48 BULLETIN 150, U. S. DEPARTMENT OF AGRICULTURE. 
expenditure for equipment and economy in operation are claimed for 
the process by its exploiters. From a priori considerations there 
appears no reason why the process should not fulfill its promised 
performance, though it does appear a little doubtful whether the oils 
can be liberated sufficiently by maceration and washing without 
bringing the material to such a fine state of subdivision that a great 
deal would be lost in the water drawn off with the oil, or too long 
a time would be required to permit the solids to separate by settling. 
At present, this apparatus has received no trial in the actual commer- 
cial rendering of salmon cuttings, and a positive opinion concerning 
it is not justified. 
A comparison of the reports of analyses of salmon and menhaden 
scrap, respectively, as reported in this paper on page 33, will show 
that the amount of oil remaining in the salmon scrap is much 
higher than that in the menhaden. While this may be due to the 
difference in the respective methods of drying the two (an explana- 
tion further suggested by the lower oil content of the two samples of 
salmon scrap dried in hot-air driers and involving the supposition 
that oils are volatilized in drying), it also may be due to the fact 
that the oils are net so easily recovered from salmon as from men- 
haden. This constitutes an additional reason why some method, if 
feasible, should be adopted whereby a more complete recovery of the 
oil is possible. The limits of the press easily are reached. 
With the abandonment of the press, the adoption of a system in- 
volving the use of an extractive recommends itself. The extraction 
of the oils with gasoline theoretically should be quantitative, and the 
exploiters of processes based on the use of this extractive claim a 
very high efficiency. The method consists of cooking the material to 
be rendered in closed retorts with steam. At the end of the cooking 
the water in the material is evaporated under vacuum. When the 
evaporation is complete, the dry residue is washed thoroughly with 
gasoline, which removes all but about 1 per cent (more accurately, 
1 per cent of the weight of the dry scrap, according to the claims 
znacle for the process) of the oils present. The gasoline extract is 
drawn off from the scrap and distilled. The oil remains as a resid- 
uum, and the evaporated gasoline is condensed and recovered. It 
is reported that there is but a slight loss in gasoline. An additional 
advantage of the method is that all of the nitrogenous constituents 
of the fish are saved, while in the ether methods there is an indefinite 
loss due to the solubility of certain of these in the water drawn off of 
or expressed from the cooked fish and thrown away. A further 
modification of the system, known as the Cobbwell system, is based on 
cooking in oil the material to be rendered, the oil being obtained 
from previous extractions. After cooking, the excess of oil may 
be drawn off, when the remainder is extracted with gasoline. 
