956 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[May 31, 1873. 
horizontally under it, separated, if need be, by a piece of 
muslin, and connection is made by a wire as usual. The 
vertical part of the copper plate, from a little above the 
liquid to the bend, should be varnished ; otherwise solu¬ 
tion principally takes place there, which causes the 
horizontal part of the plate to drop off. Holes are made 
in the silver tray with the view of shortening the com¬ 
munication between the air-surface and the copper plate 
and of facilitating the movements of the salt in solution. 
The solution itself may be contained in a shallow trough 
or saucer. 
That dissolved oxygen is absolutely necessary for this 
chemical change had been already shown ; but it was 
interesting to measure by a galvanometer the difference 
of the currents obtained by means of an ordinary, that is 
aerated, solution of copper nitrate, and one from which 
the air had been separated to the greatest possible extent. 
A Thomson’s galvanometer was employed, which had a 
resistance of 2631‘5 units at 18*3° C. Two cells were 
prepared with vertical plates and alike in all respects, 
except that the one contained an ordinary 6 per cent, 
solution of copper nitrate, and the other a similar solution 
which had been deoxygenized. Another experiment was 
made with a different pair of cells and an 11 per cent, 
solution. It was necessary to use the 1*99 shunt; and 
the following were the amounts of deflection :— 
Expt. I. 
Time after «-- 
immersion. Oxygen- Deoxygen¬ 
ized. ized. 
1 minute 
4 minutes 
12 „ 
49 „ 
78 
72 
68 
14 
9 
6 
Expt. II. 
Oxygen- Deoxygen¬ 
ized. ized. 
130 ... 11 
90 ... 8 
75 ... 6 
58 ... 3*5 
The contrast is evident. That the deoxygenized 
solution does give a deflection at all is due partly to the 
difficulty of excluding air, and partly, perhaps, at first to 
the oxygen condensed on the surface of the silver plate. 
The effect due to the water itself is inappreciable. From 
the nature of the reaction it might be expected that the 
current would gradually diminish on account of the usino* 
up of the dissolved oxygen in the neighbourhood of the 
silver ; such a diminution always does take place, at least 
after the first few vibrations of the needle. As might be 
expected, too, when the amount of action has run down 
considerably, the mere moving of the liquid so as to bring 
fresh parts of the solution against the silver augments the 
currents. 
The same resulted from stirring up the crystals of silver 
in the tray so as to expose new surfaces. If the wire 
be disconnected for a time so as to allow the oxygen to 
diffuse itself from other parts of the solution, and con¬ 
nection then made, the current will be found as strong, or 
nearly so, as before. 
A cell with the plates connected by a wire was placed 
under a bell-jar full of air over mercury. The mercury 
gradually rose inside, as might be expected from the 
absorption of the oxygen in the air. 
The necessity of oxygen and the avidity with which it 
is taken up aie both illustrated by the following experi¬ 
ment :—Two cells with horizontal plates were prepared 
alike in every respect, except that the first was filled with 
a solution simply deprived of oxygen, the second with a 
solution through which a stream of carbonic acid gas had 
been passed for some time. The first was placed in the 
air, the second in a vessel from which the air had been 
expelled by allowing carbonic acid gas to flow into it for 
an hour or two. 
The deflections obtained were as follows, the 1 *999 shunt 
being used and the temperature being 13*7° C. 
Time after immersion. 
In air. 
] minute . 
.... 165 
5 minutes . 
.... 135 
10 . 
.... 135 
In CO,. 
76 ^ 
62 
58 
As the cell in an atmosphere of carbonic acid gas 
showed nearly half as much action as that in the air, each 
cell was short circuited for twenty-three hours, with the 
expectation that any oxygen in the closed vessel would be 
used up ; and, indeed, the most prominent crystals of 
silver in the cell in carbonic acid gas became reddened, 
while a cuprous deposit extended over the whole of the 
crystals in the other cell. When, however, the short wires 
were removed and the galvanometer interposed, the cell 
in the air gave a deflection of 136, practically the same as 
before, but that in carbonic acid gas, instead of showino- a 
great decrease, rose to 80. It was then found that the 
vessel containing the latter slowly admitted air ; so the 
contents were swept out by a fresh stream of carbonic 
acid gas, and it was made properly air-tight. After con¬ 
nection by a short wire for three days the galvanometer 
indicated a deflection of 20, that of the cell in the air 
being 110, temperature 10° C. As this showed a very 
great reduction of the chemical action, carbonic acid gas 
was again passed through the vessel for an hour or two • 
and after a connection of two more days the indication of 
the galvanometer was only 3, while the other cell gave 
115, the temperature being now 10*5° C. The action, 
therefore, was at last reduced almost to nothing ; and the 
original fault in the experiment brought out, perhaps more 
clearly than would otherwise be seen, how eagerly the 
solution will absorb even minute quantities of oxygen 
from the surrounding gas. 
An important point to determine was the best strength 
of the copper nitrate solution. Six per cent, was generally 
preferred, for two reasons':—first, it gives about the maxi¬ 
mum of effect—a solution four times as strong gives less 
than half the deflection, and a solution only a quarter 
as strong gives only two-thirds ; secondly, a stronger 
solution than this 6 per cent, is apt to produce a deposit, 
not of pure cuprous oxide, but of a subnitrate, which 
was supposed to clog up the silver crystals to a greater 
extent. 
Another point investigated was the best proportion be¬ 
tween the areas of the metallic surfaces. Experiments 
were made with vertical plates, in which the silver was 
kept at a uniform size and the copper was diminished by 
covering it more and more with varnish ; and another set 
was made in which the copper remained the same, while 
the silver plate was reduced. 
The results may be thus exhibited :— 
Proportion of surfaces. 
Deflection. 
Silver. 
Copper. 
' ' Expt. I. 
Expt. II. 
Expt. III X 
1 
... 0*25 
24 
... 23 
1 
... 0*50 
... 28 
... 27 
—. _ 
1 
... 0*75 
... 31 
30 
__ „ 
1 
... 1*00 
... 33 
... 32 
... 28 
1 
... 1*33 
, - 
•. . - 
... 28 
1 
... 2*00 
. . . - 
—— 
... 32 
1 
... 4*00 
... — 
— 
... 30 
The increase of the copper surface, therefore, has com¬ 
paratively little effect. 
Proportion of surfaces. Deflection. 
Copper. 
Silver. 
Expt. I. 
Expt. II. 
Expt. Ill, 
1 
0*25 
... — 
.. , - 
7*5 
1 
... 0*50 
. « , - 
_ 
16 
1 
... 0*75 
. . . - 
• . . - 
... 21 
1 
... 1*00 
... 33 
... 32 
... 28 
1 
... 1*33 
... 41 
... 40 
- 
1 
... 2*00 
... 56 
... 54 
1 
... 4*00 
... 96 
... 92 
... - 
The increase, therefore, of the silver or negative metal 
causes an almost proportionate increase in the chemical 
action. This, doubtless, arises from the necessity of 
oxygen, and explains the value of the large surface ex¬ 
posed by the silver crystals in the tray. 
The effect of heat on the action of this cell was ex¬ 
amined ; it increases the action greatly : thus an arrange¬ 
ment which gave a deflection of 40 at 20 9 C. gave one of 
