Source: Dyes and Other Synthetic Organic Chemicals in the United States, U. S. Tariff Commission. In 1933 there were 6 makers of resins from phthalic anhydride, in 1935 there were 15, and in 1937 there were 35. The 1937 output of alkyd resins from phthalic anhydride was 58,450,032 pounds net resin, with sales of 32,583,307 pounds valued at $6,446,011. Producing plants are well scattered through northern and eastern United States. In 1936 fewer than one-third of the makers accounted for about 90 percent of the output. The domestic production of resins from maleic anhydride was reported for the first time in 1933. The output in that year consisted of experimental quantities produced by two firms. A small increase in production occurred in 1934 when another maker began operation. In 1936 there were eight producers and the output was many times that of 1934. In 1937 there were 12 makers of these resins with an output of 2,803,987 pounds and sales of 2,154,988 pounds, valued at $418,183. It is the opinion of some persons in the industry that in volume of production and sales the resins from maleic anhydride will in the near future approach that obtained from phthalic anhydride. Imports into and exports from the United States. No imports of alkyd resins have been recorded in official statistics. Exports of alkyd resin coatings and finishes are not separately shown, but data collected from the several producers show that appreciable quantities were exported in recent years, principally to Central and South American countries. 5. UREA RESINS One of the most important series of thermosetting resins is the group made by condensing urea and formaldehyde. As early as 1897 it was discovered that an amorphous condensation product was obtained from the reaction of urea and formaldehyde. The clear glass-like mass obtained led to considerable research work toward the development of a substitute for glass. It was found, however, that the resin obtained absorbed moisture, resulting in a dimming of its luster, and that on standing for a time, the condensation continued producing cracks, fissures, and disfigurements in the molded article. In 1926 a successful commercial product was developed in England by the use of thiourea. Cost of production, however, was high. The addition of thiourea gave the product greater strength and water resistance than that obtained with urea alone but retarded the rate of cure. Also the sulphur present attacked steel molds, which necessitated the use of expensive chromium plated or stainless steel molds.