CLARK CELL AS A STANDARD OF ELECTROMOTIVE FORCE. 
G2.°> 
neutralised with ZnO and filtered at 30 3 C., a small quantity of HggSO^ was added, and 
the black deposit was filtered off. In other respects the cells were the same as 
143-148, the Board of Trade directions being followed. These cells assumed the 
standard E.M.F. immediately on formation. 
Cells Nos. 155-157, made according to Lord Rayleigh’s directions from paste 
which had been in stock since Michaelmas, 1889. 
Cell No. 158 the same as Nos. 131-142. except that the zinc was amalgamated. 
Cell No. 159 the same as Nos. 143-148, except that the zinc was amalgamated. 
Cell No. 160 the same as Nos. 149-154, except that the zinc was amalgamated. 
Cells Nos. 131-136 were compared with our standards repeatedly for about a fort¬ 
night after being set up, and showed very close agreement. 
The other cells were compared by Mr. Griffiths with our cell No. 65 ; the set of 
cells described in Table IX., viz., Nos. 65, 69, 70, 77, 78, 79 had again been lent to 
him for this purpose. It appears from our Tables that No. 65 is in very close agree¬ 
ment with our standard, and we may take, therefore, this comparison as giving the 
E.M.F. of Mr. Griffiths cells in terms of the standard. 
Table XIX. —Cells constructed by Mr. E. H. Griffiths. 
Number of cell. 
Date. 
131 
132 
133 
134 
135 
136 
137 
138 
139 
140 
141 
142 
158 
143 
144 
Differences 
Feb., 1892 
1 
1 
1 
1 
2 
2 
0 
1 
1 
1 
2 
2 
3 
2 
1 
July, 1892 
0 
0 
1 
0 
-1 
0 
1 
1 
1 
1 
0 ( 
0 
-1 
3 
2 
145 
146 
147 
148 
159 
149 
150 
151 
152 
153 
154 
160 
155 
156 
157 
Differences 
Feb., 1892 
1 
1 
2 
0 
-1 
-1 
-1 
0 
-1 
0 
-1 
0 
-4 
-4 
-4 
55 
July, 1892 
2 
3 
3 
2 
2 
0 
0 
0 
0 
0 
0 
0 
-4 
-4 
-4 
Table XIX. shows the results ; the unit is slightly less than in our measurements, 
being about "0002 volt. 
In February the temperature was about 13°, in July it was 14 - 4. 
It will be seen that the cells are all fairly close to the standard. Nos. 131-148 are 
on the whole a little too high. A comparison between Nos. 158, 159, and 160, with 
the batches immediately preceding them, respectively shows that amalgamating the 
zinc has in these cases no distinct effect ; the mercurous sulphate in the solution of 
itself insures amalgamation in the cell. 
The series, Nos. 149-154, in which Mr. Griffiths’ method of clearing the zinc 
oxide or basic zinc sulphate from the solution by the action of mercurous sulphate 
