LEACHING

peared to be that reported by D'Aquin and his host of coworkers. (20). The basic ... so that the process approaches countercurrent operation, Pilot pl...
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LEACHING

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ROBERT A. EBEL CARBIDE AND CARBON CHEMICALS CO., OAK RIDGE, TENN.

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number of important papers appeared during the past year which were based upon pilot plant developments of both new processes and new equipment. Interest also was shown in relating industrial leaching performance with theory.

ing equipment for a conventional extractor. Extraction of oil is carried out on the filter with multiple washes so that the process approaches countercurrent operation, Pilot plant work was done using cottonseeds and hexane. Compared to other solvent processes demonstrated advantages were: lower solvent content of extracted cake and final miscella, lower solvent requirements, lower fine content in miscella, and lower installed equipment cost due to compactness of process. Pilot plant and laboratory tests indicated that the process was versatile and capable of extracting oil from soybeans, raw and converted rice, bran, peanuts, flaxseed, and tung press cake as well as cottonseed. Tests show that the Chayen process, commercially used for the cold degreasing of bones, may have a wider application in the extraction of fats and oils from cellular materials (16). The basic principle is the destruction of the cells of material suspended in water by shock waves propagated by high speed high frequency mechanical impulses. The process has the advantage of minimizing the degradation usually caused by heat or chemical extraction. A comparison of processing cottonseed by prepressing and extraction, by extraction of raw flakes in a basket type extractor, and by extraction of cooked meats, revealed that all three methods would be used commercially for some time t o come (34). The choice of method depends on the equipment available and the secondary crop to be processed. Production data for oil, oilseeds, and cakes in India are given and discussed from the points of view of solvent extraction, byproduct, and industrial waste recovery (60). Jute seeds extracted with petroleum ether resulted in 15% yield compared to 10% by hydraulic press (60). Bench scale experiments on simultaneous extraction and saponification operations indicated the feasibility of preparing petroselinic acid from parsley seeds (71 ). Extraction of castor oil by means of an aqueous medium was tested on a laboratory and pilot plant scale. The process depends upon selecting conditions whereby the water preferentially wets the seeds. The seed preparation consisted of roasting and grinding, and the extraction was accomplished by a series of batch treatments with water and inorganic additives (84). h continuous process for the solvent extraction of castor oil having the advantages of small material holdup, compact equipment, and resultant lower costs was given by Colbeth ( f 4 , f 7 , 1 8 ) . The castor seed and naphtha solvent are fed cocurrently to a ball mill in which the seed is ground to 20 mesh. The outlet slurry is retained in a hold tank for 30 minutes a t 160' C. ' The final steps consist of filtering the miscella from the extracted meal and separating the miscella from the solvent by decanting and evaporation. The debittering and deoiling of lupine seeds using a solvent consisting of benzene, ethyl alcohol, water, and 1% ammonia were reported (33). Methyl chloroform, ethylene dichloride, propylene dichloride, and trichlorohydrin were investigated as solvents for soybean oil. Curves of specific gravity versus concentration of soybean oil in the miscellas were presented as well as extraction rates. Propylene dichloride WUR promising but inferior to trichloroethylene which is used commercially. Arnold and Pate1 studied the effect of moisture on the continuous extraction rate of soybean flakes and cottonseed

