electrical and chemical changes. 407 
known to contain water ; and I have little doubt that similar 
effects would be produced by other fused salts containing 
only acid and alkaline matter. 
It may elucidate this part of the subject, which must at best 
be obscure, to take a view of the changes occurring in one of 
the simplest voltaic combinations, that consisting of zinc, 
platinum, and solution of sulphate of soda. It is a fact that 
zinc and platinum become electrical by contact, the zinc 
positive, the platinum negative ; and the two kinds of elec- 
tricity are apparently most intense at the surfaces where they 
are in contact with the fluid, which is too imperfect a con- 
ductor to allow them to neutralize or destroy each other : 
they consequently exert their attractive and repellent powers 
upon the elements of the menstruum ; acid and oxygen cir- 
culate to the surface of zinc, which in consequence is dis- 
solved, and alkali and hydrogen to the surface of platinum, 
of which the hydrogen is disengaged, and the equilibrium 
broken by the contact of the metals is restored by the che- 
mical changes ; so that a constant circulation, or a current of 
electricity, takes place, the power of the combination becom- 
ing feebler in proportion as the solution is decomposed, 
and acid accumulated round its positive, and alkali round 
its negative surface. 
In cases where acids or acid solutions alone are used, the 
destruction of one or both surfaces, with the tranfer of hydro- 
gen or oxygen, seems to produce the same effect ; and the 
inactivity of single circles or Voltaic piles, in which pure 
water is used or saline solutions freed from air, seems to 
show that the destruction of the surface of the oxidable 
