ANION EXCHANGE IN RESINS
1111
The first part of this study n-as carried out a t The Rice Institute under the guidance of Dr. 13. B. Weiser and Dr. W. 0. Milligan, to whom the author wishes to express his sincere appreciation. REFERENCES (1) ANDRONIKASHVILI, E . , A N D IS.4BADSE, I.: Acta Physicochim. U.R.S.S. 13,369-78 (1940). (2) BIKERMAN, J. J.: Z.physik. Chem. 115, 261-72 (1925). (3) BREDIG,G.:%. physik. Chem. Sa, 127 (1900). V. R . , AND URBANIC, A , : J. Phys. Chem. 48,125-33 (1944). (4) DAYERELL, (5) TORIKAI, R . , A N D YAMAGL-TI, Z.: Electrochem. J. (Japan) 5 , 63-6 (1941). (6) VERKON, A. A , , A N D KELSON,H. -4.: J. Phys. Chem. 44, 12-25 (1940). (7) WEISER,H.B., AVD MACK,G . L . : J . Phys. Chem. 54, 86-100 (1930).
RATES OF AKIOK EXCHAXGE I S IOS-EXCHANGE RESINS ROBERT I l U N I N
AND
ROBERT J. MYERS
Resinous Products and Chemical Company, Philadelphia, Pennsylvania Received April BS, 1947
Though considerable information is available for the various equilibria involved in ion-exchange reactions, comparatively very little data exist for the kinetics of these reactions. Some investigators (12, 15, 17) have indicated the rate of cation exchange to be exceedingly rapid, whereas others (3, l G ) have found that although the rate of cation exchange is rapid for some exchange substances, it is exceedingly slow for others. Wiegner and Muller (1G) and Cernescu (3) have shown the rat,e of exchange of cations in various silicates to be dependent upon the structure of the silicate. The time necessary for attainment of equilibrium at room temperature for clay, permutit, and chabazite (a natural zeolite) was shown by Cernescu to be 5 min., 10 days, and 92 days, respectively. The differences in these rates were attributed t o the differences in accessibility of the exchange sites. Since most of the clays swell in water and have most of the exchange sites a t the immediak surfaces, their ion-exchange rates are quite rapid. However, since natural zeolites do not swell and have exchange sites in the inner portions of the crystal that are only accessible by means of fine pores, their exchange rates are extremely Ion. This is in apparent agreement with the results of Emmett and DeWitt ( 5 ) and of Barrer and Ibbitson (2) on the rate of gas adsorption for chabazite. Sachod and Wood (la), in a recent study of the rates of ion exchange, have concluded that the eschange reactions for several cation and anion exchangers vere second-order, bimolecular reactions. They have also concluded that the IOIV activation energy for the exchange of ions on a sulfonated coal implies t,hat diffusion is not the rate-determining step. However, the results of Kachod and Wood on the rates of exchange in greensand, synthetic gel silicates, and resinous exchangers appear to imply that diffusion plays an
1112
ROBERT KUNIN APjD ROBERT J. MYERS
important r6le. du Domaine, Swain, and Hougen (4)have found the rate of exchange of ions in a synthetic gel silicate water softener to be dependent upon particle size. With respect to the kinetics of anion exchange, very little data have been reported outside of the data of Myers el aE. (ll),Sachod and Wood (12),and Martin and Wilkinson (9). From the data that do exist, conclusions as to the rate-determining steps, temperature coefficient, effect of extent of surface, etc. are quite difficult to make. Since many of the previous kinetic studies have been quite sketchy, have not included the evaluation of such factors as extent of surface, ion specics, state of hydration of exchange substance, diffusion, etc., and have been incidental to other work, a rather extensive study has been undertaken on the rates of anion exchange in anion-exchange resins. Although the existence of cation exchange has been widely demonstrated and accepted, the existence of the exchange of anions in many colloidal systems has not been as widely accepted. Many results have been interpreted as the molecular adsorption of acid rather than the exchange of anions. Although Mattson (lo), Jenny ( 6 ) , and Stout (13) have demonstrated the existence of anion exchangc in TABLE 1 Descriplion of reszns
i
=SIN
WATER CONIENT
~
NlTllOCEN CONTENI
1
APPkEEXT DENSITY
-8~
,I
Amberlite IR-4B. . . . . . . . . . . . . . Resin A , . .. . . . . . . . . . . . . . . . . . . . .
