FERMENTATION PROCESSES P. A. WELLS AND G . E. WARD Industrial Farm Products Research Division, Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C.
OR a number of years increased attention has been directed to the use of fermentation processes for the industrial utilization of agricultural products, with the result that such methods now play an important role in this field. The various fermentations occurring during the preparation of certain foods and beverages, the processing of hides and skins, the retting of flax, the curing of tobacco, etc., might be considered a kind of industrial utilization but this discussion will be restricted to those fermentation reactions which are concerned with the production of definite chemical COmpounds from carbohydrates or carbohydrate derivatives. The purpose of this paper is to indicate the direct dependence of fermenttition industries on agriculture for a SUPPb of carbohydrates, to mention certain fundamental Problems which usually arise in fermentation studies, and to discuss the position held by fermentation processes in comparison with other modern chemical methods. During the past decade a number of review papers (3, 6, 6, 0,16, 16, 18, 20, 2-49 86) have described individual processes in detail, and an extended repetition of such subject matter would be superfluousTherefore the different fermentation processes will be viewed as various aspects of their operation come under consideration in connection with the topics just outlined. That fermentation processes offer interesting possibilities is indicated by the fact that the bibliography compiled by Fulmer and Werkman (14) in 1930 lists 112 different chemical compounds which arise from the action of various organisms on organic materials, the majority of which are carbohydrates or carbohydrate derivatives. Since 1830 a large number of new products has been discovered and studied by various workers, among whom Raistrick and his school, in England, are outstanding. In view of the variety of products thus possible of realization, it is not surprising that a t one time it was believed by some observers that we were about to enter a period in which a large number of our organic chemicals would be manufactured by fermentation methods. However, there has been no such trend, and a current appraisal of the situation indicates definitely that a tremendously expanded biochemical industry is not to be expected. Deterrents may be inherent in certain biological processes in the form of excessive cost or unavailability of suitable raw material, insufficient yields, sluggish fermentations, or expensive processing operations, or they may arise as competitive chemical processes. The last factor has been looming larger recently as a result of the development of aliphatic synthetic chemistry, which has 172
perfected some purely chemical processes that may act as a barrier to the establishment of new fermentation industries or may even threaten some existing manufacturing methods. On the other hand, the economic success of many fermentation processes is recognized. Such success is due to cb variety of situations; among them are the ability of the selected organism to give a consistently good yield of a desirable product in a reasonable time from a cheap available raw material, the easy recovery of the product in a sufficiently pure condition, and, often the decisive factor, the formation in this manner of a unique product which is difficultly obtainable by other methods. Each of the three classes of microorganisms is of service in the fermentation industries. Thus, yeasts are utilized in the production of alcohol and glycerol, molds in the manufacture of citric acid, gallic acid, and gluconic acid, and bacteria in the preparation of butyl alcohol, acetone, sorbose, acetic acid, and lactic acid. Development of a Fermentation Process The development of any fermentation process from test tube to plant-scale operation follows a general course, which may be briefly outlined as follows: The first step is the observation that a given organism has the ability, to some extent, to convert a certain substrate to a desired compound. With the original condition as a starting point, experiments will be designed to determine the effect of various nutritional and environmental variations. Whenever possible, purely synthetic media will be used, since the experimenter thereby has a better knowledge and control of the constituents available to the organism. Potassium, magnesium, sulfate, phosphate, and nitrogen will be the minimum requirements in addition to the carbon compound, and the providing of very small quantities of salts of certain metals, such as iron, copper, zinc, and manganese, may prove beneficial. The problem of nitrogen supply often requires considerable investigation; some organisms utilize nitrate nitrogen, some are satisfied by ammonium nitrogen, and others, particularly certain bacteria, must be provided with complex proteinaceous materials. In recent years the identification of certain “growth factors” has indicated the partial function of some of these nitrogenous substances. Besides satisfying the qualitative requirements, it is essential that the optimum quantity of each constituent be determined. The oxygen requirements (degree of aeration), the optimum temperature, and the degree of agitation must also be evaluated. The optimum pH and the advisabiliLy of controlling acidity by the addition of a neutralizing agent such as calcium carbonate may also have to be investigated. It is thus apparent that the thorough study of a fermentation process is a complex problem. Many of the results will be unpredictable, repeated experiments will be necessary to verify conclusions, and the changing of one variable will usually require a series of new experiments to determine whether the optima of other variables have been thereby altered. Indeed, the nature of these problems is such that no process can be considered beyond improvement.
