There is no known commercial domestic production of thiourea. Imports through the New York Customs District, according to invoice analyses made by the Tariff Commission, are shown in table 90. Thiourea is dutiable at 25 percent under paragraph 5 of the act of 1930. TABLE 90.—_Thiourea: United States imports through the New York Customs District, 1931-37_ ----+--------+-------+----------+------------------------ Year|Quantity| Value |Unit value| Source |(pounds)| | | ----+--------+-------+----------+------------------------ 1931| 81,560|$24,254| $0.297|Germany and Switzerland. 1932| 19,347| 4,760| .246|Germany. 1933| | | | 1934| 15,738| 5,982| .380| Do. 1935| 29,480| 10,500| .356| Do. 1936| 81,031| 19,782| .244| Do. 1937| ([1]) | | | ----+--------+-------+----------+------------------------ [1] Not available. Source: Invoice analyses of paragraph 5, of Tariff Act of 1930. Compiled by U. S. Tariff Commission. 19. RAW MATERIALS FOR VINYL RESINS Vinyl resins are made chiefly from vinyl acetate and vinyl chloride. Description and uses. Vinyl acetate is an unsaturated ester of the hypothetical vinyl alcohol. It is made from acetylene and acetic acid, and is a colorless liquid with a pleasant sweetish odor, boiling at 73° C. On account of its tendency to polymerize to polyvinyl acetate, a trace of copper salt is added for shipment. To render the vinyl acetate chemically active again, the copper salt is removed by distillation. At present the sole use of vinyl acetate is for the manufacture of synthetic resins. (See pp. 43-50.) Vinyl chloride, a salt of vinyl alcohol, is obtained commercially from acetylene. It is a gas (boiling at about minus 14° C.) used in the manufacture of synthetic resins. Vinyl chloride mixed with vinyl acetate is polymerized to a synthetic resin. United States production. Until 1938 the one domestic maker of vinyl acetate produced only experimental lots, the bulk of our requirements being imported from Canada. In that year large units to manufacture vinyl acetate were built at Niagara Falls, N. Y., and at Belle, W. Va. The remarkable properties of safety glass made from vinyl resin sheets, together with several other new and important applications of these resins, indicate a demand for vinyl acetate sufficient to warrant these large manufacturing units. The United States patents covering the processes of manufacture of vinyl acetate are owned by the Canadian producer, who has licensed the domestic makers. Domestic production of vinyl chloride has increased from experimental quantities in 1927 to large-scale commercial output, increasing substantially each year since 1933. United States imports. There has been no import of vinyl chloride. Imports of vinyl acetate (unpolymerized), entirely from Canada, are shown in table 91.