THE ARTIFICIA.L PRODUCTION OF DIAMOND. 
87 
A repetition has been made of many of the experiments in which diamond is 
claimed to have been produced. These have given negative results in all cases 
except where iron has played a part, as for instance when olivine, Ijeing partly 
reduced by carbon or a reducing flame, small spherules of iron are produced and 
may, if the mass is quickly cooled, be found to contain diamond. 
The repetition of Moissan’s experiments under a variety of conditions and 
pressures has not only confirmed his results but has thrown, it is hoped, additional 
light on the causes operating to produce diamond in iron. 
The experiments under high pressure in steel moulds, where heating of the charge 
was effected by a central core through which current was passed, enabled Hannay s 
experiments with dipple oil to be tried under much higher pressures, and more 
thoroughly than is possible with steel tubes in a furnace. 
The Appendix gives some indication of the many substances and cliemical reactions 
tested. The results were chiefly negative. The few that were favourable were 
generally attributable, as has been said, to the presence of iron. It was noticed that 
the iron seldom contained diamond unless when so situated in the charge as to cause 
equal cooling on all sides, and it will be remembered that the experiments under atmo¬ 
spheric pressure showed this condition to be essential for the formation of diamond. 
In some of the experiments of this group considerable gaseous pressure existed up 
to 6,000 atmospheres, but it is doubtful if in these the right kind of gas was present 
or a sufliciency of heating or carburization of the iron occurred. On the whole, 
therefore, it would appear that all, or nearly all, the chemical reactions as such, 
under pressures up to 6000 atmospheres, have given negative results. 
The experiments on very rapid cooling would seem to dispel the theory that 
carbon can be caught in a state of transition, and to lead us to the conclusion uhat 
quick cooling is not in itself a cause of the occurrence of diamond in rapidly 
cooled iron. 
Moissan observed that when the spherules of granulated iron were cracked, or 
contained geodes, no diamond was ever found in them, and he attributed this to 
want of mechanical pressure. The experiments we have made not only corroborate 
this fact, but they tend to show, we think conclusively, that the cracks in the 
spherules act by allowing a free passage for the occluded gases to escape, and the 
geodes by providing cavities in which the gases can find lodgment without much 
gaseous pressure occurring in the metal.Further, the experiments have shown that 
iron when it sets does not expand with appreciable force, and that the only com¬ 
pressive forces that are brought to bear on the interior are those arising from the 
contraction of the outer layers. 
Our experiments further show tliat when a crucible of molten iron is subjected to 
pressure more than three times as great as can be produced by these contractile 
forces, the yield of diamond is not increased. On the other hand, when the 
* Conversely they may act to allow gases to enter the metal. 
