Other things being equal, the cheaper a synthetic resin, the more widely it may be applied as a substitute for other materials. As a result many an apparently useless byproduct, such as oat hulls which yield furfural, is either already used or being tested as a source of raw material. Other materials which have already found a place or may do so, are soybean meal, sugar, and certain petroleum distillates. Each of the important groups of synthetic resins has been sponsored by one or more manufacturers of established reputation and large capital resources. When a product reaches the commercial stage, after heavy research cost, its future importance is therefore usually assured. Relation of synthetic resins to their raw materials. Most of the commercially important synthetic resins are derived directly or indirectly from coal. The chart (p. 6) shows the derivation of certain synthetic resins from the principal raw materials used in their manufacture and the intermediate products back to the original source of the material. The polystyrene resins, for example, are made by polymerizing styrene or vinyl benzene. Although basically from ethylene and benzene, vinyl benzene may be formed in several ways. Ethylene is found in the gases from the destructive distillation of coal but is obtained commercially by cracking natural gas or petroleum. Styrene, found already formed in the light oil fractions from coal tar, causes gum-forming in motor benzol and certain industrial gases. When coke and lime are mixed and heated in an electric furnace to 2,000° C., calcium carbide is formed. This compound with water yields acetylene, the starting point for a long list of important products, including several types of synthetic resins. When acetylene gas is passed through acetic acid (itself obtained from acetylene) vinyl acetate is obtained. If hydrochloric acid is used instead of acetic acid, vinyl chloride is obtained. These compounds, when polymerized, yield the vinyl resins. The acrylate resins may be obtained from the same basic raw material by an entirely different procedure. Synthetic rubber is also derived from acetylene, as are acetic anhydride and acetic acid (used in making cellulose acetate plastics) and many other chemicals of commercial importance. [Illustration: Derivation of certain synthetic resins.] When naphthalene (from coal tar) is treated with air at elevated temperatures, phthalic anhydride is formed. Substituting benzene for naphthalene yields maleic anhydride. Both of these substances when condensed with glycerin, a byproduct of the soap industry, yield alkyd resins. The tar acids from coal tar, either separated or mixed, when condensed with formaldehyde give the highly important tar-acid resins. Or if formaldehyde is condensed with urea, obtained from carbon dioxide and ammonia, the urea resins are formed.