Resin B ........................ Resin C ......................
)cr rcnf
1
38.5
..I
77.1 53.0
I ~
60.4
i ~
,C)
u a m s per cc.
CL”f
14.0 14.4
13” 17.0
1
0.64 0.67 0.57 0.69
silicates, the exchange of anions in resinous “anion exchangers” has not been as ably demonstrated until recently. However, the data of Jenny ( 7 ) and Sussman (14).and the most recent excellent work of Wiklander (17) apparently indicate that resinous anion exchangers function as true ion exchangers. The data of of these investigators apparently indicate th.at the amine type of anion-exchange resins contains amine groups which are capable of accepting a proton or oxonium -.ion and thereby hecoming positively charged. In order to satisfy the la^ of electroneutrality, this charge is balanced by an anion which may be replaced or exchanged by other anions. EXPERIMESTIL
Xaterials The four commercially available anion-exchange resins employed in this study are partially described in table 1. Except when otherxise indicated, the particle size of the resins x a s 20-50 mesh. The resins \yere first thoroughly “regenerated” (hydroxyl form) n-ith a 1 S solution of sodium hydroxide and iinsed with distilled water until an aqueous suspension remained neutral after 24 hr. For all
ANIOX EXCHANGE I N RESINS
1113
runs (except those involving the effect of the degree of hydration) the resins were kept in a moist condition.
Apparatus The apparatus employed in this study consisted of a 1-liter, three-neck, roundbottom flask containing a thermometer, stirrer, and a pipet sampling device. The stirrer \vas motor driven with a device for varying the stirring rate. Since the reaction was found to be rather insensitive to small changes in temperature, no precautions were taken to thermostat the flask. However, for the experiments in which the effect of temperature was determined, the low-temperature runs were made in nn ice bath and the room-temperature effect study at 30°C. & 0.5". The stirring rates choren for this study were 200 and 4CO R.P.M. For all other runs thc tcmperaturc was 30°C. i 2".
Technique The ratcs of exchange ners obtained from runs in which the concentration in the liquid phase was followed as a function of time. Ten-gram samples were first placed in the flask and the stirring initiated. At a predetermined time, 500 ml. of the desired solution was rapidly added (about 5-10 sec.), and a t various time intervals samples ( 5 or 10 ml.) were withdrawn for analysis. The analyses for acid and base were performed in the usual manner with either standard acid or base, using phenolphthalein as the indicator. Chloride analyses were performed volumetrically according to the Vohr method. The course of the reaction was followed until equilibrium was reached. Equilibrium was usually attained within 24 hr. The rates of exchange were obtained by measuring the slopes along the curve formed on plotting milliequivalents (y) exchanged per gram versus time in minutes ( t ) . Slopes (dyldf) Jvere measured at several points along the curve and the concentration and amount exchanged recorded for each slope. By such a procedure it was possible to obtain the relationship between rate and concentration a t a constant fraction exchanged and the relationship between rate and the extent of exchange at a constant concentration. The initial rates were obt,ained on extrapolation to zero amount absorbed. Although a considerable amount of heat is liberated upon reaction betwzen the hydroxyl form of the anion-exchange resin and acid, the ratio of resin to liquid phase was such that the variation of temperature during any one run 11-as less than 1'C. The reproducibility of the rate measurements was first checked by performing several runs under very similar conditions. The results presented in figure 1 indicate that the reproducibility was quite good. The slight difference between the runs at 200 R.P.M. may easily be accounted for by the slight difference in the initial concentration. The effect of the stirring rate was investigated by comparing the rate curves obtained for two runs which were identical except for the fact that the stirring rate of one was 200 R.P.M. and that of the other 400 H.P.M. It is quite evident from the results presented in figure 1 that the effect of the stirring rate in the range studied was but slight.
