384 



VAPOR-DENSITIES. 



mercury diminished the volume of the vapor, and thus increased 

 the numbers obtained for the density. 



TABLE II. PEROXIDE OF NITROGEN. 



Experiments at less than Atmospheric Pressure. 



PLAYFAIB AND WANKLYN, TROOST, NAUMANN. 



The same table includes two experiments of Troost,* by Dumas* 

 method, but at the very low pressures of 35 mm and 16 mm . In such 

 experiments we cannot expect a close agreement with the formula, 

 for the same error in the determination of the weight of the vapor, 

 which would make a difference of '01 in the density in experiments 

 at atmospheric pressure, would make a difference of '21 or '47 in the 

 circumstances of these experiments. In fact, the numbers obtained 

 differ considerably from those demanded by the formula. 



There remain four experiments by Play fair and Wanklynt in 

 which Dumas' method was varied by diluting the vapor with 

 nitrogen. The numbers in the column of pressures represent the 

 total pressure diminished by the pressure which the nitrogen alone 

 would have exerted. They are not quite accurate, since the data 

 given in the memoir cited only enable us to determine the ratios 



* Compte* Rtndus, t. Ixxxvi (1878), p. 1395. 



t Trant. Roy. Soc. Edinb., vol. xxii (1861), p. 463. 



