42 BULLETIN 150, U. S. DEPARTMENT OF AGRICULTURE. 



coolest and wettest material. In this way the maximum moisture- 

 absorbing capacity of the gases is made use of and their heat entirely 

 is utilized. To make such a procedure possible, a lower initial tem- 

 perature of the gases would be necessary to prevent the ignition of the 

 hot, dry material ; and it is probable that a longer drier and a more 

 prolonged intermixture of the material and the driying agent would 

 be necessary. A point might be reached where the energy necessary 

 to rotate the drier for the increased length of time" would cost more 

 than the heat units conserved would justify. This is a matter which 

 could be determined by experimentation. 



In a drier of the above type use is made both of the heat units and 

 of the drying action of a current of gas. The matter is entirely dif- 

 ferent from the evaporation of water in a closed vessel, where the 

 evaporation of each unit weight or volume of water is accompanied 

 by the absorption of a definite amount of heat. To be sure, all 

 evaporation is so accompanied. But it is remembered that water is 

 evaporated by a current of air without the application of artificial 

 heat. And, too, the hotter and drier the stream of air the more rapid 

 the evaporation. In the hot-air drier this combined action is made 

 of use. 



The fish-fertilizer industry as developed on the Atlantic coast has 

 found the above-described continuous and automatic apparatus the 

 most satisfactory for meeting the demands of that industry. On the 

 basis of that verdict one is inclined to believe that this machinery 

 most advantageously could be applied to the large-scale rendering of 

 salmon-cannery waste, provided the proper modifications were intro- 

 duced to make it entirely adapted to that sort of material. We do 

 not regard the past failures of this machinery as significant of any 

 fundamental unfitness, but rather of a lack of attention given the re- 

 quirements of the new material to which it is applied. In the present 

 stage of knowledge of the subject it appears that the continuous- 

 process machineiy conforms most nearly to the ideal equipment. 



Benclering apparatus of various other forms are to be had. Many 

 of these forms have been applied with success to the rendering of 

 garbage and tankage. Some are designed with a view especially to 

 the suppression of all disagreeable odors, others to the recovery of a 

 larger percentage of the oils present. The latter usually involve the 

 use of petrol or gasoline as the extracting agent, which effects a 

 more complete recovery of the oils. This may obviate the necessity 

 both of a press and a drier, the cooking, drying, and extracting being- 

 accomplished in one container, the retort. Theoretically, such proc- 

 esses for the recovery of oil are most nearly ideal. Whether they 

 can be applied successfully to the rendering of fish, viewed from the 

 commercial standpoint, remains to be demonstrated in this country. 



