NITROGEN. 175 



and nearly the same weight of sulphuric acid. Nitric acid is evolved and distils 

 over into the receiver, which is to be kept cool during the operation by pouring 

 cold water upon it or by surrounding it with pieces of ice. Examine the 

 properties of nitric acid thus made, and use it for the tests mentioned below. 

 How much pure nitric acid can be obtained from 50 grammes of potassium 

 nitrate? Weigh the acid which you obtain in the experiment and compare 

 this weight with the theoretical quantity. 



Nitric acid is an almost colorless, fuming, corrosive liquid, of 

 a peculiar, somewhat suffocating odor, and a strongly acid 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 1.403 at 25 C., is com- 

 posed 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 absolute nitric acid ; it has a specific gravity of 1.054 at 

 25 C. 



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

 and emits vapors of the same color. Specific gravity 1.45 to 1 50. 



FIG. 40. 



Distillation of nitric acid. 



Nitric acid is completely volatilized by heat ; it stains animal matter 

 distinctly yellow and destroys the tissue ; it is a monobasic acid, form- 

 ing salts called nitrates. These salts are all soluble in water, for 

 which reason nitric acid cannot be precipitated by any reagent. 



