QUICKSILVER 293 



terior coating of varnish. Mercury vermilion is now used 

 chiefly for red colors in oil paintings, lithography, etc. 



Mercury is extracted by heating the ore in a retort or 

 a furnace; the metal is expelled as a vapor, which is subse- 

 quently condensed in cooling chambers and collected. 



Up to the present time mercury has been extracted from 

 its ores solely by the dry process. Various chemical and elec- 

 trolytic methods have heen proposed repeatedly and numer- 

 ous experiments made, but without commercial success. 



Perhaps the development of electric current generated 

 by water power in localities where the use of fuel is nearly 

 or quite prohibitive will render profitable the extraction of 

 the metal by some electrolytic process. 



The principal ore of mercury is cinnabar, mercuric sulph- 

 ide, accompanied at times wdth minute globules of native 

 mercury. The metal may be extracted from the ore by a 

 simple distillation, either in a retort or in a shaft furnace, 

 and though mercury may be separated from cinnabar in 

 numerous ways, only two methods are now used on a large 

 scale. One is based on the decomposition of the ore at a 

 high temperature by air, forming metallic mercury and sul- 

 phur dioxide gas in accordance with the reaction : HgS + O3 

 = Hg + SO3(360°C.) . The other accomplishes the decomposition 

 by the use of lime or iron which combines with the sulphur 

 and sets free the mercury in accordance with the reactions : 

 4HgS + 4CaO=4Hg+3CaS+CaX04, and HgS+Fe=FeS+Hg, 

 respectively. These chemical decompositions take place at 

 temperatures above the boiling point of mercury so that the 

 latter is expelled in gaseous form and subsequently con- 

 densed and collected in coohng chambers. 



The most important commercial use of mercury is in 

 the extraction of gold and silver from certain ores by the 

 amalgamation process; the precious metals becoming alloyed 

 with the mercury, form a heavy amalgam, which is sepa- 

 rated by gravity from the fine sands and the taiUngs of 

 the ore suspended in water. Owing to the avidity with 

 which mercury combines with impurities, thereby becoming 

 subdivided into innumerable minute globules which will not 

 coalesce, considerable quantities of the metal are lost during 



