A Continuous Process for Electrolytic Regeneration of Chromic Acid

Ralph H. McKee, Shoo Tze Leo. Ind. Eng. Chem. , 1920, 12 (1), pp 16–26. DOI: 10.1021/ie50121a006. Publication Date: January 1920. ACS Legacy Archive...
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y

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I t is impossible t o secure this by the use of air as t h e source of oxygen. The theoretical N H 3 concentration demanded by t h e reaction 4NH3 502 18.8N2 Pt = 4NO -I- 18.8N2 6Hz0 4- P t (IS) is 1 4 . 4 per cent, yet, when using saturated air as the source of oxygen, i t will be observed t h a t t h e ideal oxygen requirements are not fulfilled on a 1 4 . 4 per cent NH3. The decreased oxygen content then merely favors the nitrogen formation reaction and greatly decreased oxidation efficiencies occur under these conditions, particularly in large plant operations. Of course, a process for selectively abstracting t h e undesirable excess of nitrogen in a 1 4 . 4 per cent “3air mixture would solve t h e problem. P R E S S U R E INFLUENCE-The change O f Volume as indicated b y Reaction 1 5 is exceedingly small. Whether pressure has any great selective influence upon the above two reactions as carried out in a commercial manner is problematical. Since a t ordinary atmospheric conditions i t has been previously indicated t h a t the theoretical equilibrium called for a conversion of N H 3 t o NO a t above 99 per cent with all temperatures up t o 1 2 0 0 ’ C., i t did not seem worth while t o worry a great deal over the pressure factor as a means of increasing the conversion efficiencies. The influence of this factor upon the capacity opens a possible source of investigation, yet other factors seemed t o be of greater importance for the initial studies. ( T o be concluded i n our n e x t i s s u e )

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A CONTlNUOUS PROCESS FOR ELECTROLYTIC REGENERATION OF CHROMIC ACID’ By Ralph H. McKee and Shoo Tze Leo DEPARTMENT O F CHEMICAL ENGINEERING, COLUMaIA YORKCIrY

UNIVERSITY,

NEW

Received July 8, 1919

The problem of developing a continuous process for electrolytic regeneration of chromic acid from waste liquor is one of considerable commercial importance. Chromic acid is one of the most important oxidizing agents used in chemical processes for the oxidation of organic compounds. During oxidation the chromic acid in the solufion is reduced t o chromium sulfate, which usually goes t o the sewer. To recover the chromic acid from this waste liquor by a chemical process is not advisable, not only for commercial reasons b u t also on account of the difficulties and complications involved in such processes. Hence a process of electrolytic regeneration of the chromium solution, if completely worked out t o the point of commercial application, would be not only a matter of scientific interest but a real contribution t o industrial development. As an illustration, factories employ chromic acid solution for oxidation of organic compounds in the manufacture of camphor, organic acids, etc. At Submitted by Shoo Tze Leo in partial fulfillment of the requirement for the degree of Doctor of Philosophy in the Faculty of Pure Science, Columbia University, New York City.

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present, in one Kew Jersey plant, this spent liquor with about I O per cent chromium oxide, amounting t o about 2 0 0 , 0 0 0 lbs. per month, is run t o waste. If the process for electrolytic regeneration of this waste liquor can be worked out t o commercial advantage, i t means t h a t not only the trouble of disposing of acid and troublesome waste liquor and of preparing fresh chromic acid solution will be avoided, but the cost‘of sodium bichromate and sulfuric acid will be replaced by a relatively insignificant expense for electric current. LITERATURE

T h e electrolytic regeneration of chromic acid was first attempted by Fitzgerald in 1 8 8 6 , ~ using acid chromic salt solution as the anode liquor and zinc sulfate as the cathode liquor. T h e process was not practical because of the loss of zinc sulfate. I n 1893, Dr. Karl Haussermann2 described a process in which he prepared chromate from sodium chromite by electrolytic oxidation in alkaline solution and then transformed t h e chromate into bichromate. I n 1899, Dr. F. Regelsberger3 did some work along the line of electrolytic oxidation of a chromic salt

of chromic salt in acid the cathode employed was either lead, iron, nickel, or copper, the anode being lead, . Later, Dr. Karl Elbs4 in his manual gave a summary of the process of oxidizing chrome alum in acid solutions. According t o Dr. R e g e l ~ b e r g e ri,t~is the lead dioxide formed on the surface of t h e lead anode t h a t really acts as t h e agent for the oxidation of chromic salt t o chromic acid. * I n this connection Muller and Sollera made a n investigation in 1905 concerning the behavior of a lead dioxide anode ahd showed i t t o act catalytically as in the oxidation of iodic acid into periodic acid. Before this time, in 1898, Meister Lucius and Bruningr had taken out two patents, one in Germany and the other in Great Britain, in which a cyclic process for sulfuric acid concentration in connection with the electrolytic regeneration of chromic solution was devised. The process is t o place the chromic acid solution in the cathode section in place of pure sulfuric acid and then t o pass a n electric current long enough t o oxidize the corresponding liquid in the anode section. The anode liquor is t o be used directly in the works whereby chrpmium oxide is again formed and is then allowed t o flow into the cathode section when i t is again t o be electrolyzed. The solution used in the previous run in the cathode section is now used in the anode section. Before the second electrolysis 1

Brit. Patent 5,542 (1886).

2

Z.angew. Chem., 1893, 363; and Wickop, “Die Herstellung der Alkali

Bichromate,” 191 1. 8 2. angew. Chem., 1899, 1123. 4 “Elektrolytische Darstellung chemische Praparate,” 1902. 6 2. Elektrochem , 6 , 308. 6 Ibid., 11, 863. 7 Ibid., 6, 256, 0. Imray, J . SOC.Chem. I n d , 18, 685; D R. P. 103,860, June 12, 1898; Brit. Patent, 15,724, July 18, 1898; cf. also Le Blanc, Electrochem.

