188 



Mr. J. B. Hannay on the 



[Feb. 26, 



critical point, the sudden fall in volume corresponding to the boiling 

 line has disappeared, and although the curve does not coincide with 

 the air curve, it is regular and shows no sign of liquefaction having 

 occurred. Our experiments were made at temperatures further 

 removed from the critical point than this, and as no sudden change 

 in solubility could be detected in passing from the liquid state to these 

 high temperatures, we conclude that, in these experiments, we have 

 further proof of the perfect continuity of the liquid and gaseous 

 states, and also a complete proof of the solubility of solids in gases. 



II. " On the Artificial Formation of - the Diamond." By J. B. 

 Hannay, F.R.S.E., F.C.S. Communicated by Professor G. 

 G. Stokes, D.C.L., &c, Sec, U.S. Eeceived February 19, 

 1880. 



(Preliminary Notice.) 



While pursuing my researches into the solubility of solids in gases, 

 I noticed that many bodies, such as silica, alumina, and oxide of zinc, 

 which are insoluble in water at ordinary temperatures, dissolve to a 

 very considerable extent when treated with water-gas at a very high 

 pressure. It occurred to me that a solvent might be found for carbon ; 

 and as gaseous solution nearly always yields crystalline solid on with- 

 drawing the solvent or lowering its solvent power, it seemed probable 

 that the carbon might be deposited in the crystalline state. After a 

 large number of experiments, it was found that ordinary carbon, such 

 as charcoal, lampblack, or graphite, were not affected by the most 

 probable solvents I could think of, chemical action taking the place 

 of solution. 



A curious reaction, however, was noticed, which seemed likely to 

 yield carbon in the nascent state, and so allow of its being easily dis- 

 solved. When a gas containing carbon and hydrogen is heated under 

 pressure in presence of Certain metals its hydrogen is attracted by the 

 metal, and its carbon left free. This, as Professor Stokes has sug- 

 gested to me, may be explained by the discovery of Professors Liveing 

 and Dewar, that hydrogen has at very high temperatures a very 

 strong affinity for certain metals, notably magnesium, forming ex- 

 tremely stable compounds therewith. 



When the carbon is set free from the hydrocarbon in presence of a 

 stable compound containing nitrogen, the whole being near a red heat 

 and under a very high pressure, the carbon is so acted upon by the 

 nitrogen compound that it is obtained in the clear, transparent form 

 of the diamond. The great difficulty lies in the construction of an 



