402 VAPOR-DENSITIES. 



greater. The deviation from the calculated values is therefore in 

 the same direction and about such in quantity as we should expect.* 



M. Wurtz has remarked that the average value of S (the density 

 of the possible perchloride) is nearly identical with the theoretical 

 density of the perchloride, and appears inclined to attribute the 

 variations from this value to the errors of experiment. Yet it appears 

 very distinctly in Table IX, in which the experiments are arranged 

 according to the value of TT (the pressure due to the possible per- 

 chloride), that S increases as TT diminishes. The experiments of 

 MM. Troost and Hautefeuille show that the coincidence remarked by 

 M. Wurtz is due to the fact that on the average in these experiments 

 the deficiency of the density of the possible perchloride (compared 

 with the theoretical value) is counterbalanced by the excess of density 

 of the protochloride. When TT > 400, the effect of the deficiency in 

 the density of the possible perchloride distinctly preponderates ; when 

 TT < 250, the effect of the excess of density in the protochloride 

 distinctly preponderates. But the magnitude of the differences con- 

 cerned is not such as to invalidate the general conclusion established 

 by the experiments of M. Wurtz, that the dissociation of the per- 

 chloride may be prevented (at least approximately) by mixing it with 

 a large quantity of the protochloride. 



Table for facilitating calculation. The numerical solution of equa- 

 tions (10), (11), (12) and (13) for given values of t and p may be 

 facilitated by the use of a table. If we set 



(17) 



lOOOD^D-D,) , lOOO(A-l) 



L - lo " = lQ S (2 -Ay ' 



we have for peroxide of nitrogen, 



L=|^J|+logp- 9-451; (19) 



for formic acid, 



L=^3+logp-9-641; (20) 



for acetic acid, 



OKOA 



(21) 



* The deviation of the protochloride of phosphorus from the laws of ideal gases shows 

 the impossibility of any very close agreement between such equations as have been 

 deduced in this paper and the results of experiment in the case of gas-mixtures in which 

 this substance is one of the components. With respect to the question whether future 

 experiments on the vapor of the perchloride (alone, or with an excess of chlorine or of 

 the protochloride) will reduce the disagreement between the calculated and observed 

 values to such magnitudes as occur in the case of the protochloride alone, it would be 

 rash to attempt to anticipate the result of experiment. 



