ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT (9) LIeissner, J., Brit. Patent 465,570 (Oct. 23, 1036) ; Ger. Patent 655.339 (Jan. 13, 1938). (10) Ibid., Ger. Patent 710,826 (;\up. 14, 1941). (11) Ibid., 732,742 (Feb. 11, 1943). (12) Meister, Lucius, and Brcining (now Farbwerke, floch8t), Ger. Patent 201,623 (June 10. 190G). (13) Othmer, D. F., ISD. ENG.CHEM.,33, 1106-12 (1941). ~ ~ Ibid., , 34, 246 (1942). (14) Othmer. D. F., Jacobs, J. J., and I , e ~ J., (15) Othmer, D. F., and Kleinhans, H., Ibid., 36, 447 (1941). (16) Sohmicl, Arnold, Z . ges. Schiess-rc. Sprengstoflw., 22, 169-73. 201-6 (1927).
(17) Shorygin, P. P., Topchiev, A. V. and Ananina, V., A , , 6.Gen. Chmi. ( C S.8.R ) , 8, 981 5 (1938). (18) StaatEmijnen, Limburg, Holland, Gel. Patent 858,245 ( S o v . 25, 1948'1 _. _. I .
(19) Weiler-ter-Neer, Uerdingen "Rh. (now Chem. Fabrikon), I b f d . , 228,544 (July 24, 1909). (20) TVestfkIisch-.4nhaltische Sprengstoff A.G., Ibid., 274,854 (Sept. 27, 1912). (21) Wilhelm, H., U. S.Patent 2,109,873 (hlarch 1, 1938). Rhzcaivm for
review December 2, 1953.
AccEP,r&D
I'ehruary
18, 1954.
Continuous Production of Hexamethylenetetramine FRITZ MEISSNER
AND
ERNST SCHWIEDESSEN
DONALD
The Firm o f J. M e h e r , Cologne, Germany
,
F. OTHMER Polyfechnic Inrtifufe, Brooklyn I, New
York
A
new continuous process for hexamethylenetetramine production allows the direct addition of the formaldehyde and the ammonia in the gaseous phase to the reactor. The formaldehyde may come directly and unpurified from an efficient and specially devised oxidation unit fed with methanol and integrally a part of the production unit. The heats of hydration of the two gases and the heat of the reaction accomplished in an aqueous phase are removed by vaporization of water from the reactor, which i s actually a specially fitted still pot. In order to prevent losses of either ammonia or formaldehyde gas, their effective concentrations in the reactor must be very low, or they would pass off with the vapors and be lost to the reaction. The optimum temperature of the reaction may be controlled b y varying the total pressure at which the reaction mixture i s allowed to boil or b y controlling the partial pressure by the presence of noncondensable gases. The reaction under these desirable conditions i s extremely fast. In continuous plant reactors i t is from 2 to 3 metric tons per day for a reactor of relatively small size with a yield on a one-pass basis of above 99% for both ammonia and formaldehyde. The solid hexamine i s removed continuously from the reactor either as fine white crystals or as a solution of any desired concentration. The heat of the reaction and of the hydration of the starting gases performs the entire water removal and eliminates the need of additional evaporative equipment and heat.
H
E X A ~ I E T H Y L E ~ E T E T R ~ or ~ ~ hexamine I I S ~ ~ has hecri
known for nearly 100 years as product of the reaction of 6 molecules of formaldehyde and 1 nlolecules of ammonia (6'). This inteiesting and symmetrical chemical structure has been carefully investigated. The carbon atoms are so positioned that lines joining them form a regular octahedron, and the nitrogen atoms are at the points of a circumscribed pyramid. \Then nitrated, hexamine gives compounds that are among the most powerful explosi One is knovr-n as Cyclonit, but in this country it is generally called Hezogen or RDX. This ingwdient of the so-called blockbuster bombs caused the production of hexamine t o reach very high levels in the United States, Germany, and ot8her countries participating in \Torid \Tar 11. Its application in peacetime iucludes important uses in the production of molding plastics, vulcanization accelerators, and various Raterproof resins and adhesives. Hexamine is the starting material for the production of various phsrmaceut'icals.
Prior Development of Hexamine Production Methods Hexamine is formed by the reaction of aqueous ammonia Trith aqueous formaldehyde arcording to the following reaction: 1
See summary on page 718.
