272 METALS. 



of nitric oxide and hydrogen, passed through a tube con- 

 taining heated platinum black, issues from the tube as 

 ammonia and water. The hydrogen has entered into 

 combination with both of the elements of the nitric 

 oxide, producing two new compounds. 

 Why isplati- 683. OTHER USES OF PLATINUM. The 

 num. superior m0 st important use to which platinum is 



to ot her metals _ . 



for chemical applied in the arts, is in the manufacture 

 apparatus? o ^ ^Q^^I apparatus. Its extreme in- 

 fusibility and resistance to acids, adapt it especially to 

 this purpose. In the manufacture of oil of vitriol, for 

 example, no other material excepting gold could well 

 take the place of the platinum vessels, in which con- 

 centration is effected. Platinum crucibles are also in- 

 valuable, as they may be exposed to the fire of a blast 

 furnace without injury. Nothing less than the most 

 intense heat of the oxyhydrogen blow-pipe, or galvanic 

 battery, is sufficient to fuse this metal. 



ALLOYS. 



. 684. The compounds of metals with 



alloy? Give metals are called alloys. The following 



fiontf P bras S are amon g the more important. 

 and other al- Brass is copper, lightened in color by 

 the addition of one-fourth its weight of 

 zinc. 



German silver is a kind of brass, still further whitened 

 by nickel. Its exact composition has been given in 

 another place. An alloy of 30 parts silver, 25 of nickel, 

 and 55 of copper forms a nearly perfect substitute for 

 silver for all ornamental purposes. 



