A Useful Distilling Head. Robert R. Russell and Calvin A . VanderWerf, University of Kansas, Lawrence, Kans.
Aqueous Lead Dithizone Color Standards. Louis Silverman, Materials Engineering Chemical Laboratory, Westinghouse Electric Corporation, East Pittsburgh, Pa.
.for a simple, compact, total condensation variable aqueous color standards to match the red color of D take-off distilling head suitable for reduced as well as atmosP lead dithizone in carbon tetrachloride may be prepared with pheric pressure fractionations, in which temperature readings are cobalt nitrate. EMAND
ERMANENT
not obscured by condensing vapors, prompted the construction of the head described. The best features of several existing heads have been incorporated in the design without loss of compactness.
The thermometer, A , with ground joint, is external, thus facilitating readings. Liquid trap D prevents the vapor from bypassing the thermometer bulb. Holdup is less than 1 mi. Atmospheric pressure fractionations are made by leaving the exhaust port, G, open. For work a t reduced pressure, the vacuum line is connected to this port. The arrangement of stopcocks [ E , 3-way; F, simple 2-way; and N , Newman, IXD.ENG. C m x , AXAL.ED., 14, 902 (1942)] makes it possible for the operator to interchange receivers without disturbing the vacuum system. This arrangement also eliminates the necessity for an expensive and bulky receiver for vacuum work. A roundbottomed flask with standard-taper joint is all that is required. Rapid and precise adjustment of the rate of take-off is made possible by the extended arm length on the Newman stopcock. At temperatures above 100' C., portion B-C may be wrapped with asbestos tape to prevent heat loss, and a t much higher temperatures this portion may be heated by means of a resistance wire.
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Lead in amounts of 0.01 to 0.2 mg. is frequently determined colorimetrically as lead dithizone (1-6). The red color usually fades within 24 hours. If the analyst uses the simpler one-color method for lead dithizone, permanent color standards will be of value. In daylight the red tints of aqueous cobalt nitrate solutions match those of lead dithizone in carbon tetrachloride solution from 0.01 to 0.20 mg. (0.001 to 0.02%) of lead. In Figure 1, absorption curves for lead dithizone and cobalt nitrate are plotted and the maximum absorption wave lengths are 520 and 515 mp, respectively. Since the wave lengths of maximum absorption of the aqueous and nonaqueous solutions are only 5 mp apart and the curves are similar (in the red region), aqueous cobalt nitrate solutions may be used for the visual determination of the concentration of lead dithizone in carbon tetrachloride. A complete set of aqueous cobalt nitrate solutions may be calibrated in terms of transmittancy or of lead conrentration. ;iqueous cobalt nitrate solutions have been employed as permanent standards with a Duboscq instrument. In the production of copper Kith low (0.005 to 0.025%) lead content, progressive analytical checks on the lead content may be obtained during the processing, using the lead dithizone procedure, with the aqueous cobalt nitrate solutions as standards. The procedure may also be applied to bronzes lo[ 5\5 , 0 which contain about 425 520 700 0.01% lead. The tin WAVE LENGTH, Y is usually removed as oxide; nickel (0 to -LEAD OlTHlZONE I N CC14 C O B M T NITRATE I N WATER 5 % ) and zinc (0 to lO%)donot interfere. Figure 1 The lead dithizone curves are similar to those which have appeared in the literature (4). The data presented were obtained with a Beckman spectrophotometer.
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LITERATURE CITED
Bambach, K., IICD. ENG.CHEM.,AXAL.ED.,11, 400 (1939). Bsmbarh, K., and Cholak, .J., Jr., Ibid., 13, 504 (1941). Hubbard, P. M., Ibid., 9, 493 (1937). Koselka, F. L., and Klucheskj , E. E., Ibid., 13, 484,492 (1941). (5) Park, B., and Lewis, E. J., I b i d . , 7, 1S2 (1935). (6) Winter, 0.B., Robinson, H. M., Lamb, F. W., and iMiller, E. J., Ibid., 7,265 (1935).
(1) (2) (3) (4)
