SEPTEMBER 15,1939
ANALYTICAL EDITION
leaf can be tested on both top and bottom surfaces by placing it between two test papers with moist pads above and below. If permanent records of the tests are desired, brown or blue prints may be made from the iodine-starch test paper. The prints must be exposed accurately to bring out the tartar emetic spots without smudging the paper. Iodine-starch prints fade considerably after one or two months. The sensitivity of the test has been increased by diluting the coating mixture. A paper prepared as described above gave a distinct reaction with 0.0005 cc. of a solution containing 2.0 grams of tartar emetic per liter, or 1.0 microgram of tartar emetic. A more sensitive paper prepared from the above formula with the sodium bicarbonate doubled, and diluted with seven parts of water reacted to 0.1 microgram of tartar emetic. Figures 1and 2 are photographs of prints taken from grapefruit leaves dusted with varying known amounts of tartar emetic. It will be noted from Figure 1 that the tartar emetic concentration can be tested within the range of 0.9 to 10 micrograms per square centimeter using the more sensitive paper mentioned above. With the higher concentrationsnamely, 0.02 to 0.13 mg. per square centimeter-paper prepared from the undiluted mixture may be used. The results are shown in Figure 2. The photographs indicate the degree of precision obtainable under the prescribed conditions. The distribution of tartar emetic on citrus leaves after being
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sprayed with tartar emetic solutions is much less uniform than that obtained by dusting.
Interfering Substances The materials that may be expected to interfere with the test are reducing substances in general. Some of the materials found to interfere are sodium arsenite, glue, and molasses. The paper is not very sensitive to arsenious oxide or Paris green, probably owing to the low solubility of these compounds. Sucrose, glucose, fructose, galactose, arabinose, and xylose were found t o be nonreactive, or so nearly so that there would be no interference. Strong ammonia solution, calcium hydroxide, and potassium carbonate reacted with the paper. Strong alkalies in general react with iodine to give hypoiodites, Summary Iodine-starch test papers have been prepared for the purpose of obtaining distributional and semiquantitative analyses of leaf surfaces for tartar emetic. The test is sensitive to 0.9 microgram per square centimeter. Known quantities of tartar emetic have been deposited on paper as a standard of comparison. Substances that reduce iodine interfere with the test for tartar emetic. Literature Cited (1) Treadwell and Hall, “Analytical Chemistry,” 7th Ed., Vol. 11, p. 581, New York, John Wiley & Sons, 1930.
Ejector-Type Evacuator for Wet Assay Systems EDGAR J. POTH, Stanford University School of Medicine, San Francisco, Calif.
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HE elimination of corrosive fumes evolved in wet assay methods such as Kjeldahl digestions frequently presents a problem, especially in poorly planned laboratories. One is faced with the problem of disposing of corrosive fumes as well as removing them from a given system. For the elimination of fumes created in many microanalytical procedures, a small digestion chest is presented (Figure 1, G). It is made of stainless steel, has a removable top, and, after use, can be washed out thoroughly. It can be placed on a hot plate. The ejector or jet pump is constructed of Pyrex glass and operates with high efficiency on low-pressure steam. The fumes are brought into direct contact with live steam, which in turn is condensed by a spray of cold water. In this way the corrosive materials either react with the steam or are dissolved in the condenser water. Furthermore, they are highly diluted and can be dumped directly into the ordinary laboratory draina,ge system. The pump will handle liquids as readily as vapors and so it is not necessary to have traps for liquids condensing in or introduced into the system. In the construction of this pump it is well to determine experimentally the position where any particular jet gives the greatest efficiency with the steam pressure available. A.
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Steam inlet and jet
B. Vacuum outlet t o oonneot with digestion system C . Condenser
D. Spray condenser G . Digestion box made of stainless steel H. Hot plate I. Fume and spillway t o be oonneoted with B X. Male half of steam jet, 6 mm. in inside diameter Y . Female half of steam jet, 12 mm. in inside diameter, slightly tapered. Gap between X and Y measures 4 mm. Dimensions in millimeters. Design on right best suited for system of small capacity; design on left, illustrated with sump and overflow water trap, best for systems of large capacity.
FIGURE1. EJECTOR-TYPE EVACUATION PUMP (See designation8 a t left)
