An interesting application is in the construction of corrosion-resistant chemical plant equipment. In 1922 the German firm of Saureschutz Gesellschaft was incorporated to fabricate equipment composed of a special acid-resisting type of phenolic resin and asbestos. Sometime later its manufacture was started in the United States. All sorts of industrial plant equipment is now available, including cylindrical and rectangular tanks up to 9 feet in diameter and 12 feet high, piping for corrosive liquids and gases, valves, pumps, fans and ventilators, filter press plates and frames, buckets, dippers, etc. Another new use is for making matrices in which to mold rubber printing plates. Such plates are used at present chiefly in printing cotton and paper bags but extensive experimentation promises to broaden their use. The matrix is made of fiber board of very open structure impregnated with tar-acid resin in the process of manufacture. 4. ALKYD RESINS Description and uses. The alkyd resins, used principally in paints, varnishes, and lacquers, are a group of condensation products synthesized by reacting polyhydric alcohols, such as glycerin and the glycols, with dibasic organic acids, such as phthalic, maleic, succinic, and sebacic. The condensation product is almost always modified to give properties to the resin desirable or essential to the specific application contemplated. The modifying agent may be a drying, semidrying, or nondrying oil; the fatty acid of an oil; a natural resin, such as rosin; a synthetic resin of the tar-acid group or of the urea-formaldehyde type; or other substance. Up to the present time unmodified alkyd resins have not been commercially important. A wide variety of types is obtained by the use of different materials and different modifiers. The variations begin with the dibasic acid used, and with the polyhydric alcohol used. The modifications possible are practically endless, and almost any fixed oil or the corresponding fatty acid, and most of the natural or synthetic resins may be used. The importance of the modifier is shown by the proportion used in most alkyd resins. On the average, approximately 50 percent of the total weight of the drying and semidrying alkyd resin products is modifier, 30 percent dibasic acid, and 20 percent polyhydric alcohol. The proportions will, of course, vary with individual types. Certain types on the market contain only 25 percent modifier while others have as much as 75 percent. In a new industry such as this, rapid changes in types and applications must be expected. Extensive research is being carried on by various groups. The raw material makers are seeking cheaper products or those with special properties; the resin makers are investigating an endless number of modifications, and the makers of surface coatings are testing most of the new types offered. Development and patents.