3Q2 THE ALLOTROPISM OF CHLORINE. [MEMOIR XX. 



and its Relation with Certain Cases of Isoraerisrn in 

 their Combinations." He shows that of the elementary 

 bodies now known, many undoubtedly exist in several 

 allotropic states, and infers that all are liable to anal- 

 oomis modifications. He indicates that the isomerism 



o 



of compound bodies is due sometimes to the different 

 modes in which the atoms of which their constituent 

 molecules consist are grouped, and sometimes to the dif- 

 ferent allotropic states in which one or the other of those 

 elements is found. Thus, as M. Millon has remarked, 

 the intrinsic difference between carburetted hydrogen 

 gas (CH) and ottar of roses (CH), which are isomeric 

 bodies, may perhaps consist in this, that in the former 

 the carbon is under the form of common charcoal, and in 

 the latter under the form of diamond. 



The following instances from Berzelius may serve as 

 examples of these allotropic states : 



Carbon is known under three forms charcoal, plum- 

 bago, and diamond. They differ in specific gravity, in 

 specific heat, and in their conducting power as respects 

 caloric and electricity. In their relations to light, the 

 first perfectly absorbs it, the second reflects it like a 

 metal, the third transmits it like glass. In their rela- 

 tions with oxygen they also differ surprisingly ; there 

 are varieties of charcoal that spontaneously take fire in 

 the air, but the diamond can only be burned with diffi- 

 culty at a high temperature in pure oxygen gas. The 

 second and third varieties do not belong to the same 

 crystalline form. 



Silicon exists also under two forms. In its first it 

 burns with facility in the air under a slight elevation of 

 temperature. But if it be previously exposed to a strong 

 red heat it changes into the second variety and becomes 

 incombustible, so that it will not oxidize when placed 

 with nitrate of potash in the hottest part of a blowpipe 



