On Hydrolysis in Aqueous Salt- Solutions. 365 



Of course it is not pretended that this expression is the 

 most convenient for the purposes of calculation: the approxi- 

 mate value of the conical angle which is given by a series of 

 spherical harmonics is that which should be employed ; but 

 it may be well to give the complete expression in the above 

 form, which I have not seen published anywhere. 



XXXVI. On Hydrolysis in Aqueous Salt-Solutions. 

 By John Shields, B.Sc, Ph.D.* 



ON dissolving potassium cyanide in water it is partially 

 decomposed into potassium hydrate and hydrogen cya- 

 nide. This action of the water in producing decomposition is 

 called hydrolysis. Probably all salts are hydrolysed in aqueous 

 solution to a certain extent, but in the majority of cases the 

 amount of hydrolysis is so excessively small that the means 

 which we have at our command are not sufficiently delicate to 

 enable us to detect it. Besides the salts there is another im- 

 portant class of compounds, namely the esters, which are sus- 

 ceptible to hydrolysis on being mixed with water. Methyl 

 and ethyl acetate, for example, are decomposed by water to a 

 considerable extent into acetic acid and the corresponding 

 alcohol. The extent to which hydrolysis takes place is regu- 

 lated by the law of mass action as enunciated by Guldberg and 

 Waage. In all cases we are dealing with a state of chemical 

 equilibrium or balanced action which is usually represented 

 thus : — 



KCN + HOH -^-*- KOH + HON, 

 or 



CH 3 COOC 2 H 5 + HOH <— *" C 2 H 5 OH + CH 3 COOH, 



the sign c y being substituted for the ordinary sign of 

 equality as suggested by Yan't Hoff. 



Now, a, priori, we should expect a substance, for example 

 potassium cyanide, which is formed from chemically equivalent 

 quantities of acid and base to be neutral, and we have every 

 reason to believe potassium cyanide, as such, to be so. Its 

 solution in water, however, as is well known, has a strongly 

 alkaline reaction, and the above explanation of hydrolysis 

 furnishes us with no reason why the solution should react 

 alkaline rather than acid, since the hydrolysed fraction of the 

 potassium cyanide still exists in the solution as chemically 

 equivalent quantities of acid and base. Here Arrhenius' 

 theory of electrolytic dissociation comes to our aid, and shows 

 us that although we may have in the solution equivalent 



* Read before the Swedish Academy of Science, Stockholm, 11th 

 January, 1893. Communicated by the Author. 



Phil. Mag. S. 5. Vol. 35. No. 215. April 1893. 2 C 