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Types of Materials Utilized The interest of this symposium in the relation of fermentation chemistry to agriculture warrants a brief discussion of the type of farm products which are consumed by the fermentation industries. The primary requisite for fermentable carbohydrate substance may be satisfied by raw materials of various forms and of differing degrees of purity, according to the demands of the particular fermentation process. The largest industry, the production of industrial alcohol, utilizes almost exclusively blackstrap molasses because of its low cost and its abundance. However, a great variety of carbohydrate-rich raw materials are suitable for this fermentation, and the utilization of any single crop is principally a matter of economics. In 1937,75.7 per cent of the alcohol produced was obtained from molasses, 8.4 per cent from grains, principally coru, malt, and rye, while 15.2 per cent was of synthetic origin. The recent active movement fostering the use of corn and artichokes for the production of power alcohol will he discussed by P. B. Jacobs (page 162). The butyl alcohol-acetone fermentation is able to utilize a wide variety of starch-oontaining materials, such as corn, rice, rye, wheat, and cassava as well as sugar-containing materials. In recent years there has been a decrease in the use of grains in this industry, which has adapted its operations to the use of molaeses, a cheaper carbohydrate source. The mold-fermentation process for the production of citric acid requires close control of the composition of nutrient solutions, and i t is understood that in past years a high grade of sucrose has been used as the carbon source. However, it is rumored that a portion of this industry is now utilizing molasses as the raw material. The industrial production of lactic acid is accomplished by the bacterial fermentation of various materials, such as 1110lasses, refined glucose, hydrolyzed starch, or the lactose of crude wheys. This use of whey, a voluminous by-product of the dairy manufacturing industry, has heen studied for some time hut has attained large-scale application only recently (4, W). The choice of raw material for the lactic acid fermentation is dependent on factors such as the association of the fermentation industry with other industrial processing operations yielding fermentable material, and the grade of lactic acid desired, due consideration being given to the limitation of purification operations which will be economically possible. The production of gluconic acid, involving the direct oxida-
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tion of an aldose sugar, finds commercial glucose the logical raw material. One of the more difficult, hut no less important, fields of application of fermentation chemistry lies in the utilization of more resistant forms of carbohydrate, such as cellulose and pentosans, which are the chief constituents of many of the farm wastes such as corncobs, cornstalks, and straw, and ais0 of trade wastes such as oat hulls, cottonseed hulls, and sawdust. Methods for the production of fuel gas by the anaerobic fermentation of these farm wastes, along with sewage sludge, have been rather well worked out and are applied to a limited extent a t the present time. The cost of collection of the waste material is considered to he a limiting factor in the extension of this process. The thermophilic fermentation of cellulosc to acetic acid and ethyl alcohol appears attractive, as does also the alcoholic fermentation of sugars derived from wood waste. In utilizing these types of waste materials, the organisms may act directly on the polysttccharide material, or the wastes may he subjected to a preliminary acid hydrolysis. The former method is, in general, cheaper and simpler, hut the latter treatment may have definite value if the organisms do not readily attack the more complex Carbohydrate units or if isolation of certain of the constituents is desired, as in the Bergius process which is now operated in Germany for the conversion of wood to sugars for food and fermentation purposes. Fulmer and his eo-workers ($0)recently made a noteworthy contribution on the utilization of the pentosan portion of oat hulls. This fraction, which consists principally of xylans, is made available by a mild acid hydrolysis which leaves the cellulose unaffected. The hydrolyzate is capable of replacing almost half of the corn mash in the butyl alcohol-acetone fermentation. It is probable that similar waste materials could he utilized in this way. It is thus apparent that most of the fermentation processes exhihit considerable latitude in the type of raw material which can he utilized, although all these materials have their origin in agricnltural pursuits. In this country the use of molasses and corn greatly exceeds the utilization of other raw materials. In Germany potato starch has been a preferred raw material for the manufacture of lactic acid and alcohol, and in France beets have been a favored crop for use in the distilling industry. An interesting example of the flexibility of fermentation processes and the form which carbohydrate materials may assume is presented in a recent report (1) on the nature of molasses imported from Cuba. Since 1936, to circumvent susar auotas imnosed bv the SAA, Cuban pro&ce;s have cokerted"their surplus cane juice into a strong invert sugar sirup, which is sent to this country as a hightest molasses containing 75 to 80 per cent sugar, practically all as invert sugar, with very little sucrose. In contrast, the old standard molasses contained about 55 per cent sugar, of which the major portion was sucrose. Thr new high-test molasses has been found entirely satisfactory in the production of alcohol
Submerged and Surface Fermentations Fermentations may he separated into twu categories, depending on whether the organisms develop submerged in the solution or form a pellicle or pad on the surface of the medium. Most bacterial and yeast processes are of the former type, whereas the majority of molds and someof the aerobic bacteria. notsblv the acetic acid bacteria, naturally develop on 6 e surface.
