I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
January 1948
I
being released. These will not be included in this review, partly because of the limited interest of most of the papers but also because the more widely applicable papers may be published in more accessible literature. For instance, the N.A.C.A. report of McAdams, Nicolai, and Keenan, which was listed last year as an N.A.C.A. report, was published again (8.9) in a more generally available journal. Thacker and Hands (43) reported some experimental results on low frequency induction heating as applied to small scale chemical plants, and a book was published on radio frequency ieating by Brown, Hoyler, and Biefwirth (6). LITERATURE CITED
(1) Alexander, J., and Hindin, S. G., IND.ENG.CHEM.,39, 1044 (1947). (2) Anonymous, Engineers’ Digest, 4,213 (1947). (3) Arthur, J. R.,and Linnett, J. W., J . Chem. Soc., 1947,416. (4) Breidenbach, E. P.,and O’Connell, H. E., Trans. Am. Inst. Chem. Engrs., 42, 761 (1946). (5) Brown, G.H., Hoyler, C. N., and Bierwirth. R. A., “Theory and Application of Radio Frequency Heating,” New York, D. Van Nostrand Co., Inc., 1947. (6) Close, P. D., Heating, Piping Air Conditioning, 19, No. 1, 101 (1947). (7) Colburn, A. P.,Drew, T. B., and Worthington, H., IND.ENQ. CHEM.,39,958 (1947). (8) Collins, S.C., Chem. Eng., 53,No. 12,106 (1946). (9) Comings, E. W., and Nathan, M. F., IND.ENQ.CHEM.,39,964 (1947). (10) Coons, K.W.,Hargis, A. M.. Hewes, P. Q., and Weems, F. T., Chem. Eng. Progress, 43,405 (1947). (11) Corcoran, W.H., Roudebush, B., and Sage, B. H., Ibid., 43, 135 (1947). ENG.CHEM., 39,62 (1947). (12) Donohue, D.A.,IND. (13) Ford, C.E.,C h m . Eng., 54,No. 1, 92,132 (1946). (14) Gardner, H.S.,and Siller, I., Trans. Am. SOC.Mcch. Engrs., 69, 687 (1947). (15) Harbart, W.D.,Petroleum Refiner, 26,706 (1947). (16) Hawkins, G. A., and Agnew, J. T., Purdue Univ. Eng. Expt. Sta., Research Series No. 98 (1947). (17) Heialer, M.P.,Trans. Am. SOC.Mech. Engrs., 69,227 (1947). (18) Housman, J. G.,P e t r o l b n Refiner, 26,89 (1947). (19) Hurd, N.L., IND. ENG.CHEM.,38,1266 (1946).
mz
41
(20) Johnson, W. B.,and Nade, w. M., Ib% 39,971 (1947). (21) Jolly, F.J., Trans. Am. SOC.Me&. Engrs., 69,155 (1947). (22) Katz, D.L.,Hope, R. E., Datsko, 5. C., and Robinson, D. B., Refrig. Eng., 53,211 (1947). (23) Ibid., 53,315 (1947). (24) Kayan, C. F.,Ibid., 54, 143 (1947). (25) Kopp, S.,and Farkas, G. B., Petrolaum Processing, 2,449 (1947). (26) Leva, M., IND. ENQ.CHEM.,39,857 (1947). (27) Lobo, W.E.,and Skaperdas, G. T., Chem. Eng. Progress, 43,69 (1947). (28) Lukomskii, S. Bull. acad. sci. U.R.S.S., Classe sci. tech., 1946,1753. (29) McAdams, W. €I., Nicolai, L. A., and Keenan, J. H., Trans. Am. Inst. Chem. Engrs., 42,907 (1946). (30) Mack, D. E., and Uhl, V. W., Chem. Eng., 54, No. 10,115 (1947). (31) Nottage, H. B.,Heating, Piping Air Conditioning, 19,No.9,127 (1947). (32) Ogden, F. F.,and White, J. F., Refrig. EZLQ., 52,411 (1946). (33) Parmelee, G. V., and Huebscher, R. G., Heating, Piping Xir Conditioning, 19,No. 8,115 (1947). (34) Piret, E. L., James, W., and Stacy, M., IND.ENG.CHEM.,39, 1098 (1947). (35) Powell, 5.T., Trans. Am. Soc. M e c h . Engrs., 68,905 (1946). (36) Rohsenow, W. M.. and Hunsaker. J. P., Ibid.. 69,699 (1947). (37) Rowley, F.B.,Jordan, R. C., and Lander, R. M., Refrig. Eng., 53,35 (1947). (38) Silver, L.,2nd. Chemist, 23,380 (1947). (39) Simpson, W. M., and Sherwood, T. K.,Refrig. EI&g.,52, 535 (1946). (40) Slegel, L.,and Hawkins, G. A., Purdue Univ. Eng. Expt. Sta., Research Series No.97,1-15 (1946). (41) Smith, U. W., Heating, Piping Air conditioning, 19,No. 10. 118 (1947). (42) Tepe, J B., and Mueller, A. C., Chem. Eng. Progress, 43, 267 (1947). (43) Thacker, G.O.,and Hands, C. H. G., J. Soc. Chem. 2nd.. 66,211 (1947). (44)Trumpler, P. R., and Dodge, B. F., C h m . Eng. Progress, 43,75 (1947). (45) Westcott, R. M., Refrig. Eng., 54,15 (1947). (46) Whistler, A. M., Petroleum Rejker, 26,750 (1947). Trans. Am. SOC.Mech. Engrs., 69,683 (1947). (47) Whistler, A. M., (48) Zieman, W. E.,and Katz, D. L., Petroleum Refiner, 26, 620 (1947).
v..
RECEIVED November 4, 1947.
ION EXCHANGE ROBERT KUNIN, THE
RESINOUS PRODUCTS
AND CHEMICAL COMPANY, PHILADELPHIA, PA.
A
ri
