470 PROCEEDINGS OF THE AMERICAN ACADEMY. 



fifth point of the above series was obtained in the inverse way, during 

 melting, proceeding from low to high pressures. The pressure corre- 

 sponding to —4° is so low that the elastic after-effect must be small, 

 but still it is noteworthy that this point shows- the greatest deviation 

 from the straight line. This inverse procedure at —4° was necessary 

 in this case because of the low pressures, the friction of the packing 

 being so great that pressure could not be reduced suihciently below 

 the equilibrium pressure to induce solidification from the subcooled 

 liquid when the regular procedure of running from high to low pressures 

 was adopted. 



The correction applied to the change of volume for the thermal dila- 

 tation of the gasolene (the fluid transmitting pressure in this set of 

 experiments), was not determined directly at all points of the curve, 

 but only at the two end points. At 0° the correction is 0.9 per cent, 

 and at —22° is 2 per cent. The correction was assumed linear for 

 intermediate points. It makes no difference within the limits of error 

 whether temperature or pressure is taken as the independent variable 

 of this linear relation, and there seems little probability that the error 

 so introduced can exceed this 0.1 per cent. The tables give the values 

 corrected both for the thermal dilatation of the gasolene and for the 

 elastic deformation of the cylinder. This latter correction is 0.2 per 

 cent at the maximum. 



The values of A F are shown in Figure 6. The open circles are the 

 observed points. The solid circle at —22° was not an observed point, 

 but is the value required at the triple point by the conditions of con- 

 sistency with the other data. In the AT diagrams for the other 

 equilibrium curves the values at the triple points are indicated in the 

 same way. 



As an additional check on the values found here there is the known 

 change of volume at 0° as found by other observers. The recent work 

 of Leduc seems the most accurate. He gives for the value of the 

 density of ice at 0°, 0.9176, from which the change of volume is found 

 to be 0.0900 cm.^ per gm. The value of AV at o° as found by Leduc 

 is taken as the origin in the diagram. It is seen that the other points 

 are perfectly consistent with this value, thus confirming the accuracy 

 of the method. The relation connecting change of volume with tem- 

 perature is nearly linear, the curve being slightly concave toward the 

 temperature axis. Four of the points, including Leduc's, lie sensibly 

 on the curve ; one is 1 per cent too high, and the other 1.5 per cent 

 too low. 



This value of Leduc is higher than that of most other observers, but 

 the discrepancy seems to be due to occluded air, which Leduc took 



