199
V O L U M E 2 6 , N O . 1, J A N U A R Y 1 9 5 4 Table 111. Determination of Calcium in Presence of Magnesium Calcium, h l g .
Taken
5
Found 2.014 2.013 2.016 2.014 2.014 2,017 1.984 2.014 1.990 2.014 1.986 2.014 1.979 2,014 4.052 4.044 4.011 4.044 3.991 4.044 4.035 4,044 3.10 mg. of zinc added.
Magnesium Added, Mg.
Error
0.00
0.05 0.10 0.15 1.49 1.19 1.39 1.73 0.21 0.82 1.31 0.22
70
0.41 0.83 2.07 2.07 1.07 4.14 0.41 2.07 4.14 0.005
of time a t a p H of 4. At least 99% of the Versenate was displaced from the titanium-Versenate chelate a t a pH of 2. It was possible to titrate zirconium in the presence of smaller amounts of titanium with a fair degree of accuracy if equilibrium was reached in the back-titration with iron(II1) before recording the absorbancy readings. However, the time required for such a titration was over 30 minutes, and the results indicated the necessity of a carefully standardized procedure for satisfactory results. For example, after excess Versenate was added to a solution containing 1.94 mg. of titanium(1V) and 5.164 mg. of zirconium, the pH was adjusted to 4.0 and the excess Versenate n a s backtitrated with standard iron(II1) solution. The amount of zirconium found was 5.197 mg., or an error of 0.64%. On the other hand, if, during the back-titration of the excess Versenate in a similar solution of titanium and zirconium, 1 ml. of excess iron(II1) was added and this solution was allowed to stand 30 minutes before titrating the excess iron, the zirconium found was 6.3% low. There is also a tendency for the titanium to precipitate from solution after the iron has displaced the Versenate 0 from the titanium-Versenate chelate, so that the ahsorbanci- readings are not too stahle
peroxide complex was capable of reacting with Versenate to form another complex ion that contained titanium, peroxide, and Versenate. Furthermore, from the titrations it was apparent that the titanium-hydrogen peroxide-Versenate complex or chelate was more stable than the original titanium-Versenate chelate. It was possible to follow the course of the formation of the titanium-hydrogen peroxide-Versenate complex by a spectrophotometric titration of a titanium-hydrogen peroxide solution with Versenate a t a wave length of 450 mp and a t a pH of 1.9 (hydrogen peroxide concentration was 0.3%). This titration gave a good titration plot and an end point that corresponded t o a complr’x having a one to one titanium to Versenate ratio.
Table V. Titration of Zirconium with Standard Versenate -~ Zirconium, Mg. Error, Taken Found 72 5.164 5.164 5 . I64 5 164
a
5.163 5.144 5.129 5.147
0.02 0.39 0.67 0.33
3.010“ 5.037a
3.0 2.5
p H of final soilltion was 1 .L’
.llthough titanium can be determined when hydrogen peroxide is present by either a direct titration with T’ersenate using a wave length of 450 mp or by a back-titration of excess Versenate with iron(III), there seem to be few advantages of these methods over other exiqting volumetric and photometric procedures for titanium 4CKNOW LEDGIIEVT
The financia! aid of a predoctoritl fellowship to the first author from the Eastman Kodah C’o is gratefully acknowledged LITERATURE CITED
-
_ _
Table IV.
_.
-
~
Determination of Cadmium in Presence of Zinc
Cadmium, RIg. Taken Found
Zinc Added, RIg.
Error.
A
(1)
Cheng, K. L., Iiurtz, T., and Bray, R. H.. ANAL.CHEM.,24, 1640
(1952). (2) Kinnunen, J., and Merikanto, B., Chrmist Anulyst, 41, 76 (1952). (3) Pribil, R., Koudela, Z., and Matyska, B., Collection Czechosloo. Chein. Communs., 16, 80 (1951). (4) PTibil, R., and hlatyska, B.. Ibid., 16, 139 (1951). ( 5 ) Sweetser, P. R., aiid Bricker, C . E., ANJIL.CHEM.,24, 1107 (1952). (6) Ihid., 25,253 (1953). RECEIVED for review N a y 27, 1933. .Irreptrd Octohi*r 27, 1953
Picrates of Alkylpyridines-Correction I n an effort to reduce the stability of the titanium-Versenate chelate further, hydrogen peroxide was added to the titanium solution. It mas hoped that by forming the titanium peroxidd complex the titanium-Versenate chelate would not form and no new chelate containing Versenate would be produced. Homever, when an excess of Versenate was added to an acid titanium solution containing 0.3% hydrogen peroxide and the p H of this solution mas adjusted to 2 to 4, iron(II1) was able to react only with the excess Versenate. The titanium-Versenate chelate in the presence of hydrogen peroxide was now stable enough to prevent the iron(II1) from displacing the Versenate from this complex. The amount of titanium found by this method, however, was slightly low (0.7 to 1.5Yo), indicating that perhaps a small amount of the Versenate was still displaced by the iron(II1). The spectra of the titanium-peroxide system and the titaniumhydrogen peroxideversenate system (Figure 3) showed that the normal titanium-hydrogen peroxide maximum of 390 mG ( pH 1.7) was shifted to a wave length of 365 mp but the shape of the curve remained the same. This would indicate that the titanium-
Work subsequent to the publication of “Picrates 01 hlkylpyridines. Identification by X-Ray Diffraction Powder Patterns” [Janz, G. J., and Solomon, Raymond, AXAL.CHEM.,25, 454, 1775 (1953)l has shown that the data cannot be used ae standards of reference. The target of the chromium tube suffered contamination with tungsten and iron. Thus, rather than monochromatic Cr-K, radiation, the spectrum contained, in addition, the Cr-Kp, Fe-K,, Fe-Kgl, and W-L,, TV-Lp,, W-Lgz lines. The powder patterns contained many extraneous lines leading to erroneous values for the interplanar spacings, and relative intensities. While these data can readily be corrected for the erroneous d spacings, it is not possible to correct the relative intensities of the lines. Further work, using pure Cr-K,, or Cu-K, radiation is necessary if data for use as absolute reference standards for the alkylpyridine picrates are desired. GEORGEJ. JANZ Department of Chemistry Rensselaer Polytechnic Institute Troy, N Y.
