May 15, 1933
INDUSTRIAL AND ENGINEERING
concentration of stannous chloride if it is small are known to affect the rate of formation of the suspension, the time concentration curve should be determined by each analyst for the conditions under which he will make his determinations. No substances were found to interfere with this determination except the noble metals such as gold and platinum which form colloids and obscure in whole or in part the colloidal arsenic. SUMMARY
1. When an excess of stannous chloride is added to mercuric chloride dissolved in concentrated hydrochloric acid, no cloudiness appears if the concentration of the mercuric chloride is as low as 0,00001 M . 2. Bettendorff’s test made in the absence of mercuric chloride will detect the arsenic in 10 cc. of 0.00001 M arsenic trioxide dissolved in concentrated hydrochloric acid. The faint brown color appears in about 10 minutes. 3. When, in addition to saturated stannous chloride, enough mercuric chloride to produce a concentration of 0.00001 M is added to solutions of arsenic trioxide in concentrated hydrochloric acid, colorations appear immediately when concentrations of arsenic trioxide are as low as 0.00001 M and in one minute with concentrations as small as 0.0000001 M with respect to arsenic trioxide.
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4. The presence of mercuric chloride hastens the appearance of the coloration due to arsenic in Bettendorff’s test after boiling with potassium chlorate. 5. The presence of mercuric chloride reduces the concentration of hydrochloric acid required for Bettendoxff’s test from more than 5 M to 3 M when the concentration of arsenic trioxide is 0.001 M . 6. The time required for the appearance and development of the arsenic suspension is a function of the concentration of mercuric chloride in the solution. This behavior may be used to determine the concentrations of mercuric chloride in concentrations as low as 0.00000002 M . 7. The preferred procedure is to compare the increasing depth of color in experimental suspensions to prepared standards. Several comparisons may be made. LITERATURE CITED (1) Blyth and Cox, “Foods and Their Composition and Analysis,” 7th ed., p. 439, Charles Griffin & Co., London, 1927. (2) Ibid., p. 442, Figure 78. (3) Feigl, Mikrochem., 10,305 (1931). (4) Feigl and Krumholz, Ber., 62, 1138 (1929). (5) Hahn, Ibid., 65, 840 (1932). (6) Mellor, “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. IX, p. 241, Longmans, 1929. (7) Muhe, H., 2. anal. Chem., 55, 359-63 (1916). RBCEIVED September 14, 1932.
Loading Combustion Tube in Carbon and Hydrogen Determination on Liquids J. R. BAILEY,Chemical Laboratory, University of Texas, Austin, Texas
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N CONNECTION with research on petroleum bases, involving many analyses of liquid samples for carbon and hydrogen, the direct introduction of the sample into the combistion tube from a pipet has proved more satisfactory than the use of a boat or a glass bulb. A standard weighing pipet (Figure 1) of 2.5 cc. capacity is employed, and, to avoid trapping air a t the delivery end of the pipet, a capillary hole- A- is drilled through the mantle below its ground-glass connection. I n loading the combustion tube, a removable layer of copper oxide, constituting about half of the charge, is transferred to a Thiele reservoir of 100 cc. capacity, and then the tube is secured in a rigid vertical position in a stand (Figure 2) which carries a projecting plate a t the lower end, with a cup B for insertion of the tube and a hinged clasp C above for keeping it plumb. A brass pipet holder is attached to the combustion tube a t D; the pipet, held a t the stopcock with the index finger and thumb of one hand, is withdrawn from its mantle and the projecting end above the bulb is inserted through a circular hole (slightly inclined) in the guide plate F , far enough to allow the outlet end to pass into a slit leading to the conical seat E. On release of the pipet, the bulb is adjusted to its conical support and the pipet is centered automatically just above the FIGURE1
combustion tube in such alignment that, on introduction of the sample, every drop descends to the permanent layer of copper o x i d e , without i m p i n g i n g along the sides of the combustion tube. The pipet can be quickly returned to the mantle for weighing and after the pipet holder is detached the Thiele reservoir is placed over the combustion tube and copper oxide s h a k e n in above the sample. This procedure in analysis of liquids of low volatility insures complete comb u s t i o n and reduces to a minimum the danger of a mishap in m a n i p u l a t i o n , which might result in loss or contamination of sample. e
ACKNOWLEDGMENT Credit is due W. L. Benson , m e c h a n i c i a n in this laboratory, for construction of the metal equipment described in this paper. IGURE
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RECEIVBD February 17, 19aa.