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the cathode solution is richer in sulfuric acid t h a n or a mixture of both was added t o the electrolyte so the anode solution b u t this time the excess migrates t h a t the cathode potential was reduced t o such extent t o the latter,solution. A cyclic process is thus carried t h a t the reduction of the chromic acid by hydrogen out in which the chromic acid solution is alternately formed a t the cathode was avoided. placed in the anode and cathode chambers, thus preSchmiedtl made a special study in 1909 concerning venting the accumulation of a n excess of sulfuric acid the addition of various agents. Some of his work in i t and making i t possible t o maintain the solution is of technical use. He found, for example: a t a given concentration during its regeneration by ADDITION CURRENT EFFICIENCY At Start At Finish electrolysis. Per cent Per cent Per cent 8 2 . 2 71.3 No addition . . . I n 1899, Darmstadterl developed a process in which 93.4 86.2 KF 1 .o 92.8 73.9 KF 0.1 he tried t o regulate the current density in such a manner 98.2 82.8 NaZHPOd 1.0 as t o make the migration of sulfate ion equal t o t h e Small quantities of boric acid, potassium cyanide and diffusion rate, so t h a t the sulfuric acid concentration sodium vanadate and molybdate also had marked effect. would be balanced. I n the same year Darmstadter2 secured another German patent in which he stated The mechanism of these actions is not understood. t h a t the current was t o be stopped for a time t o let the diffusion of the solution go on as referred t o in t h e L IN€ previous patent. I n regard t o the electrolytic oxidation in alkaline solution, t h e Chemische Fabrik Griesheim-Electron3 worked out a process in 1901 by using a mixture of chromium sulfate and sodium sulfate solutions which was kept alkaline. A soluble anode such as chromium or ferrochromium was used. T h e same firm4 developed in the same year another process which was the same as the above, except t h a t 61ASS %€AK€R an insoluble anode was used instead of a soluble anode. Le Blanc5 discussed this subject a t length and laid special emphasis on the question of diaphragm. One 4OOc c. of the methods he used t o prepare a n acid-resistant diaphragm was t o make plates which are rather plastic 100 c c. before heating by using a mixture of 2 5 per cent alumina and 7 5 per cent silica. The chief difficulty in preparing POROUS CUP such a porous diaphragm lies in combining good conductivity with good mechanical strength. Pb I n 1913, Paul Askenasy and A. Revai6 tried t o develop a technical process of chromic acid regeneration without t h e use of a diaphragm. They conducted their experiments by using high cathode current densities, b y adding magnesium sulfate, chromium sulfate, potassium sulfate, sodium sulfate, etc. Earlier, in 1905,Le Blanc' developed another process which dispensed with the use of diaphragms by employing vessels in which the cathode and anode chambers were separated by partitions which did not extend entirely t o the bottom of the vessel. The chromic FIQ.I-DISCONTINUOUS CELLFOR ELECTROLYTIC REGENSRATION OF salt solution was introduced a t such a rate as t o insure CHROMIC ACIDPROM WASTE the requisite quantity of acid in t h e cathode chamber Although there is considerable literature on the subfor the quiet progress of electrolysis. The current density was regulated so t h a t the fresh addition of ject of electrolytic regeneration of chromic acid soluchromic salt solution would be first acted upon by the tion, i t is apparent t h a t this problem is far from being completely solved. First, no special emphasis has denser current. Still another process which dispensed with the use been laid upon the nature and quantity, if any, of of a diaphragm was developed by the Chemische Fabrik t h e particular organic materials present in the Buckaus in 1906, by which alkali sulfate or acetate chromium waste t o be oxidized, a condition on which the success or failure of the process is likely t o depend. 1 D. R . P. 117,949, Nw. 3, 1899. 2 D. R . P 138,411, June 8, 1900. Second, the information given lacks the essential de8 D. R. P. 143,320, Feb. 8, 1901. tails t o insure a complete success of technical operation. * D. R . P. 146,491, March 26, 1901. Third, all the processes described in the literature are 8 Z. Elektrochsm., 7, 290. e Ibad, 19, 344-62. discontinuous, which means high labor cost and inD. R . P. 182,287, March 14, 1905, French Patent 362,195, Jan. 5, 1906; convenience in handling, consequently rendering the U. S. Patent 883,651. March 31, 1908.

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8 D. R. P. 199,248, May 9, 1906; Brit. Patent 9,636, April 25, 1907; U. S. Patent 895,930, Aug. 11, 1908.

1

istry.

Dissertation, Charlottenburg, 1909; Allmand, Applied Electrochem-

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process prohibitive economically for commercial applications. I t is apparent t h a t detailed experiments overcoming these difficulties must be made before t h e process is ready for commercial use.

t o be tested run in. The iodine liberated was titrated against standard 0 . 2 N sodium thiosulfate solution and the amount of chromium oxidized calculated. I-ELIMINATION OF O R G A N I C SIATTER A N D POSSIBILITY

EXPERIMENTAL WORK

O F REGENERATION

The present investigation divided itself into three parts: I-Elimination of organic matter and possibility of regeneration. 11-Determination of conditions in detail. 111-Continuous operation. G E N E R A L PLAN-Before each Of the Steps (as Outlined above) is taken up in detail, i t is desirable t o describe here the general plan which was followed in the early experiments. The discontinuous cell as shown in Fig. I consisted of a glass cylindrical jar with either an asbestos or porous clay cup placed in the center as a diaphragm. The anode of cylindrical shape was placed outside the cup, while the cathode was a narrow plate inside. These electrodes were made of lead. Their sizes varied for different experiments. The electrolyte consisted of the waste liquor with or without addition of sulfuric acid. In each experiment the waste liquor was first filtered through a sand bath about 2 in. deep t o remove any suspended organic matter. TESTING SAMPLES-During each experiment samples were taken from time t o time t o ascertain the acidity of the solution and the progress of oxidation. The acidity was determined by titrating against 0 . 5 N NaOH with phenolphthalein as indicator and the acid present calculated as sulfuric acid in grams per liter. The amount of chromium oxidized was determined by the iodine method. Ten cc. of I O per cent KI solution were taken, 5 cc. conc. HC1 added, and the sample

We start out in the solution of our problem with a qualitative determination of the possibility of the process. It involves two steps: ( a ) Elimination of organic matter; and ( b ) possibility of regeneration. ( a ) E L I M I N A T I O N O F O R G A N I C MATTER-The first step towards working out a continuous process for electrolytic regeneration of chromium from waste liquor is t o destroy whatever organic matter may be present in the solution. As has been said before, the waste liquor a t hand came directly from a factory in New Jersey. It contained about 230 g. sulfuric acid per liter and chromium sulfate t o a n extent of about g o g. chromium oxide equivalent per liter. There was also present organic matter left over from the process of oxidation. This organic matter is objectionable and the quantity of i t such t h a t i t gave a strong odor and a n oily appearance t o the waste. So long as the organic matter is present the process of regeneration by oxidation will be always subjected t o reversal condition, i. e., chromic acid will be reduced by the organic matter present. It was suggested t h a t a steam distillation of t h e waste liquor or a n extraction by a mineral oil might largely remove the organic matter. Tests showed t h a t neither of these was effective. Apparently t h e method of simply using t h e current is the best, if the organic matter can be destroyed by i t and not too much electric energy consumed in t h e process. This gives also, perhaps, the distinct advantage of labor and equipment economy in t h a t i t is only a single process instead of several processes.

