t8o ESSAYS AND OBSERVATIONS 



the neck, which continued perfe<flly dry to 

 the end of the experiment. 

 '"We now perceive the reafon, why crude 

 and calcined magnefia, which differ in many 

 fefpeds from one another, agree however in 

 compofing the fame kind of fait, when dif- 

 folved in any particular aeid; for the. crude 

 magnefta feems to differ from the calcined 

 chiefly by containing a confiderable quantity 

 of air, which air is unavoidably diflipated 

 and loft during the difTolution, 



From but experiments, it feems probable, 

 that the increafe of weight which fome me- 

 tals acquire, by being firfl drffolved in acids, 

 and then feparated from them again by alkalis, 

 proceeds from air furniflied by the alkalis. 

 And that in the aiirum fulminans, which is pre- 

 pared by the fame means, this air adheres to 

 the gold in fuch a peculiar manner, that, in 

 a moderate degree of heat, the whole of it 

 recovers its elaflicity in the fame inflant of 

 time; and thus, by the violent fhock which 

 it gives to the air around, produces the loud 

 crack or fulmination of this powder. Thofe 

 who will imagine the explofion of fuch a mi- 

 nute portion of fixed air, as can refide In the 

 iiurum Julmina?is^ to be infufficient for the 



exceffiye 



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