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CHAPTEE XIII. 



METALLIC OXALATES. 



1. THERE exists a certain number of non-nitrogenised com- 

 pounds, formed in a regular manner, i.e. from the elements, in 

 consequence of a succession of exothermal reactions, which, 

 nevertheless, through heating or a shock capable of determining 

 decomposition, give rise to explosive phenomena. They are 

 compounds of such a kind that their elements have not reached 

 the most stable state of combination, i.e. the state to attain 

 which they have liberated the greatest possible amount of 

 heat. 



We have, for instance, silver and mercuric oxalates bodies 

 which detonate when suddenly heated or submitted to a violent 

 shock. Such a decomposition converts them into carbonic acid 

 and metal, in consequence of a real internal combustion by 

 which the oxygen of the metallic oxide attacks the oxalic acid 

 and completely oxidises it. This combustion, however, is only 

 possible when the heat it liberates surpasses that of the 

 oxidation of the metal plus the heat of neutralisation of the 

 metal. In other words, in order that an oxalate may possess 

 such properties, the reaction 



M 2 C 2 4 = 2C0 2 + M 2 



must be exothermal. Such is the fundamental condition which 

 distinguishes explosive oxalates from such as are not. 



2. Let us elucidate these notions by calculating the heat 

 brought into play by the decomposition of the principal metallic 

 oxalates. 



For this purpose the heat of formation of dissolved oxalic 

 acid from its elements * was first measured 



H 2 + C 2 (diamond) + O 4 water = H 2 C 2 O 4 (dissolved) (90 grms.) 

 liberates + 1947 Gal. 



1 " Annales de Chimie et de Physique," 5 e srie, torn. vi. p. 304. 



