1037
V O L U M E 2 4 , N O . 6, J U N E 1 9 5 2
suction and the residue washed with acetic acid. The analysis is run directly on the clear filtrate, as described (6).
Table 111. Recovery of Technical Benzene Hexachloride from Soil Samples
CONCLUSIONS
(Weight of each sample 50 grams)
Material Sandy loam Sandy loam extracto Sandy loam
Technical Benzene R ~ ~ Hexachloride, Y (cncor- Blank, Added Recovered rected). % P.P.M. 0 5 ... 0.1 0 0 .. 62 65 i 65 92 93 103
Clav soil Claj. soil extracta Clay soil Muck soil Muck soil extracta
0
3
...
0.06
0 0 62
35 0 62 88
...
0.7
100
..
90 a
...
..
98
Extracted with acetic acid.
proper amounts of zinc dust (about 8.0 grams) and malonic acid (about 5.0 grams) are added. The subsequent dechlorination and nitration are carried out in a specially designed all-glass apparatus. The final absorbancy is read on a Beckman Model B spectrophotometer or other suitable instrument. The details of the analytical procedure have been described ( 6 ) . Soils. For soils high in organic content, a sample of soil containing 50 to 100 micrograms of benzene hexachloride is weighed directly into a 300-nil. Erlenmeyer flask and extracted with 75 ml. of glacial acetic acid for 30 minutes a t room temperature by means of a magnetic stirrer. The suspension is filtered under
~
~ Schechter-Hornstein . ~ ~ ~ The colorimetric determination of benzene hexachloride can best be carried out on a methylene chloride extract of unroasted peanuts. If extracts of roasted peanuts or of peanut butter are analyzed, corrections of about 0.3 p.p.m. have to be made, depending perhaps on the degree of roast. This coirection may be determined by running a sample of the same variety of peanut and of approximately the same degree of roast through all the steps of the analyses and subtracting this blank benzene hexachloride value from the apparent amount of benzene hrxachloride found in the suspected sample. I n general, this colorimetric method can be applied directly to soils. I n the one case in which an appreciable interference was encountered, extraction n ith acetic acid folloived by direct analy?is of the extract gave satiqfactory results. LITERATURE CITED
(1) Baernstein, H. D., IND. Ex;. C m w , ANAL.ED.,15, 251 (1943). Bost, R. W., and Nicholson, F., Ibid., 7 , 190 (1935). Mathews, F. E., J. Chem. Soc., 61, 103 (1892). Meunier, J., Compt. rend., 114, 75 (1892). Schechter, bl. S., and Hornstein, I., .~N.AL. CHEM., 24, 544
(2) (3) (4) (5)
(1952). RECEIVED for review December 8, 1951. Accepted January 24,1952.
Reduction of Carbon Disulfide at Dropping Mercury Electrode I. M. KOLTHOFF, P . E. TORES,
AND
R . W. RAMETTE
School of Chemistry, Znicersity of Minnesota, Minneapolis, Minn.
T JVAS accidentally observed that carbon disulfide yields reA study of
I duction waves a t the dropping mercury electrode. these waves is described in this paper.
-411 chemicals used were of ordinary reagent grade or better. Quantitative measurements were made n i t h a manual polarograph, while a Sargent Model X X I and a Leeds & Northrup Type E were used for qualitative work.
MOLARITY OF CARBON DISULFIDE
x
103
Figure 2. Proportionality of Current to Concentration
I -/ 0
I -I.2
I
-L 4
I
-I, 6
I
-A8
-
V O L T S VS. S.C.E
Figure 1. Cathodic Waves 1. 2. 3.
4 X 1 0 - 4 171 carbon disulfide i n 0.1 M potassium chloride in
presence of 0.006% gelatin and 4 X 10-4 M copper chloride Same, without copper chloride Residual current
Carbon disulfide is very volatile in aqueous solutions. I n order to obtain reproducible results it was necessary to work a t temperatures close to 0" C. A cracked ice bath maintained the cell temperature at about 2' C. Oxygen was removed by using 0.1 M sodium sulfite, which also served as supporting electrolyte. The solution could not be bubbled with nitrogen, as this would remove some carbon disulfide. A.solution of carbon disulfide in methanol m-as standardized by weight, and added from a microburet inserted through the stopper of the polarographic cell. The methanol content of'the resulting solution did not exceed
1038
A N A L Y T I C A LC H E M I S T R Y
1%. Mixing WRE done by a magnetic stirrer. Polarograms and current m ~ a u r e m e n t swere made within 2 minutes after mixing.
