FISH PRODUCTS 127 



present in the skin has been replaced by oil. The oiled 

 skins are then piled in a warm place. The oil gradually 

 oxidizes probably owing to some fermentation process 

 and the skins become yellow and very hot. From time 

 to time the skins are strewn on the floor to cool and then 

 re-piled, the process being repeated until the oxidation 

 of the oil is complete. In France the freshly-oiled 

 skins are hung in hot stoves, and the oxidation of the 

 oil is completed in one operation. 



The skins are then dipped in water and passed through 

 hydraulic presses, by which the surplus oil is removed. 

 This surplus thick, oxidized oil is known as " degras " 

 or " moellon," and is used for stuffing leathers that have 

 already been tanned. Stuffed leathers are supple and 

 impervious to water, and are used for harness, belting, 

 etc. A further quantity of oil may be removed from the 

 " chamoised " leather by treating it with potash or 

 carbonate of soda, " sod " oil being recovered from the 

 extract by neutralization with sulphuric acid. The value 

 of sod oil for oiling dressed leather is due to a resinous 

 acid of unknown composition, that is soluble in alkali 

 but insoluble in petroleum ether. 



Enamel or patent leather is generally coated, after 

 tanning, with a linseed oil varnish, boiled with prussian 

 blue, and dried in a steam heated chest at 70 to 80 C C., 

 the process being repeated until a sufficiently thick 

 coat is produced. Fish oils are now used successfully 

 in place of linseed oil. The enamel leather produced, 

 although not quite so glossy as that made with linseed 

 oil, is said to be more pliable. 



Fish oils are also employed in the manufacture of 

 such closely-related, although happily diverse, substances 

 as soap and margarine. All animal and vegetable 

 fats and oils are essentially compounds of glycerine, 

 with one or other of three acids : palmitic, stearic and 



