INORGANIC NITROGEN FERTILIZERS 85 



this preliminary heating may be omitted. The liquor then 

 passes down through the still proper, which consists of about 

 six or eight sections, each forming a small still in itself. 

 Steam is passed up through these columns in the opposite 

 direction to that in which the ammonia liquor flows down. 

 By these means some of the ammonia compounds present 

 in the liquor are broken up by the action of steam and 

 heat. Ammonium hydrogen sulphide produces ammonia 

 and hydrogen sulphide, both of which pass away : NH 4 HS 

 ^ NH 3 -f H2S. Ammonium hydrogen carbonate breaks 

 up into ammonia, water and carbon dioxide : NH 4 HCO 3 

 v^ NH 3 -j- H 2 O -f- CO 2 . Ammonium cyanide gives ammonia 

 and prussic acid : NH 4 CN ^ NH 3 -f HCN. All these gases pass 

 away out by the wide exit tube. A considerable amount of 

 fractionation takes place in such a still, so that the ammonia 

 coming out at the top is not admixed with an unreasonable 

 proportion of steam. The ammonia liquor, having lost 

 some of its constituents as described above, passes into a 

 lower section, where it is mixed with lime. Milk of lime 

 is prepared in a separate vessel by blowing in steam, the 

 rough lumps of lime being usually separated by a perforated 

 diaphragm from the rest of the tank : CaO + H 2 O = Ca(OH) 2 . 

 A pump forces the lime and water into the lower part of the 

 main still, where a steam pipe maintains agitation. In this 

 part of the apparatus ammonium chloride and ammonium 

 sulpho-cyanide and other non-volatile compounds of ammonia 

 yield up their acid portion to the lime, so that the ammonia 

 is set free, 



2NH 4 C1 + Ca(OH) 2 = 2NH 3 + CaCl 2 + 2H 2 O 

 2NH 4 CNS + Ca(OH) 2 = 2NH 3 + Ca(CNS) 2 + 2H 2 O 



The limed liquors then pass out through a side tube into 

 a smaller still, where distillation by steam is continued. 

 By these means the ammonia is completely removed 

 from the liquors, and waste lime passes out through the 

 exit. This waste lime is sometimes retained, and can be 

 used in place of the old-fashioned gas lime for application to 

 the soil as a fertilizer. With correct working, little lime is 



