[ 55 8 ] 
that have as different Qualities. It would lead us 
too far beyond our prefent Defign, to give a parti- 
cular Account of each of thefc ; but as they are ufed 
in many of our Manufactures, it feems worthy In- 
quiry, to know what Sorts are generally ufed, and 
what are the fitteft to be ufed in them. 
The Workmen in England make two general 
Kinds of it, which they diflinguifh by the Names of 
Pearl-afh and Pot-afh. The firft is a mere lixivial 
Salt, which is fuppofed to be the only Ingredient 
of any Efficacy in Pot-afh ; but, upon Trial, there 
is found to be a great Difference between them, 
efpecially in making Soap. The Salt is fo weak in 
the Pearl-afh, that it does not intirely diffolve and 
unite with the Fat. The Reafon feems to be, that 
thefe Salts are diffolved in Water, in order to ex- 
traft them, by which they lofe many of their cauftic 
igneous Parts; whereas in Pot-afh, the Salts are cal- ’ 
cined and fluxed in an open Fire, with the ignited 
terreflrial Parts of the Afhes, which makes "them 
more fharp and corrofive : They are likewife incor- 
porated with the Coal, and fuliginous Parts of the 
Vegetables they are made of, or with the refinous 
Parts of Fir, which gives them the fulphureous Qua- 
lity above-mentioned, and makes a kind of Soap of 
Tartar , or Hepar Sulphuris , in all Pot-afh,* which 
makes thefe Salts fo ready to diffolve, and incorpo- 
rate with OiJ, or other pinguious Subflances. 
This is perhaps the Reafon, why the Cineres 
RuJJict are ordered for this Purpofe, inftead of a 
mere lixivial Salt, by the College of Tbyficians in 
their late Difpenfatory. The Soap made of them 
muff be impregnated with their heating fulphureous 
.Quality, 
