52 CHEMICAL FERTILIZERS 



space, the coal practically fills the retort, which is heated 

 from the outside, the heat gradually penetrating to the 

 centre. The gas eventually takes its course to the top of 

 the retort through the comparatively cool central core, 

 whence it immediately enters the ascension pipe at a low 

 temperature, and is drawn off with little direct contact 

 with the highly-heated sides of the retort. An attempt is 

 also made to keep the larger lumps of coal towards the 

 central part, and thus assist the passage of the gas up the 

 cooler regions. The average yield of ammonia from vertical 

 retorts is said to be about 7 Ibs. per ton of coal, whereas 

 from horizontal retorts it is only about 5 Ibs. per ton, but 

 practical experience of both kinds of retorts places the 

 difference at a slightly lower figure. The by-product 

 recovery coke-oven is a large rectangular chamber, which 

 is almost completely filled with coal, leaving only a very 

 small space at the top for the exit of the gas. This coke- 

 oven, therefore, combines some of the features of both the 

 vertical and horizontal gas retorts. The centre of the 

 charge remains at a comparatively low temperature until 

 the end of the distillation. The temperature of the flues 

 used for heating the retort is usually over 1090 C. (2000 F.), 

 whilst that of the gas leaving the oven is little over 540 C. 

 (1000 F.). A small amount of the gas must come into 

 contact with the hot walls and top of the oven, but owing 

 to the large size of the retort this is only a small fraction. 

 As the result of distillation the nitrogen of the coal is dis- 

 tributed in the following manner : with ordinary illuminating 

 gas retorts 12-17 % is in the form of ammonia, 1-2 % 

 is in the form of cyanides, 45-60 % is left in the 

 coke, and from 4-35 % is evolved in tar and gas. The 

 distribution of the nitrogen in the ammonia liquor is 98 % 

 as ammonia, ij % as cyanides, and the rest as sulpho- 

 cyanides and ferro-cyanides. In coke-ovens the distribution 

 of nitrogen is as follows : about 15 % is in the form of 

 ammonia, i \ % is in the form of cyanides, 45 % is left in the 

 coke and 40 % is given off in the tar and gas. If coal is 

 quickly carbonized a much larger proportion of nitrogen is 



