7/29/2019 6f95588ab4e795a4faf131c84df8f931

1/4

Direct Titration of SulfatesFurther Studies with Tetrahydroxyquinone as an Internal Indicator

R. T. SHEEN AND H. L. KAHLER, W.H. & L. D. Betz, Philadelphia, Pa.C H R O E D E R (1 ) recentlyS uggested a direct titrationmethod for sulfates with the useof tetrahydroxyquinone as a ni n t e r n a l i n d i c a t o r . A directtitration method of this typeoffers cons iderab le advan tageover other rapid method s whereoutside indicators, back-titra-tions, or filtrations are required.T h e m e th od a s d e s c r i b ed b yS 'c h ro ed er a llows the d i rec ttitration of sulfate in a samplewith a standar d barium chloridesolution, the end p oint being in-

dicated by the a ppearan ce of t hered bariu m salt of tet rahy drox y-quinone. An extensive bibliog-raphy on sulfate determinationswas given in Schroeder's paperand further reference is no t re-quired a t this time.

The direct titration method for deter-mination of sulfates with th e use of tetra-hydroxyquinone as an internal indicatoris described. Sulfates can be determinedby this method up to 30,000 p. p. m. Phos-phates up to 60 p. p. m . can be eliminatedby pH control. Isopropyl alcohol is foundto be as satisfactory as ethyl alcohol forreducing solubility of barium sulfate andhastening the precipitation. The use ofsodium chloride to sharpen the end pointin concentrations above 2000 p. p. m. ofsulfate is described. Results obtained bythis method check gravimetric analyseswithin a n average of 3 per cent. Compari-son of results with the Betz-Hellige methodis given.

Schroeder suggested the dispersion of the tetrahydroxy-quinone with a large amount of potassium chloride to give adilution th at could be readily handled by using a few tenth sof a gram of th e dry mixture for each determ inatio n, thisdry dispersion being necessary because the solutions of tetra-hydroxyquinone are not sufficiently stable t o be added tothe sample in this form. This method of adding the tetra-hydroxyquinone to the sample was followed in the presentinvestigation. (Th e prepared tetrahydroxyquinone-potas-sium chloride mixture has been named by this laboratoryTH Q and will be referred to a s such throughout this paper.)The method suggested by Schroeder limited the range ofsulfate in a 25-cc. sample between 80 and 800 p. p. m. andfurthe r suggested the use of equal quantities of ethyl alcoholor alcohol denatured by formula No. 30 or 3-A to reduce thesolubility of th e barium sulf ate and has ten the precipitation,titrating with 0.025 N barium chloride in a solution neutral-ized to the acid side of the phenolphthalein end point. Phos-phate w as found to be an interfering ion.It was the aim of this investigation to extend the sulfaterange, which was found possible. and to find a diluent thatcould be used in place of ethyl or denatured alcohol, becauseof t he difficulty of obtaining either the ethyl or the dena turedalcohol in many plants, owing to certain government re-strictions. Isopropyl alcohol was found to answer this pur-pose. Elimination of the pho spha te ion is desirable and itwas found tha t this ion could be eliminated up to 60 p. p . m.by changing the pH value of the titrating solution to abou t4.0.

ExperimentalThe indicator used throughout this study was manufac-tured in the Betz laboratory and considerable quantities ofthis material hav e been supplied to the field.Detailed directions are given below for a determinationof sulfate by direct titration using THQ as the indicator.MATERIALSND REAGENTS. tandard barium chloride solu-tion, the strength varying from 1 cc . = 1 mg. of SO1 to 1 cc . =

C U D t o measure the m ixture.

