p>Davy's hope that the new instrument of research placed in the hands of +chemists by Volta would be used in the decomposition of supposed simple +substances was soon to be realized. A year after the lecture "On some +Chemical Agencies of Electricity," Davy was again the reader of the +Bakerian Lecture; this year (1807) it was entitled, "On some New Phenomena +of Chemical Change produced by Electricity, particularly the Decomposition +of the Fixed Alkalis; and the Exhibition of the New Substances which +constitute their Bases; and on the General Nature of Alkaline Bodies."</p> + +<p>In his first experiments on the effect of the electrical current on potash +and soda, Davy used strong aqueous solutions of these alkalis, with the +result that hydrogen and oxygen only were evolved. He then passed the +current through melted<span class='pagenum'><a name="Page_197" id="Page_197">[Pg 197]</a></span> potash kept liquid during the operation by the use +of a spirit-lamp, the flame of which was fed with oxygen. Much light was +evolved, and a great flame appeared at the negative pole; on changing the +direction of the current, "aeriform globules, which inflamed in the air, +rose through the potash."</p> + +<p>On the 6th of October 1807, a piece of potash was placed on a disc of +platinum, which was made the negative pole of a very powerful battery; a +platinum wire brought into contact with the upper surface of the potash +served as the positive pole. When the current was passed, the potash became +hot and soon melted; gas was evolved at the upper surface, and at the lower +(negative) side "there was no liberation of elastic fluid, but small +globules, having a high metallic lustre, and being precisely similar in +visible characters to quicksilver appeared, some of which burst with +explosion and bright flame as soon as they were formed, and others +remained, and were merely tarnished, and finally covered by a white film +which formed on their surfaces."</p> + +<p>When Davy saw these metallic globules burst through the crust of fusing +potash, we are told by one of his biographers, "he could not contain his +joy, he actually bounded about the room in ecstatic delight; and some +little time was required for him to compose himself sufficiently to +continue the experiment."</p> + +<p>This was the culminating point of the researches in which he had been +continuously engaged for<span class='pagenum'><a name="Page_198" id="Page_198">[Pg 198]</a></span> about six years. His interest and excitement were +intense; the Bakerian Lecture was written "on the spur of the occasion, +before the excitement of the mind had subsided," yet, says his +biographer—and we may well agree with him—"yet it bears proof only of the +maturest judgment; the greater part of it is as remarkable for experimental +accuracy as for logical precision." But "to every action there is an equal +and opposite reaction:" immediately after the delivery of the lecture, Davy +was prostrated by a severe attack of illness, which confined him to bed for +nine weeks, and was very nearly proving fatal.</p> + +<p>That the phenomenon just described was really the decomposition of potash, +and the production of the metal of which this substance is an oxygenized +compound, was proved by obtaining similar results whether plates of silver, +copper, or gold, or vessels of plumbago, or even charcoal, were used to +contain the potash, or whether the experiment was conducted in the air, or +in a glass vessel from which air had been exhausted, or in glass tubes +wherein the potash was confined by mercury. The decomposition of potash was +followed within a few days by that of soda, from which substance metallic +globules were obtained which took fire when exposed to the air.</p> + +<p>But the analysis of potash and soda was not sufficient for Davy; he +determined to accomplish the synthesis of these substances. For this +purpose he collected small quantities of the newly discovered<span class='pagenum'><a name="Page_199" id="Page_199">[Pg 199]</a></span> metals, by +conducting the electrolysis of potash and soda under experimental +conditions such that the metals, as soon as produced, were plunged under +the surface of naphtha, a liquid which does not contain oxygen, and which +protected them from the action of the surrounding air.</p> + +<p>A weighed quantity of each metal was then heated in a stream of pure dry +oxygen, the products were collected and weighed, and it was found that +solutions of these products in water possessed all the properties of +aqueous solutions of potash and soda.</p> + +<p>The new metals were now obtained in larger quantity by Davy, and their +properties carefully determined by him; they were named <i>potassium</i> and +<i>sodium</i> respectively. They were shown to possess all those properties +which were generally accepted as characteristic of metal, except that of +being heavy. The new metals were extremely light, lighter than water. For +some time it was difficult to convince all chemists that a metal could be a +very light substance. We are assured that a friend of Davy, who was shown +potassium for the first time, and was asked what kind of substance he +supposed it to be, replied, "It is metallic, to be sure;" "and then, +balancing it on his finger, he added in a tone of confidence, 'Bless me, +how heavy it is!'"</p> + +<p>Davy argued that since the alkalis, potash and soda, were found to be +oxygen compounds of metals, the earths would probably also be found<span class='pagenum'><a name="Page_200" id="Page_200">[Pg 200]</a></span> to be +metallic oxides. In the year 1808 he succeeded in decomposing the three +earths, lime, baryta and strontia, and in obtaining the metals <i>calcium</i>, +<i>barium</i> and <i>strontium</i>, but not in a perfectly pure condition, or in any +quantity. He also got evidence of the decomposition of the earths silica, +alumina, zirconia and beryllia, by the action of powerful electric +currents, but he did not succeed in obtaining the supposed metallic bases +of these substances.</p> + +<p>So far Davy's discoveries had all tended to confirm the generally accepted +view which regarded alkalis and earths as metallic oxides. But we found +that the outcome of these views was to regard all salts—and among these, +of course, common salt—as oxygen compounds.<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> Acids were oxygen +compounds, bases were oxygen compounds, and as salts were produced by the +union of acids with bases, they, too, must necessarily be oxygen compounds.</p> + +<p>Berthollet had thrown doubt on the universality of Lavoisier's name +"oxygen," <i>the</i> acidifier, but he had not conclusively proved the existence +of any acid which did not contain oxygen.</p> + +<p>The researches of Davy naturally led him to consider the prevalent views +regarding acids, bases and salts.</p> + +<p>Muriatic (or as we now call it hydrochloric) acid had long been a +stumbling-block to the thorough-going Lavoisierian chemists. Oxygen could +not<span class='pagenum'><a name="Page_201" id="Page_201">[Pg 201]</a></span> be detected in it, yet it ought to contain oxygen, because oxygen is +the acidifier. Of course, if muriatic acid contains oxygen, the +salts—muriates—produced by the action of this acid on alkalis and earths +must also contain oxygen. Many years before this time the action of +muriatic acid on manganese ore had been studied by the Swedish chemist +Scheele, who had thus obtained a yellow-coloured gas with a very strong +smell. Berthollet had shown that when a solution of this gas in water is +exposed to sunlight, oxygen is evolved and muriatic acid is produced. The +yellow gas was therefore supposed to be, and was called, "oxidized muriatic +acid," and muriatic acid was itself regarded as composed of oxygen and an +unknown substance or <i>radicle</i>.</p> + +<p>In 1809 Gay-Lussac and Thenard found that one volume of hydrogen united +with one volume of the so-called oxidized muriatic acid to form muriatic +acid; the presence of hydrogen in this acid was therefore proved.</p> + +<p>When Davy began (1810-11) to turn his attention specially to the study of +salts, he adopted the generally accepted view that muriatic acid is a +compound of oxygen and an unknown radicle, and that by the addition of +oxygen to this compound oxidized muriatic acid is produced. But unless Davy +could prove the presence of oxygen in muriatic acid he could not long hold +the opinion that oxygen was really a constituent of this substance. He +tried to obtain direct evidence<span class='pagenum'><a name="Page_202" id="Page_202">[Pg 202]</a></span> of the presence of oxygen, but failed. He +then set about comparing the action of muriatic acid on metals and metallic +oxides with the action of the so-called oxidized muriatic acid on the same +substances. He showed that salt-like compounds were produced by the action +of oxidized muriatic acid either on metals or on the oxides of these +metals, oxygen being evolved in the latter cases; and that the same +compounds and water were produced by the action of muriatic acid on the +same metallic oxides.</p> + +<p>These results were most easily and readily explained by assuming the +so-called oxidized muriatic acid to be an elementary substance, and +muriatic acid to be a compound of this element with hydrogen. To the new +element thus discovered—for he who establishes the elementary nature of a +substance may almost be regarded as its discoverer—Davy gave the name of +<i>chlorine</i>, suggested by the yellow colour of the gas (from Greek, = +<i>yellow</i>). He at once began to study the analogies of chlorine, to find by +experiment which elements it resembled, and so to classify it. Many metals, +he found, combined readily with chlorine, with evolution of heat and light. +It acted, like oxygen, as a supporter of combustion; it was, like oxygen, +attracted towards the negative pole of the voltaic battery; its compound +with hydrogen was an acid; hence said Davy chlorine, like oxygen, is a +supporter of combustion and also an acidifier.</p> + +<p>But it was very hard to get chemists to adopt<span class='pagenum'><a name="Page_203" id="Page_203">[Pg 203]</a></span> these views. As Bacon says, +"If false facts in Nature be once on foot, what through neglect of +examination, the countenance of antiquity, and the use made of them in +discourse, they are scarce ever retracted."</p> + +<p>Chemists had long been accustomed to systems which pretended to explain all +chemical facts. The phlogistic theory, which had tyrannized over chemistry, +had been succeeded by the Lavoisierian chemistry, which recognized one +acidifier, and this also the one supporter of combustion. To ascribe these +properties to any element other than oxygen appeared almost profane.</p> + +<p>But when Davy spoke of chlorine as an acidifier, he did not use this word +in the same sense as that in which it was employed by the upholders of the +oxygen theory of acids; he simply meant to express the fact that a compound +containing chlorine as one of its constituents, but not containing oxygen, +was a true acid. When Gay-Lussac attempted to prove that hydrogen is an +<i>alkalizing principle</i>, Davy said, "This is an attempt to introduce into +chemistry a doctrine of occult qualities, and to refer to some mysterious +and inexplicable energy what must depend upon a peculiar corpuscular +arrangement." And with regard to Gay-Lussac's strained use of analogies +between hydrogen compounds and alkalis, he says, "The substitution of +analogy for fact is the bane of chemical philosophy; the legitimate use of +analogy is to connect facts together, and to guide to new experiments."<span class='pagenum'><a name="Page_204" id="Page_204">[Pg 204]</a></span></p> + +<p>But Davy's facts were so well established, and his experiments so +convincing, that before two or three years had passed, most chemists were +persuaded that chlorine was an element—<i>i.e.</i> a substance which had never +been decomposed—and that muriatic acid was a compound of this element with +hydrogen.</p> + +<p>Berzelius was among the last to adopt the new view. Wöhler tells us that in +the winter of 1823, when he was working in the laboratory of Berzelius, +Anna, while washing some basins, remarked that they smelt strongly of +oxidized muriatic acid: "Now," said Berzelius, "listen to me, Anna. Thou +must no longer say 'oxidized muriatic acid,' but 'chlorine;' that is +better."</p> + +<p>This work on chlorine was followed up, in 1813, by the proof that the class +of acidifiers and supporters of combustion contains a third elementary +substance, viz. iodine. As Davy's views regarding acids and salts became +developed, he seems to have more and more opposed the assumption that any +one element is especially to be regarded as the acidifying element; but at +the same time he seems to admit that most, if not all, acids contain +hydrogen. Such oxides as sulphur trioxide, nitrogen pentoxide, etc., do not +possess acid properties except in combination with water. But he of course +did not say that all hydrogen compounds are acids; he rather regarded the +possession by a substance of acid properties as dependent, to a great +extent, on the nature of the elements other<span class='pagenum'><a name="Page_205" id="Page_205">[Pg 205]</a></span> than hydrogen which it +contained, or perhaps on the arrangement of all the elements in the +particles of the acid. He regarded the hydrogen in an acid as capable of +replacement by a metal, and to the metallic derivative—as it might be +called—of the acid, thus produced, he gave the name of "salt." An acid +might therefore be a compound of hydrogen with one other element—such were +hydrochloric, hydriodic, hydrofluoric acids—or it might be a compound of +hydrogen with two or more elements, of which one might or might not be +oxygen—such were hydrocyanic acid and chloric or nitric acid. If the +hydrogen in any of these acids were replaced by a metal a salt would be +produced. A salt might therefore contain no oxygen, <i>e.g.</i> chloride or +iodide of potassium; but in most cases salts did contain oxygen, <i>e.g.</i> +chlorate or nitrate of potassium.</p> + +<p>Acids were thus divided into oxyacids (or acids which contain oxygen) and +acids containing no oxygen; the former class including most of the known +acids. The old view of salts as being compounds of acids (<i>i.e.</i> oxides of +the non-metallic elements) and bases (<i>i.e.</i> oxides of metals) was +overthrown, and salts came to be regarded as metallic derivatives of acids.</p> + +<p>From this time, these terms—acids, salts, bases—become of less importance +than they formerly were in the history of chemical advance.</p> + +<p>In trying to explain Davy's electro-chemical theory I have applied the word +<i>affinity</i> to the mutual action and reaction between two substances<span class='pagenum'><a name="Page_206" id="Page_206">[Pg 206]</a></span> which +combine together to form a chemical compound. It is now necessary that we +should look a little more closely into the history of this word <i>affinity</i>.</p> + +<p>Oil and water do not mix together, but oil and potash solution do; the +former may be said not to have, and the latter to have, an affinity one for +the other. When sulphur is heated, the yellow odourless solid, seizing upon +oxygen in the air, combines with it to produce a colourless strongly +smelling gas. Sulphur and oxygen are said to have strong affinity for each +other.</p> + +<p>If equal weights of lime and magnesia be thrown into diluted nitric acid, +after a time it is found that some of the lime, but very little of the +magnesia, is dissolved. If an aqueous solution of lime be added to a +solution of magnesia in nitric acid, the magnesia is precipitated in the +form of an insoluble powder, while the lime remains dissolved in the acid. +It is said that lime has a stronger affinity for nitric acid than magnesia +has. Such reactions as these used to be cited as examples of <i>single +elective affinity</i>—single, because one substance combined with one other, +and elective, because a substance seemed to choose between two others +presented to it, and to combine with one to the exclusion of the other.</p> + +<p>But if a neutral solution of magnesia in sulphuric acid is added to a +neutral solution of lime in nitric acid, sulphate of lime and nitrate of +magnesia are produced. The lime, it was said, leaves the nitric<span class='pagenum'><a name="Page_207" id="Page_207">[Pg 207]</a></span> and goes +to the sulphuric acid, which, having been deserted by the magnesia, is +ready to receive it; at the same time the nitric acid from which the lime +has departed combines with the magnesia formerly held by the sulphuric +acid. Such a reaction was said to be an instance of <i>double affinities</i>. +The chemical changes were caused, it was said, by the simultaneous affinity +of lime for sulphuric acid, which was greater than its affinity for nitric +acid, and the affinity of magnesia for nitric acid, which was greater than +its affinity for sulphuric acid.</p> + +<p>If a number of salts were mixed, each base—supposing the foregoing +statements to be correct—would form a compound with that acid for which it +had the greatest affinity. It should then be possible to draw up tables of +affinity. Such tables were indeed prepared. Here is an example:—</p> + + + +<div class='center'> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td colspan="2"><i>Sulphuric Acid.</i></td></tr> +<tr><td align='left'>Baryta.</td><td align='left'>Lime.</td></tr> +<tr><td align='left'>Strontia.</td><td align='left'>Ammonia.</td></tr> +<tr><td align='left'>Potash.</td><td align='left'>Magnesia.</td></tr> +<tr><td align='left'>Soda.</td></tr> +</table></div> + + +<p>This table tells us that the affinity of baryta for sulphuric acid is +greater than that of strontia for the same acid, that of strontia greater +than that of potash, and so on. It also tells that potash will decompose a +compound of sulphuric acid and soda, just as soda will decompose a compound +of the same acid with lime, or strontia will decompose a compound with +potash, etc.</p> + +<p>But Berthollet showed in the early years of this<span class='pagenum'><a name="Page_208" id="Page_208">[Pg 208]</a></span> century that a large +quantity of a body having a weak affinity for another will suffice to +decompose a small quantity of a compound of this other with a third body +for which it has a strong affinity. He showed, that is, that the formation +or non-formation of a compound is dependent not only on the so-called +affinities between the constituents, but also on the relative quantities of +these constituents. Berthollet and other chemists also showed that affinity +is much conditioned by temperature; that is, that two substances which show +no tendency towards chemical union at a low temperature may combine when +the temperature is raised. He, and they, also proved that the formation or +non-formation of a compound is much influenced by its physical properties. +Thus, if two substances are mixed in solution, and if by their mutual +action a substance can be produced which is insoluble in the liquids +present, that substance is generally produced whether the affinity between +the original pair of substances be strong or weak.</p> + +<p>The outcome of Berthollet's work was that tables of affinity became almost +valueless. To say that the affinity of this body for that was greater than +its affinity for a third body was going beyond the facts, because the +formation of this or that compound depended on many conditions much more +complex than those connoted by the term "affinity." Yet the conception of +affinity remained, although it could not be applied in so rigorous a way as +had been done by the earlier chemists. If an element,<span class='pagenum'><a name="Page_209" id="Page_209">[Pg 209]</a></span> A, readily combines +with another element, B, under certain physical conditions, but does not, +under the same conditions, combine with a third element, C, it may still be +said that A and B have, and A and C have not, an affinity for each other.</p> + +<p>This general conception of affinity was applied by Berzelius to the atoms +of elements. Affinity, said Berzelius, acts between unlike atoms, and +causes them to unite to form a compound atom, unlike either of the original +atoms; cohesion, on the other hand, acts between like atoms, causing them +to hold together without producing any change in their properties. Affinity +varies in different elements. Thus the affinity of gold for oxygen is very +small; hence it is that gold is found in the earth in the metallic state, +while iron, having a great affinity for oxygen, soon rusts when exposed to +air, or when buried in the earth. Potassium and sodium have great +affinities for oxygen, chlorine, etc.; yet the atoms of potassium and +sodium do not themselves combine. The more any elements are alike +chemically the smaller is their affinity for each other; the more any +elements are chemically unlike the greater is their mutual affinity; but +this affinity is modified by circumstances. Thus, said Berzelius, if equal +numbers of atoms of A and B, having equal or nearly equal affinity for C, +mutually react, compound atoms, AC and BC, will be produced, but atoms of A +and B will remain. The amounts of AC and BC produced will be influenced by +the greater or less affinity of A and B for C;<span class='pagenum'><a name="Page_210" id="Page_210">[Pg 210]</a></span> but if there be a greater +number of A than of B atoms, a greater amount of AC than of BC will be +produced. In these cases all the reacting substances and the products of +the actions are supposed to be liquids; but BC, if a solid substance, will +be produced even if the affinity of A for C is greater than that of B for +C.</p> + +<p>In some elements, Berzelius taught, affinity slumbers, and can be awakened +only by raising the temperature. Thus carbon in the form of coal has no +affinity for oxygen at ordinary temperatures; it has remained for ages in +the earth without undergoing oxidation; but when coal is heated the +affinities of carbon are awakened, combination with oxygen occurs, and heat +is produced.</p> + +<p>But why is it that certain elementary atoms exhibit affinity for certain +others? It depends, said Berzelius, on the electrical states of these +atoms. According to the Berzelian theory, every elementary atom has +attached to it a certain quantity of electricity, part of which is positive +and part negative. This electricity is accumulated at two points on each +atom, called respectively the positive pole and the negative pole; but in +each atom one of these electricities so much preponderates over the other +as to give the whole atom the character of either a positively or a +negatively electrified body. When two atoms combine chemically the positive +electricity in one neutralizes the negative electricity in the other. As we +know that similar electricities repel, and opposite electricities attract<span class='pagenum'><a name="Page_211" id="Page_211">[Pg 211]</a></span> +each other, it follows that a markedly positive atom will exhibit strong +affinity for a markedly negative atom, less strong affinity for a feebly +negative, and little or no affinity for a positively electrified atom; but +two similarly electrified atoms may exhibit affinity, because in every +positive atom there is some negative electricity, as in every negative atom +there is some positive electricity. Thus, in the atoms of copper and zinc +positive electricity predominates, said Berzelius, but the zinc atoms are +more positive than those of copper; hence, when the metals are brought into +contact the negative electricity of the copper atoms is attracted and +neutralized by the positive electricity of the zinc atoms, combination +takes place, and the compound atom is still characterized by a predominance +of positive electricity.</p> + +<p>Hence Berzelius identified "electrical polarity" with chemical affinity. +Every atom was regarded by him as <i>both</i> positively <i>and</i> negatively +electrified; but as one of these electricities was always much stronger +than the other, every atom regarded as a whole appeared to be <i>either</i> +positively <i>or</i> negatively electrified. Positive atoms showed affinity for +negative atoms, and <i>vice versâ</i>. As a positive atom might become more +positive by increasing the temperature of the atom, so might the affinity +of this atom for that be more marked at high than at low temperatures.</p> + +<p>Now, if two elementary atoms unite, the compound atom must—according to +the Berzelian<span class='pagenum'><a name="Page_212" id="Page_212">[Pg 212]</a></span> views—be characterized either by positive or negative +electricity. This compound atom, if positive, will exhibit affinity for +other compound atoms in which negative electricity predominates; if +negative, it will exhibit affinity for other positively electrified +compound atoms. If two compound atoms unite chemically, the complex atom so +produced will, again, be characterized by one or other of the two +electricities, and as it is positive or negative, so will it exhibit +affinity for positively or negatively electrified complex atoms. Thus +Berzelius and his followers regarded every compound atom, however complex, +as essentially built up of two parts, one of which was positively and the +other negatively electrified, and which were held together chemically by +virtue of the mutual attractions of these electricities; they regarded +every compound atom as a <i>dual</i> structure. The classification adopted by +Berzelius was essentially a dualistic classification. His system has always +been known in chemistry as <i>dualism</i>.</p> + +<p>Berzelius divided compound atoms (we should now say molecules) into three +groups or orders—</p> + +<p><i>Compound atoms of the first order</i>, formed by the immediate combination of +atoms of two, or in organic compounds of three, elementary substances.</p> + +<p><i>Compound atoms of the second order</i>, formed by the combination of atoms of +an element with atoms of the first order, or by the combination of two or +more atoms of the first order.</p> + +<p><i>Compound atoms of the third order</i>, formed by<span class='pagenum'><a name="Page_213" id="Page_213">[Pg 213]</a></span> combination of two or more +atoms of the second order.</p> + +<p>When an atom of the third order was decomposed by an electric current, it +split up, according to the Berzelian teaching, into atoms of the second +order—some positively, others negatively electrified. When an atom of the +second order was submitted to electrolysis, it decomposed into atoms of the +first order—some positively, others negatively electrified.</p> + +<p>Berzelius said that a base is an electro-positive oxide, and an acid is an +electro-negative oxide. The more markedly positive an oxide is, the more +basic it is; the more negative it is, the more is it characterized by acid +properties.</p> + +<p>One outcome of this teaching regarding acids and bases was to overthrow the +Lavoisierian conception of oxygen as the acidifying element. Some oxides +are positive, others negative, said Berzelius; but acids are characterized +by negative electricity, therefore the presence of oxygen in a compound +does not always confer on that compound acid properties.</p> + +<p>We have already seen that silica was regarded by most chemists as a typical +earth; but Berzelius found that in the electrolysis of compounds of silica, +this substance appeared at the positive pole of the battery—that is, the +atom of silica belonged to the negatively electrified order of atoms. +Silica was almost certainly an oxide; but electro-negative oxides are, as a +class, acids; therefore silica was<span class='pagenum'><a name="Page_214" id="Page_214">[Pg 214]</a></span> probably an acid. The supposition of +the acid character of silica was amply confirmed by the mineralogical +analyses and experiments of Berzelius. He showed that most of the earthy +minerals are compounds of silica with electro-positive metallic oxides, and +that silica plays the part of an acid in these minerals; and in 1823 he +obtained the element silicon, the oxide of which is silica. On this basis +Berzelius reared a system of classification in mineralogy which much aided +the advance of that branch of natural science.</p> + +<p>By the work of Berzelius and Davy the Lavoisierian conception of acid has +now been much modified and extended; it has been rendered less rigid, and +is therefore more likely than before to be a guide to fresh discoveries.</p> + +<p>The older view of acid and alkali was based, for the most part, on a +qualitative study of the reactions of chemical substances: bodies were +placed in the same class because they were all sour, or all turned +vegetable blues to red, etc. This was followed by a closer study of the +composition of substances, and by attempts to connect the properties of +these substances with their composition; but when this attempt resulted in +the promulgation of the dictum that "oxygen is the acidifying principle," +it began to be perceived that a larger basis of fact must be laid before +just conclusions could be drawn as to the connections between properties +and composition of substances. This larger basis was laid by the two +chemists whose work we have<span class='pagenum'><a name="Page_215" id="Page_215">[Pg 215]</a></span> now reviewed. Of the life of one of these men +I have already given such a sketch as I can from the materials available to +me; of the life of the other we happily possess ample knowledge. Let us now +consider the main features of this life.