OILS. 



draulic arrangement is most effective . 

 (See Press, Hydraulic) The oil is 

 collected as it flows into appropriate 

 casks or vessels. The cake is now 

 boiled, heated by hot water, or press- 

 ed between hot plates in the hydrau- 

 lic press ; by this means more oil is 

 obtained, which, if water be used, 

 rises, after a time, to the surface, and 

 may be skimmed off. Coarse oils, as 

 castor, hemp, cotton, &c., can be 

 heated in an oven, or over flues, or 

 parboiled in the first case ; but olive, 

 almond, and table oils should not be 

 heated, the second drawing being fit 

 only for machinery. The cake or 

 marc is always serviceable as food 

 or manure. Sometimes oils are ob- 

 tained by merely bruising, and then 

 boiling in a great deal of water, the 

 floating produce being taken off by 

 skimming; but this is a very objec- 

 tionable method for table oils. For 

 farther particulars, see the oil plants. 



OILS AS MANURE. Train oil 

 and blubber have been recommended, 

 and much used in composts as ma- 

 nures ; and, from some of the re- 

 sults, many farmers have taken up 

 an idea that oils are great fertilizers. 

 Train oil and other animal oils con- 

 tain impurities rich in nitrogen, and 

 their decay produces a fertilizing ac- 

 tion, but otherwise it is difficult to 

 understand that oils should be, to any 

 extent, manures. The idea is prob- 

 ably erroneous, although of very an- 

 cient date ; but the old writers were 

 altogether in the wrong in calling 

 night soil and such bodies oily 

 compounds ; they do not, therefore, 

 speak of real oils in many of their 

 observations. 



OIL jMILL. This is made in sev- 

 eral ways, but the most common is 

 that called the edge mill, the stones 



I of which are large and heav}% See 



■ Figure. 



532 



