6

of which science possesses a record, lasted from 1799 till 1806, and was maintained on both sides with a power of reasoning and a respect for truth and propriety which have never been surpassed. The fullest development of Berthollet's views appeared in his celebrated work entitled Essai d'une Statique chimique,' which was published in 1803. The great idea developed in this book is that chemical affinity and astronomical attraction are different manifestations of an identical property of matter, which led the author to regard not only the energy of affinities as producing chemical reactions, but also the influence of the masses.

In a great number of reactions this influence does undoubtedly govern the progress of decomposition or combination; it augments or diminishes the proportion of compounds which are formed or destroyed in a reaction, but it does not govern the proportions in which the elements unite in these compounds. On this latter point Berthollet held a different opinion; he maintained that mass does exercise an influence upon the combining proportions of two bodies when no physical condition is present to determine the separation of a compound in fixed proportions. Thus, when an acid acts upon a base in such a manner as to produce a soluble salt, the point of neutrality undoubtedly corresponds to fixed proportions of combined acid and base; but if an excess of one or other of these elements be added, it also will enter into combination, and, moreover, in variable proportions, till a physical property--cohesion, for example-determines the separation of a compound of fixed proportions. In a great number of chemical

combinations, therefore, this fixity in the proportions of elements may be observed; but, in the opinion of Berthollet, they are exceptional cases, to which it would be wrong to ascribe the dignity of a general law.

Proust, on the contrary, maintained the generality of this law. If it is impossible, he says, to make an ounce of nitric acid, an oxide, a sulphide, or a drop of water in other proportions than in those which nature, from all eternity, has assigned to these compounds, we must. acknowledge that for chemical combinations there is a sort of balance,' which is subject to the immutable laws of nature, and which, even in our laboratories, determines the relation of the elements in these compounds. The latter are of several orders. The most simple are generally formed of two elements-at most of three, very rarely of four. But these compounds of a simple order may combine with each other, so as to form more complex compounds; in other cases they are merely mixed together. In these mixtures the proportion of the elements is naturally subject to variation; in all chemical combinations properly so called it is, on the contrary, fixed.

The opinion of Proust was well founded; it won the day, in spite of the opposition of his powerful antagonist; and we cannot too much admire the persevering energy and discernment displayed by the chemist of Angers in this contest, when he took one by one the arguments of Berthollet, and opposed to the facts collected and arranged by the latter in support of his theory fresh facts and fresh analyses of his own, which, it must be confessed, were not always models of

accuracy. The superior intelligence, however, of an accurate and lofty mind saved him from error in the discussion of results, and made up for the insufficiency of the methods of that time.

This great truth of the fixity of chemical proportions was, then, definitely established in the year 1806. But the discussions between Berthollet and Proust, which agitated the scientific world during the first years of this century, only gave an incomplete idea of it, for they dealt solely with the composition of each compound taken individually. The question as to whether sulphide of antimony was a constant compound, and whether this was also the case with the sulphides of iron, the oxides of tin and cobalt, was answered in the affirmative by Proust, in the negative by Berthollet. It is now definitely decided in the affirmative. We must not, however, forget that Proust. and Berthollet only attacked the question from one side, for there is another. It is true that this sulphide of antimony, these sulphides of iron, and, in fact, that all sulphides present a fixed composition; and, again, it is equally true that in every metallic oxide the metal and the oxygen unite in invariable proportions. But this is not all. Analysis shows, further, that the relations between quantities of different metals uniting with a fixed weight of sulphur are the same as those between different metals uniting with a fixed weight of oxygen. Independently, therefore, of the fact of fixity, there is the further fact of the proportionality of the combining quantities or weights of bodies; and the case in question is not an exceptional one, but

belongs to a whole order of similar facts-is, in short, a law.

We have, in demonstrating this law of proportionality, employed as examples the very compounds. which enabled Proust to establish the law of fixity. It may, however, be demonstrated under a more general and striking form.

A is a certain weight of a simple body.

B is a certain weight of another simple body, which is exactly sufficient to form with a the combination a B. The relation

B

is constant.

c is a certain weight of a third simple body, exactly sufficient to form with A the combination A C. The re

D is a certain weight of a fourth simple body, exactly sufficient to form with A the combination A D. The

Let us now take the second body B, and form combinations between this body and the third c and the fourth D. Experience shows us that the quantities c and D which combine with A will also combine with B -in other words, that the weights of the bodies B, C, D, which formed definite compounds with A, are unchanged when they combine with each other. From the fact of. the existence of compounds AB, A C, A D, we may assume the existence of compounds B C, B D, C D, in which the quantities A, B, C, D, are constant. In short, there

exists between all compound bodies formed by the union of two elements such a definite relation of composition that we have only to determine the proportions in which the most widely differing elements unite with one of their number, and we shall also have determined the proportions in which they combine with each

other.

This is the law of proportionality, discovered by Richter, who lived at Berlin towards the close of the last century.

For many years another German chemist-C. F. Wenzel-was considered the author of this great discovery. It was attributed to him by Berzelius.' M. Dumas also claims it for him,2 and all chemical treatises

The following are the terms in which Berzelius claimed for Wenzel the discovery of the proportionality of quantities of acids and bases which exactly saturate each other:-' He published the result of these experiments in a memoir entitled Lehre von den Verwandtschaften, or the Theory of Affinities, at Dresden in 1777, and proved, by singularly accurate analyses, that this phenomenon (the preservation of neutrality after the mutual decomposition of two neutral salts) was due to the fact that the quantities of alkalies and earths which saturate a given quantity of the same acid are the same for all acids; so that if we decompose, for example, calcium nitrate by potassium sulphate, the potassium nitrate and the calcium sulphate obtained will preserve their neutrality, because the quantity of potash which saturates a given quantity of nitric acid is to the quantity of lime which saturates the same quantity of nitric acid as the potash is to the lime which neutralises a given quantity of sulphuric acid.'— Traité de Chimie, French edition, 1831, t. iv. p. 524.

2 Chemical Philosophy, p. 200. The error concerning the part attributed to Wenzel in the discovery of the law of proportionality has been corrected by several scientific writers-first by Hess (Journal für praktische Chemie, t. xxiv. p. 420); then by Schweigger, in the work entitled Uber stöchiometrische Reihen im Sinne