on the Preservation of Metals by Electro-chemical Means. 93° 
that whatever lengths of wire of 1-300th of an inch were used, 
there was no diminution of the protecting effect of the zinc; 
and the experiment was carried so far as to employ the whole 
of a quantity of extremely fine wire, amounting to upwards of 
forty feet in length, and of a diameter equal only to 100-98742 
of an inch, when the results were precisely the same as if the 
zinc and copper had been in immediate contact. 
Pieces of charcoal, which is the worst amongst the more per- 
fect conductors, were connected by being tied together, and 
made the medium of communication between zinc and cop- 
per, upon the same principles, and with the same views as 
those just described, and with precisely the same conse- 
quences. 
In my first experiments upon the effects of increasing the 
length or diminishing the mass of the imperfect or fluid con- 
ducting surface in interfering with the preserving effects of 
metals, I used long narrow tubes; but I found them very in- 
convenient ; and I had recourse to the more simple method of 
employing cotton or tow for this purpose. 
Several feet of copper wire in a spiral form were connected 
with a small piece of zinc wire of about half an inch in length. 
The zine and a portion of the copper were introduced into 
one glass, and the coils of copper wire were introduced into 
other glasses, so as to form a series of six or seven glasses, 
which were filled with sea water, and made part of the same 
voltaic arrangement, by being connected with pieces of tow 
moistened in sea water. 
It was found in these experiments, that when the pieces of 
tow connecting the glasses were half an inch in thickness, the 
preserving effect of the zinc in the first glass was no where 
diminished, but extended apparently equally through the whole 
series, 
When the pieces of tow were about the fifth of an inch in 
thickness, a diminution of the preserving effects of the zinc 
was perceived in the fourth glass, in which there was a slight 
solution of copper; in the fifth glass this result was still more 
distinct, and so on till in the seventh glass there was a con- 
siderable corrosion of the copper. 
When the tow was only the tenth of an inch in thickness, 
the preserving effect of the zinc extended only to the third 
glass; and in each glass more remote, the effect of corrosion 
was more distinct, till in the seventh glass it was nearly the 
same as if there had been no protecting metal. All the che- 
mical changes dependent upon negative electricity were suc- 
cessively and elegantly exhibited in this experiment. In the 
first glass, containing the zinc, there was a caemilie and 
lasty 
