186

FLUIDITY AND PLASTICITY

Fig. 71, show that in general the salts which occupy the largest
volume in solution correspond to those having the highest fluidity
curve II, but silver seems to be strongly exceptional. Here
again we have evidence that fluidity is proportional to the free
volume. The cause of the volume change is also the cause of
the negative curvature.

Ammonium iodide according to Getman (1908) and Ranken
and Taylor (1906) shows negative curvature but it goes into
solution with contraction, according to Schiff and Monsacchi.
There is thus a lack of parallelism between the two properties of
which one further example may be cited. In ammonium nitrate
solutions, the expansion is least in a 7-weight per cent
solution arjtd yet the fluidity is a maximum in this solution at
some temperature between 25 and 40°C. Since we are dealing
with inflected curves signifying simultaneous dissociation and
chemical combination, these anomalies are to be expected. The
limiting volume is continually changing and the specific volume is
for that reason no measure of the free volume. There is need
for further work in this very important field.

Attempts have been made by Wagner and others to assign
to each element a specific viscosity effect in solution. The fluidi-
ties of nitrates, chlorides, and sulf ates of certain metals in normal
solution at 25°C are given in Table XLVII as modified from
Wagner. The table shows that the fluidity of the nitrates is

TABLE XLVII.—A COMPARISON OP THE FLUIDITIES OP VABIOTTS METALS
AND ACID RADICALS IN NORMAL SOLUTION AT 25°C (AFTER WAGNEE)

N03
C13
S04
N03
Cl
NO3 SO4

K
114 7
113 3
101 2
1 012
1 133

K/H .
1 053
1 081
0 974

H .......
108 9
104 8
102 5
1 039
1 062

K/Na ..
1 095
1 112
1 112

Na .....
104 7
101 9
91 0
1 027
1 151

K/Zn
1 195
1 199
1 239

Zn .......
96 0
94 5
81 7
1 015
1 175

K/Mg ......
1 201
1 218
1 239

Mg
95 5
93 0
81 7
1 26
1 169