724
+
GCH,O C 4KH3 4 CaHi?K\'r GHz0 The reaction is jtrongly exothermic. The normally expected tomnperature rise should not, take place, since at, too high a temperature there is the danger of producing by-products. Early Commercial Production. The first plants for production of hexamine operat,ed at, a react,ion temperat,ure of about 20" C., and used aqueous solutions of formaldehyde and ammonia as raiv materials. In some cases (2) a part of the ammonia was gaseous. The Ion- reaction temperature and the relatively great, heat of reaction have always been difficult t o rontrol. To provide the cooling Eurfaces, large unit,s of correspondingly large volumes were necessary. The procedure was batchwise and required a8 much as 36 hours per charge. Thc hexamine obtained in solution (10 to 20% depending on the concent,ration of the raw materials) was concentrated in vacuum (about 40 mm. Hg.) until hexamine was crystallizcd during a continuous addition of a,mmonia. After this operation, requiring 24 hours, thc product obtained was recrpstallizcd t o pharmaceutical grade hexamine ( S , ? ) . Continuous Processes Using Anhydrous Ammonia. J,ater development work was aimed a t making the process continuous, increasing the speed of the reaction, and obtaining a more con-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46,No. 4
UNIT PROCESSES ~~
~
centrated hexamine solution by facilit'ating the evaporat'ion. The last aim was reached by the use of ammonia gas and a formaldehyde solution that \vas as concentrated as possible. B y introduct'ion of gaseous ammonia into more concentrated formaldehyde solut,ion new difficulties appeared, however. The violent absorption that resulted caused shocks which endangered the building and equipment. This problem was solved by preventing the gaseous ammonia from reacting with the concentrated formaldehyde solution. Instead a stoichiometric amount' of ammonia was added t,o balance the formaldehyde which xvas added and recirculakd in a large excess of hexamine solution in a packed column ( 5 ) . Control of the reaction temperature was possible in this system by cooling in outside coolers, and the concentration of the formaldehyde solution could be fixed a t any value by cont'rol of the rate of circulation and the volume of the system. The final hexamine solution had a concentration of about 20%. Furthermore, proper conduction of t,he reaction increased the react,ion temperature to 40" to 50" C. wit,hout forming an excess of decomposition products. It was necessary t o avoid too high concentrations of formaldehyde in the reaction solution ( 2 2 ) . Cooling surface and cooling water were also economized and higher readion rates were obtained. The cooling problem, however, increased since the heat of react,ion is much higher when using gaseous than aqueous ammonia. Local temperature rise was feared a t the point of ammonia introduction, but this danger was overcome by injecting liquid ammonia in the reaction apparatus ( 1 1 ) . h decrease in reaction heat. was obtained by taking advantage of the heat of vaporization of liquid ammonia; this producod a disadvantage because of the contaminating compounds in the ammonia which create a product of inferior quality. Heat Recovery for Use in Evaporation of Product. A process was developed for facilitating the evaporation of the final product. A part of the reaction heat W:LS used in exchangers to heat the evaporator (10). Usually, even with 25% final hexamine solution, there is only a small difference between t'he reaction temperature and that which may be used for evaporation. This complicates the design of heat transfer equipment. In another method, the reaction was performed between paraformaldehyde and ammonia dissolved in methanol, and t,he hexamine which is insoluble in methanol precipitated ( 1 ) . Unfortunately, the methanol was so diluted by the water formed in the reaction that the precipitated hexamine redissolved. Furthermore, the use of paraformaldehyde is relatively expensive. Process Using Column and Solvent for Extraction of Product. It is impossible to produce anhydrous formaldehyde in the single reaction apparatus it'self, and a secondary unit was used (4). I n this process, formaldehyde was continuously stripped from a normal formaldehyde solution in a pressure distillation column. The dry gas obtained (dissolved in an organic liquid) was then reacted in another vessel with ammonia. The organic liquid used was chosen because it dissolved water readily but dissolved hexamine only slightly. The water formed in the reaction, therefore, dissolves in the organic liquid, and the hexamine formed precipitates aftler sat,uration is reached. The mother liquid containing the water of reaction and a small amount of hexamine is continuously decanted and used as the feed to the previously mentioned distilling column together with the original aqueoufi formaldehyde. The small amount of hexamine dissolved is hydrolyzed during the boiling, and the solvent goes overhead together with the hydrolysis products of the hexamine and the formaldehyde. These may or may not be separated. This process is theoretically interesting but is probably of no practical importance because of the relatively large heat requirement and the inevitable loss of hexamine dissolved in the solvent. I t s decomposition and the recovery of starting reactants is far from quantitative under the given conditions. From the stand-
April 1954
point of heat requirements, some of the evaporation of the formaldehyde solution can be obtained from the process; however, the water of reaction must be evaporated, and additional heat must be added to evaporate the solvent, to dehydrate the formaldehyd;, to hydrolyze the hexamine dissolved in the entrainer, t o heat up the entrainer to the high temperature of the column, and to produce the considerable amount of reflux for the column. The process requires a complicated equipment setup, and the reactor needs exceptionally good cooling because of the heat of condensation of the solvent and the heat of reaction which is increased by the heat of dehydration.
