ANALYTICAL CHEMISTRY
1582
If it is desired to outgas the purified material a t very low pressures in a system free of lubricant, the cow can be connected to an all-glass highvacuum system a t joint C and the liquid poured directly into a suitable container for subsequent diqtillation in a high vacuum. Before such distillation is performed, the liquid can be frozen in liquid air and the cow sealed off below C to eliminate the lubricant from the high vacuum system. The application of this apparatus to the purification of benzalchloride has been discussed ( 5 ) .
scheme of a test for cyanide ( 2 ) in case both nitrogen and halide have been found present, and a procedure for the reinoval of cyanide if present. ADDENDUM TO SYSTEMATIC TESTS (1)
Figure 2. Tubular Vessel, Showing Inlet Tube
ACKNOWLEDGMENT
The authors would like to express their appreciation to 1). E. Sampson, glassblower a t the University of North Carolina, who made the apparatus, and to Marcus E. Hobbs and Douglas G. Hill for their advice and interest. LITERATURE CITED
(1) Craig, L. C., 1x0. ENG.CHEM., AN.~L.ED.,12, 773 (1940) (2) Keavs. J. L.. Ibid.. 15. 391 (1943). (3) Piper, J. D., Kerstein, N. A., and Fleiger, A . G., Ibid., 14, 738 (1942); 9,403 (1937). (4) Quackenbush, F. W., and Steenbock, H., Ibid., 14, 736 (1942). (5) Scheraga, H. A . , and Hobbs, M . E., J . Am. Chem. SOC., 70, 3015 (1948). R B C ~ I V EJuly D Q, 1948.
Systematic Qualitative Tests for Certain Acidic Elements in Organic Compounds Elimination of Interference by Cyanide EDWARD L. BENNETT AND CARL NIEMANK Calijornia Institute of Technology, Pasadena, Calif.
B-I. Tests for Halogen. In a I- to 1.5-mm. thin-walled capillary a 4- to 5-mm. column of the aqueous extract of the pyrolysis residue is allowed to react with a 3- to 4-mm. column of a solution 0.5 F in silver nitrate and 3 F in nitric acid. The formation of a white or yellow precipitate within 30 seconds indicates the presence of cyanide, chloride, bromide, or iodide. If nitrogen has been found to be absent (A), the test for bromide or iodide (B-2) and the test for iodide (R-3) are performed If nitrogen has been found to be present the remainder of the aqueous extract is transferred with a capillary pipet to a 2-ml beaker, 1 drop of a solution 0.1 F in sodium acetate and 0.1 F in acetic acid is added, and the beaker is covered with a circle of filter paper impregnated with 1 drop of a reagent freshly prepared by mixing equal volumes of 0.015 F aqueous cupric acetate and one half saturated aqueous benzidine acetate ( 2 ) . The appearance of a blue spot on the paper within a few seconds indicates the presence of a cyanide. If cyanide is present, the filter paper is removed and the mixture is heated gently on a hot plate until the test for cyanide with a fresh circle of filter paper, impregnated with the cupric acetate-benzidine acetate reagent, i= negative. Then the test is repeated for halide (B-1) and if positive (chlorine, bromine, or iodine present) tests B-2 (for bromide 01 iodide) and B-3 (for iodide) are performed. RESULTS OBTAINED WITH MODIFIED SYSTEMATIC SCHEME
Cyanide can be detected without difficulty with the cupric acetate-benzidine acetate reagent when as little as 1 microgram of cyanide is present in the aqueous extract of the pyrolysis residue. -4 more seusitive test is not required; if less than I microgram of cyanide is present in the aqueous extract no significant interference by cyanide is observed. If cyanide is present in the aqueous extract of the pyrolysis residue, even in amounts as great as 100 to 200 micrograms, i t can be removed by the recommended procedure to the point where no precipitate is obtained in the test for halide (B-1) if halogens are absent and where bromide and iodide in amounts as lorn as 5 to 10 micrograms can be detected without difficulty. To date there has been no indication that the amount of cyanide that may be formed during a pyrolysis can cause any difficulty in the tests for sulfur, arsenic, and phosphorus ( 1 ). LITERATURE CITED
SYSTEM for the detection of nitrogen, ehlorine, bromine, A iodine, arsenic,sulfur, and phosphorus in a single 1-mg. sample of an organic compound was based upon pyrolysis of the
(1) Bennett, E. L., Gould, C. W., Jr., Swift, E. H., and Niemann, Carl, ANAL.CHEM.,19, 1035 (1947). (2) Feigl, F., “Qualitative Analysis by Spot Tests,” New York, El-
sample in the presence of zinc and calcium oxide (S), detection of the evolved ammonia in the event that nitrogen were present, followed by subsequent tests for the other elements using the pyrolysis residue. For the detection of halides a portion of the rwidue was extracted with water and the aqueous extract was tested for halide with silver nitrate, for bromide or iodide with fluorescein-chloramine-?‘, and for iodide with starch-nitrite. During the past two years students have occasionally reported the presence of halide in nitrogenous compounds containing no halogen. This spurious test har its origin in the fact that some nitrogenous compounds when pyrolyzed with zinc and calcium oxide will occasionally form cyanide as well as ammonia and the student observing the formation of a precipitate of silver cyanide will report the presence of halogen. A41thoughit is unlikely that an experienced observer would be misled, the fact that cyanide ion may also prevent the formation of eojin or tetraiodoeosin, as well as the starch-iodine color, thus offering the possibility that bromine and iodine may be reported absent when actually present, suggested the desirability of modifying the system to avoid all possible difficulties. T h e interference by cyanide has been provided for in the modified tests described below by the addition to the systematic
(3) Johns, I. B., “Laboratory Manual of Micro-Chemistry,” Minneapolis, Minn., Burgess Publishing Co., 1942.
(1)
1
sevier-Nordemann Co., 1939.
RECEIVED December 27, 1948. Contribution 1260, Gates and Crellin Laboratories of Chemistry, California Institute of Technology.
Determination of Saponification Number SIR: In the article on “Determination of Saponification Sumber” [Englis, D. T., and Reinschreiber, J. E., ANAL.CHEM., 21, 602 (1919)], the curves for Figures 1 and 2 were transposed. The figure shown as 2 should appear over the title for Figure 1 and vice versa. This fact is readily evident from the descriptive matter on the graphs. A statement in the sentence starting at the bottom of page 604 requires correction, I t should read: “When the water content
