176 ESSAYS snp OBSERVATIONS 
properties with thofe of the other abfor- 
bent earths, of which there plainly appear- 
ed to me to be very different kinds, altho’ 
commonly confounded together under one 
name. | was indeed led to this examina- 
tion of the abforbent earths, partly by 
the hope of difcovering a new fort of lime 
and lime-water, which might poflibly be 
a more powerful folvent of the ftone than 
that commonly ufed ; but was diflappoint- 
ed in my expectations, 
‘Ihave had no opportunity of feeing 
Hoffman’s firft, magnefia, or the liquor from 
which it is prepared, and have therefore 
been obliged to makemy cxRenmea up- 
on the fecond. 
In order to prepare it, I at firft e aploy- 
ed the bitter faline liquor called bittern, 
which remains in the pans after the eva- 
poration of fea-water. But, as that liquor 
is not always eafily procured, I afterwards 
made ufe of a fait called Ep/om falt, which 
is feparated from the bittern by cryftalli~ 
zation, and is evidently compofed of mag 
nefia and the vitriolic acid, 
THERE 