50 mg. of SOa, standardized gravi-metrically. An in d ic a to r com-posed of disodium tetrahydroxy-quinone ground with dried potas-sium chloride in a 1 to 300 ratio,and passing a 100-mesh screen.Eth yl alcohol or alcohol denaturedby formula No. 30 or No . 3-A, ori s o p r o p y l a l c o h o l . Phenol-phthalein indicator and bromo-cresol green indicator (if phos-phates are present). Sodium chlo- ,ride crystals, c. P.P R O C E D U R E. C a r e f u l l yneutralize a 25-cc. sample contain-ingup t o a p ro x i m a t e l y 2000p. p. m. of S& with approximately0.02 N hydrochloric acid until justacid to phenolphthalein. Thetemperature of the sample shouldbe below 35" C. and it is advisableto work between 20" and 25" C.Add either 25 cc. of ethylalcoholor alcohol denatured by formulaNo. 30 or No. 3-A or isopropylalcohol. Introduce the THQ , theamount to be determined fromTable I. It is best to use a smallSwirl the flask to dissolve th e THQ:the solution will be colored'a deep yellow. Titrate with standa

7/29/2019 6f95588ab4e795a4faf131c84df8f931

2/4

12 8 INDUSTRIAL AND ENGINEER ING CHEMISTRY VOL. 8, NO. 2TABLE1. TITRATIO NF S O DIUMU L F A T E

(All t itrations were carried out a t pH 8.3. 25 cc . of ethy l alcohol, denaturedwith No. 3-A or 30, were used.)so4Present

P. p . m.

2 04 07 7 . 01 0 12 0 240 4485b5 0 4

6 2 090 71550b100521323019

240338765426542667 5 5 89690b

108561550815508621711b34117

so4F o u n dP. . m.

1 9 . 93 7 . 57 4 . 99820 439 94 0 651 6

00 29 0 4154716122 0 9 63 0 3 0

2 3 0 8401655095 2 8 77 3 4 39 4 4 1

1101515106157352098032729

Error T H Q% Gram

- 0 . 5 0 . 1- 6 . 3 0 . 1- 3 . 5 0 . 1- 3 . 0 0 . 2+ 1 . 0 0 . 2- 1 . 1 0 . 2- 4 . 0 0 . 2+ 2 . 4 0 . 2

- 2 . 9 0 . 2- 0 . 3 0 . 2- 0 . 2 0 . 24 - 0 . 4 0 . 2- 1 . 7 0 . 21 0 . 3 0 . 4

- 3 . 9 0 . 4+ 3 . 7 0 . 4$ 1 . 7 0 . 4- 2 . 5 0 . 4- 2 .8 0 . 4- 2 . 5 0 . 4

+ 1 . 4 0 . 6- 2 . 6 0 . 04 - 1 . 4 0 . 0- 3 . 4 0 . 8- 4 . 0 1 . 0

BaClz Usedcc.

1 cc . = 1 . 0 4m g . of Soda0 . 4 80 . 9 01 . 8 02 . 3 54 . 9 09 . 6 01 1 . 2 01 2 . 3 0

1 cc . = 4.07m g. of 8043 . 6 55 . 5 59 . 5 09 . 9 01 2 . 8 518.001 cc . = 1 0 . 4 9mg. of 9045 . 5 09 . 5 71 3 . 1 31 2 . 8 01 7 . 5 02 2 . 5 01 cc. = 5 2 . 4 5mg. of 8045 . 2 57 . 2 07 . 5 09 . 9 51 5 . 6 0

a 0. 1 cc . b lank was subtracted from values obtained when 1 00. of BaClr =b 2 5 cc . of isopropyl alcohol.1 . 0 4 m g . of 804.

were added to allow the proper observation of the end point.Th e char acter of th e color of th e end point changed som ewhat,owing to t he presence of t he precipitated barium su lfate, be-coming more intens e in higher concentrations. The resultsobtained are presented in Table 11.Isopropyl alcohol was used on some samples as indicatedwith equally successful results. Stan dard dippers were em-ployed to measure the THQ indicator, each dipper holding0.2 gram of the indica tor. The results presented in Table I1show tha t the method is applicable for the de termination ofsulfates up to approximately 30,000 p. p. m. of sulfate orapproximately a 3 per cent solution of sulfate. All titratio nsin the tab les are averages of tw o or more values, none of th evolumes of barium chloride used deviating from each otherby more than 3 per cent. An arithmetical average of forty-two determinations gave a 2.4 per cent error; twelve resultsof the forty-two w ere high, showing tha t in general resultshad a tendency to be slightly low. It has been found ad-vantageous to use varying amounts of th e T HQ dependingon the sulf ate range in which th e determination is being made(Table I) .

