Mr. Mafjey on Saitptre, 20$. 
flefs, we cannot give the lead ear to—of its being 
drawn from the air—of its being generated in 
Vegetables and animals—of its being found upon 
the furface of old walls—and, to conclude the 
whole, of its being formed without the adiftance 
of a fixt fait; all which mud be found equally 
repugnant to reafon and experience, which we 
may bring the ordinary pra&ice of making falt- 
petre to confirm. 
And here, we cannot help expreding our fur- 
prize, that fo much time has been fpent by many 
ingenious perfons in the difcovery of new methods 
of making faltpetre, w'hen it mud be obvious, 
that, in cafe they fucceeded, there is none 
that could be more plain, fimple, and lefs ex- 
penfive, than the old and approved one, of which, 
vve fhall now proceed to give a more particular 
account. 
•In large and populous towns, the faltpetre 
makers chiefly make ufe of the rubbilh of old 
houfes, the ruins of old vaults and cellars, &c, 
Thefe they collect, and, having reduced them to 
a coarfe powder, elixiviate with about one third 
the quantity of wood-alhes j in which ley, when 
boiled down to a due confidence, the crydals of 
faltpetre are found to (hoot. During the boiling, 
large quantities of marine fait are formed in 
this lixivium, which, crydallizing whild the lit 
quor is hot, are taken out with perforated ladles. 
The 
