1872.] 



on Supersaturated Saline Solutions. 



343 



condensation of floating vapour, or a deposit of film-forming dust, and so 

 is brought into the nuclear condition. 



It was further stated that when a lens of oil is resting on the surface of 

 a solution, the flask may be rapidly rotated or briskly shaken, so as to 

 break up the oil-lens into a multitude of minute globules, giving the solu- 

 tion the appearance of an emulsion ; but that by repose the solntion regains 

 much of its transparency, without any separation of salt ; but that if, while 

 the flask is being turned round, a sudden jerk be given to it, so as to 

 flatten some of the globules- against the side, the solution instantly becomes 

 solid. 



The powerful action of films in putting an end to the state of supersatu- 

 ration being thus established, it occurred to one of us, who had already 

 succeeded in explaining a number of obscure phenomena on the principle 

 of surface-tension *, that that force, properly handled, would suffice to 

 account for most, if not all, the varied phenomena of supersaturation. Ac- 

 cording to this view, whatever tends greatly to lower the surface-tension 

 of a supersaturated saline solution, causes a separation of salt, and at once 

 puts an end to the condition of supersaturation. 



In order to test this view, a large number of experiments have been per- 

 formed by one of us during the last six months, consisting of repetitions 

 of former experiments or of new ones suggested by one or both of us. All 

 these experiments have been performed in the open air at Highgate, near 

 London, the object being to avoid all possible miscarriage from the effects 

 of floating dust in the air of a room. It had been suggested that some of 

 the former results as to the action of films might have been vitiated from 

 this source ; and although this does not appear to have been the case, yet 

 it is with much satisfaction that the experimenter refers to the greater faci- 

 lity and certainty with which experiments of this kind are conducted in 

 the open air, as compared with those made in a room. In the open air a 

 gentle wind would sometimes blow over the mouths of the flasks, sufficient 

 to produce a low musical note, without any nuclear action, unless a speck 

 of soot or a small insect were carried into the solution ; but in general, in 

 order to prevent evaporation, the flasks were kept covered with watch- 

 glasses or small beakers, except when performing an experiment. 



The salt used in the following experiments was sulphate of soda, in large 

 crystals, not effloresced, one of three strengths being adopted as circum- 

 stances required, and which will be indicated when necessary, namel}', 1 part 

 of salt to 1 of water, 2 parts of salt to 1 of water, and 3 parts of salt to 1 

 of water. Every solution was first made in a large flask, and filtered boiling 

 into eight or ten small flasks, which were reboiled, covered with watch- 

 glasses or beakers, and carried on a tray into the open air. The same ex- 

 periment was repeated on a number of these solutions of the same strength. 



* " Sur la Tension superficielle des Liquides," par G-. Van der Mensbrugghe, Repeti- 

 teur a l'Universite de Gand. Memoires couronnes par l'Acad. Royale de Belgique, 

 tome xxxir. 18G9. See also Phil. Mag. for Dec. 1869 and Jan. 1870. 



