54 CHEMICAL FERTILIZERS 



The gas is then passed through a washer, where it is both 

 purified and cooled, and is then generally passed straight 

 into the acid absorber to produce sulphate of ammonia 

 directly. The Mond gas method exceeds all others for 

 efficiency in converting the nitrogen of coal into ammonia. 



The Distillation of Peat. The problem of drying peat 

 has attracted much attention, but the great difficulty in the 

 economic utilization of this material has always been its 

 high percentage of water which amounts on the average to 

 about 90 %. The removal of a portion of this water is 

 comparatively simple, but to reduce the peat to a useful 

 dry commodity is a long and expensive process. Newer 

 processes have shown, however, that it is possible to distil 

 peat which contains about two-thirds of its weight of water, 

 under which circumstances the yield of ammonia is especially 

 high. The Woltereck process claims to produce 30 Ibs. of 

 ammonia per ton of dry peat, or per 3 tons of peat of the 

 degree of wetness which can be used in that plant. 



Gas Lime. After the removal of ammonia in the process 

 of making gas from coal, the gas still contains as impurities 

 hydrogen sulphide, carbon dioxide and carbon disulphide, 

 as well as thiophene and other organic sulphur compounds. 

 When no effort is made to purify the gas beyond removing 

 hydrogen sulphide, the iron oxide method of purification is 

 adopted, but when an effort is made to remove carbon 

 disulphide and carbon dioxide, the gas is passed through 

 purifiers, consisting of large cast-iron boxes containing 

 layers or wooden grids, on which is placed slaked lime. 

 These boxes are made gas-tight either by a rubber joint or 

 a water lute. As a rule, there are at least three or four 

 boxes, and when the gas enters the first, the carbon dioxide 

 and hydrogen sulphide are quickly absorbed, and then the 

 carbon disulphide combines with the calcium sulphide first 

 produced, forming calcium thio-carbonate. These reactions 

 are explained in the equations 



(1) Ca(OH) 2 + CO 2 = CaCO 3 -f H 2 O 



(2) Ca(OH) 2 + H 2 S = CaS+2H 2 



(3) CaS + CS 2 = CaCS 3 . 



