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XLIII. Oil the Atomic Volume and Crystallhie Condition of 

 Bodies, and on the Change of Crystalliiie Form by means of 

 Heat. 5y Dr. Hermann Kopp*. 



IN a former paper (PoggendorfF, Jji7i. xlvii.) I have en- 

 deavoured to show that a relation subsists between the 

 vou mes in which bodies unite in forming chemical com- 

 pounds, in addition to that which is known to exist with re- 

 spect to their weights. Gay-Lussac had already shown that 

 gaseous compounds combine with one another according to 

 volumes ; but this observation had not been extended to solid 

 or liquid compounds. Hence the object of my inquiries was 

 to examine the atomic volumes in which the latter combine, 

 in contradistinction to their atomic weights ; to which atten- 

 tion had hitherto been exclusively directed in examining their 

 chemical composition. 



The numbers representing the atomic volumes of bodies 

 are proportional, just as the atomic weights are ; and 

 the atomic volume of any body may be deduced from its 

 atomic weight, merely by dividing the latter by its specific 

 gravity. But it is evident that these numbers must vary ac- 

 cording to the system of atomic weights adopted ; hence in 

 the following paper, that scale of equivalents in which oxygen 

 is equal to 100 is adopted, and not what is still retained by a 

 few chemists, in which hydrogen is regarded as unity. The 

 formulas of the compounds examined are generally those of 

 Berzelius. 



It is not sufficient to affirm that bodies unite according to 

 their respective atomic weights and volumes : we must also 

 comprehend clearly what is meant by the application of these 

 terms. Nor is this difficult ; for the idea of mass is represented 

 by atomic weight ; whilst a regular and definite volume is evi- 

 dently represented by a crystal. 



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 de- 

 pendent upon our idea oimass (that is of atomic weight), whilst 

 our idea of specific weight is connected with the mass con- 

 tained in the same volume. From these considerations the 

 following law may be deduced: 



The specijic weight of isomorphous bodies is j)^'oportional to 

 their atomic weight; or, isomorphous bodies possess the same 

 atomic volume. 



* Communicated by the Author. 