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HE literature on leaching operations, as in past years, haE originated predominantly in the sugar, metallurgical, and oilseed industries. An effort was made in this review t o emphasize studies and development work on the unit operation of leaching itself; however, relevant laboratory experiments and some new ideas disclosed by patents are cited. The literature indicated a considerable interest in relating leaching theory to industrial practice. THEORETICAL Scheibel (66) developed the concept of free solution and solution adhering to the solid as two distinct phases and showed the relationship to other diffusional operations. When the solution adhering is constant, well-known liquid-liquid extraction charts are available for estimating operating conditions. When the adhering solution is not constant, a n ingenious graphical method by Scheibel is available now. A further contribution was the use of an efficiency, similar to Murphree efficiency in distillation, in the graphical method which is capable of giving realistic stage efficiencies in leaching operations. Smith (73) correlated published data on the extraction of soybean, corn, cottonseed, flaxseed, wheat germ, and peanut flakes and grits by various solvents and expressed the results by an empirical equation. The rate constant was proportional to the diffusivity of oil and solvent, the reciprocal of the temperature, the viscosities, and approximately with the reciprocal of the pulp thickness squared, Oplataka and Miklos (65)continued their development of the theory of the diffusion process in sugar refineries baaed upon Fick's law. The derived equations were applied to industrial systems but indicated that they are applicable to many other systems of countercurrent extraction. In an additional paper (64) the effect of hydrodynamical mixing on the extraction ratc was investigated from both a theoretical and an experimental viewpoint. Under normal conditions of diffusion batteries, mixing losses are about 4%. Residence-time distribution of material flowing through beds of solids was analyzed mathematically by Dancltwerts (f9), and the use of models for solutions was discussed also. A nomograph for predicting diffusion coefficients in liquids was published by Othmer and Thakar (66). The data required are the solute molecular structure, the solvent viscosity a t 20" C., and the ratio of the molal latent heat of vaporization of the solvent to that of water. Other sources reviewed solid-liquid extractor calculations, confirmed the usefulness of Fick's law for continuous countercurrent equipment in sugar refineries, and pointed out the need for equations for countercurrent discontinuous equipment (4, 68).

O I L SEED PROCESSES The most interesting development in the oilseed field appeared to be that reported by D'Aquin and his host of coworkers (20). The basic element in their development is the substitution of a continuous horizontal vacuum filter with associated slurry126

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meats by hexane and trichloroethylene. It was concluded that the effect was of minor importance under usual plant conditions ( 7 ) . The conclusions from a study of the extraction of soybean meal with ethyl alcohol were that the moisture content of the meal must be less than 1% and that of alcohol less than 5% for optimum results (86). Other variables reported that relate to efficiency were the effect of particle size, amount of alcohol, number of extractions, and time of extraction. Impure solid fatty acids in flake form were purified by leaching with volatile organic solvents in a tower (36). The amounts of impurities were sufficient to allow full penetration of the flakes by the solvent but were insufficient to cause disintegration of the flakes proper. An excellent review by Piskur (69) of the literature on fats, oils, and soaps appeared and included a section on the production processing of fats and oils. Other detailed reviews of equipment, leaching conditions ( 1 2 , 34, 42, 49), and chemistry (37, 66) were published also. A number of Japanese patents were reported (60, 78, 88) as well as domestic patents covering materials handling a t the extractor ( 4 7 , 8 3 )and filtration-extraction (11,SQ). Ken techniques of pretreating cottonseed (62), soybeans ( 7 0 ) , and castor beans (36)were given.

SUGAR PROCESSES 15xtraction of sugar beet juice at low temperatures with the aid of sulfur dioxide was carried out on a semi-industrial scale ( 2 3 ) . The results were compared with standard diffuser on the basis of nitrogen content of juice and pulp, filterability of juice, ash content of spent pulp, and suitability of pulp for livestock feed. In each instance the low temperature process was superior. Travagali (82) reported that small additions of calcium carbonate to beets in a pilot plant diffusion battery decreased the purity of the diffusion juice but yielded higher purity light juices than were obtained in a normal acid extraction. A material balance on the sugar in a continuous countercurrent extraction of beets in a diffusion battery was checked as a means of improving the process efficiency ( 6 7 ) . Sugar loss in the exhausted pulp could be reduced 25 to 62% by pressing the pulp and returning the press liquor to process. The major part of the indeterminate sugar loss (in the battery) was attributed to biological destruction. A comparison of centrifugal extraction and standard diffusion on beet root pulp was made ( 2 4 ) . The color and lime content of the juice from the centrifuge were superior, but in all other respects the diffuser juice was equal. The problem of re-using diffusion and pulp press waters due to familiar waste water problems was discussed, and a number of installations were described emphasizing optimum operating conditions (66). Bishop (10) devieed a continuous process for the extraction of pure pectin from sugar beet wastes. The pulp is refluxed with alcohol and benzene to remove wax and gum, digested in water, acidified and heated, and finally filtered. The pectin is in the filtrate and can be separated by distillation and precipitation operations. The rate of plasmolysis of beet cells was reported to be unimolecular and approximately the same as the diffusion of sucrose at 50' C.; a t higher temperatures the rate was greater relative to sucrose (67).