1114
ROBERT KUNIN AND ROBERT J. MYEXS
I’ariables studied In this investigation the effects of concentration, anion species, particle size, neutral salts, temperatures, amount exchanged, stirring rate, and state of hydration upon rate of eschange were studied. Anion systems were studied which included the anion-exchange processes commercially designated as acid adsorption, regeneration, and anion interchange. For the acid adsorption cycle, hydrochloric, sulfuric, phosphoric, and acetic acids were studied in the range 0.01-1.0 N . The regeneration rates were studied using sodium hydroxide (0.1 N ) as regenerant for a resin which had previously adsorbed chloride. Rates of anion interchange were obtained for the interchange of chloride and sulfate ions by following the rate of exchange on the addition of sodium sulfate to a resin saturated with chloride.
5.
a a E
P ‘-
1115
ANION'EXCHhhGE IN RESINS
DllYETER
O4IYY.
v) 150
a
5
10
I5
20
25
30
T I M E (MINUTES)
FIG.2 Effect of particle size on rate of adsorption of hydrochloric acid b y Amberlite IR-4B
FIG.3. Effect of particle size on parabolic rate constant
(where yt and yware the number of milliequivalents adsorbed at time t and at equiYt against librium, respectively, and where k is a constant), by plotting -
Y-
4,one
finds that fair agreement is obtained and that the slopes of these lines are pro-
1116
ROBERT KUNIN AND ROBERT J. MYERS
portional t o the reciprocal of the diameter of the particles. This is in perfect agreement with the diffusional theory and is quite similar to the results obtained by Barrer and Ibbitson (2) on the diffusion of gases in zeolites. In order to determine the effect of the state of hydration of the resin gel upon the rate of exchange, the rate of exchange for an air-dry sample of Amberlite IR-4B was compared with the rate of exchange for an identical sample that had been pre-soaked in water for several hours. The air-dried sample of resin contained less than 5 per cent moisture, whereas the pre-soaked resin contained approximately 60 per cent moisture. The rates of anion exchange were compared with 0.1 normal hydrochloric acid at room temperature. The data for this experiment, as shown in figure 4, indicate that initially the rate of exchange
a E W
10
TIME
0
20
n
30
(MINUTES)
FIG.4 . Effect of state of hydration on rate of adsorption of ' hydrochloric acid lite IR-4B.
for the pre-soaked sample \\-as much higher than for the air-dried sample. However, after the first 5 min. the differences became much smaller, indicating that for resins that were not fully hydrated, the initial rate of exchange would depend markedly upon the rate ot hydration. In view of these results all resins were kept fully hydrated for subsequent rate measurements.
Effect of concentration and amount exchanged upon the rate of exchange The effects of concentration and the amount exchanged were investigated by determining the rate curves for varying concentrations of acids. In order that the effects of concentration and extent of exchange could be separated, the rates (as determined by the slopes of the exchange-time curves) were obtained at various concentrations for. n fised concentration. This was determined for
ANION EXCHAKGE I N RESINS
1117
several acids (acetic, hydrochloric, sulfuric, and phosphoric), using ilmberlite IR-4B. For the remaining resins, rate curves Tyere obtained for two concentra-
I
TIME(MINUTES)
FIG 5. Rates of adsorption of acetic acid by .4mbrrlite IR-4B
067BN-
/
5-
z
a
IL
? 0 v) 4 v)
3-
z W
23
2-
O
00355N
w
g
J
1.
