218 METALS AND THEIR COMBINATIONS. 



6. Use Gutzeit's or Marsh's test as described under analytical re- 

 actions for arsenic. 



Tin, Sn = 118.8 (Stannum). This metal is found in nature chiefly 

 as stannic oxide or tin-stone, SnO 2 , from which the metal is easily 

 obtained by heating with coal : 



Sn0 2 + 2C = Sn + 2CO. 



Tin is an almost silver-white, very malleable metal, fusing at the 

 comparatively low temperature of 228 C. (440 F.). It is used in 

 many alloys, in the silvering of looking-glasses by tin-amalgam, and 

 chiefly in the manufacture of tin-plate, which is sheet-iron covered 

 with a thin layer of tin. 



Tin is bivalent in some compounds, quadrivalent in others. These 

 combinations are distinguished as stannous and stannic compounds. 



Stannoas chloride, SnCl 2 (Protochloride of tin). Obtained by 

 dissolving tin in hydrochloric acid by the aid of heat : 

 Sn + 2HC1 = SnCl 2 + 2H. 



Sufficiently evaporated, the solution yields crystals of the composi- 

 tion SnCl 2 .2H 2 O. Stannous chloride is a strong deoxidizing agent, 

 frequently used as a reagent for arsenic, mercury, and gold, which 

 metals are precipitated from their solutions in the metallic state. It 

 is used also in calico printing. 



Stannic chloride, SnCl 4 (Perchloride of tin). Stannous chloride 

 may be converted into stannic chloride either by passing chlorine 

 through its solution or by heating with hydrochloric and nitric acids. 



Analytical reactions. 

 (Stannous chloride, SnCl, 2 , and stannic chloride, SnCl 4 , may be used.) 



1. Add hydrogen sulphide to solution of a stannous salt: brown 

 stannous sulphide is precipitated (Plate V., 7) : 



SnCl 2 + H 2 S = 2HC1 f SnS. 



The precipitate is soluble in ammonium sulphide. 



2. Add hydrosulphuric acid to a solution of a stannic salt : yellow 

 stannic sulphide is precipitated (Plate Y., 8) : 



SnCl 2 + 2H 2 S = 4HC1 -f SnS 2 . 



The precipitate is soluble in ammonium sulphide. 



3. Sodium or potassium hydroxide added to a stannous salt, pro- 

 duces a white precipitate of stannous hydroxide, Sn(OH) 2 . The same 