INORGANIC PROCESSES Lindquist (46) reported the upgrading of manganese ores by caustic soda leaching. Spent liquor was regenerated with lime to remove silicate. A process for leaching manganese ores with sulfur dioxide solutions was given by Wyman ( 8 7 ) . The success of this process depends on the addition of a petroleum fraction and emulsifying agent to control the rate of formation of the dithionate ion, sulfate, and acid in the system. Manganese ores that have been heat-treated under reducing conditions may be leached with a solution containing at least 140 grams per liter

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ammonia and 38.5 grams per liter carbon dioxide (21). Additions of 0.1 to 30/, of hydroxylamine salts, ferrous salts, and soluble sulfites and sulfides increased both the rate and extent of extraction. Slternatively, the reduced ore may be extracted with a solution containing a t least 200 grams per liter ammonia and an ammonium salt of a corresponding soluble manganese salt ( 2 7 ) . Mixing porous materials with manganese ores prior to leaching was reported to facilitate the operation (41), .I study of five Kansas clays was reported in which alumina was extracted by first sintering with lime and then leaching with sodium carbonate solutions. Interesting process variables investigated were ratios of lime to alumina, sintering temperatures, annealing, and effect of sodium chloride additions on the leaching operation (@). Crude calcium aluminates were treated with strong sodium carbonate solutions a t 50" to 60' C. (74). The alumina was leached as well as siliceous impurities which were then eliminated by leaching a second batch of crude aluminate with the first leach liquor. By varying conditions the final liquor contained no sodium carbonate but some lime. Yields of 92% alumina from caustic leaches of bauxite were reported in Japan (76, 79). Ting (81) reported an extraction of alumina and potash from alumite. The first leaching step was treatment of the 300-mesh ore with 10% sulfuric acid, and the second was extraction of calcined basic alum with hot water. A pilot plant development using an ammonia leach for Lynn Lake nickel-copper-cobalt sulfides was reported by Forward (28). The leaching is done continuously in a two-stage autoclave at 125 pounds per square inch gage and 150' to 220' F. The first stage is fed with flotation concentrate and recycle liquor. The partially leached solids go to the second stage where fresh ammonia is supplied. The extracted solids are filtered and discarded, whereas the leach liquor goes to a continuous still to recover excess ammonia and to decompose thiosulfate and trithionate. A chemical separation of cobalt, copper, and nickel follows. A flotation concentrate of complex sulfide ores of copper, iron, lead, and zinc was leached with 607, sulfuric acid and then water (62). Conditions were such that, the leach liquor contained zinc and the residues were suitable for separation by selective flotation methods. A cyclic process was proposed for leaching a mixture of leach chromate and vanadate with sulfuric acid to leave lead sulfate as the residue (68). The oxidation and ammonia leaching of nickel, cobalt, and copper ores were treated in a paper discussing recent advances in metallurgy (IS). Suge and Mii (48, 76) extracted sulfur ores with organic solvents. First the ore is dehydrated at a temperature less than the melting point of sulfur, then the dehydrated ore is extracted with the solvent heated to a temperature above the melting point of the sulfur and, finally, the sulfur is crystallized out of the leach liquor by cooling.

