236 DR BROWN ON THE PRODUCTION OF SILICON FROM PARACYANOGEN. 



merical result is somewhat unsatisfactory on account of the circumstances which 

 have just been mentioned as affecting the condition of anhydrous paracyanogen, 

 it is here presented in the form of an experimental formula. Process Triturate 

 crude paracyanogen with an excess of carbonate of potassa, and fuse the mixture 

 two hours at a full white heat in a closed platinum crucible. Paracyanogen dis- 

 appears ; there is no free carbon in the white saline product ; but it yields a con- 

 formable proportion of silicic acid, when treated in the ordinary method of analysis 

 for that compound. There must be a considerable excess of carbonate ; for, as 

 will be shewn immediately, platinum is apt to draw off some of the silicon in its 

 jn-ocessus e latenti, unless it be well protected. This process is more striking when 

 subborate of soda is substituted for potassa ; for when the product is treated with 

 acids there is no effervescence of carbonic acid ; and it must be remembered, once 

 for all, that in every professed process of transformation, the disappearance of 

 carbon is to be accounted for, as well as the new formation of silicon. 



In conclusion, the average results of my observations on crude paracyanogen, 

 prepared in the apparatus described in the introduction, are, that it contains very 

 nearly a third of its own weight of condensed cyanogen, and that it yields, to the 

 three operations which have just been described, a weight of silicon never less 

 than an eleventh, and never more than a twelfth, under the calculable weight of 

 constituent carbon, the cyanogen of absorption being dissipated in the course of 

 the processes. 



II. On the formation of mixed Amorphous Compounds of Silicon with Copper, Iron, 

 and Platinum, by the reaction of Paracyanogen on these Metals. 



1 . The double copper-tube, described in the fourth section of my paper on 

 Paracyanogen, having been packed with bicyanide of mercury, and accidentally 

 kept at a white heat for more than an hour, it was found on examination to con- 

 tain not a trace of paracyanogen. It was lined with a film, more than a line in 

 thickness, of a very friable, reddish, metallic substance, which separated from the 

 copper on concussion, and fell out in broken blistered scales. Pulverised, it lost 

 its metallic lustre, and assumed a dingy brown-black colour. Nitric acid dis- 

 solved copper and left a fine^black powder, like well triturated charcoal, which 

 was observed to be distinctly brown when viewed by light transmitted through 

 water holding it in suspension. The rigorous application of the reagents men- 

 tioned above (pp. 247-8) proved it to be silicon. The copper compound was 

 several times made intentionally, -and the result of three analyses was, that it 

 contained from 30 to 40 per cent, of silicon. This and the two substances which 

 follow are said to be mixed, because, in accordance with the principle of definite 

 proportions, which is now universally recognised as the law of chemical constitution, 