-0OOSBN 5
IO
15
20
25
30
31
_o
40
45
SO
SS
60
T I M E (MINUTES)
FIQ.6. Rates of adsorption of hydrochloric aacid c d by Amberlite IR-IB
tions of hydrochloric acid. The rate curves for these experiments may be seen in figures 5 , 6, 7 , 8. If the rates are taken for various degrees of adsorption or
1118
ROBERT KUh'IN AND ROBERT J. MYERS
exchange, the rates are directly proportional to the concentration for a fixed quantity exchanged. This is quite evident from the plots in figures 9, 10, 11.
5 102N 0 490N
a
02575N
OI226N
a0651H
a0192N
a
IO
IS
20
2s
30
4s
40
36
-
50
s KI
TIME (MINUTES)
FIQ.7. Rates
of adsorption of sulfuric acid by Amberllte I R 4 B
01871 H
-
00934N-
I
.
5
.
10
.
I5
.
20
.
25
.
30
.
Js
.
40
.
45
.
SO
.
55
.
60
TIME (MINUTES)
FIG.8. Rates of adsorption of phosphoric acid by Amberlite IR-4B
As:might be expected for a diffusional process, a t any fixed concentration the rate is dependent upon the extent of exchange. This is in accord with the diffusion theory. It is quite interesting to note that the rates of exchange for
1119
ANION EXCHANGE IN RESINS
e)
the various acids on Amberlite IR-4B are HC1 = CHsCOOH Whereas the initial rates,
< HsSO, < HsPO,.
, may be expressed by the equation
($!)
=
kC
(figure 12), the rates as a function of the extent or degree of exchange cannot be
FIG.9. Rates of adsorption of hydrochloric acid by .4mberlite I R 4 B
expressed by the same equations. However, the following equations appear to describe the relationships:
log
($)
HaPo,
=
k log C(y=
- yt)
4
1121
ANION EXCHANGE IN RESINS
It is quite interesting to note that with the exception of Resin A, all resina apparently behaved quite similarly, although there are variations in exchange capacities. Application of the diffusion equation, !!!- = IC&
Y-
(figures 13, 14), to
these resins apparently indicates that the rate-determining step is one of diffusion for the resins other than Resin A. Resin A yields results which indicate that an appreciable fraction of the exchange is somewhat independent of diffusion and
CONCENTRATION
(NORMALITY)
FIG.12. Initial rates of acid adsorption by Amberlite IR-IB
takes'place at the surface. This is in agreement with the fact that this resin is supposedly prepared on a porous base. Mobility of exchangeable ions In figure 15 is shown the effect of interrupting a rate study prior to attainnient of equilibrium by separation of the liquid and solid phases. On resuming the reaction, it is quite evident that the rate of exchange is much greater than it
4.m 7 -5
a 1122
ASION EXCHAKGE IK RESIKS
1123
would have been had no interruption taken place. This efl’ect is undoubtedly due to a dilution of the surface chloride ions, brought about by exchange ivith some of the internal hydrosyl ions.
Effect of temperature The effect of temperature (figure 16) was investigated by lowering the teniperature to 1°C. and following the rate of exchange, utilizing 0.1 iL’ and 0.5 S hydrochloric acid on hmberlite IR-4B. Although an appreciable lowering of the rate x i s observed for both concentrations, t>hecalculated energy of activation as obtained from the slope of the plot of log rate vs. 1/T was 6600 cal. This value is approximately equal to that obtained for the diffusion of hydrochloric acid in water.
I
R E b C T l O N INTERRUPTED I F O R 24 HOURS
I
I
TIME (MINUTES)
FIG.15. Effect of reaction interruption on the rate of adsorption of hydrochloric acid by Amberlite lR-4B.
