Permarient Colours cf Cpake'Ecdks. 221 



No fubftances, whofe interftices are occupied 

 by air, differ more from air, in their fpecific 

 denfity, ihan metallic calces do. For which rea- 

 fon, the reflexions made ac the furfaces, which 

 intercede thofe media, are extremely ftrong. 



The Light, reflefted from the molecul^e of 

 air contained in the interftices of metallic calces, 

 is tranfmitted throuo-h the thin I'ranfoarenc 

 Matter of the calces which cover them, and is 

 thereby tinged, according to their refpe6live 

 colours. 



It is evident that calces, obtained from Tran- 

 fparent Metallic Solutions, by the evaporation 

 and expulfion of their aqueous, and faline, parts, 

 confift of Tranfparent Matter : for, the metallic 

 particles in the folutions, and in the calces, are 

 the fame, and the opacity, or tranfparency, of 

 the folutions, and calces, arife from the differ- 

 ence of the media, which intercede the metallic 

 particles in the one, or the other, of thofe ftates. 



Calces, united with pellucid colourlefs glafs, 

 are tranfparent i and metallic glaffes, which are 

 formed by fufion of the calces, are alfo tranfpa- 

 rent. For they conftitute folid, fmooth, maffes, 

 devoid of fuch pores as are capable of admitting 

 the entrance of air. 



The exigence of air, in the calces of metals, 

 is clearly eftabliflied by numerous chymical ex- 

 periments. From thefe it appears, that metals, 

 during their calcination, copioufly abforb the 



ambient 



