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DR S. M. JOHNSTON ON THE BOILING AND FBEEZING POINTS OF 



boiling point of their solutions. The curves, fig. 10, for which percentage hydration for 

 both freezing and boiling points are plotted against the number of gramme equivalents 

 per litre, indicate that'for lithium chloride and calcium chloride the percentage hydration 

 is greater at the lower temperature for the same concentration. As, however, salts are 

 generally more soluble at high than at low temperatures, it will be seen that the 

 maximum hydration for calcium chloride and lithium chloride from freezing-point 

 observations and boiling-point observations are almost the same. 









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PERCENTME HYDRATION 



Fig. 10. 



In fig. 11, p. 8 S'l, curves have been drawn for which gramme equivalents per litre 

 have been plotted against percentage hydration at the boiling point. These show that 

 for those salts which hydrate least there is a falling off of hydration for the higher 

 concentrations, whilst for those which hydrate most the maximum hydration does not 

 decrease, but reaches a stationary value, or a value approximately so. The above 

 curves also show that the amount of hydration at the same concentration differs very 

 considerably for the various salts, and that the maximum hydration also varies with the 

 salt. For some salts it is very much greater than for others, but has not been obtained 

 greater than 85 per cent. 



For several salts, such as sodium bromide, chloride, and iodide and potassium iodide, 

 the above tables show that the number of molecules of water of hydration per molecule 

 of dissolved substance is almost constant for the salt under consideration, whether we 

 view hydration as molecular and ionic, or only ionic. So that from the point of view 



