469 



and silicon. In the first place, however, they could not succeed in 

 obtaining a pure cyanide of that metal. For whether they decom- 

 posed the cyanide of potassium, or the hydrocyanate of ammonia con- 

 taining an excess of hydrocyanic acid, by neutral acetate of lead, by 

 this salt acidulated with acetic acid, or by tribasic acetate, they 

 constantly obtained a compound containing a large quantity of a 

 hydrated basic acetate of lead ; and they were not more success- 

 ful when they substituted other salts of lead for the acetate as a 

 precipitant, such as the nitrate, basic nitrate, nitrite, chloride, 

 or iodide. It was impossible, therefore, to obtain atomic results 

 with the cyanide of lead. But several of the precipitates, obtamed 

 in the ways now mentioned, were subjected nevertheless to Dr 

 Brown's process, and there was obtained a brown substance, which 

 they expected to prove to be silicon. ^Vhen fused, however, with 

 carbonate of potash, instead of yielding more than twice its weight 

 of silica, it gave only a tenth of its weight of a yellowish-white sub- 

 stance, which was not examined with any particular care, but which 

 seemed to correspond with silica in its leading properties. 



The Cyanides of copper and zinc were also rejected after adequate 

 trials ; and recourse was then had to the Cyanide of silver, which, it 

 is well known, may be readily obtained pure and definite in com- 

 position. When similarly treated as in the process with cyanide of 

 lead, it was converted by heat into a brown powder, with the loss 

 of only a 400th of its weight ; and when this was fused with car- 

 bonate of potash, there was obtained from the product a notable 

 quantity of a substance corresponding in properties with silica, but 

 still much inferior in quantity to what ought to have been obtained, 

 had the whole carbon of the cyanide become silicon. 



The authors next mentioned the results they obtained with the 

 Ferrocyanides. The Ferrocyanide of potassium, when heated with 

 carbonate of potash at a white heat, according to Dr Brown's earlier 

 process, yielded them a saline mass, in which, in many trials, they 

 could obtain only traces of a substance corresponding with silica in 

 properties. Ferrocyanide of lead also yielded traces ; Prussian 

 blue none ; Ferrocyanide of copper rather more than the similar 



salt of lead. 



They then turned to Paracyanogen, which they treated repeatedly 

 by Dr Brown's method of fusion with carbonate of potash. They 

 were foiled, however, in obtaining his results. Paracyanogen ob- 

 tained from cyanide of mercury, and purified by boiUng it first with 

 water, and then with Bolution of carbonate of potash, gave off, not 



