ANALYTICAL CHEMISTRY
1854 celerating voltages available, only white radiation. Furthermore, the effective wave length of this white radiation is dependent on the accelerating voltage used. It m-as desired that the effective wave length used in this procedure be adjusted as closely as possible to the point a t which carbon and hydrogen have the same absorption coefficients. This was done empirically by determining the absorbances, at a number of different primary voltages, of three pure hydrocarbons covering the extremes of carbon-hydrogen ratios; benzene and n-heptane represented the extremes, and methylcyclohexane represented an intermediate ratio. The absorbances, as drum readings, were plotted against primary voltages (Figure 2). The curves representing this relationship cross at a primary voltage of 76. 9primary voltage of 80 instead of 76 n a s chosen for this procedure for two reasons. Because of the design of the meter, it was easier to set the primary voltage reproducibly a t 80 than a t 7 6 . Secondly, the maximum error a t 80 volts that could be caused by variations in carbonhydrogen ratio was about the same as the precision of the method-namely, -I 0.02% sulfur. Accuracy and Precision. Accuracy in this paper refers to the average deviation between the per cent sulfur obtained by the gravimetric procedure and that obtained by the x-ray method. The gravimetric procedures used by this laboratory are well established and regularly checked. Their accuracy is knov-n to be better than the precision of the x-ray method. Furthermore, all the gravimetric sulfur values given in Table I were run a t least in duplicate. To obtain the accuracy of the present method, the deviation of the drum reading from the calibration curve, in terms of per cent sulfur, was recorded for each sample in Table I. The maximum deviation was &0.04% sulfur and the average was 10.02%.
After long experience with repeat samples, the precision of the method has been determined t o be the same as the accuracynamely, &0.02% sulfur. COYCLUSIOh s
It is estimated that the man-hours saved by use of the sulfur analysis just described, and the tetraethyllead analysis using the same instrument, has been sufficient to pay for the instrument in less than 8 months. One operator can run between 30 and 40 sulfur determinations in a day, alloffing time for instrument warm-up and check, notebook work, and reporting. One determination, including cleanup, requires about 10 minutes. The accuracj- of the method is well within the limits required for the great bulk of the samples submitted to the laboratory, not including, of course, gasolines-the sulfur contents of n-hich are too lox to be handled by the present x-ray method. LITER4TURE CITED
(1) Calingaert, G., Lamb, F. W,, hiiller, H. L., and Xoakes, G. E., A N A L . CHEY., 22, 1238 (1950). (2) Hughes, H. K., and Hochgesang, F. P., Ibid.,22, 1248 (1950). (3) Hughes, H. K., and Wilczemki, J. W., Proc. Mid-Year Meeting Am. Petroleum Inst., 3051 IIII), 11 (1950). (4) Kehl, TT. L., and Hart, J. C., Proc. 28th Ann. Meeting A m . Petroleum Inst., I11 (1948). ( 5 ) Levine, S.W., and Okamoto, A. H., ANAL.CHEM.,23, 699 (1951). (6) Rich, T. .4.,and llichel, T. C.. Gen. Eke. Rec., 50, So. 2, 45 f 1947). (7) Vollmar, R. C., Petterson, E. H., and Petruaaelli, P. A , .%SAL. CHEM.,21,1491 (1949). (8) Zemany, P. D., Winslow, E. H., Poelimita, G. S., and Liebhafsky, H. h.,Ibid., 21,493 (1949). ~I
RECEIVED for review June 17, 1952.
Bccepted August 23. 1952.
Estimation of Elemental Sulfur by Ultraviolet Absorption X. G. HEATLEY AND EILEEN J. PAGE Sir William Dunn School of Pathology, University of Oxford, Oxford, England
N C O N S E C T I O S with other work it was necessary to estimate
1 small amounts of elemental sulfur in aqueous suspensions, in deposits, and in solution in organic solvents, Gravimetric methOb
0%
04
D 03
0 2(
04
IGTH,
LITERATURE CITED ~
I
I
Figure 1. Optical Density of Ethanolic Sulfur Solution Containing 25 Micrograms per hll. E: y&.
= 194.5 a t 250 mp ( A ) , 239 at 264 mp (B),230 at 274 m p (C), 117.5 at 300 mp
ods were sometimes not applicable and in any case were tedious and seldom as accurate as desired. However, ethanolic solutions of sulfur were found to have a strong ultraviolet absorption. Figure 1 shows the absorption of an ethanolic solution of sulfur recrystallized from pyridine and ethanol, as measured in the Beckman absorption spectrophotometer Model DU. The solution contained 25 micrograms per milliliter. The absorption was not appreciably changed by the presence of up to 40% water in the ethanol. Beer’s law was obeyed a t concentrations of 0 t o 40 micrograms per milliliter; at 70 micrograms per milliliter the observed values were slightly lower than expected, though the instrumental errors of density measurement at this level I > 1.5) n ere high. Some other sulfur compounds ( h j drogen sulfide, sulfate, thiosulfate, etc.) have broad absorption bands in the ultraviolet and interfere. For the estimation of sulfur in biological material it is unfortunate that its peak absorption covers the wave-length range in ivhich nucleoproteins, proteins, and their components absorb most strongly However, interfering substances can probably be eliminated or allowed for by appropriate procedures. iilthough absorption curves for sulfur have been given, incidental to other studies, by Baer and Carmack ( 1 ) (in ethanol and hexane) and by Koch ( R ) (in chloroform:, no reference has been found t o Lhe use of ultraviolet absorption measurements for ita estimation.
(D)
(1) Baer, J. E., and Carmack,
M.,J . Bm. Chem.
Soc.. 71, 1215
(1949). (2) Koch, H. P., J . Chem. Soc., 1949,394. RECEIVEDfor review March 21, 1952.
Accepted August 16, 1952.