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A series of experiments using the current t o remove the organic matter by oxidation, was conducted under conditions in which the current densities, sulfuric acid concentration, etc., varied. These experiments showed t h a t i t is quite possible t o destroy the organic matter in such waste chromium liquor simply by the action of t h e current. ( b ) P O S S I B I L I T Y O F REGENERATION-The next experiment was the qualitative determination of the possibility of regeneration, i. e . , t o what extent the waste liquor can be recovered in the dxidized form a t a reasonable expenditure of electric energy. I n other words, approximately a t what energy consumption, t o what concentration of chromic anhydride in grams per liter, and with what per cent conversion of the chromium into chromic acid can this waste liquor be regenerated by electrolysis. A series of experiments proved it possible t o regenerate the chromic acid from this waste t o an extent of a t least 65 per cent conversion a t a total current efficiency of about 3 j t o 40 per cent and a t an energy consumption of I I O t o 140 g. chromic anhydride per k. w. h. One thing which must be noted here, however, is t h a t the experiments should by no means be interrupted, as a t the points of each interruption there were always sharp decreases of current efficiency and increases in energy consumption. 11-DETERMINATION OF CONDITIONS IN DETAIL (A) EFFECT O F M E C H A N I C A L STIRRING-we know t h a t oxidation, if possible, commences in every case when the anode potential has been raised above the equilibrium value for the given system. But in practice t h e polarization effects will occur t o a greater or less extent, depending upon the fact t h a t the ion capable of combining with oxygen may be exhausted and the oxidized ion may be accumulated in the immediate neighborhood of the anode. For this reason, mechanical stirring may be used advantageously t o remove or reduce the concentration polarization by preventing the accumulation of CrZO?' ion around the anode. Air stirring may have some oxidizing effect, hence may be preferred t o any m-echanical stirring device. I n four experiments, as shown in Curve I , a comparison of the results of Expt. I with those of Expt. 2, and the results of Expt. 3 with those of Expt. 4, shows plainly t h a t the air stirring helps the process of oxidation though only t o a small extent. (B)

SULFURIC ACID

CONCENTRATION

O F THE ELEC-

TROLYTE-SUlfUriC acid is highly ionized and consequently renders the electrolyte very conductive. I n Expts. I and 2, both the anolyte and catholyte consisted of t h e original waste liquor; in Expts. 3 and 4, the anolyte was the original waste liquor, but the catholyte contained 2 0 cc. concentrated sulfuric acid t o every 80 cc. waste liquor. I n t h e following experiments the solutions, unless otherwise specified, were similar t o those in Expts. 3 and 4. The sulfuric acid was added t o maintain the acid condition in the catholyte and so prevent the precipitation of chromium hydroxide after the experiment had been in operation for some time (as was the case in Expts. I and 2).

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CURVEI-MECHANICAL STIRRING CURVE

I n Expts. 3 and 4, the sulfuric acid concentration amounted t o about I O O g. per liter a t the end of t h e experiment. Consequently, the results in Expts. 3 and 4 are comparatively better t h a n those in Expts. I and 2 , as is shown by the following data: Conversion EXPERIMENT Per cent 78.4 I............... 75.5 z . . . . . . . . . . ..... 76.9 3............... ....................... 77.6

Total Current Efficiency 54.1 57.2 58.3 65.2

Grams CrOs per k. w. h. 150 155 188 22 1

To determine quantitatively the effect of sulfuric acid concentration Expts. 6 and 4 were compared, as shown in Curve 2 . To the point of 80 per cent conversion, Expt. 4 (without sulfuric acid) gives a total current efficiency of only 6 1 . 3 per cent with energy consumption of 2 0 6 g. chromic anhydride per k. w. h.; Expt. 6 (with sulfuric acid) gives a current efficiency df 7 0 per cent with energy consumption of about 240 g. chromic anhydride per k. w. h. Thus the addition of sulfuric acid seems t o produce better results so far as the per cent conversion is concerned. On the other hand, a consideration of chromic anhydride content in the solution will throw a different light on the subject. With a chromic anhydride content of about 7 7 g. per liter, both Expts. 4 and 6 give about the same results, i. e . , total current efficiency about 7 0 per cent, energy consumption about 240 g. chromic anhydride per k . w. h. It means t h a t if we consider the chromic anhydride content there is no difference with or without sulfuric acid. Besides, as shown in Curve 2, the current efficiency will be even higher and the energy consumption lower in Expt. 4 than in Expt. 6, if a further concentration of chromic anhydride in the solution is desired. Moreover, the addition of sulfuric acid would complicate factory operation.

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(C)

CONCENTRATION

OF

CHROMIC

SALTS

IN

THE

ELECTROLYTE-A process of electrolytic regeneration

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of chromic acid may be conceived as consisting of two simultaneous processes, ( a ) discharging of oxygen ion t o form elementary oxygen, and ( b ) oxidation of the depol.arizer, C r f f f , by the elementary oxygen, t o Cr20 The depoMrization of the discharged oxygen ion by Cri++ prevents t h e oxygen concentration from reaching the value necessary for gas evolution against atmospheric pressure. To the low concentration of oxygen corresponds a low electrolytic solution pressure, and the anodic potential needed for the process is consequently less t h a n would be required for the discharge of gaseous oxygen. I t is then evident t h a t the velocity of the whole process depends essentially on the velocity of the second process. If this can keep pace with t h e velocity of t h e first process, the reaction will proceed with great current efficiency. But if the depolarization by chromium ion is slow, then the concentration of oxygen a t the anode rises, its electrolytic solution pressure increases and the anodic potential necessary for the reaction becomes greater. TO.

I

CURVEZ-HzSOa

CONCENTRATION CURVE

When the potential for oxygen discharga is reached, and part of the current produces oxygen gas instead of oxidizing chromium ions, not only will the voltage necessary for oxidation be increased, but the current efficiency will fall. The velocity of depolarization is therefore of great importance in electrolytic oxidation. Hence, i t is quite obvious t h a t increase in concentration of depolarizer, chromium ion, will serve two purposes, ( a ) t o keep down the anodic potential, and ( b ) t o oppose concentration polarization t o bring about more efficient depolarization, and t o reduce current losses. Thus i t may seem worth while t o increase

