2C>4 Mr. MaJTey on Saltpetre. 
This Gentleman tells us, that if we fprinkle 
the clay floor of a tobacco houfe with ambeer 3 
which we take to be a putrid infufion of tobacco, 
and cover it with the rotten leaves, in a fort¬ 
night’s time, upon removing the leaves, we fhall 
find the floor covered with faltpetre, in the form 
of hoar froft, drawn from the air , which being 
fwept up, and elixiviated with warm water, will 
afford us a ley, that, being boiled down to the 
confidence of cream, will (hoot into cryftals of 
this fait. Now we can eaflly believe, that thefe 
fweepings, with the afliftance of wood-afhes, 
would afford us fuch a ley, but not without; and' 
'therefore muft conclude, that there is here fome 
omiffion. 
We muft farther obferve, that this Gentleman 
takes no notice of any marine fait that is formed 
in this ley, which, being found in all nitrous 
leys, muft render this account very fufpicious. 
And what may give us a more unfavourable 
opinion of this method, is, that, flnce the author 
obtained a reward of three hundred pounds from 
the Britifh Parliament for this notable difcovery, 
we have heard no more of it. 
Whilft the feveral parts or principles of which 
this faline concrete is compofed remained un¬ 
known, we might give credit to a number of 
tales refpetting its origin and formation ; which, 
at this time, without betraying the greateft weak-? 
nefs a 
