244 DR BROWN ON THE PRODUCTION OF SILICON FROM PARACYANOGEN. 



In conclusion, it is worthy of remark, that the preparation of these crystals 

 illustrates the formation of the diamond by natural operations, inasmuch as there 

 is quite as great, and the very same, difference between the amorphous and the 

 crystallized siliciurets, as there exists between the carbon of the laboratory and 

 the gems of Golconda. In further exemplification of the principle, it may be 

 added that I have obtained crystallized granules, which appear to be pure silicon, 

 by submitting a mixture of paracyanogen, and a large excess of cyanide of potas- 

 sium, to the operation which has been described in this paragraph ; but their pu- 

 rity has not yet been certified by a synthetic experiment. 



V. On the preparation of Silicic Acid by the reaction of Carbonate of Potassa on the 



Paracyanide of Iron, free and combined. 



The facts contained in the preceding section, taken in connection with the 

 process for preparing silicic acid which is mentioned at the conclusion of the first, 

 naturally led to the experiments which form the subject of this, the last part of 

 the inquiry. 



1. A quantity of paracyanide of iron was mixed with four times its weight of 

 carbonate of potassa, and the mixture ignited in a shut crucible, made of ham- 

 mered iron, during the space of four hours, and at a full white heat. On being 

 opened, the saline product presented a fine rose-red colour, which disappeared on 

 the affusion of water ; by the action of which the whole mass was resolved into a 

 transparent solution, and a loose, partially aggregated substance, resembling spongy 

 platinum in external appearance, which will be alluded to presently. Suffice it here, 

 that the latter is a pure metallic oxide. In repeating this experiment, it was occa- 

 sionally found that the solution of the saline product was tinged blue, that colour 

 being changed into a fine rose tint by evaporation to dryness, and restored by the 

 action of water. But, if the operation be not prolonged beyond four hours or there- 

 abouts, for 3000 grains, it is wholly or nearly colourless. Hydrochloric acid dis- 

 pelled carbonic acid, and threw down hydrated silicic acid from the solution under 

 examination ; and, after desiccation, followed by ignition and elutriation, the latter 

 was obtained anhydrous and insoluble. 3.04 grs. of silicic acid were extracted from 

 5 grs. of paracyanide of iron. In performing this process, and especially with a 

 view to numerical results, it is almost always necessary to purify the silicic acid. 

 The mode of purification which I adopted simply consisted of a repetition of the pro- 

 cess of separation : The product of silicic acid was ignited in three times its weight 

 of carbonate of potassa ; the silicate of potassa was dissolved out by water, and the 

 potassa was more than neutralized by hydrochloric acid ; the acid solution having 

 been evaporated to dryness, the solid residue was ignited in a clean iron cru- 



