BIT STELV.\RT J
LLOYD
Absolute maxima of conductivity in aqueous solutions have long been known. Kohlrausch and Holborn' give numerous instances of such maxima with acids, bases, and salts, including lithium chloride, zinc chloride, magnesium sulphate, sodium acetate, potassium sulphide, hydrochloric, nitric, sulphuric and formic acids, potassium, sod.ium, and ammonium hydroxides I n fact, nearly all highly soluble salts, except those of the alkalis with strong acids, and a few like silver nitrate, appear to give maxima. The writer has not noticed, however, any record of such phenomena being observed with organic solvents. n'hile studying a t different temperatures the electrolytic deposition of zinc from concentrated solutions of its chloride in glycerine, maxima Ivere observed and a short study of them made. Despite the high solubility of zinc chloride in glycerine the fused anhydrous salt dissolves very slowly until the temperature is raised well above 100'. .It 150' the salt appears to disso1x.e indefinitely, but the gradual decomposition of the glycerine in solutions held a t that temperature precluded any attempt to determine the solubility more closely. Upon cooling concentrated solutioiis made a t temperatures above 100' they solidified always to a jelly-like paste. Measurements of the conductivity of solutions of different strengths were made a t three temperatures, 50°, IOO', and Ijo'. ,In ordinary conductivity cell was used. -It the temperatures in question very little trouble was experienced from air bubbles in the liquid. The most concentrated solution used contained per cc o 2941 gram of zinc, corresponding to o 6131 gram zinc chloride. The following table contains the results of the conductivity measurements : ~
~
'
~~
~~~
Lcitvermogcn dcr TSlcctrolvtc. pagc I 4 j , r X q 8 cditton
Conductivity -\/laxima in Gljicerine I jo"
1000
Resistance i n
265
SO0
Zinc per cc Gram
Resistance i n ohms
o 2941
31 4
206
5 600
0 2000
37 39 4
2350
5; 3
I53 134 4 '33 150 S
70
2 00
'470 o 1130 0 0735 0 0367 0
$1
ohnis
2
Resistance i n ohms
1326. I IOjO
1035 1301
2 2
From the accompanying curves the position of the maxima. a t the different temperatures be fairly apparent.
Fig.
I
Evidently the concentratioii giving the maximum conductivity a t 150' had not been reached. At 100' the content of zinc for maximum conductivity is in the neighborhood of 0 . 1 3 gram per cc, corresponding to a zinc chloride content of 0 . 2 7 I gram. At 50' the maximum corresponds to a zinc
266
Stewart J . Lloyd
content of about 0 . 0 9 gram, or a zinc chloride content of 0.188 gram per cc.
Jones and Schmidt' have drawn attention t o the remarkably high temperature coefficients of conductivity in fairly dilute glycerine solutions of lithium bromide, cobalt chloride, and potassium iodide, and point out the close relationship between fluidity and conductivity in such solutions. The above solutions likewise show high temperature coefficients, as may easily be seen from the data, and the parallelism between conductivity and viscosity is very apparent, especially in the case of the most concentrated solution. At 50° it was practically solid, n-ith a correspondingly high resistance. No attempts appear to have been made to determine Am. Chem. Jour., 42, 8 8 (1909).
Conductivity L21axima in Glyccrine
26 j
just what conditions must obtain in order to bring about such maxima in aqueous solutions; whether they are due to the increasing viscosity just balancing the increase in the number of ions caused by the addition of more solute; to the addition of more solute failing to increase a t all the number of ions already present; to the virtual change of solvent due to the addition of so much solute; or to a combination of these and perhaps other causes. In the present case it appears highly probable that the rapid increase in viscosity is the important factor, a view which is being subjected a t present to quantitative examination in this laboratory. I.niz'ersity 0-f rllabanin J n i i u a r ~ f lI, 91.3
