UTILIZATION OF THE FISH WASTE OF THE PACIFIC OCEAN. 29 
COOKING. 
The upright, cylindrical retort is in general use. It is provided 
with openings in top and bottom for charging and discharging, re- 
spectively. If the fish is to be cooked under pressure the opening in 
the top is generally smaller than otherwise, so that it more readily 
may be closed and rendered tight enough to retain the steam at the 
pressure at which it is admitted to the* retort. 
The manner in which the steam is admitted and the length of time 
during which the charge in the retort is subjected to the cooking 
action of the steam vary from plant to plant. In certain instances 
the steam is injected at the bottom and allowed to permeate the mass 
of waste undergoing cooking. When it appears at and issues freely 
from the top the charge is deemed sufficiently cooked. In other cases 
the cooking is continued for 12 hours under a pressure of 20 pounds 
of steam. As each operator regards his methods as the best, it may 
be said that all of the methods give equal satisfaction. 
After cooking, the charge may be allowed to stand to settle, or it 
may be drawn off at once into the presses. If the former procedure is 
observed, much of the oil released in the cooking rises to the surface 
and is drawn off in any suitable manner. In any case the charge is 
admitted to the presses hot. As a result of the cooking the material 
may be thoroughly disintegrated to form a thin soup, or it may be 
broken up into coarse particles. The only essential seems to be the 
disintegration of the heads. 
What is considered a good practice is to run the charge as soon as 
sufficiently cooked from the retorts into a storage vat or " slush box." 
This is provided with steam coils so that the material may be kept 
hot. From this vat the cooked fish is admitted to the presses. This 
system admits of greater elasticity, making the rate of cooking inde- 
pendent of that of pressing. 
PRESSING. 
Presses of the lrydraulic or the " knuckle " type are in general use. 
Owing to the fine state of subdivision of the material to be filtered, 
the part of the press functioning as a filter must have very fine aper- 
tures in order that the separation between liquids and solids may be 
effected. The readiness with which such fine material closes the 
apertures of a filter and retards separation necessitates a very large 
filtering surface for a comparatively small amount of material. 
These conditions are fulfilled in the salmon-waste filter presses by 
the use of a heavy and compactly woven sort of burlap bagging 
("hop cloth"), in which only small portions of the waste are put to 
be pressed. 
The charge for the presses is made up in the following manner : A 
framework of 1-inch strips of wood inclosing a square of about 3 
or 4 feet is placed on a truck and over it is thrown a square of the 