Several other diluents besides isopropyl alcohol were triedan d found unsatisfactory, including diacetone, furfural, form-aldehyde, normal butyl and isobutyl alcohol, and acetone.Acetone a t first gave some promise but the end point was notas clear as with eithe r alcohol or isopropyl alcohol and resultswere not as accurate and further work on this diluent wasaban done d. Schroeder investigated the effects of ions andmixtures of ions in synthet ic solutions and st ate d tha t a tleast 320 p. p. m. of COa--, 200 p. p. m . of Alf++, 1020 ofSios--, 40 0 of Mg++, 200 of Ca++ and 200 of OH- couldbe tolerated withou t interference with the method. He alsos ta ted tha t PO4--- required excess barium chloride, owingto the insolubility of some barium salt of Pod---, and couldbe corrected by subtracting a blank from the total titration,the val ue of th e blank depending on the q uan tity of PO4---present.

Serious drawbacks to the correction method for phosphateadvanced by Schroeder are: (1) the phosphate contentmust be known and (2) corrections must be made for eachstren gth of barium chloride titra ting solution. Schroederwas working with only one strength of barium chloride butthis investigation, covering a larger range of sulfat e, requiredseveral strengths and would therefore require several correc-tion factors for phosphate.The com plete removal of t he POI--- by the aid of m etalswhose phosphates were insoluble and whose sulfates weresoluble was attempted. It was found that other complica-tions, such as the insolubility of oxides and h ydra tes of themetal an d destruction or coloring of the T HQ b y these othermetals an d the precise control of th e qua ntity or concentra-tion of th e metals required, were insurmountable obstaclesfor practical application.Knowing t ha t different bar ium sa lts of o-phosphoric acidform at different p H values, it was decided to att em pt toform a more soluble salt at a lower pH. The following pro-cedure was employed, using bromocresol green as indicator:The sam ple was neutralized ju st to th e yellow range of t heindicator, 25 cc . of alcohol were added and then the THQ.The THQ was stable in such a solution for a t l east 20 min-utes, which is considerably in excess of time to complete th etitra tion in a satisfacto ry fashion. Solutions with varioussulfate and p hosphate contents were titrated and it was foundthat by this procedure up t o 60 p. p. m . of PO4--- could betolerated without interference, and above this value excessbarium chloride solution was required to obtain th e end poin t.Table I11 shows the results obtained by this procedure forelimination of interference by phosphates.In using this lower pH value, care m ust be exercised to pre-vent excess acid being added t o th e solution, as such w ill de-stroy the THQ. Katural ly , in ti t rat ing, the pH value of th esolutions will gradually rise as the standard barium chlorideemployed has a n approxim ate p H value of 7.0. The colorof t he titr atin g medium will therefore change slightly onaccount of the bromocresol green present, tak ing on a greenishtinge with a rise in pH value. This can be discharged by adrop or two of the 0.02 N hydrochloric acid. The intensityof t he green color was held a t a minimum by use of 0.1 cc. of0.04 per c ent bromocresol green, which was found sufficient toobserve the neutraliz ation. Where work is conducted con-tinuously a t this lower pH value, it migh t prove advantageousto buffer the barium chloride stand ard solution at a lower pH.

