1893-94.] 
Dr Walker on Hydrolysis. 
261 
hydrosulphide is the same in equivalent solutions — as must be very 
nearly the case, if we judge from the course of the molecular con- 
ductivities at the various dilutions — we can calculate from the con- 
ductivities of these salts what the conductivity of a solution 
containing both of them in equivalent proportions would be. If 
they (are equally dissociated, neither will effect the dissociation of 
the other, so that we can obtain the conductivity of the mixture by 
simply taking the average of the conductivities of the components. 
]Sow, if sodium sulphide solutions are, as the saponification experi- 
ments indicate, merely mixtures of equivalent sodium hydroxide 
and sodium hydrosulphide solutions, half the molecular conductivity 
at any dilution should be equal, approximately at least, to the mean 
of the molecular conductivities of solutions of sodium hydrosulphide 
and sodium hydroxide at half the dilution. The following table 
gives the comparison : — 
Dilution. 
(Mol. Cond. of 
Mean of Mol. Cond. 
of NaSH and NaOH at 
Na,S)^2. 
(Dilution 2). 
32 
144 
145 
64 
149 
151 
128 
152 
156 
The agreement between the observed and calculated numbers may 
be deemed sufficient, as the values for sodium hydroxide were inter- 
polated from Kohlrausch’s data, which were obtained by the use of 
a very much purer water than any I could prepare from London 
water. 
All the evidence, then, tends to show that, in dilute aqueous solu- 
tions, sodium sulphide is almost entirely hydrolysed into sodium 
hydroxide and sodium hydrosulphide, while the latter is scarcely 
attacked by water at all. Thus, when one hydrogen atom of 
hydrogen sulphide is replaced by an alkali metal, the other hydrogen 
atom shows scarcely any acid properties, and this is what we might 
expect from the theory of polybasic acids given by Ostwald.* 
According to this theory, the nearer the two electrical charges on 
a bivalent negative ion are to each other, the greater will be the 
difficulty of forming this ion. Since, now, the two charges in a 
sulphide would reside on the same atom, it is not surprising that 
* Zdt. ’pluysikal. Chem,, ix. p. 553. 
