ON SOLUBILITY. 443 



Hoff , and showed that they are valid for sparingly soluble Substances ; 

 also that Boozeboom's I4 ° equation holds for the more soluble salts. 



From his own experiments on the absorption of various gases in 

 water, Winkler 19 ° found the percentage decrease in the absorption 

 coefficient between (P and 20° was approximately proportional to the 

 cube root of the molecular weight of the gas.* 



Bise of temperature was found by Delepinc 191 to cause a decrease in 

 the absorption coefficient of ammonia in methylic and in ethylic alcobols. 



£iard 18e found that the solubility temperature graphs for mercuric 

 chloride in water, methylic alcohol, ethylic alcohol, and propylic alcohol 

 all tend to meet at 2G5°, the melting-point of mercuric chloride. 



Making use of the method of least squares, Henrich 193 recalculated 

 from Bunsen's data the temperature equations for the absorption co- 

 efficients of gases. 



Roozeboom 198 discussed the solubility temperature curves of salt 

 pairs which form double salts and mixed crystals, more especially for 

 ammonium and ferric chlorides. The isothermal obtained in this caso 

 is in accord with the requirements of Gibb's phase rule, and renders 

 possible a general survey of the form of the solubility isothermals. 



This communication was followed by an account of a careful study 

 of the solubility of ferric chloride in water over a wide range of tempera- 

 ture. The graph representing his results shows four temperature 

 maxima, which correspond to the hydrates X,4H.,0 ; X,5H 2 ; X,7H 2 ; 

 and X,12H 2 0. 



Etard 20U determined the solubility of naphthalene triphenylmethane, 

 diphenylamine, and phthalic anhydride in carbon bisulphide, hexane, 

 and chloroform over the range of temperature from —60° to +90°. 

 He found the inferior limit of solubility of a substance was the melting- 

 point of the solvent. 



Besults of a somewhat similar nature to the above were obtained by 

 Schroder.- 02 This worker made use of p-dibrombenzene dis- 

 ' solved in carbon bisulphide, benzene, monobrombenzene and in 

 ether : naphthalene dissolved in henzene, chlorobenzene, and in carbon - 

 tetrachloride : and also m-dinitrobenzene dissolved in benzene, bromben- 

 zene, and in chloroform. He concluded that the solubility of Various 

 solids in different liquids is the same at temperatures equally removed 

 from the melting-point of the solid solute. 



The solubility temperature curve of a substance is once again held 

 by E~tard 20S to represent the locus of the melting-point of mixtures of the 

 dissolved substance and the solvent. True solubilities are said to be ex- 

 pressed as the amount of solute contained in 100 parts of saturated 

 solution, and not the amount which is dissolved in 100 parts of solvent. 

 In the case of ether and water a curious temperature influence 

 lb94. Wag observed by Schunche 218 .: the solubility of ether in water 

 being found to be largely influenced by change of temperature, whereas 

 in the case of water dissolving in ether the temperature influence was 

 practically nil. 



He also found the absorption of gaseous hydrogen chloride by ether 



* This was adversely criticised by Thorp and Rodger,- 1 ® 



