LIME COMPOUNDS. 113 



a solvent action upon silica, decomposing combinations of 

 it with potash, and soda, and forming silicates qf these sub- 

 stances which are soluble ; thus forming a most important 

 addition to the plant food in the soil. It gradually absorbs 1 , 

 carbonic acid from the air, and from any decomposing or- 

 ganic matter brought into contact with it, and thus slowly 

 returns to its condition of a carbonate of lime, in which it 

 is inert, excepting when it is dissolved in water. Its many 

 valuable properties will be more fully detailed in the chap- 

 ter on manures. 



CHLORIDE OF CALCIUM, is the well known chloride of" 

 lime, of daily use as a disinfectant. It has no important 

 relation to plant growth although it has a most useful effect 

 in various ways in purifying the air about farm build- 

 ings, manure yards and drains. 



SULPHATE OF LIME or gypsum, is an exceedingly val- 

 uable compound of lime and deserves special study. It is 

 composed of 32 parts of lime, 46 of sulphuric acid, and 

 21 of water; the water existing as water of crystallization 

 which is driven off when the gypsum is exposed to a heat of 

 300 degrees. This substance is a translucent, yellowish or 

 white, soft, rock ; which is easily ground into a fine powder. 

 It is inert and exercises no action upon other substances, 

 but is easily decomposed when its constituents enter into- 

 other combinations, as will be hereafter described. It is a. 

 most valuable fertilizer, supplying the crops with sulphuric 

 acid and lime, and enters in its combined form into some 

 plants. It is soluble in 400 times its bulk of water. It is 

 largely and beneficially used as an absorbent of ammonia 

 in stables and manure heaps ; exercising this action by the 

 ease with which it parts with its sulphuric acid ; giving this 

 up to the ammonia, from which it takes in exchange car- 

 bonic acid ; thus forming carbonate of lime and sulphate of 

 ammonia. 



NITRATE OF LIME, is little heard of in agricultural lit- 

 erature and yet it undoubtedly has a most interesting rela- 

 tion to plant growth. The production of nitric acid, arti- 

 ficially, in the so called "niter beds," has been already 



