188 
gen gas it did not even commence ; while, in oxy- 
gen gas, or in atmospheric air, ii acted with energy, 
and the oxygen disappeared. These facts were con- 
firmed by Mr Davy, who found, that, in gases devoid 
of oxygen, no Galvanic electricity could be excited ; 
but it was more or less abundantly developed, when 
oxygen gas was present *. 
458. But oxygen gas is necessary to combustion, 
in consequence of the great affinity, which, at a high 
temperature, it exerts towards combustible bases ; 
and, during the process, it enters into combination 
with these bases, and its latent caloric is disengaged. 
In like manner, Dr Wollaston remarks, that the ex- 
citation of Galvanic electricity depends on oxidation ; 
and that the oxidation of the metal is the primary 
cause of the electric phenomena, and is not occasion- 
ed by the electricity itself. In several experiments, in 
which silver and zinc were plunged in water, holding 
mineral acids in solution, the zinc was dissolved, and 
hydrogen gas liberated by decomposition of the wa- 
ter. It would appear, therefore, says he, that, in the 
solution of a metal, electricity is evolved during the 
action of the acid upon it f. 
459. This explanation, continues Dr Wollaston, 
receives additional confirmation from comparative ex- 
periments made with common electricity ; for, in the 
experiment already related (452.), the copper, after 
being precipitated, " was shortly redissolved by assis- 
tance of the oxidating power of common electricity J." 
* Murray's Chem. vol. i, p. 590. 1st edit. 
f Phil. Trans. 1801, p, 427- | Ibid. p. 430. 