Heat of Reaction and Solution I n the production of hexamine, the several heat quantities involved are of the utmost importance. The heat of reaction for aqueous solutions of formaldehyde and aqueous solutions of ammonia is about 55 kcal. per mole of hexamine produced. From the reaction of a 30% aqueous formaldehyde solution and a 20% aqueous ammonia solution, a solution containing 44.5 moles of water per mole of hexamine is produced. This is about a 15% solution by weight. The heat of reaction (55 kcal.) is relatively small compared with 430 kcal., the heat needed for the evaporation of the water. If this reaction is performed using gaseous ammonia, the heat of reaction required for the final aqueous solution is increased by the heat of hydrolysis and absorption of the ammonia gas when added to water. This is 8.3 kcal. per mole of ammonia, equivalent to an added 33 kcal. per mole of hexamine produced. The amount of water per mole of hexamine in this case has been diminished to 528 grams, because no water was present in the gaseous ammonia. The total heat of the reaction is now increased to (55 33) 88 kcal. per mole of hexamine, and the heat of evaporation of the water present is now reduced to 286 kcal. which indicates a saving of 28'% in the heat requirement. If the reaction is performed between gaseous formaldehyde and gaseous ammonia, the heat of reaction is increased furthermore by an amount equivalent t o the heat of absorption and hydrolysis of the formaldehyde which is 15 kcal. per mole formaldehyde. This is equivalent to an added 90 kcal. per mole of hexamine produced, and therefore the total heat of reaction is (88 90) 178 kcal. per mole of hesamine produced. The amount of water per mole of hexamine when using gaseous reactants is reduced to that formed in the reaction or 108 grams, for which 58 kcal. is the required heat of evaporation. If all the heat of the reaction (178 kcal. per mole) was available, that for the evaporation of the water (58 kcal.) would be used, and there would be an excess for other use of 120 kcal. Using the usual industrial formaldehyde solution for the production of hexamine, it is impossible to secure solid, crystalline hexamine without heat supply for the evaporation. I n the best case, the heat requirement can be reduced by about one third. This saving is worth while if in a simple operation the heat of reaction can be used.
+
+
Meissner Process for Hexamine Production Using Aqueous Formaldehyde Solutions This last mentioned problem was solved by performing the reaction in a boiling solution and utilizing the heat of reaction directly for the evaporation of the water. The starting compounds of the reaction, aqueous formaldehyde solution and gaseous ammonia, were conducted to the reaction vessel in which the evaporation of an amount of water corresponded to the heat of reaction available. It was possible to select a suitable pressure and temperature (50' to 70' C.) to give optimum conditions for the reaction. The vapors go overhead and are condensed in a simple injection condenser. If the formaldehyde solution coming unpurified
INDUSTRIAL AND ENGINEERING CHEMISTRY
725
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT from its previous manufacture lins a substantial amount of niethanol, this volatile component will pass off immediately from the reaction apparatus into the vapor from which it n a y be recovered readily. The 25 to 30% hexamine solution can be concentrated cont,inuously from the reaction apparat,uv in a continuous vacuuni distillation unit. The reaction apparatus can be simultaneously used as a crystallizer by the application of hcat so that thc hexamine ia continuously produced as filial crystal product from this one apparatus. The control of t,he correct concent,rstioricr of the react,ing coniponenis may readily be made dependent on the continuous quantitative analysis for one of the components in the off gases. The reaction goes to 98y0 completion based on the use of aqueoiis formaldehyde and ammonia (8). This method requires heat for the vaporization of the n-vater to give the crystalline product. ther disadvantage is the by other compounds such contamination of the product hexsn as the formaldehyde in the absorption kat-er and by side products obtained in the reaction. This arid other considerations indicate t,hat it would be desirable t o have a hesaniine process wherein the formaldehyde and hexamine produring units are conibined in a single processing plant.
