262 M. Berzelius on the Preparation 



when they are treated with acids they leave a small quantity 

 of silica. The copper, particularly, left a skeleton of the same 

 form as its own. It is here to be remarked that silicium, 

 which alone is not attacked by the acids, is oxidated by them 

 when its combinations with the metals are dissolved. We 

 have, however, a similar example already in rhodium, which, 

 though not attacked per se by aqua-regia, is dissolved by it 

 when alloyed with certain metals. 



Titanium, which approaches so near to silicium in its pro- 

 perties, is also insoluble in acids in the metallic state (with the 

 exception of a mixture of the fluoric and nitric acids), whilst 

 it is oxidated and easily dissolved when alloyed with other 

 metals. 



Silicium combines with potassium at a high temperature, 

 but without the evolution of a remarkable heat. It affords 

 two combinations ; one, with excess of potassium, of a dark- 

 gray, and which dissolves completely in water ; the other, with 

 less potassium, is obtained by the reduction before stated, or 

 by exposing the first to a very strong heat. It is besides pro- 

 bable that silicium may form with the metals combinations, 

 the proportions of which correspond with those of their sili- 

 cates. — I reserve these researches for another time. 



Preparation of Silicium. 

 The combustion of potassium in silicated fluoric gas re- 

 quii'es apparatus which we have not always at hand. The 

 double salts, on the contrary, which fluoric acid forms with 

 silica and potash, or soda, afford very advantageous means of 

 preparing silicium. I did not observe any difference in the 

 use of one or the other of these salts. That of soda has how- 

 ever the advantage of containing under the same weight and 

 the same volume a greater quantity of the fluate of silica. This 

 salt is used in the following manner : — It is reduced to a fine 

 powder; and in case the desiccation has made its particles ad- 

 here, and also to expel the humidity that may remain, it is ex- 

 posed to a temperature as high as it can bear without being 

 decomposed, that is to say, much above 100°. It is then put 

 by layers with the potassium into a tube of glass closed at one 

 end, which is placed in such a manner as that all the mass 

 may be heated at the same time. We may, if we choose, melt 

 the potassium and mix it, by means of a rod of iron, with the 

 salt, and then heat the mass over a spirit-lamp. Even before 

 a red heat, the silicium is reduced with a slight hissing and 

 a feeble appearance of heat. No gas is disengaged when the 

 salt has been well dried. The mass is left to cool, and then 

 treated as before described. It ought however to be dissolved 



