COTTON 
287 
OIL IN THE REFINING TANK 
Crude oil when taken from the settling tanks 
may be either shipped direct to refineries, or if, as 
is often the case, a refinery is located in connection 
with the oil mill, it may be refined at once. 
In the refining process oil is heated gently, 
stirred constantly, and treated freely with air which 
enters through a perforated pipe at bottom. Im- 
purities are still present in the crude oil, and these 
are partially gotten rid of through the free use of 
caustic soda or potash; this coagulates them, 
causing them to collect and fall to the bottom of 
the tank. The next step is to draw off the oil and 
make the final preparation for its shipment. Be- 
fore it can go, however, it must be washed with 
water in order that the potash may be dissolved 
and removed. Since oil is lighter than water, 
separation gradually takes place in the mixture and 
the oil slowly rises to the top where it is carefully 
drawn off, at last to be filtered and put into barrels. 
WHAT IS MADE FROM THE OIL 
Refined oil is known as " summer yellow" and of 
course, is of a higher commercial value than the 
crude oil. Prime summer yellow is known as 
butter oil, and is largely used in the manufacture of 
oleomargarine, butterine and even as an adulterant 
for butter itself. 
The highest grade of summer yellow is often 
subjected to cold pressure, which gives a product 
known as salad oil for cooking, dressing, and other 
household products. Then, too, large quantities 
of summer yellow have for a long time found their 
way into Italy where it is treated, to be sent later to 
