180 ANNUAL OF SCIENTIFIC DISCOVERY. 



new compounds of silicium which are of the highest importance. The 

 starting-point of them all is a curious, metallic-looking alloy of silicium 

 and calcium, which is easily prepared by fusing together silicium, chlo- 

 ride of calcium, and sodium, with certain precautions. The silicide of 

 calcium is then obtained in a button of a lead gray color and perfect 

 metallic lustre. Iu water, this slowly disintegrates, forming a mass of 

 lustrous scales like graphite, some impurities being extracted from it 

 by this solvent. Strong nitric acid does not attack the silicide, and 

 this acid affords the best means of obtaining it free from impurities. 

 The most remarkable action of the silicide of calcium is its behavior 

 with hydrochloric acid, by which it is changed into an orange-yellow 

 substance, a brisk evolution of hydrogen taking place. This yellow 

 body is called by the discoverer silicon, an inappropriate name ; as the 

 metallic basis of silica, silicium, is often called silicon, and is generally 

 known under that name in chemical books. Silicon is prepared in the 

 following way : The silicide of calcium, purified as above, is treated 

 with concentrated hydrochloric acid. An evolution of hydrogen soon 



v v dJ 



takes place, and the silicide is gradually transformed into silicon. The 

 mixture is then diluted v with six or eight times its volume of water, the 

 silicon filtered off, carefully protected from the light, well washed, and 

 finally dried in a vacuum over sulphuric acid, the bell-glass being cov- 

 ered with a black cloth. Silicon is of a bright orange-yellow color. 

 It is composed of transparent yellow laminae. It is insoluble in water, 

 alcohol, and other solvents ; when heated, it becomes of a dark orange 

 yellow. On applying a stronger heat, it takes fire with a faint defla- 

 gration and some sparkling, leaving a residue of silicic acid. 



"^The behavior of silicon when exposed to the light is very remark- 

 able. In the dark, even when moist, it remains quite unchanged. In 

 diffused light it becomes paler ; but in direct sunlight it, in a short time, 

 becomes perfectly white, and hydrogen is given off. When placed 

 under water in sunlight, hydrogen begins to be evolved immediately, 

 and continues like a fermentation until the silicon has become quite 

 white. The purer the substance, the more quickly does the change 

 take place, and several grammes are transformed in a few hours. If, 

 however, it has not been perfectly protected from the light in the 

 course of preparation, it is much longer before the whole is altered in 

 sunlight. The formula of silicon is not accurately settled ; but it con- 

 tains silicium, hydrogen, and oxygen, and is supposed to resemble an 

 organic body, in which silicium replaces the carbon. Professor Wb'hler, 

 indeed, suggests that it may, perhaps, be the type of an entire series 

 of similar bodies, and it would then open the prospect of a special chem- 

 istry of silicium as of carbon. 



" The behavior of silicon with metallic salts is curious. In the pres- 

 ence of an alkali, even of dilute ammonia, it is gradually changed into 

 silicic acid, with evolution of hydrogen. When mixed with an alkali 

 whilst this decomposition is going forward, it acts as a powerful reduc- 

 ing agent on the salts of the heavy metals. Solutions of copper or sil- 

 ver salts soon become black, and gold solutions brown. A solution of 

 lead in caustic soda is precipitated in the metallic state as a gray mass. 

 The reducing agent, in all these cases, is evidently the hydrogen in a 

 nascent condition. When silicon is thoroughly acted on by light, it is 

 converted into a white body, to which the name Leukon has been 



