THE; ARTIFICIAL 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, being 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 chemical 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 sufficiency of heating or carbunzation of the iron occurred. On the whole, 

 therefore, it would appear that all, or nearly all, the chemical reactions as such, 

 \mder 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 that 

 quick cooling is not in itself a cause of the occiirrence 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 that 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. 



