ON ELECTKOLTSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 339 



The following 7-emarhs m-e taken from a criticism of the above abstracted memoir of 

 Professor Kohlrausch, published by M. E. Boutt in the 'Journal de Physique,' 

 for September 1886. (Translated by Mr. Love.) 



'The object of M. Kohlrausch is to control the results of the experiments of 

 Messrs. Lenz, Ostwald, and Vincenti, and my experiments of 1884, and to throw 

 light on points left in dispute. To this end he works by the methods which he 

 had previously pointed out, but with excessive dilutions, attaining to O'OOOOl gramme 

 equivalents per litre. These liquids conduct scarcely better than distilled water, 

 and a thousand tiraes worse than the water supplied to the town of Wiirzburtr. 

 Experiments of this kind raise a multitude of theoretical and practical difficulties 

 which M. Kohlrausch points out in all good faith, if he has not always given them 

 a decisive solution. 



' In the first place come the difficulties due to the employment of alternatino- 

 currents and the telephone. . . . Possibly graver difficulties arise from the 

 employment of distilled water ; and these will always present themselves, what- 

 ever method be employed, if the dilution be pushed to extreme limits. In the first 

 place, it is very difficult to procure distilled water of constant composition. M. 

 Kohlrausch used rain-water distdled in a tin retort with a silver condenser, and 

 stored in large glass flasks. The conductivity of this water ranged from 1-1 to 

 1-5 X 10-'" (the conductivity of mercury being taken as unity), and was diminished 

 rather than increased after keeping in the flasks. 



'Let us admit this conductivity as accurately known. If a trace of saline 

 matter be added to the water its conductivity increases. M. Kohlrausch supposes 

 that the conductivity of the salt and that of the water simply add ; and as this rule 

 if applied to neutral salts assigns to them a molecular conductivity sensibly con- 

 stant in very dilute solution he supposes it to be sufficiently justified by experiment. 

 M. Kohlrausch admits, however, that the greater part of the conductivity attri- 

 buted to the distilled water really belongs to foreign matter^neutral salts, acids, 

 or bases — with which it is contaminated ; if some saline particles be added to this 

 water we then have to deal with a mixture of which we Imow only a single element — 

 that which has been added — the nature and proportion of the other elements remain- 

 ing unknown ; it is possible that the conductivity we wish to measure may be 

 modified by the presence of this unknown element "in a manner altogether arbitrary, 

 and which may vary from one salt to another. . . . 



' M. Kohlrausch does not admit the division of neutral salts into "normal" and 

 " abnormal," which I established on the basis of the inequality of the numbers 

 relating to the transport of the ions. If we consider only anhydrous normal salts, 

 the limiting values assigned by M. Kohlrausch are as follows : — 



NH.Cl A;/m-10« = 120.5 

 KCl „ 1216 



KNO3 „ 1215 



iK.,SO, „ 1275 



KCIO3 klm-W = lU\ 

 KI „ 1207 



AgNOj „ 1080 



'M. Kohlrausch thinks himself in a position to enunciate tiie following con- 

 clusions : — 



' 1 . For a given neutral salt the molecular conductivity tends towards a dejinite 

 limit, as the dilution is increased indefinitely. 



' 2. For the different neutral salts this number is always of the same order of 

 gnitude. The ext ■> r. ■, , -.«, ,^^ „ „ „„ -.. . __ 



(an abnormal salt). 



magnitude. The extreme values of kjm -IC are 128 for K.,SO^, and 94 for KG H 



' 3. This limiting value depends on both ions : they group themselves in the 

 order of diminishing conductivity in the manner indicated by the foUowino- table : 



Kation Anion 



Potassium. Sulphuric Acid. 



Ammonium. Iodine. 



Barium. Chlorine. , 



Silver. Nitric Acid. 



Z2 



