.2.28 Royal Society : — 'Mv. Tomlinson and Van der ^lensbrugglie 



sited a drop of a liquid of feeble tension, the drop spreads and crys- 

 tallization is determined. Now it is shown in Part II. that drops of 

 ether, of alcohol, and of similar Tolatiie 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 exceptions 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 pro- 

 bable 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 super- 

 saturated saline solutions the flasks, the filtering-apparatus, and the 

 solutions must be, as already explained by one of us, chemically clean; 

 so that in boilins and filterins; 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 

 cooling would probably becom.e solid under 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 ma^' spread over the surface with 

 nuclear action. In order, if possible, to prevent the formation of 

 such a film, the following experiment was made : — 



JExperiment 8. A solution of 1 part of Glauber's salt to 1 of 

 water, with the addition of a bit of caustic potash, was boiled and 

 filteretl into four clean flasks. ^Yhen cold, a drop of castor-oil was 

 deposited upon the surface of each of the solutions. It flattened at 

 first, but soon recovered the lenticular form. There was no nuclear 

 action during an hour. On gently shaking the flasks, the oil was 

 difl'used through the solution without nuclear action. 



In an experiment described in Part II. fragments of stearine were 

 scraped into a solution with immediate nuclear action. In such a 

 case, the stearine furnished the film-forming material that produced 

 the solidification of the solution. The solution was boiled with the 

 stearine in it ; and in cooling the stearine formed into solid disks 

 without nuclear action, although the flask was frequently shaken. 



* Poggendorif''s Annaleu. vol. csxsis. See also PLil. ITag. for April 1871. 



