336 . REPORT — 1886. 



or ' the specific molecular conductivity is equal to a constant diminished by a 

 quantity inversely proportional to the mean distance of the molecules.' 



0. The rate of diminution of klm with increasing concentration is greater the 

 higher the valency of the ions. This is ascribed to two possible causes — (a) a 

 change in the constitution of the polyvalent ion, in virtue of which it approximates 

 in behaviour to a monovalent ion, as the dilution inci'eases ; (6) the possibility that 

 the cuiTent may be in part conveyed by the water of the solution. 



6. The specific conductivity of a salt appears to be unaffected by its possessing, 

 or being destitute of, water of crystallisation. 



The above conclusions refer only to neutral salts ; acids and alkalies (including 

 alkaline carbonates) behave in a different manner. The chief facts collected by the 

 author regarding these substances are — 



1. The specific molecidar conductivity of acids and alkalies is small if the dilution 

 be very great, increases with the strength of the solution up to a certain maximum, 

 and from this point diminishes as the concentration increases. The small initial 

 value of k\m he considers (following Arrhenius and Ostwald) to be a secondary 

 phenomenon — probably due to impurities in the water — and accordingly he neglects 

 this part of the curve, and obtains the limiting value of the specific molecular con- 

 ductivity by producing the second part backwards through the maximum to the 

 line of ordiiiates. lie thus obtains as the maximum limiting velocity of the ions 

 0*4 mm I sec, under an electromotive force of 1 volt per linear millimetre. 



2. The alkalies KOH and NaOH have specific molecular conductivities dififering 

 by a small constant amount, as also have their carbonates. 



3. The monobasic mineral acids have the same specific molecular conductivity. 

 Phosphoric acid gives a not very different value if, instead of the equivalent ^HjPO^, 

 we employ the whole molecule H3PO4. 



4. Acetic acid and ammonia in dilute solution exhibit a conductivity nearly 

 proportional to m-. In strong solution they conduct very badly. 



5. Sulphuric acid is anomalous, showing, after an initial specific molecular con- 

 ductivity like that of the monobasic mineral acids, a rapid decrease to an inferior 

 value, about §rds of this. From former investigations by the author it is known 

 that the conductivity of sulphuric acid during increasing concentration exhibits 

 three maxima and two minima. The first minimum corresponds to the hydrate 

 HjSO^.HjO, and the second to concentrated H.^SO^. One of the maxima occurs 

 between this point and SO3. This behaviour points to a chemical change in the 

 structure of the molecule, depending on the concentration. 



With regard to the problem of electrolytic conduction in general, Kohlrausch 

 lays down the axiom that no electrolyte in a pure state is a good conductor, but 

 only becomes such on admixture with other bodies, this admixture being necessary 

 in order to set up the dissociation which Clausius looks upon as the cause of migra- 

 tion of the ions. In this connection the question is discussed as to whether the 

 water of a solution conducts part of the current. This our author considers proved 

 for dilute solutions of several sulphates by an old experiment of Faraday, which he 

 has confirmed. Perhaps such a circumstance would explain various anomalies. 



Kohlrausch discusses Bouty's ' law of equivalents,' which states that ' the 

 electric conductivity of dilute salt-solutions of equivalent strengths is the same for 

 different substances.' Bouty distinguishes between ' normal ' salts, which obey the 

 law, and abnormal salts, which do not ; and defines an abnormal salt as one ' whose 

 constituent ions in dilute solution travel with different velocities.' But Kohl- 

 rausch shows that some salts which would come under this definition obey Bouty's 

 law, while some of the salts which disagree with it can be shown to be ' normal,' 

 from observations on their migration-constants. He also objects to the law on 

 the ground of its inherent improbabihty, and alleges further that Bouty's method 

 of calculation in comparing his own results with those of the author is eiToneous. 



Among minor points of interest brought out by the iuvestigation are the 

 following : — 



1. The low conducting power of nearly pure water, the smallest value obtained 

 being 0-25x10-10. 



2. The phenomenon of absorption by the electrodes. The conductivity of a 



