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 entirety 
is utilized. To make such a procedure possible, a lower initial "tem- 
perature of the gases would be necessary to preyent 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 driving 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 conseryed would justify. This is a matter which 
could be determined by experimentation. 
In a drier of the aboye 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 machinery conforms most nearly to the ideal equipment. 
Eendering 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 the} T 
can be applied successfully to the rendering of fish, viewed from the 
commercial standpoint, remains to be demonstrated in this country. 
