30 BULLETIN 150, U. 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 b}^ 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 



