_Polyvinyl acetate resins._—The several commercial types of vinyl acetate resins are marketed under the trade names Vinyloid A, Alvar, Gelva, Formvar, and Mowilith. The first of these is a product of Carbide and Carbon Chemicals Co., New York, the next three are products of Shawinigan Chemicals Limited, Shawinigan Falls, Canada, and the last is made by the Interessen Gemeinschaft Industrie A. G., Germany. Vinyloid A and Gelva represent the simplest series of vinyl acetate resins and are made by polymerizing the monomer. The softening point and viscosity of the polyvinyl acetate resins increase with higher polymerization. Such resins are colorless, tasteless, odorless, thermoplastic products. They are soluble in coal-tar solvents and are compatible with certain alkyd resins, tar-acid resins, and natural resins. Films of polyvinyl acetate resin are not discolored by exposure, and after irradiation they become opaque to ultraviolet light, are hard and tough, and have good adherence and endurance. Their dielectric strength is good and they do not show a carbon track after the passage of an electric arc. Various grades having softening points from 80° to 200° C. are available. Polyvinyl acetate resins are used in making transparent papers, paper to metal laminations, glassine papers for food packaging, as a substitute for chicle in chewing gum, and as a component of paints, varnishes, and lacquers. They have the desirable properties of compatibility, durability, resistance to abrasion, and rust inhibition in the surface-coating use. Having the same refractive index as pyrex glass, they leave no line of demarcation when used as a cement for that material. They have been used to stiffen toe-caps in shoes and articles made from paper pulp suspensions. Gelvas are not molded as such because of their tendency to cold flow. They are used, however, as a binder for ground mineral fillers in advertising signs and for wood flour in molded artificial wood carvings. In nitrocellulose lacquers they improve the adhesion, luster, and toughness.