LTHOUGH the recognition of a n ion exchange phenomenon dates back to 1850 (112, IM), its utilization as a unit operation in induswy on a wide scale (outside of water softening) is still in the development stage in most instances but is rapidly gaining momentum. The interest in this field has increased rapidly in the past few years with the result that many workers have found the task of reviewing much of the early voluminousliterature to be overwhelming. However,excellentreviews on both the theory and application of ion exchange by Gedroiz ( 3 4 , Jenny GI), Meyers ( 7 4 , Randall (79), Tendelso (I&?), Walton (123), Wiegner (187, 128), and Wiklander (138)have helped considerably in this rapidly developing unit operation. The marked increase in the utilization of this new unit operation may undoubtedly be attributed to the availability of high capacity and stable synthetic organic exchangers. Within the past year or two many noteworthy contributions have been made to further our understanding and utilization of this phenomenon. Theory of Ion Exchange. The availability of high capacity and stable resinous exchangers has resulted in several noteworthy
contributions to the theory of ion exchange. Adamson and Myers (a) and Bauman and Eichhorn (14) have found that a t concentrations above 0.1 M the rate-determining step for the exchange of ions in sulfonic acid cation exchange resins was the diffusion of ions in the resin gel structure. However, at concentrations below 0.003 M , Adamson and Myers have concluded that the rate-determining step was the diffusion through a liquid film surrounding each particle. Bauman and Eichhorn consider the rate-determining step at these low concentrations to be the mass-action reaction rate between the ions at the surface of the particle. For most commerical anion exchange resins, Kunin and Myers (60) have found the rate-determining step to be the diffusion of ions through the gel particle. Juda and Carron 153) have concluded that the exchange velocities for several cation exchangers could be represented by a second-order rate equation. T4e forward and reverse rate constants yielded equilibrium 6onstants agreeing with independently measured values. Utilizing the modified mass-action equation of Rothmund and Kornfeld (84) and Walton ( l a d ) , Cannon (22) has evaluated
42
INDUSTRIAL AND ENGINEERING CHEMISTRY
the equilibrium exchange constants for a sulfonic acid cation exchange resin for many ions including amino acids. Schubert (96) has applied the law of mass action to ion exchange equilibria employing the solid solution principle of Vanselow (120)for evaluating the activities of the solid phase components. However, this method was extended utilizing the Duhem relation described by Kielland (66). Marshall (64) has attempted t o measure the activities of the exchangeable ions of silicate suspensions by means of his membrane electrodes and has eoncluded t h a t a given ion upon a given silicate is not held with a fixed bonding energy as was formerly believed. Schubert has found t h a t good agreement could be also obtained with the Langmuir adsorption relation. Bauman and Eichhorn , ( I 4 have applied the Donnon membrane equilibrium to similar cation exchange studies. Melsted and Bray (69) have made a comparison of the cation exchange equilibria for several organic exchangers and synthetic and natural silicates. Further theoretical studies of Gapon (82)on ion exchange have yielded a n adsorption equation quite similar to those described by him (82)in several earlier publications. Davis (26) has extended Jenny's statistical exchange theory to the exchange equilibria involving ions of unequal valency. Graham and Horning (36) have observed the phenomenon of anion exchange to occur with hydrous aiumina. Tendeloo et al. (109) have extended their electrochemical study of ion exchange compounds to plant root systems. A most interesting review and study has been contributed by Wiklander (131) of Sweden. In this voluminous report Wiklander reviewed the theoretical aspects of ion exchange, and presented the results of an extensive study of the anion and cation exchange equilibria for soils, silicates, and exchange resins. Another voluminous contribution from Sweden has been contributed by Samuelson (87) on the physical and chemical properties of synthetic sulfonic acid resinous cation exchangers. Gregor and Bregman (87) have attempted to