*94 it/r. MaJJey on Saltpetre. 
from nothing, but the corrupt bodies with which 
it lies in contadt; and this may fatisfy us, in 
refpedt to the fource, from which other ab- 
forbent earths may derive it. 
Other earths, in common ufe among the falt- 
petre-makers, are thofe of (tables and cow-dalls, 
that have drank up much animal urine? the 
bottoms of (linking pits and ditches, and the 
like. Thefe they take out, and lay in heaps, 
till, by repeated trials, they find them fit for 
their purpofe. It is commonly fuppofed, that, 
during this period, they draw their nitrous quality 
from the air? but for this, there is certainly no 
juft foundation, feeing they are brought to ma¬ 
turity as foon, in the clofeft vault or Cellar, as in 
the moft open expofure. The truth is, that all 
putrid juices contain many oily and mucila¬ 
ginous parts, which, till they are duly attenu¬ 
ated by putrefadtion, will not fuffer any cryftals 
to form in the leys that are drawn from thefe 
earths; and they are laid in thefe heaps, for 
this event to take place. Another end is 
anfwered by this manoeuvre. By being thus laid 
apart, thefe earths are prevented from receiving 
any fre(h fupplies of unputrid matter, which 
might contaminate the juices, that were already 
far advanced in putrefaction. 
The ingenious author of the Chemical Dic¬ 
tionary has told us. That the nitrous acid is no 
where 
