BRIDGMAN. — THERMODYNAMIC PROPERTIES OF LIQUIDS. 67 



weighed, and its weight appHed as a correction to the weight of the 

 bulb full of the chloride. The weight was about 0.03 gm. 



The piston displacement for isothermal compressibility at 40*^ 

 showed a mean discrepancy of 0.0016 inch on a total of about 2.1 

 inches. The discrepancy in the displacements for dilatation averaged 

 0.002 inch on a mean of about 0.070 inch. The larger discrepancies 

 were at the lower pressures; the mean above 2000 kgm. was 0.001 

 inch, half as much. 



It has already been mentioned that ethyl chloride is so abnormally 

 compressible that it was not possible to use the same formula as for 

 the other eleven liquids to smooth the changes of volume at 40° for 

 the tables. A formula of the same type was used, but with different 

 coefficients (see page 22). The best values of the coefficients for 

 ethyl chloride were found to be, a = 0.06723, (S = 0.17139, 7 = 

 0.04030, and 8 = —0.06261. The maximum differences between 

 the observed and the calculated change of volume were + 0.0007 

 at 3000 kgm. and -0.0024 at 9000 kgm. The four constants were 

 determined so that the curve passed through the experimental points 

 at 500, 2000, 5000, and 12000 kgm. It should perhaps be mentioned 

 that this formula is merely an empirical expression for the change of 

 volume over the pressure range of the experiment. It has no theo- 

 retical significance whatever, and should not be used for purposes 

 of extrapolation. For instance, it is seen immediately that it pre- 

 dicts an impossible behavior at infinite pressure. 



The density at 0° was taken as 0.9120. The liquid boils at atmos- 

 pheric pressure for every temperature within the range of the table. 

 The ordinary dilatation formula would have been valueless, therefore,, 

 to fix the volume at any one point of the table. The fiducial point 

 was taken at 40° and 500 kgm. from the data of Amagat,^^ who gives 

 0.9951 for the volume. The fact that the liquid boils at all tempera- 

 tures of the table at atmospheric pressure has necessitated starting 

 from 500 or 1000 kgm. as the initial point from which most of the 

 thermodynamic properties have been computed. 



The initial compressibilities given in the diagrams for 20° and 40°' 

 were taken from Amagat by interpolation and extrapolation from 22 

 atmos. The values are O.O3I63, and O.O32II; they correspond to 

 pressures somewhat higher than atmospheric. 



The volume of ethyl chloride as a function of pressure and tempera- 

 ture is given in Table XIII and in Figure 17. 



51 Amagat, 1. c. (1877). 



