558 Mr. Richard ThreJfall [March 19, 



is sufficient to render it possible that temperatures of from 3000° to 

 4000^ C. may have been reached ; it is possible that about 3000° C. 

 was actually attained at the centre of the charge. The results 

 obtained were uniform. No matter what form of carbon (excluding 

 diamond, which was not tried) was packed originally in the apparatus 

 the final product was soft well-crystallised graphite ; which agrees with 

 some results of similar experiments described by Mr. Parsons,* but 

 not with the results claimed by Dr. Ludwig.f 



In several experiments the crystalline mass of graphite was tested 

 in regard to its porosity, and this was found to be considerable — a 

 remarkable result, having in view the conditions under which it had 

 been formed. 



Another point of interest was that where the soft graphite had 

 been driven into the Acheson graphite plug at the bottom of the 

 apparatus it became extremely hard, so much so that a hard steel file 

 made little or no impression upon it. 



The main difference in treatment of this part of the graphite as 

 compared with the remainder is that it was cooled much more 

 quickly, thanks to the high heat conductivity of the Acheson 

 graphite plug. The cause of hardening has hitherto not met with 

 any satisfactory explanation. 



No appreciable quantity of carbide of magnesia was formed in 

 the experiments. The magnesia close to the graphite core contained 

 traces of carbides, but as there were always traces of iron left from 

 the drilling out process, this may be plausibly accounted for by the 

 formation of carbide of iron. 



The graphite was finally systematically searched for microscopic 

 diamonds by Staudenmaier's modification of Brodie's method of con- 

 version of graphite into graphitic acid,| or else by Moissan's modifica- 

 tion of the same method.§ A convenient means of distinguishing 

 diamond in fine powder from most or all of the substances which are 

 not separated by a liquid of density 3*84 at 4°C. is to heat the 

 powder in a silver spoon to a dull red heat in fused potassium 

 hydroxide. Check experiments showed that diamond dust easily 

 passing a sieve with 100 threads to the inch would withstand the 

 action of molten caustic potash at a temperature at which the edges 

 of the silver spoon began to melt, for five or ten minutes. Crystals 

 of alumina or of carborundum are entirely destroyed by this fusion, 

 but the diamond particles seemed to have undergone no change. In 

 fact the individual fragments could be recognised under the micro- 

 scope after passing through the ordeal. 



I am led to consider that my experiments indicate that no whole- 

 sale transformation of amorphous carbon or graphite into diamond 



* Proc. R.S., 79. t Zeits. fur Electrochemie, 1902, 273. 



X Ber. 1898, xxxi. 1485. § Electric Furnace, 49, translation. 



