62. NITKIC ACID. 80 



tube, particularly if it is held over white paper and looked 

 through lengthwise. 



If a nitrate is mixed in a test-tube with strong sul- 

 phuric acid and the mixture is allowed to cool, and a con- 

 centrated sohition of ammonio-ferrous sulphate is then 

 poured slowly down the sides of the tube so as to float 

 on the surface of the liquid in it, a colored ring is formed, 

 the tint of which may range from a rose color to a dark 

 brown, according as little or much nitric acid is present. 



If a solution of a nitrate is poured into a test-tube con- 

 taining 2-3 grms. of a mixture of clean iron filings and 

 granulated zinc, or of sodium amalgam, and 5-6 c.c. of a 

 strong solution of potash or soda are added, and the mix- 

 ture is heated to boiling, ammonia is set free ; its presence 

 in the tube may be detected by moistened turmeric-paper, 

 or by holding in the tube 'a drop of Nessler's solution, 

 suspended on the end of a glass rod ; this solution will be 

 colored reddish-brown. 



A delicate test for nitric acid in rain-water consists in 

 acidifying 100 c.c. of the water with 2 or 3 drops of con- 

 centrated sulj)lmric acid, adding 2 or 3 pieces of pure 

 zinc, and, immediately, a freshly prepared mixture of 

 potassic iodide with a little boiled starch paste ; the pres- 

 ence of nitric acid is indicated by a blue color. The re- 

 agents used should be tested by mixing them together 

 without the water. 



If the water contained nitrous acid^ it will give a blue 

 color with potassic iodide and starch paste alone. 



Quantitatiye estimation. — a. Of the numerous meth- 

 ods of determining nitric acid, that of Schlossing has 

 proved the most satisfactory in all cases, Friihling and 

 Grouven have simplified Schlossing's apparatus somewhat. 

 {Die landwirthsrJiaftlichoi Versuchs-8tationen^ 9, 13.) 



The dissolved nitrate is introduced into the flask A, of 

 about 400 c.c. capacity, whose mouth can be perfectly 

 closed by a rubber cork, through winch passes a glass 



