600 PROTOXIDE OF TIN. 



Pure tin is silver white, very soft, and so malleable, that it 

 may be beaten into thin leaves, tinfoil not being more than 

 1-lOOOdth of an inch in thickness. When a bar of tin is bent, 

 it emits a grating sound, which is characteristic; and when 

 bent backwards and forwards rapidly, several times in succes- 

 sion, becomes so hot that it cannot be held in the hand. At 

 the temperature of boiling water, tin can be drawn out into 

 wire, which is very soft and flexible, but deficient in tenacity. 

 The density of pure tin is 7-285, or 7-293 after being laminated ; 

 that of the tin of commerce is said to vary from 7-56 to 7-6. 

 Its point of fusion is 442, both by Crichton and Rudberg; 

 445.6 by Kupffer. Tin is volatile at a very high temperature. 

 The brilliancy of the surface of tin is but slowly impaired by 

 exposure to air, and even in water it is scarcely acted upon. 

 Hence the great value of this metal for culinary vessels, and for 

 covering the more oxidable metals, such as iron and copper, 

 when employed as such. Of tin three oxides are known, the 

 protoxide Sn O, deutoxide Sn 2 O 3 , and peroxide Sn O 2 . 



Protoxide of tin, Stannous oxide ; SnO, 835.3 or 66.92. Tin 

 dissolves in undiluted hydrochloric acid, at the boiling tempe- 

 rature, by substitution for hydrogen, and forms the protochlo- 

 ride of tin. From this the protoxide is precipitated by an 

 alkaline carbonate, as a white hydrate, which may be washed 

 with tepid water and dried at a temperature not exceeding 176. 

 It does not contain a trace of carbonic acid. This white pow- 

 der dried more strongly, in a retort filled with carbonic acid, 

 and heated to redness, gives the anhydrous oxide, as a black 

 powder, of which the density is 6.666. In this state the oxide 

 is permanent, but if a body at a red heat is brought in contact 

 with it in open air, it takes fire and burns, and is converted 

 entirely into peroxide. The protoxide of tin dissolves in acids, 

 and with more facility when hydrated than after being ignited. 

 This oxide is also dissolved by potash and soda, but the solu- 

 tion after a time undergoes decomposition ; metallic tin is de- 

 posited and the peroxide is found in solution. The solution of 

 a stannous salt, and of a stannic salt also, is apt to undergo 

 decomposition, when largely diluted with water, and to deposit 

 a subsalt. The stannous salts absorb oxygen from the air, and 

 have a great affinity for that element ; they convert the peroxide 

 of iron into protoxide, and throw down mercury, silver and 

 platinum in the metallic state from their solutions. The chlo- 



