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INDUSTRIAL AND ENGINEERING CHEMISTRY
minations, although i t should serve admirably for gravimetric macrodeterminations. The cost of reagent for a single microdetermination is estimated to be about 2.5 cents, which is not prohibitive.
Summary A procedure which has been successfully used for the colorimetric microdetermination of the zinc content of agronomic materials is described. The method is applicable for the determination of quantities of zinc ranging from 0.05 to 1.0 mg. After a preliminary separation of the zinc from interfering elements, 5-nitroquinaldic acid is used as a precipitating agent. The precipitate is filtered from the excess reagent, and converted into an orange-colored, water-soluble compound by reduction with stannous chloride. The intensity of color is measured by means of a photoelectric colorimeter. Precipitation of zinc by 5-nitroquinaldic acid is complete within a range of p H 2.5 to p H 8.0 after digestion for 30 minutes. Ammonium chloride and sodium chloride in concentrations greater than 0.7: \A inhibit the complete precipitation of the zinc. The intensity of color of the reduction product of &nitroquinaldic acid is independent of the acid concentration a t acidities lower than 0.8 S and of the concentration of stan-
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nous chloride. The intensity of color increases appreciably with rise in temperature of the solutions, making it necessary to carry out all readings at the same temperature.
Acknowledgment The writer wishes to acknowledge with gratitude the support given by the American Zinc and Chemical Co. for the performance of this work.
Literature Cited (1) Berg, R., “Das o-Oxychinolin, ‘Oxin,’ ” Stuttgart, Germany, Ferdinand Enke, 1935. (2) Besthorn, E., and Ibele, S., Ber., 39, 2333 (1906). (3) Boggs, H. M.,and Alben, -4.O., IND.ENQ.CHEM.,A n d . Ed., 8, 9 7 (1936). (4) Hibbard, P. L., Ibid., 6 , 4 2 3 (1934). (5) Ray, P., and Bose, M. K., Mikrochemie, 17, 11 (1935). (6) Ibid., 18, 8 9 (1935). (7) Ray, P., and Bose, M.K., Z and. Chem., 95, 400 (1933). (8) R&y,P.. and Mejundar, A. K., Ibid., 100,324 (1935). (9) Todd, W. R., and Elvehjem, C. A., J. B i d . Chem., 96, 609 (1932). (10) Wood, L. A,, Rev. Sci. Instruments, 7 , 157 (1936). (11) Y o e , J. H., and Crumpler, T. B., IND.ENO.C m x , . h a l . Ed. 7, 281 (1935). RECEIVED March 29, 1938.
A Copper Tube Preheater W. Ri4cNEVIN
AND
H. S. CLARK, Ohio State University, Columbus, Ohio
MA“’
references occur in the literature to the construction and use of preheaters or “catalyzer tubes” for burning oxidizable impurities present in air and commercial oxygen gas. The following is a description of a preheater for
i
2% TJ SHELF
RING STAND
use in microanalyses of carbon and hydrogen. In addition to being very efficient, i t has the advantages of simplicity extreme ruggedness, and low cost of construction. The preheater is made from a 1-meter length of commercial copper tubing approximately 5 mm. in outside diameter with walls 1 mm. thick. Because it has been found convenient t o stand the preheater on the shelf at the back of the desk, this length is greater than may otherwise be needed. At a distance of 30 cm. from the inlet end (see figure), the tubing is wound several times around a pipe of small diameter (1 cm.), forming a compact coil. The coil is clamped in a horizontal position at burner height. At either end of the coil, the tubing is bent downward at right angles and slightly towards the front of the desk in order to clear the shelf. The inlet and exit ends are attached Tvith rubber connections to the pressure regulator and purifying line, respectively. To prevent the rubber connections from being overheated, the two ends are surrounded by water jackets. These consist of 6-cm. lengths of 20-mm. glass tubing fitted at their lower ends over rubber stoppers of proper size. The jackets arr conveniently filled with water from a wash bottle, once a week being sufficiently often even when the apparatus is in constant use. The coil is heated with a Pittsburgh burner and wing top. When first prepared, after flushing out mith grease solvents, the copper tube is heated to redness over it,s entire length with a stream of oxygen passing through. On further heating the coil becomes filled with copper oxide scale, thus providing efficient contact with the entering gas. Two such preheaters have been in daily use in this laboratory for over 6 months without developing leaks through corrosion a t the heating surface. I n order to test the efficiency of this type of preheater, a number of blanks were run using compressed air directly from the laboratory line. Although this air was saturated with colloidal oil and other organic impurities, negligible blanks were obtained. This is probably the most rigorous test possible of the efficiency of the preheater in converting the organic vapors into absorbable products. RECEIVED March 1, 1938.
