CLARK CELL AS A STANDARD OF ELECTROMOTIVE FORCE. 
009 
their values and those of the standard are given in the first two columns of Table XII. 
In column 5 is given c—d, the difference between the E.M.F. of the Clark Y and the 
standard; it is negative, as Y had too small an E M.F. The zinc, c, was then trans¬ 
ferred to the Woulfe’s bottle, e being placed in Y. If the error is due to the zinc, 
and it retains its properties in the new liquid, the E.M.F. between b and c will be 
less than that of the standard, that between d and e will have its normal value, and 
there will be a difference of potential between the two zincs, a and c. On making 
the transference these effects took place, as is shown by the last three columns of 
Table XII., but the zinc c, when transplanted into the new liquor, rapidly changed, 
and the E.M.F. between b and c soon became nearly normal in amount. Columns G 
and 7 give the differences between the electromotive forces of c — b and e — d, respec¬ 
tively, and the Clark; while column 8 gives the difference of potential actually 
observed between a and c. It is clear that some effect had taken place in the cell Y 
on the zinc which produced the low E.M.F. observed. The liquid of X acted in a 
short time on this zinc in such a way as to counteract this effect. 
Table XII. 
Cell. 
Tempera¬ 
ture. 
Before changing zincs. 
After chan 
ging zincs. 
a — b. 
e — b. 
c — d. 
c — b. 
e — d. 
Difference 
between 
a and c. 
No. 47, 
O 
17-2 
-1 
0 
-33 
-11 
-14 
9 
on Aug. 19 
- 9 
- 4 
8 
- 3 
Q 
— O 
_ 2 
- 8 
- 2 
8 
No. 46, 
17-6 
-1 
0 
-23 
-15 
- 1 
23 
on Ang. 19 
10 
6 
- 6 
— 2 
6 
No. 45, 
16-9 
0 
0 
-23 
-21 
on Aug. 21 
-20 
-16 
-15 
• 
- 8 
- 3 
No. 44, 
16-8 
0 
0 
-36 
-501 
Immediately 
on Aug. 21 
-45 
after insertion 
-351 
In a few 
-30 
minutes 
— 25" 
-18 
-10 
- 1 
- 7 
4 i 
MDOCCXCII. — A. 
