./ W. Gihhs — EqxIJlhrhoii. of Heterogeneous Suhstancex. 241 



peroxide of nitrogen by (333), (334), and (336) will not be aliected 

 by the presence of free nitrogen, if the pressure expressed bv ^> or 

 jt),„ and contained implicitly in the symbol IJ (see equation (320) l)y 

 which D is defined) is understood to denote the total pressure dimin- 

 ished by the pressure due to the free nitrogen. The determinations 

 of Playfiiir and Wanklyn are given in the latter part of the 

 above table. The pressures given are those obtained by subtracting 

 the pressure due to the free nitrogen from the total pi-essure. We 

 may suppose such reduced pressures to have been used in the reduction 

 of the observations by which the numbers in the column of observed 

 relative densities were obtained. Besides the relative densities 

 calculated by equation (336) for the temperatures and (reduced) 

 pressures of the observations, the table contains the relative densities 

 calculated for the same tem])eratures and the pressure of one atmos- 

 phere. 



The reader will observe that in the second and third experiments 

 of Playfair and Wanklyn there is a very close accordance between 

 the calculated and observed values of D, while in the second 

 and fourth experiments there is a considerable diiference. Now the 

 weight to be attributed to the several determinations is very diifer- 

 ent. The quantities of peroxide of nitrogen which were used in the 

 several experiments were respectively .2410, .5893, .3166, and .2016 

 grammes. For a rough approximation, Ave may assume that the 

 probable errors of the relative densities are inversely proportional to 

 these numbers. This would make the probable error of the first and 

 fourth observations two or three times as great as that of the second 

 and considerably greater than that of the third. We must also 

 observe that in the first of these experiments, the observed relative 

 density 1.783 is greater than 1.687, the relative density calculated by 

 equation (336) for the temperature of the experiment and the pres- 

 sure of one atmosphere. Now the number 1.687 we may regard as 

 established directly by the experiments of Deville and Troost. 

 For in seven successive experiments in this part of the series the 

 calculated relative densities difter from the observed by less than .01. 

 If then we accept the numbers given by experiment, the efiect of 

 diluting the gas with nitrogen is to increase its relative density. As 

 this result is entirely at variance with the facts observed in the case 

 of other gases, and in the case of this gas at lower temperatures, 

 as appears from the three other determinations of Playfair and 

 Wanklyn, it cannot possibly be admitted on the strength of a single 

 Trans. Conn. Acad., Vol. III. 31 Mat, 187r,. 



