ALKALIES. 



231 



1. THE NAME is derived from that of sal ammoniac, or the mu- 

 riate of ammonia, and this from the sandy country of Lybia,* (a^orf,) 

 where the salt was first procured. 



2. DISCOVERY. The gas was discovered by Dr. Priestley, by 

 heating the aqueous solution of the shops ; he collected the gas in 

 vials filled with mercury, which was expelled by the gas. 



Process for obtaining gaseous Ammonia. 



3. PREPARATION. 



(a.) From equalparts 

 of powdered muriate 

 of ammonia, and dry- 

 slacked-\ quick lime, in- 

 timately mingled, and 

 heated moderately in 

 a glass retort ;{ we 

 receive the gas over 

 mercury, as in the an- 

 nexed cut of Dr. Hare. 

 It is very convenient 

 to displace the com- 

 mon air, by conveying 

 the gas, by a glass tube 

 into an inverted glass 

 vessel 5 as in the annexed figure, where a is the flask containing the 

 materials ; b a spirit lamp, for heat ; c the recipient, 

 and d the connecting tube. It is obvious that this pro- 

 cess is founded on the levity of the gas, which displaces 

 the air of the vessel. 



(b.) Heat the aqueous solution of ammonia to expel 

 the gas ; but this is not an eligible mode, as the water dis- 

 tils over, is condensed above the mercury, and reab- 



sorbs the gas. In the process 3, (b.) we know when 

 the recipient is full, both by the pungent smell, and by 

 bringing a feather dipped in muriatic acid near the mouth 

 of the vessel, when, if the gas is overflowing, there will 

 be a white cloud of regenerated muriate o 



fgrjL 



ammonia. When it is 



important to have the gas very dry, unslacked lime should be used ; 

 but it is apt to adhere to the glass and break it. 

 4. PHYSICAL PROPERTIES. 



* Called Ammonia. Some say in allusion to the sand ; others to the temple of 

 Jupiter Ammon. 



t That is, slacked with such a portion of water, as to remain dry. 



. In all operations for collecting gases over mercury, ground, tubulated glass re- 

 torts are better than flasks, as, from the pressure, the latter are apt to leak at the cork, 



