PROCESS FOR PURIFYING OILS AND GREASE. 299 
soapy matter, formed in the oil by the alkali, has subsided; 
the supernatant oil may then be run off and passed through 
a filter. It is stated, that oil thus operated upon will not 
tarnish the most delicate brass work, nor will it become 
thick and glutinous upon exposure to the air. The animal 
oil which the patentee prepares for lubricating purposes is 
the oil expressed from lard; and the process of refining this 
oil is exactly similar in all its details to that described above. 
Before explaining his mode of purifying tallow, so as to 
make it fit for lubricating, the patentee remarks that all tal- 
lows are not applicable, those suited to the purpose being 
such as are termed in commerce Y. C, of light yellow co- 
lour, and sweet or good home-rendered tallow. Tallow of 
such description is melted by steam or other heat, and when 
the tallow has become fluid, but before it has become much 
heated beyond its melting point, a strong solution of potash 
or soda, either caustic or in the state of a carbonate, and of 
specific gravity 1.2, or thereabouts, is added, the tallow being 
kept in constant agitation during the introduction of the 
alkali. Upon the first introduction of the alkali solution a 
very thick soapy matter is precipitated; the operation is 
completed when, upon a further addition of the alkali, this 
effect ceases to be produced ; the tallow is then heated to 
about 180° or 200° of temperature, after which it is allowed 
to rest for twenty-four hours or more, according to the quan- 
tity operated upon and the heat of the weather. When it 
is perceived that the tallow in cooling is becoming slightly 
opaque, it is run off into casks, and while cooling must be 
well stirred to prevent it from granulating. 
The process of refining and sweetening American and 
inferior lard is as follows: In using American lard, it is, in 
most cases, too soft and oily; it is, therefore, advisable first 
to extract a portion of the oil, by pressure; the lard is then 
melted by steam or other heat, and a strong solution of pot- 
ash or soda, or carbonate of these alkalies, is added, as be- 
fore, with constant agitation of the lard. It should be ob- 