</p> + + +<p><span class="smcap">Humphry Davy</span>, the eldest son of Robert and Grace Davy, was born at +Penzance, in Cornwall, on December 17, 1778, eight months that is before +the birth of Berzelius. His parents resided on a small property which had +belonged to their ancestors for several generations. Surrounded by many +kind friends by whom he was much thought of, the boy appears to have passed +a very happy childhood. Even at the age of five his quickness and +penetration were marked by those around him, and at school these continued +to be his predominant characteristics. Nurtured from his infancy in the +midst of beautiful and romantic scenery, and endowed with great observing +power and a lively imagination, young Davy seemed destined to be one of +those from whose lips is "poured the deathless singing;" all through life +he was characterized by a strongly marked poetic temperament.</p> + +<p>Humphry Davy was held in much esteem by his school friends as a composer of +valentines and love letters, as a daring and entertaining teller of +stories, and as a successful fireworks manufacturer. Such a combination of +qualities would much endear him to his boy-companions. We are told that at +the age of eight he used to mount on an empty cart, around<span class='pagenum'><a name="Page_216" id="Page_216">[Pg 216]</a></span> which a circle +of boys would collect to be entertained by the wonderful tales of the +youthful narrator.</p> + +<p>Finishing his school education at the age of fifteen, he now began his own +education of himself. In 1795 he was apprenticed to a surgeon and +apothecary (afterwards a physician), in Penzance, with whom he learned the +elements of medical science; but his time during the years which he spent +under Mr. Borlase was much occupied in shooting, fishing, searching for +minerals and geological specimens, composing poetry, and pursuing +metaphysical speculations. He was now, as through life, an enthusiastic +lover of Nature; his mind was extremely active, ranging over the most +diverse subjects; he was full of imagination, and seemed certain to +distinguish himself in any pursuit to which he should turn his attention. +During the next three or four years Davy indulged freely in speculations in +all manner of subjects; he started, as people generally do when young, from +general principles and followed these out to many conclusions. Even in his +study of physiology and other branches of science, he appears at this time +to have adopted the speculative rather than the experimental method; but +unlike most youthful metaphysicians he was ready to give up an opinion +whenever it appeared to him incorrect. By the time he reached the age of +twenty he had discarded this method of seeking for truth, and was ever +afterwards distinguished by his careful working<span class='pagenum'><a name="Page_217" id="Page_217">[Pg 217]</a></span> out of facts as the +foundation for all his brilliant theories.</p> + +<p>Davy appears to have begun the study of chemistry about 1798 by reading +Lavoisier's "Elements of Chemistry," the teachings of which he freely +criticized. About this time Mr. Gregory Watt came to live at Penzance as a +lodger with Davy's mother, and with him the young philosopher had much talk +on chemical and other scientific subjects. He also became acquainted with +Mr. Davies Gilbert—who was destined to succeed Davy as President of the +Royal Society—and from him he borrowed books and received assistance of +various kinds in his studies.</p> + +<p>It was during these years that Davy made experiments on heat, which were +published some years later, and which are now regarded as laying the +foundations of the modern theory according to which heat is due to the +motions of the small parts of bodies. He arranged two brass plates so that +one should carry a block of ice which might be caused to revolve in contact +with the other plate; the plates were covered by a glass jar, from which he +exhausted the air by means of a simple syringe of his own contrivance; the +machine being placed on blocks of ice the plates were caused to revolve. +The ice inside the jar soon melted; Davy concluded that the heat required +to melt this ice could only be produced by the friction of the ice and +brass, and that therefore heat could not be any form of ponderable matter.<span class='pagenum'><a name="Page_218" id="Page_218">[Pg 218]</a></span></p> + +<p>In the year 1798 Davy was asked to go to Bristol as superintendent of the +laboratory of a new Pneumatic Institution started by Dr. Beddoes for the +application of gases to the treatment of diseases. Davy had corresponded +with Beddoes before this time regarding his experiments on heat, and the +latter seems to have been struck with his great abilities and to have been +anxious to secure him as experimenter for his institution. Davy was +released from his engagements with Mr. Borlase, and, now about twenty years +of age, set out for his new home, having made as he says all the +experiments he could at Penzance, and eagerly looking forward to the better +appliances and incitements to research which he hoped to find at Bristol.</p> + +<p>The Pneumatic Institution was supported by subscriptions, for the most part +from scientific men. It was started on a scientific basis. Researches were +to be made on gases of various kinds with the view of applying these as +remedies in the alleviation of disease. An hospital for patients, a +laboratory for experimental research, and a lecture theatre were provided.</p> + +<p>At this time many men of literary and intellectual eminence resided in +Bristol; among these were Coleridge and Southey. Most of these men were +visitors at the house of Dr. Beddoes, and many distinguished men came from +various parts of the county to visit the institution. Davy thus entered on +a sphere of labour eminently suited for the development of his genius. With +ample mechanical<span class='pagenum'><a name="Page_219" id="Page_219">[Pg 219]</a></span> appliances for research, with plenty of time at his +disposal, surrounded by an atmosphere of inquiry and by men who would +welcome any additions he could make to the knowledge of Nature, and being +at the same time not without poetic and imaginative surroundings, by which +he was ever spurred onwards in the pursuit of truth—placed in these +circumstances, such an enthusiastic and diligent student of science as Davy +could not but obtain results of value to his fellows. The state of chemical +science at this time was evidently such as to incite the youthful worker. +The chains with which Stahl and his successors had so long bound the limbs +of the young science had been broken by Lavoisier; and although the French +school of chemistry was at this time dominant, and not disinclined to treat +as ignorant any persons who might differ from its teaching, yet there was +plenty of life in the cultivators of chemistry. The controversy between +Berthollet and Proust was about to begin; the Lavoisierian views regarding +acids and salts were not altogether accepted by Gay-Lussac, Thenard and +others; and from the laboratory of Berzelius there was soon to issue the +first of those numerous researches which drew the attention of every +chemist to the capital of Sweden. The voltaic battery had been discovered, +and had opened up a region of possibilities in chemistry.</p> + +<p>Davy began his researches at the institution by experiments with nitrous +oxide, a gas supposed by some people at that time to be capable of +producing<span class='pagenum'><a name="Page_220" id="Page_220">[Pg 220]</a></span> most harmful effects on the animal system. He had to make many +experiments before he found a method for preparing the pure gas, and in the +course of these experiments he added much to the stock of chemical +knowledge regarding the compounds of nitrogen and oxygen. Having obtained +fairly pure nitrous oxide, he breathed it from a silk bag; he experienced a +"sensation analogous to gentle pressure on all the muscles;... the objects +around me became dazzling and my hearing more acute;... at last an +irresistible propensity to action was indulged in.... I recollect but +indistinctly what followed; I know that my motions were various and +violent." Southey and Coleridge breathed the gas; the poets only laughed a +little. Encouraged by the results of these experiments, Davy proceeded to +prepare and breathe nitric oxide—whereby he was rendered very ill—and +then carburetted hydrogen—which nearly killed him.</p> + +<p>In his chemical note-book about this time, Davy says, "The perfection of +chemical philosophy, or the laws of corpuscular motion, must depend on the +knowledge of all the simple substances, their mutual attractions, and the +ratio in which the attractions increase or diminish with increase or +diminution of temperature.... The first step towards these laws will be the +decomposition of those bodies which are at present undecompounded." And in +the same note-book he suggests methods which he thinks might effect the +decomposition of<span class='pagenum'><a name="Page_221" id="Page_221">[Pg 221]</a></span> muriatic and boric acids, the alkalis and earths. Here +are the germs of his future work.</p> + +<p>After about eight months' work at Bristol he published a volume of +"Researches," which contained a great many new facts, and was characterized +by vigour and novelty of conception. These researches had been carried out +with intense application; each was struck off at a red heat. His mind +during this time was filled with vast scientific conceptions, and he began +also to think of fame. "An active mind, a deep ideal feeling of good, and a +look towards future greatness," he tells us, sustained him.</p> + +<p>Count Rumford, the founder of the Royal Institution in London, was anxious +to obtain a lecturer on chemistry for the Institution. Davy was strongly +recommended, and after a little arrangement—concerning which Davy says in +a letter, "I will accept of no appointment except on the sacred terms of +independence"—he was appointed Assistant Lecturer on Chemistry and +Director of the Laboratory. About a year later his official designation was +changed to Professor of Chemistry. This appointment opened up a great +sphere of research; "the sole and uncontrolled use of the apparatus of the +institution for private experiments" was to be granted him, and he was +promised "any apparatus he might need for new experiments."</p> + +<p>He had now the command of a good laboratory; he had not to undergo the +drudgery of systematic teaching, but was only required to give lectures<span class='pagenum'><a name="Page_222" id="Page_222">[Pg 222]</a></span> to +a general audience. Before leaving Bristol he had commenced experiments on +the chemical applications of the voltaic battery; these he at once followed +up with the better apparatus now at his command. The results of this +research, and his subsequent work on the alkalis and on muriatic acid and +chlorine, have been already described. The circumstances of Davy's life had +hitherto been most favourable; how nobly he had availed himself of these +circumstances was testified by the work done by him.</p> + +<p>His first lecture was delivered in the spring of 1801, and at once he +became famous. A friend of Davy says, "The sensation created by his first +course of lectures at the Institution, and the enthusiastic admiration +which they obtained, is scarcely to be imagined. Men of the first rank and +talent, the literary and the scientific, the practical and the theoretical, +blue-stockings and women of fashion, the old and the young—all crowded, +eagerly crowded the lecture-room. His youth, his simplicity, his natural +eloquence, his chemical knowledge, his happy illustrations and +well-conducted experiments, excited universal attention and unbounded +applause. Compliments, invitations and presents were showered upon him in +abundance from all quarters; his society was courted by all, and all +appeared proud of his acquaintance." One of his biographers says of these +lectures, "He was always in earnest, and when he amused most, amusement +appeared most foreign to his object. His great and<span class='pagenum'><a name="Page_223" id="Page_223">[Pg 223]</a></span> first object was to +instruct, and in conjunction with this, maintain the importance and dignity +of science; indeed, the latter, and the kindling a taste for scientific +pursuits, might rather be considered his main object, and the conveying +instruction a secondary one."</p> + +<p>The greatest pains were taken by Davy in the composition and rehearsal of +his lectures, and in the arrangement of experiments, that everything should +tend towards the enlightenment of his audience. Surrounded by a brilliant +society, invited to every fashionable entertainment, flattered by admirers, +tempted by hopes of making money, Davy remained a faithful and enthusiastic +student of Nature. "I am a lover of Nature," he writes at this time to a +friend, "with an ungratified imagination. I shall continue to search for +untasted charms, for hidden beauties. My <i>real</i>, my <i>waking</i> existence, is +amongst the objects of scientific research. Common amusements and +enjoyments are necessary to me only as dreams to interrupt the flow of +thoughts too nearly analogous to enlighten and vivify."</p> + +<p>During these years (<i>i.e.</i> from 1802 to 1812) he worked for the greater +part of each day in the laboratory. Every week, almost every day, saw some +fresh discovery of importance. He advanced from discovery to discovery. His +work was characterized by that vast industry and extreme rapidity which +belong only to the efforts of genius. Never, before or since, has chemical +science made such strides in this country.<span class='pagenum'><a name="Page_224" id="Page_224">[Pg 224]</a></span></p> + +<p>In 1803 Davy was elected a Fellow, and in 1807 one of the secretaries of +the Royal Society. In 1812 he retired from the professorship of chemistry +at the Royal Institution; in the same year he was made a knight.</p> + +<p>The next two or three years were mostly spent in travelling abroad with his +wife—he had married a widow lady, Mrs. Apreece, in 1812. During his visit +to Paris he made several experiments on the then recently discovered +iodine, and proved this substance to be an element.</p> + +<p>The work which Davy had accomplished in the seventeen years that had now +elapsed since he began the study of chemistry, whether we consider it +simply as a contribution to chemical science, or in the light of the +influence it exerted on the researches of others, was of first-rate +importance; but a fresh field now began to open before him, from which he +was destined to reap the richest fruits. In the autumn of 1815 his +attention was drawn to the subject of fire-damp in coal-mines. As he passed +through Newcastle, on his return from a holiday spent in the Scottish +Highlands, he examined various coal-mines and collected samples of +fire-damp; in December of the same year his <i>safety-lamp</i> was perfected, +and soon after this it was in the hands of the miner.</p> + +<p>The steps in the discovery of this valuable instrument were briefly these. +Davy established the fact that fire-damp is a compound of carbon and +hydrogen; he found that this gas must be mixed<span class='pagenum'><a name="Page_225" id="Page_225">[Pg 225]</a></span> with a large quantity of +ordinary air before the mixture becomes explosive, that the temperature at +which this explosion occurs is a high one, and that but little heat is +produced during the explosion; he found that the explosive mixture could +not be fired in narrow metallic tubes, and also that it was rendered +non-explosive by addition of carbonic acid or nitrogen. He reasoned on +these facts thus: "It occurred to me, as a <i>considerable</i> heat was required +for the inflammation of the fire-damp, and as it produced in burning a +comparatively <i>small degree</i> of heat, that the effect of carbonic acid and +azote, and of the surfaces of small tubes, in preventing its explosion, +depended on their cooling powers—upon their lowering the temperature of +the exploding mixture so much that it was no longer sufficient for its +continuous inflammation." He at once set about constructing a lamp in which +it should be impossible for the temperature of ignition of a mixture of +fire-damp and air to be attained, and which therefore, while burning, might +be filled with this mixture without any danger of an explosion. He +surrounded the flame of an oil-lamp with a cylinder of fine wire-gauze; +this lamp when brought into an atmosphere containing fire-damp and air +could not cause an explosion, because although small explosions might occur +in the interior of the wire cylinder, so much heat was conducted away by +the large metallic surface that the temperature of the explosive atmosphere +outside<span class='pagenum'><a name="Page_226" id="Page_226">[Pg 226]</a></span> the lamp could not attain that point at which explosion would +occur.</p> + +<p>In 1818 Sir Humphry Davy was made a baronet, in recognition of his great +services as the inventor of the safety-lamp; and in 1820 he was elected to +the most honourable position which can be held by a man of science in this +country, he became the President of the Royal Society.</p> + +<p>For seven years he was annually re-elected president, and during that time +he was the central figure in the scientific society of England. During +these years he continued his investigations chiefly on electro-chemical +subjects and on various branches of applied science. In 1826 his health +began to fail. An attack of paralysis in that year obliged him to +relinquish most of his work. He went abroad and travelled in Italy and the +Tyrol, sometimes strong enough to shoot or fish a little, or even to carry +on electrical experiments; sometimes confined to his room, or to gentle +exercise only. He resigned the presidentship of the Royal Society in 1827. +In 1828 he visited Rome, where he was again attacked by paralysis, and +thought himself dying, but he recovered sufficiently to attempt the journey +homeward. At Geneva he became very ill, and expired in that city on the +29th of May 1829.</p> + +<p>During these later years of illness and suffering, his intense love of and +delight in Nature were very apparent; he returned again to the simple +tastes and pleasures of his early days. His intimate<span class='pagenum'><a name="Page_227" id="Page_227">[Pg 227]</a></span> knowledge of natural +appearances and of the sights and sounds of country life is conspicuous in +the "Salmonia, or Days of Fly-fishing," written during his later years.</p> + +<p>Sir Humphry Davy was emphatically a genius. He was full of eager desire to +know the secrets of the world in which he lived; he looked around him with +wonder and delight, ever conscious of the vastness of the appearances which +met his gaze; an exuberance of life and energy marked his actions; +difficulties were encountered by him only to be overcome; he was depressed +by no misfortunes, deterred by no obstacles, led aside from his object by +no temptations, and held in bondage by no false analogies.</p> + +<p>His work must ever remain as a model to the student of science. A thorough +and careful foundation of fact is laid; on this, hypotheses are raised, to +be tested first by reasoning and argument, then by the tests of the +laboratory, which alone are final. Analogies are seized; hints are eagerly +taken up, examined, and acted on or dismissed. As he works in the +laboratory, we see his mind ranging over the whole field of chemical +knowledge, finding a solution of a difficulty here, or guessing at a +solution there; combining apparently most diverse facts; examining +phenomena which appear to have no connection; never dwelling too long on an +hypothesis which cannot yield some clue to the object of research, but +quickly discovering the road which will lead to the wished-for solution.<span class='pagenum'><a name="Page_228" id="Page_228">[Pg 228]</a></span></p> + +<p>Like so many great experimenters Davy accomplished wonders with little +apparatus. When he went abroad for the first time he took with him two +small boxes, one twenty, and the other twelve inches long, by about seven +inches wide and four deep. With the apparatus contained in these boxes he +established the elementary nature of iodine, and made a rough estimation of +its atomic weight; he determined many of its analogies with chlorine, +proving that, like chlorine, it is markedly electro-negative, and that its +compounds are decomposed by chlorine; he accomplished the synthesis of +hydriodic acid, and approximately determined the composition of iodide of +nitrogen. But when it was necessary to employ delicate or powerful +apparatus, he was able by the use of that also to obtain results of primary +importance. The decomposition of potash, soda, baryta, lime and strontia +could not have been effected had he not had at his command the resources of +a well-furnished laboratory.</p> + +<p>Davy has had no successor in England. Much useful and some brilliant work +has been done by English chemists since his day, but we still look back to +the first quarter of the century as the golden age of chemistry in this +country. On the roll wherein are written the names of England's greatest +sons, there is inscribed but a single chemist—Humphry Davy.</p> + +<hr style='width: 45%;' /> + +<p>I carried on the account of the work of Davy's great contemporary, +Berzelius, to the time when he<span class='pagenum'><a name="Page_229" id="Page_229">[Pg 229]</a></span> had fairly established dualistic views of +the structure of chemical compounds, and when, by the application of a few +simple rules regarding the combinations of elementary atoms, he had largely +extended the bounds of the atomic theory of Dalton.</p> + +<p>Berzelius also did important work in the domain of organic chemistry. By +numerous analyses of compounds of animal and vegetable origin, he clearly +established the fact that the same laws of combination, the same fixity of +composition, and the same general features of atomic structure prevail +among the so-called organic as among the inorganic compounds. In doing this +he broke down the artificial barrier which had been raised between the two +branches of the science, and so prepared the way for modern chemistry, +which has won its chief triumphs in the examination of organic compounds.</p> + +<p>By the many and great improvements which he introduced into analytical +chemistry, and by the publication of his "Textbook of Chemistry," which +went through several editions in French and German, and also of his yearly +report on the advance of chemistry, Berzelius exerted a great influence on +the progress of his favourite science. Wöhler tells us that when the spring +of the year came, at which time his annual report had to be prepared, +Berzelius shut himself up in his study, surrounded himself with books, and +did not stir from the writing-table until the work was done.<span class='pagenum'><a name="Page_230" id="Page_230">[Pg 230]</a></span></p> + +<p>In his later days Berzelius was much engaged in controversy with the +leaders of the new school, the rise and progress of which will be traced in +the next chapter, but throughout this controversy he found time to add many +fresh facts to those already known. He continued his researches until his +death in 1848.</p> + +<p>The work of the great Swedish chemist is characterized by thoroughness in +all its parts: to him every fact appeared to be of importance; although now +perhaps only an isolated fact, he saw that some day it would find a place +in a general scheme of classification. He worked in great measure on the +lines laid down by Dalton and Davy; the enormous number and accuracy of his +analyses established the law of multiple proportions on a sure basis, and +his attempts to determine the constitution of compound atoms, while +advancing the atomic theory of Dalton, drew attention to the all-important +distinction between atom and molecule, and so prepared chemists for the +acceptance of the generalization of Avogadro. The electro-chemical +conceptions of Davy were modified by Berzelius; they were shorn of +something of their elasticity, but were rendered more suited to be the +basis of a rigid theory.</p> + +<hr style='width: 45%;' /> + +<p>At the close of this transition period from the Lavoisierian to the modern +chemistry, we find analytical chemistry established as an art; we find the +atomic theory generally accepted, but we notice<span class='pagenum'><a name="Page_231" id="Page_231">[Pg 231]</a></span> the existence of much +confusion which has arisen from the non-acceptance of the distinction made +by Avogadro between atom and molecule; we find the analogies between +chemical affinity and electrical energy made the basis of a system of +classification which regards every compound atom (or molecule) as built up +of two parts, in one of which positive, and in the other negative +electricity predominates; and accompanying this system of classification we +find that an acid is no longer regarded as necessarily an oxygen compound, +but rather as a compound possessed of certain properties which are probably +due to the arrangement of the elementary atoms, among which hydrogen +appears generally to find a place; we find that salts are for the most part +regarded as metallic derivatives of acids; and we find that by the +decomposition of the supposed elementary substances, potash, soda, lime, +etc., the number of the elements has been extended, the application of a +new instrument of research has been brilliantly rewarded, and the +Lavoisierian description of "element" as the "attained, not the attainable, +limit of research" has been emphasized.</p> + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> The history and meaning of these terms is considered on p. +171, <i>et seq.</i></p></div> + +<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> For an explanation of this expression, "chemical affinity," +see p. 206, <i>et seq.</i></p></div> + +<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> These views have been already explained on pp. 182, 183.</p></div> +</div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_232" id="Page_232">[Pg 232]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap5.jpg" width="500" height="91" alt="" title="" /> +</div> + +<h2>CHAPTER V.</h2> + +<h3>THE WORK OF GRAHAM.</h3> + + +<h4><i>Thomas Graham</i>, 1805-1869.</h4> + +<p>The work of Graham, concerned as it mostly was with the development of the +conception of atoms, connects the time of Dalton with that in which we are +now living. I have therefore judged it advisable to devote a short chapter +to a consideration of the life-work of this chemist, before proceeding to +the third period of chemical advance, that, namely, which witnessed the +development of organic chemistry through the labours of men who were +Graham's contemporaries.</p> + +<p>The printed materials which exist for framing the story of Graham's life +are very meagre, but as he appears, from the accounts of his friends, to +have devoted himself entirely to scientific researches, we cannot go far +wrong in regarding the history of his various discoveries as also the +history of his life.</p> + + +<p><span class="smcap">Thomas Graham</span> was born in Glasgow, on<span class='pagenum'><a name="Page_233" id="Page_233">[Pg 233]</a></span> December 21, 1805. His father, James +Graham, a successful manufacturer, was in a position to give his son a good +education. After some years spent in the ordinary school training, Graham +entered Glasgow University at the early age of fourteen, and graduated as +M. A. five years later. It was the intention of Graham's father that his +son should enter the Scottish Church; but under the teaching of Dr. Thomas +Thomson and others the lad imbibed so strong a love of natural science, +that rather than relinquish the pursuit of his favourite study, he +determined to be independent of his father and make a living for himself. +His father was much annoyed at the determination of his son to pursue +science, and vainly attempted to force him into the clerical profession. +The quarrel between father and son increased in bitterness, and +notwithstanding the intervention of friends the father refused to make his +son any allowance for his maintenance; and although many years after a +reconcilement was effected, yet at the time when Graham most needed his +father's help he was left to struggle alone. Graham went to Edinburgh, +where he pursued his studies under Hope and Leslie, professors of chemistry +and physics respectively—men whose names were famous wherever natural +science was studied. Graham's mother, for whom he had always the greatest +respect and warmest love, and his sister Margaret helped him as best they +could during this trying time.