[ *94 ] 



periment : If this is not obferved, the flux, com- 

 municating itielf with every point or the furface of 

 the mineral body, fp reads all over it, and keeps 

 the form of this laft, which commonly is flat, 

 (Sect, xvi.) and by that means hinders the opera- 

 tor to obferve all the phcenomena which may hap- 

 pen. Befides, the flux being in too fmall a quan- 

 tity, in proportion to the body to be tried, is 

 too weak to act with all its force upon it. The 

 bed proportion, therefore, is about a third part of 

 the mineral body to the flux •, and, as the quan- 

 tity of the flux, mentioned in Sect. xx. xxii. makes 

 a globe of a due fize, in regard to the greateft 

 heat that is pofTible to procure in thefe experi- 

 ments ; the fize of the mineral body, propoied in 

 Sect. xvi. required when it is to be tried in the 

 fire by itfelf, is too large on this occafion, the 

 third part of it being here almoft fufficient. 



SECT. XXV. 



The Sal Sodje, as has been faid before, is not 

 of" much ufe in thefe experiments; nor has it any 

 particular qualities in preference to the two laft 

 mentioned falts, except that it diflblyes the Zeor 

 lites eafier than the Borax and the Sal fufibile mir 

 crocofmicum. 



This laft mentioned fait fhews almoft the fame 

 effects in the fire as the borax, and differs from 

 this in very few circumftances, of which one of 

 the moft principal is, that, when melted with 

 manganefe, it becomes of a crimfon hue, inftcad of 

 a iacinth colour, which borax takes. 



This fait is., however, for its fcarcity, ftill very 

 little in ufe, borax alone being that which is com* 

 rnonly ufedi Whenever a mineral body is melted 

 *ykh uny of thefe two hit mentioned falts, in thp 



above 



