PAINTS 183 



Non-drying oils are cheaper than drying oils because they 

 are more abundant. The important non-drying oils are 

 palm, coconut, and Japan oils obtained from plants ; black fish 

 oil, porpoise oil, and whale oil obtained from the blubber of 

 black fish, porpoises, and whales ; cod-liver oil obtained from 

 the liver of the codfish ; and neat's-foot oil made by boiling the 

 feet and bones of cattle in water. Vaseline and lubricating oils 

 are mineral oils obtained from the distillation of crude petroleum. 



The most important drying oils are linseed, hemp, and poppy 

 oils extracted by pressure from the seeds of the flax, hemp, and 

 poppy plants. Oils from corn, cotton, and rape seeds dry out 

 very slowly, but they are not really satisfactory as drying oils. 

 Linseed oil is the most desirable of the drying oils and about 

 thirty-five million gallons of it are used annually in the United 

 States. 



Paints. Paint is a mixture of linseed oil and white lead, or 

 of linseed oil and some other metallic compound. White lead 

 is a heavy white powder which mixes readily with linseed oil, 

 and is then easily spread over a surface, giving a white coating. 

 White lead spreads well and is durable, but it is extremely 

 poisonous and demands constant care on the part of the painter. 

 Frequently painters are made ill by careless handling of white 

 lead paints. Another objection to white lead is its tendency 

 to blacken in the presence of sulphurous gases. 



When paint is spread on a surface in a thin coat, the lin- 

 seed oil rapidly absorbs oxygen from the air, hardens, and 

 forms a tough film with the lead. A thick coating does not dry 

 quickly and tends to peel off; for this reason it is better to give 

 a surface several thin coatings of paint rather than a single 

 heavy one. Zinc white, or zinc oxide, is sometimes substituted 

 for lead, but it requires more oil for mixing and spreading, 

 and since linseed oil is expensive, zinc white is less in demand 

 than white lead. 



