ON SOLUBILITY, 813 
V. A. (1).—Solubility in relation to Temperature. 
From quite early times investigators have given much attention 
to the study of the nature of the change in solubility attending altera- 
tions of temperature. Among the numerous attempts which have 
been made to! find some mathematical equation which would give 
satisfactory expression to this change, the assumption was made by 
Le Chatelier that the latent heat of solution of a substance is equal 
to its latent heat of fusion. This subject was further considered by 
1896 Bancroft,? who was unable to accept Le Chatelier’s assumption 
“~* as it involved the identity of fusion and solubility graphs. He 
pointed out that in the approximation formule for these graphs, which 
are similar, the factor representing heat of fusion enters into the one 
and the factor representing heat of dissolution enters into the other; 
as these factors are not identical, neither can the graphs be identical. 
1897 Bohr *® published work on the absorption of gases in liquids 
‘ at various temperatures and gave the equation a([!—n)=k as 
representing the solubility of hydrogen, oxygen, nitrogen, carbon 
monoxide, carbon dioxide, nitric oxide, and ethylene both in water and 
in the case of several of the gases, in alcohol. In this mathematical 
expression a@=absorption coefficient, 7’=absolute temperature, and n 
and k=constants for each gas. 
The general ‘laws’ of solubility enunciated by Schréder* and 
Le Chatelier + received theoretical support from the thermodynamical 
1898 considerations published by Dahms.** This author also 
* furnished experimental evidence in support of these enunciations, 
inasmuch as satisfactory agreement was found between the theoretical 
and practical results obtained with solutions of ethylene bromide in 
naphthalene, and in certain other cases which he examined. 
1899 Estreicher ** found that the solubility curve of helium in 
: * water exhibits a minimum at 25°, being similar in this respect 
to hydrogen. It was suggested that this peculiarity is connected in 
some way with the difficulty with which these gases are liquefied. 
Franklin and Krauss *? measured the solubility of a large number 
of elements and compounds in liquid ammonia. They found that, 
whereas some substances are apparently insoluble in that solvent at 
its boiling-point, when under pressure at 25° C. they are readily 
soluble. : 
1900 A somewhat remarkable contribution to the study of 
’ solubility phenomena was made by Mylius, Funk,®* and others ,*4 
who measured the solubility of chromates, molybdates, tungstates, and 
selenates of sodium and of calcium, and contrasted the solubility- 
temperature graphs they obtained. The hydrates of calcium chromate °° 
were found to give an extraordinary set of solubility graphs, which 
were traced ** for each of the following salts from 0° to 100° C.— 
CaCrO,,H,O; CaCrO,,3H,O; CaCrO,. In each case the solubility 
was found to decrease as the temperature was raised, and the solubility 
graphs were found not to cut one another but to be nearly parallel— 
results which are not in harmony with current ideas of stable and labile 
hydrates. 
* Vide Part I., R. 202. + Vide Part I., R. 221. 
