88 THE HON. SIR CHARLES ALGERNON PARSONS : EXPERIMENTS ON 



conditions of the experiment operate to imprison the occluded gases, then the 

 yield of diamond is about the same as if the crucible had been plunged into water, 

 while if the conditions are such as to allow a free passage through the skin of the 

 ingot, the yield is at once diminished, even though the bulk pressure on the ingot is 

 the same. 



The experiment, on compressing acetylene and oxygen, has shown that minute 

 crystals, probably diamond, are produced almost instantaneously in the molten 

 surface of metal exposed on one side to gases consisting of carbon monoxide, 

 carbon dioxide, and hydrogen at very high temperature and at 15,000 atmospheres. 

 Sir WILLIAM CKOOKES' experiment described in his lecture before the British 

 Association at Kimberley in 1905 is somewhat analogous; cordite with a little 

 additional carbon was fired in a chamber, the pressure reaching 8,000 atmospheres, 

 a few crystals of diamond were found and isolated ; this result CROOKES attributed 

 'to the melting of the carbon under the temperature of explosion and crystallization 

 under the pressure on cooling. 



Under the conditions of the experiment there would be a considerable amount of 

 the surface of the chamber melted and swept into the products of the charge by the 

 turbulence of the explosion, and the spherules of iron would thus be carburized and 

 cooled while still under heavy pressure. 



In the acetylene-oxygen experiment there is a molten surface with reducing gases 

 on one side at high pressure, and on the other metal impervious to gases. In 

 CROOKES' experiment the globules of metal are surrounded by gases at high pressure. 

 In both cases the metal has solidified with the occluded gases imprisoned by the 

 high external gaseous pressure, for we have seen that the pressure of occluded 

 gases in highly carburized iron when quickly cooled cannot exceed about 1000 

 atmospheres. 



The experiments under vacua from 75 mm. up to X-ray vacua have shown 

 generally that as the vacuum is increased the yield of diamond in the crucible is 

 diminished, and that below 2 mm. none has been detected. But when alloys pre- 

 viously boiled at atmospheric pressure are quickly heated up under high vacuum 

 violent ebullition takes place, from the large volume of gases liberated, and some of 

 the contents are ejected into the vacuum chamber before they have had time and 

 sufficient temperature to part with their occluded gases, and diamond occurs in the 

 spherules so ejected. 



The gases occluded in cast iron which are given oflfwhen heated in vacua have 

 been investigated by H. C. CARPENTER and others, and the relative amounts of the 

 constituents are found to vary widely according to the previous heat treatment and 

 the nature of the gases in contact with the metal while molten and during cooling ; 

 they are carbon monoxide and carbon dioxide, hydrogen and nitrogen. 



H. C. CARPENTER (' Journal of Iron and Steel Institute,' 1911) states that, when 

 heating up a bar of cast iron in vacua in a silica tube, " After the twenty-fifth heat 