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Such surface or submerged growths are associated, in general, with aerobic or anaerobic tendencies of the organisms. I t has long been appreciated that the surface fermentations are much less efficient than the submerged type because only the lower side of the pellicle is in contact with the medium and because the reaction rate is limited to some extent by diffusion of the substrate to the active cells and of the product away from this zone. Moreover, such a system is not favorable for the intimate contacting of atmospheric oxygen, active cells, and substrate, as is required in conversions of a highly oxidative nature.
LARGEROTARYFBIRMENTBR
Aside from these fundamental disadvantages, the adaptation of such procedures to large-scale operation presents great difficulties. Since the pellicle or suTface mycelium can operate effectively only on a rather shallow layer of liquid, a large area of organism must be cultivated. Shallow pans have been found suitable for this culture. However, in comparison with vat operation, the use of such pans is wasteful of space and involves the handling of a large number of units, with attendant high labor costs and increased risk of contamination. The maintenance of the proper atmosphere about such units also requires consideration. Many attempts which have been made from time to time to modify such aerobic processes by forcing the organisms to grow submerged have met with failure, although the fact that some commercial processes are understood to be conducted in this manner indicates some degree of success in recent years. For the past decade the Bureau of Chemistry and Soils has devoted considerable attention to this problem with the result that equipment has been developed which appears to be suitable for use as a research tool and, on a greater scale, for moderately large industrial application. This apparatus consists of a horizontally mounted rotary drum, which is constructed of very pure aluminum. To the inside of the shell are attached buckets which lift and drop the medium in thin sheets as the drum revolves; the liquor and organism are agitated thoroughly and exposed to the gaseous atmosphere prevailing within the fermenter. Provision is made for the controlled entrance and exit of sterile air, and the equipment may be operated at any desired pressure from atmospheric to as high as 3 or 4 atmospheres (19). As an illustration of the benefits to be obtained by the use of this apparatus, it might be mentioned that most investigated processes which require 10 to 20 days in surface cultures are completed in 18 to 35 hours in the rotary fermenters. Furthermore, the rapid reaction is almost invariably acoompanied by an increase in yield.
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It is believed that this equipment can be of service not only in the manner mentioned above, but also in obtaining more precise and fundamental data on established vat fermentations, since the factors of aeration, pressure, and agitation can be differentiated and closely controlled. The rotary fermenters were first applied in a study of the production of gluconic acid by Aspergillus niger, with highly successful results ($8, 86). In contrast to surface fermentations, which gave approximately 60 per cent yields of gluconic acid in an incubation period of 10 to 12 days, submerged fermentation resulted in practically quantitative conversion of 20 per cent glucose solutions to gluconic acid in about 24 hours. The aeration, agitation, and pressure were of great importance in determining both the rate of fermentation and the yield. An air supply of 400 cc. per minute per liter of medium and a gage pressure of 2 atmospheres were found desirable; and satisfactory agitation was obtained by revolving the fermenter ten to thirteen times per minute. The success attained in small apparatus led to the construction of a large fermenter, of 500600 liter capacity, at the Agricultural ByProducts Laboratory a t Ames, Iowa (86). Tests made with this equipment show that processes developed in small apparatus can be translated readily to large-scale operation (I?'). Following the development of the rapid gluconic acid fermentation, attention was directed to a study of the conversion of d-sorbitol to bsorbose. Although this transformation had been known since 1897, when Bertrand reported that certain bacteria were able to oxidize a large number of hydroxy compounds of a particular configuration to the corresponding keto compounds, little work was done on the subject until the last five years, when the chemical structure of vitamin C was determined and &sorbose was recognized as one of the logical points of departure for the synthesis of the vitamin. Sorbose has been a rare sugar, but fortunately an adequate supply of sorbitol has recently come on the market as a by-product of the manufacture of mannitol by the electrolytic reduction of glucose. The conversion of sorbitol to sorbose by surface growths of bacteria is fairly