1 96 Mr. Mdjfey on Saltpetre. 
In this manner, are nitrous earths naturally 
formed in thefe parts of the world, and might, 
doubtlefs, be formed in others, though not per¬ 
haps fo expeditioufly, by throwing into (hallow 
ponds of water, natural or artificial, all forts of 
dung and carrion, with other putrid and putre- 
fiable matters; where the water, being evaporated 
by the heat of our fummers, mud certainly leave 
a mud of the fame kind and quality. 
Putrid juices and putrid vapours are difperfed 
through the earth and air, fo that there are few 
earths, of an abforbent kind, that are not, in 
fome degree, nitrous. But it is in thofe only 
that have been drenched in an extraordinary 
degree with thefe juices, or have been long ex- 
pofed to thefe vapours, that this acid is found of 
any confiderable flrength. And, even here, we find 
it but very fparingly difieminated in them, if we 
may judge from the large quantities of earth 
that mud be elixiviated, to obtain a fmall portion 
of faltpetre. Cramer has told us, that two ounces 
of faltpetre may fometimes be extrafled from 
one pound of earth, which we have reafon to 
think is an arrant fable ; fince, in the city of Paris, 
where, we may prefume, thofe earths are fele&ed 
with the bed judgment, we (hall find that one 
bufhel of earth, with half that quantity of wood- 
a(hes, will fcarce produce one pound of this fait; 
and we are informed, that it requires eight cart 
loads. 
