PROPERTIES OF NITROGEN. 31 



above the melting point of lead, and freezes at 150 degrees 

 below zero. The second is nitric oxide, which, although it 

 -contains a larger quantity of oxygen than the preceeding, 

 yet is averse to combustion and extinguishes flame. Nitrous 

 .acid is a gas, orange red in color, and is soluble in water to 

 a large extent ; by the absorption of oxygen it becomes ni- 

 tric acid. This acid is of surpassing interest to the farmer 

 because it is a form in which nitrogen enters into the 

 substance of plants and without which, in sufficient quanti- 

 ty, farm crops cannot be produced profitably. 



Nitric acid is a colorless liquid with an intensely sour 

 taste, and when combined with potash, forms the well 

 known substance, saltpeter or nitre. It exists thus com- 

 bined in large deposits in South America, and is found in 

 small quantities in large caves in the United States. In 

 combination with soda, as nitrate of soda, or Chili saltpeter, 

 it is found in very extensive beds in Peru, Chili and Boli- 

 via and other places along the Pacific coast of South 

 America. This substance is very largely used as a ferti- 

 lizer, for which purpose it is exceedingly valuable. 



Nitric acid is composed of nitrogen and oxygen combined 

 and is an exceedingly active substance. On account of the 

 large quantity of oxygen in this acid it possesses very active 

 properties and is one of the most effective oxidizing agents 

 known. It stains animal substances yellow and is thus 

 used as a yellow dye. It corrodes metals very quickly and 

 is used by engravers for "biting" in the etchings upon cop- 

 per plates ; it ignites oil of turpentine and powdered char- 

 coal, and causes such rapid oxidation of phosphorous as to 

 produce explosion. 



Another most important compound of nitrogen is that 

 with hydrogen, which is known as ammonia. This is a gas 

 of a most pungent odor and acrid caustic taste, and has 

 strongly alkaline properties. It is rapidly absorbed by 

 water, which takes up more than 700 times its bulk of it, 

 and then forms the water of ammonia or aqua ammonie of 

 the druggist. It is produced by the distillation of horn, 

 and as it was first made from deers horns, it was called 



