Theoretical chemistry from the standpoint of Avogadro's rule & thermodynamics / [Walther Nernst].

  • Walther Nernst
Date:
1911
Catalogue details

Licence: In copyright

Credit: Theoretical chemistry from the standpoint of Avogadro's rule & thermodynamics / [Walther Nernst]. Source: Wellcome Collection.

    30/840 (page 6)
    I 6 THEORETICAL CHEMISTRY away with the numerical factor in the expression of many laws of nature, so that they assume an extremely simple form; thus this system, like a good theorem, gives the physicist a quantity of detailed knowledge of the art of measurement, and of the most varied character. The four fundamental units so far generally used, and mentioned above, are not necessary. Mass may be referred to length and time by means of Newton’s law of gravitation (Maxwell): The gas equation pv = RT may by putting R=1 be used to define temperature in mechanical measure, as a quantity of energy. For various reasons such definitions are not convenient, at least at the present time, and it will be well to wait for the discovery of new laws of nature before reducing the number of fundamental units. The latter should of course be so chosen that they can be as accui’ately measured as possible ; this condition is satisfied by length, mass, time, and temperature to a high degree, but not by energy, which for that reason is not acceptable as a fundamental unit. The Indestructibility of Matter.—Numerous investigations have shown that neither by physical change of a substance, as, for example, by pressure, heating, magnetisation, etc., nor by chemical decomposition, does there occur a variation of its mass, as measured by the attraction of the earth (Lavoisier). Innumerable chemical analyses and syntheses speak for the correctness of this law; in spite of the mighty chemical processes occurring in the sun, its attraction of the planets remains unchanged—an extraordinarily sharp proof that in these processes the total mass of the sun itself remains unchanged. The question whether the weight of a product of reaction is equal to that of the reacting bodies has lately been tested by H. Landolt, with great accuracy (Zeitsch. f. phys. Chew. [1893], 12. 1 ; Sitzungsber. d. Preuss. AJcad. d. Wissensch., 1908, p. 354). It appeared that in the 15 cases investigated the change of weight due to chemical reaction was at most a millionth part, probably much less, and in no case was greater than the probable eri’or in weighing (0-03 mg.). The Transmutability of Matter.—The properties of a sub- stance vary with the external circumstances under which we study it; but, nevertheless, for a slight change of external conditions (especially of pressure and temperature) jthere corresponds only a slight change in the physical properties of a substance. On the other hand, if we bring together different substances, as, for example, sugar and water, or sulphur and iron, even when the same external conditions are maintained, there commonly occurs a deep-seated change in their properties, producing substances which on comparison with the original are very different in many respects. Thus it is possible for the same substance under the same external conditions to assume entirely different external properties : the substance is con- vertible into another.