successful, but has the disadvantage that the process is slow and the bacterial films are delicate and likely to become waterlogged, after which their activity ceases. Consideration of the problem led to the belief that such an oxidation process would be likely to respond to conditions, such as rapid aeration and increased pressure, which had already been found desirable for the submerged gluconic acid fermentation. Subsequent experimental work showed this to be the case; it was found that a 20 per cent solution of sorbitol could be almost quantitatively converted to sorbose in 33 hours (37). The sorbose was easily recovered and purified by crystallization from concentrated aqueous solutions. It is of interest to note that, although the preparation of sorbose does not involve the direct utilization of a farm product, it is none the less dependent on agriculture through the use of glucose (corn sugar) in the electrolytic production of sorbitol. The rotary fermenters have also been of service in studying fermentations which are not highly oxidative in nature, such as the conversion of glucose to &lactic acid by molds of the Rhizopus genus (33). Operation with high pressure and rapid aeration is of no value in this process, but the use of the rotary drum equipment appears to offer other definite advantages. This study is not yet concluded, but it is hoped that the process will eventually have commercial value. Thus far,
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a complete fermentation of 11-13 per cent glucose solutions is obtained in 24-35 hours, with 70-80 per cent yields of dlactic acid. The medium is very simple in composition, especially with respect to the nitrogen source, which is urea, in contrast to complex nitrogenous materials which must he used for lactic acid bacteria, In addition, the rotary fermenters have been used in a study of the further oxidation of gluconic acid to &keto gluconic acid hy Acetobadm auboqdans, the same organism which was used for the production of sorbose. These studies are still in the experimental stage hut give definite promise of resulting in a rapid, efficient process which will make available quantities of a rare material. They may result in a further extension of fermentation in the utilization of agricultural products. Since the same technique and apparatus have heen successful in the conversion of perseitol to perseulose and of glycerol to dihydroxyacetone, it is apparent that this method of cultivation of the acetic bacteria is a practical, valuahle, and general procedure. The discussion of the recent work of the Bureau of Chemistry and Soils is not intended to indicate the nonexistence of commercial processes employing submerged fermentation principles. Such methods are undoubtedly being applied industrially for the production of calcium gluconate and sorhose, hut since the details of operation are closely gnarded trade secrets, no attempt can he made to evaluate the processes. Comparison of processes developed in the government laboratories with methods disclosed in patentents granted to Kluyver (##), involving the Cultivation of oxidizing bacinvolving the teria in an aerated solution, and to Currie et d., cultivation of fihn-forming bacteria in a foam (10) and the cultivation of molds under conditions of aeration and agitation (11), indicates that this rotary drum fermentation procedure is unique in the type of agitation provided and in hemg conducted under increased air pressure. The latter factor has been shown to he very important.
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pendent of Italian supplies and brought acute distress to Italian producers. Considerable research effort has been expended on attempts to develop a submerged fermentation process for citric acid, and undoubtedly a large amount of unpublished work has been done on the problem. All reliable evidence indicates the impossibility of such technique. The reason for this failure is not definitely known, hut it appears likely that some vital derangement in the enzyme system is responsible. Kauel (31) presented an interesting interpretation of this and similar phenomena, based on oxidation-reduction potentials and a conceivable differentiation in the functions of various strata of the mycelium. Thus, the upper celle exist in an aerobic condition, being exposed to the atmosphere but not having very intimate contact with the medium. The lower cells, conversely, are in a somewhat anaerohic environment but do have direct access to the substrate, whereas the intermediate cells are subjected to a gradation in these conditions. It appears plausible that the simultaneous activity of cells existing in these various environments is necessary for the consummation of the steps required for the conversion of sugar to citric acid. It is suggested that the lower cells have a reducing action on the substrate, which is succeeded by an oxidizing action brought about by the upper cells. The mechanism of the formation of citric acid from sugar is not known.
