New York AGRICULTURAL EXPERIMENT STATION. 2I7 
culation is, as already stated, unwieldy. A combination, however, 
of simple approximate calculation with a relatively small graphical 
correction avoids both these difficulties. For the mineral acids, we 



used the formula x = Ro es xX 10°%= the concentration of the 
acid based on that of N-1000 as unity; R== the resistance of the 
acid in the cell; 4 = a graphic correction to R. The formula is 
based on the fact that, for electrolytes as strong as hydrochloric 
and sulphuric acids, dissociation is sufficiently complete at dilutions 
above N-125 to make the resistance approximately inversely pro- 
portional to the concentration. If the proportion were exact, the 
equation, + ae , would hold good. However, as the concentration 
increases from the point where dissociation is not complete, R 
becomes too large to fit the equation exactly, the proportionate 
excess increasing with the concentration. By subtracting this ex- 
cess, 4, from R, we have the equation, x an , which is exact. 
The value of 4 can easily be determined with accuracy sufficient for 
results correct to one pro mil. by graphic interpolation, plotting 
values of R as abscissae and those of 4 as ordinates. Of course, 
one can use conductivities as easily as resistances, employing the 
formula + = c (k—4); k = conductivity; but more convenient 
curves are obtained by the use of resistances. After finding the 
values of c and 4 for a cell of capacity K, the formula can be 
used with a cell of capacity K’ by multiplying c and 4 by =. 
In the case of sulphuric acid, the range of dilution (N-125 to 
N-8000) was so great that it was found convenient to use two 
cells and construct a curve for the range over which each was 
employed. The curves include the correction for the influence of 
water, since water of the same character and conductivity was em-- 
ployed in finding the values of 4 and in the subsequent experi- 
ments. This is of advantage because, when working with mineral 
acids and bases, it is doubtful whether subtracting the conductivity 
of the water gives correct results. Ostwald favors ignoring the 
effect of the water, since the impurity may be of such a nature as 
even to lower the conductivity.1. Kohlrausch,? on the other hand, 
remarks in discussing this plan: “So steht ein solches Verfahren 
volistandig in der Luft.” 
* Physico-Chemical Measurements, translated by Walker, p. 235. 
*Leit. d. Elek., p. 92. 
