of Saltpetre . $il 
The saltpetre is then to he thrown into wooden boxes, 
formed like the hooper of a mill, and having a double 
bottom. The upper bottom is supported, by means of 
pieces of wood, about two inches above the lower one* 
and is pierced full of small holes; through these holes 
the liquor drains off, and finally passes, through a hole 
made in the lower bottom, into a reservoir beneath. In 
these boxes the saltpetre is to be washed, with five parts 
of water to a hundred; this water may be used for dis- 
solving the saltpetre, in future operations; 
The saltpetre, after being well drained, and exposed 
to the air for some hours, upon proper tables for drying 
it, may be afterwards made use of for making gun- 
powder. 
But, when it is intended to make nse of the saltpetre 
for making gunpowder according to the process followed 
since the revolution, it must be much more highly dried. 
| This may be accomplished by placing it in a stove ; or, 
what is more simple, by beating it in a shallow cauldron. 
For this purpose, a layer, five or six inches in thick- 
ness, is to be put in the cauldron, which is to he heat- 
ed to 10 or 50 degrees of Reaumur’s thermometer. 
The saltpetre is to be stirred for two or three hours, 
and to be so much dried, that, when strongly pressed 
in the hand, it does not acquire any consistence, nor 
retain any form, but appears like fine dry sand. 
This degree of dryness is not necessary, when the 
gunpowder is to be made by beating with pestles. 
It is then evident that, according to the method of 
purification we have prescribed, there are two kinds of 
liquor to consider ; first, the water from the various wash- 
ings of the crude saltpetre ; secondly, the water from 
the crystalizing vessels. 
The washing of the crude salpetre is repeated three 
times, as we have already mentioned. 
