On the Elastic Force of the Vapor of Mercury. 289 



to the longer leg ; this bulk is equal to the sum of the original bulk 

 of the air, expressed in parts of the scale, and of the observed differ- 

 ence of level of the mercury, corrected for expansion. Further, 

 let I be the bulk, in parts of the same scale, which the air, alone, 

 would occupy, at the temperature and pressure of the experiment, 

 according to the laws of Gay-Lussac and Mariotte. The difference, 

 h — l, between these two columns, will be the bulk of vapor, ex- 

 pressed in parts of the same scale, at the temperature and pressure 

 of the experiment. Let P represent the combined tensions of the 

 air and mercurial vapor, at the temperature of observation, and T 

 the tension of the mercurial vapor alone, then 



L : L-Z::P : T, whence 



The quantities in the second member of this equation are all given 

 by the observations, or by calculation. This formula supposes that 



Ma 



as well as 



to air. This may not be true for temperatures and pressures near 

 to the point at which the vapor is converted into a liquid ; but we 

 have no means of correcting the small errors which may be thus 

 produced. 



From the data furnished by my experiments, and by the method 

 just stated, I determined the following numbers for the tensions of 

 the vapor of mercury, for every eighteen degrees from 446° F. to 



554° F.* 



inchesf 



Temperatures, 446°, 464°, 482°, 500°, 518°, 536°, 554°F. 

 Corresponding > 2 Q Ql 2 J7 5 263 fi 5Q8 g m 9#946 + 



tensions, 5 



♦ The observation at 572° F.,§ the highest temperature to which 

 the bath was carried, gave 12.1S7|| inches for the tension; but this 

 result having been obtained only from one observation, made while 

 the temperature was rising, is not altogether comparable with the 

 others which result from two observations, one in each series. 



* 230° and 290° C. t Millimetres. 



t Temperatures, 230°, 240°, 250°, 260°, 270°, 280°, 2&0° C. Pressure*, 58 03. 

 80.02, 105.88, 133.62, 165.22, 207.59, 252.51 millimetres. The numbers for the 

 pressures have been reduced in the translation, at the rate of 39.39 inches to tho 

 metre.— Trans. 



§ 300° (\ [| 309.40 millimetres. 



