170 THE ORIGIN AND FORMATION OF THE DIAMOND. 



with no cracks, or defects, whereby water might have subsequently 

 peiietrated into it. Diamonds have also been found containing 

 liquid carbon dioxide in their cavities. Now, if water, or water 

 va=pour in the form of steam is passed over carbon, or carbon- 

 aceous substances at a temperature of from 600*^ C. upwards 

 the water will be decomposed, carbon dioxide and hydrogen 

 being produced. At higher temperatures some carbon monoxide 

 will be formed until, at a temperature of about 1000° C, it and 

 h\'drogen are the chief products. The same reactions would 

 occur if diamonds were formed from carbonaceous substances 

 in the presence of water or water vapour, whenever the temper- 

 ature exceeded 600° C. 



Hence, when we find some diamonds containing water in some such 

 form as above, we are justified in concluding that such diamonds, 

 during their formation, cannot have been exposed to temperatures 

 at which carbon and water mutually react, or the water in them 

 would have been decom]X)sed. The same reasoning applies 

 to the presence of carbon dioxide in diamonds. Small diamonds 

 heated in melted carbonate of soda or potash, or an equi-molecular 

 mixture of the two, which melts at a temperature below 800° 

 C, act on the carbonates, decomposing them, and evolving carbon 

 monoxide. A similar action occurs when carbonaceous matter 

 !s heated in carbon dioxide, carbon monoxide being produced. 

 When, therefore, we find diamonds containing liquified carbon 

 dioxide in their cavities, we are justified in concluding that such 

 diamonds have not been formed at a temperature much higher 

 than 800° or 900° C. The high pressure under which such dia- 

 monds have been formed, is shewn by the presence of liquified 

 carbon dioxide, which at temperatures such as those mentioned 

 would amount to at least about 300 atmospheres, ancf perhaps 

 much more, and would probably intensify' the reactions I have 

 outlined. Indeed, in the case of water and carbon we should 

 probably not have free hydrogen liberated but a mixture of 

 hydrocarbons. 



Other diamonds contain inclusions that seem to indicate that 

 they had not been formed at a very high temperature. Thus, 

 some dark coloured diamonds owe their dark appearance to 

 finely divided graphite. When such diamonds are powdered 

 and the powder heated in oxygen gas it is found that the graphite 

 burns away at a temperature of about 200° C. below that at which 

 the diamond powder begins to burn. Now, there are several 

 kinds of graphite, some soft and some hard, and it is found 

 that if the soft variety is heated to a high temperature it is 

 converted into the hard kind. The harder the kind of graphite 

 is the higher is the temperature at which it begins to burn, so 

 that, as Sir William Crookes observes, the temperature of ignition 

 of any particular form of graphite enables us to judge approxi- 

 mately of the temperature at which it has been formed, or to 

 which it has subsequently been ~ exposed. Apj^lying this rule 

 to the case in point, where the graphite in some diamonds ignites 

 at a temperature some 200" C. below that at which the diamond 

 powder begins to burn, we must conclude that such graphite. 



