[ 1 3 § ] 
ther, and the whole is to be prefied flat and 
clofe. 
All this being done as quickly as poflible, the 
fird phenomenon is — A part of the fait deli- 
ad. This part, impregnated with tin, changed 
in colour, and of a thicker confidence, begins 
to froth forth from the ends of the coil. 
3d. A flrong frothing, accompanied with mo- 
derate warmth. 
4th. The emiflion of copious nitrous fumes. 
5th. Heat intolerable to the fingers. 
6th. Explofion and fire, which burft and rufe 
the tin-foil in feveral places, if it be very thin. 
After many conjectures and experiments, I dis- 
covered a property in the cupreous fait, from 
which, and the known affinities of the bodies 
concerned, thefe appearances, however new and 
Angular, may be accounted for. 
The cupreous fait properly dried and placed 
where it may receive a heat, not much greater 
than what the hand can bear, takes fire. The 
circumdances which favour this ignition, and con- 
tribute to produce it in the (mailed degree of heat, 
concur in the following convenient method of 
trying the experiment. 
A piece of foft bibulous paper is to be dipped 
in the nitrous folution of copper, and dried be- 
fore the fire two or three times alternately. Then 
it is to be approached towards the heat, as near 
as can be borne, by the hand which holds it with- 
out pain: there, if it has been diffidently dried, 
it will prefently catch fire, and burn to a brown 
calx. 
The 
