MIXTURES OF ELECTROLYTES—MACGREGOR. ala hg 
1 per cent., and for the most part considerably less, are one half 
positive and one half negative, and that whether the solutions 
are arranged in the order of conductivity, or in the order of 
mean concentration, they exhibit quite a sufficient alternation of 
sign to warrant the conclusion that they are due chiefly*at least, 
to errors in the observations and in the graphical portion of the 
calculations. 
In the case of the stronger solutions, Nos. 16-18 and 19-22, 
the alternation of sign has disappeared. In the weakest solutions 
of these two series, the differences are positive and small; but 
as the concentration increases, the differences become negative 
and take increasing negative values, the negative difference 
having its greatest value in No. 22, which is a mixture of a 
strong solution of Na Cl with asaturated solution of K Cl. The 
tendency towards a negative difference as the concentration 
increases, may be recognised also in Nos. 11 and 15; and it is 
perhaps worth noting that while the mean value of the positive 
ditferences is slightly greater than that of the negative differences 
up to a concentration of 1 gramme-molecule of salt per litre, the 
mean negative difference is the greater for higher concentrations. 
It is manifest from these results that for solutions of these 
chlorides containing less than say 2 gramme-molecules per litre, 
it is possible to calculate the conductivity very exactly, but that 
for stronger solutions the calculated value is less than the 
observed. 
The excess of the observed over the calculated conductivities, 
shews one or more of the assumptions implied in the mode of 
calculation to be erroneous. It would seem to be probable that 
the error is at any rate largely due to the assumption that the 
molecular conductivity of an electrolyte at infinite dilution is 
the same whether it exists in a simple solution or in a mixture, 
and that the discrepancy is thus due to the effect of mixing on 
the velocities of the ions. The mode of calculation assumes that 
in the mixture the constituents are not really mixed, but lie side 
by side, so that the ions of each electrolyte in their passage from 
electrode to electrode travel through the solution to which they 
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