PRODUCTION AND CONSERVATION OF FATS AND OILS. 41 
REFUSE FATS AND TRADE WASTES. 
Several important potential sources of recoverable fats and oils 
are still largely overlooked in this country. One of the most prom- 
ising of these is city garbage. Some idea of the total amount of 
grease that might be recovered from our domestic wastes may be 
gained from the actual yield of 4,000,000 pounds from the reduc- 
tion plant operated by the city of Chicago. Armour & Co. con- 
tracted to buy this quantity of grease from the city at a price of 
11.57 cents a pound in 1918, and the Emery Candle Co. pays 
13.5 cents for a similar grease obtained from Washington garbage. 
It has been stated by Mr. Bammann, of the United States Food 
Administration, an authority on the subject of garbage disposal, 
that 30,000 ; 000 pounds, over $3,000,000 worth of grease, which 
could be converted into 4,400,000 pounds of nitroglycerin and 
almost 40,000,000 12-ounce cakes of soap, goes to waste in 24 of our 
larger cities alone. If this garbage from a combined population of 
5,000,000 were properly utilized, we would get in addition to the 
grease 60,000 tons of fertilizer, sufficient to grow a 3,000,000-bushel 
wheat crop. 
It is reported on good authority that in one year the British Army 
collected from its camp kitchens wastes that yielded 1,800 tons of 
glycerin, which is equivalent to at least 40,000,000 pounds of fat. 
We are told that in Germany systematic efforts have been made 
not only to save garbage grease, but also to recover the fatty matter 
from sewage. A comparatively small . plant for the recovery of 
sewage grease has been in operation for some time on one of Boston's 
outfall sewers. As a result of these experiments, Dr. Sedgwick, 
of the Massachusetts Institute of Technology, who has been in charge 
of the plant, states that 25,780,000 tons of recoverable grease go to 
waste each year in the sewage of 97 American cities. Average 
sewage contains about 430 pounds of recoverable grease in each 
million gallons. 
More concentrated forms of fatty wastes are derived from fish 
canning and packing plants, wool scouring establishments, tan- 
neries, and similar manufacturing plants. Man}^ of these wastes, 
already looked upon as a source of valuable by-products, are recov- 
ered, purified, and marketed. In a great number of the smaller 
plants, however, especially in the fish and canning industries, the 
aggregate loss of oils is still very large. 
METHODS FOR RECOVERING REFUSE FATS. 
The garbage and similar refuse fats are recovered either by using 
a volatile solvent extraction or by the pressure cooking process. 
The raw materials from which they are obtained are neither rich 
enough in fat nor do they as a rule contain a sufficient amount of 
