&14* On the Purification 
Supposing it is wished to purify ten thousand pounds 
of crude saltpetre per day ; the number of men and utem 
sils, necessary for that purpose, may be determined ac 
cording to the following calculation* 
On Weighing and Bruising the Crude Saltpetre . 
A piece of ground must be set apart, as near the maga- 
zine as possible, for the purpose of beating or bruising 
the crude saltpetre. 
This ground must be covered with broad smooth stones, 
or with very thick boards. 
For bruising the saltpetre, wooden beaters may be 
made use of, similar to those which are used for beating 
mortar. 
Two men are sufficient for carrying the saltpetre to 
the magazine, for weighing it, and bruising it. 
On Washing the Saltpetre . 
As the three washings take up the space of two days,* 
and as each of the tubs or vats will contain only five or 
six hundred pounds of saltpetre, twenty of them will be 
necessary for the purification of ten thousand pounds. 
These tubs are to be two feet and a half in height, and 
the same in breadth. 
They must be constructed with the greatest care, that 
the water used in washing the saltpetre may not escape 
through them. 
They should be firmly fixed upon a plane, slightly in- 
clined, of such a nature that the water from the saltpetre 
cannot soak into it. This plane should be terminated by 
a gutter, to receive the water from the saltpetre, and to 
* This neither agrees with the time stated, in the beginning of the paper, as 
necessary for the three washings, nor with what has just now been said, that ten 
thousand pounds maybe thus refined per day. We notice this, lest our readers 
should think our translation erroneous. 
