Ninth Annual Summer Symposium-Analysis of Industrial Wastes
Determination of Trace Amounts of Alkyl Benzemesulfonates in Water Subcommittee on Analytical Methods, Technical Advisory Committee, Association of American Soap and Glycerine Producers, Inc. E. M. SALLEE, Proctor & Gamble Co.
F. W. M E L P O L D E R , Atlantic Refining Co.
J. D. F A I R I N G , Monsanto Chemical Co. R. W. HESS, National Aniline Division, Allied Chemical & Dye Corp.
J O H N ROSS, Colgate-Palmolive Co.
W. C. WOELFEL, Continental Oil Co. P. 1. W E A V E R , Chairman, Proctor & Gamble Co.
R A L P H H O U S E , California Research Corp. P. M. M A X W E L L , Lever Brothers Co.
An analytical subcommittee of the Technical Advisory Committee of the Association of American Soap and Glycerine Producers, Inc., has cooperatively developed a specific, quantitative infrared procedure for the determination of trace concentrations of alkyl benzenesulfonate in raw and treated water supplies. Such a method is needed because of the lack of specificity in procedures currently used in analyzing most household synthetic detergents. The method involves concentration of alkyl benzenesulfonate through adsorption on activated carbon, desorption, removal of interfering materials through several purification steps, and final quantitative estimation with infrared spectrophotometry.
T
HE rapid rise in the use of synthetic detergents for washing
.
and cleaning operations has caused some concern over the fate of these materials in waste waters. The surface-active agents in the large bulk of these detergents are anionic sulfates and sulfonates; the alkyl benzenesulfonates (.4BS) , with by far the largest share of production and a greater stability in solution, are of primary interest. Accurate analytical methods are essential to assessing the effect of this compound in the water and sewage treatment field. Methods currently available lack sufficient specificity to serve this purpose. Colorimetric methods based on methylene blue have long been used, but often give erroneous results due to interference by many organic and inorganic materials, most of which are naturally occurring substances. I n the absence of a check method, it has not been possible to determine the accuracy of these widely used procedures, and, consequently, misinterpretation8 of data have appeared in the literature. Such errors can be particularly serious a t the fractional part per million concentrations of alkyl benzenesulfonates found in river waters. Methylene blue is a water-soluble heterocyclic amine dye, which forms a slightly ionized salt with anionic detergents. The salt is soluble in organic solvents and can be extracted from the aqueous phase. Early procedures were carried out by addition of methylene blue to an acidic aqueous solution of the sample and then extraction of the colored salt with chloroform. The amount of dye found in the organic phase was taken to be equivalent to the amount of detergent present. Though satisfactory for determination of detergents in distilled water, the methods could not be satisfactorily applied to samples of interest in m-ater treatment. Some of the proved interferences can be predicted on the basis of chemical properties. Organic sulfates, sulfonates, carboxylates, phosphates, and phenols, which complex methylene blue, and inorganic cyanates, chlorides, nitrates, and thiocyanates,
F. M. M I D D L E T O N , U. S. Public Health Service
which form ion pairs with methylene blue, are among the positive interferences. Organic materials (especially amines) , which compete with the methylene blue in the reaction, cause low results. Positive errors are much more common than negative when anionic detergents are determined in natural water. I n the past few years, an extensive literature has been built in attempts to circumvent these interferences. Evans ( 5 ) proposed extraction of the complex a t two different acidities and extrapolation to a third to reduce interference in sewage samples. While some interferences R’ere prevented, others remained. Results were reproducible to about f0.3p.p.m. In an attempt to remove inorganic interferences, Degens, Evans, Kommer, and Winsor (3) used water washing of the chloroform extract. Thiocyanate concentrations higher than 5 p.p.m. were removed by precipitation or destroyed by oxidation. This procedure still gave an apparent 0.2 p.p.m. anionic detergent when applied to a 2% solution of urine. Longwell and hlaniece (6) proposed extraction of the methylene blue complex from alkaline solution. I n this way, they avoided negative interferences due to nitrogeneous material and positive interferences due to inorganic ions. Other interference, probably organic anions, has been shown to remain. All the methylene blue methods are subject to error. Though special conditions may prevent or reduce a particular interference, in general, any substance that complexes with methylene blue to form a salt soluble in organic solvent will give high results. .4ny substance that competes lyith methylene blue to complex with alkyl benxenesulfonate will give low results. All methods based on similar chemistry can be expected to show similar interferences. Some workers have recommended substitution of other amine dyes for methylene blue. The most recent are Moore and Kolbeson ( 7 ) , m-ho use methyl green and extract with benzene. Though the effects of different interferences may vary slightly, they are not prevented by this method. A logical extension of the colorimetric determination is a titration in a two-phase system using the colored dye as indicator. Similar procedures were published almost simultaneously by Epton (4)and by Barr, Oliver, and Stubbings (1). The essentials of these methods are a suitable water-soluble dye, a cationic surface-active agent for titrant, and an organic liquid to form the second phase. The dye is added to the aqueous solution of the sample, and the colored dye-alkyl benzenesulfonate complex is extracted into the organic phase. The cationic agent is used as titrant and combines more strongly with the alkyl benzenesulfonate than does the dye. Thus, the end point is indicated by a shift of color from the organic to the aqueous phase. I n more recent publications, both basic (amino) and acidic (sulfonic) dyes have been recommended. Surface-active quaternary ammonium and pyridinium salts are suitable as titrants. Both chlorinated compounds and hydrocarbons have been recom1822
