AGRICULTURAL ANALYSIS 



granite and provisionally stored therein. From the towers in 

 which the water and gases coming from the oxidation towers 

 are circulated in an inverse direction, there is obtained the 

 greatest part of the nitrate product transferred into monohydrate 

 nitric acid and dissolved in water. It is, however, very import- 

 ant not to permit the loss of the nitric products which have es- 

 caped absorption in the system of towers and are found in nota- 

 ble quantities in the gases escaping from the last one of the ves- 

 sels. In order to collect these gases an energetic absorbent is 

 used, namely, milk of lime. For this purpose there is a fifth tower 

 of wood of the same dimensions as the first four, and this is filled 

 with bricks disposed in layers and over which circulates, method- 

 ically distributed, the milk of lime. The nitrous and nitric gases 

 are retained by the lime and produce a mixture of nitrite and 

 nitrate of lime. This mixture is afterwards broken up by the 

 aid of nitric acid into the nitrate of lime and gaseous nitrous oxid, 

 which is reintroduced into the absorbent system in the manner 

 which has already been described. This breaking up of the com- 

 pound by means of nitric acid is expressed by the following equa- 

 tion : ( CaNCX ) 2 +HNO 3 = ( CaNO 3 ) 2 +H 2 O-f NO 2 +NO. 



Finally, in order to complete the operation and retain the rest 

 of the nitric gases which still escape from the milk of lime vessel, 

 these gases are made to traverse another vessel somewhat 

 smaller in dimension than the other and containing quicklime. 

 It is only in escaping from this last vessel that the gases which 

 have traversed the whole system of oxidation since their entry 

 into the electric furnace are allowed to escape into the atmos- 

 phere. The operations which have just been described permit 

 the final transformation into pure nitric acid of 50 per cent, 

 strength, of at least 95 per cent, of the oxid of nitrogen produced 

 in the electric furnace, a remarkable result for an industrial opera- 

 tion. 



276. Manufacture of Nitrate of Lime. The solution of pure 

 nitrate of lime, coming from the decomposition of mixtures of 

 nitrates and nitrites described above, is conducted, together with 

 the pure nitric acid of 50 per cent, strength, into a row of open 

 vessels of granite containing pieces of carbonate of lime of from 



