342 HEATS OF FORMATION OF THE CYANOGEN SEEIES. 



For example 



C1 2 (gas) + K 2 (diluted) = KC10 (diluted) + KC1 (in solution) 

 gives off only -j- 2 5 '4. 



There is, besides, the difference that the complex nature of 

 cyanogen and its tendency either to form polymeric compounds 

 and other condensed bodies, or to reproduce ammonia and its 

 derivatives, gives rise to a number of secondary reactions, 

 which are not observed in the case of chlorine. These reactions 

 take place all the more readily in proportion as the heat 

 disengaged by the direct reaction is itself greater, and therefore 

 furnishes a greater reserve of energy for other transformations. 



5. The union of dry potassium cyanide with gaseous oxygen, 

 to form solid cyanate 



KCN (solid) + (gas) = KCNO (solid), would give off + 102 

 - 30-3 = + 717 ; 



a very high value, being nearly three-quarters of the heat 

 (+ 94'0) disengaged in the combustion of the carbon contained 

 in the cyanide. 



These figures relate to the bodies when considered in their 

 actual state ; under which condition, up to the present, the 

 absorption of oxygen by potassium cyanide has not been 

 observed, perhaps because it has not been looked for. On the 

 contrary, if the potassium cyanide be in the melted state, the 

 absorption takes place easily, as we know. Now, the values 

 which have just been calculated may be applied approximately, 

 at a high temperature, to the same bodies in the known 

 conditions of their actual reactions ; for the melting of the 

 cyanide and that of the cyanate must absorb quantities of heat 

 which are little different. As regards the heat disengaged by 

 the oxidation of its potassic compound, cyanogen resembles 

 iodine, but, on the contrary, differs from chlorine. In fact, we 

 get 



KC1 + 3 = KC10 3 (solid) absorbs -11 



KBr + 3 = KBrO 3 (solid) - 11-1 



KI + 8 = KI0 3 (solid) gives off + 44-1 



KCN + = KCNO (solid) gives off + 71-7 



a progression which is the reverse of that which characterises 

 the union of the same metal, such as potassium, with the same 

 series of halogen bodies, such as chlorine (+ 105*0), gaseous 

 bromine (+ 100*4), gaseous iodine (+ 8 5 '4), and cyanogen 

 (+ 67-6). 



We can understand, from the above figures, why potassium 

 cyanide shows such a great tendency to become oxidised, either 

 under the influence of oxidising agents, or even under the 

 influence of the air. 



The combustible nature of one of the elements contained in 

 cyanogen is, besides, opposed to its forming the peroxygenated 