TABLE11. PHOSPHATELIMINATIO NY PH CONTROL( p H 4. 1 cc. of BaCh = 1 . 0 4 m g . o f SO1. 0.1 cc . b lank subtracted fromvalues when 1 cc. of BaCh = 1 . 0 4 m g . of 804.)so4 so4 Po4 BackPresent Found Error Present Used

P. p. m. P. p . m. % P . p . m. CC.9 8 . 89 8 . 89 8 . 89797415"

9 9 . 89 9 . 81 0 0 . 810 81 1 44 1 5

+ 1 . 0+1.0+ 2 . 04 - 1 1 . 3+ 1 7 . 50.0

1 7 . 03 5 . 2627 99 26 2

2 . 4 02 . 4 02 . 4 22 . 0 02 . 7 53 . 9 01 cc . of BaClz = 4.07 m g . of sod.

Schroeder found th at in eac h titration 0.1 cc. blank shouldbe subtracte d. This was necessary only when using thestandard barium chloride where 1 cc. of barium chlorideequals 1 mg. of SO4. Th e only ions giving interference wereFe+++, Fe++, Al+++, and POj--- in ex cess of 60 p. p . m.Iron in both the ferrous and ferric state must be ma intainedlower than approximately 5 p. p. m. This is not considereda serious drawback to the m ethod, as in boiler waters solubleiron will seldom be found to this extent with higher pHvalues, most iron being present in the insoluble form. Whereiron is present in a sample, it should be removed prior to titra -

7/29/2019 6f95588ab4e795a4faf131c84df8f931

3/4

MARCH 15, 1936 ANALYTICAL EDITION 129TABLEV. EFFECTF SINGLEON SND OTHERMATERIALS

(pH 4.values when 1 CC. of BaClz = 1.04 mg. of SO&so4 so4 BaCla

25 cc. of isopro pyl alcohol used. 0.1 cc. of blank subtracted fromCl as listed was in excessof C1 as derived from KC1 in the THQ prepared indicator.)Present Found Error Used Ion PresentP. . m. P . p . m. % cc. P. p . m.

1 cc. of BaClz = 1.04 mg. of $04;0.2 gram of THQ979798.898.898.898.898 .898.898.898.8

16461646164616461646ffi1646164616461646

9810010010098.8100989698133

16611677

13160b1o 1310813160 1279813160 1279813160 134671316Oat0 1321713160" 1279813160b,C 1279813160 1364713160b 0 1300813160 1300814160 12798

f1.0f 3 . 0+ l . 2+1.20 .0c 1 . 2-0.8-2.8-0.8+34.8

-1.6+0 .40 .0-2.2-1.1f 1 . 4-1 1CO 9f 2 . 0

-0 4-2 7-2.7f 2 . 3+0 .4-2 .7-2.7+ 3 . 5-1.2- 1 , 2-2.7

2.402.402.402.402.352.402.382.302.353.20

PO4F e + + +F e + +SiOsTannin

Cac 1c 12

626 .44150080120344688392015680

1 cc . of BaClz = 4.07 mg. O f k h ;0.2 eram of THQ9.9510.1510.109.9010.0010.2510.0010.2010.30

- Po4F e C t +Fe ++Si08Tanninc 1c 1z.2

62R.05.815008014403447840470401 cc. of BaClz = 52.45 mg. of sod;0.6 gram of T HQ

6.20 Po4 626 .1 0 F e ++ + 8 .06 .1 0 F e ++ 5 .86.4 0 Sios 15006.30 Tannin 806.10 Tannin 806.10 A1 6 . 06.5 0 Mg 14406.20 Ca 3446.2 0 Ca 3446.10 c1 23520_..

a 0.5 cc. of bromocresol green used in neutralization because of brownb 6 grams of N aCl used in titra tion .c 25 cc. of ethyl alcohol denatured by No. 3-A or 30.

color from tannin.

