[ 555 ] 
At the fame time the alkaline Salts are fluxed in 
the open Fire, and in a manner vitrified with the 
terreftrial Parts of the Afhes, which gives them their 
hard and folid Confidence j whilft: the fulphureous 
and acid Parts of the green Wood hinder them 
from turning to a perfed Glafs, or inert Calx . All 
- thefe Parts united together in the Fire, make that 
faponaceous Subftance we find in the Pot-afh thus 
made, which further hinders the Vitrification of the 
Mafs, and endows it with many of its mod pecu- 
liar and adive Properties. 
From hence we may fee how difficlut it is to 
make a Subftance endowed with all thefe Properties 
in any other manner. This is the Reafon why we 
could never before make Pot-afh equal to that of 
Rujfia, and the other Northern Countries, altho' 
we have much greater Plenty of Materials and perhaps 
better : For this Way of making it has never before 
been thought of by the Learned, or pradifed any- 
where elfe, as far as I can learn. 
Somewhat of the fame Qualities are communi- 
cated to the Englijh Pot-afh, by the Way of making 
it above-deferibed ; but in a Degree as much infe- 
rior, as dry Straw, ufed for that Purpofe, is to green 
Wood : Accordingly our Workmen find that Pot- 
afh as much inferior to the foreign, for many Pur- 
pofes. 
From this Account of the Contents and Qualities 
of Pot-afh, and the Way of making it, we may 
form fome Judgment of the other Ways of making 
ir, propofed by Authors, and fuggefted by many. 
Thus Lemery and others tell us, Pot-afh is made in 
Rujjia , and all the Northern Countries, only by 
* D d d d calcining 
