Foundations of the molecular theory / comprising papers and extracts by John Dalton, Joseph-Louis Gay-Lussac, and Amedeo Avogadro (1808-1811).

Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Foundations of the molecular theory / comprising papers and extracts by John Dalton, Joseph-Louis Gay-Lussac, and Amedeo Avogadro (1808-1811). Source: Wellcome Collection.

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    According to Dalton’s ingenious idea, that combina- tions are formed from atom to atom, the various compounds which two substances can form would be produced by the union of one molecule of the one with one molecule of the other, or with two, or with a greater number, but always without intoiinediate compounds. Thomson and Wollaston have indeed described experi- ments which appear to confirm this theory. Thomson * has found that super-oxalate of potash contains twice as much acid as is necessary to saturate the alkali; and Wollaston,t that the sub-carbonate of potash contains, on the other hand, twice as much alkali as is necessary to saturate the acid. The numerous results I have brought forward in this Memoir are also very favourable to the theory. But M. Berthollet, who thinks that combinations are made con- tinuously, cites in proof of his opinion the acid sulphates, glass, alloys, mixtures of various liquids,—all of which are compounds with very variable proportions, and he insists principally on the identity of the force which pro- duces chemical compounds and solutions. Each of these two opinions has, therefore, a large number of facts in its favour; but although they are apparently utterly opposed, it is easy to reconcile them. We must first of all admit, with M. Berthollet, that chemical action is exercised indefinitely in a continuous manner between the molecules of substances, whatever their number and ratio may be, and that in general we can obtain compounds with very variable proportions. But then we must admit at the same time that,—apart from insolubility, cohesion, and elasticity, which tend to produce compounds in fixed proportions,—chemical action * [See Alembic Club Reprints, No. 2, p. 41.] + [See Alembic Club Reprints, No. 2, p. 35.}