CLARK CELL AS A STANDARD OF ELECTROMOTIVE FORCE. 
619 
§ 29. Gouy’s Cells. 
Another modification of the cells has been suggested by M. Goijy (“ Sur une Pile 
Etalon,” ‘Journal de Physique,’ 1888.) 
It consists of zinc, zinc sulphate, mercuric oxide, and mercury. According to 
M. Gouy, the E.M.F. at any temperature, t, is given in legal volts by 
E = 1-390 — -0002 (t - 12). 
The zinc sulphate solution is prepared by boiling a saturated solution for an hour 
with a few thousandths of its own weight of oxide of silver. The liquid, when cooled 
and filtered, has sticks of zinc put into it, which precipitate any silver remaining. 
Four cells were made ; of these two, viz., Nos. 54 and 55, contain the yellow oxide, the 
other two, Nos. 88 and 89, the red oxide of mercury. The values of the E.M.F. have 
been reduced to 12° by M. Gouy’s coefficient. 
Table XVII. 
Numbers . 
54 
55 
88 
89 
r 
1-3794 
1-3793 
1-3906 
1-3896 
allies . . .s 
1-3803 
1-3806 
1-3867 
1-3806 
1-3869 
1-3890 
L 
1-3809 
• • 
1-3839 
Mean .... 
1-3803 
1-3823 
1-4875 
1-3896 
i 
, 
i 
Mean o£ two . . 
1-3810 
1-3879 
To reduce them to “ legal volts,” and so to compare them with M. Gouy’s results, 
we must multiply these results by the ratio 1063/1060, we have thus the values 1‘385 
and 1-392. The latter is nearly 2 pants in 1000 above M. Gouy’s result. 
4 k 2 
