74 PHILOSOPHY OF ZOOLOGY. 
tracted from the entire fish, (as the sprat, pilchard, and 
herring, when they occur in too great quantities to be salt- 
ed,) by boiling in water, and skimming off the oil as it ap- 
pears on. the surface. In general, however, the oil is 
obtained from the livers of fish, in which it is lodged in 
cells. As it cannot be procured completely from livers by 
mere boiling, they are allowed to become a little putrid, 
that the oil may be more readily extricated, by the ruptur- 
ing of the cells. But, along with the oil, various impuri- 
ties are likewise obtained, such as bile, and gelatmous mat- 
ter; and as these afterwards putrify, they communicate a 
disagreeable fetid odour to the oil. This fetid smell is 
greatly heightened by the charring of the oil in the bottom 
of the boilers, and the consequent production of the empy- 
reumatic odour. 
Various methods have been recommended in order to free 
train, and fish oils from the impurities with which they are 
contaminated. It is obvious, from the nature of these im- 
purities, that they may be in part be removed, by churning 
the oil along with cold, and afterwards with boiling water. 
But for the complete purification of oil, other metheds, 
more complicated and expensive, have been resorted to. 
“ If it be agitated with a little sulphuric acid, and then 
mixed with water, the oil, when allowed to settle, swims 
on the surface, of a much lighter colour than before; the 
water continues milky, and a curdy matter 1s observed swim- 
ming between the oil and the water *.” 
In the year 1761, Robert Dossie, Esq. communicated 
to the Society for the Encouragement of Arts and Manu- 
factures, various processes for the edulcoration of fish oil, 
and obtained from the Society a bounty of one hundred 
pounds. The account of these methods, which are still 

* TuHomson’s Chemistry, 4th Ed. v. p. 476. 
