568 
MESSRS. R. T. GLAZEBROOK AND S. SKINNER ON THE 
§ 22.—Consideration of errors arising at the Zinc Pole; desirability of amalgamating 
the Zinc Nos. 42-47 with Nos. 80, 81 . 605 
§ 23.—Effect of shaking on the Cells.612 
§ 24.—Set of H Cells put up by Mr. E. H. Griffiths, Nos. 91-96.612 
§ 25.—Comparison with the Board of Trade Cells.613 
§ 26.—The Temperature Coefficient of the Cells. .614 
§ 27.—Portable form of Cell, Nos. 82-83 . 616 
§ 28.— -Yon Helmholtz Standards, Nos. 101-106.618 
§ 29 — Gout’s Standards, Nos. 54, 55, 88, 89 . 619 
§§ 30-35.—Appendix and Summary.620 
Part I.—On the Absolute Electromotive Force of a Clark Cell. 
§ 1. Introduction. 
The experiments recorded in the following paper were undertaken with the object 
of testing various points in the manufacture and use of the Clark cell as a standard of 
electromotive force, specially with a view of investigating the most simple method of 
setting up a number of such cells which should have, within certain limits, a definite 
electromotive force, and of determining the limits within which, it is safe to say, that 
the E.M.F. of such a cell will lie. 
We have also determined afresh the relation between the E.M.F. of a Clark cell and 
the electrochemical equivalent of silver. The experiments have been conducted in 
the main on the lines of those described in Lord Rayleigh’s papers “ On the 
Electrochemical Equivalent of Silver and on the Absolute Electromotive Force of 
Clark Cells” (‘Phil. Trans.,’ Part II., 1884), and “On the Clark Cell as a Standard 
of Electromotive Force” (‘ Phil. Trans.,’ Part II., 1885). 
The investigation was undertaken in connection with the work of the Committee 
appointed by the Board of Trade on Standards for the Measurement of Electricity. 
Resolution No. 14 of the Report of that Committee is as follows :— 
“ That the electrical pressure at a temperature of 62° F. between the poles or 
electrodes of the voltaic cell known as Clark’s cell may be taken as not differing from 
a pressure of 1*433 volt by more than an amount which will be determined by a 
Sub-Committee appointed to investigate the question, who will prepare a specification 
for the construction and use of the cell.” 
The following paper contains an account of some of the experiments made during 
the investigation. 
In the same Report, Resolution 10 states that an unvarying current, wdiich, when 
passed through a solution of nitrate of silver in water, in accordance with the 
specification attached to this report, deposits silver at the rate of O'OOlllS of a 
gramme per second, may be taken as a current of 1 ampere. 
The specification referred to is as follows :— 
