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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
and 3, the loss of water was extremely rapid and at the end of 50 hours, the value equaled that at 100’ C.
Conclusions Identical values have been obtained by drying maltose hydrate under low pressures a t temperatures of 38” and 100’ C. A new drying technique has been developed for the removal of water of crystallization from sugar. Literature Cited (1) Assoc. Official Agr. Chem., Official and .4nalysis, 1935.
Tentative Methods of
Vol. 14, No. 1
(2) Brown, H. T., Morris, G. H. and Millar, J. H., J . Chem. SOC. Trans., 71, 73-123 (1897). (3) Browne, C. A., “Handbook of Sugar Analysis”, p. 25, New York, John Wiley & Sons, 1912. (41 Cleland, J. E., and Feteer, IT, R., ISD.ENG.CHEM.,d s - \ r,. ED., 13, 858 (1941). ( 5 ) Evans, J. W., and Feteer, W.R . , Ibid., 13, 855 (1941). (6) Lintner, C. J., and Dull, G., Ber., 26, 2533 (1893). (7) Lobry de Bruyn, C. A . , and Van Laent, F. H., Rec. tvau. cliim. Paus-Bas., 13, 218 (1894). ( 8 ) Rfeissl, J . prakt. C‘hem.. 21, 274 (1880). (9) Ost, H., Chem.-ZtO., 19, 1501 (1895). (10) Walker, P. H., J . Am. Chrm. Soc., 29, 541 (1907).
Ruthenium Dipyridyl-A
New
Oxidimetric Indicator JOSEPH STEIGRIAN, NATHAK BIRNBAUM, AND SYLVAN M. EDMONDS College of the City of New York, New York, N. Y.
I
T IS well known that various iron complex compounds of the ferrous-phenanthroline type act as high potential redox indicators. These indicators are reversible and reach equilibrium rapidly. Inasmuch as the chemistry of ruthenium parallels that of iron in many respects, a n investigation of possible indicator properties of analogous ruthenium complexes has been undertaken. The behavior of ruthenium tridipyridyl dichloride, first prepared by Burstall ( I ) , has been examined from this point of view. The results demonstrate that this complex enters into a mobile reversible oxidation in which the reduced divalent form is orange-red and the oxidized trivalent form is green in concentrated solution. At dilutions comparable with those of indicator solutions, the corresponding color change is from yellow to colorless on oxidation. I n marked contrast to the behavior of the corresponding iron complexes, both forms of the new indicator exhibit stability towards acid and do not dissociate appreciably even a t the boiling temperature. Materials Tridipyridyl ruthenium dichloride was synthesized in the manner described by Burstall (1). The complex was precipitated as the thiocyanate, which was metathesized with a slight excess of silver nitrate. The resulting solution, which was adjusted t o a concentration of approximately 0.02 molar, was used for the determination of the oxidation potential of the complex and as an indicator in the titrations described below. Solutions of ceric ammonium nitrate in molar nitric acid and ceric ammonium sulfate in molar sulfuric acid were prepared from reagent chemicals. They were standardized against Iiational Bureau of Standards sodium oxalate with phenanthrolineferrous ion as indicator ( 2 ) . Oxidation Potential The oxidation potential of the indicator was determined by titrating 0.002 molar solutions of the nitrate with 0.02 molar ceric sulfate in molar sulfuric acid and with 0.02 molar ceric nitrate in molar nitric acid. Corresponding concentrations of ferrous sulfate and ferrous nitrate were employed in the back-titration. The reference electrode was the quinhydrone in either molar sulfuric acid or molar nitric acid.
indicator is close to that of the ceric ion in sulfate solution. Thus the indicator cannot be used successfully with this particular oxidant. However, ceric nitrate in nitric acid solution possesses a higher oxidation potential than the corresponding sulfate solution. The end points are sharp with this reagent and the Eacan be read directly from the curve with ease. The molar oxidation potential found in this manner is 0.58 volt higher than that of the ferric-ferrous system, measured against the quinhydrone reference electrode. The corresponding potential on the hydrogen scale is 1.33 volts, compared with 1.44volts for ceric sulfate in molar sulfuric acid and 1.61 volts for ceric nitrate in molar nitric acid solution. The indicator solutions reached stable potentials a few seconds after addition of each increment of reagent, indicating a highly mobile, easily reversible redox system.
Application to Titration of Oxalate The direct titration of sodium oxalate in 2 molar perchloric acid solution a t room temperature with ceric nitrate is rapid precise, and accurate. Two drops of 0.02 molar indicator solution were added to 100 ml. of 2 molar perchloric acid in which from 0.12 to 0.15 gram of sodium oxalate was dissolved. The titrations were then carried out in the cold with 0.1 molar ceric nitrate. At the end point the color changes from yellow to colorless. Successive standardizations of the oxidant solution were in agreement to less than one part per thousand and checked to the same precision standardizations through ferrous sulfate and ceric sulfate, using ferrous phenanthroline as the indicator.
Acknowledgment The authors wish to acknowledge the aid of George H. Walden, Jr., of Columbia ‘C‘niversity, who first suggested this problem. One of the authors (J. S.) wishes to thank the American Platinum Co., Sewark, N. J., for the ruthenium chloride.
Literature Cited The titration curves for the sulfuric acid soIutions exhibit a point of inflection at the equivalence point. However, the end point is not sharp, indicating that the potential of the
(1) Burstall, J . Chem. SOC.,1936, 173. (2) Walden, Hammett, and Chapman, J . Am. Chem. SOC.,55, 3649 (19.73.
