NITIMMIKX AND A IK 225 



which is slightly heavier than air, forms air. It is a gas which, like 

 oxygen and hydrogen, is difficultly liquefied, and but little soluble in 

 water and other liquids. Its absolute boiling point 5 is about 140; 

 above this temperature it is not liquefiable by pressure, and at lower 

 temperatures it remains a gas at a pressure of 50 atmospheres. Liquid 

 nitrogen boils at 193, so that it may be employed as a source of great 

 cold. At about 203, in vaporising under a decrease of pressure, 

 nitrogen solidifies into a colourless snow-like mass. Nitrogen does not 

 burn, does not support combustion, is not absorbed by any of the re- 

 agents used in gas analysis, at least at the ordinary temperature in a 

 word, it presents a whole series of negative chemical properties ; this is 

 expressed by saying that this element has no energy for combination. 

 Although it is capable of forming compounds both with oxygen and 

 hydrogen as well as with carbon, yet these compounds are only formed 

 under particular circumstances, to which we will directly turn our atten- 

 tion. At a red heat nitrogen combines with boron, titanium, and silicon, 

 forming very stable nitrogenous compounds, 6 whose properties are 

 entirely different from those of nitrogen with hydrogen, oxygen, and 

 carbon. However, the combination of nitrogen with carbon, although 

 it does not take place directly between the elements at a red heat, yet 

 proceeds with comparative ease by heating a mixture of charcoal with 

 an alkaline carbonate, especially potassium carbonate or barium carbo- 

 nate, to redness, carbo-nitrides or cyanides of the metals being formed ; 

 for. instance, K 2 CO 3 + 4C + N, = 2KCN + 3CO. 7 



Nitrogen is found with oxygen in the air, but they do not readily 

 combine. Cavendish, however, in the last century, showed that nitrogen 

 combines with oxygen under the influence of a series of electric sf>arks. 

 Electric sparks in passing through a moist 8 mixture of nitrogen and 

 oxygen for instance, through air cause these elements to combine, 



5 See Chapter II. note 29. 



6 The combination of boron with nitrogen is accompanied by the evolution of suffi- 

 cient heat to raise the mass to redness; titanium combines so easily with nitrogen that it 

 is difficult to obtain it free from that element. It is a remarkable and instructive fact 

 that the compounds of nitrogen with these non-volatile elements are very stable, and 

 are themselves non-volatile. Probably in this case the physical state of the substance 

 with which the nitrogen combines, and ,the state in which the nitrogenous substance is 

 obtained, evinces its influence. Thus carbon (C = 12) with nitrogen gives cyanogen, C;>N 2 , 

 which is gaseous and very unstable, and whose molecule is not large, whilst boron (B = ll) 

 forms a nitrogenous compound which is solid, non- volatile, and very stable. Its compo- 

 sition, BN, is essentially like that of cyanogen, but its molecular weight is probably 

 greater. 



7 This reaction, as far as is known, does not proceed beyond a certain limit, probably 

 because cyanogen, CN, itself breaks up into carbon and nitrogen. 



8 Fremy and Becquerel took dry air, and observed the formation of brown vapours of 

 oxides of nitrogen on the passage of sparks. 



VOL. I. Q 



