336 ESSAYS ann OBSERVATIONS 
char-coal, and blown a little, it makes an ex- 
plofion with a fparkling and flame, like a 
piece of common falt-petre; the faline mat- 
ter is confumed or turned into flame or fmoke, 
and the pure filver is left onthe coal. By 
the way, this may be fome fort of proof, 
that the volatile acid part of nitre is not more 
a fimple elementary matter than is the fixt 
part. 
. NorwiITHsTANDING what has _ been 
fhewn, concerning the ftrong attraction be- 
tween the particles of fpirit of nitre and thofe 
of filver, and the difficulty of feparating 
them by the force of fire; yet, if a piece 
of clean copper is put into a folution of filver . 
in fpirit of nitre, the faline particles moft 
readily thake off the filver, and diffolve the 
copper: which fhews that the particles of 
copper have a flronger attractive power, with 
refpect to the fpirit of nitre, than the parti- 
cles of filver have; which difference of at- 
traction will probably arife from the different 
bulk, figure or'denfity of the particles of the 
two metals, the acid being the fame. The 
fame thing may be faid of iron, zinc, chalk, 
volatile alcaline falt and fixt falt, each of 
which attract {pirit of nitre more ftrongly 
than 
