Vast quantities of naphthalene potentially available in this country were not recovered because of the low prices prevailing until 1936. Since then an increase in the price of crude naphthalene from 1.55 cents to 2.5 cents and 3 cents per pound has stimulated production and has led to additional recovery. PHTHALIC ANHYDRIDE Description and uses. Phthalic anhydride is an aromatic polybasic organic acid anhydride made from naphthalene by vapor phase catalytic oxidation. It is marketed as white needle-shaped crystals or flakes having a melting point of 130° to 131° C. and boiling at 284° to 285° C. It is the cheapest and most widely used aromatic organic acid. Its most important use is in the manufacture of synthetic resins of the alkyd type. Other important uses are in dye intermediates; in phenolphthalein; in benzoic acid; in dyes such as indigo, phloxines, rhodamines, erythrosines; and in esters such as dibutyl phthalate (widely used as a plasticizer in nitrocellulose lacquers and films and of interest as a greaseless lubricant), diethyl phthalate (used as a perfume fixative and denaturant of alcohol), dimethyl phthalate (used as a plasticizer in cellulose acetate films), and diamyl phthalate (used as a plasticizer). Important new processes using phthalic anhydride as a raw material include the syntheses of anthraquinone, substituted anthraquinones, and benzoyl benzoic acid. Before the World War phthalic anhydride was made by heating naphthalene with sulphuric acid in the presence of mercury; the sulphuric acid acted as an oxidizer, and sulphur dioxide and carbon dioxide were liberated. This process was used in Europe and in the United States to produce the small quantities of phthalic anhydride needed for the manufacture of certain dyes and intermediates. It proved highly unsatisfactory as to operation; the yield varying widely from batch to batch. The sales price of the phthalic anhydride produced at that time was as high as $4.25 per pound, whereas it is 12 to 14 cents per pound today. In September 1916, Gibbs and Conover, working in the Color Laboratory of the Bureau of Chemistry and Soils, United States Department of Agriculture, developed a process for the synthesis of phthalic anhydride by the direct vapor phase catalytic oxidation of naphthalene. This work was done under the United States Government’s wartime investigation of the manufacture of intermediates and dyes. Gibbs and Conover were granted United States Patent No. 1,285,117 covering the basic process, and the invention was assigned to the people of the United States. This process revolutionized the manufacture of phthalic anhydride, causing the market price to drop to $2.85 per pound in 1918, to 46 cents per pound in 1920, and to 13 cents in 1930. With each decline in price new outlets were found, and domestic production increased practically every year, rising from 227,000 pounds in 1918 to 23,500,000 pounds in 1935.