NITEOGENOUS MANUEES. 227 



Simon-Carves, Otto and Semet-Solvay ovens, high, narrow, long, 

 carbonizing rapidly and at a high temperature. The furnaces 

 actually in use may be divided into two classes : — 



1. Those which are only a modihcation of the ordinary coke 

 oven, where the heating is effected by the admission of air into the 

 interior, and burning a part of their carbon as fuel (Jameson, Aitken, 

 Luhrmann types). 



2. Those in which air is not admitted into the interior, the heat 

 being applied on the outside by the combustion of the gas which 

 escapes during distillation, and after separation of tar and ammonia. 

 Almost all modern coke ovens belong to this class (Hoffmann Otto, 

 Simon-Carves, Bauer, Hussener, Semet-Solvay, etc., t}^es). Here, 

 in a few words, is the general principle followed iu coke ovens of 

 the present day. All are built, apart from numerous details, in such 

 a manner as to have a hermetically sealed chamber, from which the 

 gas distilled from the coal is aspirated mechanically without admis- 

 sion of air. The gas afterwards passes through condensers, cooled 

 on the outside by air or water, w^here they deposit the greater part 

 of the ammonia and the tar ; the small remaining portions are de- 

 composed in the scrubbers (coke columns). The residual gas is then 

 led to the tuyeres which heat the retorts, and inflamed by means of 

 a current of hot air issuing from the recuperators. After having 

 accomplished this heating, the residual gases pass into the heat 

 recuperators. Certain German coals yield 11 -5 kg. (25-3 lbs.) of 

 sulphate of ammonia. By the Semet-Solvay ovens, as much as 7 to 

 17 kg., say 15 to 37'4 lbs., of sulphate of ammonia per ton of coal 

 distilled are obtained. 



The w^orking of these ovens is regulated by various conditions. 

 The coal introduced into the oven ought, to give a good coke, to be 

 instantaneously submitted to a very high temperature, and the 

 calcination ought to be conducted rapidly and without stoppage. 

 That is w^hy the heat is transmitted by as thin ovens as possible, as 

 in the Semet-Solvay oven. In the Hoffmann Otto oven the gas 

 given off by distillation escapes through two orifices in the arch of 

 the oven and passes into gas reservoirs placed above and across the 

 ovens ; then it is lifted by aspirators, and drawn through pipes to 

 condensers and washers, in which the tar and ammonia is deposited. 

 Freed from these two substances the gas is brought back through 

 another pipe, under the sole of the ovens. The inflamed gas follows 

 alternatively vertical flues, ascending one half of the flues and 

 descending the others. In the Semet-Solvay system the flues in 

 which the gas burns, and which generally are fitted into the main 

 flue, are here independent, and consist of retorts with their encased 

 sides the one in the other, and forming a complete and tight circuit.^ 



1 The Hoffmaun Otto is 10 metres (say 40 feet) long, 0-4 to 0-6 metres (say 

 1(3 to 24 inches) wide, by 1-70 metres (say 5 feet 8 inches) high. The Semet-Solvay 