tions, as otherwise the TH Q is colored green an d destroyed.The results with Al+++ show tha t even 6 p. p. m. cannot betolerated in lower sulfate concentrations. Here again, littledifficulty is expected, as soluble Al+++ is seldom found inappreciable concentrations in boiler waters. In higher sul-fate concentrations (abo ut 13,000p. p. m.) 6 p. p. m. of A+++can be tolerated. It is believed that the sulfate content isonly indirectly responsible for this and probably the higherconcentrations of the tetr ahy drox yqui none required overcomethe interference with the Al+++. Tolerances of the variousother ions studied were in general high and in water work a tleast will exert no influence on the method. Sios-- - canbe tolerated up to 1500 p. p . m., tannin up to 80, Mg++ atleast 1440, Ca++ to a t least 344, and higher depending onthe sulfate con tent (one of these two variables determines t hetolerance of th e other , due to the solubility of calcium sul fatein the system), and C1- up to 15,000 and higher dependingon the sulfate content. Above 2000 p. p. m. of sulfates,sodium chloride can be used advantage ously to sha rpen theend point (Table V).The effe ct of temperature was studied and it was found tha tthe tem pera ture of the sample should be held below 35" C.Higher tempe ratures destroy the indicator.It was realized th at detection of the end point in this titra -tion might prove difficult for inexperienced or nontechnicaloperators, and several agents were investigated that mighttend to give a more readily discernible end point under allconditions. Th e use of xylene cyanole, a green dye, was in-vestigated a nd found to be of no aid in this work. Thisdye was selected because of its possible application in clari-fying the m ethyl orange end point in alkalimetry work.In the higher sulfate concentrations, the end point mightbe term ed as somew hat "sliding"-that is, the solution sta rtsto change color before all the sulfate is stoichiometricallyprecipitated, probably because the increased amount ofTH Q required promotes the reaction between the indicator

and the barium ion. To eliminate this difficulty, the use ofsodium chloride was found advantageous. It has been de-termined th at an y agent furnishing sodium ion and not inter-fering otherwise with the titration could be employed. Asmall amount of the solid sodium chloride added to the solu-tion where the sulfate concentration was above 2000 p. p. m.not only caused a very rapid change of color a t the e nd point,but considerably increased the accuracy of the determinat ionin this range. However, with sulfate concentrations m a-terially below 2000 p. p. m., high results were obtained, dueto a delayed end point. The results in higher ranges with th euse of this sodium chloride are presented in Table V.

TABLE . EFFECTF NaCl FOR SHARPENINGHE END POINT804 SO4 BaCh NaClPresent Found Error Used Used

P . p . m. P. p . m. % cc. Urams1 cc. of Bo H .3 0~97 108 f11.0 2 .60 0 .597 106 +9.0 2.55 0.2291 408 f 4 . 0 9 . 8 0 1. 0

1 cc. of BaClz = 10.49 mg. of 904;0.4 gram of THQ3292 3273 -0. 6 7.8 0 2.06584 6630 +0 .7 15.80 2.0

1 cc. of BaClz = 52.45 mg. of sod;0.6 gram of THQ13160 13113 - 0.4 6.2 5 4.019740 19511 - 1. 2 9.30 4 .026320 25805 -2.0 12. 30 15 .026320 26015 -1.1 12.40 5.032900 32519 -1.2 15. 50 5 .032900 32834 -0.2 15.66 10. 0n Hf3i60 13113 -0. 4 6.25 10.00.1 cc. blank subtracted when 1 cc. of BaClz = 1.04 mg. of 904. 25 cc.of ethyl alcohol denatur ed w ith No. 3-A or 30.

