50 SCIENTIFIC AGRICULTURE. 



sparingly soluble in water, so that in a state of solution, it 

 cannot enter largely into the pores of the roots, even though it 

 be abundantly present in the soil:" it probably exists in all 

 well manured soils; "but the extent to which it really acts as 

 food to living vegetables is entirely unknown." 



NITRIC ACID ITS PROPERTIES AND RELATIONS. 



Nitric acid is a compound of one part nitrogen and five of 

 oxygen: liquid nitric acid, when pure, is colorless, intensely 

 sour and corrosive, heavier than water, and boils at 187 Fah- 

 renheit. If exposed to the air, it gives off white fumes with 

 the disengagement of part of its oxygen, becomes yellow, and 

 is converted into nitrous acid. 



" True nitric acid [says Dr. Kane] has never been isolated ; 

 that substance generally spoken of as nitric acid, is a compound 

 of it with water ; it is a nitrate of water, or, as it is popularly 

 termed, liquid nitric acid, or aquafortis." This acid decom- 

 poses all organic substances rapidly, neutralizes the alkalies, 

 and oxidizes the metals, for which it has a strong affinity. 



This acid is not found in nature in an uncombined state; but 

 it occurs in combination with soda, lime and potash, in the 

 form of nitrates, in many tropical countries. In the West 

 Indies, vast quantities of nitrate of potash (salt petre) are 

 formed by nature : in Chili and Peru, immense beds of nitrate 

 of soda are also found. The origin of these salts is as follows : 

 rain water, particularly that which falls during a thunder 

 shower, contains nitrate of ammonia, when the water comes in 

 contact with the potash, soda and lime of the soil, having a 

 stronger affinity for them than for the ammonia, it unites with 

 them and forms the salts, while the ammonia is again set free 

 and escapes into the air. These salts are soluble in water, and 

 are important agents in promoting the growth of cultivated 

 plants. 