Effect of salt concentration The addition of sodium chloride to the hydrochloric acid appeared to have a noticeable effect on the rate of exchange. The results (figure 17) indicate that the rate increases with increasing concentration of sodium chloride. Although’ some exchange is evident on the addition of sodium chloride without hydrochloric acid, the extent of the neutral salt exchange is negligible. This is evident from the equilibrium values obtained for the hydrochloric acid-sodium chloride mixtures. It is apparent then that the weakness of the basicity of the hydrosyi form of the exchanger is such that exchange of anions other than OH- is negligible a t neutral pH’s. Ut.iliaing the diffusion equation of MacDougall ( 8 ) ,
1124
ROBIRT KV" AND ROBERT J. m R S
T I M E (MINUTES)
FIG.16. Effect of temperature on rates of adsorption of hydrochloric acid by Amberite IR-4B.
I I
2
.
3
4
5
6
CONCENTRATION OF NaCl [NORMALITY)
FIG.l i . Effect of sodium chloride on rates of adsorption of hydrochloric acid by Amberlite IR-4B.
where D = diffusion coefficient, [ ] = concentration, and U = mobility, one obtains excellent agreement (see table2) between the calculated and experi-
1125
ANION EXCHANGE IN RESINS
mental rates of exchange in various sodium chloride solutions. This is further evidence for the theory that diffusion is the rate-determining step in the exchange reactions being studied.
Effect of stirring rate The results (figure 1) obtained on varying the rate of stirring from 200-400 R.P.M. during the rate of exchange studies indicated that this factor hadslittle effect on the rate of exchange. This is further evidence for the diffusional mechanism. Although the results obtained on the effect of stirring in this study apparently disagree with the results obtained by Martin and Wilkinson (9), the results obtained by these investigators are apparently due to the presence of some soluble alkali that had not been rinsed from the resin. Their data apparently indicate this. TABLE 2 A comparison of the rates of anion exchange in water and in sodium chloride solutions (Hydrochloric acid on Amberlite IR-4B) U T E IN
CONCENTPATION
or KaCI Experimental
molcr )cr lilcr
0.1 1.0 5.2
I
i
1.43
2:
“&Cl/n*n
1
M
HzO
Calculated irom MacDougall’s equation (8)
1.75 2.95 3.27
1126
ROBERT KUNIN AND ROBERT J. MYERS
L
. 5
. IS. P. 25. w. 3s. 40. 40. 50. 55. 60.
10
T I M E( MIN UTES)
FIG.18. Rate of hydroxyl-chloride anion exchange on .4mberlite I R 4 B
5 l.,i:
I
1127
.4SIOX EXCHAKGE IK RESISS
-4mberlite IK-413. Hoivever, since only t\vo points (equilibrium) were obtained for the other resins, complete equilibrium isotherms were not obtained. ,4
I
Om1
0002
0003
OW4
O
W
0005
--- .
0007
0000
0009
001
E P U I L I B R I U M G O U G E Y T R A T I O N ILIILLIEQ JI I A L E N T S / M L ) FIG 20 Adsorption isotherms for Amherlite IR-4B in dilute range
i:::/ p IO, z w _I
8-
U 3
nc1-
H -zs/O' 6-/
0 w 4 A
5
2-
ai
02
o?)
04
05
06
07
08
a9
IO
comparison of the equilibrium capacities of the various resins and the variation of capacity with acid species are shown in table 3. Owing to the fact that the equilibriuni capacity was dependent upon concentration, the comparison of
1128
ROBERT KUNIN AND ROBERT J. MYERS
equilibrium capacities n as made at a concentration at which the isotherms apparently leveled oft’. The variations in the exchange capacity with respect to the various acids are quite similar to the results obtained by Myers et al. (11) : however, the data do indicate that with sulfuric acid there exists an exchange for both SO,-- and HSO,-. The adsorption or exchange in the case of phosphoric acid procceds as if HJQ- were the only ion exchanged. Keither the Freundlich nor the Langmuir isotherm was able to fit the data over the concentration racge investigated.
