COMPOUNDS OF NITROGEN WITH II V I > I ; < >< ; K N .\ N 1 > n \ YUEN 25 1 



other acid be brought into contact with ammonia it absorbs it, and in 

 so doing evolves a large amount of heat and forms a compound having 

 all the properties of a salt. Thus, for example, sulphuric acid, H SO 4 , 

 in absorbing ammonia, forms (on evaporating the solution) two salts, 

 according to the relative quantities of ammonia and acid. One salt is 

 formed from NH 3 + H 2 SO 4 , and consequently has the composition 

 NH S S0 4 , and the other is formed from 2NH 3 + H 2 SO 4 , and its composi- 

 tion is therefore N 2 H 8 SO 4 . The former has an acid reaction and the 

 latter a neutral reaction, and they are called respectively acid ammonium 

 sulphate (ammonium hydrogen sulphate), and normal ammonium sul- 

 phate, or simply ammonium sulphate. The same takes place in the 

 action of all other acids ; but certain of them are able to form normal 

 ammonium salts only, whilst others give both acid and normal ammonium 

 salts. This depends on the nature of the acid and not on the ammonia, 

 as we shall afterwards see. Ammonium salts are very similar in appear- 

 ance and in many of their properties to metallic salts ; for instance, 

 sodium chloride, or table salt, resembles sal-ammoniac, or ammonium 

 chloride, not only in its outward appearance but even in crystalline 

 form, in its property of giving precipitates with silver salts, in its solu- 

 bility in water, and in its evolving hydrochloric acid when heated with 

 sulphuric acid in a word, a most perfect analogy is to be remarked 

 in an entire series of reactions. An analogy in composition is seen 

 if sal-ammoniac, NH 4 C1, be contrasted with table salt, NaCl ; and the 

 ammonium hydrogen sulphate, NH 4 HSO 4 , with the sodium hydrogen 

 sulphate, NaHSO 4 ; or ammonium nitrate, NH 4 NO 3 , with sodium nitrate, 

 NaN0 3 . 13 It is seen, on comparing the above compounds, that the part 

 which sodium takes in the sodium salts is played in ammonium salts by 

 a group NH 4 , which is called ammonium. If table salt, as the product 

 obtained by the action of caustic soda or sodium hydroxide 011 hydro- 



15 The analogy between the ammonium and sodium salts might seem to be destroyed 

 by the fact that the latter are formed from the alkali or oxide and an acid, with the sepa- 

 ration of water, whilst the ammonium salts are directly formed from ammonia and an 

 acid, without the separation of water ; but the analogy is restored if we compare soda to 

 ammonia water, and liken caustic soda to a compound of ammonia with water. Then the 

 very preparation of ammonia salts from such a hydrate of ammonia will completely re- 

 semble the preparation of sodium salts from soda. We may cite as an example the action 

 of hydrochloric acid on both substances. 



NaHO + HC1 H 2 + NaCl 



Sodium hydroxide Hydrochloric acid Water Table salt. 



NH 4 HO + HC1 = H 2 + NH 4 C1 



Ammonium hydroxide Hydrochloric acid Water . Sal-ammoniac. 



Just as in soda the hydroxyl or aqueous radicle OH is replaced by chlorine, so it is in 

 ammonia hydrate. 