ORGANIC PROCESSES Banigan (8) reported a fundamental investigation of the diffusion rates in the solvent deresination of guayule rubber. Resinous, rubber worms obtained from ball milling the guayule shrub were compacted a t 5000 pounds per square inch to form sheets for the study. For rubber sheets in excess of I-mm. thickness, Fick's law of material diffusion appeared valid; below 1-mm. thickness the simple theory could not describe the acetone extraction. Probably this deviation was due to inhomogeneities in the sheets which in the thinner sheets very likely were greater percentagewise. The fact that the extraction curves for the thinnest sheets were similar in form to those obtained with small, spongy worms of variable size tends to confirm this view. Clark and coworkers (16) studied this problem to provide a basis for the development of a large scale extractor for the resinous worms. The variables studied were: retention time, agitation, and solvent to solids ratio. Two tons of rubber were produced and proved to be high quality by road tests. The results were com-

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pared with previous work on acetone extraction of the shrub followed by ball milling; it was concluded that extraction should follow the ball milling operation, because of the high leaching rate ofthe resinous ball mill worms. Temperature and pH effects on the leaching rate of zinc salts from rubber with acid solutions were studied by Reznek (63). The quantity of zinc leached reaches a maximum that is dependent more on temperature than on acidity; the acidity has less effect than the variations among lots of rubber. At levels below 1.5 parts per hundred the extractable zinc is minimized. Laboratory experiments showed that 166 to 196 pounds of pinitol could be obtained per ton of dry sugar pine stumps by a water leaching process. The stumpwood sawdust appeared applicable to continuous-countercurrent extraction processes (3). The potentialities of obtaining turpentines commercially from Ponderosa pine lumber and stumps were investigated by leaching with acetone and fractionally distilling the product (29). Phosphatides were obtained from tissues of cold-blooded animals by ri series of leachings ($3). The first extraction uses water t o remove soluble albumin, salts, fish tastes, and odors. ’The material is then dried and extracted by a two-step system with methanol. Yields on 50-pound runs were as high as 93%. Another two-step leaching process for obtaining nicotine appeared. The feed material was extracted with liquid ammonia; and, following recovery of the ammonia, the residue was extracted with an organic solvent to obtain concentrated nicotine ( 3 2 ) . Corilene D.G. was used both by aqueous and by kerosine treatments to degrease wool skins with no felting of the wool occurring (36). Because of a shortage of domestic montan wax in 1950, a study of the extraction of this wax from lignite was made. The occurrence of lignite was treated comprehensively, and foreign technology and investigations were discussed (69). A leaching unit for the recovery of coal resins was described which is essentially an inclined scraper conveyor with a solvent reservoir a t the lower end (44). The solids are dispersed discretely on the conveyor and flushed with solvent; the system is totally enclosed. The extraction of pectic substances from vegetable matter with hot alkali or ammonia salts was proposed (85). Agar-agar was leached from cooked sea weeds and recovered by using sawdust, rice hulls, and similar materials as filter aids (80). Amagasa and coworkers ( 1 ) studied the industrial leaching of shale oil with ammonia and methanol and compared their results with the shale oil and liquid ammonia extraction. Laboratory extractiona on drugs (9,9, 61, 61, 7 7 ) and wood were also reported (38).

REFERENCES dmagasa, M., Iimori, S. Takahashi, N., Suauki, M., and Sakakibara, H., J . Chem. SOC.Japan, Ind. Chem. Sect., 53, 12-13 (1950). Amoaurrutia, J. M., U. S. Patent 2,628,961 (Feb. 17, 1953). Anderson, A. B., IND.ENO.CHEM.,45, 593-6 (1953). Andre, Smet., Suer. belge, 71, 481-7 (1952). Andres, P., Z . Zuckerind., 2 (77), 323-4, 360-1, 394-5 (1952); 3 (78), 80-1, 113-14, 204-5 (1953). Arnold, L. K., J . Am. Oil Chemists’ SOC.,30, 80-3 (1953). Arnold, L. K., and Patel, D. J., Ibid., 30,216-18 (1953). Banigan, T. F., Jr., IND. ENG.CHEM.,45,577-81 (1953). Biniecki. S., and Ludwicki, H., Ann. pharm. franc., 11, 121-9 (1953). Bishop, A. E., U. S. Patent 2,626,706 (Jan. 27, 1953). Bonotto, M., Ibid., 2,614,911 (Oct. 21, 1952). Burohaoinski, T., Farm. Polska, 7, 162-5 (1951). Cadenhead, A. F., Can. Chem. Processing, 37, No. 5, 38-40 (1953). Carter, J. S. F., U. S. Patent 2,616,909 (Nov. 4, 1952). Chem. Eng. Proor., 49, 50 (1953). Clark, F. E., Banigan, T. F., Jr., Meeks, J. W., and Feustel, I. C., IND.ENG.CHEM.,45, 572-6 (1953). Colbeth, I. M., U. S. Patent 2,616,907 (Nov. 4, 1952). Colbeth, I. M., and Carter, J S. F., Ibid., 2,616,908 (Nov. 4, 1952). Danckwerts, P. V., Chem. Eng. Sci., 2, 1-13 (1953).

