396 



VAPOR-DENSITIES. 



The uniformity of the numbers in the last column shows the remark- 

 able precision of the determinations. At the same time it is evident 

 that the differences in these numbers are due principally to the errors 

 of observation, so that numbers obtained by interpolation between the 

 logarithms of the observed pressures will be somewhat better (on 

 account of averaging of the errors) than the original determinations. 



The values obtained by such an interpolation have been used for 

 the comparison of Horstmann's experiments with the formula (12) 

 which is given in Table VII. Unfortunately this comparison cannot 

 be extended above 25, which is the limit of Regnault's experiments. 

 The first three columns of the table give the temperatures of Horst- 

 mann's experiments, the pressures corresponding to these temperatures 

 according to the determinations of Landolt, and the density deduced 

 from Horstmann's experiments by the use of these pressures. To 



TABLE VII. ACETIC ACID. 

 Determinations of Vapor-density by Distillation. 



these columns, which are taken from Horstmann's paper, are added 

 the pressure derived from Regnault's observations by the logarithmic 

 interpolation described above, the density calculated by equation (12) 

 from these pressures and the temperatures of the first column, and 

 the densities obtained by combining Horstmann's experiments with 

 Regnault's pressures. This column is derived from the second, third 

 and fourth, as follows. If w and W denote respectively the weights 

 of vapor and of air which pass through the apparatus in the same 

 time, P the height of the barometer, and p^ the pressure of saturated 

 vapor as determined by Landolt, the densities obtained on the basis of 



Landolt's pressures, and given in the third column, are evidently repre- 



w(P p L ) 

 sented by w *^' . The numbers of the fifth column, which are 



. P L wiP D } 



represented in the same way by v w * R ', where p R denotes the 



