154 MivCarl Barus on the Pressure-Variations of 



value, I noticed that the mean G of Table VII. is nearly the 

 same as Bertrand's C for water. Hence it was selected. 



Table VIII. — Constants for Boiling-point and Pressure. 



Substance. 



A. 



B. 



C. 



Water 



Sulphur 



Cadmium 



Zinc 



Bismuth 



19324 



19776 



20-63 



2098 



21-51 



2795 

 4458 

 7443 



8619 

 12862 



3-868 

 3-868 

 3-868 

 3-868 

 3-868 



These constants could be improved by successive trials ; 

 but further work would be wasted. The data for sulphur in 

 Table II. ('7 cm. to 76 cm.), which coalesce pretty well with 

 Regnault's data (27 cm. to 388 cm.), suggest a calculation of 

 constants including both sets of results. I will supply this 

 elsewhere, since it is not essential here. Extrapolation by 

 aid of the sulphur constants, Table VIII., does not reproduce 

 Regnault's high -pressure data. 



15. In order to exhibit the point of view taken, it is 

 necessary to plot the results graphically. This is done in 

 fig. 3, in which the abscissas are pressures in centimetres of 

 mercury, and the ordinates boiling-points in degrees Centi- 

 grade. In the case of mercury I have inserted the vapour- 

 tension curve of Regnault, showing that, conformably with 

 § 6, it is uniformly lower than the present data. Points 

 computed by the constants of Table VIII. are marked. It 

 appears from an inspection of the chart that the agreement 

 between observed and computed results is nearly in keeping 

 with the errors of observation. 



The results for bismuth are particularly interesting. Un- 

 fortunately it was impossible for me to calk the crucible 

 quite tight. Hence the low-pressure boiling-point of bismuth 

 does not overlap the normal boiling-point of zinc, which 

 limits the calibration interval of the thermocouple. The 

 chart shows the interval of extrapolation to be about 270°. 

 This makes the bismuth results less certain; and the normal 

 boiling-point of bismuth deduced by Groshans's principle, 

 1550°, is possibly too high. Carnelley and Williams *, using 



* Camelley and Williams, Journ. Cheni. Soc. London, xxxv. 1879, 

 p. 565. 



