INDUSTRIAL AND ENGINEERING CHEMISTRY
736
Vol. 15, No. 12
value of unity. Figure 2 showv the working curves obtained for antimony, iron, and chromium. Figure 3 shows the final working curves, obtained from the curves of Figure 2 by correction for the residual impurities in the titanium dioxide. Table I lists the results of four analyses in quintuplicate for each of the elements, together with the average deviation from the true values. The time required for the eighty determinations was about 5 hours. Table I1 gives a comparison of results for iron in sixteen samples of titanium dioxide by chemical analysis and by the spectrochemical procedure desrribed in this paper.
Summary A technique has been described for the analysis of powders which may be dissolved in molten potassium acid PERCENT sulfate. The method has been applied FIGURE 3. WORKING CURVESCORRECTED FOR RESIDUAL IMPURITIES -_ to the determination of antimony, vanadium, chromium, and iron in titanium dioxide, analysis conditions and working curves for TABLE 11. COMPARISON OF SPECTROCHEMICAL AND CHEMICAL which are presented. The advantages derived from the appliANALYSES OF IRON IN TITANIUM DIOXIDE cation of background corrections are illustrated by working Sample Iron Found curves for a vanadium line. Chemicala Spectrochemical No. The fused salt technique of preparing samples and standards % % may be extended to many other substances which are difficult 1 0.003 0.003 0.006 2 0,006 to dissolve in the common solvents or to arc as such. The seleo0.016 0.016 3 4 0.027 0.033 tion of a flux in a particular case will be determined largely by 0.029 0.029 5 solubility considerations and by ita suitability as a spectroscopic 0.003 6 0.002 7 0.006 0.007 buffer. 0.005 8 0,005
a
aio
0 010
0.001
9 10 11 12 13 14
0.002
15 16
0.009 0.006
0.003 0,005 0.004 0.009
0.004
0.004 0.003 0.004 0.004 0,011 0,006 0.012 0.006
Colorimetric thiooyanate method.
Acknowledgment
The authors wish to express their appreciation to Leavitt Gard and to John Darby for carrying out the chemical analyses required in the testing of the method.
Literature Cited
that the slope of the background-corrected vanadium working curve is 1.063, in good agreement with the theoretically predicted
(1) Cholak, J.. and Story, R. V., J . Optical SOC. Am.. 32, 502-5 (1942). (2) Duffendack, 0. S., and Wolfe, R. A., IND.ENQ.C H ~ MANAL. ., ED.,10,161-4 (1938). (3) Pierce, W. C., and Nachtrieb, N. H., Ibdd., 13, 774-81 (1941).
Identification of Rust on Iron and Steel SIR: I n a recent article [IND. ENG.CHEM.,ANAL.ED.,15,464 (1943)l I described a sensitive test for iron rust which involved the use of gelatin-coated paper. Processed, single-weight, glossy photographic paper was recommended for the test. It has been called to my attention that two nonsensitized gelatin papers, Eastman Kodak Imbibition Paper and Defender Backing S, are available and my reasons for not using such papers were questioned. The two nonsensitieed papers mentioned are available in doubleweight stock only. I tried double-weight papers in the original tests and found that they did not adhere well to the surface being
tested unless constant pressure was applied. The single-weight paper described in the article adhered perfectly without pressure, even when applied to curved surfaces of short radius. I still prefer the desensitized single-weight paper for the reason given. I n all other respects the double-weight nonsensitized papers are satisfactory. I regret that I neglected to mention this point in the article. RALPH0. CLARK Gulf Research & Development Co. P. 0. Box 2038 Pittsburgh 30, Penna.