<span class='pagenum'><a name="Page_234" id="Page_234">[Pg 234]</a></span></p> + +<p>The young student found some literary occupation and a little teaching in +Edinburgh, and sometimes he was asked to make investigations in subjects +connected with applied chemistry. Thus he struggled on for four or five +years, during which time he began to publish papers on chemico-physical +subjects. In the year 1829 he was appointed Lecturer on Chemistry at the +Mechanics' Institution in Glasgow, and next year he was removed to the more +important position of lecturer on the same science at the Andersonian +Institution in that city. This position he occupied for seven years, when +he was elected Professor of Chemistry in the University of London (now +University College): he had been elected to the Fellowship of the Royal +Society in the preceding year. During his stay at the Andersonian +Institution Graham had established his fame as a physical chemist; he had +begun his work on acids and salts, and had established the fundamental +facts concerning gaseous diffusion. These researches he continued in +London, and from 1837 to 1854 he enriched chemical science with a series of +papers concerned for the most part with attempts to trace the movements of +the atoms of matter.</p> + +<p>In 1854 Graham succeeded Sir John Herschel in the important and honourable +position of Master of the Mint. For some years after his appointment he was +much engaged with the duties of his office, but about 1860 he again +returned to his atomic studies, and in his papers on "Transpiration of +Liquids"<span class='pagenum'><a name="Page_235" id="Page_235">[Pg 235]</a></span> and on "Dialysis" he did much in the application of physical +methods to solve chemical problems, and opened up new paths, by travelling +on which his successors greatly advanced the limits of the science of +chemistry. Graham was almost always at work; his holidays were "few and far +between." By the year 1868 or so his general health began to grow feeble; +in the autumn of 1869, during a visit to Malvern where he sought repose and +invigorating air, he caught cold, which developed into inflammation of the +lungs. On his return to London the disease was overcome by medical +remedies, but he continued very weak, and gradually sank, till the end came +on the 16th of September 1869.</p> + +<p>I have said that the seven years during which Graham held the lectureship +on chemistry in the Andersonian Institution, Glasgow, witnessed the +beginning alike of his work on salts and of that on gaseous diffusion. He +showed that there exists a series of compounds of various salts, <i>e.g.</i> +chloride of calcium, chloride of zinc, etc., with alcohol. He compared the +alcohol in these salts, which he called <i>alcoates</i>, to the water in +ordinary crystallized salts, and thus drew the attention of chemists to the +important part played by water in determining the properties of many +substances. Three years later (1833) appeared one of his most important +papers, bearing on the general conception of acids: "Researches on the +Arseniates, Phosphates, and Modifications of Phosphoric Acid." Chemists at +this time knew that phosphoric acid—that is, the substance<span class='pagenum'><a name="Page_236" id="Page_236">[Pg 236]</a></span> obtained by +adding water to pentoxide of phosphorus—exhibited many peculiarities, but +they were for the most part content to leave these unexplained. Graham, +following up the analogy which he had already established between water and +bases, prepared and carefully determined the composition of a series of +phosphates, and concluded that pentoxide of phosphorus is able to combine +with a base—say soda—in three different proportions, and thus to produce +three different phosphates of soda. But as Graham accepted that view which +regards a salt as a metallic derivative of an acid, he supposed that three +different phosphoric acids ought to exist; these acids he found in the +substances produced by the action of water on the oxide of phosphorus. He +showed that just as the oxide combines with a base in three proportions, so +does it combine with water in three proportions. This water he regarded as +chemically analogous to the base in the three salts, one atom (we should +now rather say molecule) of base could be replaced by one atom of water, +two atoms of base by two atoms of water, or three atoms of base by three +atoms of water. Phosphoric acid was therefore regarded by Graham as a +compound of pentoxide of phosphorus and water, the latter being as +essentially a part of the acid as the former. He distinguished between +<i>monobasic</i>, <i>dibasic</i>, and <i>tribasic</i> phosphoric acids: by the action of a +base on the <i>monobasic acid</i>, one, and only one salt was produced; the +<i>dibasic acid</i> could furnish two salts,<span class='pagenum'><a name="Page_237" id="Page_237">[Pg 237]</a></span> containing different proportions +(or a different number of atoms) of the same base: and from the <i>tribasic +acid</i> three salts, containing the same base but in different proportions, +could be obtained.</p> + +<p>Davy's view of an acid as a compound of water with a negative oxide was +thus confirmed, and there was added to chemical science the conception of +<i>acids of different basicity</i>.</p> + +<p>In 1836 Graham's paper on "Water as a Constituent of Salts" was published +in the "Transactions of the Royal Society of Edinburgh." In this paper he +inquires whether the water in crystalline salts can or cannot be removed +without destroying the chemical individuality of the salts. He finds that +in some crystalline salts part of the water can be easily removed by the +application of heat, but the remainder only at very high temperatures. He +distinguishes between those atoms of water which essentially belong to the +compound atom of the salt, and those atoms which can be readily removed +therefrom, which are as it were added on to, or built up around the +exterior of the atom of salt. In this paper Graham began to distinguish +what is now called <i>water of crystallization</i> from <i>water of constitution</i>, +a distinction pointed to by some of Davy's researches, but a distinction +which has remained too much a mere matter of nomenclature since the days of +Graham.</p> + +<p>In these researches Graham emphasized the necessity of the presence of +hydrogen in all true acids; as he had drawn an analogy between water and<span class='pagenum'><a name="Page_238" id="Page_238">[Pg 238]</a></span> +bases, so now he saw in the hydrogen of acids the analogue of the metal of +salts. He regarded the structure of the compound atom of an acid as similar +to that of the compound atom of a salt; the hydrogen atom, or atoms, in the +acid was replaced by a metallic atom, or atoms, and so a compound atom of +the salt was produced.</p> + +<p>Davy and Berzelius had proved that hydrogen is markedly electro-positive; +hydrogen appeared to Graham to belong to the class of metals. In making +this bold hypothesis Graham necessarily paid little heed to those +properties of metals which appeal to the senses of the observer. Metals, as +a class, are lustrous, heavy, malleable substances; hydrogen is a +colourless, inodourless, invisible, very light gas: how then can hydrogen +be said to be metallic?</p> + +<p>I have again and again insisted on the need of imagination for the +successful study of natural science. Although in science we deal with +phenomena which we wish to measure and weigh and record in definite and +precise language, yet he only is the successful student of science who can +penetrate beneath the surface of things, who can form mental pictures +different from those which appear before his bodily eye, and so can discern +the intricate and apparently irregular analogies which explain the +phenomena he is set to study.</p> + +<p>Graham was not as far as we can learn endowed, like Davy, with the +sensitive nature of a poet, yet his work on hydrogen proves him to have<span class='pagenum'><a name="Page_239" id="Page_239">[Pg 239]</a></span> +possessed a large share of the gift of imagination. Picturing to himself +the hydrogen atom as essentially similar in its chemical functions to the +atom of a metal, he tracked this light invisible gas through many tortuous +courses: he showed how it is absorbed and retained (<i>occluded</i> as he said) +by many metals; he found it in meteors which had come from far-away regions +of space; and at last, the year before he died he prepared an alloy of +palladium and the metal hydrogen, from which a few medals were struck, +bearing the legend "Palladium-Hydrogenium 1869."</p> + +<p>Within the last few years hydrogen has been liquified and, it is said, +solidified. Solid hydrogen is described as a steel-grey substance which +fell upon the table with a sound like the ring of a metal.</p> + +<p>But Graham's most important work was concerned with the motion of the +ultimate particles of bodies.</p> + +<p>He uses the word "atom" pretty much as Dalton did. He does not make a +distinction between the atom of an element and the atom of a compound, but +apparently uses the term as a convenient one to express the smallest +undivided particle of any chemical substance which exhibits the properties +of that substance. As Graham was chiefly concerned with the physical +properties of chemical substances, or with those properties which are +studied alike by chemistry and physics, the distinction between atom and +molecule, so all-important<span class='pagenum'><a name="Page_240" id="Page_240">[Pg 240]</a></span> in pure chemistry, might be, and to a great +extent was, overlooked by him. In considering his work we shall however do +well to use the terms "atom" and "molecule" in the sense in which they are +now always used in chemistry, a sense which has been already discussed (see +pp. 139-143).</p> + +<p>Many years before Graham began his work a curious fact had been recorded +but not explained. In 1823 Döbereiner filled a glass jar with hydrogen and +allowed the jar to stand over water: on returning after twelve hours he +found that the water had risen about an inch and a half into the jar. Close +examination of the jar showed the presence of a small crack in the glass. +Many jars, tubes and flasks, all with small cracks in the glass, were +filled with hydrogen and allowed to stand over water; in every case the +water rose in the vessel. No rise of the water was however noticeable if +the vessels were filled with ordinary air, nitrogen or oxygen.</p> + +<p>In 1831 Graham began the investigation of the peculiar phenomenon observed +by Döbereiner. Repeating Döbereiner's experiments, Graham found that a +portion of the hydrogen in the cracked vessels passed outwards through the +small fissures, and a little air passed inwards: the water therefore rose +in the jar, tube or flask, because there was a greater pressure on the +surface of the water outside than upon that inside the vessel. Any gas +lighter than air behaved like hydrogen; when gases heavier than air were +employed the level of the<span class='pagenum'><a name="Page_241" id="Page_241">[Pg 241]</a></span> water inside the vessel was slightly lowered +after some hours.</p> + +<p>Graham found that the passage of gases through minute openings could be +much more accurately studied by placing the gas to be examined in a glass +tube one end of which was closed by a plug of dry plaster of Paris, than by +using vessels with small fissures in the glass.</p> + +<p>The <i>diffusion-tube</i> used by Graham generally consisted of a piece of glass +tubing, graduated in fractions of a cubic inch and having a bulb blown near +one end; the short end was closed by a thin plug of dry plaster of Paris +(gypsum), the tube was filled with the gas to be examined, and the open end +was immediately immersed in water. The water was allowed to rise until it +had attained a constant level, when it was found that the whole of the gas +originally in the tube had passed outwards through the porous plug, and air +had passed inwards. The volume of gas originally in the tube being known, +and the volume of air in the tube at the close of the experiment being +measured, it was only necessary to divide the former by the latter number +in order to obtain the number of volumes of gas which had passed outwards +for each one volume of air which had passed inwards; in other words to +obtain the <i>rate of diffusion</i> compared with air of the gas under +examination.</p> + +<p>Graham's results were gathered together in the statement, "The +diffusion-rates of any two gases are inversely as the square roots of their +densities."<span class='pagenum'><a name="Page_242" id="Page_242">[Pg 242]</a></span> Thus, take oxygen and hydrogen: oxygen is sixteen times +heavier than hydrogen, therefore hydrogen diffuses four times more rapidly +than oxygen. Take hydrogen and air: the specific gravity of hydrogen is +0·0694, air being 1; the square root of 0·0694 is 0·2635, therefore +hydrogen will diffuse more rapidly than air in the ratio of 0·2635:1.</p> + +<p>In the years 1846-1849 Graham resumed this inquiry; he now distinguished +between <i>diffusion</i>, or the passage of gases through porous plates, and +<i>transpiration</i>, or the passage of gases through capillary tubes. He showed +that if a sufficiently large capillary tube be employed the rate of +transpiration of a gas becomes constant, but that it is altogether +different from the rate of diffusion of the same gas. He established the +fact that there is a connection of some kind between the +transpiration-rates and the chemical composition of gases, and in doing +this he opened up a field of inquiry by cultivating which many important +results have been gained within the last few years, and which is surely +destined to yield more valuable fruit in the future.</p> + +<p>Returning to the diffusion of gases, Graham, after nearly thirty years' +more or less constant labour, begins to speculate a little on the causes of +the phenomena he had so studiously and perseveringly been examining. In his +paper on "The Molecular Mobility of Gases," read to the Royal Society in +1863, after describing a new diffusion-tube wherein thin plates of +artificial graphite were used in place<span class='pagenum'><a name="Page_243" id="Page_243">[Pg 243]</a></span> of plaster of Paris, Graham says, +"The pores of artificial graphite appear to be really so minute that a gas +<i>in mass</i> cannot penetrate the plate at all. It seems that molecules only +can pass; and they may be supposed to pass wholly unimpeded by friction, +for the smallest pores that can be imagined to exist in the graphite must +be tunnels in magnitude to the ultimate atom of a gaseous body." He then +shortly describes the molecular theory of matter, and shows how this +theory—a sketch of which so far as it concerns us in this book has been +given on pp. 123-125—explains the results which he has obtained. When a +gas passed through a porous plate into a vacuum, or when one gas passed in +one direction and another in the opposite direction through the same plate, +Graham saw the molecules of each gas rushing through the "tunnels" of +graphite or stucco. The average rate at which the molecules of a gas rushed +along was the diffusion-rate of that gas. The lighter the gas the more +rapid was the motion of its molecules. If a mixture of two gases, one much +lighter than the other, were allowed to flow through a porous plate, the +lighter gas would pass so much more quickly than the heavier gas that a +partial separation of the two might probably be effected. Graham +accomplished such a separation of oxygen and hydrogen, and of oxygen and +nitrogen; and he described a simple instrument whereby this process of +<i>atmolysis</i>, as he called it, might be effected.<span class='pagenum'><a name="Page_244" id="Page_244">[Pg 244]</a></span></p> + +<p>Graham's <i>tube atmolyser</i> consisted of a long tobacco-pipe stem placed +inside a rather shorter and considerably wider tube of glass; the pipe stem +was fixed by passing through two corks, one at each end of the glass tube; +through one of these corks there also passed a short piece of glass tubing. +When the instrument was employed, the piece of short glass tubing was +connected with an air-pump, and one end of the pipe stem with the gaseous +mixture—say ordinary air. The air-pump being set in motion, the gaseous +mixture was allowed to flow slowly through the pipe stem; the lighter +ingredient of the mixture passed outwards through the pipe stem into the +wide glass tube more rapidly than the heavier ingredient, and was swept +away to the air-pump; the heavier ingredient could be collected, mixed with +only a small quantity of the lighter, at the other end of the pipe stem. As +Graham most graphically expressed it, "The stream of gas diminishes as it +proceeds, like a river flowing over a pervious bed."</p> + +<p>Graham then contrived a very simple experiment whereby he was able to +measure the rate of motion of the molecules of carbonic acid. He introduced +a little carbonic acid into the lower part of a tall cylindrical jar, and +at the close of certain fixed periods of time he determined the amount of +carbonic acid which had diffused upwards through the air into the uppermost +layer of the jar. Knowing the height of the jar, he now knew the distance +through which a small portion of<span class='pagenum'><a name="Page_245" id="Page_245">[Pg 245]</a></span> carbonic acid passed in a stated time, +and regarding this small portion as consisting of a great many molecules, +all moving at about equal rates, he had determined the average velocity of +the molecules of carbonic acid. A similar experiment was performed with +hydrogen. The general results were that the molecules of carbonic acid move +about in still air with a velocity equal to seventy-three millimetres per +minute, and that under the same conditions the molecules of hydrogen move +with a velocity equal to about one-third of a metre per minute.<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a></p> + +<p>The Bakerian Lecture for 1849, read by Graham before the Royal Society, was +entitled "On the Diffusion of Liquids." In this paper he describes a very +large number of experiments made with a view to determine the rate at which +a salt in aqueous solution diffuses, or passes upwards into a layer of pure +water above it, the salt solution and the water not being separated by any +intervening medium. Graham's method of procedure consisted in completely +filling a small bottle with a salt solution of known strength, placing this +bottle in a larger graduated vessel, and carefully filling the latter with +water. Measured portions of the water in the larger vessel were withdrawn +at stated intervals, and the quantity of salt in each portion was +determined. Graham found that under these conditions salts diffused with +very<span class='pagenum'><a name="Page_246" id="Page_246">[Pg 246]</a></span> varying velocities. Groups of salts showed equal rates of diffusion. +There appeared to be no definite connection between the molecular weights +of the salts and their diffusion-rates; but as Graham constantly regarded +diffusion, whether of gases or liquids, as essentially due to the movements +of minute particles, he thought that the particles which moved about as +wholes during diffusion probably consisted of groups of what might be +called chemical molecules—in other words, Graham recognized various orders +of small particles. As the atom was supposed to have a simpler structure +than the molecule (if indeed it had a structure at all), so there probably +existed groups of molecules which, under certain conditions, behaved as +individual particles with definite properties.</p> + +<p>As Graham applied the diffusion of gases to the separation of two gases of +unequal densities, so he applied the diffusion of liquids to the separation +of various salts in solution. He showed also that some complex salts, such +as the alums, were partially separated into their constituents during the +process of diffusion.</p> + +<p>The prosecution of these researches led to most important results, which +were gathered together in a paper on "Liquid Diffusion applied to +Analysis," read to the Royal Society in 1861.</p> + +<p>Graham divided substances into those which diffused easily and quickly into +water, and those which diffused very slowly; he showed that the<span class='pagenum'><a name="Page_247" id="Page_247">[Pg 247]</a></span> former +were all crystallizable substances, while the latter were +non-crystallizable jelly-like bodies. Graham called these jelly-like +substances <i>colloids;</i> the easily diffusible substances he called +<i>crystalloids</i>. He proved that a colloidal substance acts towards a +crystalloid much as water does; that the crystalloid rapidly diffuses +through the colloid, but that colloids are not themselves capable of +diffusing through other colloids. On this fact was founded Graham's process +of <i>dialysis</i>. As colloid he employed a sheet of parchment paper, which he +stretched on a ring of wood or caoutchouc, and floated the apparatus so +constructed—<i>the dialyser</i>—on the surface of pure water in a glass dish; +he then poured into the dialyser the mixture of substances which it was +desired to separate. Let us suppose that this mixture contained sugar and +gum; the crystalloidal sugar soon passed through the parchment paper, and +was found in the water outside, but the colloidal gum remained in the +dialyser.</p> + +<p>If the mixture in the dialyser contained two crystalloids, the greater part +of the more diffusible of these passed through the parchment in a short +time along with only a little of the less diffusible; a partial separation +was thus effected.</p> + +<p>This method of dialysis was applied by Graham to separate and obtain in the +pure state many colloidal modifications of chemical compounds, such as +aluminium and tin hydrates, etc. By his study of these peculiar substances +Graham introduced<span class='pagenum'><a name="Page_248" id="Page_248">[Pg 248]</a></span> into chemistry a new class of bodies, and opened up +great fields of research.</p> + +<p>Matter in the colloidal state appears to be endowed with properties which +are quite absent, or are hidden, when it is in the ordinary crystalloidal +condition. Colloids are readily affected by the smallest changes in +external conditions; they are eminently unstable bodies; they are, Graham +said, always on the verge of an impending change, and minute disturbances +in the surrounding conditions may precipitate this change at any moment. +Crystalloids, on the other hand, are stable; they have definite properties, +which are not changed without simultaneous large changes in surrounding +conditions. But although, to use Graham's words, these classes of bodies +"appear like different worlds of matter," there is yet no marked separating +line between them. Ice is a substance which under ordinary conditions +exhibits all the properties of crystalloids, but ice formed in contact with +water just at the freezing point is not unlike a mass of partly dried gum; +it shows no crystalline structure, but it may be rent and split like a lump +of glue, and, like glue, the broken pieces may be pressed together again +and caused to adhere into one mass.</p> + +<p>"Can any facts," asks Graham, "more strikingly illustrate the maxim that in +Nature there are no abrupt transitions, and that distinctions of class are +never absolute?"</p> + +<p>In the properties of colloids and crystalloids<span class='pagenum'><a name="Page_249" id="Page_249">[Pg 249]</a></span> Graham saw an index of +diversity of molecular structure. The smallest individual particle of a +colloid appeared to him to be a much more complex structure than the +smallest particle of a crystalloid. The colloidal molecule appeared to be +formed by the gathering together of several crystalloidal molecules; such a +complex structure might be expected readily to undergo change, whereas the +simpler molecule of a crystalloid would probably present more definite and +less readily altered properties.</p> + +<p>In this research Graham had again, as so often before, arrived at the +conception of various orders of small particles. In the early days of the +Daltonian theory it seemed that the recognition of atoms as ultimate +particles, by the placing together of which masses of this or that kind of +matter are produced, would suffice to explain all the facts of chemical +combinations; but Dalton's application of the term "atom" to elements and +compounds alike implied that an atom might itself have parts, and that one +atom might be more complex than another. The way was thus already prepared +for the recognition of more than one order of atoms, a recognition which +was formulated three years after the appearance of Dalton's "New System" in +the statement of Avogadro, "Equal volumes of gases contain equal numbers of +molecules;" for we have seen that the application of this statement to +actually occurring reactions between gases obliges us to admit that the +molecules of hydrogen, oxygen<span class='pagenum'><a name="Page_250" id="Page_250">[Pg 250]</a></span> and many other elementary gases are composed +of two distinct parts or atoms.</p> + +<p>Berzelius it is true did not formally accept the generalization of +Avogadro; but we have seen how the conception of atom which runs through +his work is not that of an indivisible particle, but rather that of a +little individual part of matter with definite properties, from which the +mass of matter recognizable by our senses is constructed, just as the wall +is built up of individual bricks. And as the bricks are themselves +constructed of clay, which in turn is composed of silica and alumina, so +may each of these little parts of matter be constructed of smaller parts; +only as clay is not brick, and neither silica nor alumina is clay, so the +properties of the parts of the atom—if it has parts—are not the +properties of the atom, and a mass of matter constructed of these parts +would not have the same properties as a mass of matter constructed of the +atoms themselves.</p> + +<p>Another feature of Graham's work is found in the prominence which he gives +to that view of a chemical compound which regards it as the resultant of +the action and reaction of the parts of the compound. As the apparent +stability of chemical compounds was seen by Davy to be the result of an +equilibrium of contending forces, so did the seemingly changeless character +of any chemical substance appear to Graham as due to the orderly changes +which are continually proceeding among the molecules of which the substance +is constructed.<span class='pagenum'><a name="Page_251" id="Page_251">[Pg 251]</a></span></p> + +<p>A piece of lime, or a drop of water, was to the mind of Graham the scene of +a continual strife, for that minute portion of matter appeared to him to be +constructed of almost innumerable myriads of little parts, each in more or +less rapid motion, one now striking against another and now moving free for +a little space. Interfere with those movements, alter the mutual action of +those minute particles, and the whole building would fall to pieces.</p> + +<p>For more than thirty years Graham was content to trace the movements of +molecules. During that time he devoted himself, with an intense and +single-minded devotion, to the study of molecular science. Undaunted in +early youth by the withdrawal of his father's support; unseduced in his +middle age by the temptations of technical chemistry, by yielding to which +he would soon have secured a fortune; undazzled in his later days by the +honours of the position to which he had attained; Graham dedicated his life +to the nobler object of advancing the bounds of natural knowledge, and so +adding to those truths which must ever remain for the good and furtherance +of humanity.</p> + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> A metre is equal to about thirty-nine inches; a millimetre is +the one-thousandth part of a metre.</p></div> +</div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_252" id="Page_252">[Pg 252]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap6.jpg" width="500" height="102" alt="" title="" /> +</div> + +<h2>CHAPTER VI.</h2> + +<h3>RISE AND PROGRESS OF ORGANIC CHEMISTRY—PERIOD OF LIEBIG AND DUMAS.</h3> + + +<h4><i>Justus Liebig, 1803-1873. Jean Baptiste André Dumas, born in 1800.</i></h4> + +<p>I have as yet said almost nothing with regard to the progress of organic +chemistry, considered as a special branch of the science. It is however in +this department that the greatest triumphs which mark the third period of +chemical advance have been won. We must therefore now turn our attention to +the work which has been done here.