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 at 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 at 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
1583
V O L U M E 21, N O , 1 2 , D E C E M B E R 1 9 4 9 Table I. Weight of Sample, Gram*
4.8146 4.9018 5.4181 5.3021 4.9110 5.1188
Supplementary Determinations
Approximate %of Ethanol i n Final Saponification Mixture NO. Edible Oil A 19 188.4 188.6 19 188.8 19 191.7 67 192.8 65 191.7 67
Average
188.6 182.0
Edible Oil B
5.1381 5.2870 5.0852 4.7905 5.1925 5.1029 5.1663 5.4418 4.8367 5.2680
19 19 19 19 19
66 67 68 66
69
180.4 192.6 191.8 190.8 190.6 194.6 194.8 194.8 194.6 195.2
181.1
194.8
is high and an increased hydrolysis of the soap takes place, one would anticipate higher values for the had-titration of the excess alkali with correspondingly lower saponification numbers." Hence, the results for samples 22 and 23 are anomalous and appear to be in error. Supplementary determinations under similar solvent conditions have been made, in xvhich all samples were saponified under reflux condensers. Some of the samples were then diluted with water to reduce the ethanol content to the indicated values before titration of the excess alkali. These solutions were consequently titrated a t a higher dilution than in
25. 2,4,6-Trinitrotoluene (TNT) NT crystallizes from a variety of organic solvents to give Twell farmed rods, tablets, and plates. The crystals from ethanol me elongated parallel to the e axis but other solventse.g., acetone, ether-ften give crystals elongated parallel to the b axis. There is no evidence of polymorphism for T N T
CRYSTAL MORPHOLOGY (determined by W. C. MeCrone) Cry8td System.
Orthorhombic.
the previous experiments, in which additional heating had been employed to drive off the ethanol. As a result, in the earlier experiments the period of saponification had been prolonged beyond a 30-minute period in these cases. However, in none of the experiments was there evidence of incompletely saponified oil. The results of the supplementary determinations are given in Table I. Under these oonditions, with the final ethanol content about 19%, the saponification numbers have an average more than three units lower than when the ethanol content is about 65%a value oharaoteristic of usual correct operating conditions. A further examination of the conditions which gave the high results for the original samples 22 and 23 will be made t o estahlish whether they have resulted from other cause than random error. The data reported in Table I of the original article were subjected to a statistical analysis in that a t test (Snedecor, G. W., "Statistical Methods," 4th ed., p. 75, Ames, Iowa, Iowa State College Press, 1948) was calculated for the two groups representing, respectively, 67 to 72T0and 34 to 6470 of ethanol in the find solution. The weights of oil were ohosen at random in the two groups, so as to eliminate a variance from that source. The group method of calculation was used. The t value caloulated was 0.73. Tho t values necessary for 1% and 5% levels of significance are 3.25 and 2.26, respectively. Thus, there is no significant difference between the two groups. This gives confirmation to the conclusion that the ethanol content can be varied from 34 to 72%.
D. T.E m u s J A M EE. ~ REINSCRRE~BER
University of Illinois Urbana, Ill.
LOUISA. W O L L E ~ M A N
Form and Habit. Usually elongated pardel to a or e depending on the solvent; acetone or ether ( b ) , alcohol or melt (c). Shows the forms: braohy pinacoid ( O l O ) , prism (1101, and macrodome (0611. Axial Ratio. a : b : c = 0.375:1:0.153; 0.3793:1:0.1493 ( I ) ; 0.376: 1:0.151 (3). Interfacial Angles (Polar). 061 A051 = 93'46; 110 AT10 = 138" 40. X-RAYDIFFRACTION DATA(determined by W. C. MeCrone and A. Humphries). Cell Dimensions. a = 14.99 A,, b = 40.0 &, c = 6.10 A,; a = 14.85 A,, b = 39.5 H., c = 5.96 A. (S). Formula Weights per Cell. 16. Formula Weights. 227.13. Density. 1.654 (flotation). Principal Lines I/I, 0.42
d
6.990 6.655 5.983 6.587 5.404 5.043 4.967 4.711 4.577 4.406 4.270
Figure 1. Trinitrotoluene Crystals A = Grown from melt et -m temperature; B = grown from melt at about 10" C.; C pmwn fmm a fbYmol mired fusion ~
4.141 3.989 3.844 3.745 3.678 3.497 3.423 3.330 3.255 3.143
1
...
0.03 0.46 0.13 0.07 0.14
.
...
0.05
...
0.21
...
0.05 1.00 0.10 0.11
...
0.07 0.04
d 3.049 2.991 2.915 2.867 2.781 2.721 2.668 2.589 2.539 2.430 2.356 2.293 2.235 2.171 2.132 2.058 2.027 1.994 1. 964 1.921 1.869
1/11 0.24 0.18 0.07 0.08
...
0.12 0.10 0.06
...
0.02 0.10 0.07
... ...
0.08
...
0.03 0.03
...
0.03 0.04
