cmd Proper ties of Silicium. 257 



acid. Its colour, however, was mucli tlie same as before com- 

 bustion. But this circumstance will no longer appear asto- 

 nishing, if we suppose, either that the silicium may take in its 

 combustion a lower degree of oxidation, or that, as happens 

 with boron, the silica which is formed prevents the entire com- 

 bustion of the silicium. The residuum of the combustion, 

 treated by fluoric acid, gave silicated fluoric gas, and its co- 

 lour became much darker. Thrown on a filter, well washed 

 and dried, it was pure silicium. 



Description of Silicium, and of its Chemical Relations "with other 

 Bodies. 



Obtained in the manner just related, silicium is of a dark 

 nut-brown colour, without the least metallic lustre. When 

 rubbed with steel it does not give any bright streak, and re- 

 sists the friction as an earthy body does. It is incombustible 

 in atmospheric air and in oxygen ; it does not undergo any 

 change in the flame of the blowpipe, and appears to belong to 

 the class of the most infusible bodies. These properties seem 

 opposed to what I have already said of the combustion of sili- 

 cium, which is easily accomplished when we employ that sub- 

 stance as obtained immediately after its reduction by potassium. 

 This difference in its combustibility is extremely remarkable. 

 It does not depend on an effect attributable to the fluoric acid ; 

 for, if before burning the silicium it is treated with fluoric acid, 

 a portion of silica will be extracted from it, which had been sepa- 

 rated from the fluoric acid by the potash produced by the oxida- 

 tion of the potassium by the air, before the experiment could 

 be made ; and the acid dissolves besides, especially by means of 

 heat, a portion of silicium, with evolution of hydrogen gas. 

 The silicium which then remains after filtering and washing- 

 inflames and burns with vivacity in air and in oxygen. Nor 

 can this combustibility result from a residuum of potassium ; 

 for after combustion neither fluoric acid nor fluate of silica 

 and potash can be extracted from the product : it appears to 

 me to be owing more probably to a portion of hydrogen com- 

 bined with the silicium ; for, if the silicium be burnt in oxy- 

 gen, even after having been lieated in hydrogen or in a va- 

 cuum, water will be formed, but in very small quantity rela- 

 tively to the great capacity of saturation of the silica. The 

 silicium which is obtained when the brown mass procured 

 with potassium is thrown into water is, after that, a hydrurct of 

 silicium or a siliciurct <f hxjdrogen : the reduced mass is a sili- 

 ciurel of ]>otassium^w\\\c\\ the water decomposes; the potassium 

 is converted into potash and dissolved ; the greater part of 

 the hydrogen is disengaged, and the smaller part takes the 



\i>\.r,r>. y,o.:\'2\. April \H2ry. Kk place 



