METALS. 



the plate will be so weakened that it may afterward 

 be readily broken. 



655. OTHER USES OF MERCURY. The 

 Mention^ some compounds of mercury are extensively 

 mercury. used in medicine. Corrosive sublimate, a 



poisonous chloride of mercury, is employed 

 for the destruction of vermin. It is also used in what 

 is called the kyanizing process, to impregnate wood 

 and other vegetable and animal substance, and thus 

 prevent their decay. Another important use of mer- 

 cury is found in the manufacture of barometers and 

 thermometers. It is especially adapted to the measure- 

 ment of heat, by its fluidity at low temperatures, and 

 its ready and equable expansion. 



SILVER. 



656. DESCRIPTION. Silver is a lustrous 

 scription, ores white metal of perfect ductility and malle- 



and solvents? abil j tVi Itg 1 QSS Q f ] ustre QJ1 exposure, is 



owing to the presence of a small proportion of sulphur- 

 etted hydrogen in the air. Nitric acid is its proper sol- 

 vent, though for certain purposes oil of vitriol is pre- 

 ferred. Silver is often found native, but moro fre- 

 quently combined with sulphur as silver glance. 

 Galena or sulphuret of lead always contains it in small 

 proportion, and sometimes to the amount of one or 

 two per cent. 



How is silver && PRODUCTION. Silver is prepared 



obtained? f rom t h e sulphuret, by first roasting the ore 



