v THE STUDY OF GASES 93 



C. ACID AIR AND ALKALINE AIR 



Acid air (hydrogen chloride, HC1). Glauber prepared 

 " spirit of salt" by the action of oil of vitriol on salt, 



2NaCl + H 2 SO 4 -> Na 2 SO 4 + 2HCl, 



but he was only able to collect the gas by absorbing it in water. 

 Priestley (1774) collected it over mercury as a "permanently 

 elastic fluid." He found it to be extremely soluble in water, 

 which dissolved 576 times its volume of the gas. 



Alkaline air (ammonia, NH 3 ). The pungent gas present 

 in " spirit of hartshorn " was expelled by warming, and collected 

 over mercury by Priestley (1774), who called it "alkaline air" ; 

 the name "ammonia" was given to it by Bergman in 1782. 

 Priestley also prepared it from slaked lime and sal-ammoniac, 



Ca(OH) 2 + 2NH 4 C1 -> CaCl 2 + H 2 O + 2NH 3 , 

 Slaked + sal > muriate + water + ammonia 

 lime ammoniac of lime 



and obtained a very strong spirit by dissolving it in water, 

 which absorbed 336 volumes of the gas. It differed from acid 

 air in being lighter instead of heavier than common air. 

 A mixture of alkaline air and acid air produced sal-ammoniac, 



NH 3 +HC1 -> NH 4 C1 (sal-ammoniac). 



(Ammonia.) (Hydrogen (Ammonium 

 chloride.) chloride.) 



A mixture of alkaline air and fixed air produced sal-volatile, 



2NH 3 + CO 2 -> (NH 3 ) 2 CO 2 (sal- volatile.) 



(Ammonia.) (Carbon (Ammonium 

 dioxide.) carbamate.) 



