Mr. MaJJey on Saltpetre. 215 
a thick black fcum, and is taken off with it. 
But, before the whites of eggs, &c. are thrown 
in, the boiling liquor is cooled, by adding a 
pailful of cold water. The lixivium being thus 
clarified, is treated as before. 
The ecu mere of this operation, being boiled 
again, yields a faltpetre of the fame colour with 
the firft ; and fome faltpetre goes through a third 
operation of the fame kind to give it a greater 
degree of purity. 
The bafons in which the ley is fet for the falt¬ 
petre to cryftallize, are clofely fitted with wooden 
covers, to prevent the too free entrance of the 
air, which, by cooling the liquor too foon, would 
not admit the cryftals to form of fo large a fize. 
The cryftallization is generally completed 
in two or three days; and about one fourth part 
is fuppofed to be loft in refining. 
Such is the method of making faltpetre in 
Paris, as tranfmitted to us by thofe whofe know¬ 
ledge and veracity cannot be called in queftion ; 
in which we can find no myftery or difficulty, 
or any expence that can reafonably deter us 
from engaging in undertakings of this kind. 
The tnglifn, will, in all probability, be obliged 
to employ other earths than the rubbifh of old 
houfes, which is the cafe with all our neighbours, 
that do not live in large and populous towns ; 
of which earths, we flatter ourfelves, we have 
given a full defeription. And here we cannot help 
P 4 obferving 
