I64 MADRAS FISHERIES BULLETIN VOL. XIII, 



abundant that in late autumn the yield was 48 gallons (351 lb.) per 

 1,000 fish, or above 52 per cent. But it will be seen from the 

 figures that the average yields are very moderate, say 5 per cent, 

 and that while northern fish may average from ^ to 12 per cent 

 (according to years) the warm water fish may average below half 

 that amount. These lessons are important for Madras. 



38. Qualities of oil. — Formerly, and perhaps even still in some 

 small southern factories, the oil was dark in colour and unduly 

 odorous, but modern improvements in catching and manufacturing 

 have brought about very different results. 



The standard grades for crude oil are known as A, B, C, D 

 representing " extra light crude " (A), " light crude " (B), '' brown 

 crude " (C), and " dark brown crude " (D); owing to the improve- 

 ments the bulk is of the A grade. As is well known, crude oil 

 obtained from fish while fresh is usually light and clear, with but 

 slight odour and taste; if the fish has at all decomposed, the oil is 

 darker, odorous, and bad tasted, and turbid from impurities which 

 more easily pass out from the presses than the tougher fresh tissues. 

 The rapidity with which fish are caught by the newer classes of 

 boats and nets, and brought to the factory, and the speed 

 with which the fish are cooked, pressed, and the oil separated from 

 the fish and dirty water, mainly account for these improvements, 

 while the general introduction of steam for all purposes, prevents 

 all the discolouration and odour due to scorched fish or oil. 

 Hence the importance of modern methods, and especially of 

 the use of steam. It may be noted also that fish from the open sea 

 and fat ones give a better coloured oil than those caught in bays 

 or than lean ones. 



39. The crude oil has, however, to be refined either by removal 

 of the stearine (" fish tallow ") and any remaining impurities, or by 

 bleaching, or by both. 



The crude oil contains a considerable percentage of a fairly 

 solid substance like tallow, which is called stearine. Even at 

 ordinary hot weather temperatures, say 80° to 90° F., this is fairly 

 abundant, but as the temperature falls it becomes still more notice- 

 able ; moreover oil freed from stearine by mere decantation at, say, 

 90° F., deposits more stearine as the thermometer falls. Hence to 

 secure an oil which, even in winter, shall remain fluid and limpid, 

 the crude oil is chilled to about 38^ F. either artificially or by 

 waiting till winter, and the mass thus obtained is bagged and 



