Note 37 — Chapter V

“Gay Lussac first made the remark, that a crystal of potash alum, transferred to a solution of ammonia alum, continued to increase without its form being modified, and might thus be covered with alternate layers of the two alums, preserving its regularity and proper crystalline figure. M. Beudant afterwards observed that other bodies, such as the sulphates of iron and copper, might present themselves in crystals of the same form and angles, although the form was not a simple one, like that of alum. But M. Mitscherlich first recognised this correspondence in a sufficient number of cases to prove that it was a general consequence of similarity of composition in different bodies.”—Graham’s Elements of Chemistry (1842), p. 136.

The following remarks are from a paper by Dr. Hermann Kopp, On the Atomic Volume and Crystalline Condition of Bodies, &c., published in the Philosophical Magazine for 1841:—“The doctrine of isomorphism shows us that there are many bodies which possess an analogous constitution, and the same crystalline form. Our idea of the volume (or, in other words, of the crystalline form) of these bodies must therefore be the same. From this it follows that their specific weight is connected with mass contained in the same volume. From these considerations the following law may be deduced: The specific weight of isomorphous bodies is proportional to their atomic weight, or isomorphous bodies possess the same atomic volume.”—page 255. A translation appears in the Cavendish Society, from Dr. Otto’s Chemistry, On Isomorphism, which may be advantageously consulted. See also a paper by M. Rose, translated from the Proceedings of the Royal Berlin Academy for the Chemical Gazette, Oct. 1848, entitled, On the Isomeric Conditions of the Peroxide of Tin.