Modified isomerized rubber| .000 | Do. Hard rubber | | Casein | | Cellulose compounds: | | Ethyl cellulose | .0003-.0007 | Do. Cellulose acetate sheet | ([1]) | Do. Cellulose acetate molding | ([1]) | Do. Cellulose nitrate | | ------------------------------+-------------------+----------- [1] Positive and injection 0.002-0.003; semipositive 0.005-0.007; flash 0.008-0.009. NOTE.—The values for the properties in this table are based upon maximum and minimum figures submitted to Modern Plastics by a number of manufacturers of each type of material. Differences in test procedures and sizes of test specimens may lead to erroneous conclusions in some cases if direct comparisons are attempted. Special grades of materials are often available which excel in one particular property. Source: Modern Plastics, vol. 15, No. 2, opp. p. 120. October 1937. Table 17 lists the properties which affect appearance and gives in addition to the color range, the clarity, material, the burning rate, the effect of age and sunlight, the refractive index, and the machining quality of each synthetic resin. Table 18 lists molding properties of synthetic resins. Of special interest are the possibilities of using a resin in injection molding. The thermoplastic resins and plastics (see softening point in table 20) are generally preferred to the thermosetting materials for injection molding because they permit the reuse of material otherwise wasted. Table 19 lists the strength properties of the synthetic resins; table 20 the heat properties; table 21 the electrical properties; and table 22 the resistance to acids, alkalies, and solvents. All of these qualities are important in some uses and each quality may be paramount in a few. Each material has its limitations and its special advantages and the consuming industry must choose the one best suited to its purposes. The tie-up between specific properties and particular uses is exemplified by vinyl resins, which because of their great elasticity at low temperatures, are used in safety glass, and by the polystyrene resins, which because of their electrical properties at high frequencies, are used in laminated electrical parts. As production of the various resins increases new uses will probably be found for most of them. TABLE 19.—_Synthetic resins and other plastics: Strength properties_