610 
MESSRS. R. T. G-LAZEBROOK AND S. SKINNER ON THE 
Since with the new zincs the cells Y give normal readings, we infer that the rest of 
their contents were not at fault, though there probably was some difference between 
the solutions in X and Y, for the zinc from Y soon became right when put into X. 
Since the new zincs were inserted the cells have remained nearly normal. 
It will be remembered that the fall noted in the cells described in Table YI. was 
also corrected by the removal of the grey deposit. 
The evidence we have collected on these points is not conclusive, and we are still 
engaged in experiment. There is no doubt that there is a tendency in many cases 
for cells set up with good materials to fall in E.M.F. at first. This drop appears to 
reach a maximum, and in good cells to correct itself fairly soon. In other cells the 
recovery is very slow ; indeed, the experiments must go on for some time longer 
before we can say in all cases whether it will be complete. In such cells a grey 
deposit is formed on the zinc. This deposit is mainly mercury.On removing it 
from the zinc the E.M.F. rises ; the same is the case on substituting an amalgamated 
zinc for the original one; but it is not clear whether this happens because some 
action of the nature of amalgamation is required to prevent slight impurities in the 
zinc sulphate from having an injurious effect, or because even with a pure zinc and 
mercurous sulphate solution an amalgamated surface is required, or again, because the 
action which has led to the formation of the grey deposit has removed from the 
solution injurious impurities. These points are still under examination. 
We are also inclined to think that a trace of acidity in the solutions is useful in 
preventing the formation of the grey deposit; on this point also we are continuing the 
work.! The slight acidity in time corrects itself by its action on the zinc. The 
important fact remains that the formation of this grey deposit must be, as far 
as possible, prevented, and, if it does form, the deposit must be removed. 
The experience of Dr. Schuster with regard to this grey deposit somewhat 
resembles our own. He has kindly sent us the results of measurements of a set of 
rather large cells prepared from commercial sulphate. 
Soon after being set up these cells were tested against some cells made two years 
since. Taking the E.M.F. of this set as unity, the new cells were as follows :— 
* It is only necessary to dip the grey covered zinc rods for a moment in a dilute acid to obtain a 
bright amalgamated surface ; no fresh mercury is required. Dr. Schuster informs us in a letter that 
he has analysed the grey deposit, and found it to be nearly pure mercury. 
t The solutions used in the bad cells Nos. 42-47 were, as tested by litmus paper, distinctly less acid 
than those employed in the good cells Nos. 72-79. While the solution in the cell No. 90 is now less 
acid than that in the bottle from which the cell was originally filled. 
