sulphurous and the sulphuric; and these acids form, with earthy or alkaline bases, sulphites and sulphates; while sulphur directly combined with another element, forms a sulphuret. The term oryd (now usually written oride) expressed a lower degree of combination with oxygen than the acids. The Méthode de Nomenclature Chimique was published in 1787; and in 1789, Lavoisier published a treatise on chemistry in order further to explain this method. In the preface to this volume, he apologizes for the great amount of the changes, and pleads the authority of Bergman, who had exhorted De Morveau "to spare no improper names; those who are learned will always be learned, and those who are ignorant will thus learn sooner." To this maxim they so far conformed, that their system offers few anomalies; and though the progress of discovery, and the consequent changes of theoretical opinion, which have since gone on, appear now to require a further change of nomenclature, it is no small evidence of the skill with which this scheme was arranged, that for half a century it was universally used, and felt to be far more useful and effective than any nomenclature in any science had ever been before.

CHAPTER VII.

APPLICATION AND CORRECTION OF THE OXYGEN THEORY.

SINCE

a chemical theory, as far as it is true, must enable us to obtain a true view of the intimate composition of all bodies whatever, it will readily be supposed that the new chemistry led to an immense number of analyses and researches of various kinds. These it is not necessary to dwell upon; nor will I even mention the names of any of the intelligent and diligent men who have labored in this field. Perhaps one of the most striking of such analyses was Davy's decomposition of the earths and alkalies into metallic bases and oxygen, in 1807 and 1808; thus extending still further that analogy between the earths and the calces of the metals, which had had so large a share in the formation of chemical theories. This discovery, however, both in the means by which it was made, and in the views to which it led, bears upon subjects hereafter to be treated of.

The Lavoisierian theory also, wide as was the range of truth which it embraced, required some limitation and correction. I do not now

speak of some erroneous opinions entertained by the author of the theory; as, for instance, that the heat produced in combustion, and even in respiration, arose from the conversion of oxygen gas to a solid consistence, according to the doctrine of latent heat. Such opinions not being necessarily connected with the general idea of the theory, need not here be considered. But the leading generalization of Lavoisier, that acidification was always combination with oxygen, was found untenable. The point on which the contest on this subject took place was the constitution of the orymuriatic and muriatic acids;—as they had been termed by Berthollet, from the belief that muriatic acid contained oxygen, and oxymuriatic a still larger dose of oxygen. In opposition to this, a new doctrine was put forward in 1809 by Gay-Lussac and Thenard in France, and by Davy in England;—namely, that oxymuriatic acid was a simple substance, which they termed chlorine, and that muriatic acid was a combination of chlorine with hydrogen, which therefore was called hydrochloric acid. It may be observed, that the point in dispute in the controversy on this subject was nearly the same which had been debated in the course of the establishment of the oxygen theory; namely, whether in the formation of muriatic acid from chlorine, oxygen is subtracted, or hydrogen added, and the water concealed.

In the course of this dispute, it was allowed on both sides, that the combination of dry muriatic acid and ammonia afforded an experimentum crucis; since, if water was produced from these elements, oxygen must have existed in the acid. Davy being at Edinburgh in 1812, this experiment was made in the presence of several eminent philosophers; and the result was found to be, that though a slight dew appeared in the vessel, there was not more than might be ascribed to unavoidable imperfection in the process, and certainly not so much as the old theory of muriatic acid required. The new theory, after this period, obtained a clear superiority in the minds of philosophical chemists, and was further supported by new analogies.'

For, the existence of one hydracid being thus established, it was found that other substances gave similar combinations; and thus chemists obtained the hydriodic, hydrofluoric, and hydrobromic acids. These acids, it is to be observed, form salts with bases, in the same manner as the oxygen acids do. The analogy of the muriatic and fluoric compounds was first clearly urged by a philosopher who was

