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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    the real condition of the atomic numbers in the follow- ing: — ‘‘ In many cases it is not easy to fix upon the true atomic weight of a body. We can always infer that the weight of one body that enters into combination with another, either denotes the atomic weight of the body, or at least a multiple or submultiple of that weight ; but in some cases it may be very difficult to determine which of the three.” These statements hold true, whether we take oxygen or hydrogen as unity ; and whether we admit the ex- istence of atoms, or not. It has been supposed by some, that the doctrine of determinate proportions is a mere expression of facts, and essentially different from the atomic hypothesis, which is founded on the assumption of the finite divisibility of matter; or, in other words, on the atomic constitution of bodies. It appears to me, that there is as much hypothesis in one doctrine as in the other. We say that an indivisible atom of hydro- gen = 1, combines with an indivisible atom of oxygen = 8; and the latter combines with an indivisible atom of mercury = 200. Here, it may be said, are three gratuitous-assumptions : first, that the combining quan- tities are atoms; secondly, that they are indivisible ; and, thirdly, that the bodies combine atom to atom. But in the doctrine which professes to embody facts only, we can detect these same three assumptions tacitly involved. According to this mode of expressing the phenomena, a certain quantity: of hydrogen — the least that enters into combination—is called unity, even although it consists of 2 volumes; this is the very same position, in another form, that has been considered objectionable in the atomic hypothesis of Dalton. The quantity of oxygen with which this unites, is the least that enters into combination ; and the quantity of mer- | cury with which thislast unites, is also the least that enters into combination. Here, then, we have three bodies taken in the least quantity that enters into combination. How does this quantity differ from an atom rightly understood? An atom'does not mean a quantity which