196 METALS AND THEIR COMBINATIONS. 



Analytical reactions. 



(Silver nitrate, AgNO 3 , may be used.) 



1. Add to solution of a silver salt, hydrogen sulphide or ammonium 

 sulphide : a dark-brown precipitate of silver sulphide is produced : 



2AgNO 3 -f H 2 S = 2HNO 3 + Ag 2 S. 



2. Add hydrochloric acid, or any soluble chloride : a white, curdy 

 precipitate of silver chloride is produced, which is insoluble in dilute 

 acids, but soluble in ammonium hydroxide and in potassium cyanide. 



AgNO 3 + NaCl = NaN0 3 + AgCl. 



3. Add potassium chromate or dichromate : a red precipitate of 

 silver chromate, Ag 2 CrO 4 , is formed (Plate II., 7). 



4. Add sodium phosphate : a pale-yellow precipitate of silver 

 phosphate, Ag 3 PO 4 , is formed, which is soluble in ammonia and in 

 nitric acid. 



5. Alkali hydroxides precipitate dark-brown silver oxide, soluble 

 in ammonia water. 



6. Potassium iodide or bromide gives a pale-yellow precipitate. 

 (See above.) 



7. Metallic copper, zinc, or iron precipitates metallic silver. 



Mercury, Hydrargyrum, Hg- = 199.8 (Quicksilver}. Mercury is 

 found sometimes in small globules in the metallic state, but generally 

 as mercuric sulphide or cinnabar, a dark-red mineral. The chief 

 supply was formerly obtained from Spain and Austria ; now, how- 

 ever, large quantities are obtained from California ; it is also 

 imported from Peru and Japan. 



Mercury is obtained from cinnabar either by roasting it, whereby 

 the sulphur is converted into sulphur dioxide, or by heating it with 

 lime, which combines with the sulphur, while the metal volatilizes, 

 and is condensed by passing the vapors through suitable coolers. 



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

 temperature ; it solidifies at 40 C. ( 40 d 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.). 



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. 



