t 186 j 



SECT. XVI. 



Of thofe things that are to be afiayed, only a 

 fmall pie^e muft be broke off for that purpofe, not 

 bigger than that the flame of the candle (Sect, vii. 

 xlv.) may be able to act upon it at once, if re- 

 quired ; which is fometimes ne^effary ; for in- 

 ftance, when the matter requires to be made red 

 hot throughout. A piece of about an eighth part 

 of an inch fquare is reckoned of a moderate fize, 

 and fltteft for experiments; feldom more, but 

 rather lefs. This proportion is only mentioned as 

 a direction in regard to the quantity, th* figure 

 being of no confequence at all, a piece broke off 

 from a {tone feldom or never happenin g to be 

 fquare. But here it is to be obierved, rhat the 

 piece ought to be broke as thin as pofiible, at 

 lead the edges : The advantage thereof is eafily 

 feen 5 the fire having then more, influence upon 

 the fubjecl, and the experiment being quicker 

 made. This is particularly neceffary to be ob- 

 ferved when fuch (tones are to be allayed, which 

 although in fome refpects fufible by themfelves, 

 yet refift confiderably the action of the fire ; be- 

 caufe they may by thefe means be brought into 

 fufion, at leaft at their edges, which elfe would 

 have been very difficult if die piece had been 

 thick. 







SECT. XVII. 



Some of the mineral bodies are very difficult to 

 keep fteady upon the charcoal during the experi- 

 ment, before they are made red hot ; becaufe, as 

 foon as the flame begins to act upon them, they 

 fplit afunder with violence, and difperfe. Such 



often 



