514 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
The amalgam dropping-electrodes were similar to those used 
by Maclnnes and Parker 13 , The amalgam was allowed to drop 
slowly into two small half-cells through capillary tubes con- 
nected to a common container. These capillary tubes were about 
cne millimeter in diameter and were fitted with stop -cocks to 
regulate the flow. To insure good contact between the amalgam 
electrodes, platinum wires were fused into each of these capil- 
lary tubes just below the stop-cocks; these were then joined by 
a copper wire. 
Numerous experiments were made to determine the most suit- 
able concentration of the amalgam. A concentration of .002 
per cent was observed to give the best results. It was found 
that by dropping from 20 to 30 drops per minute no appreciable 
bubbling occurred on the electrode. The voltage remained very 
constant for several minutes. The galvanometer would waver 
off slightly occasionally, but it would immediately return upon 
the formation of another drop of the amalgam. 
All measurements of electromotive force were made with a 
Wolff potentiometer in connection with a sensitive Leeds and 
Northrup, “Type H, ” wall galvanometer. Differences of po- 
tential of .01 millivolt were easily detected in the aqueous solu- 
tions, but owing to the greater resistance in the more dilute non- 
aqueous solutions it was sensitive only to .05 millivolt. A Cad- 
mium-Weston cell which had been recently standardized and 
occasionally rechecked against a similar element certified by the 
Bureau of 'Standards was used as the standard of reference. Al- 
though its temperature coefficient is practically negligible, this 
cell was kept in an insulated glass beaker, suspended in the 
constant temperature bath. All measurements were made at 25°. 
The constant temperature bath used was mechanically stirred, 
electrically heated and electrically controlled at 25° ± .01. 
In all cases at least four cells of each combination were meas- 
ured. This, together with the fact that more than one electrode 
was used in each solution certifies to the degree of accuracy ob- 
tained in this work. 
DISCUSSION. 
The experimental results obtained are to be found in the ac- 
companying tables. Table I contains the observed and calcu- 
lated electromotive forces and the transport number of the ca- 
13 Loe. cit. 
