308 HEATS OF FORMATION OF THE CYANOGEN SERIES. 



exact an idea as possible of experiments of this kind, and of the 

 difficulties which they present. Of course, we could not expect 

 the same degree of accuracy as in experiments of short duration, 

 but, nevertheless, the errors can hardly exceed '05 of the total 

 value. 



4 Calculation from tfo theoretical reaction. It now remains 

 for us to deduce from the numbers observed the values which 

 are applicable to the reaction taken from a theoretical point 

 of view. For this purpose, the same weight is taken of the 

 same solution of concentrated hydrochloric acid, viz. 35 grms. 

 (or a weight very near to this, in which case the results are 

 afterwards referred to this weight by proportional calculation) ; 

 it is dissolved in the same quantity (500 cc.) of water at the 

 same temperature ; then the heat, Q 3 , disengaged is measured. 



This quantity being known, the difference, Q! 4- Q 2 Q 3 , 

 represents exactly the heat disengaged by the conversion of the 

 weight employed of pure hydrocyanic acid by means of hydro- 

 chloric acid (diluted), into formic acid (diluted), and ammonium 

 chloride (diluted), as the initial state and the final state are 

 absolutely identical. Multiplying this quantity by the ratio of 

 the equivalent (HCN = 27 grms.) to the weight of hydrocyanic 

 acid actually employed, we obtain the heat disengaged in the 

 theoretical reaction 



HON" (pure and liquid) + HC1 (diluted) + 2H 2 

 = H 2 C0 2 (diluted) + TH 4 C1 (diluted). 



The following numbers were found by experiment, + 11-54 and 

 f 10'76, or, on an average, + 1115. 



5. From this is deduced the heat of formation of hydrocyanic 

 acid from its elements, carbon (diamond), gaseous hydrogen, and 

 gaseous nitrogen 



H + C + N = HCN (pure and liquid), absorbs - 22'6. 

 In short, supposing the initial system to be 



5H + C + N + 2 -f- HC1 (diluted), 

 and the final system 



H 2 C0 2 (diluted) + NH 4 C1 (diluted), 

 we pass from one to the other by two different processes. 



FIRST STEP. 



H 2 + C + 2 = H 2 C0 2 (pure) disengages + 93-00 



H 2 C0 2 (pure) and water + Q'10 



N + H 3 = NH 3 (in solution) + 21-00 



NH 3 (diluted) + HC1 (diluted) = NH 4 C1 (diluted) ... + 12-45 



Sum + 126-55 



