366 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
tive analysis. To avoid possible side reaction we, however, chose to 
use the sulfate in dil. sulfuric acid. Careful testing of the material 
bought on the market 3 showed the presence of even a trace of 
iron to be doubtful. The solution was kept in an atmosphere of 
hydrogen by means of the apparatus of Knecht and Hibbert 4 as 
improved by Thornton and Chapman. 5 
A standard potentiometer, ia highly sensitive galvanometer and 
other standard apparatus were used. The end-points obtained 
by (titrating titanous salt against either oxidizing agent were always 
marked by very sharp and large changes in potential. 
In the experiments of Table I the procedure was as follows. 
Into the titration vessel containing 50 cc. about 0-1 N ferric alum 
TABLE I 
TITRATION OF TITANOUS SULFATE ELECTROMETRICALLY 
WITH PERMANGANATE THROUGH THE MEDIUM 
OF FERRIC IRON 
KMnO* cc. 
TffiSCLL cc. 
TkCSCLL 0.05 N times 
47.10 
33.50 
1.406 
47.12 
33.50 
1.407 
48.91 
34.85 
1.403 
47.08 . 
33.50 
1.405 
47.05 
33.49 
1.405 
Average 1.4052 
made up to about 150 cc. with recently boiled dil. sulfuric acid, 
was passed a rapid stream of washed carbon dioxide for several 
minutes. The electrodes were inserted, stirring was commenced 
and titanous solution was rapidly added in sufficient quantity, but 
not enough to prevent a liberal excess of ferric iron. Per- 
manganate was then added until the voltage rose to the indicated 
end-point as shown by the curve constructed from the data of a 
previous titration. The concentration of the permanganate was 
0.05165 N. 
The determinations of Table II were parallel with the deter- 
minations in Table I, except that the titanous solution was run into 
a measured volume of permanganate until the end-point was 
indicated by the voltage. 
Though some chemists may regard it as not good practice to add 
a reducing solution to permanganate, and doubtless such a pro- 
cedure is not best in some cases, particularly in that of oxalic acid, 
3 From the LaMotte Chemical Company. 
4 Knecht and Hibbert, “New Reduction Methods in Volumetric Analysis,” Hong- 
mans, Green and Co., p. 47; 1918. 
5 Thornton and Chapman, Jour. Am. Chem. Soc., 43, 91 (1921). 