</p> + +<p>The ancients drew no such distinction between portions of their chemical +knowledge, limited as it was, as is implied by the modern terms "organic" +and "inorganic chemistry." An organic acid—acetic—was one of the earliest +known substances belonging to the class of acids; many processes of +chemical handicraft practised in the olden times dealt with the manufacture +of substances, such as soap,<span class='pagenum'><a name="Page_253" id="Page_253">[Pg 253]</a></span> leather or gum, which we should now call +organic substances. Nor did the early alchemists, although working chiefly +with mineral or inorganic substances, draw any strict division between the +two branches of chemistry. The medical chemists of the sixteenth century +dealt much with substances derived from plants and animals, such as benzoic +and succinic acids, spirit of wine, oils, etc. But neither in their +nomenclature nor in their practice did they sharply distinguish inorganic +from organic compounds. They spoke of the <i>quintessence</i> of arsenic and the +<i>quintessence</i> of alcohol; they applied the term "oil" alike to the +products of the action of acids on metallic salts and to substances +obtained from vegetables. But towards the end of the seventeenth century, +at the time that is when the phlogistic theory began to gain pre-eminence, +we find gradually springing up a division of chemical substances into +mineral, animal and vegetable substances—a division which was based rather +on a consideration of the sources whence the substances were derived than +on the properties of the substances themselves, and therefore a division +which was essentially a non-chemical one.</p> + +<p>About a century after this, systematic attempts began to be made to trace +some peculiarity of composition as belonging to all compounds of organic, +that is, of animal or vegetable, origin. As very many of the substances +then known belonging to this class were more or less oil-like in their<span class='pagenum'><a name="Page_254" id="Page_254">[Pg 254]</a></span> +properties—oils, fats, balsams, gums, sugar, etc.—organic substances +generally were said to be characterized by the presence in them of the +<i>principle of oil</i>.</p> + +<p>Such a statement as this, although suited to the conceptions of that time, +could not be received when Lavoisier had shown chemists how Nature ought be +examined. With the definite conception of element introduced by the new +chemistry, came an attempt to prove that organic compounds were built up of +elements which were rarely found together in any one compound of inorganic +origin. Substances of vegetable origin were said by Lavoisier to be +composed of carbon, hydrogen and oxygen, while phosphorus and nitrogen, in +addition to those three elements, entered into the composition of +substances derived from animals. But neither could this definition of +organic compounds be upheld in the face of facts. Wax and many oils +contained only carbon and hydrogen, yet they were undoubtedly substances of +vegetable or animal origin. If the presence of any two of the three +elements, carbon, hydrogen and oxygen, were to be regarded as a sufficient +criterion for the classification of a compound, then it was necessary that +carbonic acid—obtained by the action of a mineral acid on chalk—should be +called an organic compound.</p> + +<p>To Berzelius belongs the honour of being the chemist who first applied the +general laws of chemical combination to all compounds alike,<span class='pagenum'><a name="Page_255" id="Page_255">[Pg 255]</a></span> whether +derived from minerals, animals, or vegetables. The ultimate particles, or +molecules, of every compound were regarded by Berzelius as built up of two +parts, each of which might itself be an elementary atom, or a group of +elementary atoms. One of these parts, he said, was characterized by +positive, the other by negative electricity. Every compound molecule, +whatever was the nature or number of the elementary atoms composing it, was +a dual structure (see p. 164). Organic chemistry came again to be a term +somewhat loosely applied to the compounds derived from animals or +vegetables, or in the formation of which the agency of living things was +necessary. Most, if not all of these compounds contained carbon and some +other element or elements, especially hydrogen, oxygen and nitrogen.</p> + +<p>But the progress of this branch of chemistry was impeded by the want of any +trustworthy methods for analysing compounds containing carbon, oxygen and +hydrogen. This want was to be supplied, and the science of organic +chemistry, and so of chemistry in general, was to be immensely advanced by +the labours of a new school of chemists, chief among whom were Liebig and +Dumas.</p> + +<p>Let us shortly trace the work of these two renowned naturalists. The +life-work of the first is finished; I write this story of the progress of +his favourite science on the eighty-second birthday of the second of these +great men, who is still with us a veteran crowned with glory, a true +soldier in the<span class='pagenum'><a name="Page_256" id="Page_256">[Pg 256]</a></span> battle against ignorance and so against want and crime.</p> + +<hr style='width: 45%;' /> + +<p><span class="smcap">Justus Liebig</span> was born at Darmstadt, on the 12th of May 1803. The main +facts which mark his life regarded apart from his work as a chemist are +soon told. Showing a taste for making experiments he was apprenticed by his +father to an apothecary. Fortunately for science he did not long remain as +a concoctor of drugs, but was allowed to enter the University of Bonn as a +student of medicine. From Bonn he went to Erlangen, at which university he +graduated in 1821. A year or two before this time Liebig had begun his +career as an investigator of Nature, and he had already made such progress +that the Grand Duke of Hesse-Darmstadt was prevailed on to grant him a +small pension and allow him to prosecute his researches at Paris, which was +then almost the only place where he could hope to find the conditions of +success for the study of scientific chemistry. To Paris accordingly he went +in 1823. He was so fortunate—thanks to the good graces of the renowned +naturalist Alexander von Humboldt—as to be allowed to enter the laboratory +of Gay-Lussac, where he continued the research on a class of explosive +compounds, called <i>fulminates</i>, which he had begun before leaving +Darmstadt.</p> + +<p>A year later Liebig was invited to return to his native country as +Professor of Chemistry in the small University of Giessen—a name soon to<span class='pagenum'><a name="Page_257" id="Page_257">[Pg 257]</a></span> +be known wherever chemistry was studied, and now held dear by many eminent +chemists who there learned what is meant by the scientific study of Nature.</p> + +<p>The year before Liebig entered the laboratory of Gay-Lussac there came to +Paris a young and enthusiastic student who had already made himself known +in the scientific world by his physiological researches, and who was now +about to begin his career as a chemist.</p> + +<p>In that southern part of France which is rich in memories of the Roman +occupation, not far from the remains of the great aqueduct which spans the +valley of the Gardon, at no great distance from the famous cities of Arles +and Nîmes, was born, in the town of Alais, on the 14th of July 1800, <span class="smcap">Jean +Baptiste André Dumas</span>.</p> + +<p>The father of Dumas was a man of considerable culture; he gave his son as +good an education as could be obtained in the little town of his birth. At +the age of fourteen young Dumas was a good classical scholar, and had +acquired a fair knowledge of natural science. But for his deficiency in +mathematics he would probably have entered for the examination which +admitted those who passed it to join the French navy. But before he had +made good his mathematical deficiencies the troublous nature of the times +(1814-15) obliged his parents to think of some other profession for their +son which would entail less sacrifice on their part.</p> + +<p>Like his great fellow-worker in after life he was<span class='pagenum'><a name="Page_258" id="Page_258">[Pg 258]</a></span> apprenticed to an +apothecary, and like him also, he soon forsook this sphere of usefulness.</p> + +<p>Desirous of better opportunities for the study of science, and overpowered +by the miseries which war had brought upon the district of his birth, Dumas +persuaded his father to allow him to go to Geneva. At Geneva Dumas found an +atmosphere more suited to his scientific progress; chemistry, physics, +botany, and other branches of natural science were taught by men whose +names were everywhere known. He began experiments in chemistry with the +crudest and most limited apparatus, but even with these he made discoveries +which afterwards led to important work on the volumes occupied by the atoms +of elementary substances.</p> + +<p>About the year 1818 Dumas became acquainted with Dr. J. L. Prévost, who had +returned from studying in many of the most famous medical schools of +Europe. Invited by Prévost to join in an investigation requiring medical, +botanical and chemical knowledge, Dumas now began a series of researches +which soon passed into the domain of animal physiology, and by the +prosecution of which under many difficulties he laid the foundations of his +future fame.</p> + +<p>But along with his physiological work Dumas carried on a research into the +expansion of various ethers. This necessitated the preparation of a series +of ethers in a state of purity; but so difficult did Dumas find this to be, +so much time did he<span class='pagenum'><a name="Page_259" id="Page_259">[Pg 259]</a></span> consume in this preliminary work, and so interested +did he become in the chemical part of the investigation, that he abandoned +the experiments on expansion, and set himself to solve some of the problems +presented by the composition and chemical properties of the ethers.</p> + +<p>Dumas would probably have remained in Geneva had he not had a morning visit +paid him in the year 1822. When at work in his laboratory one day, some one +knocked and was bidden come in. "I was surprised to find myself face to +face with a gentleman in a light-blue coat with metal buttons, a white +waistcoat, nankeen breeches, and top-boots.... The wearer of this costume, +his head somewhat bent, his eyes deep-set but keen, advanced with a +pleasant smile, saying, 'Monsieur Dumas.' 'The same, sir; but excuse me.' +'I am M. de Humboldt, and did not wish to pass through Geneva without +having had the pleasure of seeing you.'... I had only one chair. My visitor +was pleased to accept it, whilst I resumed my elevated perch on the drawing +stool.... 'I intend,' said M. de Humboldt, 'to spend some days in Geneva, +to see old friends and to make new ones, and more especially to become +acquainted with young people who are beginning their career. Will you act +as my cicerone? I warn you however that my rambles begin early and end +late. Now, could you be at my disposal, say from six in the morning till +midnight?'" After some days spent as Humboldt had indicated the great +naturalist left Geneva.<span class='pagenum'><a name="Page_260" id="Page_260">[Pg 260]</a></span> Dumas tells us that the town seemed empty to him. +"I felt as if spell-bound. The memorable hours I had spent with that +irresistible enchanter had opened a new world to my mind." Dumas felt that +he must go to Paris—that there he would have more scope and more +opportunities for prosecuting science. A few kind words, a little genuine +sympathy, and a little help from Humboldt were thus the means of fairly +launching in their career of scientific inquiry these two young men, Liebig +and Dumas.</p> + +<p>In Paris, whither he went in 1823, Dumas found a welcome. He soon made the +acquaintance and gained the friendship of the great men who then made +natural science so much esteemed in the French capital. When the year 1826 +came, it saw him Professor of Chemistry at the Athenæum, and married to the +lady whom he loved, and who has ever since fought the battle of life by his +side.</p> + +<p>Liebig left Paris in 1824. By the year 1830 he had perfected and applied +that method for the analysis of organic compounds which is now in constant +use wherever organic chemistry is studied; by the same year Dumas had given +the first warning of the attack which he was about to make on the great +structure of dualism raised by Berzelius. In a paper, "On Some Points of +the Atomic Theory," published in 1826, Dumas adopted the distinction made +by Avogadro between molecules and atoms, or between the small particles of +substances which remain undivided during physical actions, and the<span class='pagenum'><a name="Page_261" id="Page_261">[Pg 261]</a></span> +particles, smaller than these, which are undivided during chemical actions. +But, unfortunately, Dumas did not mark these two conceptions by names +sufficiently definite to enable the readers of his memoir to bear the +distinction clearly in mind. The terms "atom" and "molecule" were not +introduced into chemistry with the precise meanings now attached to them +until some time after 1826.</p> + +<p>Although the idea of two orders of small particles underlies all the +experimental work described by Dumas in this paper, yet the numbers which +he obtained as representing the actual atomic weights of several +elements—<i>e.g.</i> phosphorus, arsenic, tin, silicon—show that he had not +himself carried out Avogadro's hypothesis to its legitimate conclusions.</p> + +<p>Two years after this Dumas employed the reaction wherein two volumes of +gaseous hydrochloric acid are produced by the union of one volume of +hydrogen with one volume of chlorine, as an argument which obliged him to +conclude that, if Avogadro's physical hypothesis be accepted, the molecules +of hydrogen and chlorine split, each into two parts, when these gases +combine chemically. But Dumas did not at this time conclude that the +molecular weight of hydrogen must be taken as twice its atomic weight, and +that—hydrogen being the standard substance—the molecular weights of all +gases must be represented by the specific gravities of these gases, +referred to hydrogen as 2.</p> + +<p>I have already shortly discussed the method for finding the relative +weights of elementary atoms<span class='pagenum'><a name="Page_262" id="Page_262">[Pg 262]</a></span> which is founded on Avogadro's hypothesis, +and, I think, have shown that this hypothesis leads to the definition of +"atom" as the smallest amount of an element in one molecule of any compound +of that element (see p. 142).</p> + +<p>This deduction from Avogadro's law is now a part and parcel of our general +chemical knowledge. We wonder why it was not made by Dumas; but we must +remember that a great mass of facts has been accumulated since 1826, and +that this definition of "atom" has been gradually forced on chemists by the +cumulative evidence of those facts.</p> + +<p>One thing Dumas did do, for which the thanks of every chemist ought to be +given him; he saw the need of a convenient method for determining the +densities of compounds in the gaseous state, and he supplied this need by +that simple, elegant and trustworthy method, still in constant use, known +as <i>Dumas's vapour density process</i>.</p> + +<p>While Dumas was working out the details of this analytical method, which +was destined to be so powerful an instrument of research, Liebig was +engaged in similar work; he was perfecting that process for the analysis of +organic compounds which has since played so important a part in the +advancement of this branch of chemical science. The processes in use during +the first quarter of this century for determining the amounts of carbon, +hydrogen, and oxygen in compounds of those elements, were difficult to +conduct and gave untrustworthy<span class='pagenum'><a name="Page_263" id="Page_263">[Pg 263]</a></span> results. Liebig adopted the principle of +the method used by Lavoisier, viz. that the carbon in a compound can be +oxidized, or burnt, to carbonic acid, and the hydrogen to water. He +contrived a very simple apparatus wherein this burning might be effected +and the products of the burning—carbonic acid and water—might be arrested +and weighed. Liebig's apparatus remains now essentially as it was presented +to the chemical world in 1830. Various improvements in details have been +made; the introduction of gas in place of charcoal as a laboratory fuel has +given the chemist a great command over the process of combustion, but in +every part of the apparatus to-day made use of in the laboratory is to be +traced the impress of the master's hand. A weighed quantity of the +substance to be analyzed is heated with oxide of copper in a tube of hard +glass; the carbon is burnt to carbonic acid and the hydrogen to water at +the expense of the oxygen of the copper oxide. Attached to the combustion +tube is a weighed tube containing chloride of calcium, a substance which +greedily combines with water, and this tube is succeeded by a set of three +or more small bulbs, blown in one piece of glass, and containing an aqueous +solution of caustic potash, a substance with which carbonic acid readily +enters into combination. The chloride of calcium tube and the potash bulbs +are weighed before and after the experiment; the increase in weight of the +former represents the amount of<span class='pagenum'><a name="Page_264" id="Page_264">[Pg 264]</a></span> water, and the increase in weight of the +latter the amount of carbonic acid obtained by burning a given weight of +the compound under examination. As the composition of carbonic acid and of +water is known, the amounts of carbon and of hydrogen in one hundred parts +of the compound are easily found; the difference between the sum of these +and one hundred represents the amount of oxygen in one hundred parts of the +compound. If the compound should contain elements other than these three, +those other elements are determined by special processes, the oxygen being +always found by difference.</p> + +<p>Soon after his settlement at Giessen Liebig turned his attention to a class +of organic compounds known as the <i>cyanates</i>; but Wöhler—who, while Liebig +was in Paris in the laboratory of Gay-Lussac, was engaged in studying the +intricacies of mineral chemistry under the guidance of Berzelius—had +already entered on this field of research. The two young chemists compared +notes, recognized each other's powers, and became friends; this friendship +strengthened as life advanced, and some of the most important papers which +enriched chemical science during the next thirty years bore the joint +signatures of Liebig and Wöhler.</p> + +<p>I have already mentioned that when it was found necessary to abandon the +Lavoisierian definition of organic chemistry as the chemistry of compounds +containing carbon, hydrogen and oxygen, and sometimes also phosphorus or +nitrogen, a definition<span class='pagenum'><a name="Page_265" id="Page_265">[Pg 265]</a></span> was attempted to be based on the supposed fact that +the formation of the compounds obtained from animals and plants could be +accomplished only by the agency of a living organism. But the discovery +made in 1828 by Wöhler, that <i>urea</i>—a substance specially characterized by +its production in the animal economy, and in that economy only—could be +built up from mineral materials, rendered this definition of organic +chemistry impossible, and broke down the artificial barrier whereby +naturalists attempted to separate two fields of study between which Nature +made no division.</p> + +<p>We have here another illustration of the truth of the conception which +underlies so many of the recent advances of science, which is the central +thought of the noble structure reared by the greatest naturalist of our +time, and which is expressed by one of the profoundest students of Nature +that this age has seen in the words I have already quoted from the preface +to the "Lyrical Ballads," "In Nature everything is distinct, but nothing +defined into absolute independent singleness."</p> + +<p>From this time the progress of organic chemistry became rapid. Dumas +continued the researches upon ethers which he had commenced at Geneva, and +by the year 1829 or so he had established the relations which exist between +ethers and alcohols on the one hand, and ethers and acids on the other. +This research, a description of the details of which<span class='pagenum'><a name="Page_266" id="Page_266">[Pg 266]</a></span> I cannot introduce +here as it would involve the use of many technical terms and assume the +possession by the reader of much technical knowledge, was followed by +others, whereby Dumas established the existence of a series of compounds +all possessed of the chemical properties of alcohol, all containing carbon, +hydrogen and oxygen, but differing from one another by a constant amount of +carbon and hydrogen. This discovery of a series of alcohols, distinguished +by the possession of certain definite properties whereby they were marked +off from all other so-called organic compounds, was as the appearance of a +landmark to the traveller in a country where he is without a guide. The +introduction of the comparative method of study into organic chemistry—the +method, that is, which bases classification on a comparison of large groups +of compounds, and which seeks to gather together those substances which are +like and to separate those which are unlike—soon began to bear fruit. This +method suggested to the experimenter new points of view from which to +regard groups of bodies; analogies which were hidden when a few substances +only were considered, became prominent as the range of view was widened. +What the gentle Elia calls "fragments and scattered pieces of truth," +"hints and glimpses, germs, and crude essays at a system," became +important. There was work to be done, not only by the master spirits who, +looking at things from a central position of vantage, saw the relative +importance<span class='pagenum'><a name="Page_267" id="Page_267">[Pg 267]</a></span> of the various detailed facts, but also by those who could only +"beat up a little game peradventure, and leave it to knottier heads, more +robust constitutions, to run it down."</p> + +<p>Twenty years before the time of which we are now speaking Davy had +decomposed the alkalis potash and soda; as he found these substances to be +metallic oxides, he thought it very probable that the other well-known +alkali, ammonia, would also turn out to be the oxide of a metal. By the +electrolysis of salts formed by the action of ammonia on acids, using +mercury as one of the poles of the battery, Davy obtained a strange-looking +spongy substance which he was inclined to regard as an alloy of the +metallic base of ammonia with mercury. From the results of experiments by +himself and others, Davy adopted a view of this alloy which regarded it as +containing a <i>compound radicle</i>, or group of elementary atoms which in +certain definite chemical changes behaved like a single elementary atom.</p> + +<p>To this compound radicle he gave the name of <i>ammonium</i>.</p> + +<p>As an aqueous solution of potash or soda was regarded as a compound of +water and oxide of potassium or sodium, so an aqueous solution of ammonia +was regarded as a compound of water and oxide of ammonium.</p> + +<p>When the composition of this substance, ammonium, came to be more +accurately determined, it was found that it might be best represented as a<span class='pagenum'><a name="Page_268" id="Page_268">[Pg 268]</a></span> +compound atom built up of one atom of nitrogen and four atoms of hydrogen. +The observed properties of many compounds obtained from ammonia, and the +analogies observed between these and similar compounds obtained from potash +and soda, could be explained by assuming in the compound atom (or better, +in the molecule) of the ammonia salt, the existence of this group of atoms, +acting as one atom, called ammonium.</p> + +<p>The reader will not fail to observe how essentially atomic is this +conception of compound radicle. The ultimate particle, the molecule, of a +compound has now come to be regarded as a structure built up of parts +called atoms, just as a house is a structure built up of parts called +stones and bricks, mortar and wood, etc. But there may be a closer +relationship between some of the atoms in this molecule than between the +other atoms. It may be possible to remove a group of atoms, and put another +group—or perhaps another single atom—in the place of the group removed, +without causing the whole atomic structure to fall to pieces; just as it +may be possible to remove some of the bricks from the wall of a house, or a +large wooden beam from beneath the lintels, and replace these by other +bricks or by a single stone, or replace the large wooden beam by a smaller +iron one, without involving the downfall of the entire house. The group of +atoms thus removable—the compound radicle—may exist in a series of +compounds. As we have an oxide, a sulphide, a chloride, a nitrate,<span class='pagenum'><a name="Page_269" id="Page_269">[Pg 269]</a></span> etc., +of sodium, so we may have an oxide, a sulphide, a chloride, a nitrate, +etc., of ammonium. The compounds of sodium are possessed of many properties +in common; this is partly explained by saying that they all contain one or +more atoms of the element sodium. The compounds of ammonium possess many +properties in common, and this is partly explained if we assume that they +all contain one or more atoms of the compound radicle ammonium.</p> + +<p>The conception of compound radicle was carried by Berzelius to its utmost +limits. We have learned that the Swedish chemist regarded every molecule as +composed of two parts; in very many cases each of these parts was itself +made up of more than one kind of atom—it was a compound radicle. But the +Berzelian system tended to become too artificial: it drifted further and +further away from facts. Of the two parts composing the dual molecular +structure, one was of necessity positively, and the other negatively +electrified. The greater number of the so-called organic compounds +contained oxygen; oxygen was the most electro-negative element known; hence +most organic compounds were regarded as formed by the coming together of +one, two, or more atoms of oxygen, forming the negative part of the +molecule, with one, two, or more atoms of a compound radicle, which formed +the positive part of the molecule.</p> + +<p>From this dualistic view of the molecule there naturally arose a +disposition to regard the compound radicles of organic chemistry as the +non-oxygenated<span class='pagenum'><a name="Page_270" id="Page_270">[Pg 270]</a></span> parts of the molecules of organic compounds. An organic +compound came gradually to be regarded as a compound of oxygen with some +other elements, which were all lumped together under the name of a compound +radicle, and organic chemistry was for a time defined as the chemistry of +compound radicles.</p> + +<p>From what has been said on p. 268, I think it will be evident that the idea +of <i>substitution</i> is a necessary part of the original conception of +compound radicle; a group of atoms in a molecule may, it is said, be +removed, and another group, or another atom, <i>substituted</i> for that which +is removed. Berzelius adopted this idea, but he made it too rigid; he +taught that an electro-negative atom, or compound radicle, could be +replaced or substituted only by another electro-negative atom or group of +atoms, and a positively electrified atom or group of atoms, only by another +electro-positive atom or compound radicle. Thus oxygen could perhaps be +replaced by chlorine, but certainly not by hydrogen; while hydrogen might +be replaced by a positively electrified atom, but certainly not by +chlorine.</p> + +<p>The conceptions of compound radicles and of substitution held some such +position in organic chemistry as that which I have now attempted to +indicate when Dumas and Liebig began their work in this field.</p> + +<p>The visitors at one of the royal <i>soirées</i> at the Tuileries were much +annoyed by the irritating vapours which came from the wax candles used<span class='pagenum'><a name="Page_271" id="Page_271">[Pg 271]</a></span> to +illuminate the apartments; Dumas was asked to examine the candles and find +the reason of their peculiar behaviour. He found that the manufacturer had +used chlorine to bleach the wax, that some of this chlorine remained in the +candles, and that the irritating vapours which had annoyed the guests of +Charles X. contained hydrochloric acid, produced by the union of chlorine +with part of the hydrogen of the wax. Candles bleached by some other means +than chlorine were in future used in the royal palaces; and the unitary +theory, which was to overthrow the dualism of Berzelius, began to arise in +the mind of Dumas.</p> + +<p>The retention of a large quantity of chlorine by wax could scarcely be +explained by assuming that the chlorine was present only as a mechanically +held impurity. Dumas thoroughly investigated the action of chlorine on wax +and other organic compounds; and in 1834 he announced that hydrogen in +organic compounds can be exchanged for chlorine, every volume of hydrogen +given up by the original compound being replaced by an equal volume of +chlorine.</p> + +<p>Liebig and Wöhler made use of a similar conception to explain the results +which they had obtained about this time in their study of the oil of bitter +almonds, a study which will be referred to immediately.