ANALYTICAL CHEMISTRY
1496 __-
The mean of a t least three readings was taken in each esperiment. It can be seen from Cadmium Oxide __ Error for Zinc Zinc Oxide Error for Cadmium the results that the error does Expt. Taken, Found, Taken, Found, Diff.. Diff., No. gram gram grain gram inn. 7' Mean mg. yo Mean not exceed 0.6%; hence it may 1 0.2298 0.2287 0 1003 0.0997 -1 1 -0.47 .., . -0.6 -0.59 .,. . be concluded that sodium thio2 0,1149 0.1112 0.1003 0.0999 -0.7 -0 60 - 0 . 5 5 -0 4 -0.39 -0.50 sulfate reacts quantitatively 3 0.1149 0.1141 0.1505 0,1497 -0.8 -0.60 .. . . -0.8 -0.53 ,... with cadmium hydroxide and basic zinc carbonate. Further, theuse of sodium thiosulfate for The wet, purified precipitate of cadmium hydroxide n-as comthe estimation of cadmium and zinc, is both rapid and simple. pletely transferred t o a glass-stoppered Erlenmeyer flask. About Use of sodium hydroxide for the separation of cadmium and 10 ml. of saturated, carefully neutralized solution of sodium thiozinc requires less time than hydrogen sulfide separation of the sulfate were then added, the mixture was vigorously shaken, and two . the liberated alkali was titrated with 0.1 IY hydrochloric acid, using methyl orange indicator. The results are shorvn in Table This method allows rapid estimation of cadmium and zinc I. whether they be present alone, or in their mixtures, as in alloys, Estimation of Zinc. Ea& zinc carbonate was precipitated and in various medicinal preparations. from an aliquot of zinc chloride stock solution by adding sodium bicarbonate. Khen sodium carbonate was used as a precipitant, the precipitate did not settle easily. The use of sodium carbonate ACKNOWLEDGMENT as a precipitant in some cases led to the formation of a double The author's sincere thanks are due to hf. S. Telang for his zinc-sodium carbonate which, on solution in sodium thiosulfate, yielded seriously high results. suggestions, and to L. C. Copeland, the Kew Jersey Zinc Co. The precipitate of basic zinc carbonate was further treated (of Pa.), for his valuable criticism. with sodiuin thiosulfate and the amount of zinc determined, as in the case of cadmium. The results are shoxvn in Table 11. LITERATCRE CITED Estimation of Cadmium and Zinc in Their Mixtures. Cadmium hydroxide was precipitated from an aliquot of stock solution con(1) Fock and Kluss. Ber., 23, 534 (1890). taining cadmium and zinc, in the form of chlorides. -4 slight ex(2) Raseinheim and Davidson, 2. anorg. Chem., 41 2387 (1904). cess of sodium hydroxide, sufficient to ensure the solution of the (3) Ray, P. R., and Das-Gupta, J., J . Indian Chem. SOC.,5 , 483 zinc, was added. (1928). After washing the precipitate and treating it with sodium thio(4) Tillu, RI. If.,and Telang, hI. S., J . Indian Chem. SOC.,I n d . &. sulfate, cadmium was estimated. The filtrate, containing zinc, A-eus Ed., 5, 134 (1942). was neutralized with hrdrochloric acid, Concentrated to a smaller ( 5 ) Tillu, 11.AI., and Telang, hI. S., J . Univ. Bombay, 11, 8B (1942). volume, and treated with sodium thiosulfate. The amount of RhcEIvED for review Norember 29, 1951. Accepted June 2, 1952. zinc TvaF then determined. The results are shown in Table 111. Table 111. Estimation of Cadmium and Zinc, in Their llixtures, Using Sodium Thiosulfate
Determination of Water by Karl Fischer Titration in the Presence of Ferric Salts AKDERS 11. LIURENE, rrblker Laboratory, Rensseluer Polytechnic I n s t i t u t e , Troy, A'. Y .
T E R R I C salts interfere in the determination of water by l+ titration with Karl Fischer reagent This interference (1).
closes, however, as the titration proceeds, and the end point is obtained by the normal opening of the eye.
is caused by reduction of the metal ion, by the reagent, with simultaneous liberation of iodine. It has been shown that reduction of the ferric ion may be eliminated by complexing it with 8-quinolinol (&hydroxyquinoline). Solid or liquid samples containing ferric salts can be titrated directly by the following simple procedure. Reagents. 8-Quinolinol, Methanol Solution. Dissolve 9 t o 10 grams of reagent grade 8-quinolinol in 100 ml. of absolute methanol. Procedure. Cover the electrodes of the Karl Fischer titrating flask with dry methanol. Introduce three or four times the theoretical amount of 8-quinolinol solution needed t o react with thc iron in the sample ( 3 moles of 8-quinolinol per mole of iron), Bring this mixture t o the end point v-ith the titrant. Introduce the sample, arid titrate t o the end point directly, or add an pxcess of the Karl Fischrr reagent and back-titrate with standard water in methanol. I n this work a Serfass ( 2 ) unit (Arthur H. Thomas Co., Philadelphia, P a . ) with a cathode ray tube indicator mas used for detecting the end point. The eye of the cathode ray tube exhibits opening when the iron sample is introduced. The eye
This method has been applied to the determination of water in ethereal and alcoholic solutions of ferric salts. The results from some determinations are shown in Table I . Sample 1 was reagent grade hydrated ferric chloride. Iron was determined by reduction and titration with ceric sulfate, the ferric chloride n-as calculated, and the balance assumed to be water. Sample 2 was ferric ammonium sulfate dodecahydrate. Samples 3 and 4 were prepared by adding anhydrous ferric chloride to standard water in methanol solutions. A dry box mas used for this operation. Samples 5 and 6 were prepared by adding known amounts of water to a mixture of anhydrous ferric chloride, anhydrous hydrochloric acid, and anhydrous isopropyl ether. Other complexing agents, potassium thiocyanate, a-benzoin ouime, and cupferron, were also tried. None \vas satisfactory.
Table I.
Water Determinations in Solutions of Ferric Salts
Sarnole
Substance Analyzed
The author wishes t o express his thanks to L. G. Bassett, under whose supervision this work was completed. This work was partially supported by contract No. At-(30-1> 562 with the LJ. S. Atomic Energy Commission.
ether solution 0.013 M FeCli in HC1-isopropyl ether solution
134 3 rng. 1 1 33 mg,/rnl. 8 61 mg./inl.
Water Present 40 53%
Water Found 40 61% 133.7 mg. 1 1 . 3 6 mg./ml. 8 . 6 4 rng./inl.
19 99 :ny/ml.
2 0 . 1 0 inp./:nI.
1 . 1 8 mg./ml.
1 . 17 mg./ml.
DISCUSSIOV
ACKNOWLEDGMENT
LITERATURE CITED
(1) Mitchell, J., Jr., Smith, D M., .4shby, E. C., and Bryant, W. M.D., J . Am. Chem. SOC.,63, 2927 (1941). (2) Serfass, E. J., IND. ENG.CHEY.,ANAL.ED., 12, 536-9 (1940). RECEIVED for review April 25. 1952.
Accepted June 28. 1952
