CONVENIENT STANDARD CELL 
169 
A CONVENIENT STANDAKD CELL. 
DIED UNG HUONG AND J. N. PEARCE. 
Until recently both the Clark and the Weston cells have served 
as standard sources of electromotive force. Both of these con- 
sist of an amalgam of a metal as the anode covered by a satur- 
ated solution of the sulphate of the metal and this in conjunc- 
tion with mercury and mercurous sulphate which serves as the 
cathode. 
Clark cell; (Hg-Znl-ZnSO^-HgaSO.-Hg. 
Weston cell: (Hg-CU-CdSO^-Hg^SO.-Hg. 
For various reasons the acceptance of the Clark cell as a 
standard has been discontinued. The Weston cell, chiefly on 
account of its approximately negligible temperature coefficient, 
is now the sole accepted standard of electromotive force. 
The object of this investigation was to make a study of amal- 
'gam cells of the Weston type and to determine whether there 
may not be other amalgam cells which might serve as suitable 
and convenient standards of electromotive force. 
With this idea in mind, amalgams of several metals were pre- 
pared and used as anodes against the mercury as cathode. Of 
these the copper amalgam cells appeared most favorable. They 
present at least one distinct advantage, viz., all of the con- 
stituents of the cell are easily obtained in a very pure form. 
A number of these cells have been prepared, their reproduci- 
bility has been determined and their temperature coefficients 
measured. 
EXPERIMENTAL. 
Mercury. The so-called ‘‘chemically pure” mercury (Kahl- 
baum) was further purified by vigorously shaking with pure 
dilute nitric acid. The acid and the dissolved impurities were 
then completely removed by shaking ten times with successive 
portions of hot distilled water. The mercury and the water 
were then separated by means of a separatory funnel and the 
mercury allowed to trickle through a dry filter. 
Mercurous Sulphate. Kahlbaum’s chemically pure mercurous 
sulphate was shaken with five successive portions of a saturated 
solution of copper sulphate. After each shaking the mercurous 