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the chromic salt content in the regeneration of the waste. A careful consideration will indicate, however, t h a t such an increase by means of concentration is undesirable. I t must be realized t h a t concentration of chromic salt by evaporation, when the sulfuric acid content is about 2 3 0 g. per liter, israther inadvisable, both because of the difficulty in handling and the high cost in operation. Another way of changing the concentration of the chromic salt is t o dilute the waste t o a certain extent. From what has been said, such procedure will no doubt tend t o make the results less favorable in so far as the question of depolarization is concerned. Furthermore, if the change of sulfuric acid is considered carefully, it is apparent t h a t a dilution of the waste will decrease not only the chromic salt content, but also the sulfuric acid strength. I t means t h a t i t will give not only a low concentration of chromic acid in the finished solution, but also a low current efficiency and high energy consumption for a definite amount of conversion. For all these reasons i t is concluded t h a t the change of chromic salt content in the waste either by evaporation or by dilution is not feasible. increase ( D ) C U R R E N T D E N S I T Y A T T H E ANODE-An in current density will a t least bring about two things, ( a ) an increase in anodic polarization and ( b ) a rise in anodic potential. With a high current density, not only more oxygen ions are discharged in a given time but also the layer of depolarizer around the anode becomes rapidly depleted. Both may cause an increase in the concentration of oxygen gas a t the anode and in consequence there will be greater current losses. High current density invariably increases the overvoltage of oxygen. Therefore, in case the substance is very difficult t o oxidize, it would be advisable t o use high current density because i t will raise the overvoltage. Under these conditions, a n increase in current density will tend t o bring the potential of oxidation and t h a t of free oxygen discharge further apart by raising the overvoltage of oxygen, thus remedying the situation. Hence, the effects of the change of current density may act favorably’ or otherwise according t o the conditions. Experiments (4,7, 8, 9, IO, 1 1 and 12) with a current density of 2, 3, 4, 7, 9, I, and 0.5 amperes per square decimeter, respectively, have been carried out for the purpose of studying the effect of current density (Curve 3). Comparison shows t h a t Expts. 4, 11, and 1 2 with a current density of 2, I , and 0.5 amperes per square decimeter, respectively, give better results t h a n t h e rest, and the last experiment (Expt. 12) is the best. It gives 7 7 per cent conversion a t a concentration of 91 g. chromic anhydride per liter, a total current efficiency of 7 2 per cent and a n energy consumption of 2 7 6 g. chromic anhydride per k. w. h. (E) TEMPERATURE-An increase in temperature will ( a ) increase the conductiv;ty of the electrolyte and consequently reduce energy consumption, ( b ) increase the velocity of diffusion of the depolarizer, and (c) lower the overvoltage of oxygen and thus facilitate

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t h a t the cathode size of the former experiment was only one-half t h a t of the latter. As the results show, a decrease in the size of the cathode for the same anode does not make any appreciable difference. EXPERIMENT

CrOa per Liter Grams

.............. 91.0 ............... 9 0 . 2

12. 15

C U R V E 3-CURRENT

DENSITY CURVE

the discharge of gaseous oxygen. Hence a n increase in temperature will always be favorable so far as the energy consumption is concerned but i t is limited by the effects of the last two conditions. With complete oxidation a rise in temperature always acts favorably because it increases t h e velocity of diffusion of the depolarizer; with incomplete oxidation of substances not easily oxidizable made possible by the overvoltage of oxygen, the reverse may hold because it facilitates t h e discharge of oxygen. According as one or the other of these two effects predominates i t will be better t o work a t a high or low temperature. I n comparison with Expt. 4, carried out a t room temperature, Expts. 13 and 14 were carried out a t IO' C. and 55' C., respectively. Curve 4 shows t h a t room temperature (Expt. 4) gives t h e best results and the yield becomes poorer if the temperature is either raised or lowered. This indicates t h a t a t a low temperature the diffusion of chromium ion is too slow t o give a good efficiency, while a t a high temperature the efficiency is lessened somewhat, probably by the discharge of oxygen.

Con-

version Per cent 77 76

Total Current E5ciency Per cent 72.8 72.8

276 293

( G ) M A T E R I A L APiD C O M P O S I T I O N O F ANODE-An anode t o be suitable for the purpose a t all must conduct electricity well and must not be attacked chemically or disintegrated t o any great extent when in use. Moreover i t exerts specific influence in two ways: One in virtue of its oxygen overvoltage, and the other depending on its catalytic influence on the reactions between oxygen and the substance t o be oxidized. When dealing with a substance t h a t is only oxidized with difficulty a t a very high anodic potential, i t is best t o use an anode which will increase the overvoltage of oxygen. I n chromic acid regeneration, however, there is not much choice as t o what kind of anode will suit the purpose. Nickel and iron will not stand the acid conditions, amorphous carbon or graphite will not work very well under oxidizing conditions, platinum gives practically zero result on oxidation and duriron is attacked by the acid under the experimental conditions. Lead is the only commercially available material which can be readily adapted for this purpose. Furthermore a lead anode forms lead dioxide on the surface, which possibly acts as a catalytic agent between oxygen and the chromic salt. I n fact, one author has even said t h a t i t is the lead dioxide t h a t actually oxidizes the chromic salt. Hard lead has been used as the anode for these experiments and i t has been found satisfactory.

(P) R E L A T I V E SIZE O F THE C A T H O D E T O THE ANODE-

I n electrolysis without diaphragm i t is generally known t h a t a high current density a t anode and low current density a t cathode will be in favor of reduction, while t h e reverse in favor of oxidation, because the chemical action varies with the electrode surface. I n this case, however, the relative size of the cathode t o the anode may not make any difference since a diaphragm is provided and the reducing effect of the cathode on the anode liquor is thus prevented. I n order t o determine this, Expt. 15 was carried o u t as in Expt. 1 2 (current density, 0.j ampere per square decimeter, room temperature, etc.) except

CrOa per

k. w. h Grams

CURVETEMPERATURE CURVE

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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY (H) P R E L I M I N A R Y TREATMENT O F

