258 M. Berzelius on the Preparation 



place of the potassium in combining with the silicinm. If the 

 hyflrnvetted siliciura is put into an open platinum crucible, and 

 slowly heated until redness commences, and then after being- 

 covered carried to a white-red heat, the silicium loses its com- 

 bustibility ; and treated with fluoric acid, which now dissolves 

 no more of it, becomes perfectly pure, without sustaining the 

 great loss which takes place when we begin by burning it. — 

 When the hydruretted silicium is very quickly brought to a 

 red heat, it takes fire, because the hydrogen cannot burn at a 

 lower temperature without inflaming the silicium at the same 

 time. If the silicium does not burn completely m this case, 

 that circumstance does not arise from the production of an 

 inferior degree of oxidation, but from the access of oxygen 

 being prevented by the silica formed. Besides the loss of hy- 

 drogen which the silicium sustains at an elevated temperature, 

 it undergoes a further change ; it loses the property of dis- 

 solving in fluoric acid, is contracted in bulk, and takes a darker 

 colour. This circumstance has certainly as great an influence 

 in diminishing its combustibility as the loss of its hydrogen. 

 In the state of least condensation in which it is obtained, 

 when just separated from the potassium by means of water, it 

 may be compared, as to its combustibility, to the porous hy- 

 drogenated charcoal of lint, which takes fire by the sparks of 

 a steel, but which loses this property after having been ex- 

 posed to an elevated temperature. The incombustibility of 

 silicium is besides so great, that the small quantity of it which 

 remains on the filters may \)e found by burning them and 

 treating the ashes with fluoric acid. 



Silicium, even when dry, stains and strongly adheres to the 

 glass vessels in which it is kept. When it is treated with 

 fluoric acid, the liquid is covered with a little pellicle, which 

 envelops, as fat oils do, each drop that is taken from it. This 

 pellicle rises on the sides of the vessels so long as they are 

 damp, and then appears, by refraction, of a clearer colour than 

 the silicium which is under the liquid. 



Silicium is a non-conductor of electricity. That which has 

 become incombustible by its exposure to a strong heat does 

 not undergo any change, if, whilst red-hot, chlorate of potash 

 is thrown upon it. It is not attacked by saltpetre until the 

 temperature is raised sufiiciently to decompose the nitric acid, 

 and the affinity of the alkali begins to act ; but at a white heat 

 it is acted upon with great energy by that salt. 



With carbonate of potash, silicium burns very easily with 

 a vivid inflammation ; carbonic oxide is given out, and the re- 

 duced carbon imparts a black colour to the mass. The in- 

 candescence is so much the more intense, and the temperature 



leqnires 



