Of course, every one knows that the conception of the discontinuity of "matter" appears in ancient history. And, when we descend to modern times, Boyle (1627-91) speaks of corpuscles, Boerhaave (16681738), Albrecht von Haller's master, of massulæ. Moreover, Dalton was a youth of only seventeen when the most important developments occurred. First, and with special reference to the framework of possible method, we have Lavoisier's (1743-94) celebrated memoir, "Reflections concerning Phlogiston," where he dismisses the dominant theory in sarcastic terms,[1] and establishes the quantitative method on a firm basis. In the same year (1783) Bergman (1735-84), the last of the great phlogistic chemists, published his notable work on what he called "elective attraction" (i. e., affinity), a phenomenon attributed by him to the attraction between the most minute particles. Naturally, Bergman's table of "single elective attractions in the moist way, and in the dry way," with its curious alchemical signs, was a description of qualitative relations. It marked the beginning of investigation of mass action, and provoked the striking researches of Berthollet (1748-1822), who, in 1799, presented his paper, "Recherches sur les lois de l'affinité," out of which grew his major work, "Essai de statique chimique" (1803). The main result of his assault upon Bergman was to show that chemical change depends, not merely upon the affinities of the substances involved, but upon their quantities. In other words, a new method asserted itself. For, as Berthollet says:
To find the affinity of two substances towards a third, in accordance with the conception we have now gained of affinity, can mean nothing other than to determine the ratio in which this third substance divides itself between the two first.
Therefore, chemical change hinges upon the nature of the relative masses of the substances involved, but, "to determine the ratio of the affinities of two substances towards a third. . . is attended by unsurmountable obstacles." Here was the blank wall, so to speak, that shadowed Berthollet's services till the time of Guldberg and Waage (1864). As Berthollet stood to Bergman, so did Proust (1755-1826) to Berthollet. Baffled in every attempt to determine the distribution of salts in solution, Berthollet had good reason to doubt the doctrine of constant composition. Here was Proust's opportunity. Having distinguished between "combinations of elements" and "associations of combinations," the latter variable under analysis, Proust was able to enunciate the law of fixed proportions—in his own words, "Election and proportion [i. e., affinity and fixity of composition] are the two poles about which revolves immutably the whole system of true compounds, whether produced by Nature or by Man"; or, as Lothar Meyer phrases it, "Definite chemical compounds always contain their con-
- ↑ Cf. "Œuvres," Vol. II., pp. 623 f.
