330 BABCOCK. 



specific volume v, it is possible to calculate the values of the saturation 

 specific heats of both the liquid and the vapor, over the same tempera- 

 ture range, provided certain thermodynamic quantities for the 

 substance in question are known. This computation will be given 

 later. 



Drawing the pressure-volume diagram for a substance, in the 

 neighborhood of the licjuid-vapor region, it is possible to indicate 

 graphically the path over which the heating takes place, during a 

 determination of fij,. This path is shown by AB in Figure 2. The 

 saturation specific heat of the liquid is the specific heat determined 

 by heating along the liquid line CE; and the saturation specific heat 

 of the vapor is that determined by heating along the vapor line DE. 



The measurements described in this paper yield the specific heat 

 along the line AB. 



III. Apparatus. Specifications. 



1. Calorimeter. Figure 3. 



a. Calorimeter Tube. 



Material steel; inside diameter 62 mm.; wall thickness 

 1 mm.; length 270 mm. Supported by steel pins from 

 asbestos board cover 7 mm. thick. All metal projections 

 from calorimeter through cover capped with asbestos 

 board. 



b. Calorimetric Fluid. 



5153 grams of mercury. Advantages: low vapor pressure, 

 negligible vaporization, low heat capacity per unit volume, 

 high heat conductivity. 



c. Liquid Container. Calorimeter Stirring. 

 Constructed from seamless steel tube, outside diameter, 

 46 mm., wall thickness, 4 mm., length 250 mm. Designed 

 to withstand critical pressure of liquid ammonia: 112.3 

 atmos. Hexagon nut milled on each end of barrel. Hexa- 

 gon caps screwed on both ends. Gaskets, thin sheet 

 copper. Joints and barrel tested to 135 atmos. Filling 

 plug screwed into upper cap. Hemispherical joint, set 

 up dry. Six 1.6 mm., stirring fins milled lengthwise of 

 barrel. Container mounted in bearings in calorimeter. 

 Oscillated by stirring shaft and gearing, driven by small 

 motor. Geared to rotate three turns in each direction. 