1823
V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6 mended as solvents. The methods are most applicable for concentrations of 100 to 1000 p.p.m. Results are questionable betueen 10 and 100 p.p.m. and of little value a t lower concentrations. Because the chemistry involved is the same, the titrimetric method is subject to the same interferences as the colorimetric. I n samples as complex as surface waters, it is evident that unequivocal results can be obtained only if the alkyl benzenesulfonate can be separated from interferences. Previous work has shown that prevention of interference by one type of interfering material does not suffice for others. Therefore, several different separation steps are necessary to remove the various types of interference. Many samples also require concentration. CURRENT STUDIES
Early in 1954, analytical chemists from Atlantic Refining, California Research Corp., Continental Oil, Monsanto Chemical, National Aniline, and Procter & Gamble met to discuss the development of a specific, accurate method for the determination of ABS-type surface-active agents in water and sewage. Later, representatives of Colgate-Palmolive, Lever Brothers, and the U. S. Public Health Service joined the group, which was formalized as a subcommittee of the Association of American Soap and Glycerine Producers’ Technical Advisory Committee. It was clear from the outset that colorimetric methods, as outlined above, would not suffice to determine the true concentration of alkyl benzenesulfonate present in any given water sample. Infrared spectrophotometry offered the best hope for unequivocal identification and quantitative determination a t the concentrations of interest. It was also early realized that a standard reference would be necessary. Pure alkyl benzenesulfonate is hygroscopic and unsuited for this purpose. Commercially available package detergents vary widely in composition of surface-active material, and are subject to unannounced formula changes. Therefore, a quantity of typical commercial alkyl benzene was obtained from each of four manufacturers, composited, sulfonated, and analyzed in several laboratories by conventional methods. The standard material is a dry powder containing sodium sulfate and 62.4% alkyl benxenesulfonate. This material was used in the collaborative work, and is available for use as a reference standard for preparing infrared calibration curves. The decision to point for an infrared procedure for the determination of alkyl benxenesulfonate in water supplies brought up several new problems, n hich would not normally be faced in a short colorimetric method. Probably the most important of these is the need to concentrate the alkyl benzenesulfonate from dilute solutions, so that sufficient is present to make the infrared determination. Also, because alkyl benxenesulfonate is not soluble in the organic solvents used for quantitative infrared 1% ork, possible complexing agents which would overcome that problem had to be investigated. Other problems, such as the removal of materials n hich would obscure the infrared spectrum, and other purification steps, n ere investigated as they came up. Early efforts in this work were independent, with different organizations working on different aspects of the problem. After the proper developmental stage had been reached, the various individual efforts mere combined into a single procedure. Thus, the final method is a cooperative achievement, and credit can be given only to the group as a whole. Concentration of Sample. To achieve the necessary concentration, evaporation was considered, but this would be slow and would concentrate all other materials present a t the same rate as the alkyl benzenesulfonate. On the other hand, selective adsorption followed by elution would both concentrate and partially purify the sample. Activated carbon is a promising adsorbent for accomplishing the purpose. Absolute requirements are quantitative adsorption of
alkyl benxenesulfonate from the sample and reproducible recovery by elution from the carbon. Various carbons were evaluated in distilled water. The methylene blue colorimetric procedure was used to check completeness of adsorption and recovery. I n a distilled water-alkyl benzenesulfonate system, this method is accurate. Nuchar C-190 (West Virginia Pulp and Paper Co.) was used by Braus, hliddleton, and Walton ( 2 ) for recovering organic materials from water. Unground Suchar C-190, screened to “on 30 mesh,” is much easier to handle during adsorption and desorption. I t has nearly the capacity of the pulverized material, and has been used to concentrate synthetic detergents for qualitative infrared examination (8). From trials n-ith a number of solvents and conditions, it n a s found that a batchwise extraction of the carbon, with mixed solvent and alkali, gave the most complete recovery. A 1 to 1 mixture of methanol and benzene which is 0.01S in potassium hydroxide extracts 85% of the adsorbed alkyl benzenesulfonate in an hour and an additional extraction for 2 hours removes 50 to 75% of the remainder. This was established by tagging alkyl benzenesulfonate with sulfur-35 and running tests with 10 and 1 p.p.m. solutions.
