XVIII. On Chemical Philosophy. By Mr.Matruzw ALLAN, 
vie Lecturer. 
[Continued from p. 58.] 
Essay Vil. . 
Tue Garvanic AppaRATUs consists of alternate arrangements 
of copper and zinc plates, the sides of which are placed in con- 
tact with an acid solution; the acid has a stronger attraction for 
the zinc than for the copper; the oxygen too of the water is 
aided in its attraction for the zinc by that contained in the acid ; 
in this way the water and acid are decomposed: the oxygen 
of both is abstracted; part of it combines with the zine, but 
the greater part assumes the gaseous form. In consequence of 
assuming this gaseous form, there must, it is evident, be a pro- 
digious demand for this caloric or ethereal power, to give and 
support this new state of existence which it assumes; and at 
the same time a still larger quantity of hydrogen, the other con- 
stituent of water, is set at liberty, and of course there is here 
demanded a still larger quantity of this power to give it also the 
gaseous form*. It is this demand which explains the effects 
produced by the galvanic arrangement, and the explanation is 
this :—The demand is made through the nearest and best con- 
ductor, which in this arrangement must be the copper ; the cop- 
per is thus robbed of its natural quantity (as is the negative con- 
ductor by the revolutions of the cylinder of the electric machine, 
‘ to be explained presently), and, of course, instantly démands 
“ its due and relative share” from the earth and surrounding 
medium. This supply from the earth and surrounding medium 
is No sooner received, than it is instantly absorbed by the oxygen 
and hydtogen assuming the aériform state; and this current 
during its passage exhibits the correctness of the law already 
briefly hinted at,—that bodies are, relatively to others, positive 
when they are relatively worse conductors. ‘The copper, the 
zinc, and the solution, are relatively to each other in positive and 
hegative states of existence. But though the galvanic action 
might, and does in some measure, accumulate in the solution, on 
the principle of its being the worse conductor; yet this accumu- 
lation is in part prevented, by the current demanded to sup- 
port the changes going on, which stream or current is carried by 
the conducting power of the metals: so that in this way, as I 
have already pointed out, there is produced by chemical means 
a current of this power, as there is by mechanical means in’ 
* It has been frequently repeated, that in every change of existence ca- 
lorie is given out ov absorbed, in the form either of electricity, of galvanism, 
of caloric, or of light. 
Vol. 52, No.244, Aug, 1818. pha electric 
