ON THE EXPANSION OF SALINE SOLUTIONS. 55 



No. 67 was sliglitly greater than that of No. 68, so that the solution in 

 No. 67 exposed a larger invaporating surface. This second cause of 

 variation is not so great as the first. 



An interesting comparison could be made between the results of 

 invaporation experiments and the vapour tensions of the corresponding 

 saline solutions ; but it will be necessary to await the completion of a 

 suflBcient number of experiments to permit the plotting of curves, in 

 order that the comparison may be advantageously made. 



Report of the Committee, consisting of Professor Tilden, Professor 

 KAMS.iT, and Dr. W. W. J. Nicol (Secretary), appointed for the 

 purpose, of Investigating the Nature of Solution. 



Supersaturation of Salt Solutions.^ — The various physicalconstants of 

 supersaturated and non-saturated solutions were examined in two ways. 

 (1) Starting with a non-saturated solution of a salt at a high tempera- 

 ture it was allowed to cool and thus to become more and more concen- 

 trated till it reached its saturation point, while on further fall of tempera- 

 ture it became supersaturated; (2) solutions of the salt were prepared 

 of definite strengths, extending equal distances on either side of the 

 saturation point, and their physical properties were examined at a definite 

 temperature (20° C). The salts examined were the following: — 



Sodium sulphate, sodium phosphate, sodium thiosulphate, sodium 

 carbonate, zinc sulphate, magnesium sulphate. 



The physical constants examined were — 



Rate of expansion, specific viscosity, molecular volume, and electrical 

 conductivity. 



In no case did the curves representing the change in the value of the 

 physical constants with temperature or concentration exhibit the slightest 

 change in direction above or below the saturation point. 



These experiments show that there is no marked change in the physi- 

 cal properties of a solution when it becomes supersaturated either through 

 fall of temperature or by the addition of salt. No n- saturated, saturated, 

 and supersaturated solutions have therefore the same constitution ; they 

 differ only in degree, not in kind. 



Specific Viscosity of Salt Solutions.— The experiments in this direction 

 are incomplete, but new forms of apparatus have been devised which have 

 yielded highly satisfactory results. 



Preliminary experiments have been made with NaCl, KCl, NaNOs, 

 and KNO3 in diff'erent strengths of solution, the general result being to 

 cast doubts on some of the results obtained by Hannay as to the propor- 

 tionality of the retardation of flow and the amount of salt present. 



The forms of the curves for the sodium salts are essentially the same, 

 but differ completely from those for the corresponding potassium salts, 

 the latter having a minimum time of flow at a strength of 2 to 3 molecules 

 of salt per 100 water molecules and approximately the same rate as pure 

 water when tc=5 for KNO3 and KCl. 



A large number of further experiments will be required before the 



I 



Journ. Chcm. Soc 1887, p. 389. 



