CONCENTRATED AQUEOUS SOLUTIONS, AND HYDRATION OF THE SOLUTE. 883 



crystallization, the hydration per molecule may be reduced considerably below the 

 number of molecules of water of crystallization ; but for salts like lithium chloride and 

 bromide, which crystallize with only two molecules of water of crystallization, the 

 minimum water of hydration per molecule is approximately equal to the water of 

 crystallization. For the salts of ammonia series of experiments are given for 

 concentrated solutions ; those for the more dilute solutions have already been given.* 

 For these salts generally there is decrease of hydration for the most concentrated 

 solutions, but this is most noticeable with the nitrate, sulphate and chloride, and less so 

 for the iodide and bromide. 



Resume. 



(1) A minimum point has been found in most of the curves for which gramme 

 equivalents per litre have been plotted against elevation per gramme equivalent. 



(2) An increase in elevation per gramme equivalent has usually been found with 

 increase of concentration for higher concentrations than that corresponding to the 

 minimum point, but the rate of increase with concentration falls off for the higher 

 concentrations. It has been found that for ammonium chloride the elevation per 

 gramme equivalent falls off for the higher concentrations after a certain concentration 

 is reached. 



(3) The rate of increase of elevation of the boiling point falls off quickly for the 

 higher concentrations for calcium chloride and lithium bromide, and for several other 

 salts for which observations of elevation of the boiling point have been made, when 

 increase of elevation is compared with the number of grammes of salt added to the 

 solution. 



(4) For some salts a much larger maximum percentage hydration has been found 

 than for others. The more deliquescent salts gave the higher percentage hydrations. 



(5) The maximum percentage hydration for the same salt does not materially differ, 

 whether it be determined at the boiling or freezing point of the solution. 



(6) For the higher temperature the maximum value is obtained at a higher con- 

 centration. At the same concentration there is usually a greater percentage hydration 

 at the lower than at the higher temperature. 



(7) The number of molecules of water of hydration per molecule of salt for a highly 

 concentrated solution may be less than the number of molecules of water of crystalliza- 

 tion. If the salt considered takes up as many as six molecules of crystallization water, 

 it has been found to be much less. 



(8) On the assumption of both ionic and molecular hydration for several salts, the 

 hydration values obtained indicate by their constancy up to varying concentrations the 

 correctness of the assumption. 



(9) For other salts the indication as to ionic or molecular and ionic hydration is not 



* Trans. Roy. Soc. Edin., xlv., 233, 1906. 

 TRANS. ROY. SOC. EDIN., VOL. XLV. PART IV. (NO. 32). 128 