Industrial Fermentation Processes Calcium gluconate, which is used principally as a phannaceutical, has heen supplied to the market for almost a decade, and present production has heen unofficially estimated a t 500,ooO pounds per year. An alternate method of preparation, the electrochemical oxidation of glucose, appears to have been displaced in this country hy the fermentation process. Sorbose has been marketed for two or three years. As far as is known, the entire production, which is unofficially estimated a t 100,000 pounds per year, is employed in the chemical synthesis of vitamin c. The citric acid fermentation, which is dependent on the action of certain strains of the mold Aspergillzls nQer on suitable substrates, such as glucose, sucrose, or molasses, is of special interest hecause of its eminently successful industrial application and hecause i t is the outstanding example of surface fermentation conducted in shallow pans. It is understood that the pans are about 2 to 3 inches deep and 3 feet square. Estimates indicate that the continuous use of a t least lifteen thousand such pans would he required to yield the annual domestic output of the acid, which now exceeds 1O,ooO,OOO pounds. Although the process has been in commercial operation only about fifteen years, i t has vitally aEfected the citric acid markets of the world. A recent review (S4) shows that prior to 1925 the citrus industries of Italy supplied about 90 per cent of the total demand for the acid, hut the exploitation of the fermentation method in the United States, Belgium, England, and Czecho-Slovakia has made the world inde-
SEALLOW PANFERDCENTATION Kanel points out that citric acid and also succinic and fumaric acids are characterized by the fact that although they are oxidation products of sugar, they contain carbon atoms which are more reduced than any such atoms in the sugar molecule. He considers this to indicate that various oxidation-reduction systems are involved in these transformations. He reports that a certaiu strain of Rhizopus nipieans which produced fumaric acid under surface cultivation yielded lactic acid hut no fumaric acid when grown submerged a t a low rH (0 to S), and a mixture of lactic and fumaric acids when grown submerged a t a higher rH (8 to 14).
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mands, with the result that attention has again been directed to methods capable of supplementing the production from soap works. At least two purely synthetic processes appear promising. In Europe considerable attention is being given the preparation of glycerol from diethoxyacetone (2); in this country favorable reports have been made (#$) on the production of glycerol from propylene, which is obtained in considerable quantities from the cracking of petroleum oils. The propylenc is chlorinated to 1, 2, 5trichloropropane, which is then hydrolyzed by alkali. Production costs by this method are said to be less than 6 cents per pound, whereas fermentation glycerol could probably not be produced for twice this figure. The success of the propylene conversion would probably doom fermentation glycerol in the United States as long as petroleum reserves hold out, but the position of the birr logical product in countries lacking petroleum and in this country after exhaustion of the oil fields is another matter. Acetone is the fermentation product which has suffered most from synthetic competition. A comprehensive review of this solvent, recently presented by Cooley (8),discusses itk plight in considerable detail. Before 1923 the domestic acetone production, which averaged about 10,000,000pounds per year, was realized by heating calcium acetate obtained from wood distillation. From 1923 to 1929 the production more than doubled, fermentation acetone providing almost the entire supply. Since 1929 synthetic acetone, made by the catalytic oxidation of propylene which is derived either from natural gas or, more reccntly, from petroleum-still gases, has been a constantly increasing threat t o the fermentation product. Total production rose to an all-time high of 124,012,187 pounds in 1937, sales for the same period were only 68,772,268 pounds (Sf),and the price fell as low as 4.75 cents per pound. Cooley suggested the possihiity of overproduction, which is confirmed by a comparison of the subsequently released production and sales figures. He also mentioned the difficulties of the fermentation companies in dealing with the problem. The concurrently formed butyl alcohol cannot be made to carry an undue share of the burden because of the danger of competition from substitutes, and new uses for acetone are
