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The manufacture of citric acid in Italy is now centered mainly in two large modern factories located at Palermo and Messina. Although crystallization of citric acid direct from lemon juice is apparently feasible (I, 4l), the usual practice in Italy is first to separate it as the calcium salt which, on decomposition with sulfuric acid, yields the free acid in crystallizable form. The method of preparing crude calcium citrate is briefly as follows: The clarified lemon juice, which contains from 4.5 to G per cent citric acid, is heated to boiling and then neutralized with lime and calcium carbonate with constant stirring. The insoluble tricalcium citrate is filtered and washed thoroughly with hot water until the washings remain colorless. The dried salt, which usually contains from 67 to 70 per cent citric acid, is sold on a 64 per cent citric acid basis; a premium is paid for percentages in excess of that figure. Molinari (36) states that approximately 100,000 lemons are required to produce 300 kg. of calcium citrate of this strength, or about 150 lemons per pound. Citric acid is prepared from the crude calcium citrate by adding gradually a slight excess of sulfuric acid to the sus- pension of the salt which is stirred continuously. The mix- ture is boiled, and the calcium sulfate which separates is filtered off and washed. The acid liquors are then concen- trated in vacuum evaporators in two stages; in the first stage the remaining calcium sulfate is separated after con- centration to about 28’ BB., and in the second stage it is concentrated further to 48-50’ BB. The concentrated liquors are then discharged and allowed to crystallize. The crude citric acid thus obtained is re- dissolved and treated to remove metallic impurities and coloring matter; then the purified liquors are concentrated in vacuum at 60’ to 65” C. The pure acid was formerly crystallized in lead-lined or wooden containers, but in modern practice crystallizers constructed with stainless steel, alumi- num alloys, or rubber are used. The formation of normal crystals usually required from 4 to 5 days. The crystals are separated from the mother liquors by centrifuging and washing in the centrifuge with pure citric acid solution. The yield of acid from lemons varies from 15 to 50 pounds per ton of fresh fruit, depending chiefly on the time of harvest. The methods employed in the California citrate industry were completely described by Wilson (64), and a description of the process used in the West Indies was given by Browne (11) and by Warneford and Hardy (49). In addition to the citric acid from lemons in California, some is also produced from pineapple waste from the canning industry. According to Pilhasky (38), about 250,000 pounds of calcium citrate were produced in 1926 from this source. The Hawaiian citric acid industry is a comparatively recent development, although for a number of years about 100,000 pounds of calcium citrate were annually shipped to the United States. However, all of the available citrate from pineapple waste is now converted to citric acid in a modern plant erected in Hawaii during 1930 (45). The total annual production capacity is estimated at 750,000 to 1,000,000 pounds, Shipments of citric acid from Hawaii to the United States have increased steadily since 1930 and in 1935 amounted to approximately 1,000,000 pounds, or about 10 per cent of the total production in the United States during that year. Future of the Industry The fermentation citric acid industry is now well estab- lished. Manufacturers consuming this acid are assured of adequate supplies, regardless of crop failures and other con- ditions. The price trend since the first commercial develop- ment in the United States has been steadily downward, de- spite the fact that producers are protected by an almost in- surmountable tariff barrier to foreign competition. The present low price of citric acid has undoubtedly been respon- sible for t,he increased domestic consumption of this product which has taken place during the past few years. Important new developments in the industry can be ex- pected shortly. The use of citric acid in the synthesis of certain types of plastics and other products has been in- dicated previously. Such uses would provide an outlet for large quantities of this acid. It is probable that expansion of existing production facilities in the fermentation citric acid industry will take place in the near future. The use of cheap carbohydrate materials for citric acid manufacture and lower operating costs, due to improved technic, may make possible further price reductions which will probably lead to greater demand and consumption of this product. Al- though citric acid production by a true submerged growth process in yields high enough to be of practical importance has not been accomplished, the possibility still remains that this problem may be solved. Amelung (2) reported that 19 per cent yields of citric acid from sugar were obtained in a period of 40 days by employing submerged growths of A. niger.