A CELL FOR HIGH-PRECISION CONSTANT-CURRENT COULOMETRY WITH EXTERNAL GENERATION OF TITRANT

A cell has been designed for the high-precision coulometric titration, with externally generated titrant, of materials which otherwise undergo undesirable reactions at the working electrodes. With this cell potassium dichromate has been titrated, via its hydrolysis reaction, with hydroxyl ion generated at the cathode, cathodic reduction of the chromium(VI) being circumvented. In this cell 99·9% of the titrant required is generated in one chamber and transferred to another for reaction; the titration is then completed with titrant generated at a second, drip-type electrode working at much lower current. By means of commercially available Leeds and Northrup coulometric titration electrical equipment, titration of NBS 136b Potassium Dichromate gave a purity of 99·976%, standard deviation 0·005%, and of NBS 84d Potassium Acid Phthalate (done as a check) 99·991%, standard deviation 0·005%, both values being in excellent agreement with other work. © 1969.