Affinities of Poly basic Acids. 



25 



worthy of attention. He measured the heats of neutralisa- 

 tion of the first and second molecules of a base with the 

 molecules of dibasic acids of the oxalic acid series, with 

 formation of solid salts. He obtained the following 

 results : — 



ist KOH ... 

 2nd KOH... 



Oxalic. 



Malonic. 



Succinic. 



Sulphuric. 



34,280 

 24,690 



27,870 

 20,700 



25,260 

 21,150 



47,800 

 33,600 



The particular point of importance in these observations is 

 that in every case the second molecule of the base liberated 

 less heat than the first, while in measurements of the heat 

 of neutralisation in aqueous solution the reverse was fre- 

 quently observed by Thomsen. Massol pointed out that 

 while the heat of neutralisation of formic acid with 

 potassium hydrate and formation of a solid salt is 25,800 

 units, that of oxalic acid, which may be regarded as a 

 carboxyl derivative of formic acid, has more than twice as 

 great a heat of neutralisation, as though the two carboxyls 

 effect a mutual strengthening of one another. It is seen 

 from the above table that when one of these carboxyls is 

 neutralised, the acid salt of oxalic acid acts like formic acid, 

 and has almost the same heat of neutralisation. 



The results, then, at which he arrived, Massol attri- 

 buted to a reciprocal action between the acid groups — 

 an action which is less in degree in malonic and succinic 

 acids, in which the carboxyl groups are further apart from 

 one another. 



Berthelot, in a note to Massol's paper, pointed out that 

 the greater heat liberated by the first molecule of base is a 

 necessary consequence of the fact 1 that a dibasic acid com- 

 bines with its own normal salt to form an acid salt in the 

 solid state with disengagement of heat. 



1 Ann. Chim. Phys.^ 5. IV. 130. 



