34U HEATS OF FORMATION OF THE CYANOGEN SERIES. 



SECOND STEP. 



K + I (solid) = KI (in solution) + 74-7 



C (diamond) 4- N + 1 (solid) = CNI (in solution) ... x 



Sum ... + 74-7 + x 



X = - 41 ; 



a value which applies to cyanogen iodide in solution. For solid 

 iodide, we get 



C (diamond) + N + I (solid) = CNI (solid), - 38-2. 



4. Union of iodine with cyanogen. 



CN + I (solid) = CNI (solid) + 0'9. 

 CN + I (gas) = CNI (solid) + 6-3. 



These values are very little less than that of the heat of 

 formation of liquid cyanogen chloride, or + 9 -9. They are less 

 than the values relating to solid iodine chloride (+ 121) and to 

 solid iodine bromide (+ 1*9). The difference, however, is not 

 very great ; another confirmation of the general analogy of all 

 these components (see p. 338). 



5. Substitution. The substitution of iodine for the hydrogen 

 of hydrocyanic acid, with the simultaneous formation of hydri- 

 odic acid and cyanogen iodide 



HCN (gas) + I 2 (solid) = CNI (solid) + HI (gas), would absorb 



- 131. 



Thus this reaction does not take place in a direct manner. But, 

 on the contrary, we note the action of iodine on cyanides, which 

 takes place owing to the extra energy, due to the action of the 

 alkaline iodide. This is the calculation, all the bodies being 

 brought to a similar state 



KCN (solid) + I 2 (solid) = KI (solid) + CNI (solid) ... + 13-3 Cal. 



AgCN (solid) + I 2 (solid) = Agl (solid) + CNI (solid) ... + 11-6 

 i[Hg(CN) 2 (solid) + 21, (solid) = HgI 2 (solid) + 2CNI (solid) ]+ 6-0 



Here, it may be repeated, there is disengagement of heat due 

 to the formation of the metallic iodide : which formation is 

 necessary in order to ensure the combination between the 

 cyanogen and iodine. 



6. It had already been found convenient to study the thermal 

 formation -of cyanogen bromide from bromide and dissolved 

 potassium cyanide, but this formation is almost immediately 

 followed by secondary reactions, which are indefinitely pro- 

 longed and cast a doubt on the numerical results observed at 

 first. Therefore it was thought advisable to suppress them. 



12. POTASSIUM CYAN ATE. 



1. Pure potassium cyanate was decomposed by means of 

 dilute hydrochloric acid. If a quantity of water is used, 



