NITROGEN AS AMMONIA 211 



on the other hand not only makes potassium available and 

 neutralizes soil acidity, but it also flocculates heavy soils 

 and puts them in much better physical condition. The 

 reason chemically is analogous to the action of sodium nitrate, 

 except that calcium carbonate is formed instead of sodium 

 carbonate. Moreover, there is an excess of calcium in basic 

 calcium nitrate. This residue of calcium carbonate in the 

 soil has many other benefits which are taken up in detail 

 in Chapter XII. Unfortunately calcium nitrate can not be 

 obtained so readily as sodium nitrate, although when it 

 can be purchased, it is not far from the same price as the 

 latter. 



II. NITROGEN AS AMMONIA 



159. Ammonium Sulphate. — In addition to the nitrate 

 nitrogen mined as nitrate of soda and manufactured as 

 nitrate of lime, there is produced an ammonia nitrogen 

 fertilizer called ammonium sulphate, (XHJoSO-i, which 

 contains about 20 per cent, nitrogen as it appears on the 

 market. Ammonium sulphate is obtained for the most 

 part as a by-product in the destructive distillation of soft 

 coal. Coal contains from 1 to 2 per cent, nitrogen, of which 

 about 15 per cent, is recoverable. In other words, from one 

 ton of coal may be produced about twenty pounds of am- 

 monium sulphate. For years none of this valuable material 

 was saved, and even now not much more than one-third of 

 the amount produced is recovered. 



(a) How Made. — If soft coal is burned in the air all the 

 nitrogen escapes as elemental nitrogen and cannot be re- 

 covered, but if coal is heated in closed retorts, it undergoes 

 destructive distillation whereby coke and combustible gases 

 are formed, the latter containing part of the nitrogen in the 

 form of ammonia. Soft coal is treated in this way in the 

 manufacture of coke, coal gas, or producer gas, and in any 

 one of these processes it is possible to save the ammonia. 

 The coke ovens have been the greatest source of loss, for in 

 the past no attempt was made to save any of the gases, 

 and even now not as many by-product coke ovens are in 

 use as should be, although the coke and steel concerns are 



