DR BROWN ON THE PRODUCTION OF SILICON FROM PARACYANOGEN. 233 



tracted high temperature, at which it is conducted, always plasters more or less 

 of the silicon produced over the inside of the tube or crucible; and that circum- 

 stance, together with the formation of microscopical quantities of silicic acid 

 at the expense of the included air of the apparatus, and the difficulty of obtaining 

 numerical results in white-heat operations, rendered it impossible to estimate the 

 loss sustained by given weights of paracyanogen, during the prolonged ignition, 

 with any thing like exactitude. Accordingly, having been persuaded that the 

 product of these decompositions was ignited silicon, I endeavoured in vain to 

 discover how much could be procured from different quantities of paracyanogen ; 

 for, it is to be observed, no metallic vessel could be used on account of the quick 

 and powerful reaction of nascent carbon and silicon on all the ignited metals. As 

 only an already silicated apparatus could be employed, it became desirable to 

 effect the decomposition at a temperature which should neither admit of the par- 

 tial combustion of nascent silicon in the included air, nor corrode the instrument. 

 Now GAY-LUSSAC observed that nitrogen appeared in his cyanogen product of 

 the decomposition of bicyanide of mercury when paracyanogen Avas left in the 

 retorts ; I found, in experiments on the condition of crude paracyanogen, that 

 whenever it is raised to near the lowest visible red heat, absorbed cyanogen is 

 driven away mixed with nitrogen ; and, in some unrecorded experiments, I had 

 observed that no temperature, except that of full white, was so conducive to the 

 extrication of nitrogen, as one just short of a visible glow ; so that there was a 

 clue to the solution of the problem. The next experiments illustrate this point. 



5. A quantity of paracyanogen, black and voluminous, was closely shut up 

 in a Berlin crucible, and kept twenty days in a sand-bath, the temperature of 

 which was maintained as steadily as possible at about 800 or 900 Fahr., and 

 always, at all events, below the point of ignition. It was then found that the 

 decomposition was complete, there being left not a trace of either paracyanogen 

 or carbon. The product, however, was remarkably different in appearance from 

 those of the former experiments. Not nearly so dark, it resembled burned coffee 

 in colour ; in form it was a soft light powder, very hygrometric, and soiling the 

 fingers, instead of a compact cinder. In this condition it burned before the flame 

 of the blowpipe for a little, producing a white ash, and then shrunk without fusion 

 into a denser and darker form, in which it was not readily combustible. In fine, 

 it was unignited silicon ; for it answered to the other characters of that substance, 

 which have been already indicated in connection with the analogous ignited pro- 

 duct of the same operation, performed at a high white heat in the course of an 

 hour or two. This simple experiment has been often repeated, and it has been 

 observed, by periodical examinations of the material during the process of reduc- 

 tion, that the change is gradually effected, and that twenty days are very nearly 

 the time required for the full decomposition of 10 grs. of paracyanogen. One 



VOL. XV. PART I. 3 R 



