384 EEPOET— 1886. 



' Against this we remark that chemical knowledge is mainly based on the re- 

 action of electrolytes, which seem in chemistry to play the same role as gases do in 

 the mechanical theory of heat. For the rest, the idea of an electrolyte has an 

 application much wider (according to the law of Hittorf ) than one is accustomed to 

 attribute to it. And reactions in general seem to manifest a considerable analogy 

 to those of electrolytes, so that one could perhaps in the future enlarge the theory 

 given for electrolytes, until it becomes, with some modification, applicable to all 

 substances.' 



Remaeks on tee above Memoik. 



The criticism of the first part of Dr. Arrhenius' memoir given above being some- 

 what stringent, I thought it best to send a proof copy to the author in case h& 

 might wish to reply. He has favoured me with a letter touching on various 

 points, and in order to assist in the elucidation of them it seems most satisfactory 

 to print it here, numbering its paragraphs so as to make it easy to connect them 

 with the parts of my criticism to which they refer (see pp. 357-364). It would seem 

 that I have been misled by the form in which the paper is written, especially by 

 the italicised and numbered statements with which it abounds, into criticising parts 

 of it from rather too elevated a stand-point, as if the statements were intended 

 for rigorous laws. 0. L. 



Translation of a letter received from Dr. Arrhe7iius respecting the above Criticism. 



' Dear Sik, — Yesterday evening I received your friendly postcard and a copy of 

 your criticism on my work. For both I thank you, and at once proceed to give an 

 answer thereto as the subject requires. 



'1. To your remarks against my experimental method (" I must confess to 

 surprise, &c. . . . self-induction and electro-chemical capacity being so mixed 

 up in it ") I wish to observe that self-induction in the galvanometer coil has no 

 effect. Self-induction possibly occurs in the rheostat, as well as electrochemical 

 capacity in the liquid. Quite the same sources of error, however, occur ia 

 Kohlrausch's method also, to the same or even a higher degree ; and on considera- 

 tion you will hardly deny this.' The alternating currents used by him have just 

 about the same total intensity as mine, so polarisation is about the same in the two 



• This opens a large question, viz., how far it is advisable to depend on the use of 

 alternating currents as a device for avoiding polarisation difficulties. At first sight 

 it might seem as if the mere fact of alternation was a sufficient safeguard ; but when 

 the extreme rapidity of rise and decay of polarisation is remembered, confidence in 

 alternating currents is much diminished. In his early experiments Kohlrausch used 

 a sine inductor, and in his later researches carefully considered the effect of the 

 disturbing elements (see Jubelband, Poffff. Ann., page 290). With a simple harmonic 

 current of small period it is possible for self-induction and polarisation capacity to 

 neutralise each other's effect; and in any case it is comparatively easy to take 

 them into account. The equation to the current is — 



L^i'+ EC ^ AqiU^ Esinw!;; 

 dt Jo 



„ E sin {nt — (p) 



where R tan (/> = 7iL — L. 



V{^-^(-^-i)"} 



n 



p is calculable from the following data : the decomposition products oi^^ milligramme 

 of water on two platinum plates, each one metre square, give an E.M.F. of one 

 DanieU ; consequently, knowing L, p, E, and measuring C* with a dynamometer, it is 

 possible to calculate the true value of R. Or, by arranging that the polarisation 

 coefficient p is equal to m^L, all disturbance vanishes, and the resistance can be 

 measured quite simply by a bridge method. Unless the question of electro-chemical 

 capacity be thus considered, and either eliminated by calculation or proved to be 

 negligible by experiment, the presumed advantage of alternating currents in deal- 

 ing with electrolytic resistance is illusory. O. L. 



