626 
MESSRS. R. T. GLAZEBROOK AND S. SKINNER ON THE 
Table XXII. 
Values of E.M.F. of 
Place of experiment. 
69-71 
69-29 
69-12 
| Berlin. 
- 2 
29 
29 
Berlin. 
- 4 
23 
25 
Berlin. 
- 4 
25 
26 
Cambridge .... 
- 4 
21 
24 
Cambridge .... 
- 3 
19 
20 
Cambridge .... 
• • 
22 
25 
The differences between the cells at Berlin and at Cambridge are practically the 
same. Thus, we may fairly suppose they have not been affected by the journey. 
Dr. Kahle states that it is his experience that an H cell always has a rather lower 
E.M.F. than one with a porous pot put up with the same materials. On this point 
we have made no direct experiments. 
§ 34. Third form of the Board of Trade Memorandum. 
As experience has been gained in the construction of the cells, the Board of Trade 
Memorandum has been somewhat modified. We give it in its third form here. 
The cells constructed in accordance with it are not readity portable, and may possibly 
in time get damaged by the accidental contact of the mercury and zinc. To avoid 
this the porous pot of the Feussner cell, or the cork diaphragm used by Professor 
Carhart, may with advantage be employed. 
Memorandum on the Preparation of the Clark Standard Cell. 
Definition of the Cell. 
The cell consists of zinc and mercury in a saturated solution of zinc sulphate and mercurous sulphate 
in water, prepared with mercurous sulphate in excess, and is conveniently contained in a cylindrical 
glass vessel. 
Preparation of the Materials. 
1. The Mercury .—To secure purity it should be first treated with acid in the usual manner, and 
subsequently distilled in vacuo. 
2. The Zinc .—Take a portion of a rod of pure redistilled zinc, solder to one end a piece of copper 
wire, clean the whole with glass paper, carefully removing any loose pieces of the zinc. Just before 
making up the cell dip the zinc into dilute sulphuric acid, wash with distilled water, and dry with a 
clean cloth or filter paper. 