Production of Formaldehyde l'omaldehyde is usually produced through the catalytic olidation of methanol. An air-methanol mixture at approximately 600" C. is passed over a copper or silver contact catalyst. With provision for heat exchange with the exit gases, the greatest poltion of the methanol is converted to formaldehyde, water, and hydrogen. Another small portion ol the methanol may be oxiucli as (:arbon monoride, carbon dioxide, and formic acid while the remainder passes unchanged over the catalyst. The exit gases, a t approxilnately 600" C,, containing nitrogen, hydrogen, formaldehyde, Inrthanol, steam, carbon dioxide, and carbon monoxide are cooled to approximately 100" C. and are passed through a very active absorption medium t o absorb completely the formaldehyde and the methanol. Most of the methanol is also removed from the formalin $elution, and aft,er rectification it, is recycllid to the procws :LS coiicentrnted methanol.
Meissner Process for Production 06 Crystalline Hexamine without Heat
If the formaidohydt protiiici ion process is int egrateci in the hexamine process, the formaldehyde in the exit gaseous mixture from the converter may pass directly t o t,he hexamine reactor. Then it would be possible to vaporize all the reaction water formed by the use of only part of the reaction heat. It should be possible t o remove the formaldehyde from the gas mixture leaving the formaldehyde unit b y conducting a quantitative reaction with added ammonia even without the prior physical separation of the other components present in this mixed gas stream. If a special reactor were nsed with aqueous formaldehyde t,hr reaction could be accomplished with excellent yields a t the boiling point of t,he reaction solution although previously the reaction could not be accomplished at such a high temperature. The gases from the formaldehyde converter are first cooled to approximately 100' t o 150" C. in a heat exchanger that produces steam, are then passed t o the special reaction apparatus and reacted with gaseous ammonia. The temperature in the reaction apparat,us is at the boiling point,, controlled t o 50" t o 70' C. either by adjustment OF the tot,al pressure directly or by control of the partial pressure of inert gas. The exit gas--vapor mixture from the reactor is practically free of formaldehyde and ammonia and, after passing through a condenser, may be wasted. Jlethsnol, if present, would he re126
covered horn these off gases or from t,he condensate, for no COW densation of methanol is possible in the reaction apparatus. BPcause of its hydrogen content (approximately 18 to 20%) thii off gas may be used for combustion--for example under a generator. The ready control of the formaldehydr t>o ammonia raiio iinsintained by the automatic regulation of the quantitat,ivo amount of ammonia feed determined by analysis of off gasw. Crystallized hexamine is produced continuousl), in 1111. ai)pnratus at 98% of theory. The slurry is papsed to a csontinuonu centrifuge where the crystals are separated, washed, and completely dried. The washing of the crystals can be done with aboni 1 liter of distilled water per ltilograrn of hexamine. Wc7'ash solutions are returned to the reaction appamtus, and the \vater is vaporized by means of the reaction heat. To separate the very small amount of side productj which are formed in the reaction, the mother liquor from the reactor is pumped through adsorption filters and continuously purified. The adsorptjion-filtration of the mother liquid and the washing of the crystals prevent carry-over of impurities and result in a very pure hexamine product,. Furthermore, t,here are no impurit,ies brought) in by the viater usually used for absorption of the' formaldehyde. Decomposition in the reaction viwel is almost completely avoided because o€ the small r e d e n c e time and t hv small concentration of the formaldehyde. Furthermore, thcl mother liquid is circulated continuously through absorption filters for purification, and thc producc~tikcyamiiir is c.oiiipl'lrt,rly odorless and chemically pure.
