1872.] 



on Supersaturated Saline Solutions. 



347 



not sufficiently lower the tension of a solution = 5'2 to produce a rupture 

 of equilibrium. 



It was also stated that bisulphide of carbon £=3*3 to 3' 5, and chloro- 

 form=2'98 to 3'12, formed lenses on the surface of the solution, and that 

 on gently agitating the flask they fell to the bottom, where they remained 

 permanently without any nuclear action. Creosote — 3 behaves in the 

 same manner. Now, in any one of these cases, the tension t-\-c must be 

 greater than 4*5, and hence there can be no separation of the salt. 



We now pass on to consider the second proposition, namely, that if on 

 the surface of a supersaturated saline solution there be deposited a drop 

 of a liquid of feeble tension, the drop spreads and crystallization is deter- 

 mined. Now it is shown in Part II. that drops of ether, of alcohol, and 

 of similar volatile liquids, as well as of certain oils, both volatile and fixed, 

 spread over the surface of the solutions and act as powerful nuclei. On 

 the surface-tension theory, a liquid such as ether, of which the tension = 1 '88, 

 or alcohol =2*5, or wood-naphtha =2*11, or oil of lavender =2*9, must 

 spread on the surface of a supersaturated solution of Glauber's salt of which 

 the surface-tension is as high as from 4 to 5*2. This is true in a large 

 number of cases that have been observed, and so far the phenomena are 

 consistent with the theory ; but there are cases in which liquids of low 

 tension, such as oil of turpentine=2*2 to 2*4, and some varieties of castor- 

 oil =2*5, do not form films, but well-shaped lenses, and remain as such 

 during many hours and even days. Quincke seems to have met with cases 

 of this sort in his elaborate inquiry on the capillary phenomena of the 

 common surface of two liquids*; and he endeavours to account for these ex- 

 ceptions to the general law by the statement that if a lens-shaped drop of a 

 liquid 2 (of low tension) remain on the free surface of a liquid 1 (of much 

 higher tension) without spreading itself out, then it is certain that in most, 

 and probable that in all cases the free surface of liquid 1 is rendered impure 

 by a thin layer of a foreign liquid 3. Now in experiments on supersaturated 

 saline solutions, the flasks, the filtering-apparatus, and the solutions must be, 

 as already explained by one of us, chemically clean ; so that in boiling and 

 filtering a solution into clean flasks in which it is boiled up again, covered 

 over, and left to cool in the open air of the country, it is difficult to imagine 

 the existence of such a film as M. Quincke refers to. Moreover, did such a 

 film exist, the solution in coolingwouldprobablybecomesolidunder its action. 

 Indeed this sometimes happens in the case of flasks that have been already 

 used in experiments on the nuclear action of oils ; for, however carefully 

 they are cleansed, it may happen that one or two out of a dozen may not 

 be quite clean, so that, in the cooling of a boiling solution, a film detached 

 from the walls of the flask may spread over the surface with nuclear action. 

 In order, if possible, to prevent the formation of such a film, the following 

 experiment was made : — 



Experiments. A solution of 1 part of Glauber's salt to 1 of wafer, 

 * Poggendorffs Annalen, vol. exxxix. See also Phil. Mag. for April 1871. 



