VAPOR-DENSITIES. 395 



determinations (previously unpublished) of Wiillner, which somewhat 

 exceed his own. (On the other hand, the observations of Bineau 

 substantially agree with those of Regnault.) 



If we compare the observations of Horstmann with the values given 

 by equation (12), on the basis of Landolt's pressures, we find a very 

 marked disagreement, as may be seen by the following numbers, 

 which relate to the highest temperatures of Horstmann's experiments, 

 where the disagreement is least : 



Temperature - - 63'1 62-9 59'9 51 '1 49'0 487 44 -6 41'4 



Pressure (Land.) - HO'O 109*2 97*0 69*0 63'4 63*0 53'1 46'6 



Density cale. eq. (12) - 3'67 3*67 3'69 375 377 377 379 3-81 



Density obs. - 3'19 3'11 3'12 3'16 2-89 2'98 275 2-62 



It will be observed that while the values obtained from equation (12) 

 increase with diminishing temperatures, the values obtained from 

 Horstmann's experiments diminish. This diminution continues as 

 far as the experiments go, until finally at 12 or 15 the densities 

 are only one half as great as those obtained by Bineau, by direct 

 experiment at the same temperatures and at somewhat less pressures, 

 in a series of observations which bear every mark of a very excep- 

 tional precision. (Compare Tables VII and IV.) The explanation 

 of this disagreement is doubtless to be found in the values of the 

 pressures employed in the calculations, and it will be interesting to 

 see how the results may be modified by the adoption of different 

 pressures. 



In determinations of the pressure of saturated vapors, too great 

 values are so much more easily accounted for than errors in the 

 opposite direction, especially when the pressures are small, that 

 especial interest attaches to the lowest figures which are supported by 

 a competent authority. The experiments of Regnault* were made 

 with three different preparations of acetic acid, of which the second 

 was once, and the third twice, purified by distillation over anhydrous 

 phosphoric acid. Each distillation considerably diminished the pressure 

 of the saturated vapor, the effect of the second distillation being about 

 half that of the first. The numbers obtained with the third prepara- 

 tion are given in the following table with their logarithms, and the 

 differences of the logarithms for one degree of temperature : 



Temperature. Pressure. log. pressure. diff. per 1*. 



971 6-42 -8075 



12-12 7-33 '8651 



14-33 8-42 -9253 



14-87 8-59 '9340 



17-23 9-85 -9934 



19-84 11-455 1-0590 



22-37 13-15 1-1189 



25-28 15-36 1'1864 



* M6m. Acad. Sciences, vol. xxvi, p. 758. The experiments date from 1844. 



