Foundations of the molecular theory : comprising papers and extracts by J. Dalton, J.L. Gay-Lussac, and A. Avogadro, 1808-11.

  • Dalton, John, 1766-1844.
Date:
1893
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Licence: Public Domain Mark

Credit: Foundations of the molecular theory : comprising papers and extracts by J. Dalton, J.L. Gay-Lussac, and A. Avogadro, 1808-11. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    VII. We shall now make a few applications of our principles to saline compounds, which will furnish us with the opportunity of examining an important point in the theor}' of these compounds. M. Gay-I.ussac has shown that the neutral carbonate, fluoborate, and muriate of ammonia are composed of equal volumes of ammonia gas and of the respective acids. Let us pause to consider the carbonate. On our hypothesis, this salt is composed of one molecule of carbonic acid with one molecule of ammonia—i.e. (according to the values previously given and independently of any division), of one molecule of molecule of potassium at 40.5, in accordance with the quantity of oxygen by weight in the substance, and has taken the molecule of oxygen to be 7.5. Assuming, as we have done, this last molecule to be nearly twice as great, the molecule of potassium will also be ■doubled, viz., about 81, if we adopt the other assumptions of Davy. But it may be that in potash one molecule of potassium takes two of oxygen, in which case we should again have to double the last value and make it 162. It might also be (fqr the analogy drawn from other metals is not in this case a very safe guide) that two molecules of potassium combine with one of oxygen, which would bring back the molecule of potassium to 40.5. It is on the assumption of this last value for the molecule of potassium that Davy finds 32.9 for that of oxymuriatic acid, calculat- ing from the composition of muriate of potash, and assuming that this salt is formed of one molecule of potassium with one of acid. If we suppose the molecule of potassium to have a different mass, we must admit another relative number of molecules in the muriate, since both from our hypothesis and from the density of the gas, 32.9 is very nearly the molecule of oxymuriatic acid. On the sup- position that the molecule of potassium is 81, and that in sulphide of potassium the combination is molecule to molecule, the molecule of sulphur will be about 27 instead of 13^ as found by Davy on the latter assumption, which will bring about between this result and that derived from sulphurous acid according to our calculations the agreement which exists between Davy's values.