Heat of adsorption or exchange The heat of adsorption as calculated from the data obtained for the reaction between hydrochloric acid and Amberlite IR-4B at 1°C. and 30°C. is 8.1 kg.-cal. p r mole. The heat of adsorption as measured calorimetrically was found t o be 8.7 kg.-cal. per mole. TABLE 3 Equilzbrium capacities of several resins
I
PESlN
ACID
ACID CONCENTI4TION
CAPACITY
g,om
Amberlite IR-4B . . . . . . . . . . ,-. Amberlite IR-4B . . . . . . . . . . . Amberlite IR-4B . . . Amberlite IR-4B. . . . . .” .’ . . . . . Resin-$. . . . . . . . . . . . . . . . . . .! . Resin A , .. . . . . . . . . . . . . . . . . . . . Resin C . . .. . . . . . . . . . . . . . . . . . . .
.-,I
~~
HCl CHsCOOH HrSOa
I
HzPOa HC1 HCI HC1
~
,
0.5 0.5 0.5 0.5 0.5
~
1
’
9.20 6.45 11.6 27.7 9.29 7.00 7.43
mi:
3 60 2.53 4.55 10.9 1.49 2.00 2.44
~
* Apparent
volume of resin corresponding t o a bed volume. DISCUSSIOh- OF RESULTS
The results obtained in this study indicate that the rate-determining step for the exchange of anions in most exchange resins is apparently the rate of diffusion of the ions through the gel structure. Considerable evidence is available to support this theory: ( 1 ) The fact that the rate of exchange is dependent upon the particle size of the resin is in excellent agreement with the “diffusion theory.” According to the parabolic diffusion law (1): -
=
kz/t
!4m
k is a function of the diameter of the particle. The data presented in figures 2’and 3 illustrate this effect quite Tvell. (2) The fact that the rate of stirring had but a negligible effect on the rate agrees with the theory that diffusion is the rate-determining step and not the rate of acid supply to the resin surface. (5)The kinetics of the exchange appears to support the diffusion theory quite well, since the rate is dependent upon the degree of saturation of the resin particle
AUION EXCHANGE I N RESINS
1129
as well as upon the concentration. (4) The dependence of the rate upon the age of the partially saturated resin also supports the diffusion theory, in that this effectcan only be explained by the diffusion and exchange of ions from the outer portion of the resin into the inner portion of the resin, thereby permitting the outer portion to exchange anions a t a greater rate. This evidence, as shown in figure 14, also indicates the exchangeable ions to be quite mobile. (6) The fact that the activation energy of the exchange for the reaction between hydrochloric acid and the hydroxyl form of the .4mberlite resin is of the order of the activation energy for the diffusion of hydrochloric acid in water is in good agreement with diffusion being the rate-determining step. (6) The effect of neutral salts upon the reaction rate between hydrochloric acid and the hydroxyl form of the resin is also in agreement with the diffusion theory, in that the effect of anion concentration upon the rate agrees with the diffusion equation of MacDougall (8). In view of the results obtained.in this study, it is quite apparent that the rates of anion exchange in most commercial anion-exchange resins are dependent upon the particle size, the temperature, the concentration, the degree of resin saturation, the ionic species entering the exchange, and the gel structure of the resin, and that the actual ion-exchange process is practically instantaneous as the ions diffuse into the sphere of the exchange site. These conclusions are essentially identical with those of Jt’iegner and Muller (16) and Cernescu (3) on the rates of cation exchange in silicates. Were all the exchange positions located at the surface of the gel particles the exchange rate would no longer be dependent upon the diffusional process but would depend only upon the rate of supply of ions to the resin surface and upon the rate of diffusion of ions from the resin surface. All resins stddied, with one exception, apparently exhibited very little surface exchange. The exception, Resin A, appears to have a larger fraction of its total exchange at the surface than the other resins. However, since the particle-size distributions of the various resins were not identical, it is difficult to compare the various rate constants quantitatively. The effect of anion species on the rate of exchange is quite interesting and is indicative of anion exchange rather than molecular acid adsorption. Were hydrochloric, acetic, sulfuric, and phosphoric acids adsorbed molecularly, one would expect hydrochloric acid to have the faster rate because of its higher diffusion coefficient. Tbe increase in rate with increasing functionality of the acid may possibly be due to the greater charge on the anion and therefore a greater attractive force. .Ilthough one may argue that phosphoric acid and possibly sulfuric acid .at higher degrees of acidity are only monobasic, in the intermicellar liquid of the resin particle (especially where a large concentration of hydroxyl ions is still available) the system may be sufficiently alkaline for complete neutralization of the polybasic acids. The fact that acetic acid and hydrochloric acid (both monobasic acids) exhibit similar rates, although they hare widely different ionization constants, is in agreement with this concept. The weakly acid nature of acetic acid is exhibited in the final equilibrium capacity.
