290 JOSEPH STRUTHERS 



name hydrargyrum. Its atomic weight is 199.8. Aside from 

 bromine, mercury is the only elementary metal which exists 

 in a liquid form at ordinary temperatures. It is a bright tin 

 white liquid, and, when free from impurities, the globules re- 

 tain a perfectly spherical shape. The luster is mirror like, and 

 like that of silver it is preserved in air free of sulphurous gases. 

 Mercury, when cooled to a temperature of -38.8° C, is trans- 

 formed into a tin white, ductile, malleable mass, softer than 

 lead and crystallizing in octahedrons. During the cooling it 

 contracts uniformly until the temperature of solidification is 

 reached, at which point a considerable contraction takes place, 

 and, as a consequence, the solidified mercury will sink below 

 the surface of liquid mercury. At 0° C. the specific gravity of 

 mercury is 13.596 and at -38.8° C. the specific gravity of 

 soUdified mercury is 14.193. In very thin films the liquid 

 metal is transparent and of a violet blue color when viewed by 

 transmitted light. 



The specific heat of solidified mercury (between-78° 

 C.and-40°C.) is 0.0247; that of liquid mercury (between 

 0°C. andlOO°C.) is 0.0333. Its thermal conductivity is 667, 

 compared with that of silver taken at 1,000, and its elec- 

 trical conductivity at 22.8°C. is 1.63, silver at 0°C. being 

 taken at 100. 



The boiling point of mercury at the standard pressure 

 of 760 mm. is 357.25°C. Above this temperature it becomes 

 a transparent, colorless vapor, having a density of between 

 6.7 and 7.03, referred to air as a unit. The density of gaseous 

 mercury compared with hydrogen is 100.92, and as its atomic 

 weight is 199.8, this element in a gaseous form consists of 

 monatomic molecules. Mercury gives off vapors at all tem- 

 peratures. This may be illustrated by suspending a piece 

 of gold leaf above the surface of mercury in a stoppered bottle ; 

 the gold leaf will slowly assume a white color from the forma- 

 tion of gold amalgam on the surface. 



In its liquid and gaseous forms mercury is poisonous, 

 producing salivation when taken either internally through 

 the lungs or stomach or by absorption through the pores of 

 the skin. Mercury is not tarnished by exposure to the air, 

 nor is it acted on by many gases; hence it is an invaluable 



