INDUSTRIAL USES OF PLANTS 393 



elastic films. Those with a high capacity for oxygen are known as 

 drying oils, and are very important as solvents in the paint and 

 varnish industries. The semi-drying oils absorb oxygen much 

 more slowly, and never form as tough and elastic a film as the 

 drying oils. The non-drying oils never undergo oxidation to form 

 a film, hence are of no use in the paint or varnish industries but 

 are very useful in the manufacture of soaps, as lubricants, and as 

 foods. The plant fats and waxes are solid at ordinary tempera- 

 tures, and are likewise used as foods and in the manufacture of 

 soaps and other toilet or medical preparations. 



The list of drying oils has long been headed by linseed oil, 

 derived from the seed of the flax plant. Flax grown for its seed is a 

 shorter, more bushy strain of the same plant that is grown for its 

 fiber, discussed in Chapter 20. The Dakotas and Minnesota pro- 

 duce most of the linseed grown in the United States, which pro- 

 duces only a small amount of the world's total crop. Argentina 

 leads in world production, followed by Russia, India and Uru- 

 guay. Flaxseed yields about one-third of its weight in oil, which 

 is removed by both hot and cold pressing methods. Oil which has 

 been heated to about 65° C, known as boiled linseed oil, dries 

 more rapidly than does raw oil, but the film is supposed to be 

 less durable in the case of boiled oil. About two- thirds of the lin- 

 seed oil used in the United States is consumed by the paint and 

 varnish industries. The remainder is used in the manufacture of 

 linoleum, oilcloth, putty, printers inks, and soaps. 



Tung and ghinawood oils are produced from the nuts of two 

 closely related Chinese trees, the tung-oil and the mu trees of 

 the Spurge Family. The oils are widely used in waterproof 

 varnishes, and have become so important an item of United 

 States imports that cultivation of the trees has been started in 

 Florida and certain other of the Gulf States. The initial plantings 

 have been very successful and highly profitable, and further 

 planting of the tung oil trees is being encouraged in certain 

 localities. The trees will grow on soils unfitted to the production 

 of other crops, but are highly sensitive to frost. In addition to 

 being quick drying when employed in varnishes, these oils yield 



