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OILS 



and again the difference is shown in the fact of some oils drying completely, while 

 others only thicken and become rancid. 

 The following is a list of the Non-drying Oils and their specific gravity : 



The non-drying oils are used as food, for illuminating purposes, and for the greas- 

 ing of machinery, &c. 



The following is a list of the Drying Oils : 



The drying oils are used principally for varnishes and for painters' colours. As 

 the quicker they dry the more valuable they are for these purposes, it is desirable 

 still to increase their natural siccative properties as much as possible, and this is 

 generally effected by boiling the oils with litharge (oxide of lead), by which a certain 

 portion of the litharge is dissolved by the oil ; but in what way this process tends to 

 increase the siccative properties of the oil is not understood. Chevreul stated that 

 it is not necessary to boil the oils, that a much lower heat acts quite as well. Liebig 



