666 CREATIVE CHEMISTRY duce a material harder than wood, but just as easily worked, nearly oilproof, and having good electrical insulating properties. Lumber may now be treated with the appropriate chemicals to prevent dry Fig. 287. Removing an oak board from the urea tank. (Courtesy of the U. S. Forest Products Laboratory.) Fig. 288. Taking an oak board, previously soaked in urea, from the drying oven in plasticizing experiments. (Courtesy of the U. S. Forest Products Laboratory.) rot, infestation by termites, or shrinking and swelling in dry and damp weather, respectively. Wood can be made plastic by soaking it in a concentrated solution of urea, drying, and then heating it to the boiling-point of water, at which temperature it can be When cooled, the readily shaped. wood retains its shape and resists further action of moisture. Sawdust and chips can be treated in this way and then pressed in molds when hot, forming products practically as strong as wood. 2. Cellulose Dissolved and Reprecipitated. Rayon, once called artificial silk, but really a new type of fiber entirely unrelated and in many ways superior to silk, is produced by dissolving cellulose in the proper solvent and then forcing the solution through small openings into a solution that precipitates the cellulose again in the form of fine threads. There are four different processes involved in the manufacture of rayon. Over 80 per cent of the rayon is now produced by the viscose process, in which cellulose is transformed into cellulose xanthate by the action of caustic soda and carbon disulfide. The cellulose xanthate is then dissolved in caustic soda solution. The properties of rayon depend upon the nature of the manufacturing process. Rayon used in the cord fabric of tires has a high strength and durability at elevated temperatures. For dress fabrics a sheen higher than that of silk or the dullness of chalk may be achieved.
"BETTER THINGS" FROM CELLULOSE 667 Filaments finer than silk make possible very soft fabrics. Rayon cut into small lengths and the new irregular thick and thin yarns have created entirely new textures in fabrics. Transparent velvet, dull satins, and textiles rivaling in beauty the finest cashmere are all made from rayon. Fig. 289. Wood may be twisted or bent after urea treatment. (Courtesy of the U. S. Forest Products Laboratory.) The cellulose in viscose, as the thick yellow cellulose solution is called, may also be regenerated in the form of transparent sheets, one well-known type of which is "cellophane," cellulosic film. Ribbons, straws, and sausage casings are but a few of the products made by the viscose process. The E. L du Pont de Nemours and Company's "Fiber D" is a new rayon fiber with a high degree of permanent crimp and other characteristics now available only in wool. This new fiber appears promising as a substitute for wool in carpets, upholstery materials, wall coverings,