35® Dr. percival’s Account of a 
I have not leifure, at preferit, to profecute thefe expe- 
ments farther, and fiiall therefore content myfelf with 
making a few general obfervations on the facts that have 
been advanced. 
1. This pot-afh is a true fixed vegetable alkali, and a 
product of putrefadlion which has not, that I recolledt, 
been noticed by the chymifts. A very celebrated writer 
has even in exprefs terms afferted, that “ all vegetables, 
“ not excepting thofe which in their natural itate fur- 
“ nifh afhes containing much fixed alkali, when burnt, 
“ after their acid has been altered by a complete putre- 
u fadtion, leave afhes intirely free from alkali (i) . 
2. The quantity of alkali contained in this pot-afh. 
may, with fome probability, be eftimated at one-third 
of its weight; whereas the w r hite Mufcovy allies are faid 
to yield only one-eigth part <c) : Of its impurities fulphur 
is the raoft injurious to its bleaching powers, and fhould 
in the preparation of it be carefully feparated. A longer 
continued and more gentle calcination in a furnace fup- 
plied with a fufficient current of air might, perhaps, 
anfwer this end. But the moll effectual method would 
be to lixiviate the falts with pure water, after a moderate 
fufion, and then to evaporate them flowly to drynefL 
(b) macquer’s Di&ionary of Chemiftry, article Alkali* 
(c) home on Bleaching, p. 157, 
4 
it 