Table I.
Completeness of -4dsorption and Desorption Using Activated Carbon (Figures are in terms of
Original
ABS
Concn., Sample
P.P.11.
Adsorption of ABS in Filtrate,
%
yo of ABS in original sample) Recovery,
R
1st extr.
2nd extr.
Residual on Carbon,
70
Total ABS Accounted
72
The data are summarized in Table I. One gram of carbon m-as shaken with 100 ml. of solution and filtered. Adsorption is 99.6% complete a t both 10 and 1 p.p.m. concentrations. This indicates a distribution between carbon and solution of about 250 to 1. Recovery by desorption was more than 95% in all four cases. To check a still lower concentration of alkyl benzenesulfonate, and also check results using a carbon column, 20 liters of 0.1 p.p.m. radioactive alkyl benzenesulfonate nere passed through a column containing 100 grams of the granular Nuchar C-190. The entire effluent from the column was evaporated to dryness and counted. The residual concentration in the water after adsorption \vas shown to be 0.1 p.p.b. (99.9% adsorbed). Thus, when passed through a column, the solution is quickly depleted and quantitative adsorption results. Also, recovery by the two extractions of the carbon was again more than 95% complete. Some collaborators, in testing the carbon adsorption-desorption step by adding known amounts of alkyl benxenesulfonate to samples, have reported as 104 as i o to 85% absolute recovery. Calibration curves set up in each laboratory correct for this. Isolation and Infrared Determination. Concentration by the carbon adsorption-desorption technique yields sufficient alkyl benzenesulfonate for an infrared measurement, but materials that would interfere must first be removed. Treatment with hydrochloric acid hydrolyzes organic sulfates, phosphates, and other similar interferences. Petroleum ether extraction removes the organic fragments from the hydrolysis, hydrocarbons, alcohols, sterols, and other materials more soluble in organic solvents than in aqueous alkali. Final isolation is best accomplished by extraction into chloroform of an alkyl benzenesulfonate-amine complex. This serves to remove inorganic salts and Tyater-soluble organic material, and converts the alkyl benzenesulfonate to a form suitable for
1824
ANALYTICAL CHEMISTRY
infrared determination. As the quantitative measurement is made in the 9.5- to 10-micron region and the entire 2- to 15micron spectrum is used qualitatively, an aliphatic amine is preferable. The 1-met'hylheptylamine was the most effective of the many tested, and has been adopted in the recommended procedure. The amount of complex present, when dissolved in either carbon tetrachloride or carbon disulfide, can be determined by measuring absorption at the peaks near 9.6 and 9.9 microns. Good qualitative identification is obtained by use of a smear. Typical infrared spectra are shown in Figure 1. The distinctive features are the sulfonate absorption a t 8 to 8.5 and 9.58 microns, and the substituted benzene ring absorptions a t 8.77, 9.90, and 12.04 microns. The triplet at 7.16, 7.27, and 7.34 is characteristic of certain polypropylene side chains. Figure 2 is a composite photograph shon-ing origiiial and final sample size, the carbon column, an infrared spectrophotometer, and a typical infrared curve. Cooperative Testing. The infrared procedure has been used in the cooperating laboratories to analyze water samples from the Ohio River below Cincinnati. Alkyl benzenesulfonate is readily adsorbed on many types of solid material, such as the cla;--type silt often suspended in river vaters. I n fact, on many such samples, the solids contain a much higher concentration than the solution itself. Khether or not this is a factor of importance in the anal n-ater samples depends on the total amount of solids actually present. Though in most cases the alkyl benzeiiesrilfonate in true solution may be of greater interest, the removal of solids from the several hundred gallons of river rrater required in this case for a cooperative test of a ne\\- analytical procedure was not practical. Consequently, the results reported are the total pipsent in the Ohio River. Samples were collected by passing the water through carboil columns from a manifold connected to a gasoline-driven pump (see Figure 3). Effluent from the columns m-as measured to determine sample size. Seven different laboratories analyzed the sample taken Nov. 22, 1965. Results are summarized in Table