1130
BAL KRISHir’h AND SATYESHWAR GHOSH SUIM3fIARY
A study of the rates of anion exchange in resinous exchangers has indicated the rate-determining step to be the diffusion of ions through the gel structure and has shown that the rate is dependent upon factors such as ( I ) particle size, ( 2 ) ion species, ( 3 ) concentration, (4) temperature, ( 5 ) degree of exchange saturation, ( 6 ) degree of hydration of resin, and ( 7 ) degree of mixing of exchangeable ions. The authors are indebted to Mr. Edward Iiyser for his extensive assist,ance in the laboratory during the course of the study. REFEREXCES (1) RARRER,R . M.: D i f u s i u n in and throuqh Solids. University
(5) (6) (7) (8) (9) (11) (12) (131 (11) (15) (16) (17)
Press, Cambridge
(1943). EMMETT, P. H . , A N D DEWmr, T. It’,: J . A m Chem. SOC.65, 1263-62 (1943). JESNY, H . : Kolloidch?m. Reihefte 23, 428-i2 (1927). JENNY,H.: J . Colloid Sei. 1, 33 (1916). MACDOTGALL, F. H . : .J. Phys. Chem. 38, 945 (1938). G,. J., A N D WILIINEOK.J . : Gastroenterology 6, 315 (1946). ~IARTIK ., A K D WIKLAXDEH, L.: Soil Sci. 49, 100-53 (1940). ~ I Y E X SR,. J., E.ksric6, J. W . , A N D URQI’HART, D . : Ind. Eng. Chem. 33, 12-70 (1941). F. C . ANI) WOOD,W.:J . Am. Chem. SOC.66, 1380-4 (1944). XACHCD, STOCT,P. P . : Proc. Soil. Sci. SOC.Am. 4, 177 (1939). , C., A K D WOOD,W.;Ind. Eng. Chem. 37, 618 (1915). SI.SSI\IAN,S., X ~ c a o n F. WALTON,H. F.: J . Franklin Inst. 232, 318 (1041). WIEOKER,G., A N D .\I?LLER,K . L Y : Trans. 3rd Intern. Congr. Soil Sei. 3, 5-28(1936). WIKLANDER, I,,: Ann. Roy. Agr. Coll. Sweden 14, 1-171 (!946).
ON THE HETEROGENEOI-S CATALYTIC ACTIT’ITY OF COLLOIDAL SILVER I S THE REDUCTIOS OF SIIJVER ACETATE B;iL Iilt ISIIiYA Ah-D SATYESHW’IR GHOSH I’hysicul Chcmislr!/ Laboratory, Cniversit!) of Allahabad, Allahabad, I n d i a
Receiced October 16, 1946 Revised eopll receii3ed A p r i l 16, 1947
The rble of silver as catalyst in the reduction of silver salts has been studied by Sheppard (10) in the silver nitrate-sodium sulfite reaction. Livingston and Lingane (8) have observed catalysis by silver in the reduction of silver ions by hydroquinone. Much valuable work has been done in this connection by James, who has studied the reduction of silver ions (2, 3, 4, 5) and of precipitates of silver chloride ( G ) . Chakarvarti and Ghosh (1) have observed catalysis by
