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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    assume sulphurous acid to be composed of 95.02 * of oxygen to 100 of sulphur, or rather of suljrhuric radical, instead of 92. In order now to determine the mass of the molecule of the sulphuric radical, it would be neces.sary to know what proportion by volume this radical in the gaseous state would bear to the oxygen in the formation of sul- phurous acid. The analogy with other combinations already discussed, where there is in general a doubling of the volume or halving of the molecule, leads us to suppose that it is the same in this case also, i.e. that the volume of the sulphur as gas is half that of the sulphurous acid, and consequently also half that of the oxygen with which it combines. On this supposition the density of sulphur gas will be to that of oxygen as 100 to -”■5.——, or 2 47.51; which gives 2.323 for the density of gaseous sulphur, taking that of air as unity. The masses of the molecules being according to our hypothesis in the same ratio as the densities of the gases to which they belong, the mass of the molecule of the sulphuric radical will be to that of hydrogen as 2.323 to 0.07321, or as 31.73 to i. One of these molecules combined, as we have said, with two of oxygen, will form sulphurous acid (division of tlie molecule being left out of account), and combined with yet another molecule of oxygen, will form sulphuric acid. Accordingly, sulphurous acid should be analogous to * [Erroneously 92.02 in the original.] t This was written before I had seen the Memoir of Davy on oxymuriatic acid, which also contains new experiments on sulphur and phosphorus. In it he determines the density of sulphurous acid gas, and finds it to be only 2.0967, which gives new force to the above considerations. If we adopt this density, we find that in sulphurous acid 100 jiarts by weight of sulphur take iii of oxygen, and in sulphuric acid 167 instead of 138; but perliaps this density of sulphurous acid, according to Davy, is somewhat too low.