on each peak. K i t h the exception of two unexplained, low results, the values found are in excellent agreement. I n addition to this cooperative sample, a number of the laboratories individually checked the method by determining recovery of alkyl benzeneaulfonate added to local river B aters. Khen corrected for the amount already present, at least 95% v a s accounted for in all cases. The cooperating organizations also investigated the applicability of a colorimetric conclusion to the infrared procedure. This seemed logical, as the concentration and purification steps in the procedure essentially isolate the alkyl benzenesulfonatefrom interferences. The sulfonate-amine comples can easily be broken by boiling nith aqueous alkali. After the amine had been boiled off, and suitable dilutions made, colorimetric results checked well n i t h the infrared values. -!it present, the work of the committee is directed toward finding a referee method suitable for determining alkyl benzenesulfonate in sewage. Preliminary results are promising, but no cooperative samples have yet been analyzed. Another real need is for a short, accurate method suitable for use in water treatment plants. SUMM.4RY
The infrared method presented is lengthy, and it is possible that fe\\- laboratories engaged in routine water analyses will have the necessary equipment. I t does, however, for the first time, permit accurate Ppecific determination of alkyl benzenesulfonate in water. For these reasons, the method will find its
11. Calibration curves were prepared in each laboratory by using the entire procedure on alkyl benzenesulfonate in distilled n-ater. Choice of spectral solvent is left to the individual laboratory. Both carbon disulfide and carbon tetrachloride have been used
2
4
6 WAVE
8 LENGTH
Table 11. Ohio Kiber Cooperative S a m p l e (P.p.m. ABS b j infrared method) Wave Length, p Gallons 9 6 9 9 Laboratory of Pample ABS Content, P.P.hI.
34 0
A B C
0 0 5 5 41 0 35 0
D
E F G
IO IN MICRONS
0 15 0 13 0 14 0.14 0 06 0 14 0 10
3; 27 28 56
12
14
F i g u r e 1. I n f r a r e d spectra of alkyl benzenesulfonatemethylheptylamine complex
0
os
0 13
0 15 0.15 0 13 0.13
0 10
0 1.5
0.11 0 11
V O L U M E 28, N O . 12, D E C E M B E R 1 9 5 6
gure 2.
1825
I n f r a r e d d e t e r m i n a t i o n of alkyl henaenesulfonate
greatest use in running referee analyses and checking the accumcy of proposed short methods. The steps in the method and the principle8 behind each can he summarieed as follows:
,._ >
"
."*\
1. Adsorption of ABS on activated carbon (nucnar cI-mu1. This concentrates the ABS and separates it from many interferences. The technique quantitatively collects the ABS from concentrations as low as a few parts per billion. 2. Desorption from the carbon with alkaline benaenemethanol. At least 95% of the ABS can he recovered in this manner.
3. Acid hydrolysis. This destroys interferences such as organic sulfates, phosphates, and other bydrolvsable substances. 4. Petroleumether wash. Hydrocarbons, alcohols, and sterols are among the materials removed by petroleum ether extraction from alkaline solution.
5. Amine extraction. The ABS is quantitatively extracted in chloroform 8.8 a complex of 1-methylheptylamine, and, thus, is separated from inorganic salts and water-soluble organic material. 6. Infrared determination. Inirared examination after evaporation of the chloroform shows nearly pure ABS-amine complex remaining. A carbon tetrachloride or carbon disulfide solution of this residue can be used far quantitative determination by measuring the absorption a t 9.6 and 9.9 microns.
Figure 3.
Collection of cooperative s a m p l e s
Co.. 230 Park Ave., New York 17, N. Y.). On 30-mesh (U. S. -> -~~~~ 500 ml. of mZh&nol.
Filter carbon, wash with 100 m! .of mkth-
INFRARED METHOD I_.__..
