are needed to race the product through that zone with the best results in pre serving the food? In 1907 W. D. Richardson and E. J. Scherubel presented a paper before theAMERICAN CHEMICAL SOCIETY on the com
parative effects of ordinary freezing and more rapid freezing by convection. Z. Plank and Ehrenbaum and Reuter in 1916 made a more comprehensive study. They were followed by Harden F. Taylor and Clarence Birdseye, who conducted de velopmental work, mechanical and chemi cal. The zone of optimum crystal formation was determined through experiments in the percentage-temperature curve needed for quick-freezing. Experiments by Plank showed that, between the temperatures of 31° to 25° F., about 75 per cent of the total water content is frozen. This was termed the zone of maximum crystal formation. In the General Foods method, a machine
resembling a large metal box is used. When the front and rear sliding doors of this machine are pushed back, the opened box shows a series of multiple metal plates placed one above another. The plates are made of aluminum alloy. They contain curved passages through which the refrigerant is circulated. Normally the plates are held apart with an opening between them greater than the thickness of the product to be frosted. This is accomplished by pins in the four corners of the plates resting on pins in vertical guide bars. This arrangement of pins allows the plates to be freely lifted to insert products and dropped to make contacts on both sides of the product being frozen. There is virtually no waste material on quick-frozen foods, for the waste is utilized as by-products. When Birds Eye pur chases sides of beef, the parts not used are turned back to the processor to be sold as fresh meats. The accumulation of vines and pods, for example, in one central place
makes possible the utilization of waste ma terial which could not be used if col lected in small quantities. Pods and vines are used as ensilage. Parts of fish not used as frosted fillets are used as fertilizer. The elimination of waste cuts down on transportation and storage, important factors, especially under present wartime conditions. One of the greatest problems in the de velopment of quick-freezing was to bridge the gap between the laboratory and the ultimate consumer. It required many millions of dollars of investment, years of development work, and overcoming count less obstacles. Today Birds Eye foods are served in hundreds of thousands of homes; in institutions—hotels, restaurants, and hos pitals; on the high seas; and in the Army. The development is remarkably geared to war economy in every way, and will con tinue to render increasing service after the war.
Molecular Distillation K. C. D. H I C K M A N , Distillation Products, Inc., Rochester, Ν . Υ
SOON after molecular distillation was first studied by commercial labora tories, it was found that the vitamins could be stripped from various natural oils in the molecular still, leaving the main bulk of oil unaltered and thus available for other industrial use. Vitamin A was particu larly amenable to this treatment, since the fish liver oils in which it occurs pro vided a bulk of raw material and a ratio of value to bulk which was well suited to the stage of d e v e l o p m e n t that the molecular still had reached in the middle 1930's. Vitamin A exists in fish liver oils as a mixture of esters, with the palmitate predominating. The d e v e l o p m e n t of stills t o o p e r a t e economically at the high temperatures at which the esters distill ( 2 2 0 ° to 270° C.) required the parallel evolu tion of large pumps to carry away the great volume of gases evolved and yet maintain a pres sure of a millionth of an atmosphere. VOLUME
20,
NO.
23
The design of machinery to distill the vitamin A esters was begun in Eastman Kodak Laboratories before 1930. From 1934 onwards the project was sponsored jointly by Eastman Kodak and General Mills until transferred to Distillation Products, Inc., which continues to be con cerned chiefly with the distillation of the oil-soluble vitamins.
Figure 1 .
