397 
electrical and chemical changes. 
to all the metals, and sulphur, which is negative with respect 
to the oxidable metals, by their combinations with metals 
respectively positive to them, produce compounds negative 
with regard to those metals. And in the chemical changes, 
the results are such as must ultimately restore the equili- 
brium, hydrogen or sulphuretted hydrogen passing to the 
negative side, and oxygen to the positive side ; so that the 
oxides are revived ; and not only is the equilibrium restored, 
but the poles sometimes changed. Thus tin that has tarnished 
in acid, remains for some time negative in solution of alkali, 
but gradually as the oxide upon it is revived by the hydrogen 
determined to this surface, it loses its negative power ; and 
the other surface, now tarnished by the action of the alkali, 
gains this power, whilst the opposite surface becomes 
positive. 
V. Of electrical combinations, consisting of two imperfect , and 
one perfect conductor ; or two fluids and a metal , or charcoal . 
To understand clearly the nature of the action in this kind 
of electrical combination, it is necessary to consider the 
nature of imperfect conducting bodies, water, or saline solu- 
tions. These bodies may be regarded as having the same 
relations to electricities of very low intensity, that elastic 
fluids have to the electricities of glass, sealing wax, or the 
common machine. They communicate the electrical pola- 
rities of the metals, but do not appear capable of receiving 
such polarities, or at least of retaining them ; and the elec- 
trical equilibrium, when broken in them, seems to be rapidly 
restored by a new arrangement or attraction of certain of their 
MDCCCXXVI. 3 F 
