130 ON SUPERSATURATED SOLUTIONS. 



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BY G. GRENFELL, M.A., F.G.S. 



Read February 1st, 1877. 



IN all our textbooks it is stated that exposure of a supersaturated 

 solution to air, or contact with ordinary surfaces, will cause 

 the solution to crystallize. In explanation of this assumed fact 

 several theories have been advanced. 



First;, there is the theory of M. M. Violette and Gernez, that 

 the crystallisation is caused by the air introducint^- a crystal of the 

 same salt in the same state of hydration. 



Secondly, Professor Tomlinson, F.R.S., holds that the crystalli- 

 sation is caused by adhesion of the salt to a greasy surface. 



Thirdly, Mr. Jeannel declared that simple contact with a solid 

 substance causes crystallisation. 



Fourthly, M. Loewel attributed it to catalysis, which may mean 

 anything or nothing, and is in fact only another way of stating that 

 we know nothing about it. 



Lastly, it has been suggested, though not established by any 

 conclusive experiment, that absorption might be the cause of the 

 crystallisation. 



