and Propcriies ofSilicium. 263 



in a great quantity of water ; so that the liquid, which becomes 

 alkahne by the oxidation of the potassium, may be as dihited 

 as possible, and have less tendency to oxidate and dissolve the 

 silicium. It is for this reason that the mass ought not to be 

 treated with hot water, — that the liquid has not lost its alka- 

 line quality by the washing. It is afterwards boiled with 

 water, and washed with hot water until no stain is left by 

 the evaporation of a drop of liquid. For this purpose much 

 time is generally requisite, and much water must be used. The 

 silicium obtained by, this process contains hydrogen ; but in a 

 smaller quantity, however, and perhaps in the same manner 

 as the common charcoal of wood, which Davy considers as hy- 

 drogenated carbon. It contains also silica, which proceeds 

 principally from the potassium before the reduction, being oxi- 

 dated a little, and then separating a quantity of silica corre- 

 sponding to tire alkali formed : but the alkali which is formed 

 after the reduction, when it dissolves the mass in the water, 

 dissolves a portion of the double salt in excess, without se- 

 parating the silica from it. This silica ought to be taken away 

 by means of fluoric acid ; but as the silicium would dissolve 

 in the acid, we must begin by rendering it insoluble and m- 

 combustible : if it were made to burn in air, a portion of in- 

 combustible silicium would indeed be obtained after treat- 

 ment by fluoric acid ; but ordinarily two-thirds of it would 

 be lost by the combustion. This loss is prevented by heating 

 nearly to ignition the dried silicium containing hydrogen in 

 an open crucible : this degree of heat is maintained some time, 

 and then it i§ raised little by little to a perfect red heat. If 

 the silicium become inflamed, the crucible should be covered 

 directly, and the temperature lowered, which will instantly 

 stop tiie ccmibustion. When the calcination is finished, the sili- 

 cium is incombustible in air, and is no longer attacked by 

 fluoric acid, if it does not contain any foreign metal, iron or 

 manganese for example ; for in this case the alloy would be en- 

 tirely dissolved with disengagement of hydrogen. After ti'eat- 

 ment by the acid, the silicium is washed and dried. It might 

 be thought that this incombustibility is caused by an extremely 

 thui pellicle of silica; but I dried the silicium in a vacuum, 

 and tiien heated it to redness hi the air, and I did not find any 

 change of weight. 



The silica may be reduced by heating it witli potassium : 

 but it happens either that the combination, rich in potassium, 

 becomes eiuirely dissolved in the water; or else, when the heat 

 is suflicieiit to expel the excess of potassium, that the silicate 

 of potash l()rmed melts into a vitreous mass, and envelops 

 the silicium, which thence ac(|uires a clearer colour. Part of 



the 



