352 . EEPORT — 1888. 



tlie interruption would amount to at most 25 Daniells. That is, the same maximum 

 as was found for the polarisation also with large platinum plates in dilute sulpliuric 

 acid. Now, with thin wires a great deal of ozone, peroxide of hydrogen, and per- 

 sulphuric acid is evolved at the anode ; at plates only commou oxygen. As the 

 electromotive force of polarisation has the same value in either case, it is to he con- 

 cluded from the facts that the evolving of those hyper-oxides has no influence 

 upon the polarisation ; and, further, that the primary electrolytical process hy which 

 the strength of the polarisation is chiefly conditioned is the very same during the 

 development of common oxygen as at the evolving of O^jH.fi.^ and S2O3H2 from 

 dilute sulphuric acid. 



IV. The influence of the formation of SiO^H.^ on the polarisation may he judged, 

 too, from the electromotive behaviour of platinum in S^OgH.,. I found the electro- 

 motive force 



Hg I Hg.SO, I SO,H.,aq | S,OgH,aq | Pt^O-rS Dan. 

 Zn fSO^H.aq 1 SoOgH, aq | Pt = 2-06 Dans. 



From which may he calculated 



Pt I SO^H^aq I SAH^aq | Pt = 0-Gl Dan. 



In this last cell the process effected hy the galvanic current is the reduction of the 

 persulphuric acid, according to the formula 



S,0«H,aq = 2S0,H,aq + 0. 



Its heat of formation (Berthelot, ' Corapt. Rend.' 00, p. 3.31, 1880) is equivalent to 

 0-56 Daniell. It is to be concluded from the conformity of the found with the 

 calculated value that the reduction of the persulphuric acid in that cell is a 

 primary electrolytic process. Besides, it must seem very probable that the forma- 

 tion of SoOgllj at the anode, also corresponding to the inverse process, is a primary 

 electrolytic process. To its chemical heat of formation a polarisation of the 

 anode of 0'56 Dan. would correspond. Generally, however, neither the polarisa- 

 tion alone is given by the chemical heat, nor is S^Ogllj alone formed under any 

 circumstances at the anode. 



Reply to Professor Armstrong's Criticisms regarding the Dissociation 

 Theory of Electrolysis. By Svante Arehenids. 



In his communication at Manchester to the Electrolysis Committee of the 

 British Association, Professor Armstrong has honoured my views on electrolysis 

 with a critical analysis from a chemist's point of view. In the following lines I 

 will attempt to show how the chief objections that he has made can be removed, 

 and also that his views present difficulties which greatlj' militate against their 

 acceptance. 



1 and 2.' Professor Armstrong finds it difflcult to explain why some single 

 bodies, e.g., silver iodide, conduct electrolytically, whereas other pure bodies, e.g., 

 water or hydrogen chloride, are non-conductors. We certainly are bound to 

 assume that fused silver iodide is to a sensible degree dissociated into its ions, and 

 that the dissociated parts of the non-conductor escape our observation. But it 

 may be remarked that no exact comparison can be made between the two cases, 

 silver iodide being examined at temperatures above 530° (the melting-point of Agl), 

 H^O and HCl at ordinary temperatures, it being very probable that dissociation 

 increases rapidlj' with the temperature. Also, too much stress must not be laid on 

 the behaviour of pure bodies or of concentrated solutions, as experience shows that 

 dilute solutions are characterised by very remarkable regularities, analogous to 

 those which obtain in the case of gases, and that these regularities vanish as the 

 solutions attain a greater degree of concentration ; indeed, there seems to be no 

 connection between the facility with which compounds are electrolytically dis- 

 sociated in dilute solutions and the stability of the same compounds in the pure 



' The numbers correspond with same numbers in Professor Armstrong's paper 

 above referred to, ' Comparison between the Views of Dr. Arrhenius and Professor 

 Armstrong on Electrolysis.' See 1887 Report, p. 354. 