Mast samples studied have contained both solid and liquid phases and the alkyl henaenesulfonste has been highly concentrated on the solids. For accurate analyses, therefore, it is essential that the solids be representatively sampled or excluded.
Special Reagents. Nuchar C-190, unground (obtainable from Industrial Chemical Sales Division, West Virginia Pulp & Paper
~~~~r~~~~~ ~~,
(not including any residue from solvent). The solution for extracting carbon is made up of 500 ml. of thiophene-free benzene, 420 ml. of methanol, and 80 ml. of approximately 0.5N alcoholic potassium hydroxide. 1-Methylheptylamine, Eastman No. 2439. The solution for extracting alkyl benaenesulfonate is 400 mg. (20 drops) of 1-methylheptylamine in 400 ml. of chloroform. Prepare fresh daily.
ANALYTICAL CHEMISTRY
1826
Buffer eolution. Dissolve 6.8 grams of potassium dihydrogen phosphate in 1 liter of water. Adjust to p H 6.8 to 6.9 with 25y0 sodium hydroxide. Standard .4BS for calibration (obtainable from the Association of -4merican Soap & Glycerine Producers, Inc., 295 Madison 9ve., New York 17, N. Y.). Special Equipment. Carbon adsorption tube. Glass column about 2 X 24 inches containing 100 grams of carbon. Stainless steel or brass screens of about 30 mesh divide the carbon into sections of (from the top), 20, 30, 40, and 10 grams (see Figure 4). Volumetric flasks, 2-ml. or 5-ml. Glassware must be free of contamination. A thorough rinse x i t h 1 to 1 hydrochloric acid must be used to remove adsorbed ABS. pH meter. Buchner funnel, 500-ml., medium porosity, sintered glass.
,
40 grams-
I1
IN
I I
I I O grams
W
w
r2
Figure 4.
Carbon adsorp-
tion tube
Calibration Curve. Place 25 mg. of standard ABS in a &gallon glass vessel and dilute with about 4 gallons of distilled water. Mix thoroughly and, using Tygon tubing, siphon the entire solution through the carbon column. Determine the ABS on the carbon as described in the procedure. Repeat with 20, 15, 10, 5, and 0 mg. of ABS. Make two calibration curves by plotting the milligrams of ABS added as the abscissa and the absorbances of the maxima a t 9.6 and 9.9 microns as the ordinate. The baseline technique is best used in determining the absorbance of the maxima. Procedure. Estimate the concentration of ABS present in the sample. Calculate the volume of sample required to supply 10 to 25 mg. of ABS. If 2 liters or lea!, measure about 10 grams of granular carbon (Nnchar C-190) into a 2-liter glass-stoppered graduated cylinder, add the sample, and shake well for 2 minutes. Filter on a medium-porosity, sintered-glass Buchner funnel. If more than 2 liters of sample is required, pass through the column of the carbon at the rate of 10 gallons or less per hour. Transfer the carbon from the Buchner funnel or column (treating the sections separately) to porcelain evaporating dishes and dry a t 105' t o 110" C. Brush the dried carbon from each dish into separate 2-liter bottles or flasks with standard-taper necks and add 1 liter of 1 to 1 benzene-alcohol which is 0.04N in potassium hydroxide. Add boiling chips and reflux under an air condenser for 1 hour. Filter with a vacuum through a mediumporosity sintered-glass Buchner funnel, dralv off all liquid, release the vacuum, and add 100 ml. of methanol. Stir with a glass rod and draF off the wash viith a vacuum. Wash a second time with another 100-ml. portion of methanol. Return the carbon to the flask, add solvent as before, and reflux for 1 hour. While making this second extraction, evaporate the solvent from the first extract and washes. Carry out this evaporation in
