xxx Of the Method of rendering very finfthle 
marble, which was kept continually warm by fome lighted 
coals fet underneath. This done, fome chafing-difhes, con- 
taining burning charcoal, were placed upon the large infulated 
plate. The combuftion of the coals was helped by a gentle 
wind. Some minutes after, the iron wire, by which the large 
infulated plate was connected with the metal plate of the con- 
denfer, was taken off ; then the metal plate being removed from 
the marble by its infulated handle, and prefen ted to Mr. ca- 
vallo’s electrometer, made the balls of it diverge with negative 
electricity. The experiment was repeated by placing upon the 
large infulated plate four veflels, containing iron filings and 
water, in dead of the chafing-difhes : then fome vitriolic acid 
was poured into thole four veffels, fufficient to caufe a vigor* 
ous effervefcence, and when the ftrongeff ebullition was going, 
to iubfide, the metal plate of the condenfer was removed from 
over the marble ; and being examined, not only electrified' 
the electrometer with negative eleCtricity, but gave a fenlible 
fpark. At this time having tried to obtain eleCtricity from the 
evaporation of water, the effeCts were equivocal or hardly fen- 
fible ; the fame thing happened a few days after, when, 
however we obtained clear ligns of electricity from thofe effer- 
vefcences, which produce fixed and nitrous air. Thofe experi- 
ments were made in a lame room . 
O 
One day the electricity ariling from the evaporation of water 
feemed to be pofitive ; but fubfequent experiments, and other 
circumftances, indicate that fuch a phenomenon muff be attri- 
buted to a miffake. 
Once on repeating thefe experiments in company with Mr. 
le roy, member of the R. A. of Sciences, we could not obtain 
any electricity from the evaporation of water or from corn- 
buff ion, the weather being extremely damp ; but the effer- 
vefcence of iron filings and diluted vitriolic acid produced elec- 
tricity enough to afcertain that it was negative, though it 
afforded no fpark. 
A fihort time before I left Paris I once more repeated the expe- 
riment of the effervefcence of iron filings, &c. with fuccefs. 
This experiment was made in the laboratory of Mr. billaum, 
an inffrument-maker and lover of eleCtricity. 
o 
0 
The 
