IN AQUEOUS SOLUTION, AND THE EXISTENCE OF COMPLEX IONS. 
137 
partly, into complexes of the nature of (C'd L L^), ;iiul tliat a })ortiou (jf the curreut 
being carried hy these, the ciiange in ct)ncentration in the neighl)ourliood of tlie anode 
becomes increased by tlie amount of neutral salt carried by tliis complex anion. 
.Referring again to the variation in for other salts, he says {ibid., p. 546-7) : 
“ Die 1)edeutende Abhiingigkeit der Ueberfiihrungszahlen von der Concentration 
der Losung erklart sich in derselben Weise, wie bei dem Doppelsalze (ICd + IK). 
Mit der Zunahrne des Wassers zerfalleii die Doppelatome in immer wachsender Zahl 
in die einfachen, der Strom wird daher immer mehr von den einfachen geleitet, welche 
bei stark Verdiinnung allein vorhanden sind. 
“Nur durch diese Deutuno- vermao- ich den Thatsachen a^erecht zu Averden, und 
stehe nicht an, dieselbe auf das Verhalten sammtlicher Salze, Avelche zur Magnesia- 
gruppe gehdren, zu ubertragen. Die schon frliher fur einen Theil derselljen angege- 
benen Ueberfiihrungen sind ebenfalls in hohem Grade Ann der Concentration abbiingig 
und Avlirden, wenn nocb concentrirtere Losungen in binreicbender Ausdebuung 
untersucbt Averden konnten, fiir das Anion ebenfalls die Einbeit uliersteigen.” 
More recently Bredig (‘Zeit. f Phys. Cbemie,’vol. 13, 262, 1894) has pointed out 
the possibility of explaining this difficulty by means of complex ions, and Noyes 
iloc. cit.) assumes the existence of complex anions BaClg or BaCl^. in solutions ot 
barium chloride so dilute as - - . 
10 
The most natural assumption tliat can be made as to the manner in Avhich such a 
salt as magnesium chloride AAnuld ionize, is that there Avould be first fiArmed the tAvo 
+ — 
ions MgCl and Cl, and that on further dilution the former of tliese Avould dissc'ciate 
+ 4 * — 
into the simple ions Mg and Cl. Noyes (‘ Zeitschr. f Physik. Cbemie,’ 9, 618), from 
a study of the solubilities of such salts, concludes that this is the case, but the 
formation of such ions (comjAlex cations) would lead to a change in j) exactly the 
opposite of that Avhich actually occurs, and it is possible that his results could be as 
AA'ell exjDlained by the sujAposition of complex anion, e.g., (MgCbCL). The tendency 
toAvards the formation of complex ions is discussed fully lAy Abegg and Bodlander 
(‘Zeitschr. f Anorg. Chemie,’ vol. 20, 471, 1899), Avho shoAv that these are formed always 
by the combination of a free electrically charged ion with an electrically neutral 
molecule, the latter may be of the nature of a salt or not. As an example of the 
former, the complex K 3 Fe(Cu)g is formed of the simple cation K and the complex 
anion Fe(Cn)g"', Avhich latter is formed from the neutral part Fe(Cn )3 and tlie 
simple anion Cn~. 
Similarly, the complex anion of the jAeriodides I 3 is formed by the union of the anion 
I Avith the neutral molecule L. This definition also includes the case of the douljle 
salts, Avhich difier only from the ferrocyanides and others in the greater tendency 
of the complex to dissociate into its component parts wlien dissolved in Avater. 
VOL. CXCVJII.-A. 
T 
