TARNISH. 261 



combine with oxygen of itself, (or without 

 aid). 



Q. WHICH of the METALS is capable of 

 resisting oxidation altogether ? 



A. Plat'inum; in consequence of 

 which, the graduated arcs of delicate 

 instruments for observation are made of 

 platinum instead of any other metal. 



Q. Why is PLAT'INUM used for the graduated 

 arcs of delicate mathematical instruments, instead of 

 any other metal ? 



A. Because it will never oxidize; 

 but retain its bright surface in all 

 weathers free from both rust and tarnish. 



Q. Before platinum was discovered, which of 

 the metals was employed for the same purpose ? 



A. Gold. 



Platinum, (a white metal), so called from "plata," 

 the Spanish word for silver. It was first introduced 

 into England by Mr. Wood, (A. D. 1749) from South 

 America. 



Q. For what other SCIENTIFIC purposes is 

 PLAT/INUM now used ? 



A. For crucibles in which acids are 

 employed, and for galvanic batteries. 



Q. Why are CRUCIBLES (in which acids are 

 employed) made of PLAT/INUM ? 



A. Because the acid would act upon 



