80 THE HON. SIR CHARLES ALGERNON PARSONS : EXPERIMENTS ON 



semi-transparent, the gas present being chiefly hydrogen. (Paper by PARSONS and 

 SWINTON, January 16, 1908, ' Koy. Soc. Proc.,' A, vol. 80.) 



In this latter experiment the surface action appeared to be much less in proportion 

 to the incipient change of the under layer to graphite, and the impression is that at 

 1890 C. the temperature of bulk transformation is being approached, also that 

 carbon monoxide, carbon dioxide, nitrogen, hydrogen, and iron, one or more, act as 

 catalysts in the change of diamond to graphite. 



Experiments on the Oxidation of Alloys of Iron when Molten. 



Iron was melted in a carbon crucible and highly carburized ; when it had somewhat 

 cooled, the other elements were added, in small percentages of aluminium, silicon, 

 calcium, magnesium, manganese, iron sulphide, collectively and in some cases singly ; 

 the crucible was then removed from the furnace and superheated steam blown 

 through a carbon tube into the metal ; energetic action took place and much heat 

 was evolved ; on analysis, after destroying the graphite, a bulky transparent 

 crystalline residue remained. 



With aluminium alone the crystals were chiefly crystallized alumina, and with the 

 other elements the spinels and other crystals were produced ; all were transparent 

 and colourless, but when chromium was added some rounded crystals occurred 

 resembling pyrope. When submitted to sulphur dioxide and carbon dioxide the 

 result was the same, but less residue was produced. Under the microscope there 

 appeared to be a small proportion of very small crystals like diamond ; these burnt 

 in oxygen. When the bulky residue was placed in a test-tube with the double 

 nitrate of silver and thallium, and the density adjusted so that a diamond floated 

 midway between the top and bottom, there collected into its immediate neighbourhood 

 after a time an amount of the small crystals which was estimated to be about 5 per 

 cent, of the total residue. 



One prolonged treatment of hydrofluoric acid had no apparent effect on the bulky 

 residue, and it required so many treatments to destroy it that we failed to isolate the 

 very small particles whose size did not exceed ^ mm. ; they were probably lost by 

 flotation. These experiments were repeated many times with the same result, but 

 they merit further investigation, with steam under high pressure and conditions 

 favourable to the formation of larger crystals. 



Note. MARSDEN observed in silver the association of black diamond with 

 crystalline alumina, silicide of carbon, &c., ' Roy. Soc. Proc.,' 1880. 



Experiments in Vacuo. 



The presence of diamond in some meteorites suggested a series of experiments 

 under various degrees of vacuum up to the highest obtainable.* 



* Also an impression suggested itself in 1907 that hydrogen had an adverse effect on the formation of 

 diamond. 



