SILVER. 101 



leaving the acid, and will float on the surface of the 

 fluid. If polished steel be dipped into this, it will 

 be covered with a coating of metallic gold. This 

 process is employed for gilding kncets, and other 

 surgical instruments, to defend them from rust. 



Gold easily alloys with mercury, which is, there- 

 fore, much employed for extracting it from the 

 substances with which it is mixed in its natural 

 state. The mercury, being volatile, is driven off 

 by heat, and the gold remains free. 



Gold in its purest state is too soft to be used as 

 coin ; it is, therefore, alloyed with n of copper. 

 Jeweller's gold generally contains considerably 

 more. 



Gold seems to have been one of the earliest 

 known of the metals. The ancients were lavish 

 in its use, and it is still frequently used in 

 ments among savage tribes* 



SILVER. 



Silver is often found native, or in the metallic 

 state, but it is most usually combined with other 

 metals, or sulphur. In its native state it fre- 

 quently assumes an arborescent form. The richest 

 silver mines are in Mexico and Peru ; but others 

 exist in many countries. Lead ore. very frequently 

 contains a quantity of silver, and sometimes it is 

 worth extracting. 



Silver is of a brilliant white colour. It is very 

 ductile and malleable ; may be drawn into fine 

 wire, and beaten into thin leaves ; but it is inferior 

 to gold in these qualities. 



Silver fuses when heated red hot, and may be cast 

 into moulds, but is not thus converted into oxide 



H 3 