ORGANIC

MATTER

-It has already been stated t h a t before every experiment the waste was filtered through a sand filter 2 in. deep in order t o remove any suspended organic matter. Incidentally, however, one experiment was carried out under t h e same conditions as Expt. 4, but gave a much poorer result, especially during the first 4 hrs. Investigation showed t h a t this was due t o inefficient filtration of the waste liquor through t h e sand filter, indicating t h e importance of this preliminary treatment in the process. (I) DIAPHRAGM-The lack of a satisfactory diaphragm has probably hindered or prevented the commercial success of many promising electrolytic processes. A diaphragm must not be attacked or disintegrated by the electrolyte, and i t must be able t o stand mechanical strain well. A frequent renewal or repairing of the diaphragm will involve not only a high expense but also interruption or disturbance of the operations, which must be avoided in commercial work. Furthermore, a diaphragm must not be permeable t o the liquid except by the slow process of diffusion, so t h a t the anolyte and catholyte will not commingle until after a considerable period. I n other words, t h e proper porosity of t h e diaphragm calls for careful study. On the other hand, a diaphragm material should offer little resistance t o diffusion or migration of ions so t h a t the electric resistance will not be so great as t o be prohibitory. All these considerations limit the diaphragm composition t o a very few materials which will be available and suitable for electrolytic processes on a commercial scale. I n case of chromic acid regeneration, three kinds of diaphragm materials may be considered: Asbestos cloth, porous clay, and electro-filtros. The first few experiments were carried out with a n asbestos cloth cup; t h e rest of the non-continuous experiments with a porous clay cup. The asbestos cloth becomes brittle rather easily due t o action of the acid. Porous cups approach nearest t o the ideal of what a diaphragm material should be. But they are generally satisfactory for laboratory purposes only, not for large scale operation, as they are not cheap and are not available in commercially useful sizes and shapes a t the present time. Electro-filtros proved t o be the best diaphragm material t o be used in the chromic acid regeneration. It is not appreciably attacked or altered by the solutions and has a rather low electric resistance; i t stands mechanical stress well and, under the conditions used, is permeable practically only t o diffusing liquids and migrating ions. It is constructed of grains of silica, which are cemented together with a small percentage of a fused siliceous binding material and can be made in many different commercial sizes and shapes. This was the diaphragm used in the continuous runs on a rather large scale. ( K ) DISPENSING WITH DIAPHRAGM-AS referred t o in the literature, attempts had been made t o dispense with the use of a diaphragm in the electrolytic regeneration of chromic acid, but careful examination ndicates t h a t such attempts could not be successful.

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The bell jar devised by Le Blanc will not work smoothly because of the fact t h a t in case of chromic acid regeneration the raw waste and the finished solution would not be very different in specific gravity, as they would be in t h e case of alkaline cells, a condition which is essential for the success of the method. Another method in dispensing with the use of a diaphragm, as also referred t o in the literature, was t o use some chemical agents such as sodipm acetate, ammonium acetate, etc., in order t o reduce the cathodic potential so t h a t i t would not interfere with the process of oxidation. This device is not successful either, as the hydrogen gas always comes off a t the cathode and the chromic acid produced is reduced by the hydrogen gas t o a greater or less extent, no matter how much t h e cathode potential might be reduced. It means low current efficiency, high energy consumption, and consequently larger cost in use. ( L ) CATALYSIS-ASreviewed in the literature, there are some chemicals such as potassium fluoride, secondary sodium o-phosphate, etc., which may be added as catalytic agents in chromic acid regeneration. These may be helpful in improving the yield of oxidation and consequently reducing the cost of manufacturing. Just t o what extent each of these catalytic agents would affect the process of regeneration can be determined only by careful experimentation, a n d time was not taken t o go into these details in the present research. (M) N A T U R E O F THE WASTE LIQUOR-A11 the experiments described so far were carried out with t h e waste liquor, which was received in September 1918; additional waste liquor was received later. Two experiments were carried out with the second lot of waste liquor, one with a current density of 2 amperes, the other with t h a t of 0 . 5 ampere per square decimeter. From results of these experiments, i t is evident t h a t the second lot required somewhat more electric energy t o destroy the organic matter at the beginning of the experiment, because of t h e greater quantity of organic materials present; after t h e organic matter was destroyed, it worked about the same as t h e first lot. Accordingly it gave slightly lower current efficiency, and required slightly higher energy consumption than the first waste for a given per cent conversion of the chromic acid, as shown in the following comparison : WASTE

LIQUOR

C. D. Anode Amps./ Sq.Dm.

.. . . . . . . . . . .. . . . . . . . . . . . .. .. .. .. .. .. .. .. ..

First.. . . . First.. . . . Second.. . . . . Second..

2.0 0.5 2.0

0.5

Conversion Per cent 77.6 77.0 76.8 77.9

111-CONTINUOUS

CrOs per Liter

CrOs per Current k. w. h. Efficiency Grams.

91.7 91.0 85.8 87.0

65.2 72.8 55.0 62.3

221 276, 173. 245,

OPERATION

The last and most important step in solving completely the problem of developing a continuous process for electrolytic regeneration of chromic acid from waste is t o work out t h e conditions under which t h e process can be carried out in a continuous operation. Thus far only the technical details for t h e discontinuous part of the process have been worked on. To make the process commercially applicable, however,

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1920

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y

t h e market prices and the cost of regeneration of the product must be considered. The price of sodium bichromate has, of course, fluctuated greatly during the war period and has been dropping since the armistice was signed. Curve 5 shows both the normal prices before the war and the fluctuation during the war period. While i t is interesting t o note the war fluctuations, Curve 5 shows t h a t the lowest price for sodium bichromate since 1907 is 4.62 cents per pound, which means about six cents per pound of chromic anhydride equivalent. I t is probable t h a t the price will be somewhat higher. Thus a fairly stable price after the war for sodium bichromate may be safely estimated a t seven t o eight cents per pound of chromic anhydride equivalent.

Year C U R V E 5-PRICE

C U R V E FOR SODIUM

BICHROMATE (1907-1919)

From the data obtained by experiments so far, the energy consumption under the most favorable conditions for the first waste is 2 7 6 g., and for the second waste 24j g. chromic anhydride per k. w. h. These figures are based upon the chromic acid content of about 80 g . per liter, because i t is the value commercially desired for the chromic acid strength before i t can be used for oxidation purposes. It means that for the equivalent of every pound of chromic anhydride produced a n energy consumption of two k. w. h. is required. At the cost of $30 per h. p. year (0.5 cent per k. w. h.) for the electric energy, the cost for electricity alone in producing equivalent amount of one pound of chromic anhydride will be about one cent. If the cost of power is $60 per h. p. year, the normal figure for generating electricity from steam, the cost for one pound of chromic anhydride equivalent will be about two cents. This does not, of course, take into account power losses, and the costs of installation, labor, repair, and operation. Labor cost is always a large item, if not the largest, i n the cost of manufacture of a product. This is especially true in the case of chromic acid regeneration on a discontinuous operation, because i t requires ex-

