V O L U M E 27, NO. 6, J U N E 1 9 5 5
951
Rinse out the titration vessel with distilled water and then add
The value for Bureau of Standards S o . 98 is shown as a range, since only tT7-o values were available on the certificate (0.06yo sulfur trioxide and 0.08% sulfur trioside) and they did not seem to warrant use of a definite value of 0.028% sulfur.
50 ml. of starch solution, 2 ml. of hydrochloric acid, and enough standard potassium iodate solution t o give a faint blue color to the mixture. Insert the boat with sample into the Combustion tube and center it in the combustion tube liner in the hot zone (1310’ to 1320” C.) of the furnace. Replace the stopper and, with the three-way stopcock in the oxygen line turned to the off position, set an interval timer for the 1-minute preheat period. After the sample has heated for 1 minute, turn the stopcock to admit oxygen at the rate of approximately 1 liter per minute. This flow rate should not be changed - after the factor has been established. As the sulfur dioxide flows into the starch-iodide solution it is titrated continuously with the standard potassium iodate solution, keeping the solution a faint blue color a t all times. Each operator should determine from experience the depth of blue color he prt=fcrs for the end point and use that end point for a11 determinations. This titration should not take more than 3 minutes. Rinse the titration vessel n-ith distilled water and prepare for the next determination. Turn off the oxygen a t the three-way stopcock, remove the inlet stopper, withdraw the boat, and visually inspect it to see whether a good fusion has taken place. Discard the hoat n i t h fusrd mateiinl, as the boats are not reused in this method. The sulfur content of the sample is calculated thus: (Buret reading - correction for steel flux) X factor =
Table 111. Percentage of Sulfur. Bureau of Standards Samples Sample KO.
la 88 97 98
Combustion Method.
hv.
0.27 0.027 0.017 0 027
Combustion Method, Range of 1 3 Runs 0.273-0.216 0.025-0.028 0.016-0.018 0.026-0.028
ACKXOFLEDG3IENT
Acknorvledgnient for preliminary work on temperature of combustion and use of t i n ns n flus is made t o E. R. Vance, Timken Roller Bearing Co. The rew1tP of his work hnve nut been publiPhed. LITERATURE CITED
yo S
(1) Am. Soc. Testing lIaterials, Philadelphia. Pa.. “Book of ASTXI Standards,” Designation C 25-47, Vol. 3 , p. 22S, 1952. ( 2 ) .Zm. Soc. Testing Materials, Philadelphia, Pa., “ AIethods for Chemical .Inalysis of lletals,” 1950. ( 3 ) Hillehrand, TV. F., and Lundell, G. E. F.. “.Ipplied Inorganic .Inalysis,” Wiley, X e w T o r k , 1929. (4) Laboratory Equipment Corp., St. Joseph, Ilich.. “Instructions
The factor is obtained from Sational Bureau of Standards samples of the same approximate compoqition and sulfur content as the unknown samples. R E X LTS
The method gave highly reproducible and accurate results n-hen the combustion values Lvere compared against National Bureau of Standards samples of limestone ( S o . la), dolomite (No. 88), and clays (h’os. 97 and 98). The certificate values shown in Table I11 are the values for sulfide sulfur and sulfur trioxide taken from the certificates and recalculated to total sulfur.
Certificate Value. (Recalculated) 0.27 0.027 0.017 0.024-0.03‘7
for Leco Sulfur Deterininator for Iodometric AIethod with Special .Iccelerator. ” 1950. ( 5 ) Vance. E . R., Tiniken Roller Bearing Co., Canton, Ohio, personal communication. RECEIVED for r e r i e x October 7 . 19.54. Accepted February 7 , 1955. Presented a t t h e Pittsburgh Conference on .\nalytical Chemistry and Applied SpectroscoL>y, March 2, 1933. Published with the permission of t h e State Geologist, Indiana Department of Conservation, Geological S u r r e y .
Test for the Vicinal Dithiol Group DAVID H. ROSENBLATT and GEORGE N. JEAN Chemical Corps Medical Laboratories, Army Chemical Center,
Manganous acetate in a system containing pyridine and water may be used as a specific reagent for vicinal dithiols. Eleven representative monothiols and one nonvicinal dithiol fail to give the test. Under suitable conditions vicinal dithiols may be estimated in the presence of monothiols and nonvicinal dithiols.