TABLE I . RESULTS BTAINEDN ACTUAL OILER-AND FEED-WATER AMPLESPercentage ErrorSulfate Found ~ Based on GravimetricSample Gravimetric T HQ Betz-Hellige THQ Beta-Hellige

1234567891011

9 . 12062272214619833231566219323602484

9 .42042771214589492227761221424337494

8 .72052170014009700225067215022500455

f 3 . 3-1.0$22.7-1.4-0.2-3.4-1.7-7.6+1.0t 3 . 1f 2 . 1

-4.4+0 .6-4.4-3.0-4.0-1.3-2.8+ 1 . 5-2 . 0-4.7-6.0

Only a few tests were made adding sodium chloride withsulfate concentrations below 2000 p. p. m., but these weresufficient to indicate th at a delayed end point producing highresults was obtained. Th e effect of the sodium chloride whena titration is carried at pH 4 an d in the presence of variousions was found to give the same results a s a t pH 8.3.Th e final tes t of th e method was obta ined by comparingresults by titrations of a number of boiler-water samples toresults obtained by gravimetric analysis and precipitation asbarium sulfate. A compa rison of resu lts was also ma de bythe Betz-Hellige method recently proposed ( 2 ) , his being par-ticularly applicable to accurate sulfate determinations inlower concentrations. As the sulfate cont ent of boiler wa tersamples will not usually run above 2000 to 3000 p. p. m., andit was desired to test above this range, some samples contain-ing a fairly high sulfate co ntent were taken and c oncentratedby evaporation.Fairly good agreement was obtained thr oughout th e range,the perce ntage error being greate r in the lower concentrations.Below 100 p. p. m., greater acc uracy will be obtained by theBetz-Hellige method, while in the higher concentrations, the

7/29/2019 6f95588ab4e795a4faf131c84df8f931

4/4

130 INDUSTRIAL AN D ENGINEERING CHEMISTRY VOL. 8, NO. 2tetrahydroxyquinone gives the better result . Results can p. p. m., can be tolerated by adjusting the pH value of thebe expected to check with gravimetric with an average of sample before ti tratio n to approximately 4.0 with the aid ofabout 3 per cen t error. bromocresol green as an indicator. With th e exception ofi ron and a luminum, ot ,her ions n o rm a l l ypresent in boiler feed waters give no difficulty.

Total Dis- It was found that solid sodium chloride couldHard- solved be used to advantage to sharpen end pointsSample ness C1 HCOa COa OH Solids Fe Si02 Po4 PH with s ulfat e concentrations above 2000 p. p. m.

A comparison of gravimetric, tetrahydroxy-.p .m. P.p .m. P.p .m. P .p .m. P,p .m. P. p . m. P. p .m. P.p . m. P. p . m,1 24 4 14 . . . . . .. . ... .. . . 6. 757 10.9 quinone, and Betz-Hellige metho ds on boiler-40 72 .. 56 40 700 ... ..4 12 224 . .5 2 496 ,. 448 156 4432 . . . . 11.5 ceptable results in all concentrations were7 2 116 . 116 762 5700 0. 5 69 0 254 .. i52 540 5932 0.5 19 25 11.910

TABLE II. ANALYSISOF SOLUTIONSSED

3 58 12 60 ii6 .. .2 2208. . o.5.. 3o. ii l water and boiler-feed samples shows tha t ac-6 0 1408 . . 2552 320 19330 1: s 4 0 11.91.9 obtained. It is believed th at this method of8 88 12 29 . . . .. . .. . .. .. 6.9 sulfate determination will have possible ap-

Analysis about same a8 No. 9. 804 ncreased b y NaZsO4 plication in determ inatio n of sulfates in fuel,11 13 190 .. 264 62 . . . ... .. j7 ll. cemen t, rubber, and numerous othe r fields.During the pas t 3 months over 5000 water samples havebeen analyzed in the Betz laboratories employing the tetra-hydroxyquinone method for the sulfate determin ation. Overten o perators are employed in this work a nd no difficulty hasbeen experienced with this method.