Vol. 46, No. 1

(20) D’Aquin, E. L., Vix, H. E. E., Spadaro, J. J., Graci’, A. V., Jr., Eaves, P. H., Reuther, C. G., Jr., Molaison, L. J., McCourtney, E. J., Crovetto, A. J., and Gastrok, E. A,, IND. ENO.CREW,45,247-54 (1953). (21) Dean, R. S., and Fox, A. L., U. S. Patent 2,621,107 (Dee. 9, 1953). Dietrich, R., Ger. Patent 812,388 (Aug. 30,1951). Doorman, F. A., Verhaart, M. L. A., van der Vlies, G. S., and Waterman, H. I., Chimie & indu8trie, 66,471-9 (1951). Dorfeldt, W., 2. Zuckerind., 2 (771, 379-83 (1952). Dunning, J. W., U. 5. Patent 2,618,643 (Nov. 18,1952). Forward, F. A., Am. Inst. Mining Met. Engrs., Mining Eng., 5 , NO. 6,576-81 (1953). (27) Fox, A. L., U. S. Patent 2,625,462 (Jan. 13, 1953). (28) Frohlich. E., Zucker. 5.487-90 (1952). (29) Goldblatt, L. A., and Burgdahl, A,‘ C., IND.ENO.CHENI.,44, 1634-6 (1952). (30) Grimaud, G., Zucker, 6, No. 5, 95-9 (19b3). (31) Hatt, H. H., Strasse, P. H. A., and Troyahn, W. J., U. 5. Patent 2,640,841 (June 2,1953). (32) Hidaka, T., et al., Japan. Patent 3048 (June 12,1951). (33) Hillmann, G., and Radde, E. M. H., U. S. Patent2,615,905 (Oct. 28,1952). 30,45-8 (1953). (34) Hutohins, R. P., J . Am. Oil Chemists’ SOC., (35) Innes, R. F., and Pankhurst, K. G. A., J . SOC.Leather Trades’ Chemists,36,358-63 (1952). (36) Jenness, L. G., U. S. Patent 2,593,458 (April 22, 1952). (37) Julian, P. L., Catalyst, 37, 314-16 (1952). (38) Kathpalia, Y. P., and Dutt, S., Indian Soap J., 17, 285-7 (1952). (39) Kempe, R., Ger. Patent 817, 445 (Oot. 18, 1951). (40) Kinney, E. D., State Geol. Survey Kansas, Bull. 96, 301-28 (1952). (41) Kirk, P., Danish Patent 75,042 (Dec. 1,1952). (42) Kyokaishi, Y. K., J . Oil Chemists’ Soc. (Japan), 1, 111-14 (1952). (43) Langen, E., U. S. Patent 2,637,666 (May 5, 1953). (44) Lewis, H. E., Ibid., 2,630,377 (March 3, 1953). (45) Lindquist, R. V., Trans. Am. Inst. Mining Met. Engrs., 196, Tech. Pub. 3486B (1953). (46) Madon, P., I d . Agr. et aliment, 69, 193-200 (1952). (47) Manning, A. H., Brit. Patent 670,958 (April 30, 1952). (48) Mii, T., Japan Patent 258 (Jan. 29, 