No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 203 



oil or fat " (Lewkowitsch). Seeing that fish oils contain when 

 absolutely fresh and properly prepared, practically no fatty acids, 

 the acidity of a fish oil is good evidence as to its proper or impro- 

 per preparation, purification, and storage. 



Acid oils are unfit for use as edible or medicinal oils if the 

 acidity is marked, say, above 5 per cent, owing to the sharpness 

 of their taste, and also to the effect on the mucous membrane, as 

 may be noticed in the usual test, by taste, when an acid oil pro- 

 duces a catching of the throat ; they are equally unsuitable as lubri- 

 cants owing to the action of the acids on metals. It is probable 

 also that acid oils actually contain less glycerine than normal, 

 since the glycerine separated by the decomposition may have been 

 lost in washing the oil. For soap-making acid oils are not unsuit- 

 able since free fatty acids are more easily saponified than neutral 

 oils ; they are said however to have a higher saponification value. 

 Acidity is easily removed, however, with some loss and expense ; 

 see below s.v. " Rcjim'ng.'' 



The varying acidity in the above table is probably due to care- 

 less preparation and storage; being usually prepared in primitive 

 fashion by persons of small knowledge and capital, the oils, as 

 shown elsewhere, rapidly develop acidity ; see especially para- 

 graphs 59, 71, 03, 107, 112, 115, 119, 123, 126. 



95. Uses. — The uses of fish oil have been mentioned in paragraph 

 4 supra, and in the extract in paragraph 93, to which may be added 

 the following extract from the Imperial Institute Bulletin for 

 April — June 1914, pages 259-260. 



" The. use o*" menhaden oil for paint appears to be on the increase in 

 the United States, and according to Toch (Journ, Indust. and Eng. Chem., 

 191 1, 3,627), it is the best fish oil for this purpose, as up to 75 per cent 

 it can be used in admixture with linseed oil, the paint still standing 

 exposure to air well. Its use for painting interiors of bui'dings is not 

 advisable on account of the unpleasant smell. It is also claimed that paint 

 made with menhaden oil is more resistant to heat than linseed oil paint, 

 and is therefore suitable for use on boilers and chimneys. It can also be 

 used in printing ink manufacture, and according to Toch {/oc. cit.) it is more 

 flexible and less liable to crack than linseed oil, so that it can be used for 

 patent leather manufacture, although it produces a peculiar efflorescence 

 when used for this purpose. The most suitable ' drier ' for use with men- 

 haden oil paints is stated to be a tungate drier." 



Tungate driers are salts of lead and manganese prepared with 

 the fatty acids from tung oil. 

 8 



