THE ARTIFICIAL PRODUCTION OF DIAMOND. 77 



Since my paper in 1907, the experiment of heating iron in a carbon crucible and 

 transferring it to a steel die and subjecting it to 11,200 atmospheres pressure has 

 been repeated, and it has been found that if the iron is allowed to set before the 

 pressure is applied the amount of diamond is much greater than if pressed when very 

 hot and molten, and that it is then about the same as when the crucible is cooled in 

 water. The only reason that suggests itself to account for this is, that when 

 pressure is applied while the iron is very hot some of the latter permeates the carbon 

 of the crucible, and because of the greater specific heat and lesser conductibility of 

 the carbon, the iron next to and in the carbon remains molten after the ingot has 

 been cooled by direct contact with the steel cup on the face of the plunger. Thus, 

 when cooling, the occluded gases have a free exit from the ingot, through the molten 

 metal (which is pervious to gas) into the carbon of the crucible, and are not retained 

 in the ingot to the same extent as when it is set and enclosed in an envelope of 

 colder iron impermeable to the gases before pressing. 



The experiments of BAKADUC MULLER (' Iron and Steel Institute, Carnegie 

 Scholarship Memoirs,' 1914, p. 216), on the extraction of gases from molten steel, 

 showed that steel is permeable to gases down to 600 C. 



Other Experiments. 



The action of water on carbide of calcium, and of concentrated sulphuric acid on 

 sugar for 6 hours under pressure of 30,000 atmospheres were tried ; in both cases 

 amorphous carbon was formed and no diamond. 



HANNAY'S experiments were repeated, where paraffin and dipple-oil with the alkali 

 metals, especially potassium, were sealed in steel tubes and subjected to a red heat 

 for several hours. The analysis gave no diamonds ; in fact it became apparent that 

 when hydrocarbons or water were relied on to produce pressure, the latter could only 

 exist for a short time at the commencement, for when a red heat was reached the, 

 hydrogen escaped through the metal, and the oxygen combined with the steel. 



We did not analyse the steel tubes themselves. Many experiments were however 

 tried with central heating under the press at 6000 atmospheres, and nothing was 

 obtained of interest with the substances used by HANNAY, unless, as previously 

 mentioned, some iron was present. FRIEDLANDER'S experiment was repeated, where a 

 molten globule of olivine, in a reducing flame, or with carbon added, was stated by 

 him to contain minute diamonds. An experiment was made with molten olivine in a 

 carbon crucible in a wind furnace stirred with a carbon rod, with and without an 

 electric current passing between the rod and crucible. 



Many experiments were also tried at 6000 atmospheres under the press with 

 central heating with olivine associated with carbon, hydrocarbons, bisulphide of 

 carbon, water, &c., also with blue ground from Kimberley instead of olivine. The 

 results of the analyses were in all cases negative, except occasionally when metallic 

 iron was present. Thus in some cases the olivine or blue ground was partially 



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