ON ELECTROLYSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 369 



According to (4A; [that is, (4) with ^ = 0, y = 0], — is always positive, eo — 



an 



(28) The more one adds a body to a system in equilibrium, the more will the 

 opposite bodies be formed. 



Then if the hody is water, and one adds it to a salt, one has immediately the 

 following consequence : — 



(29) Every salt dissolved in loater partially splits up into acid and base. The 



quantity of these products of decomposition is so miu:h the more con- 

 siderable as acid and base are feebler and quantity of water greater. 



Let a and b be the coefficients of activity of salt and water, j3 and y the same 

 for acid and base ; then ia the majority of cases aS is enormously smaller than /3y ; 

 consequently for small values of « * (in the case of strong acids and strong bases n 

 can without inconvenience rise as high as 10,000) we can neglect the term 

 ab (n + l)/Oy — ab) in comparison with the radical, and so — 



-^/^7^:, c«) 



0y 

 If, on the contrary, n is excessively great, one gets — 



x£il (7) 



These two formulae indicate that — 



(30) The amount of salt decomposed by moderate dilution is approximately 



proportional to the square root of the quantity of water used to dissolve 

 it. 



(31) A salt is completely split up if the watei' used to dissolve it is infinite. 



What is here said about water is evidently applicable to every other dissolviug 

 electrolyte. 



On this subject (the decomposition of salts by water) one reads in the work of 

 M. Berthelot (p. 199), ' The process of decomposition by water of the salts of feeble 

 acids is not always the same. Sometimes it iocreases little by little, either inde- 

 finitely with each addition of water, or tending towards a certain limit 



Sometimes, on the contrary, the decomposition of a neutral salt is accomplished 

 almost wholly by the first dose of water.' 



Thus, 1st. The salts of strong acids with strong bases are not decomposed. 

 According to prop. 30 they ought to be. At the same time the example of the 

 previous section shows that the salt NaNOg is only decomposed "ISpercent. by 100 

 equivalents of water. Such quantities cannot be observed by any thermic means 

 (at least, not by any that M. Berthelot employed). This is the reason for supposing 

 that these salts are not decomposed at all. ... On the other hand, the salts 

 of strong acids with feeble bases are notably decomposed by water. Ammoniacal 

 salts behave in this manner. In M. Berthelot's work there are a crowd of examples. 



2nd. Salts of feeble acids are notably decomposed. For example, ammonic 

 borate is decomposed 59'6 per cent, by 100 equivalents of water. Such quantities 

 are well marked by thermal actions. Nevertheless, from what we have just said, 

 the decomposition ought to be illimitable. The reason why M. Berthelot has in 

 certain cases only found a limited decomposition is probably because his thermal ex- 

 periments did not permit the employment of more than 1,000 equivalents of water, 

 and because the decomposition is at first proportional to the square root of the 

 quantity of water added (later still less) ; whence the first dose of water has an 

 eflect equal to that of the three following doses, &c. 



3rd. As for salts which are almost wholly decomposed by the first addition of 

 water, they are those for which ^y is less than ab (alcoholates, for example"* . 



' n means the number of equivalents of added substance — for instance, water — 

 for each equivalent of original substance — e.g., salt. 



1886. B B 



