336 METALS AND THEIR COMBINATIONS. 



Mercury is the only metal showing the liquid state at the ordinary 

 temperature ; it solidifies at -40 C. (-40 F.), and boils at 357 C. 

 (675 F.) ; but is slightly volatile at all temperatures ; it is almost 

 silver-white, and has a bright metallic lustre ; its specific gravity is 

 13.56 at 15 C. (59 F.). 



Pure mercury should present a bright surface even after agitation with air; 

 when dropped on paper it should form globules which roll about freely, retain 

 their globular form and leave no streaks. Commercial mercury is often con- 

 taminated with tin, lead, bismuth and zinc. Such impurities cause a trail of 

 dross when globules are made to roll over paper. 



Mercury can be purified by repeated distillation, or by covering the metal 

 with nitric acid and agitating the mass frequently during two days. The total 

 of the base metals, with some mercury, pass in solution, which is washed out with 

 water, after which the mercury is dried by setting it in a warm place. 



Mercury is peculiar in that its molecule contains but one atom, at 

 least when in the state of a gas ; in the liquid and solid states it may 

 contain two atoms, like most other elements, but we have as yet no 

 means of proving this fact. 



Mercury forms, like copper, two series of compounds, distinguished 

 as mercuric and mercurous compounds. In the former, mercury is 

 bivalent, while in mercurous compounds the atom exerts a valence of 

 one. It was long supposed that this was due to the fact that two 

 mercury atoms were joined together, each atom thereby losing one 

 of its points of affinity, leaving but one point for combining Avith 

 another atom or radicle. This view necessitated the existence of two 

 mercury atoms in the molecule of every mercurous compound, the 

 composition, for instance, of mercurous chloride being CIHg-HgCl or 

 Hg 2 Cl 2 . There are, however, good reasons to believe that mercury is 

 univalent in mercurous compounds, the composition of mercurous 

 chloride being, consequently, HgCL Similarly, copper is assumed to 

 be univalent in cuprous compounds. 



Mercury is not affected by the oxygen of the air, nor by hydro- 

 chloric acid, while chlorine, bromine, and iodine combine with it 

 directly, and warm sulphuric and nitric acids dissolve it. 



Mercury is used in the metallic state for many scientific instruments 

 (thermometer, barometer, etc.); for making amalgams; for extracting 

 gold from the ore ; for manufacturing from it all of the various mer- 

 cury compounds, and those official preparations in which mercury 

 exists in the metallic state. 



These latter preparations are : Mercury with chalky mass of mercury, 

 or blue pill, mercurial ointment, and mercurial plaster. Mercury exists 

 in a metallic, but highly subdivided, state in these preparations, which 

 are made by intimately mixing (triturating) metallic mercury with 



