i a Mr. woulfe’s Experiments on 
made Fife of, and which, for want of being well burnt, 
retained yet their clayey nature; confequently a portion, 
and that not a fmall one, of the clay, is diflolved by the 
alkaly ; allum muft therefore in his manner be obtained, 
as clay is the matrix, or at leaft contains the earth of 
allum. It is rather a tedious operation to make the liquor 
filicum , and efpecially in any quantity; for the mixture 
is very fubjecft to froth and boil up in the crucible, and 
the operation is not compleat until this boiling up ceafes, 
and the mixture melts thin. Hence it is natural to con- 
clude, that a large portion of the clay of a Paris crucible 
is diflolved by the alkaly during this long operation. 
In order to difcover whether the cryftal, quartz, or flint, 
contained any acid, I put in practice the method which I 
publiflied in my laft paper on mineral fubftances, to dif- 
cover the acids of horn fllver and horn mercury ; but X 
could not find they contained any. 
On the change of cryflal into felenitical /par. 
The cryftal on which I tried the following experi- 
ments, and which is partly changed into felenitical fpar, 
is to be found in that moft excellent mufeum collected 
by Dr. hunter. This cryftal comes from near Freyberg 
in Saxony, and is called in German nieren-formiger cry- 
3 Ml 
