314 HEATS OF FORMATION OF THE CYANOGEN SERIES. 



FIRST STEP. 



H 2 C0 2 (pure) + water ... +0-08 



H 2 C0 2 (diluted) + NH 3 (diluted) + 12-0 



Separation of solid ammonium formate + 2'9 



NH 4 CH0 2 (solid) = HCN (liquid) + 2H 2 (liquid) ... + x 

 HC1 (diluted) no change. 



Sum + 15-0 + x 



SECOND STEP. 



NH 3 (diluted) + HC1 (diluted) + 12-4 



H 2 C0 2 (pure) + water + O08 



NH 4 C1 (diluted) + H 2 C0 2 (in solution) = HCN (liquid) 



+ HC1 (diluted) + 2H 2 -11-15 



Sum ... + 1-3 

 x = - 15 + 1-3 = - 137 Cal. 



In fact, the salt, when melted, is really destroyed, with the 

 production of water and hydrocyanic acid, both in a gaseous 

 form ; it thus absorbs, besides the 137 Cal. mentioned above, 

 the heat necessary for the vaporization of these two substances, 

 i.e. a value approximately 1 = (57 4- 19*3) + F, where F is 

 the heat of fusion of the salt. This gives then - 387 4- F, 

 which amounts to about 36 Cal. 



A similar absorption would no doubt be produced if the 

 ammonium formate could exist in a gaseous form and be decom- 

 posed as such. 



In short, the formation of formonitril from ammonium formate 

 absorbs, whatever hypothesis is adopted, a great quantity of 

 heat ; a result in accordance with what happens in most decom- 

 positions. 



We may go further than this. In fact, the dehydration of 

 ammonium formate is effected by two stages, formamide and 

 water being first produced 



NH 4 CH0 2 = CNH 3 + H 2 0. 



The liquid formamide was acted upon by means of con- 

 centrated hydrochloric acid, so as to give the opposite reaction. 

 From the numbers observed it was deduced that the theoretical 

 reaction, i.e. in the case of the use of diluted acid, would give 

 off + 1*4 Cal., a value which is probably too low, and is given 

 here with some diffidence, as the formamide, being in the liquid 

 state, cannot be guaranteed pure. It is practically applicable 

 to the change of formamide (in solution) into ammonium 

 formate (in solution), the value deduced being -f- 1. 



We conclude, from these figures, that the decomposition of 

 the melted ammonium formate into gaseous formamide and 



1 The term approximately is used, because the heats of vaporisation of the 

 bodies concerned in the experiment at the temperature of decomposition of 

 ammonium formate (180 to 200) are not the same as at the boiling points. 



