1912] 



oil Heat Froblem.- 



583 



importance of the critical point. Other relations between the pro- 

 perties of a body and its critical constants are of i-nterest, and are 

 given in the following table : — 



Table III.— Corresponding Temperature Relations 

 Liquid coefficient of expansion varies 



Liquid coefficient of compressibility 



varies as . 

 Liquid internal latent heat varies as . 

 Capillary constant varies as 

 Gas inversion point varies as 

 Volume of gas molecule varies as 

 Maximum density varies as density at 



1/Tc 



1/Pc 



Te 



Pc- 



Tc 



Tc/Po 



Tc 



The vaporization of ice at - 78° C. can be 

 demonstrated by the apparatus shown in Fig. 3. 

 A is a small bulb packed in solid CO^, tilled 

 Avith ice in the form of frozen water-saturated 

 cotton wool, which gives a large surface. This 

 vessel is connected to the U-tube B immersed 

 in liquid air. The tube and the bulb are highly 

 exhausted by an air pump connected at the ;-5-way 

 cock 1), and then by charcoal C cooled in liquid air. 

 The deposit is first seen in the form of a ring 

 in the limb of the U-tnbe nearest the bulb A. 

 Vaporization is very slow, and takes almost an 

 hour before the deposit is sufficient to be easily 

 visible. 



With gas thermometers working under small 

 gas pressure reliable results can be obtained, 

 provided the differences in the height of the 

 mercury columns are read by means of a catheto- 

 meter, and proper precautions taken in filling 

 with the gas. A simple form of gas thermometer 

 with the volume of the bulb as small as 5 or 6 c.c. 

 is shown in Fig. -1. In small apparatus, where a 

 more l)ulky instrument could not be used, this 

 form works in a satisfactory way, giving readings 

 within 0'5°. when tilled with helium or hydrogen 

 under an initial pressure of 273 mm. at the / \ 

 melting-point of ice. The following diagram v J 

 (Fig. .")) shows the type of the graphical curves ^-^ 

 given by such thermometers ; exhibiting a slight Fig. 4. 



deviation from the theoretical straight line con- 

 necting absolute temperature and pressure. The various substances 

 used in the calibration of such thermometers are marked on the 

 curves. The deviations from the theoretical line are much ex- 

 aggerated in the diagram. They are due to the variation in the 



