28 
PROFESSORS W. E. AYRTON AND J. PERRY 
Therefore the electro-motive force of a Latimer Clark’s cell should be 
Yolts. 
(Platinum, Mercury) =-p0'156 
(Mercury, Mixture, Amalgamated zinc) = -f- 0“200 
(Amalgamated zinc, Platinum) = +1'12 5 
1-481 
The real value of the electro-motive force of the cell being about 1'46 volts. 
A contact 
difference 
Date. 
The following — 
Has to the following— 
At— 
of 
Remarks. 
potentials, 
in volts. 
° c. 
26/4/78 . 
Amalgamated zinc 
Copper . 
18 
+ 0-894 
Tin. 
18 
+ 0-463 
1 of sulphuric acid with 
18 
-0-429 
5 of distilled water 
by weight. 
if >’ 
1 of sulphuric acid with 
-0-431 
18 
— 0-858 
Wiping the zinc surface increases the 
10 of distilled water 
by volume. 
reading, showing that the half-liquid 
surface of the amalgam introduces some 
indefiniteness. 
if if 
18 
-0-424 
if if 
Distilled water . . . 
18 
+ 0 090 
Readings go down rapidly, but wiping the 
strip of amalgamated zinc dipping into 
the water brings them up again. 
a a 
Strong sulphuric acid . 
18 
+ 0-848 
As the zinc was rapidly acted on slightly 
by the strong sulphuric acid, it required 
re-amalgamating after every few obser¬ 
vations, 
27/4/78 . 
99 if 
Saturated zinc sulphate 
19 
-0-284 
Ho falling off in the readings. 
The induction plates were now regilt. 
12/5/78 . 
Carbon .... 
Zinc. 
21-5 
-0-045 
„ .... 
Copper. 
21-5 
-0-370 
,, .... 
Lead.. 
21-5 
-0-858 
if .... 
Mercury. 
21-5 
+ 0-092 
Platinum . . . 
21-5 
-0143 
15/5/78 . 
Carbon .... 
Zinc. 
22 
-1-143 
Carbon slightly warm, having been washed 
and dried by heating. 
The experiments of carbon with liquids constitute a separate paper. 
21/5/78 . 
Distilled water 
Sulphuric acid . . . 
+ 1-319 
rising to 
+ 1 600 
The connexion between the liquids was made by a glass rod dipped previously into 
distilled water, and the legs of which rested one in each of the porcelain dishes. 
During each of the experiments the readings gradually rose, but if the glass rods were 
taken out, redipped in distilled water, and replaced, they returned to then’ original 
value. In case this might be due to the drying up of the him of water on the surface 
of the connecting glass rod, the connexion between the liquids after the next experi¬ 
ment was made in the following way. In addition to the wetted glass rod, the legs 
