FUEL BY-PRODUCTS 51 



When the temperature of distillation is low, the gas 

 given off is poor in hydrogen, but rich in hydrocarbons of 

 high illuminating power. As coking proceeds, the ovens 

 become hotter, the gas loses illuminating power, the per- 

 centage of hydrogen steadily increases, whilst the hydro- 

 carbons decrease in proportion. As the process of coking 

 continues, the ammonia produced in unit time decreases in 

 amount, until 24-39 hours after starting, when it is prac- 

 tically nil. The temperature steadily rises towards the 

 end of the process. Ammonia decomposes on heating, so 

 that if ammonia gas is passed through a tube filled with 

 broken porcelain, at 600 C. (1112 F.), 34 % of the ammonia 

 is decomposed with a slow flow of gas, and 21 % with a 

 rapid flow, whilst at 780 C. (1436 F.) the decomposition 

 is complete. It is necessary, therefore, that the temperature 

 of the top of the oven should be kept as low as possible. 

 As the oven is heated from the side, and charged from the 

 top, this state of affairs is at least approximated to. De- 

 composition of ammonia may also take place owing to inter- 

 action with red-hot carbon, with the ultimate production of 

 ammonium cyanide. By estimating the quantity of cyanide 

 in the liquors, the amount of hydrocyanic acid produced 

 per 100 parts of ammonia is found to be under 2 parts at 

 about 540 C. (1000 F.), and about 2| parts at 560 C. 

 (1200 F.). In the horizontal gas retort there is a compara- 

 tively small retort, heated all round by the flue gases. The 

 coal is charged into this red-hot retort, lies in a thin layer 

 at the bottom, and cools the retort. As distillation pro- 

 ceeds, the temperature of the retort rises, and the gases come 

 into contact with the hot sides and top of the retort. That 

 decomposition undoubtedly takes place is proved by the 

 thick deposits of carbon on the roof of the retort. Towards 

 the end of distillation the charge becomes very hot, further 

 decomposition takes place, and no ammonia is produced. 



The use of the vertical gas retort has enabled the gas 

 industry to overcome some of these difficulties. With this 

 type of retort there is an upright cylinder, and the coal is 

 charged from the top. Instead of having a large free 



