ANALYTICAL EDITION
146
The first two columns of Table I contain the experimental data for Figure 2. The last three columns were obtained from a careful large-scale plot of these data. Application of the above to from the third and fourth columns of the table results in the following: FIRST POTJDNTIALSDIFF. E 0.1482 VI 0.9 0.7 -0.0214 Vz = 1 . 6 E% 0.1268 0.7 -0.0316 E3 = 0.0952 Vs I2 . 3 0.7 -0,0217 Ed = 0.0735 V4 = 3 . 0
-
VOLUMES
SnCOND DIFF.
k;
EL
-
v = V?DD- kD‘
E
-0.0102 = D’
+o. 0099
[1.6 X (O.OZOl)]
THIRD DIFF.
+0.0201 = D
- [0.7X (-0.0102)l
0.0201 0.03216 0.00714 0.0201 = 1.955 CC.
+
Of the determined for 1‘ 1.955 cc., with the point of maximum rate of change of E with Ti as fixed by a carefully drawn plot of the derivative, 2.0 cc., shows that the difference is well within the accuracy of the titration. A number of exactly silnilar titrations were made, differing only in the amount of acid added initially, and the end points determined by both methods. The results are listed in Table 11. The analytic results were rounded to the nearest 0.1 CC. for computing the last column. The differences rarely exceed the probable error in drawing the AE/AI‘
Vol. 4, No. 1
versus V curve and are never greater than 0.2 cc. of 0.1 N solution.
II. CoMPARIsoN OF GRAPHIC AND ANALYTIC FOR DETERMINING ENDPOINT OF ELECTROMETRIC TITRATIOS TITRATION VOLUMEOF 0.1 N NaOH Graphio Analytio Diff.
TABLE
cc *
la Ib 2a 2b 3a 3b 30 3d4
7.6 7.6 4.0 4.0 4.6 4.7 4.65 4.7
cc .
7.671 7.647 3.880 3.867 4.617 4.752 4.593 4.545 4.775 4 1.25 1.181 5 7.7 ’ 7.576 0 11.3 11.394 7s 2.0 1.965 7b 2.1 1.923 8a 0.8 0.705 8b 0.8 0.722 9a 3.9 3.930 9b 3.9 3 938 5 Titration ourve visibly unsymmetrical so that two selected for analytic solution.
-0.1 0.0 $0.0
$0.1 0.0 -0.1 +0.06 io.2 -0.1 +0.07 +0.1 -0.1 0.0 +0.2 $0.1 +0.1 0.0 0.0 sets of points were
If the indicator f?htrode is highly reversible, as is the quinhydrone electrode except in appreciably alkaline solution, and comes quickly to equilibrium with the solution, by exerting some care in making the titration the four necessary equidistant Points may be obtained directly without recourse to any Plotting. I n this case it is safest to calculate from at least two sets Of points* R=Q=IV=DAuguet 4, 1931,
A New Microanalytical Test for Carbon Disulfide NATHANIEL TISCHLER, Iowa Staie College, Ames, Iowa
A
REVIEW of the literature shows only three tests for that the test is possibly applicable to double-bonded sulfur carbon disulfide sufficiently sensitive to be considered compounds generally. A series of colorimetric standard concentrations of chemimicroanalytical tests: Feigl and Weisselberg’s (3) tests with Hector’s base and nickel acetate and with formaldehyde and cally pure carbon disuKide precipitated by equivalent amounts plumbate; Feigl and Chargaff’s (8) iodine azide test. These of the reagents has been prepared wherever quantitative detests, however, present certain disadvantages. Hector’s base terminations of traces of carbon disulfide in solution were is not readily available; the formaldehyde-plumbate test made, but it is undoubtedly possible to make more exact requires undue precautions of procedure; sodium azide is ex- quantitative measurements by the use of a colorimeter. The ,writer has applied this microanalytical test to toxicotremely explosive; and the test itself is not sufficiently rapid. A new microanalytical test, based on the formation of the logical studies, and has found it well suited to them; a few brown copper salt of diethyldithiocarbamic acid from carbon drops (as littletas 0.1 cc.) of insect blood showed the presence disulfide, diethylamine, and copper acetate, suggested itself of carbon disulfide when the insects were exposed to saturated to the writer on noting a brief resume (4) of Mayer and Fehl- vapors:of the fumigant for 2 minutes. man’s patented method of precipitating carbon disulfide from gas by absorption with a mixture of amines and metallic ACKNOWLEDGMENT oxides (5), and on recalling Callan and Henderson’s recent Grateful acknowledgment is made to Dr. Ralph M. Hixon use of diethyldithiocarbamic alkaline salts as microcoloriand to Dr. Charles H. Richardson who offered helpful sugmetric reagents for copper (1). Thereagentsused are as follows: 1% (by volume) diethylamine in absolute alcohol; gestions and criticisms, and to Rohm & Haas Company for a fellowship grant for the physiological investigation of the 0.05% (by weight) copper acetate C. P. in absolute alcohol. To test for the presence of carbon disulfide, 1 cc. of diethyl- insecticidal toxicity of carbon disulfide. amine solution and 5 drops of copper acetate solution are LITERATURE CITED added to 1cc. of the solution to be tested. Colorless solutions in acetone, chloroform, ether, and alcohol give a golden-yellow (I) Callan, T., and Henderson, J. A. R., Anal&, 54,650 (1929). color a t a carbon disulfide concentration of 1 to 100,000, a (2) Feigl, F.,and Chargaff, E., Z.anal. Chem., 74,376-80 (1928). (3) Feigl, F., and Weisselberg, K., Ibid., 83,93-104 (1931). pronounced yellow at 1to 500,000, and a faint but perceptible (4) Holta, J. C..and Huff, W. J., Proc. Am. Gas Assocn., 1436-9 tinge a t 1 to 1,000,000. I n aqueous solutions, a precipitate (1927). is formed, but the sensitiveness is the same. ( 5 ) Mayer, M., and Fehlman, A., German Patent 216,463 (Jan. 19, 1908); British Patent 174 (Jan. 4, 1909). Dimethylsulfide and ethyl mercaptan, pure and 1 to 100, failed to give the reaction. However, pure thioacetic acid June 12,1931. gave a similar reaction to carbon disulfide, and it is suggested RECEIVED
