270 THE CHEMISTRY OF THE SUN. [CHAP. 



known exception, is absorbed or given out. What is it doing ? 

 if it is not in some way or other controlling the passage from 

 one molecular group to another ? These allotropic conditions, 

 occurring very obviously to us in certain limits at our ordinary 

 temperature and pressure are, possibly, but special cases of 

 group-condensation common to all bodies, represented by Dalton's 

 law of multiple proportions. We can indeed imagine a condition 

 of things in which the difference between iron in the ferrous 

 and ferric chlorides (FeCl 2 and Fe 2 Cl 6 ) would be as obvious as 

 the difference between ordinary and amorphous phosphorus. 



In certain classes of so-called organic substances this group- 

 ing of simpler groups to more complex actually takes place, 

 and is recognised under the term polymerisin for instance, 

 with cyanogen compounds of oxygen we have a simple thing 

 like cyanic acid (CNO) say, which will form a series of com- 

 pounds, and we have its so-called polymers, C 2 lSr 2 2 , or C 3 N" 3 O 3 , 

 which will each form a series of compounds, these groups of 

 more complex nature forming, by their combination, group- 

 individuals with related but not identical properties with the 

 simplest or fundamental group. 



In many cases the amount of this condensation may be 

 determined by the vapour densities. In others, again, a disso- 

 ciation takes place at a certain limit of temperature, a simpler 

 or fundamental group being the resolution product. 



The resemblance between these cases of polymerism and 

 especially those elementary bodies which exhibit allotropism, is 

 at least striking. 



In the one case, the organic complex bodies, the range of ex- 

 istence is in most cases within our easy attainment ; in the so- 

 called elementary stuffs it is less frequently the case. We can 

 certainly convert ordinary phosphorus and sulphur into allo- 

 tropic and most likely polymeric forms, but we do not know as 

 yet how many atoms more are contained in the polymeric forms 

 of these substances than in their simpler states. 



