ON SOLUBILITY. 437 



1c . ftr An examination of the solubility of tlie acids of the oxalic 



series was carried out by Henry, ni who observed an alternating 

 variation in solubility ; acids containing an even number of carbon atoms 

 being far less soluble than those containing an odd number of carbon 

 atoms.* When classified in this manner it was noticed that each group of 

 acids showed a diminishing solubility as the molecular weight increased. 

 An investigation by Raupenstrauch 113 of the solubility of the silver 

 salts of various acids of the acetic series led this author to the conclusion 

 that the solubility in general, as also the increase in solubility with rise 

 of temperature, is always greater for the lower members of a homo- 

 logous series. The salt of an fso-acid was found to be more soluble 

 than the same salt of the normal acid, although no general rule could 

 be framed. 



,qop These results were, in the main, substantiated by a similar 



research with salts of acids of the oxalic series carried out by 

 Miczynski 119 . 



..qq-7 Sedlitzlcy 132 studied the solubility of various salts of acids of 



similar constitution — namely, isovaleric, methylethylacetic, and 

 iso-butyric acids — but was unsuccessful in discerning any connection 

 between solubility and constitution. 



1 qqo Further evidence was published by Carnelley and Thomson 136 



in support of the connection previously discovered by them be- 

 tween solubility and fusibility (regarded as indicative of molecular sym- 

 metry).! They found this relationship existed not only among isomeric 

 acids, but, with few exceptions, could be extended to their salts; the 

 general rule being that salts of the more soluble and more fusible acids 

 are also more soluble than the corresponding salts of the less fusible and 

 less soluble acids. 



1 Q„ n An important paper by Doyer 1G6 contains results of measure- 



ments of solubility coefficients of ammonia and also of the amines. 

 The values for the amines show an apparent lack of agreement ; however, 

 this discordancy is noticed in their other physical constants, notably in 

 the vapour tension measurements : — 



-„„„ Roo'zeboom 198 discussed the solubility curves of salt pairs 



which form double salts and mixed crystals — more especially for 

 ammonium chloride and ferric chloride. 



It had been previously stated by Le Chatelier that of two hydrated 

 forms of a substance, the one containing less water is more soluble in 

 water than the more highly hydrated form. This rule was called into 

 question by Kurnakoff, 19i who cited several exceptions, notably 



* In 1877 Baeycr noticed a similar relationship between the melting-points o{ 

 the acids of this series, those containing even numbers of carbon atoms having 

 higher melting-points than those with an odd number, the melting-point of the 

 former decreasing, of the latter increasing, with increase in molecular weight. 



t Vide Section JV. A. 



