No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 2.^1 



filled with any convenient filtering medium ; one of these was 

 obtained fortheTanur Yard. For details the text-books and trade 

 catalogues must be consulted. 



130. Dehydration. — Oil pressed from fish which themselves con- 

 tain some 75 per cent of water, is boiled and washed with water, 

 and consequently retains an appreciable amount of water however 

 carefully separated in the ordinary way, viz., by settlement. This 

 process is lengthy because the water is suspended in very minute 

 particles throughout the oil, and consequently, though heavier than 

 the oil, finds difficulty is sinking through the viscid fluid. 



Hence oil apparently well separated, will yield a considerable 

 deposit of rather dirty water if kept undisturbed for a few weeks 

 in a tall receptacle; the process is also somewhat imperfect and, 

 in any case, demands a long period, which involves the obvious 

 disadvantages of locking up capital for a long time and of requir- 

 ing large storage, together with the still greater disadvantage 

 that the water (and impurities contained in it) prejudicially acts 

 upon the oil in which it is suspended ; hence acidity and rancidity, 

 while purchasers always discount the water contents by a deduction 

 from price. Moreover, water, even when pure and in very small 

 quantity, prevents oil from complete clearness, since the minute 

 particles reflect the light and cause apparent, but not real, turbidity. 

 Hence for the best oils, especially for edible and medicinal 

 purposes, the oil must be thoroughly dehydrated before storage. 



In paragraphs 119 and 120 supra, modes of drying are detailed, 

 and for the best class of oils, steam drying is strongly advised, the 

 dried oil being passed at once by a pipe from the steam drier 

 direct to the storage receptacle which should be filled full and 

 closed. Complete dehydration is sometimes obtained by the use 

 of calcium chloride, plaster of Paris, or even common salt ; these 

 may be mixed in the form of rough powder with the oil which is 

 then filter pressed, or the oil may be passed (filtered) through a 

 layer of the material. These latter refinements are only needed 

 where absolutely dry oil is required. 



Heating must be cautiously effected, especially where the oil is 

 of high class or for edible purposes ; if effected by the primitive 

 process of open fire heating it is certain to darken considerably 

 and may be badly scorched ; even with steam or in a bath of 

 calcium chloride solution, the heat should be no higher or of longer 

 duration than is necessary since there may otherwise be an 