23

cessive labor in handling, such as charging fresh waste, discharging finished solutions. The labor question cannot be too strongly emphasized, and is the reason why attention should be given t o working out a continuous process for chromic acid regeneration. A continuous operation would permit feeding the fresh waste liquor in a t one part and drawing out the finished solution a t the other part of the cell, giving a continuous flow of electrolyte. The only interruption would be for replacing the electrodes occasionally. Continuous operation appears very simple but consicleration of its technical details reveals many difficulties t o be overcome, among which is the adjustment of the sulfuric acid concentrations both a t the anode and a t the cathode chambers, difficult even on a discontinuous operation, where Le Blanc proposed t o exchange the anode and the cathode liquors in each subsequent operation. This will not do for a continuous operation, however, as the anode and cathode liquors cannot be exchanged but must be constant a t all times. Otherwise the change in sulfuric acid concentration would develop t o such a stage t h a t the process must be necessarily interrupted and some means for modifying the strength applied before the electrolytic oxidation can be resumed. I n the process devised the fresh waste is fed directly into the bottom a t one end of the cathode chamber, overflowing through a n orifice a t the other end of the same chamber into the anode chamber in which the level of the electrolyte is kept slightly lower. The finished solution is then drawn out continuously a t the opposite end of the anode chamber, either by a siphon or overflow. I n this way not only a continuous flow of electrolyte is insured but also the finished solution can be removed from the cell continuously. Moreover, a complete adjustment of the sulfuric acid concentration is accomplished. The acid concentration in the cathode chamber is restored by feeding in fresh waste, while in the anode chamber i t is reduced and balanced by the overflow liquor from the cathode chamber. Thus the sulfuric acid concentration in both chambers will remain practically constant and the continuity of the process assured. The next technical problem is the construction of the cell, the shape of which is important. For laboratory purposes a beaker or large jar with diaphragm cup inside is naturally the most convenient arrangement, but on a commercial scale a rectangular tank is much preferred because it is not only easier t o construct but far more convenient t o handle in the plant. The complete arrangement of the cell with both mechanical and electrical connections is shown in Fig. I . The diaphragm used here is electro-filtros. The next consideration is the concentration of chromic acid which we wish t o maintain in the anode chamber a t all times, i. e., the strength of the finished solution. According t o ordinary commercial practice a solution of about 7 0 g. chromic anhydride equivalent is advisable to use as oxidizing agent. Therefore, the anolyte, and consequently the finished solution, in the continuous process should be maintained above this limit.

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

24

In accordance with these conditions and arrangements, the first continuous experiment was 'conducted with t h e second lot of waste liquor, as follows: Anode: 7.7 sq. dm. Cathode: 5.0 sq. dm. Anolyte: 5000 cc. second waste, containing 200 g. sulfuric acid, and 80 g. chromium oxide per liter. Catholyte: 550 CC.second waste, with the same content as the anolyte. Diaphragm: Electrb-filtros, 6 X 3 X 12 in. box. With air circulatioq. C. D. CurAnode Inflow Total Temp. rent Amps./ Volt- per Hour Inflow Outflow Hour OC. Amps. Sq. Dm. age Cc. cc. cc. 4.0 70 490 490 8 1 3.9 55 710 710 8 1

The analysis and calculations of the above experiment gave the following results: GRMXSCHROMIC ANHYDKTDS

Anolyte Start per Hour Liter Total 426 7th.. 8 5 . 3 372 llth 74.5

....

Hour 7th 11th

Anolyte Finish per Liter Total 410 74.5 381 72.8

CrOs Actually Produced Grams 0.0 9.0

Current Efficiency Per cent 0.0 22.5

...... ......

Current 70 40

Power

CxV

0.22 0.13

CrOs per k. w. h. Grams 0.0 70.0

These results show t h a t current efficiency for the first 7 hrs. was zero, while for the last 4 hrs. was only 22.5 per cent, a poor result t h a t may be due t o either of t h e following reasons or both: ( a ) t h e reducing effect of t h e cathode on the waste; ( b ) the lack of sufficient chromic salt in the anolyte t o produce a n efficient depolarization.

(a)

THE REDUCING DEFECT OF THE CATHODE O N THE

the fresh waste liquor is circulated from the cathode chamber t o the anode i t is quite possible t h a t the organic matter present has been reduced further by the cathode action; thus reduced, i t may require much more current t o destroy the organic matter present t h a n would be the case in fresh waste; hence i t gives a low current efficiency. Consideration of the possible remedy discovers several methods. One is t o avoid cathode circulation, i. e., t o feed all the fresh waste liquor directly into the anode chamber instead of passing i t first into the cathode compartment. This would be the best and simplest solution of the problem but in view of t h e importance of the balance of the sulfuric acid concentration i t is impossible in continuous operation. Another method is t o reduce the cathode action by decreasing the cathode surface. It will be recalled t h a t the size of the cathode does not make much difference in a discontinuous run, since a diaphragm is provided. But when the effect of further reduction of the organic matter is considered it is clear t h a t decreasing the size of the cathode may hinder cathodic action and consequently reduce the current losses. Thus the decrease of the cathode surface may have a direct bearing on the subject. ( b ) T H E LACK O F SUFFICIENT C H R O M I C S A L T I N THE WASTE-when

ANOLYTE TO PRODUCE A N EFFICIENT DEPOLARIZATION

-It has been pointed out t h a t the lower the ratio of the chromic salt t o the chromic acid, the lower will be the current efficiency. This is perhaps the reason why the result of the first 7 hrs. in the above experiment was far worse than t h a t of the last 4 hrs.

Vol.

12,

No. I

One of the possible ways t o overcome this difficulty is t o divide the process into two or more steps, i. e . , first t o oxidize the waste t o about 40 g. chromic anhydride per liter, and then t o oxidize the latter t o the finished solution of the desired chromic anhydride content, say 7 0 g. per liter. In this way most of the chromic anhydride will be produced a t comparatively high current efficiency and only a small fraction of i t a t low current efficiency, i. e., the average current efficiency will be much increased. But any chromic anhydride in the solution is completely reduced while passing through the cathode chamber. I n the oxidation of the solution containing about 40 t o 50 g. chromic anhydride per liter t o a solution of 7 0 g. per liter, the former solution cannot be fed through the cathode chamber first, conseouently the sulfuric acid concentration is not balanced and the process is again not continuous. Another method is t o add chromic salt t o the anode liquor a t the beginning so as t o increase the ratio of this salt t o the chromic anhydride or t o use a waste liquor of higher chromic salt content a t the start. While i t may be disadvantageous t o concentrate the waste by evaporation, as said before, i t might not be a t all inconvenient t o use a solution of high chromic acid content as the oxidizing agent, so t h a t the waste liquor will be always high in chromic salt content. Therefore, this will be the best for furnishing enough chromic salt in the anode liquor t o insure efficient oxidation. On these two methods, ( a ) the decrease in cathode surface, and ( b ) t h e use of a solution of high chromic salt content in the anode chamber a t the start, are based the following experiments, carried out with t h e same waste liquor (second lot) and with other conditions as in the previous experiment, except the decrease in cathode surface (two small cathodes, I O X 6 = 60 sq. cm. each, instead of one large cathode, I O X 2 5 = 2 5 0 sq. cm.). c. n Inflow Total Temp. C. 4th.. , , 25 l l t h .... 30 19th .... 31

Hour

Current Amps. 10

10 10

Anode Amps./ Sq. Dm. 1.2 1.2 1.2

Voltage 4.6 4.4 4.4

per Hour Cc. 70 70 70

In-

flow cc. 280 770 1330

Outflow cc. 280 770 1330

The analysis and calculations of this experiment gave the following results: -Grams Anolyte Start Hour Der Liter Total 4th ............ 73.8 368 11th 73.8 368 19th.. 73.8 368 CrOa Actually Produced Power Hour Grams Current cxv 0.184 21.0 50.0 4th.. 0.313 87.5 11th 37.0 0.352 100.0 19th.. . . . 4 1 . 3

............ ..........