T
HE use of compounds containing thiol groups on adjacent
carbon atoms, especially of 2,3-dimercapto-l-propanol (variously knon-n as D T H , British antilewisite, B.4L, or dimercaprol), in the treatment of arsenical and heavy metal poisoning has been a subject of continuing interest. I n a comprehensive Stocken review of the literature on 2,3-dimercapto-l-propanol, and Thompson (11 ) indicated that few studies had been made of the chemical reactions of this substance. The only analytical method for aliphatic vicinal dithiols noted by those authors is that of Aldridge (I), which the present ttuthors have found to be long and involved. to require hazardous reagents and expert technique, and to be applicable, in its present form, only to very dilute solutions. Other authors (a,9, 10) have noted the color with heavy metals, and the reactions of 2,3-dimercapto-l-propanol limitations of these reactions for analytical methods. It was the object in the present study to evolve a relatively simple test as a part of the positive identification of 2,3-dimercapto-l-propanol.
Md.
I n particular the authors wanted to distinguish it from 1,3-di mercapto-2-propanol, which presents similar physicochemica properties. The difference b e h e e n the reaction of 2,3-dimercapto-l-propanol with manganous acetate in pyridine and that of 1,3-dimercapto-2-propanol was first observed by the authors during a study of the conductometric titration of these dithiols with heavy metal acetates in pyridine ( 7 ) . I t was noted that there was a substantial difference in the conductances of the dithiol solutions after addition of manganous acetate, and, more rdevant to the present work, that rrhen the nitrogen sweep was terminated and the solutions were exposed to air there were decreases in both conductance and color (dark green). These decreases were comparatively rapid in the case of the 1,3-dimercapto-2-propanol. whereas the color produced by 2,3-dimercapto-l-propanolappeared sufficiently stable for colorimetry. Under similar conditions, 2-mereaptoethanol produced a much less intense coloi (lavender) and a far lower conductance. I t has been reported (2) that manganous ion fails to give a cola! reaction with 2,3-diniercapto-l-propanolor to catalyze its oxidation in neutral aqueous solution. I t is also noteworthy that toluene-3.1-dithiol.under the acidic conditions of the test for tin ( 1 3 ) , forms neither a colored complex nor a precipitate with as much as 1% manganous sulfate. On the other hand, there is
ANALYTICAL CHEMISTRY
952 evidence in the literature that in sufficiently alkaline solution manganous ion can form colored complexes ( 4 , 22). EXPERIMENTAL
Apparatus. The Beckman Model DC spectrophotometer v ith quartz cells of 0.996-cm. light path was used for absorbance measurements. A Klett-Summerson photoelectric colorimeter with a No. 5G filter mas employed for colorimetric measurements. Materials. Monothiols were obtained from commercial sources. 2,3-Dimercapto-l-propanolwas purified bv precipitation as the mercury mercaptide and regeneration N ith hydrogen sulfide, followed by distillation a t 2.7 mm. 1,3-Dimercapto-2-propanol was made from 1,3-dibromopropanol according to the general procedure of Sjoberg ( 8 ) . Toluene-3,4-dithiol was prepared according to directions in "Organic Analytical Reagents" (13),and lj2,3-propanetrithio1 by the method of Miles and h e n (6). -411 thiol solutions were made up in isopropyl alcohol and uied the same day. All manganous aretste solutions rvere mad? up in vatt.1. f ~ o m C.P. lln(OCOCH8)2 i H & .
