1902.] on the Ions of Electrolysis. 41 



= HCl + Na2S04. In the first of these experiments we take as the 

 electrolyte a concentrated solution of potassium hydrogen sulphate 

 KHSO4. This gives the ions K and HSO4. The latter go to the 

 anode and there, on being discharged, form persulphuric acid, or its 

 ions, and potassium persulphate K2S2O8, being sparingly soluble, 

 crystallises out. This is the method by means of which Dr. Marshall 

 discovered the persulphates. The next experiment will illustrate the 

 formation and discharge at the anode of the anion SO4. We have 

 here dilute sulphuric acid with which is mixed a little manganous 

 sulphate MnS04. The ion SO4 when discharged, adds itself to 

 2MnS04 and forms manganic sulphate Muo(S04)3, recognised by its 

 red colour. This, even in acid solution, is quickly hydrolysed, giving 

 insoluble manganic hydrate. 



The other point I wish to illustrate is the application of Guldberg 

 and VVaage's principle to ions. Without entering into any general 

 discussion of this question, I shall merely say that theory leads to the 

 result that the addition of a soluble acetate to a solution of acetic acid 

 diminishes the concentration of H ions, and so makes the solution 

 less effectively acid. This was experimentally proved by Arrhenius 

 in 1890,* by measuring the rate at which cane-sugar is inverted by 

 acetic acid alone, and with varying quantities of sodium acetate 

 added to it. But as such an experiment cannot be made visible to 

 a large number of spectators at once, I thought of a way of showing 

 the same thing, which, while not capable of the same degree of 

 accuracy, would prove the principle qualitatively. I have here a 

 solution of ferrous acetate to which I have added enough acetic acid 

 to prevent the precipitation of ferrous sulphide on the addition of 

 sulphuretted hydrogen. I add sulphuretted hydrogen, of course no 

 precipitate is formed. I now add a solution of sodium acetate mixed 

 with rather more than three equivalents of acetic acid, so as to make 

 it plain that the effect is not due to the formation of an acid acetate, 

 and you see that we have at once a precipitate of ferrous sulphide. 

 To show that the addition of the water has not produced the result, 

 I add to another portion of the same solution as much water, and you 

 see that no precipitation takes place. 



I have not spoken of non-aqueous solutions. At the rise of the 

 dissociation theory, these were generally supposed to be non-con- 

 ductors, but many of them have now been examined both by scientific 

 workers in the old world, and very specially by our colleagues on the 

 other side of the Atlantic, and been found to conduct electrolytically. 

 It seems likely that these investigations will throw much light on 

 the influence of the solvent on the conductivity of the dissolved salt. 

 Particularly interesting is the relation, indicated in some cases, 

 between the specific inductive capacity of a solvent and the dissocia- 

 tion of the dissolved salt. But this is one of the questions not yet 

 ripe for treatment in a discourse such as this. 



* ArrheniuB, Zeitschrift f. phyaik. Chemie, v. p. 1 (1890). 



