212 On the Purification 
In these three operations, thirty-live parts of water to 
a hundred of saltpetre, according to the quantity of it 
meant to be purified, are employed in washing. 
These washings are founded upon the principle which 
establishes, that cold water dissolves the muriate of soda, 
(sea-salt,) the earthy nitrates and muriates, and the co- 
louring principle, while it scarcely acts upon the nitrate 
of potash, (pure saltpetre.) 
The water from these three washings, therefore, con- 
tains the muriate of soda, the earthy salts, the colouring 
principle, and a small portion of nitrate of potash, the 
quantity of which is in proportion to the muriate of soda, 
which determines its solution. 
The water from the crystalizing vessels contains that 
portion of muriate of soda, and of earthy salts, which 
were not dissolved by the washings, also a more consi- 
derable quantity of nitrate of potash than was contained 
in the water of the washings. 
The water which is employed at the end of the pro- 
cess, to wash and whiten the crystals placed in the wood- 
en box, holds in solution only a small quantity of nitrate 
of potash. 
These liquors therefore are of a very different nature. 
The waters proceeding from the washings, may pro- 
perly be called mother-waters ; they ought to be collect- 
ed together in basons, and treated with potash, according 
to the usual method. At the refinery called cle V Unite, 
they are evaporated to sixty- six degrees, and the muriate 
of soda is taken away, as fast as it is deposited ; this so- 
lution is saturated with potash, in the proportion of two 
or three to the hundred ; it is then suffered to settle, and 
the liquor is afterwards decanted into crystalizing ves- 
sels, in which are thrown twenty parts of water to a 
hundred, that all the muriate of soda may be kept in so- 
lution. 