60
40
300
400
i
I
500
600
x)O
WAVE LENGTH h 4 ~
Figure 1. Spectral absorption of 2,3-dimercapto-l-propanol manganous complex in pyridine-2propanol-water (4: 1: 1)
2,3-dimercapto-l-propanolis oxidized by the air more rapidly in pyridine and in aqueous solution than in alcohol; manganous acetate, in pyridine (but not, in water) is also oxidized by the air, as evidenced by the rapid coloring of concentrated solutions; and the presence of a greater ratio of n-ater to pyridine than t h a t 0.lM finally arrived at, or the use of aqueous buffers-e.g., trishydroxymethylaminomethane adjusted to pH 8.3 with hydrochloric acid-instead of pyridine result in excessively rapid fading. The color developed with aqueous buffer solutions was brown, rather than green. [In one series of esperiments methyl Cellosolve was used as a solvent for BbL, but it interfered seriously with the test,, decreasing the niasimum color and delaying its attainment (which is usually instantanequs when excess manganous acetate is present).] RESULTS
Fading. Under the condition^ of these esperiments it n-as inevitable that fading, due to oxidation, should occur during spectrophotometric measurements. The error thus introduced \vas minimized by exact timing. The use of a large excess of manganous acetate accelerated fading someivhat, and the proportionate fading rate increased with derreajing concentration of the dithiol. Absorption Spectrum. The spectrum of the complex formed from 0.OlOM manganous acetate and 0.013.11 or 0.0011J1 2,3dimercapto-1-propanol \vas determined for the range 320 to TOO mM (Figure 1). For the curve in Figure 1, the molar absorptivities ( 3 ) were calculated on t'he assumption that complet'e reaction had occurred and t,hat there n'as no volume change on mixing the solvents. The values for maxima and minima thus obtained are shown in Table I. The choice of a particular wave length or colorimeter filter for quantitative determinations is someivhat arbitrary, since the spectrum contains no sharp peaks; when it is convenient to employ larger concentrations of the dit,hiol it' may be advisable to choose a minimum in thr absorption curve. Larger concentrations have t,he advantage of greater stability toward oxidation, both for the unreacted dithiol and for t8hecomplex. Linearity of the Test. The linearity of absorbance (optical density) a t 490 mp versus 2.3-dimercapto-1-propanolconcentration was established with 0.01223/ manganous acetate and dilutions of a 0.012351 2.3-dimercapto-1-propanolstock solution. Result,s are shoxvn in Table 11. The linearity of the resnlts is evidentlj- only fortuitous, as it appears that a t the concentrations involved formation of the complex is not quite complete. This is shoivn by an esperiment in Tvhirh 0.00683J1 2.3-dimercapto-l-
Table I. Molar Absorptivity of Jlanganous Acetate General Procedure for Spectrophotometric Measurements. Complexes of Dithiols Four milliliters of pyridine, 1 ml. of manganous acetate solution, 2,3-Diniercapto-l-propanol Toluene-3,4-dithiol and 1 ml. of thiol solution are pipetted, successively, into a 30-ml. JYave Molar Wave 11olar-beaker. Timing and addition of the thiol solution are begun length, abaorptirity length, absorptirity simultaneously. ;Is soon as the thiol solution has been added the mir index inir index beaker is swirled vigorously. At 20 seconds the solution is poured 333 0 . 3 x 103 337 !.C!5 X 10' Maxima into the quartz cell. The spectrophotometer is balanced and the 3 7 x 102 550 a . 3 X 102 575 absorbance is then read a t eyactly 1 minute, and a t intervals Xinima 494 1 9 x 102 33.5 6 . 9 X 103 thereafter if desired. Blanks consist of 494 4 . 6 x 109 a mixture of 4 nil. of pyridine, 1 ml. of water, and 1 ml. of 2-propanol. The choice of water, rather t h i n t h e aqueous Table 11. Tests for 2,3-Dimercapto-l-propanolUone and Mixed with manganous acetate reagent, in this miy1,3-Dimercapto-2-propanol ture was made because manganous aceAbsorbance a t 490 X u tate in the presence of pyridine is l l o l a r Concentration 0.0122.1.I Manganous Acetate 0 122.11 Xanganous Acetate initially colorless but gradually becomes n $,.A:"" colored, so that a fresh blank would have been necessary for each determina.. 0.0088 .. 0 005 0 003 0.003 .... tion. 0,059 37 21i 0 094 0 063 0.085 .... 0 0025 28 0 . 1 3 5 0 188 0 139 17 The considerations that led to the final 0.107 ,... 0 0049 23 0.221 13 0 286 0 215 0.248 .... 0 0074 choice of solvents, subject to some vari21 0 300 10 0 379 0 296 0.330 0 0008 . . . . ation, are these: When the reaction 18 0 173 0.390 0 365 9 0.403 .... 0 0123 .. 0.016 0 009 0 010 0.010 0.0122 between 2,3-dimercapto-l-propanoland 54 0,084 0 184 0 10.5 39 0 172 0,0098 0 0025 manganous ion takes place in pure pyri32 0 216 0.148 21 0 186 0 . 2 3 5 0.0073 0 0049 24 0.218 0 286 15 0 241 0.283 0 0049 dine solution, the resulting color changes 0 0074 21 0 380 0.301 10 0.342 0 306 0.0024 0 0098 gradually from green to cherry red, which fades and ultimately disappears:
