344 Messrs. C. Tomlinson and G. Van der Mensbrugghe [May 16, 



The points to which this experimental inquiry tended are included in 

 the four following propositions : — 



I. That a supersaturated saline solution contained in a catharized flask 

 will remain liquid so long as its free surface, or the surface in contact with 

 the sides of the flask, does not undergo in one or many points a notable 

 diminution of surface-tension. 



II. That if we deposit on the surface of a supersaturated saline solution a 

 drop of a liquid of feeble tension, it spreads, and crystallization takes place 

 immediately or after a short time. 



III. That while a liquid of feeble tension produces crystallization after 

 a time more or less short, a liquid of considerable contractile force (such 

 as pure water) not acting chemically on the solution, may be brought into 

 contact with it without producing change of state. 



IV. That as a liquid of feeble tension produces crystallization, so a solid 

 covered more or less with a film of such liquid produces change of state, 

 either at once or after a short time. 



But before any conclusions could be drawn from the results of experi- 

 ments as to the relation between the surface-tension of liquids and the 

 state of supersaturation in saline solutions, it was necessary to measure 

 the surface-tension of the solutions of Glauber's salt operated on. Ac- 

 cordingly the following data were determined, first, for a solution con- 

 taining 1 part of salt to 1 of water, and, secondly, for a solution containing 

 2 parts of salt to 1 of water. The diameter of the capillary tube was 

 1-598 millim.* 



Specific gravity of the solution 1 salt to 1 water at 17° C. = 1-198. 



The capillary height 1 1 millims. 



The specific gravity of the other solution = 1*289. 



The capillary height 8*7 millims. 



These data give, according to the formula i— r 'h'd ^ n w j 1 - c j 1 ^ - g ^ 



A 



tension, h the height, d the density, and r the radius of the tube), for the 

 superficial tensions of the solutions in question, not a greater value than 

 from 4 to 5 *2. 



If the states of supersaturation of saline solutions depend on the main- 

 tenance of surface-tension, according to the first proposition, any force or 

 substance that produces a notable diminution of such tension will cause the 

 state of supersaturation to cease. 



Such a force is heat, while such substances as camphor, benzoic acid, 

 &c. have a marked effect in lowering the superficial tension of water, and 

 in doing so undergo those remarkable gyrations which are so well known. 



And first with respect to heat, applied, not so as to affect the whole 

 solution, but locally, so as to raise the temperature at one part or point of 

 the surface, while the other parts remained at the temperature of the 

 atmosphere. 



* The tube was calibrated by Dr. E. J. Mills, F.C.S. &c. 