</p> + +<p>The progress of this bold innovation made by Dumas was much advanced by the +experiments and reasonings of two French chemists, whose<span class='pagenum'><a name="Page_272" id="Page_272">[Pg 272]</a></span> names ought +always to be reverenced by students of chemistry as the names of a pair of +brilliant naturalists to whom modern chemistry owes much. <i>Gerhardt</i> was +distinguished by clearness of vision and expression; <i>Laurent</i> by +originality, breadth of mind and power of speculation.</p> + +<p>Laurent appears to have been the first who made a clear statement of the +fundamental conception of the unitary theory: "Many organic compounds, when +treated with chlorine lose a certain number of equivalents of hydrogen, +which passes off as hydrochloric acid. An equal number of equivalents of +chlorine takes the place of the hydrogen so eliminated; thus the physical +and chemical properties of the original substance are not profoundly +changed. The chlorine occupies the place left vacant by the hydrogen; the +chlorine plays in the new compound the same part as was played by the +hydrogen in the original compound."</p> + +<p>The replacement of electro-positive hydrogen by electro-negative chlorine +was against every canon of the dualistic chemistry; and to say that the +physical and chemical properties of the original compound were not +profoundly modified by this replacement, seemed to be to call in question +the validity of the whole structure raised by the labours during a quarter +of a century of one universally admitted to be among the foremost chemists +of his age.</p> + +<p>But facts accumulated. By the action of<span class='pagenum'><a name="Page_273" id="Page_273">[Pg 273]</a></span> chlorine on alcohol Liebig +obtained <i>chloroform</i> and <i>chloral</i>, substances which have since been so +largely applied to the alleviation of human suffering; but it was Dumas who +correctly determined the composition of these two compounds, and showed how +they are related to alcohol and to one another.</p> + +<p>Liebig's reception of the corrections made by Dumas in his work furnishes a +striking example of the true scientific spirit. "As an excellent +illustration," said Liebig, "of the mode in which errors should be +corrected, the investigation of chloral by Dumas may fitly be introduced. +It carried conviction to myself, as I think to everybody else, not by the +copious number of analytical data opposed to the not less numerous results +which I had published, but because these data gave a simpler explanation +both of the formation and of the changes of the substances in question."</p> + +<p>One of the most important contributions to the new views was made by Dumas +in his paper on the action of chlorine on acetic acid (1833), wherein he +proved that the product of this action, viz. <i>trichloracetic acid</i>, is +related to the parent substance by containing three atoms of chlorine in +place of three atoms of hydrogen in the molecule; that the new substance +is, like the parent substance, a monobasic acid; that its salts are very +analogous in properties to the salts of acetic acid; that the action of the +same reagents on the two substances is similar; and finally, that the +existence of many derivatives<span class='pagenum'><a name="Page_274" id="Page_274">[Pg 274]</a></span> of these compounds could be foretold by the +help of the new hypothesis, which derivatives ought not to exist according +to the dualistic theory, but which, unfortunately for that theory, were +prepared and analyzed by Dumas.</p> + +<p>I have alluded to a research by Liebig and Wöhler on oil of bitter almonds +as marking an important stage in the advance of the anti-dualistic views. +The paper alluded to was published in 1832. At that time it was known that +<i>benzoic acid</i> is formed by exposure of bitter-almond oil to the air. +Liebig and Wöhler made many analyses of these two substances, and many +experiments on the mutual relations of their properties, whereby they were +led to regard the molecules of the oil as built up each of an atom of +hydrogen and an atom of a compound radicle—itself a compound of carbon, +hydrogen and oxygen—to which they gave the name of <i>benzoyl</i>.<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> Benzoic +acid they regarded as a compound of the same radicle with another radicle, +consisting of equal numbers of oxygen and hydrogen atoms. By the action of +chlorine and other reagents on bitter-almond oil these chemists obtained +substances which were carefully analyzed and studied, and the properties of +which they<span class='pagenum'><a name="Page_275" id="Page_275">[Pg 275]</a></span> showed could be simply explained by regarding them all as +compounds of the radicle <i>benzoyl</i> with chlorine and other atoms or groups +of atoms. But this view, if adopted, necessitated the belief that chlorine +atoms could replace oxygen atoms; and, generally, that the substitution of +an electro-positive by a negative atom or group of atoms did not +necessarily cause any great alteration in the properties of the molecule.</p> + +<p>Thus it was that the rigid conceptions of dualism were shown to be too +rigid; that the possibility of an electro-positive radicle, or atom, +replacing another of opposite electricity was recognized; and thus the view +which regarded a compound molecule as one structure—atoms in which might +be replaced by other atoms irrespective of the mutual electrical relations +of these atoms—began to gain ground.</p> + +<p>From this time the molecule of a compound has been generally regarded as a +unitary structure, as one whole, and the properties of the molecule as +determined by the nature, number, and arrangement of all the atoms which +together compose it.</p> + +<p>The unitary conception of a compound molecule appeared at first to be +altogether opposed to the system of Berzelius; but as time went on, and as +fresh facts came to be known, it was seen that the new view conserved at +least one, and that perhaps the most important, of the thoughts which +formed the basis of the Berzelian classification.</p> + +<p>Underlying the dualism of Berzelius was the conception<span class='pagenum'><a name="Page_276" id="Page_276">[Pg 276]</a></span> of the molecule as +an atomic structure; this was retained in the unitary system of Dumas, +Gerhardt and Laurent.</p> + +<p>Berzelius had insisted that every molecule is a dual structure. This is +taking too narrow a view of the possibilities of Nature, said the upholders +of the new school. <i>This</i> molecule may have a dual structure; <i>that</i> may be +built up of three parts. The structure of this molecule or of that can be +determined only by a careful study of its relations with other molecules.</p> + +<p>For a time it seemed also as if the new chemistry could do without the +compound radicle which had been so much used by Berzelius; but the pressure +of facts soon drove the unitary chemists to recognize the value of that +hypothesis which looked on parts of the molecule as sometimes more closely +associated than other parts—which recognized the existence of atomic +structures within the larger molecular structures. As a house is not simply +a putting together of so many bricks, so much mortar, so many doors and +windows, so many leaden pipes, etc., but rather a definite structure +composed of parts, many of which are themselves also definite structures, +such as the window and its accessory parts, the door with its lintel and +handle, etc., so to the unitary chemists did the molecule appear to be +built up of parts, some of which, themselves composed of yet smaller parts, +discharged a particular function in the molecular economy.<span class='pagenum'><a name="Page_277" id="Page_277">[Pg 277]</a></span></p> + +<p>A general division of a plant might describe it as a structure consisting +of a stem, a root, and leaves. Each of the parts, directly by its +individual action and indirectly by the mutual action between it and all +the other parts, contributes to the growth of the whole plant; but if the +stem, or root, or leaves be further analyzed, each is found to consist of +many parts, of fibres and cells and tissue, etc. We may liken the plant to +the molecule of an organic compound; the root, the stem and the leaves to +the compound radicles of which this molecule is built up, and the tissue, +fibres, etc., to the elementary atoms which compose these compound +radicles. The molecule is one whole, possessed of definite structure and +performing a definite function by virtue of the nature and the arrangement +of its parts.</p> + +<p>Many years elapsed after the publication of the researches of Dumas, and of +Liebig and Wöhler, before such a conception of the molecule as this was +widely accepted by chemists. The opposition of the older school, headed by +their doughty champion Berzelius, had to be overcome; the infallibility of +some of the younger members of the new school had to be checked; facts had +to be accumulated, difficulties explained, weak analogies abandoned and +strong ones rendered stronger by research; special views of the structure +of this or that molecule, deduced from a single investigation, had to be +supplemented and modified by wider views gained by the researches of many +workers. It was not<span class='pagenum'><a name="Page_278" id="Page_278">[Pg 278]</a></span> till 1867 that Liebig, when asked by Dumas at a dinner +given during the French Exhibition to the foreign chemists, why he had +abandoned organic chemistry, replied that "now, with the theory of +substitution as a foundation, the edifice may be built up by workmen: +masters are no longer needed."</p> + +<p>Laurent and Gerhardt did noble work in advancing the unitary theory; to +them is largely due the fruitful conception of types, an outcome of Dumas's +work, which owed its origin to the flickering of the wax candles in the +Tuileries during the royal <i>soirée</i>.</p> + +<p>Chlorine can be substituted for hydrogen in acetic acid, and the product is +closely related in its properties to the parent substance; various atoms or +groups of atoms can be substituted by other groups in the derivatives of +oil of bitter almonds, but a close analogy in properties runs through all +these compounds: these facts might be more shortly expressed by saying that +acetic and trichloracetic acids belong to the same <i>type</i>, and that the +derivatives of bitter-almond oil likewise belong to one <i>type</i>.</p> + +<p>Laurent carried this conception into inorganic chemistry. Water and potash +did not seem to have much in common, but Laurent said potash is not a +compound of oxide of potassium and water, it is rather a derivative of +water. The molecule of potash is derived from that of water by replacing +one atom of hydrogen in the latter by one atom of potassium; water and +potash belong to the same type.<span class='pagenum'><a name="Page_279" id="Page_279">[Pg 279]</a></span></p> + +<p>Thus there was constituted <i>the water type</i>.</p> + +<p>Light was at once thrown on many facts in organic chemistry. The analogies +between alcohol and water, some of which were first pointed out by Graham +(see p. 235), seemed to follow as a necessary consequence when the molecule +of alcohol was regarded as built on the water type. In place of two atoms +of hydrogen combined with one of oxygen, there was in the alcohol molecule +one atom of the compound radicle <i>ethyl</i> (itself composed of carbon and +hydrogen), one atom of oxygen and one of hydrogen. Alcohol was water with +one hydrogen atom substituted by one ethyl atom; the hydrogen atom was the +atom of what we call an element, the ethyl was the atom of what we call a +compound radicle.</p> + +<p>Gerhardt sought to refer all organic compounds to one or other of three +types—the water type, the hydrochloric acid type, and the ammonia type. As +new compounds were prepared and examined, other types had to be introduced. +To follow the history of this conception would lead us into too many +details; suffice it to say that the theory of types was gradually merged in +the wider theory of equivalency, about which I shall have a little to say +in the next chapter.</p> + +<p>One result of the introduction of types into chemical science, associated +as it was with the unitary view of compound radicles, was to overthrow that +definition of organic chemistry which had for some time prevailed, and +which stated that<span class='pagenum'><a name="Page_280" id="Page_280">[Pg 280]</a></span> organic chemistry is "the chemistry of compound +radicles." Compound radicles, it is true, were more used in explaining the +composition and properties of substances obtained from animals and +vegetables than of mineral substances, but a definition of one branch of a +science which practically included the other branch, from which the first +was to be defined, could not be retained. Chemists became gradually +convinced that a definition of organic chemistry was not required; that +there was no distinction between so-called organic and inorganic compounds; +and they have consented, but I scarcely think will much longer consent, to +retain the terms "organic" and "inorganic," only because these terms have +been so long in use. The known compounds of the element carbon are so +numerous, and they have been so much studied and so well classified, that +it has become more convenient for the student of chemistry to consider them +as a group, to a great extent apart from the compounds of the other +elements; to this group he still often gives the name of "organic +compounds."</p> + +<hr style='width: 45%;' /> + +<p>Liebig continued to hold the chair of Chemistry in the University of +Giessen until the year 1852, when he was induced by the King of Bavaria to +accept the professorship of the same science in the University of Munich. +During the second quarter of this century Giessen was much resorted to by +students of chemistry from all parts of the world, more especially from +England. Many men who<span class='pagenum'><a name="Page_281" id="Page_281">[Pg 281]</a></span> afterwards made their mark in chemical discovery +worked under the guidance of the professor of Stockholm, but Giessen has +the honour of being the place where a well-appointed chemical laboratory +for scientific research was first started as a distinctly educational +institution. The fame of Liebig as a discoverer and as a teacher soon +filled the new institution with students, who were stirred to enthusiasm as +they listened to his lectures, or saw him at work in his laboratory. +"Liebig was not exactly what is called a fluent speaker," says Professor +Hofmann, of Berlin, "but there was an earnestness, an enthusiasm in all he +said, which irresistibly carried away the hearer. Nor was it so much the +actual knowledge he imparted which produced this effect, as the wonderful +manner in which he called forth the reflective powers of even the least +gifted of his pupils. And what a boon was it, after having been stifled by +an oppressive load of facts, to drink the pure breath of science such as it +flowed from Liebig's lips! what a delight, after having perhaps received +from others a sack full of dry leaves, suddenly in Liebig's lectures to see +the living, growing tree!... We felt then, we feel still, and never while +we live shall we forget, Liebig's marvellous influence over us; and if +anything could be more astonishing than the amount of work he did with his +own hands, it was probably the mountain of chemical toil which he got us to +go through. Each word of his carried instruction, every intonation of his +voice bespoke regard; his approval was<span class='pagenum'><a name="Page_282" id="Page_282">[Pg 282]</a></span> a mark of honour, and of whatever +else we might be proud, our greatest pride of all was having him for our +master.... Of our young winnings in the noble playground of philosophical +honour, more than half were free gifts to us from Liebig, and to his +generous nature no triumphs of his own brought more sincere delight than +that which he took in seeing his pupils' success, and in assisting, while +he watched, their upward struggle."</p> + +<p>Liebig had many friends in England. He frequently visited this country, and +was present at several meetings of the British Association. At the meeting +of 1837 he was asked to draw up a report on the progress of organic +chemistry; he complied, and in 1840 presented the world with a book which +marks a distinct epoch in the applications of science to industrial +pursuits—"Chemistry in its Applications to Agriculture and Physiology."</p> + +<p>In this book, and in his subsequent researches and works,<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a> Liebig +established and enforced the necessity which exists for returning to the +soil the nourishing materials which are taken from it by the growth of +crops; he suggested that manure rich in the salts which are needed by +plants might be artificially manufactured, and by doing this he laid the +foundation of a vast industry which has arisen during the last two decades. +He strongly and successfully attacked the conception which prevailed<span class='pagenum'><a name="Page_283" id="Page_283">[Pg 283]</a></span> among +most students of physiology at that time, that chemical and physical +generalizations could not be applied to explain the phenomena presented by +the growth of living organisms. He was among the first to establish, as an +induction from the results of many and varied experiments, the canon which +has since guided all teachers of the science of life, that a true knowledge +of biology must be based on a knowledge of chemistry and physics.</p> + +<p>But Liebig was not content to establish broad generalizations and to leave +the working out of them to others; he descended from the heights of +philosophical inquiry, and taught the housewife to make soup wherein the +greatest amount of nourishment was conveyed to the invalid in the most +easily digestible form; and has he not, by bringing within the reach of +every one a portion of the animal nourishment which else had run to waste +in the pampas of South America or the sheep-runs of Australia, made his +name, in every English home, familiar as a household word?</p> + +<p>On the death of Berzelius in 1848, it was to Liebig that every chemist +looked for a continuation of the annual Report on the progress of +chemistry, which had now become the central magazine of facts, whither each +worker in the science could resort to make himself acquainted with what had +been done by others on any subject which he proposed to investigate. From +that time to the present day Liebig's <i>Annalen</i> has been the leading +chemical journal of the world.<span class='pagenum'><a name="Page_284" id="Page_284">[Pg 284]</a></span></p> + +<p>Of the other literary work of Liebig—of his essays, his celebrated +"Chemical Letters," his many reports, his severe and sometimes harsh +criticisms of the work of others—of the details of the three hundred +original papers wherein he embodied the results of his researches, I have +not time, nor would this be the place, to speak.</p> + +<p>Honoured by every scientific society of any note in the world, crowned with +the highest reward which England and France can offer to the man of science +who is not an Englishman or a Frenchman—the Copley Medal and the +associateship of the Institute—honoured and respected by every student of +science, loved by each of the band of ardent natures whom he had trained +and sent forth to battle for the good of their race, and, best of all, +working himself to the last in explaining the wonders of Nature, he "passed +into the silent land" on the 18th of April 1873, leaving the memory of a +life nobly devoted to the service of humanity, and the imperishable record +of many truths added to the common stock of the race.</p> + +<hr style='width: 45%;' /> + +<p>The life-work of Dumas, other than that which I have already sketched, is +so manifold and so varied, that to do more than refer to one or two leading +points would carry us far beyond the limits within which I have tried to +keep throughout this book. In one of his earliest papers Dumas adopted the +atomic theory as the corner-stone of his chemical system; he was thus led +to an experimental<span class='pagenum'><a name="Page_285" id="Page_285">[Pg 285]</a></span> revision of the values generally accepted for the +atomic weights of some of the elements. Among these revisions, that of the +atomic weight of carbon holds a most important place, partly because of the +excellency of the work, but more because of the other inquiries to which +this work gave rise.</p> + +<p>Dumas's experiments were summed up in the statement that the atom of carbon +is twelve times heavier than the atom of hydrogen. The experimental methods +and the calculations used in this determination involved a knowledge of the +atomic weight of oxygen; in order accurately to determine the value to be +assigned to this constant, Dumas, in conjunction with Boussingault, +undertook a series of experiments on the synthesis of water, which forms +one of the classical researches of chemistry, and wherein the number 16 was +established as representing the atomic weight of oxygen. Stas, from +experiments conducted at a later time with the utmost care and under +conditions eminently fitted to gain accurate results, obtained the number +15·96, in place of 16, for the atomic weight of oxygen; but in a paper +recently published by the veteran Dumas, a source of error is pointed out +which Stas had overlooked in his experiments, and it is shown that this +error would tend slightly to increase the number obtained by Stas.</p> + +<p>As the values assigned to the atomic weights of the elements are the very +fundamental data of<span class='pagenum'><a name="Page_286" id="Page_286">[Pg 286]</a></span> chemistry, and as we are every day more clearly +perceiving that the mutual relations between the properties of elements and +compounds are closely connected with the relative weights of the elementary +atoms, we can scarcely lay too much stress on such work as this done by +Dumas and Stas. Not many years after the publication of Dalton's "New +System," the hypothesis was suggested by Prout that the atomic weights of +all the elements are represented by whole numbers—that of hydrogen being +taken as unity—that the atom of each element is probably formed by the +putting together of two, three, four, or more atoms of hydrogen, and that +consequently there exists but a single elementary form of matter. Among the +upholders of this hypothesis Dumas has held an important place. He modified +the original statement of Prout, and suggested that all atomic weights are +whole multiples of half of that of hydrogen (that is, are whole multiples +of 1/2). The experiments of Stas seemed to negative this view, but later +work—more especially the important critical revision of the results +obtained by all the most trustworthy workers, conducted by Professor Clarke +of Cincinnati, and published by the Smithsonian Institution as part of +their series of "Constants of Nature"—has shown that we are in no wise +warranted by facts in rejecting Prout's hypothesis as modified by Dumas, +but that the balance of evidence is at present rather in its favour.</p> + +<p>It would be altogether out of place to discuss<span class='pagenum'><a name="Page_287" id="Page_287">[Pg 287]</a></span> here an hypothesis which +leads to some of the most abstruse speculations as to the nature of matter +in which chemists have as yet ventured to indulge. I mention it only +because it illustrates the far-reaching nature of the researches of the +chemist whose work we are now considering, and also because it shows the +shallowness of the scoffs in which some partly educated people indulge when +they see scientific men occupying themselves for years with attempts to +solve such a minute and, as they say, trivial question as whether the +number 15·96 or the number 16 is to be preferred as representing the atomic +weight of oxygen; "for in every speck of dust that falls lie hid the laws +of the universe, and there is not an hour that passes in which you do not +hold the infinite in your hand."</p> + +<p>Another and very different subject, which has been placed on a firm basis +by the researches of Dumas, is the chemistry of fermentation. By his work +on the action of beer-yeast on saccharine liquids, Dumas proved Liebig's +view to be untenable—according to which the conversion of sugar into +alcohol is brought about by the influence of chemical changes proceeding in +the ferment; also that the view of Berzelius, who regarded alcoholic +fermentation as due simply to the contact of the ferment with the sugar, +was opposed to many facts; and lastly, Dumas showed that the facts were +best explained by the view which regarded the change of sugar into alcohol +as in no way different from<span class='pagenum'><a name="Page_288" id="Page_288">[Pg 288]</a></span> other purely chemical changes, but as a change +brought about, so far as our present knowledge goes, only by the agency of +a growing organism of low form, such as yeast.</p> + +<p>In 1832 Dumas established at his own expense a laboratory for chemical +research. When the Revolution of 1848 broke out Dumas's means were much +diminished, and he could no longer afford to maintain his laboratory. The +closing of this place, where so much sound work had been done, was +generally regarded as a calamity to science. About this time Dumas received +a visit from a person of unprepossessing appearance, who accosted him thus: +"They assert that you have shut up your laboratory, but you have no right +to do so. If you are in need of money, there," throwing a roll of +bank-notes on the table, "take what you want. Do not stint yourself; I am +rich, a bachelor, and have but a short time to live." Dumas's visitor +turned out to be Dr. Jecker. He assured Dumas that he was now only paying a +debt, since he had made a fortune by what he had learnt in the medical +schools of Paris. Dumas could not however in those troublous times turn his +mind continuously to experimental research, and therefore declined Dr. +Jecker's offer with many protestations of good will and esteem.</p> + +<p>New work now began to press upon Dumas; his energy and his administrative +powers were demanded by the State. Elected a member of the National +Assembly in 1848, he was soon called by<span class='pagenum'><a name="Page_289" id="Page_289">[Pg 289]</a></span> the President of the Republic to +office as Minister of Agriculture and Commerce. He was made a senator under +the second empire. He entered the municipal council of Paris about 1854, +and was soon elected to the presidency. Under his presidency the great +scheme for providing Paris with spring-water carried by aqueducts and +tunnels was successfully accomplished; many improvements were made in the +drainage of the city; the cost of gas was decreased, while the quality was +improved, the constancy of the supply insured, and the appliances for +burning the gas in the streets were altered and rendered more effective.</p> + +<p>Nominated to succeed Pelouze as Master of the Mint in 1868, Dumas held this +honourable and important position only until the Franco-German war of 1870. +Since that date he has relinquished political life; but as Permanent +Secretary of the Academy Dumas now fills the foremost place in all affairs +connected with science, whether pure or applied, in the French capital.</p> + +<p>In the work of these two chemists, Liebig and Dumas, we find admirable +illustrations of the scientific method of examining natural appearances.</p> + +<p>In the broad general views which they both take of the phenomena to be +studied, and the patient and persevering working out of details, we have +shown us the combination of powers which are generally found in separate +individuals.</p> + +<p>Dumas has always insisted on the need of comparing properties and reactions +of groups of bodies,<span class='pagenum'><a name="Page_290" id="Page_290">[Pg 290]</a></span> before any just knowledge can be gained as to the +position of a single substance in the series studied by the chemist. It has +been his aim as a teacher, we are assured by his friend, Professor Hofmann, +never to present to his students "an isolated phenomenon, or a notion not +logically linked with others." To him each chemical compound is one in a +series which connects it directly with many other similar compounds, and +indirectly with other more or less dissimilar compounds.</p> + +<p>Amid the overwhelming mass of facts which threaten nowadays to bury the +science of chemistry, and crush the life out of it by their weight, Dumas +tracks his way by the aid of general principles; but these principles are +themselves generalized from the facts, and are not the offspring of his own +fancy.