DR BROWN ON THE PRODUCTION OF SILICON FROM PARACYANOGEN. 243 



when the operation is conducted on a large scale, there often occur imperfect 

 crystals of considerable dimensions, varying from a fourth to half an inch. 

 Sometimes they are found in the form of irregular globular bodies, pitted on 

 the surface, and cellular within; and, indeed, the particles of the sediment 

 under examination generally present a somewhat rounded appearance at the 

 edges, although they affect the octohedral shape, and are many of them seen 

 to be very perfect octahedres when viewed on the field of the microscope. In one 

 operation I procured half an ounce of these little eight-sided crystals, and have 

 worked with glass, porcelain, black lead, iron, and platinum vessels, with equal suc- 

 cess. This is a difficult process, however, and one must be content to make seve- 

 ral trials before a fine product be obtained ; but, although it is not easy to produce 

 a perfect specimen, it is the simplest thing in the world to satisfy one's self of the 

 change which is effected. Nay, it is impossible to make cyanide of potassium by 

 the common process without performing this transformation ; for, if the charred 

 product be washed, and inspected with a good microscope, the crystals are seen 

 bright and clear among the paracyanide ; and the latter may be burned and dis- 

 solved away, so as to leave the siliciuret by itself. The more care bestowed on the 

 operation, the greater the proportion of crystallized product ; and the quantity is 

 only increased by previously adding cyanide, and observing the precautions of the 

 formula which has been given. I have examined many such products, prepared by 

 others in ordinary routine as well as by myself, and have never failed to confirm 

 this observation, till I have at length come to the conclusion, that the production 

 of silicon from paracyanogen has been performed by every one who has decom- 

 posed the ferrocyanide of potassium by heat, in order to procure the cyanide of 

 the same metal. This explains the fact, that Berzelius found the charred product 

 under consideration to yield its own weight of peroxide of iron on simple combustion, 

 and inferred that it was therefore a bicarburet of that metal : It may have been 

 paracyanide mixed with some unobserved and unburned siliciuret. Analogous 

 compounds of copper, bismuth, and some other metals, have been formed in a 

 similar way, but it is unnecessary to describe them at present.* 



* These products were described in a paper read before the British Association in 1839, and pub- 

 lished, in abstract, in vol. ix. of its Transactions. They were described as crystallized carburets ; but I 

 distinctly stated that I had not analyzed them, and grounded my conclusion regarding their composition 

 solely on synthetic evidence ; and so far I was really in the right, for, although they are siliciurets, their 

 ingredients are carbon and iron. I then believed them to be true carburets, having been misled by the 

 observation, that a mixture of the crystalline and the uncrystalline products gave carbonic acid with oxide 

 of copper, the uncrystallized product being now known to be mere unreduced paracyanide of iron. As my 

 inaugural dissertation was never published (except an unimportant subsection of it), I gratefully acknow- 

 ledge the honour conferred on it by the Medical Faculty of the University of Edinburgh, by taking this 

 opportunity of stating that the investigation of this process was the main subject of one of the four Prize 

 Theses for 1839. 