characterize cation exchange resins by means of a titration curve in a neutral salt solution. Kunin and Myers (59) have concluded that acid adsorption on an anion exchange resin is actually a n exchange of anions rather than a molecular adsorption. The theory of an ion exchange column operation has received considerable attention recently. Adamson and Myers ( 2 ) have applied the heat transfer theory, and Tompkins and Mayer (117) have formulated a theory based upon a n analogy to distillation. Walters (121, 122) has attempted the theoretical solution of the ionic exchange process in a zeolite column under equilibrium conditions and under conditions where the rate of reaction is the important factor. Sillen (99) has also attempted the solution of an exchanger column for the exchange of two univalent cations, assuming the exchange reaction follows the bimolecular rate law An interesting potentiometric method was devised by these workers for obtaining the concentration history (C/CO) curves. Although the work of Dole (27) and Klotz (57) is not directly related to ion exchange, their treatment of a n adsorbent column, especially their critical bed depth concept, should prove of considerable use in the field of ion exchange. Water Softening. Although many new applications have been found for ion exchange, the water-softening field still remains as the foremost and largest scale ion exchange operation. Whereas siliceoup exchangers are still being used for softening on a large scale, the m e of synthetic organic exchangers in industrial and domestic so! rcners is rapidly increasing. Myers (72) and Bauman (13, 15) have reviewed the use of ion exchange resins in the water softening field. Streicher, Pearson, and Bowers (104) presented the results of a n excellent study of the operation of a siliceous exchanger. Their study was interesting in that the effects of such variables as bed height, flow rate, temperature, etc., were carefully evaluated and described. Johns (56) and Maxwell (67) have described the maintenance and operation of several commercial water-softening plants utilizing siliceous ion
Vol. 40, No. 1
exchangers. The applicability of a n exchange unit for softening water t o be used in the quality textile industry has been briefly reviewed and strongly recommended by Miedendorp (YO), Nessler (76),and Miller (71). Some economic aspects of water softening have been briefly reviewed by Gallaher and Weckwerth (81). Kimsey (66) has briefiy reviewed the softening of municipal water supplies in England A contribution by Kostrikin, Prokhorov, and Mamet (68) describes the Russian development of water-softening techniques and their use of ion exchange. Simonsson (100) presented a n interesting review and study of the siliceous exchangers used commercially for water-softening purposes. This study included a literature review of the molecular structure, chemical composition, preparation, and methods for testing the stability of natural and synthetic zeolites. Astafev and Astafeva (11) reported on water-softening ability of humus coals. Gault and P ' o n g (33) have investigated the use of technical lignin for softening water. Deionization. The process of deionizing solutions by means of ion exchange is probably the second most important process which is dependent upon ion exchange. Although most of the deionization operations are concerned with the removal of salts from water supplies, in order t o produce a water comparable t o distilled water, other uses for this operation w e being found. The de-ashing of raw sugar solutions is receiving more and more attention. Behrman (16), Vallez (119), Shafor (98),Rawlings (80, 81), Gustafson (40),and others have obtained patents describing the use of ion exchange resins for the removal of salts from raw sugar solutions. Hadorn (48) has purified fruit juices using ion exchange resins. Haagensen (41) has reviewed the results of a test in which 20,000 gallons of sugar juice were purified by an ion exchange process. A report of the British Intelligence Overseaa Service (18) indicates that the Germans were able to de-ash sugar solutions during the war using ion exchange resins. Riley apd Sanborn (83) have quite thoroughly reviewed the economics and conditions for demineralizing cane sugar and beet sugar extracts by a n ion exchange