﻿108 MEIGS ON THE RELATION OF 



each other in compounds according to equal, and others according to unequal numbers 

 of atoms. 



In 1809, from his own experiments, and those performed in company with Hum- 

 boldt, Gay Lussac clearly demonstrated that gases combine with each other by definite 

 volumes as well as by definite weights, and that the volume of a gaseous compound 

 is distinctly related to that of one or both of its constituents. Prout, Thompson and 

 others, by their researches, afterwards showed that this law embraced vapors, and 

 also the vapors of certain bodies which possess the elastic form only when combined 

 with permanent gases. 



Recently Dr. Hermann Kopp of Giessen has attempted to extend the volume-theory 

 in another direction. He endeavors to show, — and with remarkable success, — that 

 all bodies in forming chemical compounds, unite by definite volumes in addition to 

 equivalent weights ; that every body, whether elementary or compound, has a specific 

 atomic volume ; that as atomic weights are proportional, so are atomic volumes ; that 

 whilst atomic weight gives us the idea of mass, a crystal is the representative of a 

 regular and definite volume. From considerations of this nature he enunciates the 

 following law : " The specific weight of isomorphous bodies is proportional to their 

 atomic weights ; or, isomorphous bodies possess the same atomic volume."* 



From the numerous examples adduced by Kopp, of the validity of this law, we 

 may legitimately infer that the phenomenon of isomorphism may be expressed by 

 saying, that many elementary and compound bodies tend strongly to assume the same, 

 or, at least, but a slightly differing volume. Furthermore, all crystallization is the 

 assumption of a form or regularly defined volume, the specifically regular outline or 

 contour of whic'h is dependent upon the power and freedom of the aggregating force. 

 In the study of the volume of a body, then, is in all probability involved the study of 

 the cause of cohesive attraction, isomorphism, dimorphism, trimorphism, polymeric- 

 isomorphism, and all the interesting though obscure phenomena of crystallization. 

 Evidence of a very high character exists for supposing that identity in the arrange- 

 ment of atoms is the immediate predisposing cause of identity in form or volume. 

 Sameness in number does not appear necessary, for examples exist of isomorphous 

 bodies having unequal numbers of atoms. Reasoning in this channel, we are con- 

 strained to seek for the cause not only of isomorphism, but of all crystallization, in 

 that force, whatever it may be, which is capable of arranging an equal or unequal 

 number of atoms into the same volume. Now, many crystals, when once formed, 

 will maintain themselves unchanged under very varying external conditions. Hence 

 it may be inferred that the force which gave form to a portion of matter, which 

 created the crystal, so to speak, must exist with and in it, otherwise that form could 

 not be preserved. Just as in the organic world, the parent imparts its vital powers 



„* London Philosophical Magazine, 3d series, Vol. 18, p. 255. 



