163 
1914 -15.] Vapour Densities of the Ammonium Halides. 
from 7 to 14 observations were made. The precision of the mean values 
varied from it:0’7 per cent, to ±2*8 per cent. The least consistent results 
were obtained at the lowest temperatures, because at these temperatures 
the weight of material vaporised was the smallest. 
Ammonium Chloride. 
Temp. 
V.P. 
Density, 
g. per c.c. 
Per cent. Dissociation = a. 
Observed. 
Interpolated. 
280 
135-0 
0-000135 
55-5 
66-8 
290 
185-3 
0-000169 
67-1 
66-0 
300 
252-5 
0-000230 
64-2 
65-2 
310 
341-3 
0-000307 
63-8 
64-4 
320 
458-1 
0-000406 
63-3 
63-6 
330 
610-6 
0-000531 
63-6 
62-8 
It will be noted that the vapour density increases with rise in 
temperature. This is due, of course, to the rapidly increasing total pressure 
of the saturated vapour. The diagram (fig. 1) shows the observed densities 
(I), in relation to those calculated for zero dissociation (II), and for complete 
dissociation (III), respectively. In consequence of the form of the relation 
