612 
MESSRS. R. T. GLAZEBROOK AND S. SKINNER ON THE 
zincs, being generally plunged into the more solid part of the paste, were immediately 
amalgamated. 
§ 23. Effect of Shaking on the Cells. 
The history of these cells illustrates another point. Dr. Hopkinson called our 
attention to the fact that he had observed that while slight mechanical shaking did 
not affect the E.M.F. of a good cell it produced considerable change in the E.M.F. of 
one which was too low. This fact we have repeatedly verified. 
Thus, on August 12, Nos. 41, 45, 46, and 47 were all to low. Their E.M.F. in 
each case rose considerably when the cell was tapped, but fell back towards the old 
value when the tapping ceased. Cell No. 40 was right, and no effect was produced by 
tapping it. 
The effect of the shaking would appear to take place through its bringing fresh 
zinc surfaces into contact with the solution. 
A similar result took place with some cells which were too high, only, in this case, 
the E.M.F. was lowered. Thus, on August 6th, No. 68 was 56 too high ; on tapping, 
its E.M.F. fell till it was only 23 too high; it then rose to about its original value ; 
and hence, on further tapping, fell to within 5 of the standard. Cells No. 71 and 72 
were quite unaffected by the tapping, remaining within 1 or 2 of the standard 
throughout. Another cell sent us to test was about 20 too high ; on slight tapping it 
fell to about 10. 
Thus, it appears that slight tapping produces a change in bad cells; we have never 
found it produce any change in good ones. 
§ 24. Mr. E. H. Griffiths’ II Cells. 
Table XIII. contains details of a set of II cells, constructed in February, 1888, by 
Mr. E. IT. Griffiths, which have been subject to much careful examination. They 
were tested against the Board of Trade cells. The results are important, because 
the cells are very consistent among themselves, and, at the same time, they are 
undoubtedly wrong. They appear to be unsaturated, and have, in consequence, a 
lower temperature coefficient than our cells, and agree with them more nearly at low 
than at high temperatures. It is clear, then, that a set of cells may be made which 
will agree among themselves, and yet be wrong. Mr. Griffiths writes as follows of 
the materials used :— 
“ Re-distilled zinc and mercurous sulphate were used. The solution of zinc sulphate 
was allowed to stand and not used unless it deposited crystals of the proper form. 
The mercury was some which I had purified and distilled myself.” 
The first three series of observations given in the table were made by Mr. Griffiths. 
The temperature was in each case nearly 15°, and the observations were corrected to 
15° by the use of Lord Rayleigh’s coefficient. This coefficient is clearly wrong for 
