54 



VAPOR NUCLEI AND IONS. 



where p, p f , p 3 , are observable with certainty. While equation (5) is 

 variously useful in checking the results, it does not admit of the indi- 

 vidual determination of p 2 and p\. For this purpose, however, the 

 equations (1) and the second and third of group (2) are available, with 

 the results (for dry air) 



6 p 2 = p{k-c)/kpc/k 



p'^p'{k-c)/kpc/k 



since p l c / k is given in equation (4). 



Using these equations, the data of table 17 were computed, in con- 

 nection with incidental results tested for the purpose. 



Table 17. Values of adiabatic (/>,) and isothermal (p 2 , p\) pressure for dry air. Pres- 

 sures computed from the initial pressures (/> = 76, p') and the final common isothermal 

 pressure p 3 of the communicating fog and vacuum chambers with other similar 

 data. Volume ratio ^/F =0.064; temperature 20 . 



Checked p' 2 + P2 v/V = p 3 (i + v/V). 



t Observed as soon as possible at the fog chamber. Nearly same later. 



J Observed as soon as possible at the vacuum chamber. v"\ = Pi nearly. 



The data of table 17 are computed for dry air throughout and are 

 given in fig. 27a, graphically.* The results of the table are very impor- 

 tant. In the first place, it will be seen not only that isothermal pressures 

 or nearly isothermal pressures are not observed, but that the effect of the 

 vacuum chamber is preponderating. Thus the pressure at the latter 

 (p r/ i) read off as soon as possible and nominally adiabatic is within 1 mm. 

 of p 3 . Similarly the computed adiabatic pressure (pj) is within a few 



*The curve (p 2 ) is of no interest here and should be disregarded. 



