Royal Society. 223 



In tlie absence of any other even plausible theoiy_, and in view 

 of the fact that all its legitimate consequences are in perfect har- 

 mony with observation whenever they can be brought to the 

 test, the received law of pressure is, I maintain, the only rea- 

 sonable one. 



XXVII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 145.] 



May 16, 1872.— Francis Galton, M.A., Vice-President, in the Chair. 

 T^HE following communication was read ; — 

 -^ '^On Supersaturated Saline Solutions. — Part III. On a relation 

 between the Surface-tension of Liquids and the Supersaturation of 

 SaUne Solutions." By Charles Tomlinsou, F.E.S., and G. van der 

 Mensbrugghe. 



It was stated by one of us in Part II. * that when a drop of a 

 liquid is deposited on the surface of a supersaturated saline solution, 

 it will do one of three things — (1) mingle with the solution without 

 any nuclear action, (2) spread out into a film with powerful nuclear 

 action, or (3) assume the form of a lens, without any separation of 

 salt. It was further stated that when a hquid forms a film or a lens, 

 it does so according to the general proposition, that if a drop of 

 a liquid B, with the surface-tension d, be placed on the surface of 

 another liquid A, with the surface-tension a, the drop will spread into 

 a film, if « >5 + c (c being the tension of the common surface of the 

 liquids A and B) ; but if, on the contrary, a<b-j-c, the drop will 

 remain in the form of a lens. Hence, if B spread on A, A will not 

 spread on the surface of B. When the liquids A and B mingle in all 

 proportions, chas no value. The spreading of the drop may also be 

 interfered with by the superficial viscosity of the solution, or the 

 greater or less difficulty in displacing the superficial molecules. 



It was also stated that if a greasy smear be made upon the clean 

 interior surface of a fiask above the solution, and the fiask be in- 

 clined so as to bring a portion of the solution against such smear, 

 the hquid does one of two things : (1) it breaks up into well-defined 

 globules, which roll over the smear without loss of tension, in which 

 case the smear has no nuclear action ; or (2) as soon as the solution 

 reaches the smear its edge flattens and becomes ragged, in which 

 case the smear is nuclear and the salt separates. 



A glass rod drawn through the hand becomes covered with a 

 smear or film ; or the same rod, by exposure to the air, contracts 

 a film by the 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 sur- 

 face of a solution, the flask may be rapidly rotated or briskly shaken, 



* Philosophical Transactions for 1871, p. 52. 



