184 
\ 
positive electricity of the common machine is able, 
under different circumstances, to effect both decom- 
position and combination. 
452. But the ingenious experiments of Dr Wollas- 
ton farther shew, that the negative electricity of the 
same machine, like that of the Voltaic battery, effects 
only decomposition. He coated a portion of silver- 
wire, m of an inch in diameter, with sealing wax, 
and, by cutting through the middle of the waxed 
portion, exposed a section of the wire. The two 
coated extremities of the divided wire were then im- 
mersed in a solution of sulphate of copper, placed in 
an electric circuit between the two conductors of a 
common machine; and sparks, taken at one-tenth 
of an inch distance, were passed, by means of 
the wires, through the solution. After one hundred 
turns of the machine, the wire which communicated 
with the negative conductor had a precipitate form- 
ed on its surface, which was evidently copper ; but 
the opposite wire had no such coating. Upon re- 
versing the direction of the current of electricity, the 
order of the phenomena was of course reversed ; the 
copper being shortly redissolved by assistance of the 
oxidating power of positive electricity, and a similar 
precipitate formed on the opposite wire. A similar 
experiment, made with gold wire, in a solution of 
corrosive sublimate, had the same effect *. These 
facts, therefore, seem clearly to prove, that, by the 
common machine, as well as by the Voltaic battery, 
decomposition only is effected at the negative pole; 
* Phil. Trans, an. 1801, p. 429. 
