METALS AND THEIR ORES. 45 



in which it is present by powdering coarsely, and then 

 exposing to strong heat in a kiln. The bismuth is melt- 

 ed only, and runs into a trough at the bottom. 



88. Manganese. The ores of this metal are some of 

 them composed of but two ingredients, as the oxyds and 

 sulplmrets ; and others are very compound, containing 

 silica, iron, lime, magnesia, etc. The peroxyd is used by 

 the chemist for obtaining oxygen gas, and is employed 

 largely in bleaching. Some of the salts of this metal are 

 used in calico printing. Manganese gives a violet color 

 to glass. 



89. Mercury. This is the only metal that is liquid in 

 all ordinary temperatures. It becomes solid at 39 be- 

 low zero, and therefore can not be used in thermometers 

 in the arctic regions. It crystallizes in cubes. It is 

 sometimes found native, commonly in globules scattered 

 here and there, but sometimes in such quantities that it 

 can be dipped up in pails. It is related that the mines 

 of mercury in Mexico were discovered by a hunter, who, 

 as he clambered up a mountain, caught hold of a shrub, 

 which, giving way at the root, let out a stream of what 

 he supposed was liquid silver. The rapidity with which 

 this metal runs, occasioned by its great weight, gave to 

 it the name of quicksilver. The purity of the mercury 

 is judged of by the workmen by watching it as it is 

 dropped upon glass. If in running, instead of preserv- 

 ing fully its characteristic globular shape, it forms a 

 queue, or drags a tail, as it is expressed, there is lead or 

 some other impurity present. Mercury is used in a va- 

 riety of ways. It is the liquid used in barometers, and 

 generally in thermometers. It is used for silvering mir- 

 rors, an amalgam being formed with tin for this purpose. 

 Its disposition to amalgamate with other metals is made 

 use of extensively in extracting gold and silver from the 

 impurities with which they are mixed, as described in 

 213, Part II. Then there are various preparations and 

 combinations of this metal employed in medicine. The 



