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I. Z1,OTOTTYiiJ .\SD I. 11. KOLTHOFF
Tho a i i ~ k ~ cisi ,indeljtcd t o Professor J . TT. IlcBnin Tor his careful reading of the first draft of this paper arid for constructive discussions arising therefrom. He also 11-ishes to thank Professors C. R. Sollcr and R. -1.Ogg for specific information. REFERESCES ADAX,S.IC.,A N D SHUTE,€1.I,.: Trans. Faraday So?. 34, 75s (1938). ADDISOS,C. C.: J. Chem. Soc. 1943,535; 1944,252. BIGELOW, S. L., AXD WASHBL-RS, E. R.: J , Phys. Chem. 32, 321 (192s). BOSD,W.S.,ASD PELS,11. 0 . :Phil. May. 24, 864 (193i). BOCTARIC, A , , 9 N D BERTIIIER, P.: J. chim. phys. 36, 1 (1939). DOSS, K . S. G . : Kolloid-Z. 86,205 (1939). FORD, T. F., A N D WILSOS,D. A. : J. Phys. Chem. 42,1051 (1938). FRETSDLICH,H . : colloid arid C‘apdlary C‘hemisfry, translated from the 3rd German edition by 13. S.Hatfield. E, P.Dutton and Company, Ken- York (1926). (9) HISS,R. : “ c b e r die zeitliche h d c r u n g tier Spannung reiner Fliissigkeitsoberflachen,” Dissertation, Ifeidelberg, 1913. (10) KOFLER,I,.: Die S a p o m h e . J . Springer, Vienna (1927). (11) ?\lcB.~-rs, J . IT., FORD,T. F., ASD XILLS, G . F . : J. -Am. Chem. Soc. 62, 1319 (1940). (12) MCBAIS,,J. w., ASD SPEXCER, w.J-.: J. :lm. Chem. Soc. 62,239 (1940). ~ I C B A I S,J,, W.,A N D SHARP,E. R . : J. Am. Chem. Soc. 63, 1422 (1941). (13) MCBAIS,J. W., A N D WOOD, 1,. -4.: I’roc. Roy. Soc. (London) A174, 286 (1940). (14) NILSER, S.R.:Phil. Mag. [6113,06 (1907). (15) D U Sot%, L . : Equilibrcs scipcrjlciels des soluliorjs colloxdales. Masson e t Cie., Paris (1929). (16) NUTTISG,G. C., LOSG,F . A , , ASD HARKITS, W.D.: J. Am. Chem. SOC. 62,1496 (1940). (17) RAYLEIGH, LORD:Proc. Roy.Soc. (London) 47,281 (1890). (18) ROSS,SYDSET: J. Am. Chem. SOC. 67, 990 (1945). (19) SZYSZHOTTSKI, B. I-.: Z. physil;. Chem. 64, 385 (190s). (20) TSCHESCHE, R . : .Ingen-. Chem. 48, 569 (1935). (21) WARD,A. F . H . , ATD T O R D - ~I,.: I . S a t u r e 154, 146 (19-14). (1) (2) (3) (4) (5) (6) (7) (8)
POLXROGR,tPHIC BBEHAIZT’IORO F _ZLI* of barium and strontium has been discuwd. The polarographic behayior of calcium has been studied by Kimura (2) in the presence of tetrnethylammorlium salts as supporting electrolytes. He frnind that the calcium waves start a t about - 2 . 2 volts (us. the saturated calomel t)lrctrode = S.C.E.). The waves diqplaycd pronounced mavima which could
POL.\IIOGRAPHIC
357
D E T E R J I I S . I T I O S O F C.LLCIUJ1
not be suppressed. Consequently, calcium could not be drterniined polarographically. In the present paper we have investigated the polarographic behavior of calcium in water and in n-ater-ethanol mixtures. -4 procedure has been developed for the polarographic determination of calcium, and al-o of the simultaneous determination of barium, strontium, arid calcium when present together. For experimental details reference is made t o the previous paper (7).
A a.
IC
C c
I
c
H
a -1.825
-2.025
-2.225
-2.425
V.
FIG.1. Calcium-ion maxima in 7%ater and in water-ethanol mixtures. Tetraethylammonium iodide as supporting electrolyte. 0 0012 S calcium. Initial drop time. 3.0 sec. CALCIUJI JVAVES IS S I h I P L E c.~LcIL-~I-Iox SOLUTIOS'j
The current-voltage vun-es of calcurn S ~ O \ T r-ery . pronounced maxima in water solutions. The usual maximum suppressors do not eliminate this maximum. I n the present ~ o r itk ~ r a sfound t h a t in ethanol-u-ater mixtures the masima of calcium x-aws are considerably suppressed. T h e shape of the T I - ~ T ~ Cii~ \c;~ll as
388
I. ZLOTO7VSKI AXD I .
31. I i O L T a O F F
the height of the calcium-io11 ninxinin T\-:I- found to be tlependent greatly on the alcohol concentration. 111 :~queoiisnirditini the i v a ~PS shoiv very acute peakb which change t o smoothly 1 oiintlrd C U ~ V C Pin nirdin containing over 50 per cent ethanol. The hcight l)rwnx>- inialler, thc highpi the alcohol concentration (figure 1 i .
It ik ;o i w c,mphtl.ized that tlic lieiglit of the o h e i v e d niasrna increases with t1,e a m u m t of calcitim in the d u t i o n . €IOUever, there is no linear proportion:ilitr het:\-een the ~ ~ t t i ~ v:iti i ttlw potcntinl :It \\hidl the peak of the curx-e is
3SO
POLdROGKhPHIC DETER~IIS.