-DECEMBER
Stills for processing vitamin A oils
10,
1942
The vitamin A esters, introduced commercially in 1937, were first produced by five-stage falling-film stills having a ca pacity of about 400 gallons of crude oil a day. The vacuum was maintained by condensation pumps of the "fractionating" type. In the effort to reduce cost and increase throughput a new kind of molecu lar still was devised which employed rapidly rotating plates to spread the oil in a thin uniform film for distillation. An installation of 21 centrifugal stills, 32 inches in diam eter, was completed in 1941 together with 23 centrifugal units with 14-inch rotors. The 32-inch stills accommodate about 40,000 gallons m o n t h l y and are used almost exclusively for proc essing vitamin A oils. A view of this installation at Dis tillation Products is shown in Fig ure 1. Of the other fatsoluble v i t a m i n s , only the tocopherols (vitamin E) at pres ent warrant com mercial distillation. 1561
The separation of vitamin Κ is not attrac tive by this means because it occurs in low concentration even in the richest practica ble soybean oil, of which about one-third of a gallon must be distilled to provide one human day dose of the vitamin. The distillation of vitamin D from tuna and sardine oil has likewise become unattrac tive since the manufacture of synthetic vitamin D 3 has been perfected. The production of vitamin Ε is now paralleling that of vitamin A. Starting with soybean, cottonseed, and corn oil, a crude distillate is produced which can be concentrated excellently by multiple redistillations. The final steps by which the potency is raised to 40 to 80 per cent mixed tocopherols are performed at Dis tillation Products on the 14-inch stills shown in Figure 2. Research in the steroids and the oilsoluble vitamins is being furthered in about equal degree by the molecular still and the Tswett absorption column. Recent advances include the production of pure crystalline vitamin A and its esters, crystalline α-tocopherol acetate, and ytocopherol palmitate, and isolation of the new provitamin A, which has been named Kitol, by Embree and Shantz.
Figure 2.
American Medicinal Chemistry Ch Chicago, Ill. E. H . VOLWILER, Abbott Laboratories, North Chic
WHILE it is true that science is o n e of the very few pursuits of mankind which maintains a semblance of internationality, even in wartime, the major and outstanding contributions of our own nation have been vital. This is especially true in the field of medicinal chemistry. There seems to remain in the minds of some a vestige of the false idea that a majority of the outstanding drugs originated abroad. A very brief résumé of American contributions will show some examples of the fundamental contributions made in our country. General anesthesia, as we know it t o day, had its origin in the period from 1842 to 1847, when Morton, Long, and Wells— Americans all—introduced the use of ether. Following the discovery of procaine in 1904, new local anesthetics of real value were developed here. The most generally recognized intravenous anesthetic was developed in the United States less than ten years ago. Progress in hypnotics and sedatives owes more to developments in this country during the last twenty years than to work in any other land. This was paralleled b y the discovery of the effectiveness of a similar product for the control of epilepsy. Constrictors of capillaries are very largely of domestic origin, beginning with epinephrine (adrenalin) and continuing through
1562
many analogs of ephedrine, as benzedrine. Our chemists have led in the development of potent new germicides which as a group perhaps outrank those of any other nation. One of the newest antiseptic agents, gramicidin, discovered in the United States, has led to significant further developments in such studies. Penicillin, discovered in England in 1929, has been the subject of considerable attention in American laboratories during recent years. Sulfanilamide owes its present status to successive major contributions by German, French, English, and American investigators, and later sulfa drugs have been largely of domestic origin. Ehrlich's discovery of the arsphenamines failed to lead to important further developments of antisyphilitic agents for a number of years, but during the last decade important contributions have occurred, practically all of American origin. Very shortly after the blockade during World War I cut off arsphenamine supplies, our chemists were producing adequate quantities of good quality products, and domestic production has since been measured only in terms of high quality, much lower cost, and greatly enlarged volume. Among the most significant discoveries in the medicinal field, during the last twenty-five years, were most of the important hormones used today. Thyroxin,
CHEMICAL
the principal male and female sex hormones, insulin, liver extract, adrenal cortex hor mones—ail claim an American parent hood. Similarly the blood anticoagulants, heparin and dicoumarol, whose possibilities as aids in surgery and certain disease con ditions are constantly increasing, have an American origin. In the vitamin field, too, the contri butions have been many. Vitamin A and its first isolation in crystalline form; the preparation of vitamin D ; the discovery and syntheses of ascorbic acid, thiamine, nicotinic acid, pyridoxine, pantothenic acid; and, in a different category, vita min Κ—all owe a considerable part of their advanced status to the work of able American investigators. Of direct interest during the war are developments in the field of blood and blood substitutes. The preparation of immense volumes of dried human blood plasma, and, still more recently, of blood albumin, is of typical American origin. The array of examples could be greatly extended. Briefly summarized, American ingenuity and application in the medicinal field have led to many advances of major importance. Fortunately no one nation will ever contribute all the great ideas in any one field; one can ask only that his country should do more than its share, and this the United States has done.
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ENGINEERING
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