president's address — SECTION B. 57 



A large number of reactions occur in liquefied ammonia in 

 which the grouping NH2 plays a part analogous to that played by 

 the OH group in aqueous solution. As for example, in neutrali- 

 sation — 



KNH2 + NH4CI = KCl + 2NH3 

 compare K OH + (OH3CI) = K CI + 2H2O 

 in water solution. 



Or in hydrolysis, as 



BCI3 + 6NH3 = .3NH4CI4- B(NH2)3 

 compare B CI3 + 6 HgO = (3 H CI + 3 HgOj-f B(0H)3. 



If now we consider the electrolysis of potassium iodide in 

 sulphur dioxide we shall find a striking similarity of behaviour to 

 that already described for water and for ammonia. 



When such a solution is electrolysed it has been found that 



(a) at the cathode 



(1) sulphur is hberated and (2) potassium sulphite is 

 formed ; 



(b) at the anode, iodine is liberated, or if the anode consists 



of zinc or iron this may pass into solution as an iodide. 



The behaviour at the cathode is consistent with the supposition 

 that the sulphur dioxide ionises into sulphur cations $■■•• and 

 sulphite ions 2 SO3". The sulphur ions are discharged just as the 

 hydrogen ions are in the cases already discussed and just as the 

 hydroxyl and amido ions accumulate in those cases, so here the 

 sulphite ions accumulate and combine with the potassium ions K' 

 as they arrive at the cathode under the directive action of the 

 current, being precipitated on the cathode as a crystalline deposit 

 of potassium sulphite. 



The solvent action of the iodine ion as it arrives at the anode is 

 precisely analogous to the corresponding action of certain anions on 

 certain anodes in aqueous solution. 



In the case of solutions in sulphur dioxide the sulphites are 

 analogous to hydroxides in water solution and to amides in 

 ammonia solution, but with the difference that the potassium 

 sulphite happens to be insoluble in sulphur dioxide. 



The consideration oi .he quantitative relations that have been 

 disclosed during the many investigations that have been undertaken 

 on molecular conductivity on hydrolysis and alhed phenomena 

 leads to the conclusion that the ionic theory is the basis of 

 which the foregoing analogies have been discussed in its present 

 form ^is inadequate to express every aspect of the quantitative 

 behaviour of conducting solutions ; but it appears to me that this 

 theory will require rather to be modified and extended than to be 

 discarded. 



