21 8 
Mr. Maffey on Saltpetre . 
with an earthy bafis, from which the earth mud 
be precipitated, and a fixt fait introduced in its 
ftead, to convert it into a true faltpetre. 
Wood-afhes, upon account of the fixt alkali 
they contain, are very proper for this purpofe, 
and the faltpetre makers, by mixing thefe afhes 
with the earths they elixiviate, perform a com¬ 
plex operation in chemiftry; they decompoie 
one fait, and com pole another. 
But as it is the fixt alkali, in the wood-afhes, 
that alone acts upon the nitre with an earthy 
bafis, it follows, that if we extrad this alkali 
from them, by elixiviation and evaporation, it 
will be brought into a fmaller compals, and fup- 
ply the place of a large quantity of wood-afhes. 
The fixt alkali, or fait extraded from wood- 
afhes, is known, in commerce, by the name of 
Tot-ajh , and is made in large quantities in 
Sweden, Denmark, and in all the northern parts 
of Germany; nor is it hard to procure pot-afh 
of a good quality in France, fo that we have 
always a fimple, ealy, and cheap method of fup- 
plying the place of wood-alhes in thofe pro¬ 
vinces where they are fcarce or dear, and the 
bufmefs of faltpetre-making contracted upon 
this account. 
And we can affine the reader, that where 
wood-allies are found in the greateft plenty, 
pot-afh will be found far preferable to them for 
the following realons. 
In 