V O L U M E 2 7 , N O . 6, J U N E 1 9 5 5
953
0.91
oa07-
!B
06-
v)
2
01-
04-
0.4
01
/ C2,3-DIMERCAPTO-I-PROPANOLI C 2,3 -0IMERCAPTO-I- PROPANOL1 + L Mn (OCOCH.)zl
Figure 2. Continuous variations plot for 2,3dimercapto-1-propanol m a n g a n o u s acetate reaction, w i t h [2,3-dimercapto-l-propanol] [-Mn(OCOCH,),] = 0.00684M
+
propanol was tcst,ed n.ith incmising concentrations of manganous acetate (Table 111, 2,3-dim~~capto-l-propanol). Nature of Complex. In an attempt to determine the composi11) complex! tion of the 2,3-dimercapto-l-propanol-manganese( to manganous acetate \vas the ratio of 2,3-dimercapto-l-propanol changed according to the method of continuous variations ( 5 ) , and the greatest absolhartce obtained at) 490p was plotted (Figure 2) against t,hc ratio If of 2,3-dimercapto-l-propanolconcentration t o the a n i of 2.3-dimercapto-I-propanol plus manganous acetate conceiitratioii in the mixture (this sum kept constant a t 0.006846/). Although the greatest absorbance \vas obtained at' t,he 1-minute reading n.heii manganous ion was in excess. it took 2 to 4 minutee to x2:ic.h grtx:iteit, absorbance xhen R wa,< between 0.60 and 0.80. Thrl absorbance maximum, according to the plotted valueP, occurred :it a ratio of 0.6, indicating that the absorbing substanre i.s a complex of 2,3-dirnercapto 1 propanol with manganow ion j i i the ratio of 3 to 2. Severt,heles, this conclusion m;ty lir opeti t o question, since the extended tangents to the cnda of the eurve meet near a point correspondin5 t o a :3 to 1 complex. In other ~ o r d sthe . absorbance produced by a given concentration, 9. of milrtganoua ion in the presence of a large excess of 2.3-dimerc~apto-l-1,r.opanolwa3 about three times as great as the absorbslice produced by concent,ration X of 2.3dimercapto-1-propanol in the pi'esence of a large excess of manganous ion. The discrepancy thus found map be due to a combination of such factors as fdirig, incompleteness of reaction, and rate of attainmctit, of ecjuilihriuni. or to the existence of more than one complex. Specificity of Reaction. -4nunitier of mono- and dithiols, including 2,3-dimercapto-l-1)r3panol, were screened b y carrj-ing out the test with 0.012.11 ninnganous acetate solutions and thiol solutions in n-hich the sulfhydryl concentration \vas 0.016S, and measuring the a!isor!,anrr colorimetrically. A positive test was recorded if the colorimeter reading was more than 10% of that given by 2.3-dimereapto-1-propanol. Under these condit,ions positive tests were obtained with 2.3-dimercapto-1-propanol, ethanedithiol, 1,2,3-propanetrithiol. and toluene-3,4-dithiol, whereas propyl, isopropyl. tert-butyl, isoamyl, and decyl mercaptans, and thiophenol, thioglycolic acid, thiomalic acid, thiolacetic acid, 2-mercaptoetbanol, 3-1nereaptopropane-1.2-diol,and 1.3-
dimercapto-2-propanol gave negative tests. K h e n the reactants n-ere mixed, a fleeting in the test for 1,3-dimercapto-2-propanoI green color was observed, which had disappeared by t,he time a measurement could be made; a few minutes later the solution began to turn brown. The tests of 2-mercaptoet,hanol and 3merc:rptopropane-l,2-diol produced a very light lavender color, which might be suitable for colorimetry a t higher concentrations. ethaneOf t8he reacting compounds, 2,3-dimercapto-l-propanol, dithiol, and 1.2,3-propanetrithioI gave green complexes whereas toluene-3,4-dithiol gave an orange-brown complex that faded less rapidly than the green ones. Due to the difference in color between the manganous complexes of the aliphatic dithiols and that of toluene-3,4-dithiol, t.he molar absorptivities of the latter at the masima and minima (Table I ) were determined in a manner similar to that described for 2,3-dimercapto-l-propanolunder Absorption Spectrum. Mixtures. The effect of monomercaptans on the color developed h j r manganous acetate with 2,3-dimercapto-l-propanol appears to be small (see n-decylmercaptan, Table IV). Although 1,3-dimercapto-2-propanol gives virtually no immediate color with manganous acetate, it enhances the color produced by the reaction of manganous acetate with 2,3-dimercapto-l-propanol (Table 11-1. This is further borne out by experiments in Jvhich
o 2,3-DIMERCAPTO-I-PROPANOL
IN 2-PROPANOL
0.4- x 2,3- DIMERCAPTO-I-PROPANOL IN 2- PROPANOL CONTAINING SUFFICIENT I,3-DIMERCAPTO-2- PROPANOL TO BRING TOTAL DlTHlOL CONCENTRATION TO 0 0123 M
81 0.002 0.004 0.006 0008 MOLARITY OF 2,3-DIMERCAmO-I- PROPANOL IN
0.010
0.012
2-PROPANOL
Figure 3 . Interference of 1,3-dimercapto-2-propanol i n test for 2,3-dimercapto-l-propanolu s i n g h i g h concentrat i o n of m a n g a n o u s acetate (0.122.W)
Table 111. Dithiol Tests of 2-Propanol Solutions Containing 0.00683.M 2,3-Dimercapto-l-propanoland Mixture of 0.00683.11 2,3-Dimercapto-l-propanol with 0.00725.W 1,3-Dimercapto-2-propanol ~,,,lpo,ls ~ I Acetate Concentration, llolarity 0 0048 0 0091, 0 0192 0 0288 0 0480
Table IV.