1952). (49) Mills, M. R., “An Introduction to Drying Oil Technology,” Part I, London, Pergamon Press Ltd. (1953). (50) Miyamoto, I., Japan Patent 2323 (May 15, 1951). (51) Nordstig, J., Astensson, M., and Attholm, I., Svensk Farm. Tidskr., 56, 477-81, 489-97 (1952). (52) Ono, K., Kameda, M., Kanno, H., and Iaumi, N., Science Repta. Research Insts. Tdhoku Univ., 4A, 506-20 (1952). (53) .--, O~lataka.G.. and Miklos., T.., Acta Chim. Acad. Sci. Huno.. 2. 383-426 (1952). (54) Ibid., 2,427-49 (1952). (55) Othmer, D. F., and Thakar, M. S., IEJD. ENG.CHEM.,45, 58993 (1953). (56) Parekh, H. V., Chem. Age (India) Ser., 6,139-47 (1952). (57) Paul, J., and Guerin, J., Ind. Agr. et aliment, 69, 381-6 (1952). (58) Perrin, T. S., and Banner, R. G., U. S. Patent 2,628,154 (Feb. 10,1953). (59) Piskur, M. M., J. Am. Oil Chemists’ SOC.,30, 197-212 (1953). (60) Ramaswamy, T. S., Venugopal, T., and Parameswaran, V., Indian Soap J . , 17, 241-3 (1952). (61) Rath, S., U. 9. Patent 2,620,750 (Feb. 24, 1953). (62) Reuther, C. G., Jr., LeBlanc, M. F. H., Jr., Batson, D., and Knoeptler, N. B., J . Am. Oil Chemists’ SOC.,30, 28-32 (1953). (63) Resnek, S., J. Am. Pharm. Assoc., 42, 288-9 (1953). (64) Rice, J. V., U. 8. Patent 2,615,808 (Oct. 28, 1952). (65) St. Bottger, J., Zuckerind., 2 (77). 345-53 (1952). (66) Scheibel. E. G.. Chem. Ena. Proor., 49.354-8 (1953). (67j Schneider, F.,’and Hoffman;-Walbeck, H. P., Zucker-Beih., No. 5,70-7; No. 6,100 (1952). (68) Schoenemann, K.. and Voeste, T., Fette u. Seifen, 54, 385-93 (1952). (69) Silvig, W. A., Ode, W. H., Parks, B. C. and O’Donnell, H. J., U.8. Bur. Mines, Bull. 482 (1950). (70) Singer, P. A., Deobald, H. J., U. S. Patent 2,609,299 (Sept. 2, . 1952). (71) Skellon, J. H., and Spence, J. W., Chemistry & Industry, 1952, 691. (72) Smet, A., Ger. Patent 815,638 (Oct. 4, 1961). (73) Smith, Allen S., J . Am. Oil Chemists’ SOC.,29, 421-5 (1952). (74) SociBtB des ciments franpais, French Patent 976,614 (March 20,1951). (75) Suge, K., Japan Patent 259 (Jan. 29, 1952). (76) Sugimoto, S., et al., Ibid., 2228 (May 8 , 1951).

