304 SMITH'S INTERMEDIATE CHEMISTRY 



monia by downward displacement of air. The long tube is closed 

 by a short rubber tube and a clip at the bottom (not shown). 

 The " dropper " contains water, and is closed at the tip with 

 soft wax. A few drops of water, squirted into the flask by 

 pinching the " dropper," dissolve at once so much of the gas 

 that the water rushes in, like a fountain, through the longer 

 tube, when the clip is opened. 



Chemical Properties. Ammonia, as we have seen, is 

 not very stable, and decomposes rapidly and almost completely 

 above 700. A discharge of sparks from an induction coil has 

 the same effect more gradually, and so a sample of the gas con- 

 fined over mercury in a closed tube may be shown to double in 

 volume when decomposed. Every two molecules give four: 



2NH 3 ->3H 2 + N 2 . 



The most characteristic property of ammonia is that it com- 

 bines directly with acids, giving ammonium salts : 



NH 3 (gas) + HC1 (gas) -> NH 4 C1 (solid particles). 



It combines also with water at low temperatures to give ammo- 

 nium Tiydroxide^T^H^OK^or "ammonium oxide (NH 4 ) 2 0, white 

 solids melting around 80. These compounds are unstable 

 at ordinary temperatures, so that a solution of the gas, in a great 

 excess of water, is the only form of ammonium hydroxide con- 

 venient for use : 



Ammonium Hydroxide. This substance, as indicated by 

 the way in which we have written its formula, is a base. The 

 ions are (OH)~, given by all bases, and (NH 4 ) + , ammonmm-ion, 

 which is found also in the salts mentioned above. The latter is a 

 compound positive radical, playing the part of a univalent metal- 

 lic element, such as Na or K. 



As a base, ammonium hydroxide, although rather weak (little 



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