1872.] Electricity. 131 
not act chemically upon those metals, have their origin in the temporary 
changes of cohesion of the layers of metal and liquid which are in immediate 
and mutual contact, and that these currents may therefore be considered as 
very delicate tests of the kind and amount of temporary molecular movements 
produced by small causes. 
If a piece of amalgamated zinc is made to touch a piece of platinum 
in the presence of acidulated water, the well-known extraction of hydrogen 
bubbles takes place from the latter metal. Whilst trying a series of 
such experiments, and also some of a similar nature, Professor Thomas 
Bloxam observed an unequal evolution of bubbles from some parts of the 
platinum plate, and accordingly submitted the matter to inquiry. The 
first series of experiments had for their obje@ to ascertain the amount of 
gas evolved in a given time from a zinc and platinum plate in contad. 
Expt. 1. A tube graduated to 1 cubic inch was filled with water acidulated with 
one-sixth of strong sulphuric acid; a strip of platinum as obtained from the 
apparatus makers was cut 7 in. long, } in. wide, and introduced into the tube, 
which was then inverted upon a small plate of amalgamated zinc also standing 
in the same acid and water. The time at starting and at the termination was 
accurately recorded, as also the temperature and pressure throughout all the 
experiments. Time resulting from a mean of many experiments was 22 
minutes. Expt. 2. The strip cleaned by heating it in oil of vitriol, and 
thoroughly rinsing in distilled water, gave as a mean result—time 14 minutes. 
Expt. 3. The strip merely passed through the finger several times. Time 28 
minutes. It will be seen from these results that the platinum as it leaves the 
instrument makers is absolutely, so to speak, chemically dirty; but the mere 
contact with the hand is sufficient to materially modify the action. The strip 
cleaned by oil of vitriol was dipped for a moment into solution of common 
salt, and again tried, when the time required for collecting the cubic inch 
of hydrogen was nearly doubled. The strip having been made dirty by 
touching, was ignited in the flame of a good Bunsen lamp for one minute, and 
then arranged in the cubic inch tube. The time required was 15 minutes, 
thus showing that it had been in great measure cleaned, though hardly so 
satisfactorily as in the heating with oil of vitriol. Expt. 4 was devoted to the 
action of copper negative plates in similar strips to the platinum; the mean 
results in these cases were that copper cleaned with nitric acid and washed in 
distilled water gave the cubic inch of hydrogen in 21 minutes. The 
strip passed through the fingers as in the platinum experiment. Time required 
28} minutes. A strip of copper oxidised by heating in air furnished the 
hydrogen in 10 minutes. It would appear from these results, that copper 
behaves ina similar way as to cleanness of surface as platinum, and that the 
oxidised surface tends rather to facilitate the liberation of the hydrogen—per- 
haps from mechanical action, like platinised silver. Expt. 5. Platinised silver, 
as obtained from the makers, arranged in the same way as the foregoing 
experiments, furnished the 1 cubic inch hydrogen in 2} minutes. A strip 
cleaned with oil of vitriol as usual, time 2} minutes. A strip made dirty by 
the fingers, time 3 minutes. Hence it appears that the mechanical action of 
the platinum surface is of great importance, as has been well known, and that 
as received from the makers it is very considerably cleaner than the new 
platinum, because, probably, of its method of preparation. It was also found 
that, comparing smooth with mechanically roughened surfaces of platinum,the 
latter furnished the hydrogen in two-thirds of the time taken by the former. 
Expt. 6. A ceil of Smee’s battery was examined by the galvanometer, using in 
every case a regular strength of acid, the same wires and all conditions the 
same, when the following results were obtained :—The negative plate not 
chemically cleaned, deflection = 52°. Negative plate chemically cleaned, 57°. 
Negative plate made dirty by fingers, 48°. The platinum taken off the surface 
gave deflection 50°. Here it appears, then, that the cleaning of the surface of 
the platinised silver materially diminishes the resistance due to the counter- 
current and polarisation. The last series of experiments were directed to 
ascertain the influence of chemically clean surfaces upon electrolysis. A vol- 
tameter, the electrodes of which were in their ordinary state, was attached to 
