336 HEATS OF FORMATION OF THE CYANOGEN SERIES. 



3. Heat of formation of cyanogen chloride from the elements. 

 This quantity is easily deduced from the above value. Let the 

 initial system be 



C + N + Cl + 2H 2 +0 2 + water ; 

 and the final system 



C0 2 (gas) + NH 4 C1 (in solution). 

 We pass from one to the other, by two different methods : 



FIEST METHOD. 



C (diamond) +0 2 = C0 2 (gas) + 94-0 



Solution of C0 2 + 5*6 



HC1 = HC1 (in solution) + 39-3 



NH 3 = NH 3 (in solution) + 21-0 



Union of NH 3 + HC1 = NH 4 C1 (in solution) ... + 12-45 



Sum +172-35 



SECOND METHOD. 



+ 138 



2(H 2 + 0) = 2H 2 



C + N + Cl = CNC1 (liquid) 



CNC1 (liquid) + 2H 2 + water = C0 2 (in solu- 

 tion) + NH 4 C1 (in solution) + 61'7 



Sum x + 199-7 



whence, 



x = - 27-35. 



This is the quantity of heat absorbed during the formation 

 of cyanogen chloride from the elements 



C (diamond) + N + Cl = CNC1 (liquid) absorbed - 27'35. 



We will pass on to the gaseous compound. 



4. Vaporisation of cyanogen chloride. The heat absorbed in 

 this operation was measured in a direct manner, i.e. by sub- 

 merging in the water of a calorimeter (500 cc.) which was at 

 20 a phial containing a known weight, 2-069 grms. for 

 instance, of liquid cyanogen chloride. The phial had been 

 cooled beforehand to nearly zero and weighted with a platinum 

 wire, as already described. Only the upper point, instead of 

 being opened directly into the liquid of the calorimeter, was 

 fitted with a little worm through which the gaseous chloride 

 was given off. This gas was then conveyed outside the calori- 

 meter, and absorbed by a solution of potash. The operation 

 lasts about twenty-five minutes. All calculations being made, 

 the following number was found for the vaporisation of CNC1 

 ( = 61-5 grms.) ; - 876 Cal. absorbed. 



This value comprises 



(a) The heat of vaporisation of cyanogen chloride at + 12'7. 



(b) The heat absorbed by the liquid, which has been raised 

 from 1 to + 12-7. 