process, and concluded that the exchange method produces sugars of higher purity, and more cheaply than existing methods. Ilowever, Fitzwilliam and Yearwood (30), although quite enthusiastic about the technique of ion exchange as applied to the sugar industry, concluded that the economics of the method were prohibitive. Another interesting application of a deionizing process utilizing ion exchangers is described in a patent of Holmes (47),which suggests the de-ashing of gelatin by means of deionizing columns consisting of cation and anion exchange resins. An improvement in the quality of the treated water is claimed by a patent of Durant and Blann (28) which describes the use of a four-bed system consisting of two cation columns alternating with two anion columns. French interest in the deionizing process employing ion exchange techniques is revealed in two papers by Bocher (21) and Delaroziere ($6). Thompson and Roberts (118) have studied several factors affecting the quality of water demineralized by ion exchange. Wilkes (190) has presented a n interesting review of the design and economics of railroad deionizing installations. Although it lost much of its importance a t the end of the war, the desalting of sea water for drinking purposes still remains an interesting application of ion exchange. The use of the bariumsilver zeolite has once more been described by Akeroyd, Holmes, and Klein (3)and Meincke (68). IngIeson (@) and Consolazio, Pace, and Ivy (23) have also described a similar study. The removal of silica from water by means of a deionizing eichanger unit by the fluosilicic acid method has been suggested by Lourier and Klyaehko (61) and Bauman ( I S ) . This method involves the conversion of silica t o fluosilicic acid, an acid strong enough to be adsorbed by the anion exchanger. The conversion t o the fluosilicic acid is accomplished by the addition of an excess of hydroHuoric acid or the addition of a soluble fluoride such as sodium fluoride to the cation unit. Several papers read a t a
January 1948
c
INDUSTRIAL AND ENGINEERING CHEMISTRY
silica removal symposium held a t Pittsburgh (29) described extensive studies on the use of this method for removing silica and indicated this process t o be quite practical. Separation and Concentrations. The applicability of ion exchange to the recovery and subsequent concentration of ionic constituents offers many interesting possibilities (4). The recovery of copper from dilute solutions was the subject of a patent by Tiger and Goetz (114). According to a B.I.O.S. report (18), the Germans were able to recover coppcr and ammonia in cuprammonium rayon plants using catsionexchange resins. This same report states that during the war the Germans utilized ion exchange resins for recovering silver from photographic film residues, purifying gelatin, and recovering phenol and acetic acid from waste waters. In evaluating the importance of these German processes one must realize that, although these processes may readily be carried out, the economics of the process may be prohibitive. The Germans probably resorted to such processes because of their deficiencies in raw materials during the war. Another wartime development of an ion exchange process for isolating and concentrating valuaple ionic constituents was the recovery of alkaloids from bark extracts. Applezweig (8) has employed a cation exchanger for the recovery of atropine, scopolamine, and morphine, and Applezweig and Ronzone (9) have developed an ion exchange process for recovering the cinchona alkaloids from cinchona bark extracts. Similar studies have been described by Sussman, Mindler, and Wood (106) for the recovery of totaquine from cinchona bark and scopalamine from datura plants. The separation and concentration of amino acids by means of ion exchange have received considerable attention. Block (20) received a patent describing the use of an anion and cation exchange resin for the separation and concentration of the neutral, acidic, and basic amino acids in protein hydrolyzates. Block (19) also repoited on the use of several sulfonic and carboxylic acid resin8 for adsorbing and concentrating the basic amino acids (arginine, histidine, and lysine) in protein hydrolyzates. Wieland (129) has found the carboxylic acid resin, Wofatit C, to function satisfactorily