THE FLUIDITY OF SOLUTIONS

163

tion it follows that if we plot volumes against weight concentra-
tion, we will obtain a linear curve such as curve I in Fig. 60;
but if we plot specific volumes against volume concentrations,
we will obtain not the linear curve III, Fig. 61, but curve IV.

We have seen that the fluidity of a liquid is directly propor-
tional to its free volume, but the fluidities are additive (Eq. (25))

1.260 1.200
1.140 6er

~J

X
/
//

x%/'
Y

/'
/

Jfr
/^'m-AdditiveSp.N A/ nr-Additive Sp. s/' V- Observed
/ol.Ca!c.bi|Vo Vol.Calc. b^y Wt
l.°/0
.%>

) Ib 50 75 10 ?ene Volume Concentra'tion Ether Efh«

Fia. 61.—Specific volume-volume concentration curve of mixtures of benzene
and ether. (After D. F. Brown.)
only when we use volume percentages; hence it follows that if a
pair of liquids on mixing gave a linear specific volume-volume
concentration curve (curve III) they would also give a linear
fluidity-volume concentration curve, curve VI, Fig. 62. Since,
however, the ideal mixture gives a volume-volume concentration
curve which shows positive curvature, the fluidity-volume con-
centration curve of the ideal mixture will also show positive
curvature, curve VII, Fig. 62.