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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    to unknown laws, were it not that the hypothesis we have just proposed is based on that simpHcity of relation between the volumes of gases on combination, which would appear to be otherwise inexplicable. Setting out from this hypothesis, it is apparent that we have the means of determining very easily the relative masses of the molecules of substances obtainable in the gaseous state, and the relative number of these molecules in compounds; for the ratios of the masses of the mole- cules are then the same as those of the densities of the different gases at equal temperature and pressure, and the relative number of molecules in a compound is given at once by the ratio of the volumes of the gases that form it. For example, since the numbers 1.T0359 and 0.07321 express the densities of the two gases oxygen and hydrogen compared to that of atmospheric air as unity, and the ratio of the two numbers consequently represents the ratio between the masses of equal volumes of these two gases, it will also represent on our hypo- thesis the ratio of the masses of their molecules. Thus the mass of the molecule of oxygen will be about 15 times that of the molecule of hydrogen, or, more exactly, as 15.074 to I. In the same way the mass of the mole- cule of nitrogen will be to that of hydrogen as 0.96913 to 0.07321, that is, as 13, or more exactly 13.238, to i. On the other hand, since we know that the ratio of the volumes of hydrogen and oxygen in the formation of water is 2 to i, it follows that water results from the union of each molecule of oxygen with two molecules of hydrogen. Similarly, according to the proportions by volume established by M. Gay-Lussac for the elements of ammonia, nitrous oxide, nitrous gas, and nitric acid, ammonia will result from the union of one molecule of nitrogen with three of hydrogen, nitrous oxide from one molecule of oxygen with two of nitrogen, nitrous gas