MERCURY. 103 



resembling in appearance a vegetation, and called 

 arbo7' Diance. 



Silver is not soluble in the hydro-chloric acid 

 (muriatic acid), yet, when this acid is added to a 

 solution of nitrate of silver, it unites to the oxide, 

 and a white curdy precipitate falls down, which 

 is the muriate of silver^ or, in conformity with the 

 new nomenclature, tlie chloride of silver. If this 

 precipitate be fused by a gentle heat, a semi-trans- 

 parent mass is formed, called formerly lima cornea^ 

 or horn silvery the fused muriate of silver* 



Silver is also dissolved by the sulphuric acid, and 

 the sulphate of silver is used as a chemical test. 

 Silver also unites to sulphur and phosphorus. 



Silver, when employed for coin is alloyed with 

 copper to increase its hardness. Our coin con- 

 tains thirty-seven parts silver and three parts 

 copper. 



MERCURY. 



This metal, called also quicksilver^ is always fluid 

 when in the usual temperature of the atmosphere ; 

 but when exposed to an intense degree of cold, it 

 is frozen into a solid mass, and is then malleable. 

 The temperature necessary for this purpose is 39*^. 

 The cold is sometimes so great within the polar 

 circle as to freeze the mercury in the thermometer ; 

 but in this country that can only be effected by 

 exposing it to a freezing mixture. 



Mercury also boils at 655°, and then evaporates, 

 and may be distilled from one vessel to another. 



It is sometimes found in nature in a pure state, 

 but usually it is united to sulphur, with which it 



H 4 