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(77) Sugino, K.,and Ishikawa, T., J . Chem. SOC.Japan. Pure Chem. Sect., 73,507-10 (1952). (78) Takahashi, R.,Japan Patent 1230 (March 6, 1951). (79) Takemoto, M.,and Kishimoto, S., Ibid., 3963 (July 24, 1951). (80) Tasiro, S.,Ibid., 4081 (July 27, 1951). (81) Ting, C. W.,Taiwan Fertilizer Co., Research Bull. 8 , 38 pp. (1952). (82) Travagali, G.,I n d . saccar. ital., 45, 194-8 (1952). (83) Upton, C.B., U. S. Patent 2,641,536(June 9,1953).

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(84) Verma, J. P., Proc. Symposium Indian Oils Fats, Nat. Chem. Lab. India, 1951,pp. 130-2. (85) Walsh, C . I,.,and Adams, B. A,, Brit. Patent 669,314(April 2, 1952). c.v Chinese Chem.‘nd* 27-32 (lQ5O)* (86) (87) Wyman, W.F.,and Back, A. E., U. S. Patent 2,600,456(June 17,1953). (88) Yamaraki, R.,Japan Patent 2422 (hfay 19, 1951).

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MATERIALS HANDLING RICHARD L. SPEAKER 7117 NORTH LONACRE ROAD, MILWAUKEE 11, WIS.

Automation is a new word in industry’s vocabulary, but judging by the number of articles appearing on this subject, it has become one of the most popular already. Its meaning i s immediately clear when one views the amazing resultsthat automatically controlled motion has made in advancing materials handling of all kinds. In fact, increased use b y industry of automatic controls to help meet expanded production goals, in the face of a tight labor supply, was one of the most significant industrial trends the past year (72).

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HE&rm “automation” seems to have been coined by Ford engineers to describe the automatic handling of parts through various machinery operations in Ford’s Cleveland engine plant (1). I n this plant, most subassemblies move through all machining Operations without manual handling, Only final assembly proved too intricate to automatize. Even so, there is a possibility that even this problem child may learn the meaning of automation before long. In the design of new plants, maintaining a profitable flow between production, assembly, and shipping is a matter easily coordinated a t the blueprint stage of plant layout. However, many old-style plants have equipment set up more or less at random in various parts of multistory buildings. Because of this, the transfer of materials between operations has become their main production bottleneck. StewarbWarner (41) found a way of bringing the floors together with an ingenious solution of such a problem in one of its Chicago plants I t installed a power and free chain conveyor system connecting 12 stations strategically located in its 6-story building. The conveyor carriers are set to stop automatically at a predetermined destination, and the same carrier picks up a new load for transfer to some other station as soon as it has been unloaded. The nature of the product involved invariably determines the technique of handling operations. I n the processing of perishable produce, for example, minimum careful handling is a great asset in maintaining the value of the product. In the new plant of the Calavo Growers (California Avocados) automatic handling not only helps control quality, but reduces shipper waiting time as well ( d o ) . By manipulating electrical controls, a single operator receives lug boxes that have been stacked on floor-type conveyors by hand trucks, unstacks the boxes on an automatic device, carefully dumps the fruit, weighs it, and returns the lug boxes to the shipper. The system stops for recording the weight of each lot of boxes when a feeler (previously inserted on the last box) strikes a limit switch to stop the progress until the weight has been recorded. A similar report (40) on one-man control illustrates how the Richmond Refinery of Standard Oil of California neatly solved a problem with automation. One man a t a central control panel easily segregates and routes filled barrels either to rail, truck dock,

or to warehouse. All movements are finger-tip controlled. The response is positive, accurate, complete. Both large and small plants have profited, one way or another, from the introduction of complete or partial automation into their production lines. Much has been written about automation in chemical plants in the processing of liquids and gases. The success of one manufacturer of magnesia pipe insulation in employing automatic handling speaks well for its use in processing solid materials as well (39). The system is completely automatic, from the time the slurry is mixed until the formed magnesia pipe insulation is discharged from the molds. In this portion of the system, the unique feature is a weighing and transporting system that automatically positions under a full mixer and receives a charge of about 3000 pounds of slurry. After delivering this charge, the mixer stops, and the larry moves t o one of seven discharging positions where it feeds preset amounts into two preheaters. The larry then shuts itself off and moves to the next two preheaters where the process is repeated. After completion of the cycle, the larry returns to the mixer for the next charge. A portion of the system which is semiautomatic, but still solves a number of unique handling problems, is a combination roller and belt conveyor storage system coordinating working, storage, and shipping. In fact, it is so successful that it permits a threeshift production to match one-shift shipping without interruption. This particular installation also shows how a limited form of automation can be supplied in small plants, since this company has only about 100 employees. A new conveyor system built in connection with a chemical plant in New Jersey assures a steady supply of coal to the power plant (19). The complete mechanical coal handling system moves all coal from the time it arrives in hopper bottom cars until it is burned in the boilers. Sometimes automatic processing is hindered, because the product has assembly features specifically requiring human operators. The only way to automatize such an operation is to “design out” these manual operations. The substitution of tiny printed electronic circuits, that replace conventional wiring, to transmit electrical energy within radio and TV circuits has proved an outstanding mccess in this respect (48). Experience has shown these circuits actually eliminate parts, connections, minimize wiring errors, cut down