o4 
phase occurs, besides Ba Br, . 2H,O and Ba (OH), .8H,0, the oxy- 
bromide: 
B a 
Ba Br, . BaO . 5H,O or Bat ien _9H,0 
This salt has already been described. previously *); the other oxy- 
bromide : 
Ba Br(OH) . 3H,O 
which has also been described *) was not found at 25°. 
The system: Ba I,—BaO—H,0. 
In this system also, the isotherm of 25° has been determined; in 
addition to Bal,.7H,O, Bal, .2H,O and Ba(OH),.8H,0 the oxy- 
iodide : 
ea. 
C 5 ra 3 9 3 5 c 5 
Bal, .BaO . 9H,0 or BaC ,, -411,0 
also described previously, ovcurs as solid phase. *) 
Besides the above systems, various other ones are now being 
investigated; the results of this research will be communicated later. 
Physics. — “Accidental deviations of density in mixtures”. By Dr. 
L. S. Ornstein (Communicated by Prof. H. A. Lorentz). 
The theory of accidental deviations of density in mixtures does 
not differ, as for the principles, from that of the deviations of density 
in systems containing only one kind of molecules. To calculate these 
deviations I shall apply the canonical ensembles of Gises *). 
1.-Let us suppose a mixture of 4 substances to be in a volume 
v, n, being the number of molecules of the kind 1, n, that of the 
kind x, and nz that of the kind #. Besides the coordinates and 
moments of the centres of gravity, a number of internal coordinates 
and moments can be used to characterize the state of the mole- 
cules. Let us imagine a canonical ensemble built up of those systems. 
We shall denote by win. Win Side nee Zij the coordinates of the 
centres of gravity for the molecules of the first kind, those of the 
x-molecules will be represented by aj .. . Zin - 
In order further to characterize the system, we shall introduce 
1) BECKMANN, J. f. prakt. Chem. N. F, 27 132 (1883). 
2) BECKMANN. Ber. 14, 2156. , 
E. TassrLLy, Compt. rend. 120, 1338. 
3) | shall confine myself to a single phase, the coexistence of phases offering 
no particular difficulties. I dealt with this question in my dissertation (comp. p. 114). 
