474 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
Y for various intervals, we get the 
following values, the figures for the range 100-200 being taken from 
Amagat’s results : — 
Similarly, if we calculate 
Pressure. 
Mean Coefficient of Expansion x 10 5 between 
100-200. 
200-300. 
300-400. 
400-500. 
500-600. 
600-700. 
700-800. 
800-900. 
400 
99 
600 
3280 
4300 
700 
91 
380 
880 
1760 
1880 
1880 
1000 
84 
280 
520 
1 
1000 
1060 
1060 
1060 
1060 
The Table shows that, while for a pressure of 1000 the maximum value 
of cq is about thirteen times as great as its value between 100° and 200°, for 
a pressure of 400 the maximum value of cq is forty-three times its value 
for the same range, the maximum value thus rapidly increasing with 
decrease of pressure. 
If 
we finally calculate 
± dV 
Y dT 
or the rate of change of volume with 
temperature per unit volume at that temperature, we find that this 
quantity constantly increases with temperature to a maximum which 
again corresponds to the point where the straight part of the isopiestic 
begins and thereafter decreases as shown by the curves in fig. 5. The 
maximum values of with the corresponding values of Y and T are 
approximately as follows : — 
Pressure. 
Maximum ~ ~ . 
1 
Y. 
T. 
400 
•0124 
350 
370 
700 
•0065 
280 
428 
1000 
•0046 
235 
454 
The values of Y and T here given were obtained from curves similar to 
fig. 4, but drawn on a very much larger scale. 
Looking at the curves in fig. 4 now from another point of view, we 
see that, if a series of such isopiestics for still lower pressures could have 
been obtained, the critical constants might have been graphically deter- 
