Chap. 1 8 .] Aftion of Light and Heat on Metals. \ 1 9 



obtain it in a calcined ftate. Thus gold, if'precipitated 

 from its folution in aqua regia by an alkali, is a calx ; 

 but if precipitated by any of the inflammable lubftances, 

 as aromatic oils or fpirits of wine, or by another metal, 

 it appears in the metallic form. If metals are calcined 

 previous to being united with acids, they produce no 

 efcape of gas, becaufe being already furnifhed with 

 oxygen, they have no tendency to decompofe the 

 acid. 



Light appears to alter the colour and brilliancy of 

 fome metallic matters, independently of the action of air; 

 for when expofed to light in tranfparent vefiels well 

 clofcd, they become tarnifhed, and lofe their metallic 

 brilliancy. 



Heat applied to metals produces no other effects 

 than'expanfion and fufion, if the air is completely ex- 

 cluded, unlefs carried to fuch a degree as to volatilize 

 them ; but even in that cafe, when the heat ceafes to 

 act, they return to their original ftate. Metals, on be- 

 ing converted into vapour, boil like other fluids, and 

 even gold and filver are capable of this ftate when 

 acted on by a large concave mirror. 



Moft of the combuftible bodies acton metals. In- 

 flammable gas gives them a deeper colour, and is ca- 

 pable of reducing fome of them to the metallic ftate. 

 Sulphur, and its combinations with alkalies, called 

 hepars, act powerfully on metals. 



From what is hitherto known of metals, there is 

 every reafon to believe that they are fimple fgb- 

 ftances. 



