GREASE.
Grease varies so greatly in composition and consistency that it can hardly be classed as a distinctive oil or fat. It is obtained from refuse, bones, hides, etc., and while it contains the same constituents as tallow, the olein content is considerably greater, which causes it to be more liquid in composition. Grease differs in color from an off-white to a dark brown. The better qualities are employed in the manufacture of laundry and chip soap, while the poorer qualities are only fit for the cheapest of soaps used in scrubbing floors and such purposes. There is usually found in grease a considerable amount of gluey matter, lime and water. The percentage of free fatty acid is generally high.
The darker grades of grease are bleached before being used. This is done by adding a small quantity of sodium nitrate to the melted grease and agitating, then removing the excess saltpeter by decomposing with sulphuric acid. A better method of refining, however, is by distillation. The chrome bleach is also applicable.