ANALYTICAL CHEMISTRY
630 oxamide alone, iron reacts to form a yellowish-brown precipitate. Although this compound shows very little absorption in the wavelength region of interest in copper analysis, it acts to compete with the copper for reagent, and thus causes low result?. By use of malonic acid, however, the iron is sequestered to permit accurate determinations of copper in the presence of as much as 2.5 p.p.m. of iron; as much as 10 p.p.m. of iron can be tolerated by doubling the prescribed amount of malonic arid used, if Btandardizatiouq are made in like manner. PRECISIO‘Y 4\1) 4CCUR4CI
The applicability of the dithio-oxamide procedure w a* studied with local waters (Table I). The accuracv of the method in determining added known amounts of copper is shown in Table 11. The data presented were obtained using an Evelyn filter photometer operated on the macro scale. All measurements were made using a single selected test tube a i the cell rather than a series of matched tubes, to eliminate variations in cell constants. The general precision of the method was studied, using a Beckman Model DU spectrophotometer which was considered the most suitable instrument available for such work. The observations used were made a t two concentrations of copper (0.5 and 3.0 p.p.m.) as a check on possible instrumental variation. The two copper samples were prepared by adding the calculated amounts of standard copper solution to Baton Rouge tap water (Table I). Transmittancy values nere obtained by averaging three readings on each test solution, reporting the averages to two derimal places. As shown in Table 111, the standard deviation of
the niea~ioi ten obaervations, in terms of percentage transmittancy, was less than 0.13 and the probable error of the mean was 0.09. For a single measurement the probable error was 0.26 which, when expressed in terms of copper concentrations, indicates that a single determination should yield results correct to a 1 0 . 0 3 p.p.m. over the concentration range studied. T h e method described can be considered applicable to the direct determination of copper in potable waters. Where colored waters are to be examined the spectrophotometric procedure should be employed, using a blank of the water being analyzed for the transmittancy measurements. Although the procedure is intended for rapid determinations of copper, i t is capable of unusually good precision over the concentration ranges for which it is intended to apply. ACKNOWLEDGMENT
The authors wish to express their appreciation to the [J, S. Public Health Service for financial support of this research. The helpful criticism8 of E. L. Compere are also gratefully arknowledged. LITERATURE CITED (1) Am. Public Health Assoc., “Standard Methods for Examination of Water and Sewage,” 9th ed.. pp. 47-9, New York, 1946. (2) Feigl, F., and Kapulitzas, H. J., Mikrochemie, 8, 239 (1930). (3) R l y , P., and R l y , R. M . , Quart. J. Indian Chem. Soc., 3, 118 ( 1926). (4) West, P, W., IND.ENG. CHEW,ANAL.ED.,17, 740 (1945). RECEIVEDAugust 5, 1948.
Infrared Absorption Spectrum of Gamma-Benzene Hexachloride r i . L. CUPPLES H u r e u u of
Entomology an? Plunt Quuruntine, Beltsville, M d .
l H E iiifrared absorption spectra of the isomers of benzene hexachloride (hexachlorocyclohexane) in the rock-salt range, 2 to 15.3, provide a method for quantitatively determining the isomers in technical and purified mixtures. Daasch ( 1 ) has described a method for this analysis, including spectrograms of:
2
3
4
5
6
7
8
9
1 0 1 1
12
13
1415
from that given by Daasch in two major respects: Negligible absorption is found in the 61 region, where Daasch observed a weak, broad absorption band; and a moderately strong absorption band is found a t 1 4 . 9 6 ~which , Daasch did not observe. The writer’s observations also show a weak band a t 2 . 4 ~ . The absence of substantial absorption a t 6p is in agreement with the spectrogram of Kauer, DuVall, and Alquist, which does not include the range 14 to 15p. The existence of the band a t 1 4 . 9 6 ~has been confirmed by measurements on three samples of highly purified gamma isomer, with cell thicknesses of 0.1 and 0.5 mm., and in both carbori bisulfide and carbon tetrachloride solvent.
MICRONS
Figure 1.
Spectrum of Gamma-Benzene Hexachloride
100 grams per
liter in carbon bisulfide and carbon tetrachloride, Cell thickness, 0.5 mm.
five isomers in the range 2 to 24p. Kauer, DuVall, and Alquist ( 2 ) have published spectrograms of the isomers in the range 2 to 141. In applying this method for determining the isomers of benzene hexachloride, the writer has measured the absorption of the gamma isomer in the range 2 to 15p, using an infrared spectrometer equipped with sodium chloride prism, windows, and absorption cells, and using a solid, glass, or lithium fluoride shutter to minimize stray light. The spectrogram of ybenzene hexachloride (Figure 1 ) differs
ACKNOWLEDGMENT
The author thanks the Kava1 Research Laboratory and the Hooker Electrochemical Company for two samples (both products of the latter) melting a t 112.5-1135’ C., and the Dow Chemical Company for the third, for which a melting point was not obtained. LITERATURE CITED
(1) Daasch, L. W., ANAL.CHEM.,19,779-85 (1947). (2) Kauer, K. C., DuVall, R. B., and Alquist, F. N., Ind. Eng. Chem., 39, 1335-8 (1947). RECEIVED May 5 , 1948.
