VAPOK-DENSITIES. 379 



respectively. The two other constants were determined by the 

 experiments of Deville and Troost. 



The results of these and other experiments at atmospheric pressure, 

 all made by Dumas' method, are exhibited in Table I. The first three 

 columns give the temperature (centigrade), the pressure (in millimeters 

 of mercury),* and the density calculated from the temperature and 

 pressure by equation (10). The subsequent columns give the densities 

 observed by different authorities, and the excess of the observed over 

 the calculated densities. In the first column of observed densities, 

 we have one observation by Mitscherlich t (at 100*25) and five by 

 R. Mliller. J The three remaining columns contain each the results of 

 a series of experiments by Deville and Troost. In each series the 

 experiments were made with increasing temperatures, and with the 

 same vessel, without refilling. It should be observed that the results 

 of the three series are not regarded by their distinguished authors as 

 of equal weight. It is expressly stated that the numbers in the two 

 earlier series, and especially in the first, may be less exact. The last 

 series agrees very closely with the formula. It was from this that 

 the constants of the formula were determined. The experiments of 

 series I and II, and those of Mitscherlich and Muller, give somewhat 

 larger values, with a single exception, as is best seen in the columns 

 which give the excess of the observed density. The differences be- 

 tween the different columns are far too regular to be attributed to 

 the accidental errors of the individual observations, except in the 

 case of the experiment at 151 '8, where some accident has evidently 

 occurred either in the experiment itself or in the reduction of the 

 result. Setting this observation aside, we must look for some constant 

 cause for the other discrepancies between the different series. 



We can hardly attribute these discrepancies to difference in the 

 material employed, or to air or other foreign substance imperfectly 

 expelled from the flask. For impurities which increase the density 

 would make the divergence between the different series greatest 

 when the densities are the least, whereas the divergences seem to 

 vanish as the density approaches the limiting value. (A similar 



* TOO" 1111 has been assumed as the pressure of the atmosphere in all cases in which the 

 precise pressure is not recorded in the published account of the experiments. The 

 figures inserted in the columns of pressures are in such cases enclosed in parentheses. 

 The same course has been followed in the subsequent tables. With respect to the 

 principal series of observations by Deville and Troost (series III), it is stated that the 

 barometer varied between 747 and 764 millimeters. A difference of 13 millimeters in 

 the pressure would in no case cause a difference of '005 in the calculated densities. In 

 this series, therefore, the errors due to this circumstance are not very serious. 



\Pogg. Ann., vol. xxix (1833), p. 220. 



| Lieb. Ann., vol. cxxii (1862), p. 15. 



Comptes Rendus, vol. Ixiv (1867), p. 237. 



