t ^88 3 
iceflarily to be tried that way. To this pnrpofe k 
is befl: to make a little hole in the charcoal to put 
the Fluor in, and then to put another piece of 
charcoal as a covering upon this, leaving only a 
fmall opening for the flame to come in at, and to 
look at the proof. As this ftone will neverthelefs 
cnoftly fplit and fly about, a larger piece thereof 
than is before-mentioned, (Sed. xvi.) muft be 
taken, in order to have at leaft fomething of it 
left. 
But if the experiment is tp be made upon ^ 
Hone whofe effeds one does not want to fee in the 
fire per fe^ but rather with fluxes, then a piece of 
it ought to be forced down into melted borax^ 
(Sed. xxiii.) when always forne part of it will re- 
main in the borax, notwithftanding the greateft 
^art may fon;ietimes fly away by cracking., 
SECT. XVIIL 
As the ftones undergo great alterations when 
;expofed to the fire by themfelves, whereby fome 
of their charaderiftics, and often the mofl; princi- 
pal, are difcovered, they ought firft to be tried 
:that way j obferving what has been faid before 
.concerning the quantity of the matter, diredion of 
ithe fire, &c. The following efleds are generally 
^the refults of this experiment, viz.. 
I. Calcareous earth or ftone, when it is pure^ 
does never melt by itfelf, but becomes white and 
friable, fo as to break freely between the fingers 5 
.and, if fuifered to cool, and then mixed with 
water, it becomes jhot, juft as common quick lime. 
As in thefe experiments only very fmall pieces are 
fiifed, (Sed. xvi.) this laft effed is beft difcovered 
putting the proof on the outfide of the hand, 
a drop of water to it, when inftantly a very 
