COPPER. 133 



299. Mercury is fluid at all ordinary temperatures, 

 but, by exposure to very intense cold, it may be 

 frozen into a brilliant hard solid, looking like silver; 

 'when heated nearly to redness it boils, rises in vapor, 

 and may be distilled, just like water. When mercury 

 is kept for some time at a heat very near its boiling 

 point, it slowly absorbs oxygen, and becomes con- 

 verted into a red earthy-looking oxide. Mercury is 

 easily oxidized and dissolved by the strong acids ; it 

 forms two oxides, and both of them are salifiable 

 bases — the protoxide is black, the peroxide red; when 

 strongly heated, these oxides are decomposed into 

 metallic mercury and oxygen gas. 



300. Chlorine acts strongly on mercury, and forms 

 two chlorides, corresponding in composition to the 

 two oxides ; the protochloride, or calomel, is a power- 

 ful and valuable medicine — the perchloride, or corro- 

 sive sublimate, a violent poison. The former is in- 

 soluble in water — the latter soluble ; they are both 

 easily decomposed by alkaline solutions — calomel 

 yielding the black protoxide, and corrosive sublimate 

 the red peroxide of mercury. 



301. Corrosive sublimate has been a good deal 

 used to prevent the dry-rot of wood, cordage, &c. ; it 

 combines with some forms of organic matter, and 

 renders them less prone to change. Sulphur and 

 mercury easily combine, and form a beautiful red 

 compound, vermilion, or sulphuret of mercury ; it 

 occurs native as cinnabar, the chief ore of the metal. 



802. Copper exists naturally in the pure metallic 

 12 



