PROCESSES FOR THE CONVERSION OF CARBON INTO SILICON. 551 



rush of air took place, shewing that some cyanogen, or nitrogen, or other gas, had 

 been evolved in spite of the pressure. But the loss in this way was so slight, that 

 quantities, such as 40 grs., did not lose more than O'l gr. by the heating. 



The brown powder (diparacyanide of silver ?) obtained in this way, was fused 

 with pure carbonate of potass in a platina crucible ;* and the product of fusion dis- 

 solved in water, filtered, supersaturated with muriatic acid, evaporated to dryness, 

 and redissolved in water. A white, gritty, insoluble powder remained, having all 

 the properties of silica. But we shall return, after recounting the different pro- 

 cesses we tried, to the consideration of the proofs by which we satisfied ourselves 

 that what we term silica was really so. The quantity of silica was in every case 

 much less than it should have been, had the whole carbon of the cyanide of silver 

 been transmuted into silicon ;f and hydrocyanic acid was evolved abundantly on 

 the addition of the muriatic acid, shewing that much of the paracyanogen had 

 escaped the transformation of which, ex hypothesi, it is susceptible, and had decom- 

 posed the carbonate of potass, forming cyanide of potassium. 



The liability of the sealed glass tubes to explode, which two-thirds of them did, 

 and the difficulty of regulating the temperature where metallic ones were em- 

 ployed, were serious objections to this process. Care and attention, however, might 

 have enabled us to overcome these, but the formation of cyanide of potassium, 

 in variable quantity, destroyed the possibility of obtaining proofs that the silicon 

 had been yielded by the carbon. On this account, accordingly, we relinquished the 

 cyanide of silver. 



From the cyanides we passed to the ferrocyanides, in the expectation that, in 

 imitation of Dr BKOWN, we should be able to obtain silica in such abundance as to 

 disprove, by its very quantity, the objections that have been made to his conclu- 

 sions, on the ground that the silica was derived from the vessels or reagents made 

 use of. 



No process for this purpose could be simpler than that given by Dr BKOWN 

 for producing silica from the ferrocyanide of potassium. That salt, thoroughly 

 dried, was to be reduced to powder, and mixed with three or four times its weight 

 of pure carbonate of potass. The mixture was then to be " ignited in a shut cru- 

 cible, made of hammered iron, during the space of four hours, and at a full white 

 heat."} The saline mass obtained at the end of the heating, when treated with 

 muriatic acid, &c., as if it were soluble silicate of potass, was found by Dr BROWN 

 to yield silica so abundantly, that in one experiment 5 grs. were procured from 



* A platina crucible was used at the risk of destroying it by the fusion of the silver ; porcelain being 

 objectionable as containing silica. 



| In the only experiment of which the exact quantities are recorded, 17'9 grs. of the brown powder 

 (diparacyanide of silver V) gave of silica 0'5 gr. 



I Transactions of the Royal Society of Edinburgh, vol. xv. p. 244. 



VOL. XV. PART IV. 7 K 