Carbon disulfide yields two cathodic waves with half-wave potentials, independent of both p H and concentration, a t - 1.3 and - 1.7 volts (os. saturated calomel electrode). The presence of 0.006% gelatin completely suppresses a maximum on the first wave, The waves are of good form for analytical work (Figure 1) and in the concentration range 2 X 10-4 M to 2 X 10-8 M I a constant value of the ratio id/Crn2/3t*'6 of 2.52 X lo3 'a'liter'sec*'/z mol e.mg .'/s was found a t 2' C. for the first wave (Figure 2). The height of the second wave was 0.95 that of the first. A plot of log i/id - z for the first wave mas linear and had a slope of 0.076, indicating irreversibility. -4ssuming a two-electron sq. em. reduction, a value of the diffusion coefficient of 5.3 X per second is calculated at 2' C., while if the number is one, a value of 2.1 x 10- sq. cm. per second is found. Taking a temperature coefficient of 2% per degree centigrade] a two-electron sq. reduction would correspond a t 25' C. to D = 0.84 X cm. per second and a one-electron reduction to D = 3.3 X
sq. cni. per second. The latter value is close to that of small uncharged molecules (of the order of 3 X 10%sq. cm.per second). Hence, both waves correspond to a one-electron reduction. Probably a free radical is formed in the first reduction. The products formed in both reductions react with cupric copper, for the presence of an equimolar amount of cupric chloride in 0.1 M potassium chloride causes the disappearance of both carbon disulfide waves (Figure l), probably by a process similar to that involved when oxygen is reduced in slightly acid solution ( 1 ) . ACKNOWLEDGMENT
Acknowledgment is made to the Graduate School of the University of Minnesota for a grant n hich enabled the authors to carry out this work. LITERATURE CITED
(1) Kolthoff, I. bI., and Lingane, J. J., "Polarography," p . 309, New York, Interscience Publishers, 1941. RECEIVED for review October 26, 1961. Accepted December 13, 1951.
Improved Stirrer for Special Freezing Point Determinations SAMUEL KAYE Sational.4dcisory Committee f o r Aeronautics, Clecelund, Ohio
HE determination of freezing and melting points of many hydrocarbons and synthesis intermediates is required in the preparation of high purity fuels. Reliable freezing or melting data for some compounds are difficult to obtain because of lack of thermodynamic equilibrium ( 2 ) , supercooling, and abnormal crystallization behavior. The standard procedure for deterY
The reciprocating stirrer,n-hich, after a portion of the liquid had crystallized, frequently generated enough heat to remelt the crystals, was replaced by a rotary, vane-type stirrer. The vanes consisted of broad, thin, metallic surfaces which permeated the entire freezing tube and thus aided the establishment of thermodynamic equilibrium. Use of a freezing tube lined with powdered glass, and a seeding wire, reduced supercooling and the formation of glasses. AI'PARATU S
Figure 1 shows a .side xiew of the apparatus. A worm gear on the shaft of motor Jf drives an asle, on one side of which is at,tached an eccentric, E, for driving the standard reciprocating stirrer ( 1 ) . A set of bevel gears, B , on the oppositeside transmits power t o a vertical shaft on which a drive pulle D, is mounted. The drive pulley id fitted with a spiral spring b e p t o a second pulley, P , mounted a t the top of the stirrer shaft,, 8. This arrangement prevents breakage of the platinum resistance thermometer)
I
w'
2570r
0
1
$
2550-
RECIPROCATING STIRRER
2570/
ROTARY STIRRER
',
a
0 W
2530-
T I M E , MINUTES
Figure 2.
I
W DETAIL OF 5'
26 08-
I
Freezing Point Determination of Water REClPROCIilNG S T R R E R
Figure 1. Rotary Stirrer mining these data ( 1 ) has been modified by the use of a stirrer differing from the reciprocating stirrer of illair et al. a t the National Bureau of Standards. This has reduced or eliminated some of the difficulties
TIYE. LIINUTES
Figure 3.
Freezing Point of Benzene