It is well known that the citric acid fermentation may he displaced to a gluconic acid fermentation under suitable conditions, such as submerged cultivation in the presence of calcium carbonate. There is reason to believe that this circumrtance, in conjunction with the fumaric acid-lactic acid displacement, is of decided significance, but the full explanation of these phenomena awsits future work. The production of acetic acid by bacteria is well known as the process involved in Vinegar manufacture, and considerable acid for chemical purposes is similarly produced by the biological oxidation of dilute alcohol solutions; such procrdures are often operated in conjunction with industrial alcohol plents or yeast factories. Figures revealing the actual quantity produced in this manner are not available (%), but it is understood that the major portion of the constantly increasing output of acetic acid and its derivatives is now prepared by synthetic processes, such as the hydration and oxidation of rtcetylene. The production of glycerol by fermentation has been of great service to various nations in times of emergency, but has not been generally necessary or profitable under normal economicconditions. Thoueands of tons of glycerol for munitions manufacture were produced in Germany during the World War by the yeast fermentation of sugar solutions in the presence of sulfites which, hy the interception of the intermediate acetaldehyde, caused a displacement of the normal alcoholic fermentation. Some research was done on this process hy American chemists TABLE 1. R E C E N T DOMESTIC PRODUCTION OF CaEMlCALS DERWBD during and shortly after the war, but no serious EhYlRELY OR PARTIALLY FROM FERMENTATION INDUSTRIES commercial application of the method in the inNo. or tervening years has been officially reported, alEatabProduotion. S*lee, value. Chemical lishrnenta Pounda Pound% Dollsrs though it is rumored that the process was operated in this country during the recent glycerol shortage. The consumption of glycerol hat increaser1 markedly in the last few years. About one fourth of the present domestic production is converted into nitroglycerin which, in dynamite, Znatic mid: is finding increased application in construction ~ 2 7 , 3 2 9(SI) w,s61 (SI) is5.m ( S I ) Edible 5 (31) ...... ..... ,... Medicinal and mining work. The additional use of this ..... .~.. Tsahnioal {E1 Sexbase .... iod,666s(sii ..... .... alcohol in tobacco products, in the viscose and regenerated cellulose industries, and in the prepab Private unoffioial estimate. LI Probably 2 or 3 aynthetia. ration of glyptal resiris bas created huge d e
r
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not rapidly forthcoming. Surely future developments in this field of fermentation chemistry will justify the attention of alert observers. The utilization of microorganisms to convert carbohydrates to fat is of no immediate interest in this country but has received much attention in Germany where, during the World War, a yeastlike fungus, Endomyces vernalis, was cultivated for the purpose of obtaining fat from its mycelium. Recent attempts of Germany to attain a state of economic self-sufficiency have led to a reinvestigation of this process, with the result that strains of a different organism, Oidium lactis, have been found to be more efficient fat producers (12). It is understood that in this country sterols for vitamin D production are recovered from the yeast and mold derived from fermentation processes, such as brewing and citric acid production.
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of the extent of the fermentation industries. The figures for acetone include the synthetic production, which cannot be definitely evaluated but is very considerable.
Conclusions It is apparent that fermentation processes play an important part in converting agricultural materials to desirable chemical compounds, many of which are of industrial significance. Recently developed efficient chemical methods present very strong competition to some fermentation processes, but there is every reason to expect that, in general, fermentation procedures will continue to provide industrial chemicals and that a limited number of unique and desired compounds will provide the basis for the establishment of new fermentation industries in the future.
