174 Proceedings of Royal Society of Edinburgh. 
[sess. 
the case of the isothermal studied in greatest detail by Troost and 
Hautefeuille, viz., the isothermal of 100° G., the change of curva- 
ture took place at the point where half an atom of hydrogen was 
associated with the palladium. At other temperatures the change 
takes place at the following concentrations : — 
rp Concentration 
1 em P- (atom of H 2 to one of Pd). 
10 °, 
50°, 
100 °, 
120 °, 
150°, 
180°, 
0-60 
0-58 
0-54 
0-50 
0-44 
0-37 
If Pd 2 H were actually formed, the change of curvature ought to 
take place always at the concentration 0‘5 of an atom of H 2 , and 
/ 
under no circumstances at a lower concentration. It would he 
extremely interesting to follow the course of the isothermal at a 
very low temperature, say at the temperature of hoiliug liquid air. 
