'30 THE CULTURE OF FARM CROPS. 



rocks excepting those of an organic origin, as coal, which 

 contains 2 or 3 per cent, of it. 



Its name signifies the generator of nitre, because it exists 

 largely in this substance in the form of nitric acid and may 

 be produced from it. It may be produced from air by a very 

 simple and beautiful experiment. A small piece of phos- 

 phorus is placed in a little saucer and floated on water 

 in a dish or trough; the phosporus is set on fire and 

 covered with a bell glass. The combustion of the phos- 

 phorous produces phosphoric acid by its combination with 

 the oxygen of the air, which is all taken up in this way ; 

 this acid is absorbed very quickly by the water and the 

 nitrogen is left. It is then found to be a transparent gas, 

 without color, taste or smell ; which is unable to support 

 combustion or life. A lighted match introduced into the 

 gas is immediately extinguished and a mouse put under the 

 bell glass dies in a short time for want of oxygen. It is not 

 poisonous, but simply has no active properties, being when 

 uncombined wholly inert, and for this reason was formerly 

 -called azote, or "life destroyer." Its purpose in nature, in 

 its free state, seems to be to act as a dilutent of the exceed- 

 ingly active oxygen, and to thus adapt it to the condi- 

 tions of life. 



Water absorbs about U per cent, of its bulk of this gas, 

 ^nd it is not unlikely that plants may procure some of their 

 nitrogen from this source. 



Nitrogen is most interesting when we come to consider 

 its combinations. It combines with oxygen to form five 

 remarkable compounds. The first of these is nitrous oxide, 

 called from its peculiar effects when breathed, laughing gas. 

 This is a colorless transparent gas, of a sweetish taste and 

 soluble in water to the extent of three-fourths of the bulk 

 of the latter. It supports combustion actively, relighting 

 a glowing ember when this is plunged into it and causing 

 an intense combustion of ignited substances almost equal to 

 the effect of oxygen. At a pressure of 750 pounds to the 

 square inch it condenses into a clear liquid which boils on- 

 ly at the great heat of 11 26 degrees, which is considerably 