</p> + +<p>We have, I think, found that throughout the progress of chemical science +two dangers have beset the student. He has been often tempted to accumulate +facts, to amass analytical details, to forget that he is a chemist in his +desire to perfect the instrument of analysis by the use of which he raises +the scaffolding of his science; on the other hand, he has been sometimes +allured from the path of experiment by his own day-dreams. The discoveries +of science have been so wonderful, and the conceptions of some of those who +have successfully prosecuted science have been so grand, that the student +has not unfrequently been tempted to rest in the prevailing theories of the +day, and,<span class='pagenum'><a name="Page_291" id="Page_291">[Pg 291]</a></span> forgetting that these ought only "to afford peaceful lodgings to +the intellect for the time," he has rather allowed them to circumscribe it, +until at last the mind "finds difficulty in breaking down the walls of what +has become its prison, instead of its home."</p> + +<p>We may think that Dumas fell perhaps slightly into the former of these +errors, when he did not allow his imagination a little more scope in +dealing with the conception of "atom" and "molecule," the difference +between which he had apprehended but not sufficiently marked by the year +1826 (see p. 261).</p> + +<p>We know, from his own testimony, that Liebig once fell into the latter +error and that the consequences were disastrous. "I know a +chemist"—meaning himself—"who ... undertook an investigation of the +liquor from the salt-works. He found iodine in it, and observed, moreover, +that the iodide of starch turned a fiery yellow by standing over-night. The +phenomenon struck him; he saturated a large quantity of the liquor with +chlorine, and obtained from this, by distillation, a considerable quantity +of a liquid which coloured starch yellow, and externally resembled chloride +of iodine, but differed from this compound in many properties. He +explained, however, every discrepancy with satisfaction to himself; he +contrived for himself a theory. Several months later, he received a paper +of M. Balard's," announcing the discovery of bromine, "and on that same day +he was able to publish the<span class='pagenum'><a name="Page_292" id="Page_292">[Pg 292]</a></span> results of experiments on the behaviour of +bromine with iron, platinum, and carbon; for Balard's bromine stood in his +laboratory, labelled <i>liquid chloride of iodine</i>. Since that time he makes +no more theories unless they are supported and confirmed by trustworthy +experiments; and I can positively assert that he has not fared badly by so +doing."</p> + +<p>Another point which we notice in the life-work of these two chemists is +their untiring labour. They were always at work; wherever they might be, +they were ready to notice passing events or natural phenomena, and to draw +suggestions from these. As Davy proved the elementary character of iodine +and established many of the properties of this substance during a visit to +Paris, so we find Dumas making many discoveries during brief visits paid to +his friends' laboratories when on excursions away from Paris. During a +visit to Aix-les-Bains, he noticed that the walls of the bath-room were +covered with small crystals of sulphate of lime. The waters of the bath, he +knew, were charged with sulphuretted hydrogen, but they contained no +sulphuric acid, nor could that acid be detected in the air of the +bath-rooms. This observation was followed up by experiments which proved +that a porous material, such as a curtain or an ordinary plastered wall, is +able to bring about the union of oxygen with sulphuretted hydrogen, +provided moisture be present and a somewhat high temperature be +maintained.<span class='pagenum'><a name="Page_293" id="Page_293">[Pg 293]</a></span></p> + +<p>Again, we find Liebig and Dumas characterized by great mental honesty. +"There is no harm in a man committing mistakes," said Liebig, "but great +harm indeed in his committing none, for he is sure not to have worked.... +An error you have become cognizant of, do not keep in your house from night +till morning."</p> + +<p>Students of science, more than any other men, ought to be ready to +acknowledge and correct the errors into which they fall. It is not +difficult for them to do this: they have only to be continually going to +Nature; for there they have a court of appeal always ready to hear their +case, and to give an absolutely unbiased judgment: they have but to bring +their theories and guesses to this judge to have them appraised at their +true value.</p> + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> "In reviewing once more the facts elicited by our inquiry, we +find them arranged around a common centre, a group of atoms preserving +intact its nature, amid the most varied associations with other elements. +This stability, this analogy, pervading all the phenomena, has induced us +to consider this group as a sort of compound element, and to designate it +by the special name of <i>benzoyl</i>."—Liebig and Wöhler, 1832.</p></div> + +<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> "Animal Chemistry, or Chemistry in its Applications to +Physiology and Pathology," 1842. "Researches on the Chemistry of Food," +1847. "The Natural Laws of Husbandry," 1862.</p></div> +</div> + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_294" id="Page_294">[Pg 294]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap7.jpg" width="500" height="99" alt="" title="" /> +</div> + +<h2>CHAPTER VII.</h2> + +<h3>MODERN CHEMISTRY.</h3> + + +<p>On p. 162 I referred to the work of the German chemist Richter, by which +the <i>equivalents</i> of certain acids and bases were established. Those +quantities of various acids which severally neutralized one and the same +quantity of a given base, or those quantities of various bases which +severally neutralized one and the same quantity of a given acid, were said +to be equivalent. These were the quantities capable of performing a certain +definite action.</p> + +<p>In considering the development of Dumas's substitution theory, we found +that Laurent retained this conception of equivalency when he spoke of an +equivalent of hydrogen being replaced by an equivalent of chlorine (see p. +272). A certain weight of chlorine was able to take the place and play the +part of a certain weight of hydrogen in a compound; these weights, of +hydrogen and chlorine, were therefore equivalent.<span class='pagenum'><a name="Page_295" id="Page_295">[Pg 295]</a></span></p> + +<p>This conception has been much used since Laurent's time, but it has for the +most part been applied to the atoms of the elements.</p> + +<p>Hydrogen being taken as the standard substance, the elements have been +divided into groups, in accordance with the number of hydrogen atoms with +which one atom of each element is found to combine. Thus certain elements +combine with hydrogen only in the proportion of one atom with one atom; +others combine in the proportion of one atom with two atoms of hydrogen; +others in the proportion of one atom with three atoms of hydrogen, and so +on.</p> + +<p>The adjective <i>monovalent</i>, <i>divalent</i>, <i>trivalent</i>, etc., is prefixed to +an element to denote that the atom of this element combines with one, or +two, or three, etc., atoms of hydrogen to form a compound molecule.</p> + +<p>Let us consider what is implied in this statement—"The nitrogen atom is +trivalent." This statement, if amplified, would run thus: "One atom of +nitrogen combines with three atoms of hydrogen to form a compound +molecule." Now, this implies (1) that the atomic weight of nitrogen is +known, and (2) that the molecular weight, and the number of nitrogen and +hydrogen atoms in the molecule, of a compound of nitrogen and hydrogen are +also known.</p> + +<p>But before the atomic weight of an element can be determined, it is +necessary (as we found on p. 146) to obtain, analyze, and take the specific +gravities<span class='pagenum'><a name="Page_296" id="Page_296">[Pg 296]</a></span> of a series of gaseous compounds of that element. The smallest +amount of the element (referred to hydrogen as unity) in the molecule of +any one of these gases will then be the atomic weight of the element.</p> + +<p>When it is said that "the molecular weight, and the number of nitrogen and +hydrogen atoms in the molecule, of a compound of nitrogen and hydrogen are +known," the statement implies that the compound in question has been +obtained in a pure state, has been analyzed carefully, has been gasefied, +and that a known volume of the gas has been weighed. When therefore we say +that "the nitrogen atom is trivalent," we sum up a large amount of +knowledge which has been gained by laborious experiment.</p> + +<p>This classification of the elements into groups of equivalent atoms—which +we owe to Frankland, Williamson, Odling, and especially to Kekulé—has been +of much service especially in advancing the systematic study of the +compounds of carbon. It helps to render more precise the conception which +has so long been gaining ground of the molecule as a definite structure.</p> + +<p>A monovalent element is regarded as one the atom of which acts on and is +acted on by only one atom of hydrogen in a molecule; a divalent as one, the +atom of which acts on and is acted on by two atoms of hydrogen—or other +monovalent element—in a molecule; a trivalent element as one, the atom of +which acts on and is acted on by three atoms of hydrogen—or other +monovalent element—in a molecule; and so on.<span class='pagenum'><a name="Page_297" id="Page_297">[Pg 297]</a></span></p> + +<p>The fact that there often exist several compounds of carbon, the molecules +of which are composed of the same numbers of the same atoms, finds a +partial explanation by the aid of this conception of the elementary atom as +a little particle of matter capable of binding to itself a certain limited +number of other atoms to form a compound molecule. For if the observed +properties of a compound are associated with a certain definite arrangement +of the elementary atoms within the molecules of that compound, it would +seem that any alteration in this arrangement ought to be accompanied by an +alteration in the properties of the compound; in other words, the existence +of more than one compound of the same elements united in the same +proportions becomes possible and probable.</p> + +<p>I have said that such compounds exist: let me give a few examples.</p> + +<p>The alchemists poured a stream of mercury on to molten sulphur, and +obtained a black substance, which was changed by heat into a brilliantly +red-coloured body. We now know that the black and the red compounds alike +contain only mercury and sulphur, and contain these elements united in the +same proportions.</p> + +<p>Hydrogen, carbon, nitrogen and oxygen unite in certain proportions to +produce a mobile, colourless, strongly acid liquid, which acts violently on +the skin, causing blisters and producing great pain: if this liquid is +allowed to stand for a little time in the air it becomes turbid, begins to +boil, gets thicker,<span class='pagenum'><a name="Page_298" id="Page_298">[Pg 298]</a></span> and at last explodes, throwing a white pasty substance +about in all directions. This white solid is inodorous, is scarcely acid to +the taste, and does not affect the skin; yet it contains the same elements, +united in the same proportions, as were present in the strongly acid, +limpid liquid from which it was produced.</p> + +<p>Two substances are known each containing carbon and hydrogen united in the +same proportions: one is a gas with strong and irritating odour, and +exerting a most disagreeable action on the eyes; the other is a clear, +limpid, pleasant-smelling liquid.</p> + +<p>Phosphorus is a very poisonous substance: it readily takes fire in the air +at ordinary temperatures, so that it must be kept under water; but a +modification of phosphorus is known, containing no form of matter other +than phosphorus, which is non-poisonous, does not take fire easily, and may +be handled with safety.</p> + +<p>Once more, there is a compound of nitrogen and oxygen which presents the +appearance of a deep-red, almost black gas; there is also a compound of +nitrogen and oxygen which is a clear, colourless gas; yet both contain the +same elements united in the same proportions.</p> + +<p>But a detailed consideration of <i>isomerism</i>, <i>i.e.</i> the existence of more +than one compound built up of the same amounts of the same elements yet +possessing different properties, would lead us too far from the main path +of chemical advance which we wish to trace.<span class='pagenum'><a name="Page_299" id="Page_299">[Pg 299]</a></span></p> + +<p>The chemist is to-day continually seeking to connect the properties of the +bodies he studies with the molecular structures of these bodies; the former +he can observe, a knowledge of the latter he must gain by reasoning on the +results of operations and experiments. His guide—the guide of Lavoisier +and his successors—is this: "Similarity of properties is associated with +similarity of composition"—by "composition" he generally means molecular +composition.</p> + +<p>Many facts have been amassed of late years which illustrate the general +statement that the properties of bodies are connected with the composition +of those bodies. Thus a distinct connection has been traced between the +tinctorial power and the molecular composition of certain dye-stuffs; in +some cases it has even become possible to predict how a good dye-stuff may +be made—to say that, inasmuch as this or that chemical reaction will +probably give rise to the production of this or that compound, the atoms in +the molecule of which we believe to have a certain arrangement relatively +to one another, so this reaction or that will probably produce a dye +possessed of strong tinctorial powers.</p> + +<p>The compound to the presence of which madder chiefly owes its dyeing powers +is called <i>alizarine</i>; to determine the nature of the molecular structure +of this compound was, for many years, the object of the researches of +chemists; at last, thanks especially to the painstaking zeal of two German<span class='pagenum'><a name="Page_300" id="Page_300">[Pg 300]</a></span> +chemists, it became fairly clear that alizarine and a compound of carbon +and hydrogen, called <i>anthracene</i>, were closely related in structure. +Anthracene was obtained from alizarine, and, after much labour, alizarine +was prepared from anthracene. Anthracene is contained in large quantities +in the thick pitch which remains when coal-tar is distilled; this pitch was +formerly of little or no value, but as soon as the chemical manufacturer +found that in this black objectionable mass there lay hidden enormous +stores of alizarine, he no longer threw away his coal-tar pitch, but sold +it to the alizarine manufacturer for a large sum. Thus it has come to pass +that little or no madder is now cultivated; madder-dyeing is now done by +means of alizarine made from coal-tar: large tracts of ground, formerly +used for growing the madder plant, are thus set free for the growth of +wheat and other cereals.</p> + +<p>This discovery of a method for preparing alizarine artificially stimulated +chemists to make researches into the chemical composition, and if possible +to get to know something about the molecular structure of indigo. Those +researches have very recently resulted in the knowledge of a series of +reactions whereby this highly valuable and costly dye-stuff may be prepared +from certain carbon compounds which, like anthracene, are found in +coal-tar.</p> + +<p>These examples, while illustrating the connection that exists between the +composition and the properties of bodies, also illustrate the need there is +for giving a scientific chemical training to the<span class='pagenum'><a name="Page_301" id="Page_301">[Pg 301]</a></span> man who is to devote his +life to chemical manufactures. Pure and applied science are closely +connected; he who would succeed well in the latter must have a competent +and a practical knowledge of the former.</p> + +<p>That composition—molecular composition—and properties are closely related +is generally assumed, almost as an axiom, in chemical researches nowadays.</p> + +<p>Lavoisier defined acids as substances containing oxygen; Davy regarded an +acid as a compound the properties of which were conditioned by the nature +and by the arrangement of all the elements which it contained; Liebig spoke +of acids as substances containing "replaceable" hydrogen; the student of +the chemistry of the carbon compounds now recognizes in an organic acid a +compound containing hydrogen, but also carbon and oxygen, and he thinks +that the atoms of hydrogen (or some of these atoms) in the molecule of such +a compound are, in some way, closely related to atoms of oxygen and less +closely to atoms of carbon, within that molecule,—in other words, the +chemist now recognizes that, for carbon compounds at any rate, acids are +acid not only because they contain hydrogen, but also because that hydrogen +is related in a definite manner within the molecule to other elementary +atoms; he recognizes that the acid or non-acid properties of a compound are +conditioned, not only by the nature of the elements which together form +that compound, but also by the arrangement<span class='pagenum'><a name="Page_302" id="Page_302">[Pg 302]</a></span> of these elements. Davy's view +of the nature of acids is thus confirmed and at the same time rendered more +definite by the results of recent researches.</p> + +<p>The physical student is content to go no further than the molecule; the +properties of bodies which he studies are regarded, for the most part, as +depending on the size, the nature, and perhaps the grouping together of +molecules. But the chemist seeks to go deeper than this. The molecule is +too large a piece of matter for him; the properties which he studies are +conceived by him to be principally conditioned by the nature, the number, +and the arrangement of the parts of the molecule—of the atoms which +together build up the molecule.</p> + +<p>In these elementary atoms he has, for the present, found the materials of +which the heavens and the earth are made; but facts are being slowly gained +which render it probable that these atoms are themselves structures—that +they are built up of yet smaller parts, of yet simpler kinds of matter. To +gather evidence for or against this supposition, the chemist has been +obliged to go from the earth to the heavens, he has been obliged to form a +new science, the science of spectroscopic analysis.</p> + +<p>This subject has been considered in "The Astronomers," belonging to this +series of books; but the point of view from which the matter is there +regarded is astronomical rather than chemical. I should like briefly to +recall to the reader the fundamental facts of this branch of science.<span class='pagenum'><a name="Page_303" id="Page_303">[Pg 303]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/fig4.jpg" width="500" height="248" alt="Fig. 4." title="" /> +<span class="caption">Fig. 4.</span> +</div> + +<p>When a ray of light is allowed to pass through a glass prism and then fall +on to a white surface, the image produced on this surface consists of a +many-coloured band of light. The blue or violet part of this band is more +bent away from the plane of the entering ray than the orange part, and the +latter more than the red part of the band. This is roughly represented in +Fig. 4, where <i>r</i> is the ray of light passing through the prism P, and +emerging as a sevenfold band of coloured lights, of which the violet, V, is +most, and the red band, R, is least bent away from the plane of the ray +<i>r</i>. If the surface—say a white screen—on which the many-coloured band of +light, or <i>spectrum</i>, falls, is punctured by a small hole, so as to admit +the passage of the violet, or blue, or orange, or red light only, and if +this violet, etc., light is then passed through a second prism, no further +breaking up of that light takes place. This state of matters is represented +in the part<span class='pagenum'><a name="Page_304" id="Page_304">[Pg 304]</a></span> of the figure towards the right hand, where the red ray, <span class="smcap">R</span>, is +shown as passing through the screen, and falling on to a second prism, P': +the red ray is slightly bent out of its direct course, but is not +subdivided; it falls on the second screen as a ray of red light, R'. But if +a quantity of the metal sodium is vaporized in a hot non-luminous flame, +and if the yellow light thus produced is passed through a prism, a spectrum +is obtained consisting of a single yellow line (on a dark background), +situated on that part of the screen where the orange-yellow band occurred +when the ray of sunlight was split up by the action of the prism. In Fig. 5 +the yellow light from a flame containing sodium is represented by the line +Y. The light emitted by the glowing sodium vapour is said to be +<i>monochromatic</i>.</p> + +<div class="figcenter" style="width: 499px;"> +<img src="images/fig5.jpg" width="499" height="205" alt="Fig. 5" title="" /> +<span class="caption">Fig. 5</span> +</div> + +<p>Lastly, if the experiment is arranged so that a ray of sunlight or of light +from an electric lamp passes through a layer of comparatively cool sodium +vapour before reaching the prism, a spectrum is<span class='pagenum'><a name="Page_305" id="Page_305">[Pg 305]</a></span> produced corresponding to +the solar spectrum except that a black line appears in the position where +the yellow line, characteristic of sodium, was noticed in the second +experiment.</p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/fig6.jpg" width="500" height="324" alt="Fig. 6." title="" /> +<span class="caption">Fig. 6.</span> +</div> + +<p>Fig. 6 represents the result of this experiment: the ray of sunlight or +electric light, <i>r</i>, passes through a quantity of sodium vapour, and is +then decomposed by the prism; the spectrum produced is marked by the +absence of light (or by a dark line) where the yellow line, Y, was before +noticed.</p> + +<p>These are the fundamental facts of spectroscopic analysis: sunlight is +decomposable into a band of many colours, that is, into a spectrum; light +emitted by a glowing vapour is characterized by the presence of coloured +lines, each of which occupies a definite position with reference to the +various parts of the solar spectrum; sunlight—or the electric<span class='pagenum'><a name="Page_306" id="Page_306">[Pg 306]</a></span> light—when +allowed to pass through a mass of vapour, furnishes a spectrum +characterized by the absence of those bright lines, the presence of which +marked the spectrum of the light obtained by strongly heating the vapour +through which the sunlight has passed.</p> + +<p>The spectrum obtained by decomposing the light emitted by glowing vapour of +potassium is characterized by the presence of certain lines—call them A +and B lines. We are asked what element (or elements) is present in a +certain gas presented to us: we pass a beam of white light through this gas +and then through a prism, and we obtain a continuous spectrum (<i>i.e.</i> a +spectrum of many colours like the solar spectrum) with two dark lines in +the same positions as those occupied by the lines A and B. We therefore +conclude that the gas in question contains vapour of potassium.</p> + +<p>The solar spectrum, when carefully examined, is found to be crossed by a +very large number of fine black lines; the exact positions of many hundreds +of these lines have been carefully determined, and, in most cases, they are +found to correspond to the positions of various bright lines noticed in the +spectra of the lights emitted by hot vapours of various elementary bodies.</p> + +<p>Assume that the sun consists, broadly speaking, of an intensely hot and +luminous central mass, formed to a large extent of the elementary +substances which build up this earth, and that this central mass is +surrounded by a cooler (but yet very hot) gaseous<span class='pagenum'><a name="Page_307" id="Page_307">[Pg 307]</a></span> envelope of the same +elements,—and we have a tolerably satisfactory explanation of the +principal phenomena revealed by the spectroscopic study of the sun's light.</p> + +<p>On this assumption the central mass of glowing iron, chromium, magnesium, +nickel, cobalt, hydrogen, etc., is sending out light; a portion of the +light emitted by the glowing iron is quenched as it passes through a cloud +of cooler iron vapour outside the central mass, a portion of the light +emitted by the glowing chromium is quenched as it passes through a cloud of +cooler chromium vapour, and so on; the black lines in the spectrum are the +records of these various quenchings of this and that light.</p> + +<p>So far then the study of the solar spectrum appears to be tolerably simple, +and this study generally confirms the proposition that the material of +which the sun is composed is, broadly, identical with those forms of matter +which we, on this earth, call the chemical elements.</p> + +<p>But whatever be the composition of the sun, it is, I think, evident that in +dealing with a ray of light coming therefrom, we are dealing with a very +complex phenomenon.</p> + +<p>According to the hypothesis which is now guiding us, the solar light which +passes into our spectroscope has probably had its beginning in some central +part of the sun, and has passed through very thick layers of hot metallic +clouds, agitated perhaps by solar cyclones. Could we examine the light +coming from some defined part of the sun, we should probably<span class='pagenum'><a name="Page_308" id="Page_308">[Pg 308]</a></span> obtain +valuable information. During a solar eclipse red prominences are seen +projecting beyond the dark shadow of the moon, which covers the sun's disc. +Analysis of the light emitted by these prominences has shown that they are +phenomena essentially belonging to the sun itself, and that they consist of +vast masses of intensely hot, glowing gaseous substances, among which +hydrogen is present in large quantities. That these prominences are very +hot, hotter than the average temperature of the ordinary solar atmosphere, +is proved by the fact that the spectrum of the light coming from them is +characterized by bright lines. By special arrangements which need not be +discussed here, but which have been partly explained in "The Astronomers" +(see pp. 334, 335 of that book), it has been shown that these prominences +are in rapid motion: at one moment they shoot up to heights of many +thousand miles, at another they recede towards the centre of the sun.</p> + +<p>We thus arrive at a picture of the solar atmosphere as consisting of layers +of very hot gases, which are continually changing their relative positions +and forms; sometimes ejections of intensely hot, glowing gases occur,—we +call these prominences; sometimes down-rushes of gaseous matter occur,—we +call these spots. Among the substances which compose the gaseous layers we +recognize hydrogen, iron, magnesium, sodium, nickel, chromium, etc., but we +also find substances which can at present be distinguished only by means of +the<span class='pagenum'><a name="Page_309" id="Page_309">[Pg 309]</a></span> wave-lengths of the light which they emit; thus we have 1474 stuff, +5017 stuff, 5369 stuff, etc.</p> + +<p>Let us now turn to another part of this subject. By a special arrangement +of apparatus it is possible to observe the spectrum of the light emitted by +a glowing vapour, parts of which are hotter than other parts, and to +compare the lines in the spectrum of the light coming from the hottest +parts with the lines in the spectrum of the light coming from the cooler +parts of the vapour. If this is done for sodium vapour, certain lines are +apparent in all the spectra, others only in the spectrum of the light +coming from the hottest parts of the sodium vapour: the former lines are +called "long lines," the latter "short lines." A rough representation of +the long and short lines of sodium is given in Fig. 7.</p> + +<div class="figcenter" style="width: 285px;"> +<img src="images/fig7.jpg" width="285" height="500" alt="Fig. 7.—Long and short lines of sodium." title="" /> +<span class="caption">Fig. 7.—Long and short lines of sodium.</span> +</div> + +<p>Now, suppose that the lines in the spectrum of the light emitted by glowing +manganese vapour have been carefully mapped, and classed as long and short +lines: suppose that the same thing has been done for the iron lines: now +let a little manganese be mixed with much iron, let the mixture be +vaporized, and let the light which is emitted be decomposed by the prism of +a spectroscope,<span class='pagenum'><a name="Page_310" id="Page_310">[Pg 310]</a></span> it will be found that the long lines of manganese alone +make their appearance; let a little more manganese be added to the mixture, +and now some of the shorter lines due to manganese begin to appear in the +spectrum. Hence it has been concluded by Lockyer that if the spectrum of +the light emitted by the glowing vapour of any element—call it A—is free +from the long lines of any other element—say element B—this second +element is not present as an impurity in the specimen of element A which is +being examined. Lockyer has applied this conclusion to "purify" various +elementary spectra.