and fome can be decompounded ; neverthe- 
!efs, in a melting heat they can again be re- 
covered, or brought to their former iiate, 
by adding to them the phlogifton they loft 
during their decompofition*. 
SECT. III. 
The FIRST CLASS. 
Eartus, are thofe mineral bodies, 
not ductile, for the moft part not diffoluble in 
water or oils, and that prefervc their conftitution 
in a ftrong heat. 
SECT. IV. 
Thefe earths (Se6l. III.) are here arranged ac- 
cording to their conftituent parts, as far as hi- 
therto difcovered, and are v divided into nine or- 
ders. 
* Here occurs the fame difficulty in regard to the defini- 
tions, as was before (Se6l. I.) obferved, becaufe thefe enume- 
rated dalles are likewife blended one with another ; and there- 
fore fome exceptions muft be allowed in every one of them : 
for inftance, in the firft clafs, the calcareous earth is in fome 
meafure diffoluble in water, and pipe clay with fome others 
diminiffi fomewhat in their bulk, when kept for a long time 
in a calcining heat. In the third clafs, the calx of arfenic 
has nearly the fame properties as falts ; and there is no pof- 
lible definition of fait, that can exclude the arfenic, though, 
at the fame time, it is impoflible to arrange it elfewherc than 
among the femi-metals. In the fourth clafs it is to be ob- 
ferved, that the metals and femi-metals, perfedt or impeifed, 
have not the fame qualities common to them all; becaufe 
fome of them may be calcined, or deprived of their phlo- 
gifton, in the fame degree of fire, in which others are not in 
the leaft changed, unlefs particular artifices or proceffes are 
made ufe of: fome of them alfo may be made malleable, 
when others are by no means to be rendered fo. 7"hat the 
convex 