Absorbance a t 490 m p v i t h 2,3-Dimercapto~ ~ I-propanol 1 min. 3 nun 0 190 0 199 0 205 0 213 0 220 0 231 0 240 0 221 0 247 0 229
Absorbanre , a t~490 nip ~ i t Mixture h 1 niin 3 inin 0 225 0 215 0 274 0 252 0 324 0 289 0 330 0 286 0 295 0 261
Interference w i t h the Test for
2,3-Dimercapto-l-propanol (Using 0.01OO.lf aqueous manganous acetate) Molar Concentration in 2-Propanol Solution Absorbance 2,3-Dimercapto1,3-Diniercapton-Decyl at 1-propanol 2-propanol mercaptan 490 Alp
~
~
ANALYTICAL CHEMISTRY
954 the concentrations of 2,3-dimercapto-l-propancland 1.3-dimerrapto-2-propanol were kept constant and the manganous ion concentration was varied (Table 111). Here it was observed that a t large nianganous ion concentrations the fading of the complex formed from the dithjol mixture was such that the effect of the 1.3-dimercapto-2-propanol was apparently minimized. On the basis of these observations, the dithiol test, as applied to 2,3-dimercapto-l-propanolcontaining possible admixtures of 1,3-dimercapto-2-propanol,was revised to use a high concentration of manganous acetate in spite of the increased rate of fading caused thereby. I n this way, 2,3-dimercapto-l-propanolcontaining as much as 40% of the isomer gave absorbances attributable onlv to its 2,3-dimercspto-l-propanol content (Table 11). Furthermore, the curve for absorbance versus 2,3-dimercaptc1-1propanol Concentration was strictly linear for solutions of the pure substance over the concentration range studied. I n Figure 3 the absorbances obtained, 1 minute after mixing, n ith solutions of constant dithiol concentration but varying ratios of 2,3-dimerare plotted along capto-1-propanol to 1,3-dimercapto-2-propanol, with absorbances for varying concentrations of 2.3-dimercapto1-propanol alone (data from Table 11),with 0.122.1f manganous acetate as the reagent. With this high concentration of manganous acetate the observed molar absorptitivity is about 11 to 12% greater than that shown under Linearity of the Test. DISCUSSION
Vicinal dithiols can be estimated via their slightly dissociated colored manganous complexes in pyridine-containing solvents while monothiols, being unable to chelate, do not form such comit appears that plexes. I n the case of 1.3-dimercapto-2-propanol in addition to the probable possession of a lower stability constant, the manganous complex is destroyed much more rapidly
by dissolved oxygen than are the vicinal dithiol compleues, but we cannot infer that other nonvicinal dithiols 15 o d d behave similarly. One aspect of the interference of 1.3-dimercapto-2-propanol in the test for 2,3-dimercapto-l-propanolthat must be considered in future applications is the possibility that with other dithiol combinations the formation of mixed complexes might limit the range of usefulness of the test. I n the present analyses it n a s possible to minimize the interference of the nonvicinal dithiol component of a mixture by taking advantage of its oiidizability. K i t h other mixtures, different approaches might prove more suitable. For euample, solvent conditions could be varied, differences in absorption spectra could be euploited. or other heavy metals could be applied. Conductometric titration with heavy metal acetates in pyridine also offers hitherto unexplored possibilities. LITERATURE CITED
Aldridge, W. S . ,Biochem. J . , 42, 52 (1945). Barron, E. S. G., Rliller, 2 . B., and Kalnitsky, G., Ibid., 41, 62 (1947).
