INDUSTRIAL USES OF PLANTS 399 



or cellulose acetate rayon, is prepared by spinning out the dis- 

 solved cellulose in warm air, which evaporates the solvents, 

 chiefly acetone, and allows the fine thread of cellulose to harden. 



The oldest process of rayon manufacture, which is little used 

 now, is the cellulose nitrate process, commonly called the nitro- 

 cellulose process. This utilizes cotton linters dissolved in nitric 

 and sulphuric acids to yield pyroxylin, which is then dissolved 

 in a highly volatile solvent such as ether, alcohol, or acetone, and 

 spun into the air, where it coagulates. The resulting fibers are 

 further treated to reduce their inflammability, since they have 

 undergone part of the same treatment applied to produce gun- 

 cotton, a high explosive. 



Rayon fibers take dyes more readily than do natural fibers, 

 although their strength is not as great. Artificial fabrics tend to 

 absorb more moisture, with a greater resultant weakening, than 

 do fabrics of natural fibers. To overcome this a combination of 

 natural and artificial fibers is often used. The use of such syn- 

 thetic fibers is increasing, with continued research and im- 

 provement in their nature and production. 



Cellulose nitrate products, of which the rayon mentioned 

 above is one, diff'er according to the strength of the nitric acid 

 employed, and the temperature and length of time that the 

 cellulose is subjected to this nitration. Pyroxylin is one of the 

 lower nitrates of cellulose, and is exceedingly important in 

 industry. It is the very foundation of modern photography since 

 all photographic film formerly consisted of a thin sheet of 

 pyroxylin with a sensitive gelatin coating or emulsion. Pyroxylin 

 is soluble in a variety of solvents, and can be finished into 

 products such as celluloid, pyralin, and other plastics with the 

 use of camphor; artificial fabrics, leather substitutes, and quick 

 drying varnishes and paints. Guncotton, a high explosive, is 

 produced as the result of high nitration of cellulose, and is used 

 as a constituent of many high explosives. Smokeless powder is a 

 mixture of guncotton with the lower nitrates; cordite, one of the 

 high explosives, is a mixture of guncotton and nitroglycerin. 



Cellulose acetate products also have many important uses, 

 such as in safety film which is much less inflammable than the 

 older nitrate films, varnishes, artificial glass, and artificial fabrics. 