for the separation of the basic amino acids from the other amino acids. The use of an anion exchange resin for the recovery of a new antianemia vitamin (apparently belonging to the B complex) from liver and kidney tissue has been described in a patent issued, to PfXner, Binklcy, Bloom, and Emmett (76). The separation of metal ions by ion exchange resins has been studied by Walton (1%) for the copper-nickel, cadmium-zinc, and mercury-copper separations. Although Walton found that he could improve the separation by increasing the length of the column, the method apparently is less satisfactory than the conventional chemical methods. The separation of univalent and bivalent cations by means of an organic cation exchanger has been studied by Wiklander (1SW),who found that dilution favors the adsorption of the divalent cation. The preferential adsorption of the magnesium ion as compared to the sodium ion is the basis of two patents (5’8, 48) which describe the recovery of magnesium from sea water and brine. However, the separation techniques as developcd by the Manhattan Project are by.fsr the most important advances recently contributed in the field of ion exchange. Tompkins, Khym, and Cohn (116) have devcloped techniques for chromatographically separating with a cation exchange column the pure fission products obtained from uranium and plutonium. Marinsky and Glendenin (63) have found that the order of elution of rare earths adsorbed on a cation exchange column is the reverse of that of atomic number. These investigators have indicated that they may determine the atomic number by means of these elution curves and have claimed the first positive chemical identification of a radioisotope of element 61. Spedding and his group (101, 102) and Harris and Tompkins (43) were able to separate macro quantitites of rare earths of a high degree of purity utilizing a
43
cation exchange column. Kettele (54) has applied ion exchange techniques to the separation of the yttrium group rare earth metals. Purification. The removal of traces of sodium and copper in oils by an organic cation exchanger has been described in a patent ( 9 7 ) . Another patent (17) suggests a similar use of ion exchange for the removal of iron and copper from acid liquors. The removal of pectin methylesterase from commercial pectinase has been accomplished by McColloch and Kertesz (68) with an ion exchange resin. The removal of hydrochloric and sulfuric acids from lactic acid solution with the aid of an anion exchange resin has been described in a recent patent (46); apparently these acids are adsorbed preferentially. Polis and Meyerhoff (7‘7)have removed all traces of salts and barium from the barium salt of adenosine triphosphate using a sulfonic acid cation exchanger. The use of ion exchange for the removal of ionic impurities in nonionic solutions should prove to be of considerable importance in the future. A patent has been issued to Tyler (118) describing the disposal of sulfite waste liquors using ion exchange resins. The purification of various sols (86)and the modification of blood in order to prevent coagulation (107) has been achieved quite simply through the application of ion exchange. Ayres (19)has purified zirconia sols from iron, titanium, beryllium, and lanthanum by means of an ion exchange column. The use of ion exchange for the purification of various colloidal systems apparently performs the same task as electrodialysis and is much cheaper to operate. Ion Exchange in Analytical Chemistry. Although the use of ion exchange in analytical chemistry may not be considered as a unit operation, many important industrial uses for ion exchange have been developed as a consequence of these analytical studies. The work of Samuelson (86-95) on the application of ion exchange to analytical chemistry has been quite outstanding. Samuelson’s work has covered the use of a sulfonic acid cation exchanger in the determination of most inorganic ions and also the composition of several complex ions such as cyanides, iron phosphates, acetates, and oxalates. The analytical chemistry of the amino acids has been aided considerably through the use of ion exchange. Tiselius,Drake, and Hagdahl(115) have reported a method for separating the various amino acid groups employing active charcoal to separate the