LEAD. 181 



of its weight of tin. Oxyd of copper is used by the coloured- 

 glass makers. It forms a beautiful green glass. 



Lead is a metal of a bluish white colour, very brilliant 

 when first cut with a knife, but it soon tarnishes by ex- 

 posure to the air ; it will mark writing-paper, though in a 

 fainter manner than plumbago. It is malleable and ductile, 

 but possesses very little tenacity. Lead may be mixed with 

 gold and silver in a moderate heat, but when the heat is 

 much increased, the lead rises to the surface, combined with 

 all heterogeneous matters. Upon this property of lead is 

 built the art of refining the precious metals. If melted lead 

 be exposed to the atmosphere, a greyish-yellow powder be- 

 gins to form upon the surface. By keeping it exposed for 

 some time the powder becomes more yellow. In this state 

 it is called massicot, or yellow oxyd of lead. By a second ex- 

 posure this oxyd appears capable of combining with more 

 oxygen. It gradually changes colour, and ultimately as- 

 sumes a splendid red. In this state it is called minium or 

 red lead. The process requires considerable management 

 with regard to heat and the access of air. If the heat be 

 too great or rapid, the lead becomes converted into a flaky 

 substance, called litharge ; and a still greater heat converts 

 it into a clear, transparent yellow glass. Thin plates of lead, 

 exposed to the fumes of vinegar at a certain temperature, are 

 gradually corroded and converted into a heavy white pow- 

 der, used as paint, and called white lead. 



The ore of lead is so poisonous, that the steam arising 

 from the furnaces where it is worked, infects the grass in 

 all the neighbouring places, and kills the animals which feed 

 on it. Culinary vessels, lined with a mixture of tin and 

 lead, which is the usual tinning, are apt to communicate to 

 acid foods pernicious qualities, and require to be used with 

 great caution. The same may be said of liquors and other 

 acid substances kept in glazed ware, and of wines adulterat- 

 ed with litharge, and such other preparations of lead as are 

 sometimes used for the purpose of rendering them sweet. 



Questions. — 1. What is copper ? 2 Why is it substituted for 

 iron in some raacliinery ? 3. What is Baid of the salts of copper .'' 4. 

 What is brass: 5. What are bronze and gun-metal ? 6. Bell-inexal? 

 7. Describe lead? 8. Why is it used in refining metals? 9. How 

 does lead become oxydized so as to form masBicot, and minium ? 10. 

 What is litharge ? il. How is white lead formed ? 12. What ip said 

 of the poisonous qtialities of lead ? 

 16 



