510 Prof. J. G. MacGregor and Mr. E. H. Archibald on 



'O 



Mackay * have found no difficulty, other than the experi- 

 mental one, in concluding in the case of certain complex or 

 double salts that they do, or do not, as the case may be, 

 exist as such in extremely dilute solutions. 



In dealing with solutions of moderate dilution it has 

 generally been held that as the above relation holds 

 rigorously for extreme dilution it may be expected to hold 

 approximately for moderate dilution, and consequently (1) 

 that the differences between the actual and the volume mean 

 conductivity of a solution containing two salts which do not 

 form a double salt, will be small ; (2) that in the case of a 

 solution containing two salts which do form a double salt, 

 the differences will be of the same order of magnitude pro- 

 vided no double salt exist as such in the solution ; and (3) 

 that the observation of large differences, in the case of a solu- 

 tion of a double salt, establishes a probability of the existence 

 of double salt as such to a certain extent in the solution. 



Klein t and Bouty J have subjected the first of these 

 assumptions to experimental test. The former concluded 

 from his own observations on mixtures of potassium and 

 sodium sulphate solutions, and from Bender's § on mixtures 

 of solutions of chlorides, that the conductivity of mixtures 

 of equal volumes of equimolecular solutions is sensibly the 

 same as the arithmetic mean of the conductivities of the 

 constituents. Bouty made observations on solutions con- 

 taining lead and potassium nitrates, the chloride and nitrate, 

 chloride and sulphate, and nitrate and sulphate of potassium, 

 and the sulphates of zinc and copper, and drew the con- 

 clusion that in the case of neutral salts, simple solutions 

 of which on being electrolysed undergo equal changes of 

 'concentration at both electrodes, the conductivity of mix- 

 tures of equimolecular solutions in any proportions as to 

 volume, is equal to the volume mean of the conductivities of 

 the constituent solutions. When we examine the experi- 

 mental results on which these conclusions are based, however, 

 we find that in a considerable proportion of cases the differences 

 between observed and calculated values are considerably 

 beyond the limit of error within which conductivity can be 

 measured ; and the same is true of similar observations 

 made by Chroustchoff and PackhoffH. We find, also, 



* Amer. Cheni. Journ. xix. p. 83 (1897). . ; 



t Wied. Ann. xxvii. p. 151 (1886). 



j Ann. Chim. Phys. [6] xiv. p. 36 (1888). 



§ Wied. Ann. xxii. p. 179 (1884) : and xxxi. p. 872 (1887). 



H C. R. cviii. p. 1162 (1889). 



