NITRIC ACID. 21)3 



PROCESS FOR NITRIC ACID. 



Before decomposition. Afler decomposition. 



[Nitric acid . 677 ------------- , 789.5 Nitric acid and water. 



1207 Nitrate of potash. 1 



(.Potash . . 590 ' 



f Water . 



613.5 Oil of vitriol. ^ 



[ Sulphuric acid 501 - -^1091 Sulphate of potash i hlsul of 

 613.5 Oil of vitriol. Oil of vitriol . 613.5 613.5 Sulphate of water. / potash. 



2494 2494 2494 



In this operation twice as much sulphuric acid is employed, 

 as is required to neutralize the potash of the nitre, by which 

 means the whole nitric acid is eliminated without loss at a mo- 

 derate temperature, and a residuary salt is left which is easily 

 removed from the retort. 



With half the preceding quantity, or a single equivalent of oil 

 of vitriol, the materials in the retort are apt to undergo a vesi- 

 cular swelling, upon the application of heat, and to pass into 

 the receiver. Abundance of ruddy fumes are also evolved, that 

 are not easily condensed, and prove that the nitric acid is de- 

 composed. The temperature in this process must also be raised 

 inconveniently high towards the end of the operation, in order 

 to decompose the whole nitre. The peculiarities of the decom- 

 position here arise from the formation of bisulphate of potash in 

 the operation, the whole sulphuric acid uniting in the first in- 

 stance with half the potash of the nitre. Now, it is only at an 

 elevated temperature that the acid salt thus formed can decom- 

 pose the remaining nitre ; a temperature which is sufficient to de- 

 compose nitric acid, as may be proved by transmitting the vapour 

 of the concentrated acid through a tube heated to the same degree. 



Properties. The acid prepared by the first process is colour- 

 less or has only a straw yellow tint. If the oil of vitriol has 

 been in its most concentrated condition, which is seldom the 

 case, the nitric acid is in its state of highest concentration also, 

 and contains no more than a single equivalent of water, accord- 

 ing to Mitscherlich. The density of this acid is 1.522 at 58 ; 

 but a slight heat disengages a little peroxide of nitrogen from it, 

 and its density becomes 1.521. It boils at 187, but when dis- 

 tilled, it is partially decomposed by the heat and affords a pro- 

 duct of a strong yellow colour. Its vapour transmitted through 

 a porcelain tube, heated to dull redness, is decomposed in a 

 great measure into oxygen and peroxide of nitrogen ; and into 

 oxygen and nitrogen gases, when the tube is heated to white- 



