386 REPORT— 1886. 



' I set myself the problem to find out bow much tbe resistance actually increased 

 wben a dilute electrolyte had its volume doubled by addition of water. (If Kohl- 

 rausch's formula were true, it would be simply doubled.) Thus I started free from 

 hypothesis. The observed ratio of increase of the resistance I called " the dilution- 

 exponent." Since it changes very slowly with concentration, one need not ascertain 

 it by making every dilution from 1 to 2, but can quite well obtain a mean value of 

 it for a greater range (say 1 : 6-08) ; and the calculation ol" the mean number then 

 proceeds on purely arithmetic grounds without any special hypothesis. I hold 

 strongly, therefore, that my method of calculation is absolutely correct for mean 

 values ; and that I have always meant mean values is quite clear from page 34 et 

 seq. The number is by no means a constant. I speak continually of its variation, 

 and have tabulated the variations in Table B. I could not make its variability 

 clearer than I have done. I have taken conductivity as the fundamental quantity 

 instead of concentration, because one is always much safer in determining its abso- 

 lute value by ordinary means. You think it would have been better to tabulate r 

 instead of 2'' ; this is a matter of taste. The dilution-exponent is easy to define 

 physically ; r is not. Besides, one can more easily form a mental image of its 

 meaning. Not only Bouty, but Lenz also, and Ostwald, have discussed the change 

 of resistance on doubling dilution. 



' 5. " Kohlrausch and most authors suppose that kirn is constant for extreme 

 dilution." This he does without reservation for solutions of no extraordinary weak- 

 ness, and he thence calculates klm for extremest dilution, whereby he several 

 times gets incorrect values (too small).* The hypothesis is, however, quite natural, 

 and I have always regarded this idea of Kohlrausch as most valuable ; and I 

 sought consequently to apply this idea, and to show how to explain apparent ex- 

 ceptions to it. I never sought to " label " the statements (1), (2) and (3) as laws 

 of nature, but say definitely : " The above conclusions are deduced from ideas which 

 are in full accord with all known facts, and consequently they have the same degree 

 of exactitude as those ideas accepted by all the world " (Part I. § 15). It is quite 

 certain that the conductivity of water is very feeble, and there is no reason for 

 denying that molecules may be independent of one another in very weak solutions, 

 since they collide so seldom. I have sought to explain why in practice the mole- 

 cular conductivity is not constant even in utterly weak solutions. I have given 

 two explanations : — 1st, that tbe water used contains traces of ammonium salts 

 (especially AmjCOg, not dissolved glass as you write ; a fact more lately proved by 

 Ostwald), which explains the decrease of molecular conductivity of hydrates ; and 

 2nd, that molecular complexes are formed ; a hypothesis which is introduced into so 

 many other subjects that one need feel no difficulty in employing it. (This view a 

 reader of your exposition will hardly attain.) 



' 6. That the last work of Kohlrausch contains as you say incomparably better 

 experimental data (especially more accurate) is true enough. But without my 

 data I could not have formed a coherent picture of the whole. Besides, Kohlrausch's 

 work has in no way caused me to alter any theoretical views, but has fully con- 

 firmed me in them. 



' It is the highest problem of the natural philosopher to link together facts 

 into a connected chain. I had expected a criticism from you to take this view. I 

 concluded that you were of this opinion from your essay on the seat of voltaic 

 E.M.F. ; yet you abandon it in your criticism of the first part of my memoir. 



' As to the second part, I am very glad that you have everywhere appreciated 

 my views, and represented them in a more complete manner than I could have 

 hoped. Just a few notes. 



' 7. With regard to your remark on (14), I may say, in explanation, that almost 

 all chemists attribute the reactions of ammonia to a small portion of NH^HO in it, 

 which so soon as consumed is generated anew by equilibrium between H„0 NH3 and 

 NH^HO, so that ammonia behaves chemically just as if it consisted of nothing but 

 NH4HO. In Thomsen's and Kohlrausch's experiments, on the other hand, the 

 properties of the chief quantity, which consists of NH3, play the greatest part. 



' These remarks refer to my 1879 essay. — F. K. 