...

.....

CrOa-------Anolyte Finish Der Liter Total 73.8 389 73.8 405 73.8 409 CrOs Current per Efficiency k. w. h. Per cent Grams 42.0 114 42.5 117 41.3 117

The result of this experiment with decreased cathode surface is better than t h a t in the previous experiment. The following experiment was conducted with t h e first lot of waste liquor, with all conditions as in the above experiment except t h a t the chromic salt content in the solution was higher (total chromium oxide equivalent 96 g. per liter instead of only 80 g.).

,

Jan.,

T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY

1920

Current AmDs. 10

T:mp. Hour C. 10th.. , .25 20 32nd 25 57th

.... ...

10

10

C. D. Anode Amps./ Sa. Dm. 1.2 1.2 1.2

Inflow per Honr cc. 100.0 83.3 90.7

Voltage 4.5 4.6 4.5

Total InOutffow flow cc. cc. 1000 1000 3000 3000 5000 5000

The analysiiand calculations of this experiment gave the following results: Hour 10th 32nd.. 57th..

Grams CrOa----Anolyte Start Anolyte Finish per per Liter Total Liter Total 70.5 352 67.2 403 67.2 337 67.2 403 71.4 356 73.0 437

HnSOa per Liter Anode Cathode 194 151 152

........ 475 ...... 424 ...... 388

CrOs Actually Produced Hour Grams 10th 51 32nd.. , . . , . 79 57th 81

........ . ........

Current Efficiency Per cent 40.8 52.7 59.0

Power c x v 0.45 0.55 0.495

Current 125.0 150.0 137.5

CrOs per

k. w. h. Crrams 113 143 163

It is apparent from the above tables t h a t the results with the stronger liquor are very good. A superficial examination may give the impression t h a t the results obtained in this experiment on a continuous operation are not quite so good as those in a discontinuous run. But we must remember t h a t all the discontinuous experiments were carried out with entirely fresh waste liquor, and all the cathode liquors were discarded. If we should t r y t o regenerate the chromic acid from t h e cathode liquors as well as from the fresh waste, which would be necessary in commercial practice, the results in a discontinuous run would probably be no better t h a n those obtained in the continuous operations. Hence, the above experiment is entirely satisfactory in every respect; the current efficiency rather high; the energy consumption low; the chromic acid content of the finished solution up t o commercial standard, and, most important of all, the sulfuric acid concentration in both chambers practically constant. This experiment evidenced t h a t the efficiency of the process is usually low a t the beginning, gradually increases, and then comes t o a constant value. This is probably due t o the fact t h a t time is required for the formation of lead dioxide which is t o serve as a surface catalyzer. As emphasized before, the conditions are such t h a t the less the experiment is interrupted the better. Hence, the continuous process is especially desirable because i t insures no interruption for a long time. I n order t o find out t h e results which the second waste would give on a constant long run, the above experiment was continued with the feeding in of the second waste liquor instead of the first with the following results : T'mp. Hour C. 11th 26 35th.. . . . . . . 27 59th.. 30 83rd.. 31

........

....... .....

Current Amps. 10.3 10.0 10.0 10.0

C. D. Anode Amps./ Sq. Dm. 1.2 1.2 1.2 1.2

Voltage 4.2 4.5 4.3 4.3

Inflow per Hour Cc. 90 83 83 83

Total InOutflow flow cc. cc. 1000 1000 3000 3000 5000 5000 7000 7000

The analysis and calculations gave the following results:

--

HnSOa per Liter Hour Anode Cathode 11th 368 158 35th ............ 352 144 59th 338 122 83rd.

............ ............ .................

Anolyte Per Liter 73.0 72.2 73.8 73.8

Grams CrOs--Start Anolyte Finish Per Total Liter Total 365 72.2 432 361 73.0 438 369 73.8 442 369 74.6 448

CrOs Actually Produced Hour Grams 11th.. . . . . . . . 67 35th.. 77 5 9 t h . . . . . . . . . 73 83rd.. . . . . . . . 79

.......

Current 142 150 150 150

*

Power c x v 0.476 0.540 0.516 0.516

25

Current Efficiency Per cent 47.2 51.2 48.7 52.6 ~

CrOs per

k. w, h. Grams 141 142 141 152 ~~

~

From the above table, i't is clear t h a t the results for the second waste on a continuous operation are practically as good as those from the first waste, though the current efficiency is lower, due, apparently, t o the presence of more organic matter in the second waste liquor than in the first. To gauge the effect of higher current density, the above experiment was continued' with a current density of 2 . 4 instead of only 1.2 amperes per sq. dm. The following results show t h a t the energy consumption is much higher on account of lower current efficiency and greater voltage. However, it must be noted t h a t the capacity of the cell is somewhat increased. Temp. C. 40 40

Hour 6th 12th..

......... .......

C . D. Anode Amps./ Sq. Dm. 2.4 2.4

Current Amps. 20 20

Voltage 5.7 5.7

Inflow per Hour cc. 165 165

Total In- Outflow flow cc. cc. 1000 1000 2000 2000

The analysis and calculations gave the following results : Grams CrOs Anolyte S t a r t Anolyte Finish Per Per Liter Total Liter Total 74.5 373 67.5 405 6 7 , s 407 73.1 366 7 -

Has04 per Liter Hour Anode Cathode 6 t h . . , , . 330 122 12th.. 350 122

.....

Hour 6th 12th

CrOa Actually Produced Grams 32 41

........ ........

