July 15, 1942
ANALYTICAL EDITION
determination of small amounts of both organic and inorganic substances. I n this respect, the methods employed do not, in general, differ from those described in the voluminous literature on the subject. The tristimulus values X, Y , and 2 of a sample may be measured by setting the selector switch to a position which connects the photocell directly to the meter; then, with one of the tristimulus filters in position, but with nothing else in the light beam, the iris diaphragm is adjusted until the meter reads 100 (full scale). The sample is then inserted in the beam, and the resultant meter reading is referred to a chart which gives the corresponding tristimulus value. The Y tristimulus value (brightness) is very often specified with the z and y trichromatic coefficients to describe completely the color of a transparent sample. The instrument has also been used for the determination of haze. For this measurement, the brightness of the sample ( Y tristimulus value) is compared to the known maximum brightness of a clear sample having the same chromaticity as the unknown. Several of these instruments have been constructed in the company’s shops. At the present time others are being mnnufactured for their use by a commercial instrument maker.
Summary
A photoelectric instrament suitable for the rapid routine color grading of transparent liquid or solid naval stores
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products is described. Essentially, the apparatus consists of a light source, colored glass filters, and a photocell. The design, however, is characterized by the fact that single readings obtained with the instrument are proportional t o the ratio of the transmissions of a sample for light beams of two different colors. The electrical circuit is arranged so that the instrument scale may be expanded or contracted. I n this manner, both light and dark colored samples may be graded. Within limits, the grades obtained with the instrument are independent of dirt, haze, or imperfections in the sample. I n addition to its use as a grader, the instrument has been used as a chemical colorimeter, to obtain tristimulus values of transparent samples, and to determine haze.
Literature Cited Brice, B. A., J . Optical Sac. Am., 24, 162 (1934). Ibid., 30, 152 (1940). Evelyn, K. A., J . B i d . Chem., 115, 63 (1936). Gage, H. P., J . Optical SOC.Am., 27, 159 (1937). Gibson, K. S., Natl. Bur. Standards Letter Circ. 545 (March 8 , 1939). Hardy, A. C., “Handbook of Colorimetry”, Cambridge, Mass., Technology Press, 1936. Hunter, R. S., J . Research Nutl. BUT.Standards, 25, 581 (1940). Lange, B., “Photoelements and Their Application”, New York, Reinhold Publishing Corp., 1938. Muller, R. H., IND.ENQ.CHEM.,ANAL.ED., 11, 1 (1939). Snell, F. D. and C. T., “Colorimetric Methods of Analysis”, 2nd ed., pp. 57 ff., New York, D. Van Nostrand Co., 1936. Van den Akker, J. A., Paper Trade J., 111, 142 (1940). Wilson, E. D., U.S. Patent 2,008,410 (July 16, 1935).
A Simple Hydrogen Sulfide Generator BRYANT W. POCOCK, L. SCHOLTEN, AND PAUL J. ERICKSON Nash-KelvinatorCorporation, Lansing, Rlich.
the funnel. To start the action initially, the finger is held at the safety tube, B, and acid is pumped into C and E by the rubber compression bulb, A .
B
A
HYDROGEN sulfide generator is a necessity in any chemical laboratory where the analysis of metals is to play an important role, particularly in these days of increasing demands for metal analysis and of correspondingly growing numbers of new control laboratories, which are springing up all over the United States. The apparatus described is of a type which any chemist can probably construct from supplies already a t hand. The parts are held together by clamps and support stands. The most novel feature of the device is the delivery tube, J, which consists of a celluloid drinking straw purchased at a dime store and bent to form a circle at one end. The extreme end of the circle is crimped nearly together and the circle is bent to form a plane at right angles to the shaft. Small holes are bored into the top of the circle a few millimeters apart. The gas is delivered through these holes, thus increasing the area of contact between the gas and the liquid. (This is a modification of the Abson method for the recovery of asphalts from road mixes.) The generating flask, E , is bumped outward somewhat at the bottom, to form a small interior concavity in which the acid will collect, to facilitate complete elimination of the acid by gas pressure. The reservoir, C, is a two-way rubber compression bulb, laced on a level with the bottom of the acid flask, D. Thus C wilfalways hold enough acid t o maintain a positive siphoning action. H and F are traps, K and G are pinch clamps, and I is the preci itation flask. Ferrous sulfide sticks are placed above a layer o?glass wool in E, and hydrochloric acid is poured into D through
K
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