PROPERTIES OF ELEMENTS OF SOIL. 41 



so changed by heat. The only substance exhibit- 

 ing analogous properties, is the uret, carbon. 



Silicon burns in vapor of sulphur, and forms sul- 

 phuret of silicon. This easily dissolves in water, 

 sulphuretted hydrogen escapes, and silica remains 

 in solution. These are facts of the highest import- 

 ance in agriculture. 



69. Whether heated or not, silicon is oxidated 

 when heated with dry potash, and converted into 

 silicic acid. In its pure state, this is a rough, gritty, 

 tasteless powder. When heated, it runs like red-hot 

 ashes, and the lightest puff blows it away. It is 

 not melted in the strongest heat of a wind furnace. 

 Silicic acid exists in two states — soluble, or insolu- 

 ble in water. It is perfectly insoluble, after having 

 been heated red-hot. Sulphuret of silicon, as has 

 been noticed (68) dissolves in water, and gives sili- 

 ca, in solution. If this is evaporated, a jelly-like, 

 sizy mass is obtained, which may be again dis- 

 solved in water. Acid, added to the solution, when 

 evaporating, renders silica insoluble. Alkalies, boil- 

 ed with insoluble silica, render it soluble — no 

 change occurring in the alkali. These singular 

 changes, are due probably, to a new arrangement of 

 the particles of silica, produced by that power cal- 

 led catalysis, or the action of presence. 

 4* 