a 2-liter beaker on a steam bath. A gentle stream of nitrogen or air on the surface will hasten the evaporation. Filter off the second extract and xash the carbon as before. Add the extract and washes to the beaker containing the first extract. Discard the carbon. Evaporate sufficiently t o combine in one beaker the extracts from the 20-, 30-, and 40-gram sections of the column. Treat the extracts of the 10-gram section separately throughout the entire procedure. After the solvent has been removed, take up the residue in 50 ml. of warm water. Transfer t o a 250-ml. standard-taper Erlenmeyer flask. Rinse the beaker with 30 ml. of concentrated hydrochloric acid and add slowly to the flask (carbon dioxide is evolved). Rinse the beaker with 50 ml. of water and combine with other washings in the flask. Reflux under an air condenser for 1 hour. Remove the condenser and continue boiling until the volume is reduced to 20 to 30 ml., transfer to a steam bath, and evaporate to near dryness (a jet of air directed on the surface of the liquid will greatly aid evaporation). Take the solids up in 100 ml. of water and neutralize with a 5y0 sodium hydroxide solution to a pH of 8 to 9. Extract once with 50 ml. of petroleum ether (up t o 70y0ethanol may be added, if necessary, to break emulsions). Wash the petroleum ether twice with 25-ml. portions of water, discard the petroleum ether layer, and add the washes t o the aqueous solution. Boil off the alcohol, if it was added. Cool and transfer quantitatively t o a 250-ml. separatory funnel. Neutralize by adding dilute sulfuric acid until just acid t o litmus. Add 50 ml. of buffer solution and 2 drops of 1-methylheptylamine and shake vigorously. Add 50 ml. of l-methylheptylaminechloroform solution and 25 ml. of chloroform. Shake for 3 minutes and allow the phases to separate. If an emulsion forms, draw off the lower (chloroform) phase including any emulsion, and filter through a plug of glass wool wet with chloroform (using suction if necessary) into a 250-ml. separatory funnel. Draw off the chloroform phase into a 400-ml. beaker, and return any aqueous solution to the first separatory funnel. Wash the glass wool plug with 10 ml. of chloroform and add to the chloroform extract. Make an additional extraction with 50 ml. of l-methylheptylamine-chloroform solution and 25 ml. of chloroform. Shake 2 minutes and separate the phases as above, if necessary. Extract a third time n i t h 5 ml. of the amine solution and 45 ml. of chloroform, and a fourth time n-ith 50 ml. of chloroform. Evaporate the combined chloroform extracts on a steam bath. With 10 ml. of chloroform, quantitatively transfer the residue to a 50-ml. beaker using three 5-ml. portions of chloroform as rinses. Evaporate to dryness and continue heating on the steam bath for 30 minutes to remove excess amine. Take up the residue in about 1 ml. of carbon disulfide or carbon tetrachloride and filter through a plug of glass wool in a funnel stem (2-mm. bore) into a 2-ml. or 5-ml. volumetric flask. Dilute t o volume through the filter x i t h several rinsings from the beaker. Transfer a portion of the sample to an infrared cell without further dilution. Run the infrared absorption curve from 9.0 to 10.5 microns against a solvent blank. Measure the absorbance of the 9.6- and 9.9-micron peaks, using base lines from 9.5 to 9.8 and 9.8 to 10.1 microns. From appropriate calibration curves, calculate the concentration of ABS in the original sample. Report the values based on each wave length separately. Evaporate a 0.5- to 1.0-ml. portion of the ABS solution on a sodium chloride flat. Record the absorption spectrum from 2 t o 15 microns for positive qualitative identification of .4BS. The carbon adsorption should be used on all samples, because it separates the BBS from many of the materials present and reduces emulsion difficulties. From 10 to 50 ml. of water may be lost through a 60 X 1 em. air condenser during acid hydrolysis. This loss, while not affecting the hydrolysis, reduces the amount of water that needs to be boiled off after removal of the condenser. LITERATURE CITED
(1) Barr, T., Oliver, J., Stubbings, W. V., J . SOC.Chem. I n d . 67, 45-8
(1948). (2) Braus, H., LIiddleton, F. >I., TTalton, G., Axih~.CHEY.23, 1160 (1951). (3) Degens, P. S . ,Jr., Evans, H. C.. Kommer, J. H., Winsor, P. d., J. A p p l . Chem. 3, 54-61 (1953). (4) Epton, S. R . , Trans. Faredav SOC.44, 226-30 (1948). (5) Evans, H. C . , J . SOC. Chein. I n d . 69, Buppl. Issue 2, 576-80 (1950). (6) Longwell, J., Maniece, W. D., A n a l y s t 80, 167-71 (1955). (7) Moore, W.A,, Kolbeson, R. d.,ANAL.CHEX 28, 161 (1956!. (8) Rosen, A. A , Middleton, F. 1I.,Taylor, S . I T . , J . Am. Water Works Assoc., in press.
RECEIVED for review June 20,
1956.
Accepted September 29, 1958.
