QUICKSILVER 291 



aid to the chemist in the collection and measurement of ^^ises 

 which are soluble in or a])sorl) water. When subjected to 

 prolonged heating in the air, mercury is slowly transformed 

 into red mercuric oxide (HgO), which at a higher temperature 

 is again decomposed into its elements — mercury and oxygen. 



Liquid meicury is converted by agitation with oil or 

 by trituration with sugar, chalk, or lard into a dull gra}^ 

 powder. This process is called deadening, and is used to 

 prepare mercurial ointment, the gray powder consisting 

 simply of very finely divided mercury in the form of minute 

 globules. 



In commerce mercury is usually contaminated with 

 a small proportion of dissolved metals, which cause a globule 

 to lose its spherical shape and drag a tail behind it while 

 flowing over an inclined surface. If the mercury is shaken 

 in the air, these metallic impurities become oxidized and 

 form a black powder or ^cum, which incloses small drops of 

 the metal, thus preventing them from coalescing. Mercury 

 in this condition is said to be floured. Commercial mercury 

 is best purified b}' distillation, but for ordinary purposes the 

 impurities may be removed almost entirety by repeated agita- 

 tion with dilute nitric acid or perchlorate of iron, either of 

 which atttacks the impurities and forms with them soluble 

 nitrates and chlorides, respectively, which are removable by 

 washing with water. 



Mercury is found in nature chiefly as the ore cinnabar, 

 mercuric sulphide (HgS or Hg2S2). It occurs also, though 

 less commonly, as native mercury, which is disseminated 

 in many cinnabar deposits in the form of fine globules, some- 

 times in large quantities. From a commercial standpoint, 

 cinnabar and metallic mercury are the only ores of importance. 



With most metals mercury forms a series of alloys called 

 amalgams ; in some cases, as with the alkali metals, the f orma- 

 tion of the alloy is attended with a rise of temperature, wliile 

 in other cases, as with tin, an absorption of heat results. 

 Sodium and potassium amalgams are decomposed by con- 

 tact \vith water; yielding h3^drogen gas and an alkaline hy- 

 droxide; for this reason sodium amalgam is used in the labora- 

 tory as a reducing agent. Zinc amalgam is acted upon very 



