a20 Mr. Dslaval on the Caufe of the 



metallic coloured particles are fo diluted, that 

 the mafs appears alinofl white. 



Thefe effects are alfo produced by pulverizing, 

 or otherwife flawing, metallic falts, but not fo 

 compleatiy as by the expulfion of their water. 



By calcination, the faline matter is driven off: 

 and, when this operation is effectually performed, 

 the calces confifl: of metallic particles, which are 

 free from all extraneous matter, excepting only 

 the moleculas of air which occupy their inter- 

 flices. 



The air, which intercedes the particles of 

 metallic calces, reflects the light more ftrongly 

 than that which inrercedes vitriolic particles. 

 Becaufe the calces of metals differ more, in their 

 denfity, from air, than metallic falts differ from 

 that fluid. Therefore, each molecula of air, 

 which intercedes the metallic particles, power- 

 fully reflefts a white light, and confequently is 

 irfelf a minute white body, fuch as is feen in the 

 globules of air enveloped in the fmall bubbles 

 of water which conftitute white froth. 



But, as the fpecific denfity of metallic calces 

 greatly exceeds the fpecific denfity of water, the 

 moleculas of air, which intercede the metallic 

 particles, refleft the light ftronger than thofe 

 •which intercede the aqueous particles, in pro- 

 portion to their difference of denfity with re- 

 fpedl to that of the ambient fubftances, whofe 

 vacuities they occupy. 



No 



