228 Chemistry. [Lecture 32. 



sary for its fusion; and to prove it, expose 

 pieces of copper to heat and air, and you will 

 find them covered with a dark crust, which may 

 be easily powdered. 



Tin is not oxidized till after it is melted : when 

 exposed to an intense heat, the oxidizement is 

 attended with heat and light, or the metal takes 

 fire, and burns like a combustible substance. 



Lead also is not oxidized till after fusion, but 

 may be easily reduced to an oxide, by keeping 

 it in a heat greater than that necessary for its 

 fusion ; so that a film forms on its surface, which 

 is its oxide. If this film is removed, a new one 

 will form, and thus we may oxidize the whole. 

 But the best and quickest way is to heat the 

 lead to such a degree as is sufficient to melt the 

 oxide, there will then be no film formed on the 

 surface, but the oxide w 7 ill be melted, and float 

 distinct from the metal, and will then fall to the 

 side of the vessel. This operation is called the 

 scorification of metals. Metals are, however, 

 capable of uniting with different proportions (or 

 in the chemical language, doses) of oxygen. 

 These have been judiciously distinguished by 

 prefixing to the word oxide the first syllable of 

 the Greek numerals*. Thus the protoxide de- 

 notes the first oxide, or the metal combined 

 with a minimum of oxygen ; deutoxide the se- 

 cond oxide, or the metal combined with two 



* Thomson's Chemistry. 



