1878.] 



the Function of the sides of the Vessel, Sfc, 



195 



in long clustered cylinders, but being left undisturbed for a day or so, 

 the remaining supersaturated liquor in both cases became solid, the 

 normal salt being formed. Sodic acetate solution (6 to li) poured 

 boiling into these large shallow vessels and covered over did not 

 change during twenty-four hours. On being taken into the open air 

 and uncovered, the solutions remained some time in the liquid state, 

 but on touching the bottom of the vessel with the finger, they imme- 

 diately became solid. 



The alum solution, before referred to, deposited the normal salt in 

 large crystals, while the solution was still warm. It could not relieve 

 itself in any other way, because by its constitution it cannot form a 

 salt of a lower degree of hydration than the normal, that is, with 

 12 aq., and the throwing down of that in considerable masses, so as to 

 get rid of the state of supersaturation altogether, forcibly illustrates 

 the dependence of that state on the adhesion of the solution to the 

 sides of the vessel. 



The weather was mild while these experiments were in progress. 

 At lower temperatures the solutions would doubtless have been even 

 more sensitive. 



The result of these experiments satisfies me that the state of super- 

 saturation is dependent on the adhesion of the solution to the sides of 

 the vessel, coupled with the tension of the surface. This tension may 

 be lowered, so as to throw more work upon the other force, which it 

 may be able to bear ; but anything that effectually detaches a portion 

 of the solution from contact with the sides of the vessel, produces the 

 sudden crystallisation of the solution. 



If this view be correct, many of the phenomena of supersaturation 

 are accounted for, and the whole subject is far advanced towards that 

 obedience to law, which can alone invest it with dignity. 



