ON SOLUBILITY. 451 



1 o 7 q I n an extensive and general study of salt mixtures Riidorff 52 



examined the solubility of mixtures of salts, and found that not 



only isomorphous salts, as Hauer supposed, but also those which 



form double compounds, expel one another from solution. 



The salt mixtures employed were classified as 



(i) Where no chemical action could occur — -i.e., salts having like 



acids or bases, 

 (ii) Where chemical action may take place — i.e., salts of different 

 acids and bases. 

 ■,077 Droezer 68 found the solubility of gypsum was considerably 

 influenced by the presence in solution of certain salts, while in 

 1878. the next year Eder 71 published results showing that alkaline 

 sulphates do not affect the solubility of silver sulphate in water. 



The influence of a salt on the solubility of another salt of similar 

 character — namely, sodium chloride and potassium chloride — formed the 

 1070 subject of an inquiry by Schonach. 77 He found, when water was 

 saturated with both of these salts, the solubility of each became 

 diminished, that of potassium chloride more than sodium chloride; the 

 solubility of the mixture not corresponding with the sum of the 

 solubilities of the two salts. This difference increases with rise of 

 temperature,* the less soluble salt being removed by the more soluble 

 salt in accordance with the law of Hauer. 



A knowledge of change in the solubility of so-called sparingly 

 soluble substances owing to the presence of other substances in solution 

 QQ1 became of great importance for gravimetric analysis. This appears 

 ' to have prompted Ruyssen and Varenne 84 to investigate the case 

 of several very sparingly soluble compounds. They found, for example, 

 the solubility of silver chloride increases with the concentration of 

 silver nitrate, and also with the concentration of hydrogen chloride, 

 but no well-marked regularities were observed. Precht and Wittjen 8S 

 determined the solubility of mixtures of salts of the alkali and alkaline 

 earth metals. The more striking of the results recorded being that 

 when a mixture of potassium sulphate and potassium chloride is treated 

 with water the solubility of the potassium chloride remains practically 

 the same as in pure water; and the solubility of barium chloride when 

 in the presence of sodium chloride does not change with change of 

 temperature. 



A discussion of the solubility of metallic chlorides was published by 

 Ditte, 86 who classified these salts according as their solubility was 

 (i) increased, or (ii) decreased in the presence of hydrogen chloride. 

 Those which showed an increased solubility he subdivided into the 

 groups (i a) those soluble in water, and (i b) those insoluble ; while the 

 salts which became less soluble were classed as (ii a) separating in a less 

 hydrated state, and (ii b) in an anhydrous state. 



Nicol 102 recounts some experiments regarding the saturation 



1fi -. of a liquid by two salts dissolved simultaneously, which appear 



'to indicate that each salt dissolves independently of the other, 



and each salt increases the solubility of the other. This increased 



solubility is not considered as being brought about by any tendency to 



* Vide footnote, Section V. A (i) 1879. 