ConclusionsThe tetrahydroxyquinone method for sulfate determ inationhas been shown to be accurate up to approximately 30,000p, p. m. or a 3 per cent solution of SO4. Isopropyl alcoholcan be used with equ ally accura te results in place of e thylalcohol for lowering the so lubility of th e barium sulfate an dhastening the precipitation. Th e phosphate ion, up to 60

AcknowledgmentThe assistance of E. M . Ross on some of the preliminaryinvestigations is acknowledged. Th e suggestions an d com-ments of W. C. Schroeder are sincerely appreciated . Th eauth ors wish to acknowledge the financial assistance and spon-sorship of W. H. & L. D. Betz who made this investigation

possible. Literature Cited(1) Schroeder, W. C., IND. NG.C H ~ M . ,nal. Ed., 5 , 403-6 (1933).(2 ) Sheen, R. T., Kahler, H. L., and Ross, E. M., Ibid., 7, 262-6RECEIVEDctober 31 , 1935.

(1935).

Determination of SulfateAn Attempt to Determine Sulfate by Titration with Lead Nitrate,Using Eosin as Indicator

JOHN E. RICCI, Department of Chemistry, New York University, New York, N. Y .HIS is a report of an a ttem pt to ti tra te sodium or potas-T ium sulfate directly with stan dard lead nitrate solution,using eosin as indicator. Th e work arose from a problem ofanalysis in the phase-rule study of certa in systems involvingsulfates, in which it was desired to find a rapid method forthe direct determination of the sulfate.A titratio n with lead nit rate in t he presence of som e potas-sium iodide as internal indicator, using the appearance of theyellow lead iodide as the end point, was attempted first;after considerable work on this method, i t was given up asimpracticable. The writer then learned th at the methodhad been suggested as far back as 1853 by Levol (8),and sub-

sequently by several other chemists since that date (6, 10,l a ) , and that the same conclusion had been reached as toits inadequacy by other investigators who examined themethod ( 7 , 9, 11). (Levol was also the first to announce,in 1853, this typ e of ti tration even for chloride, us ing the a ppearance of yellow silver phosphate as the en d point, insteadof silver chromate, in an otherwise typical Mohr t i tration.)The use of potassium iodide paper as a n external indicator forthis t i tration is known as Pappenheims method ( I I ) , andalthough it was criticized as impracticable by Mohr (ZI),Vinagradov (18)as recently as 1935 found it the best of thevolumetric methods for the determination of sulfate by m eansof lead salts. Th e only othe r applications of lead salts in thevolumetric determination seem to be in certain electrometricmethods (IC,,901,nd in indirect methods, in which the sul-

fate is precipitated with a n excess of lead nitrat e (IS) r leadacetate (4,nd the excess of lead salt is titrated by chro-mate or molybd ate, respectively. Ro y ( 15 ) , suggesting thet i t ra t ion of lead by means of sulfate with fluorescein as ex-tern al indicator, mentions th e possibility of using such a titra-tion for the indirect estimation of sulfate. Apparently,however, no method has yet been suggested for the directti tration of sulfa te with lead salts by mean s of a n adsorptionindicator. Th e reader is referred elsewhere for reviews ofthe volumetric methods fo r sulfate, m ost of which involv ethe use of barium chloride as stan da rd solution (1, 16).Suggested Method

The present method makes use of eosin as an internalindicator for the direct t i tratio n of sodium or potassium su lfatewith standar d lead nitrate solution. Th e end point is indi-cated b y the ap pea ranc e of th e red lead salt of eosin, CzoHsBrrOsPb (g), bringing about a change from the yellowishflesh color of th e mixtu re of p recip itate and solution to alight but distin ct pink-red. Th e following solutions wereused:The sodium and potassium sulfate solutions were prepared

from c. P. anhydrous salts, and standardized by evaporation todryness at 250 C. an d direct weighing of the residue. Strengthsused were from 0.1 M t o 0.32 M .The lead nitrate solutions, also prepared from c. P. reagentmaterial, were standardized by treating a measured volume witha known weight of pure potassium iodate, filtering off the pre-