Current 150 150

Power C x V 0.685 0.685

Current Efficiency Per cent 21.0 27.3

CrOs per

k. w. h. Grams 46.7 60.0

For a given current density the capacity of the cell is directly proportional t o the anode surface. For a current density of 1 . 2 amperes per sq. dm., about onethird of a pound of chromic anhydride equivalent is produced in 2 4 hrs. for an anode surface of 8 sq. dm.; for a current density of 2 . 4 amperes per sq. dm., about four-elevenths of a pound is produced in 2 4 hrs. for the same anode surface. CONCLUSIONS

Consideration turns t3 the economic aspect of 'the process in a continuous operation. At a current density of about 1 . 2 amperes per sq. dm., the first waste can be regenerated a t a current efficiency of about 59 per cent and an energy consumption of about 160 g. chromic anhydride equivalent per k. w. h., and t h e second waste regenerated a t a current efficiency of about 50 per cent and an energy consumption of about 140 g. per k. w. h. I n other words, for every pound of chromic anhydride equivalent regenerated, about three k. w. h. of electric energy will be required. At a rate of $30 per h. p. year (0.5 cent per k. w. h.) t h e regeneration of chromic acid by this process costs for electric current only two cents per pound of chromic anhydride equivalent regenerated. By virtue of its continuous operation, it dispenses with excessive labor and costs production. With chromic acid a t 7 t o 8 cents per pound, there remains a good margin of profit on the process. Furthermore, sulfuric acid

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

26

is also regenerated in the process without additional cost. This means a saving of about four pounds of sulfuric acid for every pound of chromic anhydride equivalent regenerated. W k h sulfuric acid a t $14 per ton, this would amount t o about three cents for every pound of chromic acid regenerated. Accordingly the continuous process thus developed for the electrolytic regeneration of chromic acid from waste liquor gives promise of valuable technical applications.’ SUMMARY

Results obtained in t h e foregoing paper on developing a continuous process for electrolytic regeneration of chromic acid from waste liquor may be briefly summarized as follows: I-It has been found possible simply by the action of the electric current t o destroy the organic matter in waste chromium liquor without subjecting i t t o any preliminary treatment. 11-Conditions have been worked out, under which the process of regeneration can be conducted successfully as a continuous operation, i. e . , the fresh waste liquor is fed in a t one part, and the finished solution drawn out a t the other part of the cell without interruption. Careful adjustment of conditions and arrangements give good results: current efficiency fair, energy consumption low, chromic acid content of the finished solution up t o commercial standard, and, most important of all, sulfuric acid concentration in both chambers practically constant. It has been found t h a t for every pound of chromic acid regenerated only about 3 k. w. h. of electric energy are required. Furthermore the saving of sulfuric acid, which is also regenerated in the process without additional cost, will amount t o nearly as much as the cost of electric energy required (at one cent per k. w. h.) for the regeneration of the chromic acid. DETERMINATION OF THE WATER RESISTANCE OF FABRICS’? By F. P. Veitch and T. D. Jarrell LEATHERAND PAPERLABORATORY, BUREAUOF CHEMISTRY, U. S. DEPARTXENT OF AGRICULTURE, WASHINGTON, D. C. Received July 9, 1919

The waterproofing of canvas t o be used as coverings f o r outdoor use has long been practiced, but t h e World

War has naturally increased its importance not only for protective purposes but also as a means of prolonging the usefulness of canvas coverings and thus decreasing the expense of using them. I n developing simple and effectual formulas and treatments for waterproofing canvas, both for small scale application with a brush or as a spray and for application in large treating plants, and for testing deliveries of commercially waterproofed fabrics, i t has been found necessary t o develop practical and simple laboratory tests by which the effectiveness and probable durability of the waterproofing treatment may be judged. U. S. Patent Application 321,609. Acknowledgment is made to H. P. Holman and B. S. Levine, of the Leather and Paper Laboratory, Bureau of Chemistry, U. S. Department of Agriculture, for valuable assistance in developing the methods and equipment. 2 Read at the 57th Meeting of the American Chemical Society, Buffalo, N. Y.,April 7 to 11, 1919. I

1

Vol.

12,

No.

I

A number of methods have been proposed for testing the water resistance of fabrics. All of them, however, have been applied t o the new material without a n y effort even t o remove the first purely transitory resistance, and, furthermore, the literature on the subject does not reveal comparative studies of the value of t h e several tests. The results obtained by the different methods have not been satisfactorily standardized, nor have the results of laboratory tests apparently been coordinated with the behavior of fabrics exposed t o actual weathering or service tests. Gawalouskil describes an apparatus for testing t h e water resistance of fabrics by attaching a piece of cloth t o an open end of a graduated tube such as a burette and filling i t with a column of water 1 2 in. in height, The water dripping through is collected in a graduated measuring glass. He tested a large number of fabrics and found t h a t many allowed from I t o 6 cc. of water t o pass through in 5 hrs., while others required 16 t o 2 3 hrs. t o collect this quantity. Other samples allowed sufficient water t o pass in 5 hrs. t o fill the collecting cylinder. Dannerth2 describes a method for testing the water resistance by stretching and securely fastening a 21/2 in. square of the fabric across the mouth of an ordinary thistle tube. The tube is filled with distilled water a t zoo C. and the amounts of water t h a t pass through in 5 hrs. and I O hrs., respectively, are measured. A fabric which allows no water t o pass through in I O hrs. is considered first class. A high grade cravenette allowed all the water t o pass through in 5 hrs. Drops of water were visible on the outside of the sample 1 5 min. after starting the test. With a medium quality “raincloth” the outer surface of the fabric had become damp after 5 hrs. After I O hrs. half of the water had passed through. With a n umbrella cloth no water passed through in I O hrs. Heermann8 described several methods: BAG TEST-A square of the fabric, 50 X 50 cm., or 100 X IOD cm., is tied with strings by the four corners to a frame in such a way that a bag is formed. The bag is filled t o a given height with water a t the temperature of the room. The height of the column of water used varies, depending on the uses t o which the fabric is to be put. No dropping or trickling through of water should take place in 24 hrs., but sweating through or transudation is permitted. Uniform cloth, tent cloth, fabric for knapsacks and bread bags were tested by this method, using pieces 5 0 cm. square, filled with water t o a depth of 75 mm. After 24 hrs. the water may sweat through but should not drip through. The specifications for wagon covers for the Prussian State Railways prescribed that a piece 100 cm. square should be used and that the depth of water should be I O cm. After 24 hrs. there should be no dripping. Heermann considers one test as usually sufficient but in certain circumstances the same piece is dried and tested for a second or third time, in order to determine how the fabric stands wear. 1 Leipeiger Monatschrift, 1898, 221; also “Textile Fibres,” Matthews, p. 573, John Wiley & Sons, 1913; and “Technical Testing of Yarns and Textile Fabrics,” Herzfeld, p. 155, Scott, Greenwood & Son, 1902. 2 Textile Wovld Record, 34 (1908), 630; “Methods of Textile Chemistry,” Dannerth, p. 53. John Wiley & Sons, Inc., 1908. a Mechanisch- icnd Physikalisch-Technischc Text~luiite*suchunsen,Berlin, 1912, 232-239.