I'- MJWd
t I t 'fo
■/ f /> “ B!''i5f
i ■ fo 4" L v fo
I t ’-foi
jffiSW lf l| i
4 "
!78 ]
longer for tbe benefit o f the fciences,
he would no donbt have retdfied this
account. In confequence o f my experiments
I have difcovered the following
fix forts ;
r . Calcareous earth, which after being
faturated by acid of vitriol affords
a gypfum.'
2. Terra ponderofa, wliich with
acid o f vitriol gives a ponderous fpar,
and in feveral refpefts is very different
from the calcareous earth.
3. Magnefia, which, together with
acid o f vitriol, produces the Engliili
or Epfom fait.
Thefe three kinds are generally
found faturated with fixed air, and
they are on that account fubjeiff to an
effervefcence with ilronger acids.
4. Argillaceous earth, which, together
with the vitriolic acid, produces
allum.
The common argillaceous earth is
always m.ixed with filiceous earth, but
the fort here meant mull be entirely
pure.
5. Siliceous earth, which is not attacked
by any acid yet known, the
fluor
[ 379 ]
fluor acid excepted. In the dry way
it can be diffolved with a third part o f
its weight o f fixed alkali to a tranfparent
lafting glafs, which at firft is
aftefled with a ftrong effervefcence.
6. Gemmeous earth, that is not
attacked by any known acid, and
clearly diftinguiflies itfelf from the preceding
forts, by its being entirely in-
jdiffoluble, and is not fubjecl to
any effervefcence in the fire with fixed
alcali. It is found in all the gems or
precious ilones.
1 have in vain made ufe o f various
methods to feparate thefe earths into
more fimple principles, and to all appearance
others would have no better
fuccefs than I have had ; i f they
are really compounds, they are at
leaft fimple in regard to the method
known among us o f feparating fubftances,
and do not arife from one
another. Whatever has therefore been
objected to this opinion from prejudice,
cannot fublift after experiments
have been made upon that fub-
je<ff. We muil not pretend to im-
pi'Qve nature according to our notions,
but
f*-
Ti