Chemistry / [Michael Donovan].

  • Donovan, Michael, -1876
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry / [Michael Donovan]. Source: Wellcome Collection.

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    scale, divide the former by 8. If the oxygen scale be multiplied by 8, the product will be the hydrogen scale. It is now necessary to show, that the numbers them- selves, considered abstractedly as representatives of the weights of atoms, and without reference to their capa- city of expressing combining ratios, are hypothetical and useless ; and that-they may be, in reality, very dif- ferent from what we suppose them. As there are but two units employed, oxygen and hydrogen; and as both of these are contained in water, the composition of which is agreed on by all chemists; the analysis of water may be considered as the basis of the atomic hypothesis. Water consists of 1 part of hydrogen and 8 of oxygen, both by weight; or, what is the same thing, 2 volumes of the former and 1 of the latter. It is inferred, that in the 2 volumes of hydrogen there are exactly the’same number of ultimate particles, or atoms, as there are in 1 volume of oxygen. But there are no grounds for the inference, beyond a supposed probability. It originated with Mr. Dalton, and was expressed in the following words : — ‘‘ When only one combination of two bodies can be obtained, i¢ must be presumed to be a binary* one, unless some cause appear to the contrary: and when two combinations are ob- served, they must be presumed to be a binary and a ternary.’ + Water is, therefore, inferred to consist of an atom of hydrogen combined with an atom of oxygen. It is further inferred, that a given volume of hydrogen con- tains but half the number of atoms contained in the same volume of oxygen: and as the weight of oxygen in wa- ter is 8 times greater than that of hydrogen, the atom of oxygen is inferred to be 8 times heavier than that of hydrogen. The truth of the fact inferred, however, _depends on the truth of the assumption, that the two gases unite atom to atom ;—a position which may be either denied or admitted at pleasure, for it is perfectly gratuitous. It may be affirmed, as equally probable, * Mr. Dalton explains a binary compound tp mean an atom of each ele- ment in combination.