FUELS AND THEIR UTILIZATION. 49 



This system permitted the lignites to be brought in close contact with hot air 

 or the escaping fire gas, thus avoiding the loss of heat sustained through its 

 expansion in large rooms. It also allowed the regulation of the temperature 

 and removed the danger of an ignition of the coal through the sparks fre- 

 quently contained in the fire gas. 



Ludwig Ramdohr substituted in the succeeding year, very successfully, 

 super-heated steam for the hot air. On account of their expansive force the 

 aqueous vapors penetrate the coal without mechanical aid; they are chemically 

 indifferent to it and do not cause ignition even with a higher temperature. 



It may be mentioned here that if the coal refuse or dust frequently used 

 in the manufacture of briquettes is too poor in bitumen to cement the par- 

 ticles when under the press, various substances have been recommended to 

 supply the deficiency; tar, starch, potato flour, albumen, lime, gypsum, alum, 

 and others The organic compounds are objected to on account of their 

 higher price. The inorganic material increases the amount of ashes. The 

 selection of one or the other has to be governed by the surrounding circum- 

 stances. As stated previously, however, the use of an artificial cement is 

 rarely necessary in the manufacture of briquettes from lignites. A few 

 years later a drying apparatus, then in successful operation, was described, 

 consisting of a large cast iron cylinder with double walls, the chamber be- 

 tween the walls receiving the escaping steam from the engine room through 

 an aperture on one side and emitting the vapors on the other, after passing 

 them around the cylinder. The apparatus was surrounded with a wooden 

 mantle. Between both mantle and cylinder wall air was warmed and con- 

 ducted into two tubes placed on the inner circumference of the cylinder. 

 These tubes consisted of a number of small truncated cones, one over another, 

 so as to leave spaces between them. The hot air, on entering the cylinder 

 through these apertures, passed the coal, to escape through a tube of similar 

 construction in the center of the apparatus. The drying process is contin- 

 uous. The filling is done from above, using lignites which have been warmed 

 by the air escaping from the central tube. The dried lignites fall below upon 

 a revolving table, from which a scraper throws them into the receiving vessels. 



Enough has been said to indicate the direction in which the improvements 

 proceeded, and it is now only necessary to mention the different systems 

 mostly in use to complete this brief review. 



Ovens in which the Drying is Effected through Escaping Fire Gas. — 

 The apparatus consists of circular cast iron plates, generally fifteen in number, 

 each about twelve feet in diameter, and placed one over the other. A revo- 

 lution of a central axis causes a system of scrapers connected with it, two over 

 each plate, to turn the lignites upon them and gradually move them through 

 small openings from the uppermost to the lowest plate, where they are re- 



