224 PRINCIPLES OF CHEMISTRY 



Nitrogen may also be procured from many of its compounds ivitk 

 oxygen* and hydrogen^ but the best fitted for this purpose is a saline 

 mixture containing, on the one hand, a compound of nitrogen with 

 oxygen, termed nitrous anhydride, N 2 O 3 , and on the other hand, 

 ammonia, NH 3 that is, a compound of nitrogen with hydrogen. By 

 heating such a mixture the oxygen of the nitrous anhydride combines 

 with the hydrogen of the ammonia, forming water, and gaseous nitrogen 

 is evolved, 2NH.< + N 2 3 = 3H 2 O -f- N 4 . Nitrogen is procured by 

 this method in the following manner : A solution of caustic potash is 

 saturated with nitrous anhydride, by which means potassium nitrite is 

 formed. On the other hand, a solution of hydrochloric acid saturated 

 with ammonia is prepared ; a saline substance called sal-ammoniac, 

 NH 4 C1, is thus formed in the solution. The two solutions thus pre- 

 pared are mixed together and heated. Reaction takes place according 

 to the equation KNO, + NH 4 C1 == KC1 + 2H 2 O -f N 2 . This reaction 

 proceeds in virtue of the fact that potassium nitrite and ammonium 

 chloride are salts which, on interchanging their metals, give potassium 

 chloride and ammonium nitrite, NH 4 NO 2 , which breaks up into water 

 and nitrogen. This reaction does not take place without the aid of 

 heat, but it proceeds very easily at a moderate temperature. Of the 

 resultant substances, the nitrogen only is gaseous, the potassium chloride 

 is non-volatile, and is left behind in the vessel in which the solutions 

 are heated. Pure nitrogen may be obtained by drying the resulting 

 gas and passing it through a solution of sulphuric acid (to absorb, a 

 certain quantity of ammonia which is evolved in the reaction). 



Nitrogen is a gaseous substance which does not much differ in 

 physical properties from air ; its density, referred to hydrogen, is 

 approximately equal to 14 that is, it is slightly lighter than air ; one 

 litre of nitrogen weighs 1-256 grams. Nitrogen mixed with oxygen, 



the presence of a solution of ammonia, when it forms a bluish-violet solution of oxide 

 of copper in ammonia. Nitrogen is very easily procured by this method. A flask 

 is filled with copper shavings and closed with a cork furnished with a funnel and stop- 

 cock. A solution of ammonia is poured into the funnel, and caused to slowly drop upon 

 the copper. If at the same time a current of air be slowly passed through the flask 

 (from a gasholder), then all the oxygen will be absorbed from it and the nitn^ni 

 will pass from the flask. It should be washed with water to retain any ammonia that 

 may be carried off with it. 



3 The oxygen compounds of nitrogen (for example, NoO, NO, NO 2 ) are decomposed 

 at a red heat by themselves, and under the action of red-hot copper, sodium. A.V., they 

 give up their oxygen to the metals, leaving the nitrogen free. According to Meyer and 

 Langer (1885), nitrous oxide, N 2 O, decomposes below 900, although not completely, whilst 

 the decomposition of nitric oxide, NO, does not start at 1200, but is complete at 1700. 



4 Chlorine and bromine (in excess), as well as bleaching powder (hypochlorites). take 

 up the hydrogen from ammonia, NH 5 , leaving nitrogen. Nitrogen is best procured from 

 ammonia by the action of a solution of sodium hypobromite on solid sal-ammoniac. 