</p> + +<p>The spectrum of element A is carefully mapped, and the lines are divided +into long and short lines, according as they are noticed in the spectrum of +the light coming from all parts of the glowing vapour of A, or only in the +spectrum of the light which comes from the hotter parts of that vapour. The +spectra of elements B and C are similarly mapped and classified: then the +three spectra are compared; the longest line in the spectrum of B is noted, +if this line is found in the spectrum of A, it is marked with a negative +sign—this means that so far as the evidence of this line goes B is present +as an impurity in A; the next longest B line is searched for in the +spectrum of A—if present it also is marked with a negative sign; a similar +process of comparison and elimination is conducted with the spectra of A +and C. In this way a "purified" spectrum of the light from A is +obtained—a<span class='pagenum'><a name="Page_311" id="Page_311">[Pg 311]</a></span> spectrum, that is, from which, according to Lockyer, all lines +due to the presence of small quantities of B and C as impurities in A have +been eliminated.</p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/fig8.jpg" width="500" height="370" alt="Fig. 8." title="" /> +<span class="caption">Fig. 8.</span> +</div> + +<p>Fig. 8 is given in order to make this "purifying" process more clearly +understood. But when this process has been completed there remain, in many +cases, a few short lines common to two or more elementary spectra: such +lines are called by Lockyer <i>basic lines</i>. He supposes that these lines are +due to light emitted by forms of matter simpler than our elements; he +thinks that at very high temperatures some of the elements are decomposed, +and that the <i>bases</i> of these elements are produced and give out light, +which light is analyzed<span class='pagenum'><a name="Page_312" id="Page_312">[Pg 312]</a></span> by the spectroscope. Such short basic lines are +marked in the spectra represented in Fig. 8 with a positive sign.</p> + +<p>Now, if the assumption made by Lockyer be admitted, viz. that the short +lines, or some of the short lines, which are coincident in the "purified" +spectra of various elements, are really due to light emitted by forms of +matter into which our so-called elements are decomposed at very high +temperatures, it follows that such lines should become more prominent in +the spectra of the light emitted by elements the higher the temperature to +which these elements are raised. But we know (see p. 308) that the +prominences around the sun's disc are hotter than the average temperature +of the solar atmosphere; hence the spectrum of the light coming from these +prominences ought to be specially rich in "basic" lines: this supposition +is confirmed by experiment. Lockyer has also shown that it is the "basic," +and not the long lines, which are especially affected in the spectra of +light coming from those parts of the solar atmosphere which are subjected +to the action of cyclones, <i>i.e.</i> which are at abnormally high +temperatures. And finally, a very marked analogy has been established +between the changes in the spectrum of the light emitted by a compound +substance as the temperature is raised, and the substance is gradually +decomposed into its elements, and the spectrum of the light emitted by a +so-called elementary substance as the temperature of that substance is +increased.<span class='pagenum'><a name="Page_313" id="Page_313">[Pg 313]</a></span></p> + +<p>But it may be urged that Lockyer's method of "purifying" a spectrum is not +satisfactory; that, although all the longer lines common to two spectra are +eliminated, the coincident short lines which remain are due simply to very +minute quantities of one element present as an impurity in the larger +quantity of the other. Further, it has been shown that several of the +so-called "basic" lines are resolved, by spectroscopes of great dispersive +power, into groups of two or more lines, which lines are not coincident in +different spectra.</p> + +<p>And moreover it is possible to give a fairly satisfactory explanation of +the phenomena of solar chemistry without the aid of the hypothesis that our +elements are decomposed in the sun into simpler forms of matter. +Nevertheless this hypothesis has a certain amount of experimental evidence +in its favour; it may be a true hypothesis. I do not think we are justified +at present either in accepting it as the best guide to further research, or +in wholly rejecting it.</p> + +<p>The researches to which this hypothesis has given rise have certainly +thrown much light on the constitution of the sun and stars, and they have +also been instrumental in forcing new views regarding the nature of the +elements on the attention of chemists, and so of awakening them out of the +slumber into which every class of men is so ready to fall.</p> + +<p>The tale told by the rays of light which travel to this earth from the sun +and stars has not yet<span class='pagenum'><a name="Page_314" id="Page_314">[Pg 314]</a></span> been fully read, but the parts which the chemist has +spelt out seem to say that, although the forms of matter of which the earth +is made are also those which compose the sun and stars, yet in the sun and +stars some of the earthly elements are decomposed, and some of the earthly +atoms are split into simpler forms. The tale, I say, told by the rays of +light seems to bear this interpretation, but it is written in a language +strange to the children of this earth, who can read it as yet but slowly; +for the name given to the new science was "<i>Ge-Urania</i>, because its +production was of earth and heaven. And it could not taste of death, by +reason of its adoption into immortal palaces; but it was to know weakness, +and reliance, and the shadow of human imbecility; and it went with a lame +gait; but in its going it exceeded all mortal children in grace and +swiftness."</p> + +<p>There are certain little particles so minute that at least sixty millions +of them are required to compose the smallest portion of matter which can be +seen by the help of a good microscope. Some of these particles are +vibrating around the edge of an orb a million times larger than the earth, +but at a distance of about ninety millions of miles away. The student of +science is told to search around the edge of the orb till he finds these +particles, and having found them, to measure the rates of their vibrations; +and as an instrument with which to do this he is given—a glass prism! But +he has accomplished the task; he has found the minute particles, and he has +measured their vibration-periods.<span class='pagenum'><a name="Page_315" id="Page_315">[Pg 315]</a></span></p> + +<p>Chemistry is no longer confined to this earth: the chemist claims the +visible universe as his laboratory, and the sunbeams as his servants.</p> + +<p>Davy decomposed soda and potash by using the powerful instrument given him +by Volta; but the chemist to-day has thrown the element he is seeking to +decompose into a crucible, which is a sun or a star, and awaits the result.</p> + +<p>The alchemists were right. There is a philosopher's stone; but that stone +is itself a compound of labour, perseverance, and genius, and the gold +which it produces is the gold of true knowledge, which shall never grow dim +or fade away.</p> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_316" id="Page_316">[Pg 316]</a></span></p> + +<div class="figcenter" style="width: 500px;"> +<img src="images/chap8.jpg" width="500" height="99" alt="" title="" /> +</div> + +<h2>CHAPTER VIII.</h2> + +<h3>SUMMARY AND CONCLUSION.</h3> + + +<p>We have thus traced some of the main paths along which Chemistry has +advanced since the day when, ceasing to be guided by the dreams of men who +toiled with but a single idea in the midst of a world of strange and +complex phenomena, she began to recognize that Nature is complex but +orderly, and so began to be a branch of true knowledge.</p> + +<p>In this review we have, I think, found that the remark made at the +beginning of the introductory chapter is, on the whole, a just one. That +the views of the alchemists, although sometimes very noble, were "vague and +fanciful" is surely borne out by the quotations from their writings given +in the first chapter. This period was followed by that wherein the +accurate, but necessarily somewhat narrow conception of the Lavoisierian +chemistry prevailed. Founded for the most part<span class='pagenum'><a name="Page_317" id="Page_317">[Pg 317]</a></span> on the careful, +painstaking, and quantitative study of one phenomenon—a very wide and +far-reaching phenomenon, it is true—it was impossible that the +classification introduced by the father of chemical science should be broad +enough to include all the discoveries of those who came after him. But +although this classification had of necessity to be revised and recast, the +genius of Lavoisier enunciated certain truths which have remained the +common possession of every chemical system. By proving that however the +forms of matter may be changed the mass remains unaltered, he for the first +time made a science of chemistry possible. He defined "element" once for +all, and thus swept away the fabric of dreams raised by the alchemists on +the visionary foundation of <i>earth</i>, <i>air</i>, <i>fire</i> and <i>water</i>, or of +<i>mercury</i>, <i>sulphur</i> and <i>salt</i>. By his example, he taught that weighings +and measurements must be made before accurate knowledge of chemical +reactions can be hoped for; and by his teaching about oxygen being <i>the +acidifier</i>—although we know that this teaching was erroneous in many +details—he showed the possibility of a system of classification of +chemical substances being founded on the actually observed properties and +composition of those substances.</p> + +<p>Lavoisier gained these most important results by concentrating his +attention on a few subjects of inquiry. That chemistry might become broad +it was necessary that it should first of all become narrower.<span class='pagenum'><a name="Page_318" id="Page_318">[Pg 318]</a></span></p> + +<p>The period when the objects of the science were defined and some of its +fundamental facts and conceptions were established, was succeeded, as we +saw in our sketch, by that in which Dalton departed somewhat from the +method of investigation adopted by most masters in science, and by +concentrating his great mental powers on facts belonging to one branch of +natural knowledge, elaborated a simple but very comprehensive theory, which +he applied to explain the facts belonging to another branch of science.</p> + +<p>Chemistry was thus endowed with a grand and far-reaching conception, which +has been developed and applied by successive generations of investigators: +but we must not forget that it was the thorough, detailed work of Black and +Lavoisier which made possible the great theory of Dalton.</p> + +<p>At the time when Dalton was thinking out his theory of atoms, Davy was +advancing as a conqueror through the rich domain which the discovery of +Volta had opened to chemistry. Dalton, trained to rely on himself, +surrounded from his youth by an atmosphere in which "sweetness and light" +did not predominate, thrown on the world at an early age, and obliged to +support himself by the drudgery of teaching when he would fain have been +engaged in research, and at the same time—if we may judge from his life as +recorded by his biographers—without the sustaining presence of such an +ideal as could support the emotional part of his nature during this time of +struggle,—Dalton,<span class='pagenum'><a name="Page_319" id="Page_319">[Pg 319]</a></span> we found, withdrew in great part from contact with +other scientific workers, and communing only with himself, developed a +theory which, while it showed him to be one in the chain of thinkers that +begins in Democritus and Leucippus, was nevertheless stamped with the +undeniable marks of his own individuality and genius, and at the same time +was untouched by any of the hopes or fears, and unaffected by any of the +passions, of our common humanity.</p> + +<p>Davy, on the other hand, was surrounded from childhood by scenes of great +natural beauty and variety, by contact with which he was incited to eager +desire for knowledge, while at the same time his emotions remained fresh +and sensitive to outward impressions. Entering on the study of natural +science when there was a pause in the march of discovery, but a pause +presageful of fresh advances, he found outward circumstances singularly +favourable to his success; seizing these favourable circumstances he made +rapid advances. Like Lavoisier, he began his work by proving that there is +no such thing in Nature as transmutation, in the alchemical meaning of the +term; as Lavoisier had proved that water is not changed into earth, so did +Davy prove that acid and alkali are not produced by the action of the +electric current on pure water. We have shortly traced the development of +the electro-chemical theory which Davy raised on the basis of experiment; +we have seen how facts obliged him to doubt the accepted view of the<span class='pagenum'><a name="Page_320" id="Page_320">[Pg 320]</a></span> +composition of hydrochloric acid and chlorine, and how by the work he did +on these subjects chemists have been finally convinced that an element is +not a substance which <i>cannot be</i>, but a substance which <i>has not been</i> +decomposed, and how from this work has also arisen the modern theory of +acids, bases and salts.</p> + +<p>We found that, by the labours of the great Swede J. J. Berzelius, the +Daltonian theory was confirmed by a vast series of accurate analyses, and, +in conjunction with a modification of the electro-chemical theory of Davy, +was made the basis of a system of classification which endeavoured to +include all chemical substances within its scope. The atom was the +starting-point of the Berzelian system, but that chemist viewed the atom as +a dual structure the parts of which held together by reason of their +opposite electrical polarities. Berzelius, we saw, greatly improved the +methods whereby atomic weights could be determined, and he recognized the +importance of physical generalizations as aids in finding the atomic +weights of chemical substances.</p> + +<p>But Berzelius came to believe too implicitly in his own view of Nature's +working; his theory became too imperious. Chemists found it easier to +accept than to doubt an interpretation of facts which was in great part +undeniably true, and which formed a central luminous conception, shedding +light on the whole mass of details which, without it, seemed confused and +without meaning.</p> + +<p>If the dualistic stronghold was to be carried, the<span class='pagenum'><a name="Page_321" id="Page_321">[Pg 321]</a></span> attack should be +impetuous, and should be led by men, not only of valour, but also of +discretion. We found that two champions appeared, and that, aided by others +who were scarcely inferior soldiers to themselves, they made the attack, +and made it with success.</p> + +<p>But when the heat of the battle was over and the bitterness of the strife +forgotten, it was found that, although many pinnacles of the dualistic +castle had been shattered, the foundation and great part of the walls +remained; and, strange to say, the men who led the attack were content that +these should remain.</p> + +<p>The atom could no longer be regarded as always composed of two parts, but +must be looked on rather as one whole, the properties of which are defined +by the properties and arrangements of all its parts; but the conception of +the atom as a structure, and the assurance that something could be inferred +regarding that structure from a knowledge of the reactions and general +properties of the whole, remained when Dumas and Liebig had replaced the +dualism of Berzelius by the unitary theory of modern chemistry; and these +conceptions have remained to the present day, and are now ranked among the +leading principles of chemical science; only we now speak of the "molecule" +where Berzelius spoke of the "atom."</p> + +<p>Along with these advances made by Dumas, Liebig and others in rendering +more accurate the general conception of atomic structure, we found<span class='pagenum'><a name="Page_322" id="Page_322">[Pg 322]</a></span> that +the recognition of the existence of more than one order of small particles +was daily gaining ground in the minds of chemists.</p> + +<p>The distinction between what we now call atoms and molecules had been +clearly stated by Avogadro in 1811; but the times were not ripe. The mental +surroundings of the chemists of that age did not allow them fully to +appreciate the work of Avogadro. The seed however was sown, and the +harvest, although late, was plentiful.</p> + +<p>We saw that Dumas accepted, with some hesitation, the distinction drawn by +Avogadro, but that failing to carry it to its legitimate conclusion, he did +not reap the full benefit of his acceptance of the principle that the +smallest particle of a substance which takes part in a physical change +divides into smaller particles in those changes which we call chemical.</p> + +<p>To Gerhardt and Laurent we owe the full recognition, and acceptance as the +foundation of chemical classification, of the atom as a particle of matter +distinct from the molecule; they first distinctly placed the law of +Avogadro—"Equal volumes of gases contain equal numbers of molecules"—in +its true position as a law, which, resting on physical evidence and +dynamical reasoning, is to be accepted by the chemist as the basis of his +atomic theory. To the same chemists we are indebted for the formal +introduction into chemical science of the conception of types, which, as we +found, was developed by Frankland, Kekulé, and others, into the modern<span class='pagenum'><a name="Page_323" id="Page_323">[Pg 323]</a></span> +doctrine of equivalency of groups of elementary atoms.</p> + +<p>We saw that, in the use which he made of the laws of Mitscherlich, and of +Dulong and Petit, Berzelius recognized the importance of the aid given by +physical methods towards solving the atomic problems of chemistry; but +among those who have most thoroughly availed themselves of such aids Graham +must always hold a foremost place.</p> + +<p>Graham devoted the energies of his life to tracking the movements of atoms +and molecules. He proved that gases pass through walls of solid materials, +as they pass through spaces already occupied by other gases; and by +measuring the rapidities of these movements he showed how it was possible +to determine the rate of motion of a particle of gas so minute that a group +of a hundred millions of them would be invisible to the unassisted vision. +Graham followed the molecules as in their journeyings they came into +contact with animal and vegetable membranes; he found that these membranes +presented an insuperable barrier to the passage of some molecules, while +others passed easily through. He thus arrived at a division of matter into +colloidal and crystalloidal. He showed what important applications of this +division might be made in practical chemistry, he discussed some of the +bearings of this division on the general theory of the molecular +constitution of matter, and thus he opened the way which leads into a new +territory<span class='pagenum'><a name="Page_324" id="Page_324">[Pg 324]</a></span> rich in promise to him who is able to follow the footsteps of +its discoverer.</p> + +<p>Other investigators have followed on the general lines laid down by Graham; +connections, more or less precise, have been established between chemical +and physical properties of various groups of compounds. It has been shown +that the boiling points, melting points, expansibilities by heat, amounts +of heat evolved during combustion, in some cases tinctorial powers of +dye-stuffs, and other physical constants of groups of compounds, vary with +variations in the nature, number and arrangements of the atoms in the +molecules of these compounds.</p> + +<p>But although much good work has been done in this direction, our ignorance +far exceeds our knowledge regarding the phenomena which lie on the +borderlands between chemistry and physics. It is probably here that +chemists look most for fresh discoveries of importance.</p> + +<p>As each branch of natural science becomes more subdivided, and as the +quantity of facts to be stored in the mind becomes daily more crushing, the +student finds an ever-increasing difficulty in passing beyond the range of +his own subject, and in gaining a broad view of the relative importance of +the facts and the theories which to him appear so essential.</p> + +<p>In the days when the foundation of chemistry was laid by Black, Priestley, +Lavoisier and Dalton, and when the walls began to be raised by Berzelius<span class='pagenum'><a name="Page_325" id="Page_325">[Pg 325]</a></span> +and Davy, it was possible for one man to hold in his mental grasp the whole +range of subjects which he studied. Even when Liebig and Dumas built the +fabric of organic chemistry the mass of facts to be considered was not so +overpowering as it is now. But we have in great measure ourselves to blame; +we have of late years too much fulfilled Liebig's words, when he said, that +for rearing the structure of organic chemistry masters were no longer +required—workmen would suffice.</p> + +<p>And I think we have sometimes fallen into another error also. Most of the +builders of our science—notably Lavoisier and Davy, Liebig and Dumas—were +men of wide general culture. Chemistry was for them a branch of natural +science; of late years it has too much tended to degenerate into a +handicraft. These men had lofty aims; they recognized—Davy perhaps more +than any—the nobility of their calling. The laboratory was to them not +merely a place where curious mixtures were made and strange substances +obtained, or where elegant apparatus was exhibited and carefully prepared +specimens were treasured; it was rather the entrance into the temple of +Nature, the place where day by day they sought for truth, where, amid much +that was unpleasant and much that was necessary mechanical detail, glimpses +were sometimes given them of the order, harmony and law which reign +throughout the material universe. It was a place where, stopping in the +work which to the outsider appeared so<span class='pagenum'><a name="Page_326" id="Page_326">[Pg 326]</a></span> dull and even so trivial, they +sometimes, listening with attentive ear, might catch the boom of the +"mighty waters rolling evermore," and so might return refreshed to work +again.</p> + +<p>Chemistry was more poetical, more imaginative then than now; but without +imagination no great work has been accomplished in science.</p> + +<p>When a student of science forgets that the particular branch of natural +knowledge which he cultivates is part of a living and growing organism, and +attempts to study it merely as a collection of facts, he has already +Esau-like sold his birthright for a mess of pottage; for is it not the +privilege of the scientific student of Nature always to work in the +presence of "something which he can never know to the full, but which he is +always going on to know"—to be ever encompassed about by the greatness of +the subject which he seeks to know? Does he not recognize that, although +some of the greatest minds have made this study the object of their lives, +the sum of what is known is yet but as a drop in the ocean? and has he not +also been taught that every honest effort made to extend the boundaries of +natural knowledge must advance that knowledge a little way?</p> + +<p>It is not easy to remember the greatness of the issues which depend on +scientific work, when that work is carried on, as it too often is, solely +with the desire to gain a formal and definite answer to some question of +petty detail.<span class='pagenum'><a name="Page_327" id="Page_327">[Pg 327]</a></span></p> + +<div class="poem"><div class="stanza"> +<span class="i0">"That low man seeks a little thing to do,<br /></span> +<span class="i8">Sees it and does it:<br /></span> +<span class="i0">This high man, with a great thing to pursue,<br /></span> +<span class="i8">Dies ere he knows it.<br /></span> +</div><div class="stanza"> +<span class="i0">"That low man goes on adding one to one,<br /></span> +<span class="i8">His hundred's soon hit:<br /></span> +<span class="i0">This high man, aiming at a million,<br /></span> +<span class="i8">Misses a unit."<br /></span> +</div></div> + + + +<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_329" id="Page_329">[Pg 329]</a></span></p> +<h2>INDEX.</h2> + + +<p> +A<br /> +<br /> +Acids, connected by Lavoisier with oxygen, <a href='#Page_91'>91</a>;<br /> +<span style="margin-left: 1em;">Boyle's and other early definitions, <a href='#Page_171'>171</a>;</span><br /> +<span style="margin-left: 1em;">opposed in early medicine to alkalis, <a href='#Page_172'>172</a>;</span><br /> +<span style="margin-left: 1em;">grouped, <a href='#Page_173'>173</a>;</span><br /> +<span style="margin-left: 1em;">salts, <a href='#Page_173'>173</a>;</span><br /> +<span style="margin-left: 1em;">"the primordial acid," <a href='#Page_174'>174</a>;</span><br /> +<span style="margin-left: 1em;">oxygen not a necessary constituent, <a href='#Page_184'>184</a>;</span><br /> +<span style="margin-left: 1em;">new division of acids by Davy, <a href='#Page_205'>205</a>;</span><br /> +<span style="margin-left: 1em;">acids of different basicity, <a href='#Page_237'>237</a>;</span><br /> +<span style="margin-left: 1em;">modern conception of acids, <a href='#Page_301'>301</a>.</span><br /> +<br /> +Affinity, chemical, apparently suspended by electricity, <a href='#Page_191'>191</a>;<br /> +<span style="margin-left: 1em;">history of term "affinity," <a href='#Page_206'>206</a>;</span><br /> +<span style="margin-left: 1em;">tables of, <a href='#Page_207'>207</a>;</span><br /> +<span style="margin-left: 1em;">dependent on electric states, <a href='#Page_210'>210</a>.</span><br /> +<br /> +Air, composition of, determined by Cavendish, <a href='#Page_79'>79</a>;<br /> +<span style="margin-left: 1em;">Dalton's investigations, <a href='#Page_116'>116</a>.</span><br /> +<br /> +Alchemy, <a href='#Page_5'>5</a>;<br /> +<span style="margin-left: 1em;">alchemical symbols of metals, <a href='#Page_11'>11</a>;</span><br /> +<span style="margin-left: 1em;">quotations from alchemists, <a href='#Page_15'>15</a>, <a href='#Page_17'>17</a>;</span><br /> +<span style="margin-left: 1em;">alchemical poetry, <a href='#Page_18'>18</a>.</span><br /> +<br /> +Alcoates, <a href='#Page_235'>235</a>.<br /> +<br /> +Alkalis, <a href='#Page_171'>171</a>;<br /> +<span style="margin-left: 1em;">fixed and volatile, <a href='#Page_173'>173</a>;</span><br /> +<span style="margin-left: 1em;">mild and caustic, examined by Black, <a href='#Page_176'>176</a>;</span><br /> +<span style="margin-left: 1em;">connection with earths, <a href='#Page_178'>178</a>;</span><br /> +<span style="margin-left: 1em;">name of "base" given by Rouelle, <a href='#Page_179'>179</a>;</span><br /> +<span style="margin-left: 1em;">Gay-Lussac's alkalizing principle, <a href='#Page_203'>203</a>.</span><br /> +<br /> +Ammonia, discovered by Priestley, <a href='#Page_66'>66</a>.<br /> +<br /> +Atmolysis, <a href='#Page_243'>243</a>.<br /> +<br /> +Atomic theory, dawn of, <a href='#Page_117'>117</a>;<br /> +<span style="margin-left: 1em;">early views of Greek philosophers, <a href='#Page_123'>123</a>;</span><br /> +<span style="margin-left: 1em;">of Epicurus and Lucretius, <a href='#Page_124'>124</a>;</span><br /> +<span style="margin-left: 1em;">of Newton and Bernoulli, <a href='#Page_125'>125</a>;</span><br /> +<span style="margin-left: 1em;">Dalton's new views—combination in simple multiples, <a href='#Page_127'>127</a>, <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">the theory made known by Dr. Thomson, <a href='#Page_129'>129</a>;</span><br /> +<span style="margin-left: 1em;">it is opposed at first by Davy, <a href='#Page_130'>130</a>;</span><br /> +<span style="margin-left: 1em;">Dalton's rules for arriving at atomic weights, <a href='#Page_132'>132</a>;</span><br /> +<span style="margin-left: 1em;">more accurately applied by Berzelius, <a href='#Page_133'>133</a>, <a href='#Page_162'>162</a>;</span><br /> +<span style="margin-left: 1em;">diagrams of atoms, <a href='#Page_118'>118</a>, <a href='#Page_136'>136</a>;</span><br /> +<span style="margin-left: 1em;">the theory as carried out by Gay-Lussac and Avogadro, <a href='#Page_138'>138</a>, <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">conception of the molecule, <a href='#Page_140'>140</a>;</span><br /> +<span style="margin-left: 1em;">molecular and atomic weight, <a href='#Page_145'>145</a>;</span><br /> +<span style="margin-left: 1em;">Graham's work on molecular reactions, <a href='#Page_249'>249</a>;</span><br /> +<span style="margin-left: 1em;">Berzelius's dualistic views, <a href='#Page_212'>212</a>;</span><br /> +<span style="margin-left: 1em;">they are attacked by Dumas, <a href='#Page_260'>260</a>;</span><br /> +<span style="margin-left: 1em;">conception of the compound radicle, <a href='#Page_267'>267</a>;</span><br /> +<span style="margin-left: 1em;">Laurent's unitary theory, <a href='#Page_272'>272</a>;</span><br /> +<span style="margin-left: 1em;">modern conception of molecule, <a href='#Page_275'>275</a>;</span><br /> +<span style="margin-left: 1em;">revision of atomic weights, <a href='#Page_285'>285</a>;</span><br /> +<span style="margin-left: 1em;">equivalency of atoms, <a href='#Page_295'>295</a>.