aromatic amino acids, a carboxylic acid exchanger t o adsorb the basic amino acids, and a sulfonic acid cation exchanger t o adsorb the remaining amino acids. These latter amino acids are then desorbed and passed over an anion exchanger in the chloride form which adsorbs the acid amino acids. Sperber (103) has utilized an anion exchanger in the -middle chamber of an electrodialysis (three-chamber) unit as a buffer in the group separation of the basic, neutral, and acidic amino acids in protein hydrolyaates. Bergdoll and Doty (17) were able to separate the basic amino acids from mixtures and protein hydrolyzates by adsorption on Lloyd’s reagent, an aluminum silicate cation exchanger. Of interest to the tanning industry is the work of Gustavson (S9, 40), Adams (I), and Thies and Thorstensen (110) on the use of ion exchange resins for investigating the composition of chrome liquors. The method employed in these studies was based upon the adsorption of cationic chrome complexes by a cation exchange and the adsorption of the remaining anionic complexes by an anion exchange. The neutral chromium complexes were not adsorbed a t all. An ion exchange resin has helped considerably in the determination of traces of copper in milk (24), in that these trace amounts could be concentrated sufficiently so that a more accurate analysis could be performed. Riches (88) has utilized a sulfonic acid cation resin for the estimation of traces of copper, cadmium, nickel, zinc, and manganese in concentrations of 4 x 10-4 molar. The use of a semimicro ion exchange column has been dcscribed by Applezweig (7). Helrich and Rieman (46) have considerably simplified the determination of phosphorus
44
INDUSTRIAL AND ENGINEERING CHEMISTRY
pentoxide in rock phosphate with the aid of a cation exchange column. Utilization of ion exchange resins in laboratory practice has become quite common and has resulted in the availability of analytical grade exchange resins. Miscellaneous Applications. Several unusual applications of ion exchange have recently been revealed. Ryznar (85) has employed an anion exchanger for the preparation of pure iron oxide sols. On passing through an anion exchange resin in the hydroxyl form, a solution of a soluble iron salt is readily transformed into an iron oxide sol. Hazel (44) has described the properties of silicic acid sol produced by passing a solution of sodium silicate through a column of a cation exchange resin in the hydrogen form. Another interesting application of ion exchange is the use of the sulfonic acid exchangers as catalysts. Although the catalytic ability of the cation exchange complex of soils and clays has been previously reported (78), the marked activity of the hydrogen form of sulfonic acid exchangers towards reactions that are acidcatalyzed has been most interesting. Thomas and Davies (111) found a sulfonic acid cation exchange resin (hydrogen form) t o be more efficient for the hydrolysis of methyl, ethyl, and n-butyl acetates than an equivalent quantity of hydrochloric acid. Sussman (106) also found these exchangers t o be catalysts for esterifications, ester hydrolysis, sucrose inversion, etc., and found that these catalysts could be re-used without treatment. Such catalysts are being utilized in this country for the preparation of nand isobutyl fatty acids (6). Some large scale operations employing such catalysts for esterification were attempted in Germany during the war (73). Jenny (60) found that the hydroxyl form of an anion exchange resin catalyzes the mutarotation of glucose. The discussion of the use of ion exchange in the realm of agriculture may be considered out of place in a unit operations review; one should note, however, t h a t the process of growing crops utilizes much more exchanger and regenerant solution than one would ever use on an industrial scale. Since the results and observations that are reported by the soil chemists, plant physiologists, and agronomists working on ion exchange problems may contribute considerably t o t4e general problem of ion exchange, the work of these groups should be carefully studied by those interested in ion exchange. Jenny (50) and Graham and Albrecht (36) have studied the utilization of the exchangeable ions of anion exchange resins by plants. The use of a mixed anion and cation exchange