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s still isimet » 1 fndamentai miation je vuch stiler Zuations are Sestert This "mark wineers the sage of nemistry low mder our sonca vita its sartiest ane But norier a pont out the memeni bearing whe next mi jeeta of mr hartatva, vi na furier sera. that mentie, woria, mi a ura weken of is known tussey of substancest and 'n like manner the newis-tiserverzi dements, viri irm de ast sophies of themistry, have been Estributed to sei casses amring er aacges; mas pertaman, vi” vm, hæren, bara been asserted to be metals; iofae, iramae, furiae, have been ammangei w malogical to dibaribe. In there is someting vigne and mietin in the bordaces of meh diassifications and analogies: and it is presisery was this vagueness falls that the science is so cosenze er donbefall. We are led, thendors to see the dependence of Chemistry syon Classification: and is is to Sciences of Classdratica wikė me mail next proceed; as soon as we have scored the most general vies

* Paris, Life of Dory, i 372

which have been given of chemical relations, namely, the views of the electro-chemists.

But before we do this, we must look back upon a law which obtains in the combination of elements, and which we have hitherto not stated; although it appears, more than any other, to reveal to us the intimate constitution of bodies, and to offer a basis for future generalizations. I speak of the Atomic Theory, as it is usually termed; or, as we might rather call it, the Doctrine of Definite, Reciprocal, and Multiple Proportions.

CHAPTER VIII.

THEORY OF DEFINITE, RECIPROCAL, AND MULTIPLE PROPORTIONS.

Sect. 1.-Prelude to the Atomic Theory, and its Publication by Dalton.

THE

THE general laws of chemical combination announced by Mr. Dalton are truths of the highest importance in the science, and are now nowhere contested; but the view of matter as constituted of atoms, which he has employed in conveying those laws, and in expressing his opinion of their cause, is neither so important nor so certain. In the place which I here assign to his discovery, as one of the great events of the history of chemistry, I speak only of the law of phenomena, the rules which govern the quantities in which elements combine.

This law may be considered as consisting of three parts, according to the above description of it;-that elements combine in definite proportions; that these determining proportions operate reciprocally; -and that when, between the same elements, several combining proportions occur, they are related as multiples.

That elements combine in certain definite proportions of quantity, and in no other, was implied, as soon as it was supposed that chemical compounds had any definite properties. Those who first attempted to establish regular formula for the constitution of salts, minerals, and

Thomson, Hist. Chem. vol. ii. p. 279.

other compounds, assumed, as the basis of this process, that the elements in different specimens had the same proportion. Wenzel, in 1777, published his Lehre von der Verwandschaft der Körper; or, Doctrine of the Affinities of Bodies; in which he gave many good and accurate analyses. His work, it is said, never grew into general notice. Berthollet, as we have already stated, maintained that chemical compounds were not definite; but this controversy took place at a later period. It ended in the establishment of the doctrine, that there is, for each combination, only one proportion of the elements, or at most only two or three.

Not only did Wenzel, by his very attempt, presume the first law of chemical composition, the definiteness of the proportions, but he was also led, by his results, to the second rule, that they are reciprocal. For he found that when two neutral salts decompose each other, the resulting salts are also neutral. The neutral character of the salts shows that they are definite compounds; and when the two elements of the one salt, P and s, are presented to those of the other, B and n, if P be in such quantity as to combine definitely with n, B will also combine definitely with 8.3

Views similar to those of Wenzel were also published by Jeremiah Benjamin Richter in 1792, in his Anfangsgründe der Stöckyometrie, oder Messkunst Chymischer Elemente, (Principles of the Measure of Chemical Elements,) in which he took the law, just stated, of reciprocal proportions, as the basis of his researches, and determined the numerical quantities of the common bases and acids which would saturate each other. It is clear that, by these steps, the two first of our three rules may be considered as fully developed. The change of general views which was at this time going on, probably prevented chemists from feeling so much interest as they might have done otherwise, in these details; the French and English chemists, in particular, were fully employed with their own researches and controversies.

Thus the rules which had already been published by Wenzel and Richter had attracted so little notice, that we can hardly consider Mr. Dalton as having been anticipated by those writers, when, in 1803, he began to communicate his views on the chemical constitution of

*I am told that Wenzel (whose book I have not seen), though he adduces many earea in which double decomposition gives neutral salts, does not express the proposition in a general form, nor use letters in expressing it.

• Thomson, Rest, Chem, vol ii p. 288