PKOPERTIES OF THE NITEATES. 171 



Nitrate of lime. Nitrate of magnesia. 



Lime, . . 34' 5 ... magnesia, . 27'6 



Nitric acid, . . 65'5 ... nitric acid, . 72'4 



100 100 



2. Properties of these nitrates. 



a Nitrate of potash, or saltpetre, is colourless and void of 

 smell, but possesses a cooling saline taste. It crystallises in 

 long striated six-sided prisms, which do not alter in the air. It 

 dissolves in about four times its weight of water, at 60 F. 

 Heated below redness, it melts into a colourless liquid: at a 

 higher temperature, it is decomposed, giving off oxygen gas.* 

 Thrown upon red-hot coals or charcoal, it causes a vivid com- 

 bustion or deflagration ; or if it be heated nearly to redness in a 

 crucible, and a piece of charcoal or other organic matter be 

 thrown into it, the latter burns away with a vivid combustion, 

 and the nitrate is changed into carbonate, of potash. This defla- 

 grating property is common to all the nitrates. Saltpetre 

 possesses a considerable antiseptic property, and hence its em- 

 ployment in the curing of meat. 



b Nitrate of soda is also colourless and without smell, and 

 has a cooling saline taste. It differs from saltpetre in crystal- 

 lising in rhomboids like calc spar, instead of long prisms, in 

 attracting moisture and deliquescing in moist air, and in requir- 

 ing only twice its weight of water to dissolve it. When heated, 

 it melts, decomposes, and deflagrates, as the nitrate of potash 

 does. 



c The nitrates of lime and magnesia differ from those of 

 potash and soda in not readily crystallising, in being very 

 deliquescent when exposed to the air, and in being very soluble 

 in water. Like the other nitrates, they melt and deflagrate, 

 and in many localities are naturally formed in the soil. 



3. Functions of these nitrates in the soil and in the plant. 



Of the functions of these nitrates in the soil it is not easy to 

 speak. They may supply oxygen to the organic and mineral 

 matters of the soil, and thus promote their passage to a state of 



* This oxygen is derived from the nitric acid, which consists, in a hundred 

 parts, of 74 of oxygen and 26 of nitrogen. 



