400 Proceedings of the Boj/al Soci$(i/: 



tompernture and pressure, a compound was obtained, in which carbon 

 could not bo detected, but instead of it silicon, in the proportion of 28.5 

 per cent. To these remarks were added others on ferrocyanide of po- 

 tassium, which he considers to be resolved in the process into cyanide of 

 potassium evolved by subUmation, and paracyanide of iron, which at the 

 same time is decomposed, and yields disiliciuret of iron. The product 

 obtained in these two ways is, in general, partly in the form of a coaly 

 powder, partly in fused obsidian-like masses. But if the ferrocyanide 

 of potassium be heated with its own weight of cyanide of potassium, as 

 a non-reactive flux, the disiliciuret is obtained in a semicrystalline 

 form, which in fine powder is colourless, and is seen before the micro- 

 scope to be transparent like glass ; and sometimes there is an approach 

 to a crystalline form, nay, small particles may be discovered with the 

 microscope which are regular octahedres. The disiliciurets of iron thus 

 produced were treated of by the author in his Inaugural Dissertation in 

 1 839, as carburets of the metal. (See Trans. Brit. Assoc. 1839, vol. ix.) 

 Experiments were added under the present section, which satisfied the 

 author that every conceivable source of silicon, except from the para- 

 cyanogen, was provided against by the manner in which the experiments 

 of conversion were performed. Among other facts thus elicited, it ap- 

 peared, that, by successive operations in the same vessel, a greater 

 weight of disiliciuret of iron might be obtained than the weight of the 

 vessel itself. 



5. Silicic acid may be obtained by a direct process from the paracy- 

 anide of iron. The conversion thus accomplished might appear, as the 

 author conceived, more satisfactory to most persons, than any of the 

 previous operations, on account of the large scale on which the experi- 

 ments were performed. When paracyanide of iron was mixed with 

 four times its weight of carbonate of potash, and ignited in a shut cru- 

 cible of hammered iron for four hours at a full white heat, a rose-red 

 saline product was formed, from which a transparent solution was ob- 

 tained with water ; and when this was supersaturated by hydrochloric 

 acid, a bulky precipitate was thrown down, which, when purified from 

 adhering metallic oxide by fusion with carbonate of potash, solution of 

 the product in water, neutralization with hydrochloric acid, evapora- 

 tion, desiccation, and ignition, and elutriation with water to remove 

 chloride of potassium, — presented all the distinctive characters, physical 

 as well as chemical, of silicic acid. Five grains of paracyanide of iron 

 thus gave 3.04 of silicic acid ; and 30 grains of ferrocyanide of potassium, 

 similarly treated, gave 5 A grains of silicic acid. The iron crucible 

 us:din these operations did notyield a particle of silicic acid whenheated 



