124 



CHEMICAL MANUEES. 



^vho can thus obtain whatever initial temperature he desires. This 

 temperature may be somewhat high without there being any reason 

 to fear retrogradation in the superphosphate treated, for the drying 

 of the latter is so energetic that the temperature of the gas lowers 

 -considerably. Owing to the rotation of the drum and its sloping 

 position the superphosphate circulates to the opposite extremity 

 and is reduced to crumbs, consequently the interior of the granules 

 is laid bare and submitted in its turn to the action of the hot gases. 

 At the end of the drum the superphosphate falls into a "den," from 

 which it is taken to be stored. The hot air which comes from the 

 drum is not saturated with moisture ; it is therefore in great part 

 absorbed by the exhauster, mixed again with combustion gases, 

 w^hich bring it to the desired temperature, and afterwards it is 

 again sent in to the drying machine, to carry on the work of 

 desiccation. In this way the gases having already served, and still 



Fig. 32. — Moller and Pfeift'er's Dryer (vertical section). 



at 85" C. (165° F.) are again utilized, only the small quantity required 

 for rational working of the combustion is allowed to escape into the 

 air, the loss of heat is reduced to the difference between the exterior 

 temperature and that of the escaping gases. However, this circula- 

 tion cannot be indefinite, it is limited, naturally, by the final saturation 

 of the escaping gas. It is then necessary to start once more with 

 -completely renovated air so as to secure regularity in the drying. 

 This drying machine is one of the best, and has received numerous 

 applications. 



Heymann and NitscWs Process for Drying Swperplws'ph cites. — 

 Heymann and Nitsch try to utilize the heat produced by the reaction 

 of fresh superphosphate to vaporize the water brought to the surface 

 of the lumps by crushing. They manage in this way to conduct 

 drying and crushing simultaneously. The superphosphate, at a 

 temperature of . 90° C, is charged into slightly inclined rotary 

 drums, the angle of inclination of which may be regulated at will. 

 It is there crushed and sifted. The fine flour falls from the drum 

 into a pit, and when it is cooled it has acquired the necessary degree 



