178 THE ORIGIN AND FORMATION OF THE DIAMOND. 



very well be supposed to have been present in the mines during 

 their active stage. It contains a very large amount of latent 

 heat but is open to two serious objections. Under a high pressure. 

 and as the temperature rises, it rapidly polymerises into benzene; 

 and unless it i^ mixed with a considerable quantity of an inert 

 gas it is spontaneously explosive. 



Every now and then we hear of processes adopted whereby 

 diamonds have been formed by electricity. I tried this only once 

 many years ago. but I am so convinced that it is practically 

 impossible that I never now attempt it. The reason why it is 

 impossible is, of course, because diamond is a non-conductor of 

 electricity. Although minute diamonds have been formed in 

 that way, crystals of any size cannot be expected, because as 

 soon as a slight coating of diamond is formed on the electrode 

 the current is stopped at that point. The latest thing in this 

 line is, we are told, the electrolysis of carbide of calcium in the 

 electric furnace. Unless the diamond is a better conductor of 

 electricity at that temperature than it is at ordinary temperatures, 

 this process is also bound to fall. 



The presence of iron in almost all diamonds suggests that possibly 

 it may have taken some part in the formation of diamonds. Thus 

 I have supposed that oxide or silicate of iron in the presence 

 of water and carbonaceous matter at a red heat might so act. 

 We may suppose the iron to be first reduced to metal by the carbon, 

 with another portion of which it might combine to form a 

 carbide of iron ; this, in presence of water or steam, would 

 be immediately decomposed into the magnetic oxide and a 

 hydrocarbon. Those two would in turn probably mutuallv 

 decompose again and perhaps at the moment give us carbon 

 in an endothermic form that under suitable physical conditions 

 of pressure, and so on, might form diamond. Of course all 

 such theorising has to be subjected to the test of experim.ent 

 and I may say that I have made a very large number of ex- 

 periments to test such plausible theories. And though truth 

 lies at the bottom of a well, and only those who have spent 

 years over such experiments can tell how very deep in this 

 case that well is, the history of all science shows us that we shall 

 probably reach the bottom of it if we probe long enough. 



I will conclude this paper b}^ formulating the conditions under 

 which I think diamonds were formed in nature. 



First — The various foreign inclusions found in diamonds, taken 

 in connection with what we know of the chemical deportment 

 of diamond at high temperatures in the i^resence of such enclosures, 

 makes it probable that such diamonds could not have been pro- 

 duced at temperatures much, if anything, above a moderate 

 red heat, or, say, from. 600° to 800° or 900° C. 



Second — That the production of various minerals and of graphite 

 from fossils in cases of local and regional metamorphism is ana- 

 logous to what may have taken place in the diamond mines, 

 during their period of activity, excepting that in the case of 

 the latter, the conditions were much more specialised and the 

 pressure probably greater. In both cases several minerals have 