Research Developments In addition to the previously described products which are of commercial importance, there are a number of compounds which can be readily produced by fermentation methods but have not yet been of more than theoretical interest. One of these compounds is kojic acid,
which can be produced in 50-60 per cent yields by the action of Aspergillus flavus on solutions of glucose or other sugars. Kojic acid is toxic when administered to test animals (IS), and it has been suggested as a material which might arise in faulty carbohydrate metabolism. Raistrick’s school has isolated a large number of interesting products from various fungi and their nutrient solutions. It is not possible to treat this work adequately in this paper; Raistrick’s own review articles should be consulted (7, 28). In general, the yields of such products have not been large, but the elucidation of the structure of the substances, many of which have an aromatic nucleus, has been of great chemical interest. A number of polysaccharides, complex fatty acids, organic chlorine and arsenic compounds, and substanoes of bridged oxygen-ring structure have been isolated and studied. One of the important contributions is the discovery that the mycelium of Helminthospom’una gramineum contains pigments of the a-hydroxyanthraquinone type to the extent of 30 per cent of its dry weight. Such dyestuffs are difficultly manufactured by purely chemical means, and it has been suggested that the biological preparation might be of commercial value. Complete production statistics for fermentation products would be both interesting and valuable, but unfortunately it is impossible to obtain complete figures for this group of chemicals from government sources, either because the volume of production does not justify individual treatment or because the number of producers or their geographical distribution is such that the publication of statistics would be too revealing. However, figures obtained from recent reports of the Bureau of the Census and the Tariff Commission, supplemented by information privately obtained, were used in compiling Table I; in spite of unavoidable gaps the table will give some idea
Literature Cited Anonymous, Chem. & Met. Eng., 45, 216 (1938). Anonymous, Chem. Trade J.,96, 498 (1937). Backhaus, A. A,, IND.ENG.CHEM.,22, 1151 (1930). Burton, L. V . , Food Ind., 9, 571, 634 (1937). Buswell, A. M., and Boruff, C. S,,IND.ENG.CHEM.,25, 147 (1933). Chrzaszcz, T., and Janicki, J., Chemistry & Industry, 55, 884 (1936). Clutterbuck, P. W., Ibid., 55, 55T (1936). Cooley, L. C., IND.ENG.CHEY.,29, 1399 (1937). Crawford, F. M., Trans. Am. Inst. Chem. Engrs., 22, 33 (1929). Currie, J. N., and Finlay, A., U. S. Patent 1,908,225 (1933). Currie, J. N., Kane, J. H., and Finlay, A,, Ibid., 1,893,819 (1933). Fink, H., Haeseler, G., and Schmidt, M., 2. Spiritusind., 60, 74 (1937); Wochschr. Brau., 54, 89 (1937). Friedemann, T. E., Science, 80, 34 (1934). Fulmer, E. I., and Werkman, C. H., “Index to Chemical Action of Microorganisms on Nonnitrogenous Organic Compounds,” 1930. Gabriel, C. L., and Crawford, F. M., IND.ENG.CHEM.,22, 1163 (1930). Garrett, J. F., Ibid,, 22, 1153 (1930). Gastrock, E. A,, Porges, N., Wells, P. A,, and Moyer, A. J., Ibid., 30, 782 (1938). Herrick, H. T., Chem. Bull. (Chicago), 18, 35 (1931). Herrick, H. T., Hellbach, R., and May, 0. E., IND. ENG.CHEM., 27, 681 (1935). Herrick, H. T., and May, 0. E., Chem. & Met. Eng., 42, 142 (1935). Kanel, E., Microbiology (U. S. S. R.), 4, 636 (1935). Kluyver, A. J., and Hooft, F. V., U.S. Patent 1,833,716 (1936). Levey, H. A,, IND. ENG.CHEM.,News Ed., 16, 326 (1938). May, 0. E., and Herrick, H. T., IND.ENQ.CHEM.,22, 1172 (1930). May, 0. E., and Herrick, H . T., U. S. Dept. Am., Circ. 216 (1932). Moyer, A. J., Wells, P. A., Stubbs, J. J., Herrick, H. T., and May, 0. E., IND. ENG.CHEM.,29, 777 (1937). Olive, T. R., Chem. & Met. Eng., 43, 480 (1936). Raistrick, H., Ergeb Enzymforsch., 1, 325 (1932); 7, 316 (1938) Underkofler, L. A,, Fulmer, E. I., and Rayman, M. M., IND. ENG.CHEM.,29, 1290 (1937). U. S. Bur. of Census, Biennial Census of Manufactures, 1935. U. S. Tariff Comm., Rept. 132, 2nd aeries 11937). U. S. Tariff Comm., “Increased Output and Diversified Methods of Producing Acetic Acid and Its Derivatives in U. S.,” June 4, 1938. Ward, G. E., Lockwood, L. B., Tabenkin, B., and Wells, P. A., IND.ENG.CHDM.,30, 1233 (1938). Wells, P. A,, and Herrick, H. T.,Ibid., 30, 255 (1938). Wells, P. A., Lynch, D. F. J., Herrick, H. T . , and May, 0. E., Chem. & Met. Eng., 44, 188 (1937). Wells, P. A., Moyer, A. J., Stubbs, J. J., Herrick, H. T., and May, 0. E., IND. ENQ.C R ~ M29, . , 653 (1937). Wells, P. A,, Stubbs, J. J., Lockwood, L. B., and Roe, E. T., Ibid., 29, 1385 (1937). RECEIYED September 17, 1938.
