140 FLUIDITY AND PLASTICITY
the zero axis and the viscosity will then increase with the pressure
as in other liquids.
In Fig. 52 the percentage change in the time of flow is plotted
against the pressure as in Fig. 50. A saturated solution (25.7
per cent) is seen to behave unlike pure water but like other
liquids in that the pressure causes an increase in the time of
flow. The curves for other concentrations lie between those
for pure water (0 per cent) and those for the saturated solution.
The continuous curves represent measurements at 14.5° and the
dotted curves represent measurements at 2°. From a compari-
son of these it is evident that the temperature coefficient of the
percentage change in the time of flow decreases rapidly as the
conciliation of the solution is increased. This is shown more
clearly in Fig. 53 where the temperatures are plotted as abscissas
against the percentage change in the time of flow for a pressure of
600 atmospheres, i.e., the percentage change in the time of flow-
is nearly constant in the most concentrated solution. Further-
more in an 8 per cent solution at a pressure of 600 atmospheres,
the effect of pressure on the time of flow is zero at 11°. Below
that temperature, pressure decreases the time of flow; above that
temperature, it increases it.
The relation of the percentage change in the time of flow at
600 atmospheres pressure as ordinates to the percentage con-
centration as abscissas is indicated in Fig. 54. At 22.5° the per-
centage change of the time of flow is a linear function of the
concentration, but at 2° this is no longer true, the effect of the first
additions of the salt to water being much greater than subsequent
additions. The curves do not cross, hence the effect of pressure
in the concentrated salt solutions is greatest at the high tempera-
tures even up to the point of saturation. Cohen found the oppo-
site to be true of turpentine, viz., the effect of pressure is greatest
at low temperatures. According to Warburg and Sachs, ether
behaves like turpentine and benzene like sodium chloride
solutions.
Hauser (1901) found that the effect of pressure upon the vis-
cosity of water continually decreases as the temperature is
raised until it becomes zero at 32° up to 400 atmospheres. Above
this temperature the viscosity increases with the pressure as in
other liquids, and the effect becomes more pronounced as the