12 DEPAPARTMENT OF AGRICULTURE GEORGIA. [298] 



So great is the absorption and solvent power of water, 

 that it is never found chemically pure in nature. It is 

 obtained pure only by distillation, or the condensation of 

 watery vapor or steam in closed vessels. 



Rain-water is next in purity to that obtained by distilla- 

 tion. It contains no solid matter in solution, but absorbs, 

 during its fall, gases from the air. 



Well and spring-water contains not only absorbed gases, 

 but mineral matter dissolved during its percolation through 

 the earth. Lime, iron, sulphur, soda, magnesia, and other 

 minerals, are thus dissolved, frequently in such quantities 

 as to give taste, character, and even name, to the water. 



The medicinal properties of the waters of springs are due 

 to the mineral matters held in solution, and gaseous sub- 

 stances absorbed by them during their passage over mineral 

 deposits in the earth. 



The saltness of the water of the ocean, and lakes without 

 outlets, is due to the evaporation of the water, leaving the 

 salt in strong solution. 



Nitrogen is a gas which constitutes about four-fifths of 

 the air. It is colorless, tasteless, inodorous, and will nei- 

 ther support combustion nor respiration. Its chief use in 

 the air seems to be to dilute the oxygen, with which it 

 forms no chemical combination, but only a mechanical 

 mixture. It enters largely into the composition of animal 

 tissue, constituting what is known as " nitrogenous matter." 

 Chemically combined with hydrogen, it forms ammonia, 

 and with oxygen, nitric acid, both of which are valuable* 

 fertilizers. 



Salts resulting from the chemical combination of nitric 

 acid with bases are called nitrates. Wkh sodalt forms ni- 

 trate of soda ; with potash, nitrate of potash, both of which 

 are used as fertilizers. 



Though nitrogen is a necessary constituent of all plants, 

 and though it exists in such large quantities in the air, it is 

 never absorbed by plants from the air, or appropriated by 



