Claude Louis Berthollet
(Talloires, France, 1748-Arcueil, id., 1822) French chemist.He studied medicine in Turin (1768) and later moved to Paris.An academic elect in 1780, his investigations with hydrocyanic acid (prussic) and with hydrocyanic acid led him to disagree with Lavoisier on the question whether the presence of oxygen is essential in all acids.Berthollet discovered the composition of ammonia and introduced the use of chlorine as a bleaching agent.In his work on the theory of chemical affinities Chemical statics test (1803) he proposed a law of indefinite proportions for chemical combinations, as opposed to Proust's law of definite proportions.Although this law was rejected, Berthollet's idea that mass influences the course of chemical reactions was later vindicated in the law of mass action enunciated by Guldberg and Waage.
Claude Louis Berthollet
After having studied in Annecy and Chambéry, Claude Louis Berthollet graduated in medicine in Turin, and in 1770 he went to Paris, where he devoted himself to chemistry.An early follower of Georg Stahl's phlogiston theory, he opted from 1786 on Lavoisier's theory, with whom he became a friend.He taught chemistry at the École Normale Supérieure, and, after 1794, at the École Polytechnique.As a member of a scientific commission he was in Egypt with Napoleon; from him he received great honors, which he kept during the Restoration.
Claude Louis Berthollet contributed significantly to the development of industrial chemistry; he dealt in particular with dyes, introduced the use of chlorine in the bleaching of textile fibers and paper, discovered alkali hypochlorites and potassium chlorate, and investigated ammonia, hydrogen sulphide, and hydrocyanic acid.In 1789 he founded the Annales de chimie with Fourcroy and Guyton de Morveau, and together with them he was on the committee responsible for the revision of the chemical nomenclature.
Berthollet's greatest contribution to his favorite science is made up of his ideas about affinity, which he developed in Inquiries into the laws of affinity (1801) and later gathered in the Chemical static test .He modified Torbern Olof Bergman's views on affinity, introduced the concept of mass in chemical reactions, and questioned the constant relationships of components in compounds.The wrong conclusions were attacked by Joseph Louis Proust, who succeeded in showing that Berthollet had experimented with mixtures and not with true compounds.The Societé d'Arcueil, founded by him, published some of his studies on chemistry between 1807 and 1817.
His main work, Essay of chemical statics (1803), was written when he had already completely abandoned the phlogiston theory to decidedly follow Lavoisier; it also contains what Berthollet himself had published in his previous Inquiries on the laws of affinity .This makes the Essay of particular importance in the evolution of the concept of chemical affinity, which appears as the development and often as the correction of the ideas already pointed out by Bergman and other previous authors.
In opposition to Bergman, Berthollet maintains that the strength of chemical affinity depends on the mass of the substances that enter into reaction, thus revealing itself in relation to the force of gravity.From this he deduced that not only the formation but also the quantitative composition of the resulting body depended on the relationships between the masses of the components.This led to the conclusion that these components should generally be combined according to varying relationships, which was in opposition to the facts.
From 1799, and for eight years, Berthollet had a memorable discussion on this point with Joseph Louis Proust, which ended, however, with the defeat of Berthollet, since Proust demonstrated that the relations of Combination does not depend on the masses of the components, but, on the contrary, they are constant, even when the two components are combined in different proportions; in this case, said relations vary "by leaps", not by degrees, as he mistakenly believed Berthollet in the case of certain oxides or salts ( Chemical static test , II, p.399 ff.).The polemic, therefore, had brought Proust not far from the "law of multiple proportions" that every student knows.
Berthollet's failure caused Bergman's opposing ideas to regain their peak, but the fundamental concept of the Savoyard chemist was again the object of study (thanks to the research of Heinrich Rose, Marcelin Berthelot, Péan de St Gilles and others) especially through the work of Cato Maximilian Guldberg and Peter Waage in their Studies on chemical affinities (1867), who founded the well-known law of mass action, now universally recognized, and according to the which the chemical action of a substance is proportional to its active quantity.
If in the law of the dependence of the chemical affinity of the mass Berthollet should be considered as a precursor, the more positive are his merits when he clearly shows that the absolute magnitude of the chemical affinity cannot be determined (as Bergman suggested in his Physics and Chemistry Booklets ), since the "intensity" of it is strictly linked to the physical properties of the bodies in presence.Among these, "cohesion" and "elasticity" are most important.The first, in relation to the different "solubility" of the different substances; the second, with its various "volatility".Thus, he explained those curious changes in which the separation of a precipitate or the evolution of a gas determines the beginning or the end of a reaction; more precisely, he affirmed that a complete change of substances could be obtained only if (together with affinity) cohesion and elasticity were also involved, and thus new principles were established, which in time were to produce numerous and important fruits; It is fair to recognize, in this sense, that physicochemistry as a new branch of science was born with the great French researcher.
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