30 BULLETIN 150, L T . S. DEPARTMENT OF AGRICULTURE. 
burlap. This makes a shallow receptacle, which is filled to the depth, 
perhaps, of about 3 inches with the material to be pressed. Then the 
loose edges of the burlap are folded over on top of the material so 
that it is entirely covered. On top of this is placed a square, of 
about the same dimensions, of wooden slats, held together by a suit- 
able framework. On the slats is placed a second frame and a second 
square of burlap, which receives in like manner another charge of 
material. This operation is repeated until a stack of batches of 
material held thus in sections of burlap is built up of sufficient height 
to fill the press. Sheet-iron plates may be substituted for the wooden 
slats. 
In charging, the truck which is to support the charge is wheeled 
beneath the cookers or the " slush box." For this purpose a track is 
built from the press to the cookers. The cooked fish, by the manipu- 
lation of cocks and a movable spout, is permitted to flow upon the 
receptacle arranged for it. When the charge has been completed the 
truck with its burden is wheeled into the press. The pressure is 
applied until the maximum power of the press has been reached, or 
until no further amount of water and oil can be removed. 
It is desirable that the material be pressed while still hot, as the 
water expressed contains glue in solution which on cooling tends to 
harden and clog up the filter. 
When removed from the press the solids have been forced into hard 
cakes about an inch in thickness. These are shaken out of their 
burlap envelopes onto the floor, when they are ready for the driers. 
The oil and water expressed from the scrap are permitted to run 
together to receiving vats. On standing and with the aid of heat, 
the oil rises to the surface and the fine sludge which has escaped the 
filter settles out. The oil is drawn off from the surface into a series 
of vats, where it is subjected to successive simple treatments for its 
purification. Suspended solids and occluded liquids are washed from 
it by bubbling steam through it, and occasionally it is " cut " with 
sulphuric acid to effect a clarification. 
The residue pressed from the cooked fish may be saved to recover 
the glue which it contains, or it may be allowed to go to waste. The 
latter practice is the one generally adopted. For the preparation of 
glue it is thoroughly freed from solid matter and is then evaporated 
by steam coils to the desired concentration. 
DRYING. 
Of the several types of driers in use on the Pacific coast, there is 
only one employed in drying fish scrap from cannery waste which 
is at all comparable to the hot-air driers found in common use on the 
Atlantic coast. This is a drier of large size and capacity, the opera- 
tion of which involves the principle of both direct and indirect heat- 
ing. It is a rotary cylinder of iron mounted inside of an inclosing 
