388 VAPOR-DENSITIES. 



between the observed and calculated densities is '05, and the average 

 difference '016; nine experiments at pressures ranging from 29 mm 

 to 7 min , in which the maximum difference is "07 and the average '035 ; 

 and three experiments at pressures of about 3 mm , in which the average 

 difference is '17. The extraordinary precision of the determinations 

 at low pressures is doubtless due to the large scale on which the 

 experiments were conducted. All the experiments at temperatures 

 below 99 were made with a globe of the capacity of 5| liters with 

 a stem of suitable length to hold the barometric column. 



The agreement is certainly as good as could be desired, and shows 

 the accuracy of which the method of observation is capable. But 

 in no part of the thermometric scale do we find so great a range 

 of pressures as might be desired, without using pressures too low 

 for accurate results, or observations which are to be rejected for 

 other reasons. 



Acetic acid. For this substance the densities have been calculated 

 by the formula 



2-073(D- 2-073) 3520 

 (4-146-Dy " 



the constants 3520 and 11 '349 being derived from the determinations 

 of Cahours and Bineau, which with those of Horstmann and Troost 

 are given in Table IV. The experiments of Cahours and Horstmann 

 were made under atmospheric pressure, those of Horstmann* by the 

 method of Bunsen, those of Cahours presumably by the method of 

 Dumas. The numbers in the first column of the densities observed 

 by Cahours are taken from the twentieth volume (1845) of the 

 Comptes Rendus, except a few cases, distinguished by parentheses, 

 which are taken from the preceding volume (1844). The numbers 

 in the second column are taken from his Lecons de chimie generate 

 Jlementaire, 1856. These numbers seem to be based in part upon 

 new experiments and in part upon a revision of the observations 

 recorded in the Comptes Rendus, the calculations being carried out 

 to another figure of decimals. They are therefore entitled to a 

 greater weight than the numbers of the preceding column. 



The agreement of the formula with the numbers given in the 

 Lemons de chimie is very good, the greatest divergences being *080 

 at 190 and '062 at 180. But at 190 the table in the Comptes 

 Rendus agrees precisely with the formula, and at 171 (the next 

 experiment) it shows a divergence in the opposite direction. The 

 next divergences in the order of magnitude are '033, '036, '032 



* Lieb. Ann., suppl. vi, p. 65. 



