454 



Drs. Ramsay and Young on 



its particular value for each of these conditions ; and it is 

 evident that the relations between the temperatures and 

 pressures corresponding to the inferior or reversed apices, as 

 well as those corresponding to the superior apices, would each 

 form a special curve. 



The following Table gives the final results of the calculation 

 of vapour-pressures by the method of areas ; and, for the 

 sake of comparison, the actually found vapour-pressures are 

 appended. The pressures at the superior and inferior apices 

 of the isothermal curves, and also the enclosed areas, are 

 given* . 



Table VIII. 



Tempe- 

 rature. 



Vapour- 

 pressures, 



deduced 

 from areas. 



Vapour- 

 pressures, 

 mean of 

 observed. 



Pressure, 



superior 



apex. 



Pressure, 



inferior 



apex. 



Area 



abore or below 



vapour-pressure 



line. 



192 

 190 



185 



175 



160 

 150 



millim. 

 26350 



25554 

 23703 [ 



20259 [ 



15900 

 13405 



millim. 

 26331 



25513 



Old, 236231 

 New, 23763 j 



Old, 20189 \ 

 New, 20271 J 



15778 



13262 



millim. 

 26490 



25870 

 24510 



22100 



19090 

 17380 



millim. 

 26125 



24960 

 21660 



14060 



- 20 



-10400 



sq. in. 

 00425 



0-1245 

 0-4550 



1-6520 



4-710 

 7551 



The three pressure-curves — which we shall name the " ordi- 

 nary " vapour-pressure curve, the " superior" vapour-pressure 

 curve, formed by the superior apices of the isothermal lines, 

 and the "inferior" vapour-pressure curve, produced by 

 the lower apices of the isothermal lines — must, it is evident, 

 meet at the critical point ; and on mapping them, it was 

 found that this was the case. Points were chosen on these 

 curves at equal intervals of temperature, and the constants 

 for formulae of the type logp = a + ba* were calculated for 

 each. As the pressures on the inferior curve below a certain 

 temperature were negative, it was found convenient to add 

 30,000 millim. to each, which was subsequently subtracted 

 from the result. The constants for the curves are — 



* The areas are in square inches ; the scale was 2000 millim. and 

 2 cub. centim. per gram to the inch. It would be easy, if necessary, to 

 convert these data into actual work. 



