The constitution of matter / by William A. Tilden.

  • Tilden, William Augustus, 1842-1926.
Date:
[1870]
Catalogue details

Licence: Public Domain Mark

Credit: The constitution of matter / by William A. Tilden. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    with potassium, but the hydrogen cannot pass off, even at a red heat, in combi- Bation with its half of the oxygen. The two halves are inseparable, and when I say that in the molecule of potassic hydrate there is a single atom of oxygen, I merely state that fact.* It is urged by Dr. Williamson, in his recent lecture just quoted, that the objections to the atomic theory hitherto put forward have never assumed the character of open and systematic attack. This is indeed true, but it cannot be forgotten that these doubts and objections have arisen from men occupy- ing the highest rank, not only among metaphysicians, but among chemists and physicists. That chemists generally have uttered little complaint may be ascribed to a very natural disinclination to find fault with a theory which, in one form or other, has done to their science so much good service. Even those who do not place faith in the atomic theory as a truth, are not unwilling to retain it for the sake of the facihties the application of it affords for the expression and colligation of facts. Putting aside for the present abstract speculations as to the possibility of the existence of finite particles, we shall do best to confine ourselves to con- siderations which most nearly interest the chemist and physicist. I venture to offer the following examples from the category of phenomena which cannot at present be considered capable of explanation by an appeal to the doctrine of atoms. The instances I have selected are taken from the great number which might be adduced ; but, in stating them, I do so in no spirit inimical to the ordinarily received doctrine, but merely to show that our knowledge of the rationale of such phenomena is at present only imperfect. However firm our allegiance to the doctrine of atoms, it can do no harm to view it from the stand-point of an opponent. 1. The great mainstay of the belief in atoms possessing definite weight is the fact that the best known compounds present an invariable composition, which is not altered by increased or diminished pressure, temperature, and the like; and that the proportions of the constituents in any two oxides, chlorides, sulphides, etc., of the same metal are in a simple ratio to one an- other. I consider it yet remains to be more satisfactorily shown that this definite character belonging to ordinary chemical combinations passes through to the more complicated instances of which so many are known ; such, for instance, amongst others, as the following. There are certain substances, like carbon, silicon, boron, and some of the metals, which it is well known it is next to impossible to obtain in a state of absolute chemical purity. Carbon, for example, has never, so far as I know, been obtained from any form of charcoal thoroughly purified from minute quantities of hydrogen, oxygen, or nitrogen. If we take a piece of pure white sugar, and heat it in an open platinum capsule, it melts, catches fii-e, and, when the combustion is extinguished, there remains a shining brittle mass, which may be heated red-hot in the air for hours ; chlorine gas may be passed over it; it may be boiled in various solvent liquids, and dried over again at a red-heat; and, do what we may, the charcoal which remains holds a certain, but not fixed, quantity of hydro- gen most tenaciously. Now, in the original carbonaceous compound, the elements are considered to be in a state of chemical combination ; if so, it must be admitted that the hydrogen which is retained by the charcoal is also chemically combined with the carbon therein. But the proportion of carbon and hydrogen can never be expressed by a probable atomic formula. 2. There are numerous compounds, some of which are connected with the * Williamson on the Atomic Theory, Journ. Chem. See, ser. 2, vol. vii. p. 328.