Mr. Maffey on Saltpetre': 211 
publilhed, by order of the King of France* by 
fome of the molt eminent chemifts, as far pre¬ 
ferable to wood-afhes. Upon many accounts 
it has been before obferved, that Glauber, fome- 
times, threw all forts of dung into a large wooden 
velfel, and, when they had completed their pu¬ 
trefaction, percolated a fixt alkaline folution 
through them ; which furnifhed him with a ley 
of the fame kind and nature with that drawn 
from nitrous earths and wood-allies. This, we 
may prefume, gave occafion for thefe ingenious 
Gentlemen to make fome experiments this way, 
the relult of which they have given to the pub¬ 
lic. We tried this method many years ago, 
with fome fuccefs; but found it depended upon 
the maturity of the materials ; which, indeed, 
may be collected from Glauber. What the 
French writers have faid upon this fubjeft, we 
fhall give in a poftfcript; in order to remove 
every obje&ion againft our attempting to make 
faltpetre in England, upon account of the fcar- 
city of wood allies. 
This difficulty being got over, we trull nothing 
will remain, but to give fuch an account of the 
practical method of making faltpetre as may be 
relied on, and be fufficiently explicit, to prevent 
our falling into any errors. 
The faltpetre makers in Paris chiefly make 
ufe of the rubbifh of old houfes, the ruins of old 
vaults, and cellars, &c. This they reduce to a 
P 2 coarfe 
