Mr. MaJJey on Saltpetre. 197 
loads, which are perhaps fmall ones, to make one 
hundred weight. There can be no doubt, that the 
trifling value of the materials, and the fmall 
labour that is required, alone enable the faltpetre 
makers to carry on this bufinefs, and that, under 
the lame circumftances it may be carried on in 
other places. 
From the nature and conftitution of thefe 
earths, it muft be evident, that they may be 
eafily formed by methods of art, nothing more 
being neceffary than to lay calcareous earths, in 
conjunction with putrid matters, or to drench 
them with their juices, and to wait, till we .find 
them fit for our purpofe. All this is well known; 
but not fo, we apprehend, the procefs by which 
they are brought to maturity, which is the rea- 
ion that our patience is often put to too fevere 
a trial, in waiting for this event. It is a folly to 
deny, that it is yet afecret, that thefe earths derive 
their peculiar quality from the putrid matters 
with which they are connected, and that they 
are brought to maturity, entirely by putrefadion. 
Glauber, who, from the obfervations he had 
made upon the fruits and effeds of the bottom* 
of (linking ditches, feems to be the firft that 
attempted to form artificial nitre beds, threw 
into pits, covered from the rain and fun, but 
cxpofed as much as poffible to the air, all forts 
pf dung, with the cuttings of trees, refufe of 
O j gardens. 
