Tins FLUIDITY OF SOLUTION'S

175

association is altered in the mixture, so that the result is consid-
erably complicated thereby. "We have, however, a fairly simple
case in mixtures of ether and chloroform studied by Thorpe and
Kodger. Chloroform, like carbon tetrachloride, is prohably
slightly associated but ether may be regarded as unassociated.

So far as can be learned from their measurements the maximum
contraction on mixing occurs in a mixture containing less than
40 per cent of ether and perhaps less than 39 per cent; the maxi-
mum deviation of the fluidity-volume concentration curve from the
linear curve occurs in the 58 volume per cent mixture ± 3 per cent.
This corresponds to 39.8 per cent by weight. A mixture corre-
sponding to the formula (^HioO.CECla contains 38.30 per cent
ethor by weight. Guthrie has noted that heat is evolved on
mixing and that it in a maximum when the components are in
molecular proportions. The vapor-pressure, refractive index
and the freezing-point curves all give evidence of the formation
of a compound CjHioO.CHClg.

In the mixture containing 56.26 volume per cent of ether, or
one molecule of ether to one of chloroform, we will now calculate
the percentage combined. From the atomic constants already
given, p. 126, it appears that the compounds CdHioO.CHCls
should have a fluidity of 200 at the absolute temperature of -588.6°.
But actually a mixture of this composition has a fluidity of 200
at 282.9° absolute (9.9°C). Pure ether and pure chloroform
have fluidities of 200 at 216.5° and 305.3° absolute respectively,
BO that if the mixture were wholly uneombined, the absolute
temperature neeensary for a fluidity of 200 would be 216.5 X
0.5626 •+ 305.6 X 0.4374 = 255.4°. Letting x represent the
fraction of the volume of the mixture which is combined, we ob-
tain the equation

538.6s •+ 255.4(1 - a?) = 282.9

and x = 0.0971, Since at this temperature (9.9°C) less than 10
percent of the volume of the mixture is actually in combination,
it seems reasonable to assume that a dynamic equilibrium exists
between the combined and the uncombined portions. If the
Mass Law holds, we have

. cHcy