Imports of hexamethylenetetramine in 1928 came principally from the United Kingdom, the remainder from Germany. In 1929 they came wholly from Germany; in 1932 and 1933 from Belgium; and in 1934 principally from Canada, with the rest from the United Kingdom. In 1936 Belgium supplied 7,166 pounds valued at $1,368 and Germany 330 pounds valued at $142. Exports of hexamethylenetetramine are not shown in official statistics. It is known, however, that some has been exported, and that in 1933, at least, exports exceeded imports. Competitive conditions. Hexamethylenetetramine is made from formaldehyde and ammonia, of which there are ample supplies in the United States. The market for hexamethylenetetramine is limited, and imports are small. It is made in numerous foreign countries, Germany being probably the principal potential competitor. FURFURAL Furfural is an aldehyde found in oat hulls, rice hulls, corn cobs, bran, and other farm waste products. Commercially it is obtained in the United States from oat hulls and in the Soviet Union from the husks of sunflower seeds. It is a colorless liquid, boiling at 158° to 162° C. and freezing at minus 38° C. Its principal use is in synthetic resins, of which tar acid-furfural is probably the most important. These resins are used in molding, for impregnating, and in coatings. Furfural is also used as a solvent for cellulose ethers and esters, natural gums and resins, and in the manufacture of derivatives useful as rubber chemicals. Domestic production is entirely by one firm, located in Iowa. Production and sales statistics are not publishable, but the maker has stated that consumption is in “terms of millions of pounds per year.” 18. RAW MATERIALS FOR UREA RESINS The principal raw materials entering into the manufacture of urea resins are urea and formaldehyde. Formaldehyde has already been discussed (see pp. 133-135) and urea and thiourea are discussed below. UREA Urea is a white crystalline material, made by condensing carbon dioxide and ammonia under heat and pressure. It is an excellent fertilizer because of its high nitrogen content (46.6 percent) but this use is limited by its relatively high cost. Urea is an important synthetic resin material, being a constituent of urea-formaldehyde resins, known commercially under the trade names Beetleware and Plaskon. Production of urea in the United States was started in 1916, when the German supply was cut off. In 1920 the domestic output was estimated at more than 200,000 pounds of fertilizer grade. Production ceased in 1922. Urea in ammonia solution for use in the manufacture of mixed fertilizer was first produced in 1933.