40 REPORT— 1904. 
was amalgamated, in others it was merely cleaned, in no case did it 
touch the paste. With two cadmium cells set up similarly, a rod of 
cadmium amalgam contained in a glass tube perforated at a few points 
replaced the plain cadmium rod. Very steady temperatures were main- 
tained before taking observations. 
Table V. gives the results of comparisons of these Clark and cadmium 
cells. The standard adopted for the Clarks was cell No. 10, a standard 
more than two years old and fairly constant ; that for the cadmium cells 
was a third cell, No. 48, made up at the same time. 
Cells numbered E 10 and E 11 contained a different paste from that in 
C3,C7,C9. The differences between H and T are small and irregular, 
and probably explained by the non-uniformity of the surface of the zinc 
rods and slight differences in the concentration of the solution. The zine 
rods in E 10, E 11, C 3, and C7 were amalgamated ; that in C9 was 
cleaned only. 
TABLE V.—Differences in Hundredths of a Millivolt. 
Matenon Clark Cells Cadmium Cells 
Observation] — 
E 10 E11 C3 C7 | C5 49 | 47 
July 5,°04-2 —8|+0 
» 6,, |/+0 +2/4+3 
SiS iiss We ek emer (429) 759i) ase ea ma ie 
9 (tt —6l+2 O46 4-2i)498 $1947 a= qa2)  eroleemeeal 
Means |+1 -4 +2 -2,4+4 -—0,+9 +3 |+8 47 |4+2 ais “Fil 
The observations show that no such difference as 0-0004 volt exists 
between the two forms ; the difference found in 1892 is to be attributed 
to other causes, probably the pastes employed. 
APPENDIX II. 
On the Electromotive Force of a Clark Cell. By A. P. Trorrer. 
A determination of the electromotive force of the Clark cell (Wolff’s 
large pattern) in terms of the ampére and ohm, has been made recently 
at the Board of Trade Electrical Standards Laboratory. The ampére, as 
measured by the Standard Ampére Balance of the Board of Trade, was 
passed with suitable precautions through a manganin coil having a 
resistance of 1:4343, ohm at 15°-0 C., and the difference of potential 
between the ends of this coil was compared with that of the Clark cell 
upon a low-resistance potentiometer. After necessary corrections the 
electromotive force of the Clark cell was found to be 1:4329 volts at 
15°0 C. The temperature of the Clark cell was read by a thermometer 
in an oil bath in which the cell was placed, estimating to 0°-01 C. The 
cell had been kept for several months in a constant-temperature room 
and had not varied in temperature by more than 0°-05 ©, for forty-eight 
hours before the comparisons. 
