ON SOLUBILITY. 435 



-•cr-K The observations of Boisbaudran 59 on the unequal growth of 



crystal facets when a crystal is kept for a long time in a solution 

 slightly supersaturated, have considerable bearing upon the subject of 

 the physical nature of a substance influencing its solubility. Observa- 

 tions of a similar nature were made by Pfaundler, 56 who explained the 

 phenomenon of a crystal changing shape and not weight by a difference 

 in the energy of vibration on the various crystal facets. 

 -1QQ9 Camclley 8S traced the influence exerted on the solubility by 



the atomic arrangement of isomeric carbon compounds (the sub- 

 stance of lower m.p. being considered to be less symmetrical), and came to 

 the conclusion that the isomeride of less symmetrical molecular structure 

 was the more soluble. Examples of compounds of equal molecular 

 symmetry having identical solubility were furnished by the researches 

 ..„„, of Leidie 90 on the solubility of the tartaric acids ; whilst Tilden iai 

 established a similar relationship among inorganic compounds 

 to that found by Oarnelley — namely, that with isomorphous salts the 

 most soluble was also the most fusible. 



A relation between molecular volume and solubility was observed by 

 Nicol, 102 who adduced instances to show that a diminished molecular 

 volume is attended by a diminished solubility. 



With the object of ascertaining whether the state of aggregation of 

 1W a substance in any way affected its solubility, Alexejeff 11S deter- 

 mined the solubility of solid and liquid salicylic acid at one and the 

 same temperature. In the liquid state this acid was found to be more 

 soluble, as also was liquid benzoic acid more soluble than the solid at 

 the same temperature — results quite contrary to the views expressed 

 by Gay-Lussac. He also found the solubility of a hydrate was always 

 greater than that of the anhydrous substance. 



iqq „ Bodies having similar melting-points were stated, by 



Schroder 131 to have very similar molecular solubilities ; and he 

 used this relationship for calculating from published data the molecular 

 solubility of a series of inorganic sulphates, and also of their double salts 

 with ammonium sulphate. 



When studying the conditions of equilibrium between a salt and 

 water, Alexejeff (1886) noted the disturbing effect of the solution separat- 

 ing into two layers of different concentration. This question was 

 loo J. theoretically discussed by Boozeboom, 1 * 1 but his conclusions 

 were unsupported by any experimental evidence. 



Walker 15S applied the thermodynamic equation dp/dt=C/Tv, and 



.^ or . the gas equation pv — lit, to solutions, and deduced a relationship 



' ' between the solubility of a substance in any solvent and its 



brat of fusion; it was supported by experiments with p-toluidine 



dissolved in water. 



Assuming the latent heat of solution of a substance to be equal to 



1ft „. its latent heat of fusion, Lc Chatelier 221 showed the following 



' relationship may be developed from established law of solution : — 



0-002 log S - L + - = 



in which S = mol. cone, of diss, sub., L — latent heat of fusion, 

 t 9 = the m.p. of diss, sub., /. = the solidifying pt. of the solution. 



