240 ./ W. Gihbs — Equilihrimn of Heterogeneous S^ihstanees. 



densities. It will be observed that these differences are quite small, 

 in no case reaching .03, and on the average scarcely exceeding .01. 

 The significance of such correspondence in favor of the hypothesis by 

 means of which equation (336) has been established is of course 

 diminished by the fact that two constants in the equation have been 

 determined from these experiments. If the same equation can be 

 shown to give correctly the relative densities at other pressures than 

 that for Avhich the constants have been determined, such correspon- 

 dence will be much more decisive. 



Messrs. Playfair and Wanklyn have published* four determinations 

 of the relative density of peroxide of nitrogen at various temperatures 

 when"diluted with nitrogen. Since the relations expressed by equa- 

 tions (319) and (320) are not affected by the presence of a third gas 

 which is different from the gases O^ and G2 (to which m.^ and ui^ 

 relate) and neutral to them, (see the remark at the foot of page 233), 

 — provided that we take^j) to denote the pressure which we attribute to 

 the gases (x, and (t2i^- ^-i the total pressure diminished by the pressui-e 

 which the third gas would exert if occupying alone the same space at 

 the same temperature, — it follows that the relations expressed for 



* Transactions of the Royal Society of Edinburg, vol. xxii, p. 441. 



