SIMPLE COMPOUNDS. 31 



ACIDS (continued). 



Sulphur I fo^^^i^g sulphuric acid. 



uxygen / fQ^-jj^jng giUca (classed among the acids). 



4 ALKALIES ; 



^xygen I fQp^ijjg caustic lime, or calcium oxide, 

 ^xygen / forming potash, or potassium oxide. 



NEUTEAL SUBSTANCES. 



Oxygen also combines readily with metals. The 

 rust found on the unused plowshare or hoe is noth- 

 ing more nor less than the result of a chemical com- 

 bination of the iron with the oxygen of the atmos- 

 phere — iron oxide or iron rust. The green substance 

 often seen on copper coins, etc., is copper oxide or 

 copper rust, a simple compound of copper with 

 oxygen. 



Acids are also formed by the combination of hy- 

 drogen with a few elementary substances, but the 

 only one worth mentioning in this treatise is: 



Chlorine^ [ forming muriatic (or hydro-chloric) acid. 



With nitrogen, on the other hand, hydrogen com- 

 bines in the formation of an alkali that is most 

 important to the soil tiller, namely: 



Nftrogen^ I ^^^"^i^g ^^^ alkali— ammonia. 



