450 APPLIED SCIENCE 



Pure mercury is very heavy, as bright as silver, and is 

 not tarnished by air at an ordinary temperature. When 

 heated it takes up oxygen from the air and is turned into a 

 red powder (mercuric oxide). By continuing to heat the 

 mercuric oxide, the oxygen can be driven off and the mercury 

 turned back into a fluid state. Mercury becomes a solid 

 only at a great degree of cold (39 to 40 F. below zero). 



624. Uses of Mercury. Mercury is much used for making 

 thermometers and barometers. It is also used for extracting 

 gold and silver from their ores, by allowing the crushed ore 

 to flow in a thin mud over plates covered with mercury. 

 The gold amalgamates with the mercury, and is separated 

 later by distillation: 



Mercury was once much used for silvering the backs of 

 mirrors but a solution of silver has been found to be cheaper 

 for this purpose. Mercury unites with most of the other 

 metals to form alloys, called amalgams. Amalgams of silver 

 and other metals are used in filling teeth. 



Mercury is the basis of fulminating mercury, the explosive 

 powder put into percussion caps, cartridges, and fuses. Dry 

 fulminating mercury will explode violently when struck with 

 a hammer or any other hard object. When wet it is non- 

 explosive and is kept in this condition until wanted for use. 

 It can be obtained as a fine, gray powder by shaking it vio- 

 lently with flour, grease, etc., so as to coat the minute drops 

 and prevent them from uniting to form a fluid mass. Pure 

 dilute acids do not attack mercury, but concentrated nitric 

 acid dissolves it readily. 



525. Properties of Platinum. Platinum is a metal 

 discovered only in the eighteenth century. The principal 



