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The use of a specially designed coulometer and a high accuracy coulometric circuit resulted in the accurate measurement of the electrochemical equivalent and atomic weight of zinc. The experimental conditions to make possible the final precise and accurate measurements were established. These include a study of mechanical losses from the anode during the electrolysis and the corrosion of zinc in various media used in the determination. The effects of both of these sources of error may be controlled. Mechanical losses are minimized when an amalgamated electrode is used; corrosion, when an amalgamated electrode is used in an air free system. An electrolyte, 25 wt. percent NH 4 Cl and 3 molal ZnCl 2 . was used in these determinations. This report presents the account of research which was prerequisite to subsequent accurate determination of the electrochemical equivalent and the atomic weight of zinc.

An experimental study of the current efficiency in the coulometric generation of Ti(III), as a function of electrolyte composition, current density and electrode material, has been performed. The cathodes investigated include platinum, mercury and graphite. The first two are suitable for high-precision determination of uranium. The graphite surface is readily poisoned, rendering it useless for high-accuracy work. The use of mercury requires thorough removal of chloride from the system. The precision and error obtained are comparable for both the mercury and platinum cathodes, and are of the order of 50 ppm.

A new, successful approach to the determination of atomic weights of suitable elements has been demonstrated in this research. An absolute constant-current coulometric method was employed for the determination of the electrochemical equivalent and the atomic weight of zinc. The effects of possible sources of systematic error were investigated and appropriate corrections applied. The newly determined values of the two constants are 0.3387958 mg C -1 and 65.3771 respectively. The uncertainty in the atomic weight of zinc was reduced by more than an order of magnitude. The publication of partial data resulted in the revision of the value of the atomic weight of zinc by the International Union of Pure and Applied Chemistry.

The atomic weight of zinc determined coulometrically for 5 metallic reference samples is 65.377 ± 0.003 where the uncertainty figure is the 95 percent confidence interval for the mean plus an allowance for known possible sources of systematic error.

A method has been developed for the precise assay of potassium dichromate by constant-current coulometric titration with ferrous ions generated at a platinum cathode. It, is shown that one-half gram samples of the dichromate can be titrated with a standard deviation of 0.003 percent.

A method has been developed for the precise assay of halides by constant-current coulometric titration with silver ions generated at a silver anode. It is shown that a 4 milliequivalents sample of halide can be titrated with standard deviation of 0.005 percent.

An absolute method was developed for the determination of boric acid by coulometric titrimetry. The precision of the method, expressed as the standard deviation of a single determination is 0.0033 percent. Changes in the investigated titration parameters produced no significant effects on the titration results. Indications are that within the uncertainty of measurements the method is bias free.