UNION OF CYANOGEN WITH CHLORINE. 337 



(c) The heat absorbed by the gas, which has been raised from 

 127 to 197 (the average temperature during the vaporisation). 



These two last quantities are relatively small. They could 

 only be estimated exactly if we knew the specific heats of 

 cyanogen chloride in the liquid and the gaseous states at 

 the temperatures indicated. In default of any direct data, 

 approximate values were used; the total value of these two 

 quantities, moreover, representing a very small quantity as 

 compared with the heat of vaporisation itself. Let us admit 

 for these specific heats the mean value + 0*4, deduced from 

 observation made on similar liquids. Consequently, the heat 

 absorbed in the accessory operations (b and c) will be estimated 

 at 0*46 ; a correction entailing probable error amounting to not 

 more than a fourth of its value. The heat of vaporisation of 

 cyanogen chloride will be, for CNC1 (= 61*5 grms.), 8*3 Cal. 



Thus the formation of gaseous cyanogen chloride from its 

 elements 



C (diamond) + N 4- Cl + CNC1 (gas), absorbs - 357. 



These figures exceed in absolute value the heat absorbed in the 

 formation of hydrocyanic acid ; for 



H + C 4- N = HCN (gas), absorbs - 29'5. 



The formation of cyanogen chloride from the elements is, there- 

 fore, endothermal, like that of hydrocyanic acid, but even in 

 a higher degree. This circumstance explains why cyanogen 

 chloride is so apt to undergo polymeric transformations and 

 other condensations. 



5. Union of cyanogen with chlorine. From the above data 

 we deduce 



CN (gas) + Cl (gas) = CNC1 (gas) gives off + 37'3 - 357 = 



+ 1-6. 

 CN + Cl = CNC1 (liquid) + 9-9. 



These values were checked by another method. 



We know that cyanogen chloride is easily formed by the 

 action of mercuric cyanide, in solution, on chlorine. The heat 

 disengaged in this operation was measured. 



i[Hg(CN) 2 (in solution) + 2C1 2 (gas) = HgCl 2 (in solution) 

 + 2CNC1 (in solution). 



The value + 17'5 Cal. was found. 



The calculation, supposing the cyanogen chloride to be 

 liquefied instead of being in solution, would give + 29'6 ; the 

 difference does not exceed the limits allowed in experiments of 

 this kind, or the differences which exist between solution and 

 liquefaction. This is, therefore, at least an approximate check 

 on the heat of formation of cyanogen chloride. 



z 



