180 Dr. Wright on the Behaviour of Mercury as an Electrode. 
deflected to 90°, and the mercury, which lay extended against the 
side of the vessel, contracted itself into a more globular form, 
and, throwing off the liquid from its surface, appeared above the 
latter dry and bright. The instant, however, that the mereury 
had become contracted, the needle of the galvanometer returned 
to zero; indicating the cessation of the powerful current which 
had passed at the first completion of the circuit. The zine plate 
was then removed from the liquid, and the mercury, after 
remaining contracted for a short time, reassumed its elongated 
form and hid itself beneath the acid. 
Experiment 2.—The mercury was brought to the contracted 
state as before, and the zine plate quickly changed for one of 
platinum. The fluid metal now quickly extended itself ; and at 
the same time a momentary current of great energy was indi- 
cated by the galvanometer, but passing in a contrary direction 
to that obtained by the former arrangement with zine. 
Experiment 3.—The galvanometer was removed, and the zine 
brought for an instant in contact with the mereury ; by which 
means a slight addition of zine to the mercury was effected, 
The result was a contracted state of the mercury which continued 
for eight hours. The globule so contracted was then connected 
with a plate of platinum immersed in the solution, when an 
evolution of hydrogen commenced on the surface of the platinum 
which continued until the mercury suddenly resumed its’ ex- 
tended shape. : 
These experiments appear to indicate that the first effect of 
communication by a connecting wire between the mercury and 
zinc, was to set in motion a current which deposited a thin layer 
or film of hydrogen over the whole surface of the mercury. The 
metal being thus released from its attraction for the acid, 
assumed a form still more globular than it possessed in aix, in 
consequence of the support it received from the liquid surround- 
ing it. The extension of the mercury, which occurred after the 
interruption of the circuit, was probably in consequence of the 
union of the film of hydrogen with the oxygen of the atmo- 
spheric air contained in the water. 
Experiment 4.—A portion of mercury A, brought into the con- 
tracted state as in Exp. 1, was connected, by means of a thin 
wire, with a second portion of mercury B. B instantly con- 
tracted itself as if A had been a plate of zinc. 
Similar but less energetic contractions took place in mercury 
immersed in solutions of common salt, iodide of potassium, and 
other alkaline salts. 
The rapidity of contraction and extension in the mercury was 
greatly enhanced by the addition of a little nitrie acid to the 
sulphuric acid solution. Indeed, by placing the extremity of the 