Hughes, H. K., and coworkers, ASAL.CHEY.,24, 1349 (1952). Jaffe, E., Ann. chzm. (Rome),41, 397 (1951). Mellon, AI. G., "dnalytical Absorption Spectroscopy," p. 45, Wiley, Kew York, 1950. hliles, L. W. C., and Owen, L. N., J . Chem. Soc., 1950, 2943. Rosenblatt. D. H.. and Jean. G. S . .J . Phus. C h m . . in Dress. Sjoberg, B., Ber., 7 5 , 13 (1942). Spray, G. H., Biochem. J . , 41, 360 (1947). Spray, G. H., Stocken, L. A., and Thompson, R. H. S., Ibid., 41, 362 (1947).
Stocken, L. A,, and Thompson, R. H. S., Physiol. Revs., 29, 168 (1949).
Welcher, F. J., "Organic Analytical Reagents," VoI. IV, p. 161, Van Nostrand, Kew York, 1948. lbid., pp. 117, 192. RECEIVED for review September 2, 1954.
-4ccepted January 19, 1955.
Quantitative Elution of Morphine from Ion Exchange Resins CECIL H.
VAN
ETTEN
Northern Utilization Research Branch, Agricultural Research Service,
In studying the use of ion exchange resins in determination of morphine, the compound was not always completely eluted from the resin. Consequently, a study was made of the effects of degree of cross linkage of the resin and of the pII and ionic strength of the elutriant on the elution of morphine from strong cation and anion resins. Conditions were found w-hich gave quantitative elution from resins of both types. Behavior of other ampholytes and bases has been examined under the same conditions of elution. Information presented is of value in determining conditions under which these resins may be used to give quantitative separation of morphine prior to anal?sis.
B
EC.4C:SE of the ampholytic properties of morphine, its sepa-
ration from acids, baqes, and neutral molecules should he possible by successive exchange from strong cation and anion exchange resins. Separation of codeine from morphine based on this principle has been reported ( I , 6). LIorphine n as exchanged on an anion resin column. whereas codeine passed through because it contained no functional group that acted as an anion a t high pH. ?inion exchange repins have also been applied to the liberation of morphine and similar bases from their salts, permitting the subsequent titration of the free base in the effluent ( 3 . 9, l O , l / t ) . I n this paper results are reported n-hich show the effect of degree of cross linkage of the exchange resin on the elution of morphine,
U. S. Department of Agriculture, Peoria, Ill.
and the effect of p H and ionic concentration of the elutriant. Bn objective of the experiments was to find conditions under which morphine could be quantitatively removed from strong anion and cation exchange resins using micro ion eschange columns and samples of about 10 mg. The behavior of several other ampholytes and bases was examined under similar conditions of exchange. EXPERIMENTAL
Resins. Dowex 50 (a strong, sulfonic acid, cation exchange resin) and Dowex 1 (a strong, quaternary ammonium anion exchange resin) of different degrees of cross linkage were used in this study. I n particular, Dowex 50 X 1, X 2. X 4, X 8, and X ,l6 and Dowex 1 X 1, X 2, x 4, x 8, and X 10 were examined. Particle size of each resin ranged from 50 to 100 mesh. Xumbers following the X indicate the percentage of divinylbenzene used in their preparation. With larger amounts of divinylbenzene, the resins become more highly cross-linked, swell less in water, and show less volume changes with variation of solvent concentration. Exchange resins were conditioned by heating 5 bo 30 grams on a steam bath with excess 1 S sodium hydroxide. decanting, washing with distilled water, and then heating with excess 1.Y hydrochloric acid. This cycle ivas repeated until no color was observed in the supernatant. Decanting removed a port'ion of the smaller resin particles which did not settle out. The final stock resin was stored in dii;t,illed water in eit,her the hydrogen or chloride form. Procedure. Columns 8 min. in diameter, similar in design to those previously described ( l e ) ,xvere filled to a depth of 4 cm. with 0.2 to 0.6 gram of exchange resin, the xveight depending on
