PHYSICALanp LITERARY. 335 
rit of nitre is of itfelf pretty volatile, yet, — 
when it has diffolved filver, the: faline parts 
adhere fo firmly to the metallic, that a very 
{trong degree of heat is required to feparate 
them; for, if a folution of filver is fet in a 
heat that would make water boil, the light 
and watry parts indeed fly off, but afterwards 
the evaporation goes on flowly, unlefs the 
fire is confiderably increafed; and, after fe- 
-veral hours, the matter has {till the appear- 
ance of a very moift alt, which is very cor- 
i -rofive, and, in bulk and weight, greatly ex- 
ceeds the filver that was diffolved. When 
the fand-heat can make no further change on 
the mats, put it into:a crucible, and fet it ina 
pretty brifk and clear fire: thisexpells the re- 
emaining moifture and fuperfluous acid; after 
‘this the matter melts like wax, and; when 
cold, ,is, turned to: a hard fubftance; the 
cauftic quality of which, the increafe of 
weight above that of ‘the iilver, and its apt- 
snefs to. moiften, fhey, that, after all the heat 
which the mafs has fuftained; there is {till a 
good quantity of the faline part of the fpirit 
of nitre intimately incorporated with the fil- 
-yer.. Now, when a piece of this hard {tony 
fubftance is put uponia piece of ‘well kindled 
| char-coal 
