316 EEATS OF FORMATION OF THE CYANOGEN SERIES. 



SECOND STEP. 



K + C + N = KCN (crystalline) x 



i[H 2 + = H 2 (liquid)] ,. ... + 34-5 



Sum ... +34-5 + 03 

 x = + 64-8 - 34-5 = + 30-3. 



2. The direct formation of potassium cyanide from the union 

 of its elements, as expressed by chemical equation, and the 

 corresponding disengagement of heat, is not really effected at 

 the ordinary temperature. But it is admitted that it does 

 actually take place at a very high temperature, when free 

 nitrogen is made to act upon charcoal impregnated with potas- 

 sium carbonate ; i.e. under conditions where potassium is 

 generated. At this temperature, the potassium cyanide is 

 melted or perhaps even gaseous, a change of state which causes 

 an absorption of heat ; but, on the other hand, the potassium is 

 gaseous, which compensates this absorption. If free nitrogen, 

 carbon, and potassium do really combine without any other 

 intermediate reaction, such as the formation of an acetylide 

 (this formation has not been proved to take place), we should 

 be led to admit that the total synthesis of potassium cyanide 

 disengages heat, under the actual conditions of the reaction. 



Be the disengagement produced at once or by successive 

 reactions, it does not explain the total synthesis. 



3. We come now to a clearer synthesis. The union of 

 cyanogen with potassium takes place, as we know, directly. 

 This union, calculated for the following states of the substances 

 concerned 



K (solid) -f CN (gas) = KCN (crystallised), disengages 

 + 67-6 Cal. 



These figures justify the direct synthesis of potassium cyanide 

 from cyanogen. But this quantity is lower than that dis- 

 engaged by the union of the same metal, in the solid state, with 

 halogen elements in the gaseous state. 



Now, 



Cl + K = KC1 (solid) gives off + 105*6 



Br (gas) + K = KBr gives off +100*4 



I (solid) + K = KI gives off + 85-4 



This difference explains why chlorine, bromine, and iodine 

 decompose potassium cyanide in solution ; cyanogen is liberated 

 and combines, besides, with half the halogen, causing a slight 

 additional disengagement of heat 



[+ 1-6 for CNC1 (gas) ; + 4-2 for CNI (solid).] 



4. It may also be mentioned, in order to complete this 

 parallel, that the formation of potassium cyanide from the 

 hydracid (diluted) and potash 



HCN (diluted) + KHO (diluted) = KCN (in solution) + H 2 0, 



