vf Saltpetre . . 213 
The liquor which remains above the crystals, produced 
by this treatment of the mother. waters, may be mixed 
with the water of the first crystalization. The muriate 
of soda may be separated from this liquor by simple eva- 
poration ; and the nitrate of potash which it holds in solu- 
tion may be obtained from it by cooling. 
The small quantity of water made use of to whiten 
the refined saltpetre, contains only nitrate of potash; it 
may therefore be made use of for dissolving the saltpetre 
in the cauldrons. 
From the foregoing account it is evident, that a labora- 
tory destined for the purification of saltpetre, according 
to the process here described, ought to be provided with 
the following articles. 
1. Wooden beaters for bruising the crude saltpetre. 
2. Tubs or vats, in which the saltpetre is to be wash 
ed. 
3. A cauldron, in which the solution is to be made. 
4. A crystalizing vessel, of copper, or of lead, in 
which the liquor is to be cooled, and the saltpetre crys- 
talized. 
5. Baskets for draining the crystals. 
0. A wooden box, in which the crystals are to be more 
thoroughly drained, and the saltpetre washed for the last 
time. 
7. Scales for weighing the saltpetre. 
8. Thermometers and pese-liqueurs , to determine the 
degree of heat, and that of consistence. 
9. Rakes to stir the liquor in the crystalizing vessel. 
10. Skimmers to take off the crystals and put them 
into the baskets. 
11. Syphons or cranes to empty the cauldrons. 
The number of these implements, and their dimensions, 
must necessarily vary, according to the quantity of salt- 
petre proposed to be purified. 
