i: 294 3 
periment : If this is not obferved^ the flpx, CQiTiie 
municating itfelf with every point of the furface of 
the mineral body, fpreads ,ali oyer it, and keeps 
the form of this laft, which ' commonly is flat^ 
(SedL xvi.) and by that means hinders the operaT 
tor to obferve all the phcsnomena which may hap- 
pen. Befides, the flux being in too fmajl a quan- 
tity, in proportion to the bqdy to he t^ied, is 
too weak to ad with all its force upon it. The 
beft: proportion, therefore, is about a third part of 
the mineral body to the flux *, and, as the quan- 
tity of the flux, mentioqed in Sed. xx, xxii. makes 
a globe of a due fize, in regard to the greatefl: 
heat that is pofllble to procure in thefe experi- 
ments *, the fize of the mineral body, propofed in 
Sed. xvi. required when it is to be tried in the 
lire by itfelf, is too large on this occafion, the 
'third part of it being here almoft fufRcient.^ 
SECT. XXV. 
The Sal Sodx^ as has been faid before, Is not 
of much ufe in thefe experimentis ; nor has it any 
particular qualities in preference to the two laft 
mentioned falts, except that it dilTolves the Zcov 
jites eafier than the Borax and the Sal fufibile mi? 
crocofmicum. 
This laft mentioned fait fhews almofl the fame 
effeds in the nre as the borax, and differs from 
this in very few circumilances, of v/hich one of 
fne moft: principal is, that, when melted with 
niangancfe, it becomes of a crimfon hue, inftead of 
a jacinth colour, which borax takes. 
This fait is, however, for; its fcarcity, flill very 
•little in ufe, borax alone being that which is com- 
monly ufed. Whenever a mineral body is melted 
with any of thefe two laft: mentioned ialts, in the 
above 
