178 Mr. Herschel on certain motions produced in 
a very simple and interesting experiment. When the nega- 
tive wire is detached and the circuit broken, the mercury lies 
quiet at the bottom of the vessel, with the exception of a 
slight irregular motion on its surface, and now and then a 
minute gas bubble disengaged. Now touch it under the 
liquid with a clean metallic wire of any kind ( provided its 
extremity be not allayed with sodium), and a violent action 
instantly commences. The mercury rushes on all sides to 
the wire in a superficial current as if to give out its sodium, 
while a copious stream of hydrogen is given off from the 
wire, not merely at the point of contact with the mercury, 
but wherever it touches the liquid. In a word, the sodium, 
the wire, and the liquid form a voltaic combination, and the 
electricity produced by the contact is sufficiently powerful to 
decompose the aqueous portion of the latter in great abund- 
ance. The action lasts for a longer or shorter time accord- 
ingly as the mercury is more or less highly charged with the 
alkaline metal, rarely, however, for more than 10 or 12 se- 
conds, and when over, the mercury is found to have lost its 
positive property, and to be reduced to its pristine state, (pro- 
vided the contact be made with copper or platina), which a 
long immersion in the fluid without such contact would not 
have entirely effected. 
26. If the mercury thus charged with the alkaline base be 
not entirely covered with the fluid, and the metallic contact be 
made at the vertex of the globule, out of the liquid, no effect 
is produced ; but if the other end of the metallic wire be 
bent round and brought to touch the liquid at some distance 
from the mercury, the violent action above described imme- 
diately commences ; with this difference, that now the surface 
