EARTHS, 277 



SILICIUM, OR SILICON.* 



Remark. The student may omit this head until he has studied 

 the fluoric acid, and its compounds. 



1. PROCESS. 



(a.) Iron seven parts, silica five, and from { to f of soot, fused in 

 a blast furnace, gave an alloy of silicium and iron. 



(b.) Purified potassium, when heated in silicated fluoric acid gas ? 

 burns, condenses the gas, and gives a brown substance. 



(c.) This boiled in water, and dried, burns in oxygen gas, and 

 produces only silicated fluoric acid, and silica. 



(d.) " The residue, treated with fluoric acid, gave silicated fluoric 

 acid, and its color was rendered much darker." 



(e.) " Thrown on a filter, washed and dried, it was pure silicium, 

 which may be obtained also by heating potassium in a glass tube, 

 with dry silicated fluate of potash." 



(/.) " The product by being well washed with water, yields a 

 compound of silicium and hydrogen, from which the latter may be 

 detached by heating in a crucible. "f 



2. PROPERTIES. 



(a.) Color, deep nut brown, without lustre, and acquires no bril- 

 liancy from a burnisher ; no resemblance to a metal ; resists friction 

 like an earthy substance. 



Incombustible, in common air, or even in oxygen gas.J 



* Sir H. Davy, (as already mentioned with respect to lime,) by driving the potassi- 

 um through the earths heated intensely, succeeded so far in decomposing several of 

 them, that the mass exhibited metallic points, and the potassium became potash. 

 No considerable masses of metals were obtained in this way, but in general there 

 was sufficient evidence that they were decomposed, and in this manner he was the 

 first to ascertain that silica is a compound of oxygen and a base. 



t Ann. de Ch. etde Phys. Vol. XX VII, 337. Am. Jour. Vol. IX, p. 377. Hen- 

 ry, Vol. I, p. 641, 10th Ed. 



The best method of decomposing silica, is by taking it in the form of double fluale 

 of silica and potash or soda; the latter is preferred, because it contains the greatest 

 quantity of silica. To prepare it, the; aqueous solution of silicated fluoric acid is 

 mixed with the carbonate of soda, when the double salt, which is nearly insoluble, 

 precipitates, and is washed and dried at a heat above 212. This is stratified with 

 thin slices of potassium, in a glass tube, hermetically sealed at one end, and the 

 mass must be uniformly heated, and at once, by a spirit lamp. Even before ignition 

 the silica is reduced with a hissing noise, and some appearance of heat, but if the 

 matter is dry no heat is evolved. 



The resulting brown mass, after being thoroughly freed from acid and saline mat- 

 ter, by water repeatedly applied, at first cold, and in abundance, and at last boiling- 

 hot, is then ignited, to expel hydrogen. It is then washed in diluted hydro-fluoric 

 acid, to remove any siliceous particles, and is again washed and dried. For the de- 

 tails see Ure's Diet 2d Ed. p. 718, and Ann. of Phil. Vol. XXVI, p. 116. 



t When first obtained, and before it is freed from hydrogen, it burns when heated, 

 even in the open air, but if carefully ignited first, in seclusion from the air, to expel 

 the hydrogen, it becomes uninflammable. 



