304 HEATS OF FORMATION OF THE CYANOGEN SERIES. 



It is a fact worthy of mention that this number exceeds the 

 united heats of combustion of the carbon and hydrogen con- 

 tained in the hydrocyanic acid, whatever form the carbon may 

 be in. 



C (diamond) + 2 = C0 2 + 94 (charcoal) + 97 

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



+ 128-5 + 131-5 



According to these figures and this method, the formation of 

 hydrocyanic gas from its elements, H + C -f N = HCN, absorbs 

 + 128-5 - 159-3 = - 30-2 when the carbon is in the form of 

 diamond, and - 27*2 when it is in the form of charcoal. 



3. Second Method. Conversion of the hydrocyanic acid into 

 formic acid and ammonia. This change is effected by means of 

 concentrated hydrochloric acid. In addition to the data con- 

 cerned in the direct experiment we must also have the heat of 

 formation of ammonia, the heat of combination of this base with 

 hydrochloric acid, the heat of dilution of hydrochloric acid, 

 and, lastly, the heat of combustion of formic acid, carbon, and 

 hydrogen, so that we have, in all, six auxiliary data. 



A known weight of pure hydrocyanic acid was decomposed 

 in the calorimeter by means of very concentrated hydrochloric 

 acid. When the change was effected, it was proved to be com- 

 plete or practically so ; the mixture was diluted with a large 

 quantity of water, and the new quantity of heat evolved 

 measured. In a similar way was measured the heat disengaged 

 by the mixing of the same quantities of concentrated hydro- 

 chloric acid and water. 



From this was deduced the quantity of heat that would be 

 disengaged by the following reaction : 



HCN (pure and liquid) + HC1 (diluted) +2H 2 = H 2 C0 2 (in 

 solution) f NH 4 C1 (in solution); or -f 1115 Cal. 



Experiments. Some details of one of the experiments taken 

 as a type may now be given. 



Preliminary operations. The calorimeter contains 500 cms. 

 of water. It is placed in a double enclosure, in the centre of a 

 quantity of water, the temperature of which is exactly the same, 

 i.e. to within 0*1 of a degree, as that of the water in the calori- 

 meter, and that of the room in which the experiment is being 

 performed. This point is essential. 



In the centre of the calorimeter is placed a little cylinder of 

 thin platinum, of a capacity of about 50 cms., with no opening 

 at the base, and closed at the top by means of a cork coated 

 with paraffin. This cylinder floats in the water of the calori- 

 meter, in which it is immersed nearly up to its top. We first 

 introduce into it 35 grms. of hydrochloric acid, which is concen- 