resin bed in which all the nutrient ions are supplied as exchangeable ions has been studied by Arnon and Grossenbacher ( I O ) . Another important development in the use of ion exchange, although somewhat astray from the major purpose of this review, has been the utilization of finely divided anion exchange resin for the treatment of peptic ulcers ( 5 ) . Along these same lines, Martin and Wilkinson (65, 66) have reported t h a t an anion exchange resin could counteract the poisonous effects of indole, and a siliceous cation exchanger could counteract the poisonous effects of guanidine. Progress in the field of ion exchange has been appreciable for the past few years, and it is likely that, as industry becomes more acquainted with the phenomenon of ion exchange, many more applications and uses will be found for this unit operation. However, although considerable progress has been made, one important aspect of ion exchange has been grossly neglepted. This aspect involves the task of standardization of test methods and terminology. Many of the methods that are now being u,sed were originally set up for siliceous exchangers and designed for water-softening practices. This is also true for the units and terminology that are now in use. However, since exchangers are now available t h a t exhibit properties entirely different from those exhibited by the siliceous exchangers, and since there are many other uses for exchangers outside of the softening field, a dire necd existr for a standardization of test methods and
Vol. 40, No. 1
terminology. It is hoped that some organization such as the American Society for Testing Materials will undertake this task in the near future. LITERATURE CITED
.Idams, R. S., J . Am. Leather Chemists' Assoc., 41,552 (1946). Adamson, A. W. and Myers, L. S., J . Am. C h e m . Soc., 69,2836 (1947) ., Akeroyd, E.I., Holmes, E. L., and Klein, -k.,J . SOC.C h e m . Ind., 65, 28 (1946). Anonymous, C h e m . Eng., 54, No. 7, 123 (1947). Anonymous, C h e m . Eng. S e w s , 25, 1462 (1947). Anonymous, C h e m . I n d s . , 61, 381 (1947). Appleaweig, N . , IND.ENG.CHE,M., A s . 4 ~ED., . 18, 82 (1946). Applezweig, N., J . Am. C h e m . Soc., 6 6 , 1990 (1944). Appleaweig, K., and Ronzone, S., IND.ENG.C H E , h f . , 38, 576 (1946). Arnon, D . I., and Grossenbacher, K. A . , Soil Sci., 63, 159 (1947). dstafev, V. P., and Astafeva, >I. F., Ekon. Toplioa, Za.,3,32 (1946). .4yres, J. A , , J . Am. C h e m . Soc., 69,2879 (1947). Bauinan, 1%'. C., J . Am. W a t e r W o r k s Bssoc., 37, 1211 (1945). Baunian, W.C., and Eichhorn, J.,J . Am. C'hem. Soc., 69,2830 (1947). Bauman, W. C., and Skidmore, J. R.; IND.ESG.CHEM.,to be published. Behrman, A. S.,Gustafson, €1. B., and Hesler, J.'C., U. S. Patent 2,413,676 (Jan. 7, 1947). Bergdoll, M .S., and Doty, D. ll.,ISD.EXG.CHEX.,ANAL.ED., 18, 600 (1946). B.I.O.S. Rept. 621, I n t e r n . 22 (1946). Block, 1%.J.,d r c h . Biochem., 11, 236 (1946). Block, R. J.,U. 9. Patent2,386,926 (Oct. 16, 1945). Bocher, G., Ann. pharm.franc., 1, 56 (1943). Cannon. X.. Ann: iV. Y.A c a d . Sci.. ~. 47. 135 (1946). Consolazio, i V . V., Pace, N., and Ivy, 8 :C., Smithsonian Repts., Pub. 3820 (1945). Cranston, H. A., and Thompson. J. B., IKD.EXG.CHEM., ANAL.ED.,18,323 (1946). Davis, L. E., J . P h y s . Chem., 49, 473 (1945). Delaroaiere, F., C h i m i e & Industrie, 53, 329 (1945). Dole, M.,J . C h a . Phys., 15, 447 (1947). Durant, W. W., and Blann, W. A . , U. S. Patent. 2,404,367 (1946). Engrs. Soc. of Western Pa., 7th Annual Water Conf., 7, 89 (.1947). , Fitawilliam, C. W., and Yearwood, R. D. E., I n t e r n . Sugar J . 49, 69 (1947). Gallaher. W. U., and Weckwerth, H. F., J . A m . W a t e r W o r k s Assoc., 39, 147 (1947). Ganon. E. N.. J . Phws. C h e m . WS23.R.). , , 20. . 297 11946). J . G e n . ~ C h e m(U.S.S.fi.), . 13, 352'(1943). Gault, H. and Hiong, K. W., C o m p t . rend., 220, 608 (1945). Gedroia, K. K., Kolloidchem. Beihefle, 29, 149 (1929). Graham, E. R., and Albrecht, W..A,, Am. J . B o t a n y , 30, 195 (1943). Graham, R. P., and Horning, A. E., J . -4m. C h e m . Soc., 69, 1214 (1947). Gregor, H . P., and Bregman. J. I., Div. of Colloid Chern., A.C.S., Sept. 1947. Grehe, J. J.,and Bauman, 1%'. C., U. 9 . Patent 2,387,898 (Oct. 30, 1945). Zustafson, K. H., J . Colloid Sci., 1, 397 (1946). Zustafson, I
