VAPOR-DENSITIES. 



limit 2-073. Since the greater part of the measurements from which 

 this number was calculated were also used in reducing the other 

 observations of the series, the error probably affects the other obser- 

 vations, and in a somewhat increased degree. This will account only 

 for a part of the difference between the observations and the formula. 

 The remaining part of the differences in this series, and the somewhat 

 smaller differences in the next, may be due to the fact that the 

 experiments of both series were conducted with descending temper- 

 atures. Yet the experiments of the third column, which were made 

 by Dumas' method, do not exhibit any preponderance of positive 

 values for the excess of observed density, but rather the opposite. 



TABLE VI. ACETIC ACID. 



EXPERIMENTS OF PLAYFAIR AND WANKLYN. 



On the whole, these experiments furnish no decisive indication of 

 any influence of the hydrogen or air upon the vapor. They may be 

 thought to corroborate slightly the tendency observed in the experi- 

 ments of Naumann and Troost toward lower densities than the 

 formula gives at very low pressures. Yet where the experiments 

 of Naumann show the greatest deficiency in observed density (at 

 78 and 80 mm ), an experiment of Playfair and Wanklyn, at almost 

 precisely the same temperature and pressure, gives a trifling excess 

 of observed density, and at a little lower temperature and pressure, 

 where we should expect from the experiments of Naumann that the 

 deficiency would be still greater, an experiment of Playfair and 

 Wanklyn shows a great excess of density. 



By combining the experiments of Cahours, Naumann and Troost, 

 we may obtain observations of density at 130 for a very wide range 

 of pressures. For one atmosphere, we may regard the formula as 

 coinciding with the average of the numbers given by Cahours. For 

 pressures between three-quarters and one-half of an atmosphere the 

 experiments of Naumann show an excess of density; at pressures 



