ON ELECTROLYSIS IN IT$ PHYSICAL AND CHEMICAL BEARINGS, 37(^ 



As to the second case, no HCl escapes, and so the system is really homogeneous, 

 and a straightforward partition occurs. 



We believe we have proved that objections made to the theory of Berthollet 

 are avoided by the theory here presented. 



§ 20. Production of heat in chemical reactions. 



As we know, M. Thomsen considers that all bases, if they exist in the form of 

 dissolved hydrates, generate the same quantity of heat when dissolved in the same 

 quantity of an acid. This he calls 'saline thermo-neutrality.' On the other 

 hand, all acids do not generate the same heat when united to a given base — -a 

 circumstance which has appeared very odd to thermo-chemists. After what we 

 have just said, however, it appears to me possible to explain it. It is evident 

 that the thermo-chemical parity between two hydrates cannot obtain unless both 

 are in the active state. In the inactive state analogous compounds do not play 

 the role of hydrates (acids or bases), since they cannot unite to a hydrate of any 

 other nature (of contrary sign) and form water and salt. So instead of supposing, 

 as M. Thomsen does, that the hydrates are in a ' forme dissoute,' we suppose them 

 to be in the active state. After that we put forth the following very natural 

 hypothesis : — • 



The chemical 2)vocess, hy reason of which a system of one equivalent of acid (active') 

 and one equivalent of base {also active), transforms itself into a neio system, consist- 

 ing of a salt (not complex) and ivater, is accompanied by the same heat-production 

 independent of the nature of the acid or base. 



The diiferent processes which go on during the neutralisation of an acid or a^ 

 tase (both supposed partially inactive) are the following : — 



1. Neutralisation of the active parts. 



2. Transformation of inactive parts into active ones. 



3. Neutralisation of these new active parts. 



4. Formation of molecular complexes of the salt produced. 



5. Possible solidification of the salt. 



Between these five processes it is the sum of the heats produced in 1 and 3 

 per equivalent of salt formed which ought to be constant, according to tlie above 

 hypothesis. 



The existence of the processes 2, 4, and 5 explains how it happens that the 

 actual heat-production can be different in different cases. 



[Omitting 5, and considering 4 as small, the author points out that No. 2 pro- 

 cess is of least importance for strong acids and bases, and accordingly that for 

 these the heat-production may really be nearly constant. But for weak acids and 

 bases a good deal of heat is consumed in the No. 2 process. For remember that 

 ' strong ' means, in his view, ' having a high percentage of active molecules,' and 

 * weak ' means ' having very few active molecules.' Moreover, since a molecule's 

 activity is allied vdth, or equivalent to, its dissociation, it is very natural that its 

 production should be a heat-consuming process. Slight residual differences he 

 explains by No. 4 process, considering sulphates and acetates as more complex 

 than chlorides, nitrates, &c., and makes the following statement : — J 



(51) Increase of complexity is accompanied by production of heat. 



(52) Transformation from the inactive to the active state is accompanied by 



absorption of heat. 



(53) During neutralisation a feeble acid or base generates in general less 



heat on the whole than a strong one. 



Since now for salts it happens that the activity is smaller as the complexity i» 

 greater (see § 2), and the formation of molecular complexes is (by 50) followed by a 

 generation of heat, it is necessary that for salts also the transformation from 

 inactive to active state shall be accompanied by heat-absorption. But, by prop. 33, 

 bodies endowed with the smallest activity have the greatest chance of being 

 formed. Thus it follows that — 



