1123
V O L U M E 20, NO. 1 1 , N O V E M B E R 1 9 4 8 of the extraction step. The use of the extractor described effectively minimizes this difficulty and allows the full realization of all the advantages otherwise inherent in the Berenblum and Chain nncthod. LITER4TtiRE CITED
ANAL.ED.,13,
(3) Matchett, J. R., and Levine, J., ISD. ENG.CHEM., 264 (1941).
(4) Waprnan, M., and Wright, G. F., Ibid., 17,55 (1945). (5) Wollner, H. J., and Matchett, J. R., I b i d . , 10, 31 (1938).
RECEIVEDDecember 16, 1047. .\i3ed by grant3 f r o m t h e Research Board of t h e University of California, a n d t h e Committee on Growth, a c t i n s f o r t h e American Cancer Society.
(I’ Bairenscheen, H. K., .Wikr.ochim. Acta, 1, 319 (1937). ( 2 ) Berenblum, I., and Chain, E., Biochem. J . , 32, 281, 295 (1938).
Multiple Dropping Mercury Electrodes CLARK E. BKICKER
AYD
N. H. FURMAN
Frick Chemical Laboratory, t’rinceton University, Princeton, .V. J .
HE iicc of several dropping mercury electrodes connected iu Tparalld was apparently first reported in the literature by Rlc(;llvery, Hawkings, and Thode (21. A further article on this subject by De Vries and Barnhart (1) causes the authors to submit this note on unfavorable experience with the use of similar multiple electrodes in 1942. The authors’ electrode was analogous to that described by De Vries and Barnhart, but had a fifth capillary dropping from the middle of the bulb as well as four capillaries connected at the sides of the bulb. This apparatus wa= constructed primarily for making electrolyses in order to recover small but identifiable amounts of reduction products E APPLIED that mere formed upon e l e c t r o l y s i s in t h e Figure 1. Use of Slultiple Electrodes neighborhood of the halfwave potential. These
I
& volt
experiments will be described in a subsequent paper on the polarography of certain organic compounds. The authors also made experiments t,o determine whether the sensitivity could be increased or any other advantage could be derived from the use of multiple electrodes in polarographic determinations. The drop times of the various capillaries differed and irregular fluctuations in current were found a t the top of the wave, as indicated in Figure 1.
All curves of Figure 1 were taken with approximately molar cadmium chloride solution in 0.1 N potassium chloride. Curve 1 recorded with a single dropping electrode a t a sensitivity of 0.13 microampere per mm. Curve 2 recorded with the multipl? device with five capillaries dropping simultaneously, a t a sensitivity of 0.26 microampere per mm. Curve 3 recorded with a single dropping electrode at a sensitivity of 0.035 microampere per nini. The arrows point to 0.60 volt applied. Further irregular curves that were obtained are shown in Figure 2. The solution used for curves I and I1 of Figure 2 contained, per 100 ml., 2 ml. of 0.05 molar cadmium chloride and 2 1111. of 0.05 molar zinc chloride. The solution was 0.1 N in potassium chloride. Curve I is taken a t a sensitivity of 0.13 microampere per nim with a single dropping electrode and curve I1 a t a sensitivity of 0.38 microampere per nim. with the multiple electrode containing five capillaries. The solution for curves I11 and I V contained 0.002 mg. of cadmium per ml. and was 0.1 LVin potassium chloride. Curve 111 was taken a t a sensitivity of 0.013 microampere per mm. and curve IV with the multiple electrode was taken at a setting of 0.026 microampere per mm. The high sensitivity and the irregularities of the multiple electrode are such as to obscure almost entirely the position of the cadmium wave. At the high sensitivity of the galvanometer used in recording the polarogram from a solution containing only 2 micrograms of cadmium per ml. (curve IV, Figure 2), the actual cadmium wave was practically masked by the irrrgular fluctuations of the current. In view of these unfavorable findings, s o r k on the use of multiple electrode systems to increase sensitivity was discontinued. The authors have concluded that multiple dropping mercury electrodes may cause irregular fluctuations in current at the tops of polarographic waves, so that it is difficult or impossible to estimate the nave height accuratclv. LITER4TURE CITED
& d
(1) De Vries, T., and Barnhart, IT. S., Ar.41.. CHEM., 19, 934 (1947). ( 2 ) McGilvery, J., Hawkings, 1%. C., and Thode, H. G., Can. J . Research, 25B, 132 (1947).
80
E
APPLIED
Figure 2. Irregular Curves
RECEIVED .January 29, 1948.
