and Attached Water. Ill 



Infinite Solubility. 



§ 249. An examination of curves of solubility of salts in 

 water, drawn so that the ordinates are temperatures and the 

 abscissae are percentages, reveals two types of curves, which 

 differ only essentially in their right-hand or salt- saturated 

 branches. Iodide and bromide and, perhaps, chloride of 

 sodium may be taken as the type of a, fig. 3, and nitre of b f 

 fig. 3 (see § 126). The curvature of the right-hand branches 

 of both curves must diminish as we travel from the cryohy- 

 drate in the direction of the arrows, otherwise there would be 

 two temperatures at which there is the same solubility (a, fig. 

 3, dotted lines) for every solubility between certain limits ; 

 or (b, fig. 3, dotted lines) there would be two solubilities for 

 every temperature between certain limits. If we concede the 



Fig. 3. 



impossibility of these conditions, there appear to be three alter- 

 natives — the curve loses curvature either parabolically or 

 hyperbolically, or there must be contrariflexure. The first 

 would carry the conditions into the region of critical state and 

 decomposition. The second might mean, in the case of a 

 type, if such asymptote be also parallel to the ordinates, that 

 a certain per cent, ratio of salt is soluble in water at a certain 

 temperature, and at all higher temperatures; in the case of b 

 type, if such asymptote be parallel to the abscissae, that at 

 a certain temperature a finite mass of water will dissolve an 

 infinite mass of salt. 