Reaction Kinetics for Formation of Hexamine at Boiling Point of Reaction Mixture One of the conditions t,hat tends to ensure the completiori of a reaction in a boiling solution is satisfied when the end product ii nonvolatile. K i t h hexamine produced in a boiling reaction at approximately 60' C., the crystals formed are practically nonvolatile and quit(, stable. The ammonia and formaldehyde as gases are exceptionally volatile, 80 that completion of the reaction in boiling solutions without ammonia and formaldehyde loss seemed improbable. Knowing the vapor pressure in the reaction apparatus and ih(' partial pressure of ammonia and formaldehyde the maximum amounts of the two reactants which can be present in the liquid can be calculated (provided a definit,e loss in the final product? is assumed). This may be limited to 1 % of the mtering materials. Consider for example a, plant for the production of 100 Icg. of hexamine per hour from the addition of about 50 kg. of ammoniti and 130 Bg. of formaldehyde. The total amount of water vapor passing through the reaction apparatus may be calculated when using a formaldehyde converter wit,hout, caonsidering any methanol recovery. This total water will be the sum of that producetl in t,he formaldehyde plant, t h a t produced and evaporated froni the react,ion, and that used as a wash. This tot,al will he aboul 500 Bg. of water vapor per 100 kg. of hexamine. If a loss of I yo of the feeds is allowed--i.e., 1.3 kg. of formaldehyde and 0.5 lcg. of ammonia, the concentration of these materials in the vapor discharged to waste vould be h ~ l o w0.26 and 0.1 weight %, respectively. The corresponding concentration in the solution a t GO" C. can be Phown, therefore, t o approximat>e 0.5% formaldehyde anrl 0.005% ammonia. With these very small concentrations as t,hr maximum possible in the liquid, the reaction must have definitely gone t o a practically quantitative conipletion in the short m i dence time of the gases in t'he reaction apparat'us. The formation of hexamine from formaldehyde and ammonia i3 a very complex organic reaction which proceeds over a series of intermediate stages. As intermediate products there are methyl-
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 46, No. 4
UNIT PROCESSES amine, trimethylenedianiine, triinethylenetriamine, and as condensation products, various alcohols. I n order to understand the path of the reaction and its order, measurements of the reaction rates have been taken based on the concentration of the end products (9). The amount of ammonia used in moles per minute as a function of the ammonia concentration in a 1-liter reaction vessel a t 0’ C. are: Weight, % 0.8 0.6 0.41 0.2 0.016
hlolos N I I ~ / M i n u t e 0.025 0.02
0.01
0.002 0.00002
This experimental study of a very fast reaction at higher temperatures presents obvious difficulties, but if the reaction velocity is assumed to double with a temperature increase of every 10” C. then a t 60” C. and a concentration of 0.016% NH, a reaction of about 0.0013 mole per minute or 0.078 mole per hour, 13-hich equals 1.3 grams per hour, is brought about in an apparatus of 1-liter rapacity. Actually R larger concentration of reactants is possible since even larger yields are obtained per unit volume per unit time. This high velocity is more surprising, because the reactions must be brought about after the mass transfer of formaldehyde from the gas mixture to the reaction solution. This mass transfer must ti? quantitative even in a fraction of a second although the quantitative absorption of formaldehyde in an ordinary water abeorber is known t o be not so rapid. Simultaneously the solution of the ammonia and the several chemical reactions must be proceeding by their consecutive stages.
Parallel Production of Formalin Solution and Hexamine I n the design of the usual formaldehyde absorption units, it is important that the last traces of formaldehyde in the reaction gases be quantitatively absorbed. The absorption or condensation of the major portion of the formaldehyde does not involve great difficulties and can be obtained with simple condensers with the prevention of the formation of paraformaldehyde under observation of certain safety regulations. The last 30%, approximately, can be obtained only by very efficient scrubbing. The concentration of the formalin solution t o be produced determines the amount of wash water used. Since this water should be relatively small in amount, its quantitative absorption requires extensive units. The hexamine reactor is a more efficient absorber than the water scrubber. A formaldehyde solution ran be produced by the rondensation of part of the relatively rich off gases from the converter, while the condenser gases containing the remainder of the formaldehyde, which is much more difficult to absorb, are processed without separation to yield hexamine. By modification of the reaction apparatus the formaldehyde in such gases, even though of relatively low concentration, can be converted quantitatively to hexamine. The formalin to hexamine production ratio can be varied almost at will in a simple manner. The same principle is applicable where gases containing only a small amount of formaldehyde are available. I n the production of formaldehyde from methane as well as by the oxidation of methanol with excess ail, the reaction gases are always low in formaldehyde content and therefore difficult to process quantitatively. The new hexamine process brings about the reaction of the last traces of the formaldehyde from such dilute gases more readily than it may be absorbed in water.