</span><br /> +<br /> +Avogadro, his elucidation of the atomic theory, <a href='#Page_138'>138</a>, <i>et seq.</i>;<br /> +<span style="margin-left: 1em;">introduces the idea of molecules, <a href='#Page_140'>140</a>;</span><br /> +<span style="margin-left: 1em;">law known as Avogadro's law, <a href='#Page_143'>143</a>.</span><br /> +<br /> +<br /> +B<br /> +<br /> +Base (of salts), <a href='#Page_179'>179</a>;<br /> +<span style="margin-left: 1em;">basic lines in spectrum, <a href='#Page_311'>311</a>.</span><br /> +<br /> +Becher, John J., born at Speyer, <a href='#Page_26'>26</a>;<br /> +<span style="margin-left: 1em;">his three principles of metals, <a href='#Page_26'>26</a>;</span><br /> +<span style="margin-left: 1em;">his principle of inflammability, <a href='#Page_48'>48</a>;</span><br /> +<span style="margin-left: 1em;">his views on acids, <a href='#Page_174'>174</a>.</span><br /> +<br /> +Berthollet, analyzes ammonia, <a href='#Page_66'>66</a>;<br /> +<span style="margin-left: 1em;">adheres to the Lavoisierian theory of combustion, <a href='#Page_95'>95</a>;</span><br /> +<span style="margin-left: 1em;">questions doctrine of fixity of composition, <a href='#Page_126'>126</a>;</span><br /> +<span style="margin-left: 1em;">and necessary presence of oxygen in acids, <a href='#Page_184'>184</a>;</span><br /> +<span style="margin-left: 1em;">shows variable nature of affinities, <a href='#Page_208'>208</a>.</span><br /> +<br /> +<b>Berzelius</b>, Johann J., <a href='#Page_106'>106</a>;<br /> +<span style="margin-left: 1em;">determines weights of elementary atoms, <a href='#Page_133'>133</a>;</span><br /> +<span style="margin-left: 1em;">his birth and education, <a href='#Page_157'>157</a>;</span><br /> +<span style="margin-left: 1em;">works at Stockholm, <a href='#Page_159'>159</a>;</span><br /> +<span style="margin-left: 1em;">his slight appliances and large discoveries, <a href='#Page_161'>161</a>;</span><br /> +<span style="margin-left: 1em;">he reviews Dalton's atomic theory, <a href='#Page_162'>162</a>;</span><br /> +<span style="margin-left: 1em;">his views superseded by Avogadro's generalization, <a href='#Page_165'>165</a>;</span><br /> +<span style="margin-left: 1em;">he accepts law of isomorphism, <a href='#Page_166'>166</a>;</span><br /> +<span style="margin-left: 1em;">and Davy's discovery of chlorine, <a href='#Page_204'>204</a>;</span><br /> +<span style="margin-left: 1em;">his views on affinity of atoms, <a href='#Page_209'>209</a>;</span><br /> +<span style="margin-left: 1em;">his dual classification, <a href='#Page_212'>212</a>;</span><br /> +<span style="margin-left: 1em;">works at organic chemistry, <a href='#Page_220'>220</a>;</span><br /> +<span class='pagenum'><a name="Page_330" id="Page_330">[Pg 330]</a></span><span style="margin-left: 1em;">his dualism attacked by Dumas, <a href='#Page_260'>260</a>.</span><br /> +<br /> +<b>Black</b>, Joseph, born at Bordeaux, <a href='#Page_30'>30</a>;<br /> +<span style="margin-left: 1em;">his education, <a href='#Page_31'>31</a>;</span><br /> +<span style="margin-left: 1em;">his thesis on magnesia and discovery of "fixed air," <a href='#Page_33'>33</a>, <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">inquiries into latent heat, <a href='#Page_39'>39</a>;</span><br /> +<span style="margin-left: 1em;">professor at Edinburgh, <a href='#Page_41'>41</a>;</span><br /> +<span style="margin-left: 1em;">his death and character, <a href='#Page_41'>41</a>, <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;"><i>resumé</i> of his work, <a href='#Page_102'>102</a>;</span><br /> +<span style="margin-left: 1em;">his examination of alkalis, <a href='#Page_176'>176</a>.</span><br /> +<br /> +Boyle, Hon. Robert, <a href='#Page_25'>25</a>;<br /> +<span style="margin-left: 1em;">his "Sceptical Chymist," <a href='#Page_76'>76</a>;</span><br /> +<span style="margin-left: 1em;">law known as "Boyle's law," <a href='#Page_77'>77</a>;</span><br /> +<span style="margin-left: 1em;">opposes doctrine of elementary principles, <a href='#Page_93'>93</a>;</span><br /> +<span style="margin-left: 1em;">his definition of an acid, <a href='#Page_171'>171</a>;</span><br /> +<span style="margin-left: 1em;">extends the knowledge of salts, <a href='#Page_177'>177</a>.</span><br /> +<br /> +Bromine, discovered by Balard, <a href='#Page_291'>291</a>.<br /> +<br /> +<br /> +C<br /> +<br /> +Carbonic acid gas, or "fixed air," studied by Black, <a href='#Page_35'>35</a>;<br /> +<span style="margin-left: 1em;">by Priestley, <a href='#Page_57'>57</a>, <a href='#Page_69'>69</a>.</span><br /> +<br /> +Cavendish, Hon. Henry, rediscovers hydrogen, <a href='#Page_63'>63</a>, <a href='#Page_78'>78</a>;<br /> +<span style="margin-left: 1em;">and composition of water and air, <a href='#Page_78'>78</a>.</span><br /> +<br /> +Chloral, } produced by Liebig, composition determined by Dumas, <a href='#Page_273'>273</a>.<br /> +Chloroform,}<br /> +<br /> +Chlorine, discovered by Davy, <a href='#Page_202'>202</a>;<br /> +<span style="margin-left: 1em;">replaces hydrogen in organic compounds, <a href='#Page_271'>271</a>.</span><br /> +<br /> +Colloids, <a href='#Page_247'>247</a>.<br /> +<br /> +Combination in multiple proportions, <a href='#Page_127'>127</a>.<br /> +<br /> +Combustion, studied by early chemists, <a href='#Page_24'>24</a> (<i>vide</i> "Phlogistic theory");<br /> +<span style="margin-left: 1em;">studied by Black, <a href='#Page_47'>47</a>;</span><br /> +<span style="margin-left: 1em;">his views of Lavoisier's theory, <a href='#Page_51'>51</a>;</span><br /> +<span style="margin-left: 1em;">Priestley's views of combustion, <a href='#Page_62'>62</a>;</span><br /> +<span style="margin-left: 1em;">Lavoisier's experiments, <a href='#Page_83'>83</a>, <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">Liebig's combustion-tube, <a href='#Page_263'>263</a>.</span><br /> +<br /> +Compound radicle, <a href='#Page_267'>267</a>;<br /> +<span style="margin-left: 1em;">the idea of substitution, <a href='#Page_270'>270</a>, <a href='#Page_276'>276</a>.</span><br /> +<br /> +Conservation of mass, doctrine of, <a href='#Page_82'>82</a>.<br /> +<br /> +Crystallization, water of, <a href='#Page_237'>237</a>.<br /> +<br /> +Crystalloids, <a href='#Page_247'>247</a>.<br /> +<br /> +<br /> +D<br /> +<br /> +<b>Dalton</b>, John, his birth and education, <a href='#Page_107'>107</a>;<br /> +<span style="margin-left: 1em;">"answers to correspondents," <a href='#Page_109'>109</a>;</span><br /> +<span style="margin-left: 1em;">his meteorological observations, <a href='#Page_110'>110</a>;</span><br /> +<span style="margin-left: 1em;">teaches at Manchester, <a href='#Page_110'>110</a>;</span><br /> +<span style="margin-left: 1em;">colour-blind, <a href='#Page_111'>111</a>;</span><br /> +<span style="margin-left: 1em;">pressures of gaseous mixtures, <a href='#Page_113'>113</a>;</span><br /> +<span style="margin-left: 1em;">strives after general laws, <a href='#Page_115'>115</a>;</span><br /> +<span style="margin-left: 1em;">first view of atomic theory, <a href='#Page_117'>117</a>;</span><br /> +<span style="margin-left: 1em;">visits Paris, <a href='#Page_120'>120</a>;</span><br /> +<span style="margin-left: 1em;">honours conferred on him, <a href='#Page_121'>121</a>, <a href='#Page_122'>122</a>;</span><br /> +<span style="margin-left: 1em;">dies, <a href='#Page_123'>123</a>;</span><br /> +<span style="margin-left: 1em;">consideration of atomic theory (which see), <a href='#Page_123'>123</a>, <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">his "New System of Chemical Philosophy," <a href='#Page_129'>129</a>;</span><br /> +<span style="margin-left: 1em;">fixes atomic weight of hydrogen, <a href='#Page_130'>130</a>;</span><br /> +<span style="margin-left: 1em;">small use he makes of books, <a href='#Page_148'>148</a>;</span><br /> +<span style="margin-left: 1em;">inaccurate as an experimenter, <a href='#Page_149'>149</a>;</span><br /> +<span style="margin-left: 1em;">his method compared with Priestley's, <a href='#Page_151'>151</a>.</span><br /> +<br /> +<b>Davy</b>, Sir Humphry, <a href='#Page_106'>106</a>;<br /> +<span style="margin-left: 1em;">opposes the atomic theory, <a href='#Page_129'>129</a>;</span><br /> +<span style="margin-left: 1em;">accepts same, <a href='#Page_130'>130</a>;</span><br /> +<span style="margin-left: 1em;">studies the chemical aspects of electricity, <a href='#Page_185'>185</a>;</span><br /> +<span style="margin-left: 1em;">experiments on the acid and alkali said to be produced by electrolyzing water, <a href='#Page_186'>186</a>;</span><br /> +<span style="margin-left: 1em;">apparent suspension of chemical affinities by action of electricity, <a href='#Page_191'>191</a>;</span><br /> +<span style="margin-left: 1em;">discovers potassium, <a href='#Page_197'>197</a>;</span><br /> +<span style="margin-left: 1em;">and sodium, <a href='#Page_198'>198</a>;</span><br /> +<span style="margin-left: 1em;">the metallic bases of earths, <a href='#Page_200'>200</a>;</span><br /> +<span style="margin-left: 1em;">proves the elementary nature of chlorine, <a href='#Page_202'>202</a>;</span><br /> +<span style="margin-left: 1em;">Davy's birth and youth, <a href='#Page_215'>215</a>;</span><br /> +<span style="margin-left: 1em;">experiments on heat, <a href='#Page_217'>217</a>;</span><br /> +<span style="margin-left: 1em;">his work at Bristol, <a href='#Page_218'>218</a>;</span><br /> +<span style="margin-left: 1em;">inhales gases, <a href='#Page_220'>220</a>;</span><br /> +<span style="margin-left: 1em;">lectures at the Royal Institution, <a href='#Page_222'>222</a>;</span><br /> +<span style="margin-left: 1em;">discovers iodine and invents safety-lamp, <a href='#Page_224'>224</a>;</span><br /> +<span style="margin-left: 1em;">dies, <a href='#Page_226'>226</a>.</span><br /> +<br /> +Dialysis, <a href='#Page_247'>247</a>.<br /> +<br /> +Diffusion-rates of gases, <a href='#Page_241'>241</a>;<br /> +<span style="margin-left: 1em;">distinguished from transpiration-rates, <a href='#Page_242'>242</a>;</span><br /> +<span style="margin-left: 1em;">diffusion-rates of liquids, <a href='#Page_245'>245</a>.</span><br /> +<br /> +Dulong, his law of atomic heat, <a href='#Page_168'>168</a>.<br /> +<br /> +<b>Dumas</b>, Jean B. A., birth and education, <a href='#Page_257'>257</a>;<br /> +<span style="margin-left: 1em;">physiological studies, <a href='#Page_258'>258</a>;</span><br /> +<span style="margin-left: 1em;">meets Von Humboldt, <a href='#Page_259'>259</a>;</span><br /> +<span style="margin-left: 1em;">attacks the dualism of Berzelius, <a href='#Page_260'>260</a>;</span><br /> +<span style="margin-left: 1em;">Dumas's vapour density process, <a href='#Page_262'>262</a>;</span><br /> +<span style="margin-left: 1em;">ethers and alcohols, <a href='#Page_265'>265</a>;</span><br /> +<span style="margin-left: 1em;">chlorine in connection with organic compounds, <a href='#Page_271'>271</a>;</span><br /> +<span style="margin-left: 1em;">determines composition of chloral and chloroform, <a href='#Page_273'>273</a>;</span><br /> +<span style="margin-left: 1em;">studies fermentation, <a href='#Page_287'>287</a>;</span><br /> +<span style="margin-left: 1em;">member of the National Assembly, <a href='#Page_288'>288</a>;</span><br /> +<span style="margin-left: 1em;">takes office, <a href='#Page_289'>289</a>.</span><br /> +<br /> +<br /> +E<br /> +<br /> +Earths, <a href='#Page_177'>177</a>;<br /> +<span style="margin-left: 1em;">Stahl's views, <a href='#Page_178'>178</a>;</span><br /> +<span style="margin-left: 1em;">the connection between earths and alkalis, <a href='#Page_178'>178</a>;</span><br /> +<span style="margin-left: 1em;">their metallic bases, <a href='#Page_182'>182</a>, <a href='#Page_200'>200</a>.</span><br /> +<br /> +Economy of waste materials, <a href='#Page_300'>300</a>.<br /> +<br /> +Electric affinity, <a href='#Page_191'>191</a>, <a href='#Page_210'>210</a>.<br /> +<br /> +Electricity, Volta's battery, <a href='#Page_185'>185</a>;<br /> +<span style="margin-left: 1em;">used to decompose water, <a href='#Page_185'>185</a>;</span><br /> +<span style="margin-left: 1em;">new metals discovered by its help, <a href='#Page_197'>197</a>.</span><br /> +<br /> +Elements: old doctrine of elementary principles opposed by Boyle, <a href='#Page_93'>93</a>;<br /> +<span style="margin-left: 1em;">modern definition of element, <a href='#Page_95'>95</a></span><br /> +<span style="margin-left: 1em;">(<i>vide</i> "Spectroscopic analysis"—basic lines, <a href='#Page_311'>311</a>).</span><br /> +<br /> +Equivalency, conception of, <a href='#Page_294'>294</a>.<br /> +<br /> +<br /> +F<br /> +<br /> +Fermentation, studied by Dumas, <a href='#Page_287'>287</a>.<br /> +<br /> +<span class='pagenum'><a name="Page_331" id="Page_331">[Pg 331]</a></span>Fourcroy, calls Lavoisier's views "La chimie Française,", <a href='#Page_95'>95</a><br /> +<br /> +<br /> +G<br /> +<br /> +Gay-Lussac, <a href='#Page_138'>138</a>, <a href='#Page_143'>143</a>, <a href='#Page_201'>201</a>, <a href='#Page_203'>203</a>, <a href='#Page_257'>257</a>.<br /> +<br /> +Gerhardt, <a href='#Page_272'>272</a>, <a href='#Page_279'>279</a>.<br /> +<br /> +<b>Graham</b>, Thomas, early life, <a href='#Page_233'>233</a>;<br /> +<span style="margin-left: 1em;">made Master of the Mint, <a href='#Page_234'>234</a>;</span><br /> +<span style="margin-left: 1em;">his death, <a href='#Page_235'>235</a>;</span><br /> +<span style="margin-left: 1em;">studies alcoates, <a href='#Page_235'>235</a>;</span><br /> +<span style="margin-left: 1em;">formulates conception of acids of different basicity, <a href='#Page_237'>237</a>;</span><br /> +<span style="margin-left: 1em;">considers hydrogen a metal, <a href='#Page_238'>238</a>;</span><br /> +<span style="margin-left: 1em;">investigates phenomena observed by Döbereiner, <a href='#Page_240'>240</a>;</span><br /> +<span style="margin-left: 1em;">diffusion-rates of gases, <a href='#Page_241'>241</a>;</span><br /> +<span style="margin-left: 1em;">of liquids, <a href='#Page_245'>245</a>;</span><br /> +<span style="margin-left: 1em;">his atmolyzer, <a href='#Page_243'>243</a>;</span><br /> +<span style="margin-left: 1em;">his dialyzer, <a href='#Page_247'>247</a>;</span><br /> +<span style="margin-left: 1em;">studies movements and reactions of molecules, <a href='#Page_249'>249</a>.</span><br /> +<br /> +<br /> +H<br /> +<br /> +Hales's experiments on gases, <a href='#Page_34'>34</a>.<br /> +<br /> +Heat, Black's study of latent heat, <a href='#Page_39'>39</a>;<br /> +<span style="margin-left: 1em;">specific heat, <a href='#Page_98'>98</a>;</span><br /> +<span style="margin-left: 1em;">Dalton lectures on, <a href='#Page_117'>117</a>;</span><br /> +<span style="margin-left: 1em;">law of capacity for heat, <a href='#Page_168'>168</a>;</span><br /> +<span style="margin-left: 1em;">heat as produced by friction, <a href='#Page_217'>217</a>.</span><br /> +<br /> +Helmholtz, <a href='#Page_143'>143</a>;<br /> +<span style="margin-left: 1em;">vortex atoms, <a href='#Page_125'>125</a>.</span><br /> +<br /> +Hooke, Robert, his "Micographia," <a href='#Page_24'>24</a>;<br /> +<span style="margin-left: 1em;">studies combustion, <a href='#Page_34'>34</a>.</span><br /> +<br /> +Humboldt, Alexander von, assists Liebig, <a href='#Page_256'>256</a>;<br /> +<span style="margin-left: 1em;">and Dumas, <a href='#Page_259'>259</a>.</span><br /> +<br /> +Hydrochloric acid discovered by Priestley, <a href='#Page_66'>66</a>;<br /> +<span style="margin-left: 1em;">a stumbling-block to Lavoisierian chemists, <a href='#Page_200'>200</a>;</span><br /> +<span style="margin-left: 1em;">studied by Davy, <a href='#Page_201'>201</a>.</span><br /> +<br /> +Hydrogen, rediscovered by Cavendish, <a href='#Page_63'>63</a>;<br /> +<span style="margin-left: 1em;">experimented on by Priestley, <a href='#Page_66'>66</a>;</span><br /> +<span style="margin-left: 1em;">its atomic weight decided by Dalton, <a href='#Page_130'>130</a>;</span><br /> +<span style="margin-left: 1em;">Graham considers it a metal, <a href='#Page_238'>238</a>.</span><br /> +<br /> +<br /> +I<br /> +<br /> +Iodine, discovered by Davy, <a href='#Page_224'>224</a>.<br /> +<br /> +Isomerism, <a href='#Page_297'>297</a>.<br /> +<br /> +Isomorphism, law of, <a href='#Page_167'>167</a>.<br /> +<br /> +<br /> +L<br /> +<br /> +Laplace, assists Lavoisier, <a href='#Page_90'>90</a>.<br /> +<br /> +Latent heat, Black's theory of, <a href='#Page_39'>39</a>.<br /> +<br /> +Laurent, his unitary theory, <a href='#Page_272'>272</a>, <a href='#Page_278'>278</a>.<br /> +<br /> +<b>Lavoisier</b>, Antoine L., born at Paris, <a href='#Page_79'>79</a>;<br /> +<span style="margin-left: 1em;">confutes idea of transmutation, <a href='#Page_81'>81</a>;</span><br /> +<span style="margin-left: 1em;">paper on calcination of tin, <a href='#Page_84'>84</a>;</span><br /> +<span style="margin-left: 1em;">meets Priestley, <a href='#Page_61'>61</a>, <a href='#Page_85'>85</a>;</span><br /> +<span style="margin-left: 1em;">his theory of combustion, <a href='#Page_51'>51</a>, <a href='#Page_86'>86</a>;</span><br /> +<span style="margin-left: 1em;">his chemical nomenclature, <a href='#Page_96'>96</a>;</span><br /> +<span style="margin-left: 1em;">he is guillotined, <a href='#Page_99'>99</a>;</span><br /> +<span style="margin-left: 1em;"><i>resumé</i> of his work, <a href='#Page_103'>103</a>;</span><br /> +<span style="margin-left: 1em;">his views on salts, <a href='#Page_183'>183</a>, <a href='#Page_184'>184</a>.</span><br /> +<br /> +<b>Liebig</b>, Justus, birth, <a href='#Page_256'>256</a>;<br /> +<span style="margin-left: 1em;">Humboldt and Gay-Lussac, <a href='#Page_257'>257</a>;</span><br /> +<span style="margin-left: 1em;">his improved combustion-tube, <a href='#Page_263'>263</a>;</span><br /> +<span style="margin-left: 1em;">studies the cyanates, <a href='#Page_264'>264</a>;</span><br /> +<span style="margin-left: 1em;">distinction between organic and inorganic chemistry effaced, <a href='#Page_265'>265</a>;</span><br /> +<span style="margin-left: 1em;">produces chloroform and chloral, <a href='#Page_273'>273</a>;</span><br /> +<span style="margin-left: 1em;">benzoyl, <a href='#Page_274'>274</a>;</span><br /> +<span style="margin-left: 1em;">he leaves Giessen for Munich, <a href='#Page_280'>280</a>;</span><br /> +<span style="margin-left: 1em;">his practical and economic discoveries, <a href='#Page_283'>283</a>;</span><br /> +<span style="margin-left: 1em;">death, <a href='#Page_284'>284</a>;</span><br /> +<span style="margin-left: 1em;">his failure to discover bromine, <a href='#Page_291'>291</a>.</span><br /> +<br /> +Lockyer, his work with spectroscope, <a href='#Page_310'>310</a> (and <i>vide</i> "Spectroscopic analysis").<br /> +<br /> +<br /> +M<br /> +<br /> +Mayow, John, studies combustion, <a href='#Page_24'>24</a>.<br /> +<br /> +Metals, new, discovered by Berzelius, <a href='#Page_101'>101</a>;<br /> +<span style="margin-left: 1em;">by Davy, <a href='#Page_197'>197</a>;</span><br /> +<span style="margin-left: 1em;">hydrogen a metal, <a href='#Page_238'>238</a>.</span><br /> +<br /> +Meyer, his views on acids, <a href='#Page_174'>174</a>.<br /> +<br /> +Mitscherlich's law of isomorphism, <a href='#Page_167'>167</a>.<br /> +<br /> +Molecule, conception of, <a href='#Page_140'>140</a>;<br /> +<span style="margin-left: 1em;">molecular weight, <a href='#Page_145'>145</a>;</span><br /> +<span style="margin-left: 1em;">molecular mobility of gases, <a href='#Page_242'>242</a>;</span><br /> +<span style="margin-left: 1em;">movements and reactions of molecules, <a href='#Page_249'>249</a>;</span><br /> +<span style="margin-left: 1em;">modern conception of, <a href='#Page_275'>275</a>.</span><br /> +<br /> +Morveau, De, embraces Lavoisier's views, <a href='#Page_96'>96</a>.<br /> +<br /> +Muriatic acid (<i>vide</i> "Hydrochloric acid,") <a href='#Page_119'>119</a>.<br /> +<br /> +<br /> +N<br /> +<br /> +Nitric acid, discovered by Priestley, <a href='#Page_65'>65</a>;<br /> +<span style="margin-left: 1em;">produced by electrolysis, <a href='#Page_188'>188</a>.</span><br /> +<br /> +Nomenclature, Lavoisier's system of, <a href='#Page_96'>96</a>.<br /> +<br /> +<br /> +O<br /> +<br /> +Oil, principle of, <a href='#Page_254'>254</a>.<br /> +<br /> +Organic chemistry, worked at by Berzelius, <a href='#Page_229'>229</a>;<br /> +<span style="margin-left: 1em;">attempts to define it, <a href='#Page_253'>253</a>;</span><br /> +<span style="margin-left: 1em;">loose application of the term, <a href='#Page_255'>255</a>;</span><br /> +<span style="margin-left: 1em;">Wöhler's manufacture of urea abolishes distinction of organic and inorganic chemistry, <a href='#Page_265'>265</a>.</span><br /> +<br /> +Oxygen discovered by Priestley, <a href='#Page_59'>59</a>;<br /> +<span style="margin-left: 1em;">Lavoisier's experiments, <a href='#Page_87'>87</a>;</span><br /> +<span style="margin-left: 1em;">it is viewed by him as an acidifier, <a href='#Page_91'>91</a>, <a href='#Page_175'>175</a>;</span><br /> +<span style="margin-left: 1em;">Berthollet shows it not a necessary constituent of acids, <a href='#Page_184'>184</a></span><br /> +<span style="margin-left: 1em;">(<i>vide</i> "Acids").</span><br /> +<br /> +<br /> +P<br /> +<br /> +Paracelsus, <a href='#Page_13'>13</a>;<br /> +<span style="margin-left: 1em;">his pamphlet, "Tripus Aureus," etc., <a href='#Page_19'>19</a>.</span><br /> +<br /> +Petit, <a href='#Page_168'>168</a>.<br /> +<br /> +Phlogistic theory, <a href='#Page_26'>26</a>;<br /> +<span style="margin-left: 1em;">enunciated by Stahl, <a href='#Page_27'>27</a>;</span><br /> +<span style="margin-left: 1em;">abandoned by Black, <a href='#Page_46'>46</a>;</span><br /> +<span style="margin-left: 1em;">phlogiston described as a kind of motion, <a href='#Page_49'>49</a>;</span><br /> +<span style="margin-left: 1em;">discovery of dephlogisticated air, <a href='#Page_59'>59</a>;</span><br /> +<span class='pagenum'><a name="Page_332" id="Page_332">[Pg 332]</a></span><span style="margin-left: 1em;">the theory overthrown by Lavoisier, <a href='#Page_92'>92</a>.</span><br /> +<br /> +Phosphoric acid, <a href='#Page_86'>86</a>.<br /> +<br /> +Pneumatic trough, invented by Priestley, <a href='#Page_57'>57</a>.<br /> +<br /> +Potassium, discovered by Davy, <a href='#Page_197'>197</a>.<br /> +<br /> +Prussic acid, discovered by Berthollet, <a href='#Page_184'>184</a>.<br /> +<br /> +<b>Priestley</b>, Joseph, born, <a href='#Page_52'>52</a>;<br /> +<span style="margin-left: 1em;">bred for the ministry, <a href='#Page_53'>53</a>;</span><br /> +<span style="margin-left: 1em;">writes on electricity, <a href='#Page_55'>55</a>;</span><br /> +<span style="margin-left: 1em;">his pneumatic trough, <a href='#Page_57'>57</a>;</span><br /> +<span style="margin-left: 1em;">discovers oxygen, <a href='#Page_59'>59</a>;</span><br /> +<span style="margin-left: 1em;">meets Lavoisier, <a href='#Page_61'>61</a>, <a href='#Page_85'>85</a>;</span><br /> +<span style="margin-left: 1em;">goes to Birmingham, <a href='#Page_65'>65</a>;</span><br /> +<span style="margin-left: 1em;">his experiments on hydrogen, <a href='#Page_66'>66</a>;</span><br /> +<span style="margin-left: 1em;">his house burnt by rioters, <a href='#Page_71'>71</a>;</span><br /> +<span style="margin-left: 1em;">emigrates to America, <a href='#Page_72'>72</a>;</span><br /> +<span style="margin-left: 1em;">dies there, <a href='#Page_73'>73</a>;</span><br /> +<span style="margin-left: 1em;"><i>resumé</i> of his work, <a href='#Page_102'>102</a>;</span><br /> +<span style="margin-left: 1em;">his method compared with that of Dalton, <a href='#Page_151'>151</a>.</span><br /> +<br /> +<br /> +Q<br /> +<br /> +Quantitative analysis neglected by early chemists, <a href='#Page_29'>29</a>;<br /> +<span style="margin-left: 1em;">first accurately employed by Black, <a href='#Page_33'>33</a>;</span><br /> +<span style="margin-left: 1em;">used by Lavoisier, <a href='#Page_87'>87</a>.</span><br /> +<br /> +<br /> +R<br /> +<br /> +Respiration explained by Lavoisier, <a href='#Page_91'>91</a>.<br /> +<br /> +Revolution, French, its effect on Priestley, <a href='#Page_70'>70</a>;<br /> +<span style="margin-left: 1em;">Lavoisier guillotined, <a href='#Page_99'>99</a>.</span><br /> +<br /> +Richter's equivalents of acids and bases, <a href='#Page_162'>162</a>.<br /> +<br /> +Ripley, Canon, an alchemist, his poems, <a href='#Page_18'>18</a>.<br /> +<br /> +Rouelle, invents term "base," <a href='#Page_179'>179</a>;<br /> +<span style="margin-left: 1em;">his studies on salts, <a href='#Page_181'>181</a>.</span><br /> +<br /> +<br /> +S<br /> +<br /> +Salts, <a href='#Page_173'>173</a>;<br /> +<span style="margin-left: 1em;">"principle of salt" opposed by Boyle, <a href='#Page_177'>177</a>;</span><br /> +<span style="margin-left: 1em;">earth or alkali the <i>base</i> of salts, <a href='#Page_179'>179</a>;</span><br /> +<span style="margin-left: 1em;">Rouelle's inquiries, <a href='#Page_181'>181</a>;</span><br /> +<span style="margin-left: 1em;">Lavoisier's definition, <a href='#Page_184'>184</a>;</span><br /> +<span style="margin-left: 1em;">considered as metallic derivatives of acids, <a href='#Page_205'>205</a>;</span><br /> +<span style="margin-left: 1em;">alcoholic salts, <a href='#Page_235'>235</a>.</span><br /> +<br /> +"Sceptical Chymist, The," by Hon. Robert Boyle, <a href='#Page_76'>76</a>-93.<br /> +<br /> +Shelburne, Earl of, patron of Priestley, <a href='#Page_58'>58</a>;<br /> +<span style="margin-left: 1em;">to whom he grants an annuity, <a href='#Page_65'>65</a>.</span><br /> +<br /> +Spectroscopic analysis, <a href='#Page_302'>302</a>;<br /> +<span style="margin-left: 1em;">lines in solar spectrum, <a href='#Page_306'>306</a>;</span><br /> +<span style="margin-left: 1em;">the solar atmosphere, <a href='#Page_308'>308</a>;</span><br /> +<span style="margin-left: 1em;">Lockyer's mapping of the lines, <a href='#Page_310'>310</a>;</span><br /> +<span style="margin-left: 1em;">basic lines, <a href='#Page_311'>311</a>;</span><br /> +<span style="margin-left: 1em;">objections to his hypothesis, <a href='#Page_313'>313</a>.</span><br /> +<br /> +Stahl, George Ernest, born at Anspach, <a href='#Page_27'>27</a>;<br /> +<span style="margin-left: 1em;">enunciates the phlogistic theory, <a href='#Page_27'>27</a>, <a href='#Page_48'>48</a>;</span><br /> +<span style="margin-left: 1em;">his "primordial acid," <a href='#Page_174'>174</a>;</span><br /> +<span style="margin-left: 1em;">his essential property of earths, <a href='#Page_178'>178</a>.</span><br /> +<br /> +Sulphur dioxide, discovered by Priestley, <a href='#Page_66'>66</a>.<br /> +<br /> +Sulphur salts, discovered by Berzelius, <a href='#Page_161'>161</a>.<br /> +<br /> +<br /> +T<br /> +<br /> +Transmutation, confuted by Lavoisier, <a href='#Page_81'>81</a>.<br /> +<br /> +Transpiration of gases, <a href='#Page_242'>242</a>.<br /> +<br /> +Types, <a href='#Page_279'>279</a>.<br /> +<br /> +<br /> +V<br /> +<br /> +Valentine, Basil, an alchemist, <a href='#Page_15'>15</a>;<br /> +<span style="margin-left: 1em;">his views on alkalis, <a href='#Page_174'>174</a>.</span><br /> +<br /> +Van Helmont, <a href='#Page_24'>24</a>.<br /> +<br /> +Vitriols, <a href='#Page_180'>180</a>.<br /> +<br /> +Volta's electric pile, <a href='#Page_184'>184</a>.<br /> +<br /> +<br /> +W<br /> +<br /> +Water, its composition discovered by Cavendish, <a href='#Page_68'>68</a>-78;<br /> +<span style="margin-left: 1em;">nearly discovered by Priestley, <a href='#Page_68'>68</a>;</span><br /> +<span style="margin-left: 1em;">confirmed by Lavoisier, <a href='#Page_90'>90</a>;</span><br /> +<span style="margin-left: 1em;">decomposed by electricity, <a href='#Page_185'>185</a>.</span><br /> +<br /> +Weight of ultimate particles, <a href='#Page_117'>117</a>, <a href='#Page_132'>132</a>;<br /> +<span style="margin-left: 1em;">molecular and atomic, <a href='#Page_145'>145</a>;</span><br /> +<span style="margin-left: 1em;">revision of atomic weights, <a href='#Page_285'>285</a>.</span><br /> +<br /> +Wöhler, his account of visit to Berzelius, <a href='#Page_160'>160</a>, <a href='#Page_204'>204</a>, <a href='#Page_229'>229</a>;<br /> +<span style="margin-left: 1em;">studies cyanates with Liebig, <a href='#Page_264'>264</a>;</span><br /> +<span style="margin-left: 1em;">results of his discovery as to urea, <a href='#Page_265'>265</a>.</span><br /> +<br /> +Wollaston, supports atomic theory, <a href='#Page_130'>130</a>.<br /> +</p> + + +<h4>PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLES.</h4> + +<p> </p> +<p> </p> +<hr class="full" /> + +<p>***END OF THE PROJECT GUTENBERG EBOOK HEROES OF SCIENCE***</p> +<p>******* This file should be named 38246-h.txt or 38246-h.zip *******</p> +<p>This and all associated files of various formats will be found in:<br /> +<a href="http://www.gutenberg.org/dirs/3/8/2/4/38246">http://www.gutenberg.org/3/8/2/4/38246</a></p> +<p>Updated editions will replace the previous one--the old editions +will be renamed.</p> + +<p>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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