338 Mr . Gregorys Experiments on a mineral Substance . 
with distilled water and decanted from a brown powder, which 
had subsided. This powder edulcorated, dried, and ignited 
weighed of a grain ; £ of a grain was alumina, yV silica, and 
- 3 - oxide of iron. 
E. 
( 1 . ) The solution effected by potash was decomposed and 
redissolved by muriatic acid, and the contents of the solution 
were precipitated by ammonia. The subsided precipitate was 
edulcorated. 
(2.) The fluid and the edulcorating water were evaporated 
to dryness, and redissolved in distilled water. Here again, to 
my surprise, a separation took place of a white earth, more 
abundant than is usual in cases where ammonia is employed as 
a precipitant. 
(3.) This earth and the precipitate were edulcorated with 
distilled water, until it ceased to affect a solution of nitrate of 
mercury. Collected, dried, and ignited, for one hour it weighed 
whilst still warm 32 y-g-. 
F. 
(1.) This earth was placed in a crucible of platina, and 
repeatedly moistened with sulphuric acid, which was abstracted 
from it in the sand bath ; distilled water effected the solution 
of the whole, except a white powder which weighed, after 
ignition, 2 - 3 - grains. It was proved to be silica. 
(2.) This solution was now mixed with some acetat of 
potash and gradually evaporated ; large and regular crystals 
of alum were from time to time formed. A small portion of 
silica which weighed after ignition ~ of grain was deposited ; 