Advantages of Combined Process The experiments that led to the new process were undertaken to reduce the amount of heat required. Other process improve-
April 1954
ments and the saving of heat have given an industrial proccss with some advantages: 1. The combination of the formaldehyde unit with the hexamine unit combines two otherwise independent procerses and by this means and by the omission of absorption and evaporation units greatly reduces the attention and labor charges. 2. The inde endent apparatus and additional step for the separation of f%maldehyde and methanol are not required. As a result a saving of steam amounting to 3 kg. per kg. of hexamine, plus a saving of heating-steam amounting to about 6 kg. per kg. of hg;xamine totals a saving of about 9 kg. of steam per kg. of hexamine. 3 . This 9 kg, of steam would require about 200 liteis of cooling water which likewise is saved for each kg. of hexamine. 4. The elimination of the absorption and evaporation units and the improved yield per unit volume per unit time effect a saving of more than 50% of the volume of the required building to house the plant. 5 . No impurities from the absorption water or even from the formaldehyde absorption unit can contaminate the hexamine or become concentrated in the mother liquor. Furthermore, the reaction takes place under constant, uniform, and well-defined oonditionn, and i t does not take place initially in highly concentrated formaldehyde solutions as had been common. T h o possibility of the formation of polymerization and side products is almost eliminated. The excess heat of reaction over that required for evaporation of mother liquor allows the use of approximately 1 kg. of wash water per kg. of hexamine and the evaporation of this water with no heat cost. Under these conditions, the hexamine produced is completely odorless and chemically pure. 6. I n the simultarieous production of formaldehyde solution and hexamine, the formaldehyde absorption unit can be held to a fraction of the previous size required, since the remainder of the formaldehyde present in the gases, whirh is diffjcult to absorb, ran be converted to hexamine. 7 . Since formaldehyde can be converted quantitatively to hexamine from gases containing only small rtmounts, this process may be used as a means of profitably recovering and using formaldehyde. 8. The reaction apparatus is simultaneously used a$ a crystallizer and size separator so that only the crystals having the desired size are removed
For two years the new proccss has been developed and all processing features investigated in a unit having a daily capacity of 500 kg. of hexamine and about 2000 kg. of formaldehyde production It is protected by patents in almost all industrialized countries. The operation is open to the inspection of anyone interested.
Acknowledgment Appreciation is expressed for the opportunity to present tliis process developed by the firm of J. Meissner.
Literature Cited (1) Adams, R. IT., Jr., and Landt, G . E., U. S. Patent 1,774,929 (1930). (2) Altpeter, J., “Das Hexamethylentetramin und seine Yerwendung,” Halle, Wilhelm Knapp, 1931. (3) Chemnitius, F,, Chrm-Ztg., 52, 735 (1928). (4) Eickmeyer, A. G., U. S. Patent 2,542,315 (1951). (5) Fischer, H., Ger. Patent 802,457 (Sept. 2, 1948). (6) Kirk-Othmer, “Encyclopedia of Chemical Technology,” Vol. 7, N. Y . , Interscience Encyclopedia, 1951. ( 7 ) AIcLang, .J., Chem. Trade J . , 77, 325 (192.5). ( 8 ) XIeismer, F., and Schwiedessen, E., Ger. Patent Appl. >I 5,612 1 V c/12, (1951); U. S. Patent Appl. 271,628 (1952). (9) hleissner, F. and Schwiedessen, E., Ger. Patent Appls. M 14,664 IVc/l2, and hl 14,665 IVc/l2, (1952); U. S. Patent iippl. 366,064 (1953). (10) Schideler, D., et al., U. S.Patent 2,449,040 (1942). (11) SChOlr, H., Ger. Patent Appl. B 13,639, 12,, I5 (1951). (12) Weimann, iM., Ibid., 686,063 (Nov. 27, 1952). RECEIVED for review December 10, 1953.
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ACCEPTED February 18, 1954.
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