C. G. Gmeliii’s ObservaUons on the Production 
fully protected from moisture^ and assumed the temperature of 
the surrounding atmosphere, I shall not repeat these particulars 
in the account of every experiment. 
It must, farther be observed, that. the evolved electricity was 
always more intense, if the contacts were made witli some pres- 
sure, (avoiding, however, a motion to and fro,) than if the me- 
tallic plates were but lightly placed upon the powdered sub- 
stance, It might, therefore be suspected, that the evolution of 
electricity in these e xperiments in general, depends upon fric- 
tion ; but, on the other hand,^ it must be owned, that a contact,, 
if joined with pressure, is more perfect; and it will appear here- 
after, that substances of a rough nature, where the friction ought 
to be the greatest^ are just those which acquire either no electri- 
city whatever, or only a very weak one. 
I shall now proceed to the experiments themselves. 
The first substance which I tried was magnesia, as it occurs 
in commerce, and wliich contains some lime. 
Having been ignited, it imparted to the metal, when still quite 
hot, by a single contact, an intense negative electricity. After 
a short time, a point of indifference appeared ; the metal shewed, 
during some time, no traces of electricity. Very soon after, the 
opposite state of electricity was evolved, the metal was positively 
electrified, and the experiment could now be repeated several 
days with the same result. 
I now prepared a perfectly pure magnesia, by dissolving pure 
crystals of sulphate of magnesia in water, and precipitating the 
boiling solution by subcarbonate of potash, free from silica, and 
so on. This magnesia imparted to the metal, under all circum- 
stances^ a positive electricity; being itself negatively electrified, 
both when it was quite hoty and when it had assumed the tempera- 
ture of the atmosphere. The evolved electricity was Intense to 
such a degree, that the gold leaf touched the pile after a single 
contact. 
This experiment, wliich was very often repeated, appeared to 
refute the experiments of Sir H. Davy so fully, that they scarce- 
ly seemed to require any farther -refutation. 
Burned Carrara marble, which was perfectly freed from car- 
bonic acid^ by slacking it in a platina crucible, and strongly ig- 
niting it again, commonly imparted to the metal, after cooling, a 
negative electricity. This was found, in some instances, pretty 
