V.A. ii. ON SOLUBILITY. 817 
results obtained were compared with those previously recorded by 
Béttger and Kohlrausch. In the case of calcium sulphate the solubility 
of the three forms, gypsum, anhydrite, and soluble anhydrite, was 
ascertained. 
Von Antropoff *** studied the relationship between solubility and tem- 
perature in the cases of the inert gases, xenon, krypton, argon, neon, and 
helium. Centnerszwer *7* carried out similar work with potassium iodide 
and other salts when dissolved in methylic alcohol at temperatures 
up to the critical temperature of the solvent. The main conclusion 
of this latter work was the detection of a point of maximum solubility 
at 196° C., from which temperature the solubility decreased to the 
critical temperature, 266° C. 
Tyrer °° investigated the solubility of sodium iodide in ethylic and 
methylic alcohols from ordinary room temperature up to about 300° C, 
The solubility-temperature graph was found to rise at first, then to 
fall as the critical temperature is approached, and above that point 
the solubility is dependent upon the concentration of the solvent and 
decreases with rising temperature. 
1911 Interesting observations on the solubility of gaseous hydrogen 
" in the metals, iron, copper, and nickel, were made by Sieverts.4°? 
He determined the solubility of this gas in these metals at temperatures 
from 400° to 1,600° C., and found a gradual increase in the amount 
of, hydrogen dissolved as the temperature was raised, and a sudden 
increased solubility when the metals melted. 
Nasini and Ageno *?! determined the solubility of orthoboric acid 
at various temperatures, and could not detect a break in the continuity 
of the graph at 107-108°, the temperature at which that substance 
changes to metaboric acid. 
Brichaux **? carried out an investigation of the laws relating to 
vapour pressure and temperature of solutions saturated with ammonia. 
He concluded that the ammonia content of a solution is determined by 
the ‘ differential temperature —i.¢., the difference between the tempera- 
ture of an ammoniacal solution and the temperature at which water 
boils at the same pressure. The figures which he gave indicated that 
this relationship holds with considerable accuracy. 
V.A. (11).—Solubility in relation to Heat of Dissolution. 
When a substance undergoes a change of state, whether it be 
evaporation, liquefaction, crystallisation, dissolution, or some other 
manifestation of change in the state of aggregation, there is always a 
concomitant change in the energy content of the substances. In so 
far as the study of solubility is concerned, very little regard has been 
taken of the energy changes which occur, and scarcely any attempt 
has been made to correlate energy content with powers to dissolve. 
It was recorded in Part I. of this Report that van’t Hoff (1) and 
van Laar (2) deduced mathematical equations showing the relationship 
which exists between heat of dissolution, dissociation constant, and 
solubility of binary electrolytes. 
(1) d log c/dt = Q/2(1+a)T? 
(2) d log c/dt = Q(2-—a)/47?. 
1912. 34a 
