Succinic acid is a white crystalline powder melting at 185° C. and boiling at 234° C., with decomposition to succinic anhydride. It may be obtained by the reduction of maleic acid. Condensation with glycerin gives a resin tougher and more flexible than is obtained with phthalic anhydride. In 1937 there were two commercial producers of succinic acid. It is believed that small quantities are used in combination with phthalic anhydride in alkyd resins. Fumaric acid. Fumaric acid is a white crystalline powder obtained by the prolonged heating of or by the action of mineral acids on maleic acid. Fumaric acid and maleic acid are structurally identical and the former decomposes at about 280° C., forming the latter. In 1937 there was one domestic maker of fumaric acid. GLYCERIN Description and uses. Glycerin (glycerol) is a clear, colorless or almost colorless, odorless, syrupy, hygroscopic liquid. It is obtained as a byproduct of the soap and fatty acid (oleic acid or red oil and stearic acid) industries. Other sources are insignificant; glycerin can be produced by the fermentation of carbohydrates such as molasses, but when glycerin prices are low this process is not profitable. The chief commercial grades of crude glycerin are “soap lye” glycerin, a byproduct of the soap industry, containing about 80 percent glycerin, and “saponification” grade, a byproduct of the fatty acid industry, containing about 88 percent glycerin. Chemically pure grades contain about 95 percent and dynamite grades about 98.5 percent glycerin. Other grades include “30° yellow distilled” containing about 96 percent glycerin. The uses of glycerin are extremely varied, the most important being in the manufacture of alkyd resins and ester gums; in the manufacture of nitroglycerin and dynamite; as a moistening, antiseptic, and sweetening agent in tobacco; in pharmaceutical and medicinal preparations; and in certain soft drinks, soaps, and inks. United States production. The output of both the crude and the refined has increased in recent years, reaching new highs in 1937. Chemically pure glycerin constitutes about 60 percent of the total refined output and dynamite and other grades about 40 percent. In the production statistics shown in table 48, grades such as yellow distilled are included with the dynamite grade. Since large soap makers refine their own crude glycerin, the sale of crude is only a small part of the total output. Table 48 shows domestic production of glycerin by grades and table 49 production for sale. TABLE 48.—_Glycerin: United States production by grades, in specified years, 1919-37_