Mr. MaJJep on Saltpetre. jgi 
From what fource this acid is derived, is at 
prefent unknown. The moll: general opinion 
is, that it is drawn from the air 5 but to this 
there are many objections. In the fipft place, 
the aerial or univerfal acid, is generally allowed 
to be not of the nitrous , but vitriolic kind. And 
fecondly, there are many earths impregnated 
with this acid, which, in all appearance, have 
had no communication with the air, of which 
the foil at the bottoms of graves is a flagrant 
inftance. 
From the well known fa<5t, that the rubbifh 
of all fuch houfes, as have been occupied by 
the filthieft inhabitants, and of fuch clay walls, 
as have flood in the neighbourhood of dunghills, 
or wherever putrid vapours more plentifully 
abound, is always mod ftrongly impregnated 
with this acid, it is moll: natural to believe, 
that thefe vapours mud confer it upon them, 
and consequently, that it mud have its origin 
in putrid fubftancesj but to this, there are like- 
wife many objections. In the fird place, the 
recent juices of vegetables and animals, fame 
few of the former excepted, if we are not mif- 
taken, contain no kind of acid whatever and 
in a putrid date, every body knows they are 
of a volatile alkaline nature, which being the 
mod powerful objection, we fhall here princi¬ 
pally endeavour to remove ; and upon the whole, 
fhall undertake to fhew, that there is an original 
acid 
