Mr. Maffey on Saltpetre. 187 
Of this acid, the fource from which it is de¬ 
rived, and the manner in which thefe and other 
earths become impregnated with it, we (hall en¬ 
deavour to give the moft full, and fatisfaclory 
account, as well as of the practical methods of 
making faltpetre, all which might be comprized in 
a page or two, had we not a variety of chimeras 
to encounter, and this practice particularly to 
(explain. By thefe means we hope to remove 
all that myftery and obfcurity in which this fub- 
jedt has been fo long involved ; and to render the 
practice of making faltpetre as eafy and familiar 
to the Englifh, as it has long been to the French 
and Germans, fo much to the advantage of thofp 
nations. 
ON SALTPETRE. 
The great life of faltpetre in the compo- 
fition of gun-powder, has long rendered it an 
objefl of the firft importance ; upon which ac¬ 
count, the learned have fpared no pains to 
obtain the moft perfeft knowledge of it; but 
hitherto, as it l'eems, without fuccefs, as no clear 
and fatisfa&ory account has yet been given of 
it. And though the methods of making it in 
Efance, Germany, and many other parts of the 
world. 
