90 



NON-METALS AND THEIR COMBINATIONS. 



reaction. When exposed to sunlight it assumes a yellow or yellowish- 

 red color in consequence of its decomposition into nitrogen tetroxide, 

 water, and oxygen. 



Common nitric acid, of a specific gravity 1.414, is composed of 68 

 per cent, of HNO 3 and 32 per cent, of water. The diluted nitric acid 

 of the U. S. P. is made by mixing ten parts by weight of the common 

 acid with fifty-eight parts of water, and contains 10 per cent, of abso- 

 lute nitric acid; it has a specific gravity of 1.057. 



Fuming nitric acid has a brown-red color, due to nitrogen tetroxide, 

 and emits vapors of the same color. Specific gravity 1.45 to 1.50. 



FIG. 9. 



Distillation of nitric acid. 



Mtric acid is completely volatilized by heat; it stains animal 

 matter distinctly yellow ; it is a monobasic acid forming salts called 

 nitrates. These salts are all soluble in water, for which reason nitric 

 acid cannot be precipitated by any reagent. Nitric acid is a strong 

 oxidizing agent ; this means that it is capable of giving off part of 

 its oxygen to substances having affinity for it. 



The action of nitric acid upon such metals as copper, silver, and many others 

 involves two changes, viz. : displacement of the hydrogen of the acid by the 

 metal : 



Cu + 2HM) 3 = Cu(N0 3 ) 2 + 2H ; 



and the deoxidation of another portion of nitric acid by the liberated hydrogen 

 while yet in the nascent state. Thus : 



HNO 3 + 3H = 2H 2 O + NO. 



The liberated nitrogen dioxide, which is colorless, readily absorbs oxygen 

 from the air, forming red vapors of nitrogen tetroxide. 



