174 METALLOIDS. 



Its affinities being entirely satisfied by the potassa with 

 which it is combined in that substance, it lies there per- 

 fectly inactive. Sulphuric acid being stronger, has the 

 power of taking its base, 

 and expelling the acid in 

 the form of vapor. In or- 

 der to collect and condense 

 the acid fumes, the mixture 

 may be made in a test-tube, 

 the mouth of which opens 

 into a vial or flask. It is necessary to keep the vial 

 covered with porous paper or cloth, and to moisten it 

 frequently in order to maintain its coolness. Wher e 

 larger quantities are prepared, a retort and well-cooled 

 receiver are employed, as represented in the Appendix. 

 425. OXIDATION OF METALS. If a little 



What effect 



has nitric acid nitric acid is poured upon a copper coin, 

 placed in a capsule or saucer, the coin will 

 immediately begin to dissolve. It is not, strictly 

 speaking, the metal which dissolves. One portion 

 of the acid first converts the metal into oxide, by giving 

 it part of its own oxygen. It thereby destroys itself, 

 while another portion of undecomposed acid dissolves 

 the oxide which is formed. One portion, in reality, 

 sacrifices itself to satisfy the appetite of the other. Most 

 other metals are similarly acted on by nitric acid. 

 What is nitric 426. NITRIC OXIDE.* The vapors which 

 oxide? are gj ven off m the j ast experiment are 



* It will be observed that the term oxide is sometimes applied to 

 compounds of the metalloids with oxygen. (See chap, iii., Inorg. 

 Chem.) 



