POTASSIUM CYANIDE. 315 



steam will absorb about + 18 Cal. (supposing the vaporisation 

 of the formamide to absorb from 6 to 8 Cal.). 



The two stages of the dehydration of crystallised ammonium 

 formate, which is changed first into gaseous amide and then into 

 gaseous nitril, would correspond to thermal phenomena that 

 may be considered as having equal effects, the first stage absorb- 

 ing - 18 Gal, and the two stages together 36 Cal. But this 

 equality would only exist when the products are considered in 

 the gaseous state. 



Conversely, the fixing of the elements of water, either upon 

 the formamide or upon the formonitril (in solution), so as to 

 reproduce the ammonium salt (in solution), gives off a quantity 

 + 1 Cal. for the amide, and + 104 for the nitril ; quantities 

 which are very unequal but both positive. 



This is another proof of the disengagements of heat which 

 may result from simple hydration effected by the wet process, 

 and especially so from that of amides, which play a very im- 

 portant part in the study of the reactions of organic nitrogenous 

 principles, and that of animal heat. 1 



The formation of cyanides will now be explained. 



4. POTASSIUM CYANIDE. 

 1. It was found, by experiment, that at about 20 



HCN (liquid), on being dissolved in 40 times its weight of water, Cal. 



gives off ..................... +0-40 



i[2HCN (diluted) + K 2 (diluted)] ............ + 2'96 



KCN (pure), on being dissolved in 50 times its weight of water, 



absorbs ...... i.;"^ ......... ... -2-86 



From this we deduce the heat disengaged by the formation of 

 solid potassium cyanide from the elements 



K -f C -f N = KCN (crystalline) disengages -f 30'3 

 The calculation is as follows : 



Initial system; [&,+ C 2 -f N 2 -f H 2 + 0]. 



Final system ; i[2KCN (crystal.) + H 2 (liquid and separate)]. 



FIRST STEP. 



H + C -h N = HCN (liquid) absorbs - 23-8 



HCN + nAq ......... ... + 0-4 



-"K 2 + 0+r i Aq = K 2 (diluted)] ............ +82-3 



2HCN (in solution) + K,0 (in solution) = 2KCN (in 



solution) + H 2 0] ............... + 3*0 



Separation of KCN (solid) ............... + 2'9 



Sum ... + 64-8 



1 "Annales de Chiruie et de Physique," 4 e se'rie, torn. vi. p. 461. 



