MR. DANIELL ON VOLTAIC COMBINATIONS. 
119 
The second object is attained by charging' the exterior space surrounding the mem- 
brane with a saturated solution of sulphate of copper instead of diluted acid : upon 
completing the circuit the current passed freely through this solution ; no hydrogen 
made its appearance upon the conducting plate, but a beautiful pink coating of pure 
copper was precipitated upon it, and thus perpetually renewed its surface. 
When the whole battery was properly arranged and charged in this manner, no 
evolution of gas took place from the generating or conducting plates, either before or 
after the connexions were complete ; but when a voltameter was included in the cir- 
cuit, its action was found to be very energetic. It was also much more steady and 
permanent than that of the ordinary battery ; but still there was a gradual, but very 
slow, decline, which I traced at length to the weakening of the saline solution by the 
precipitation of the copper, and the consequent decline of its conducting power. 
To obviate this defect, I suspended some solid sulphate of copper in small muslin 
bags which just dipped below the surface of the solution in the cylinders ; which 
gradually dissolving as the precipitation proceeded, kept it in a state of saturation. 
This expedient fully answered the purpose, and I found the current perfectly steady for 
six hours together. This arrangement I have since improved by placing the salt in a 
perforated colander of copper fixed to the upper collar. 
Fig. 3. represents a section of this additional arrangement. ( a c fh ) is the colander 
with its central collar {b d eg), which rests by a small ledge upon the rim of the 
cylinder. The membrane is drawn through the collar, and turning over its edge is 
then fastened with twine. 
After this alteration, the effective length of the zinc rods exposed to the action of 
the acid was found to be no more than four inches and a quarter. In ascertaining 
the powers of the battery in single series, the voltameter was the same that I have 
already described ; the specific gravity of the solution of sulphate of copper was found 
to be 1198'5, and I commenced my experiments with the standard sulphuric acid, 
specific gravity 1027'3. 
With this charge, after the circuit had been completed for ten minutes, the mean 
quantity of mixed gases taken at intervals of five minutes for two hours was 2‘1 cu- 
bic inches, the results never varying more than O'] cubic inch from one another. The 
battery was then left in connexion, without the voltameter, for two hours, and again 
examined for three intervals of five minutes, when the mean quantity of gases was 
found as before. It was again left in connexion for two hours, and re-examined with 
the same result. 
Upon adding nitric acid to the solution of sulphate of copper, I found that an inju- 
rious effect was produced ; and that the mean quantity of gas in five minutes was 
lowered to T1 cubic inch : at this rate of action the battery, however, remained 
steady for six hours. 
Returning to the original solution of sulphate of copper for the exterior cavity of 
the cells, I doubled the strength of the dilute acid for the interior ; adding, for this 
i 
