156 Dr. W. Kamsden. Separation of Solids in the [June 8, 



"Separation of Solids in the Surface-layers of Solutions and 

 ' Suspensions ' (Observations on Surface-membranes, Bubbles, 

 Emulsions, and Mechanical Coagulation). - - Preliminary 

 Account." By W. KAMSDEN, M.A., M.D., Oxon., Fellow of 

 Pembroke College, Oxford. Communicated by Professor 

 F. GOTCH, F.K.S. Keceived June 8, Ptead June 18, 1903. 



In a paper published in Du Bois Raymond's ' Archiv fur Anat. und 

 Physiologic' in 1894,* I showed that mere agitation of various proteid 

 solutions brought about a separation of some of their contained proteid 

 in the form of fibrous or membrane-fibrous solids, and that it was 

 possible in this way to coagulate and remove the whole of the proteid 

 from solutions of egg-albumin. It was proved also that these de-solu- 

 tions and coagulations of proteid were not due to the action of enzymes, 

 heat, or surface evaporation, and were not appreciably affected by the 

 nature of the gas in contact with the liquid or of the vessel in which 

 the agitation was effected. 



A prolonged series of further experiments, undertaken with a view 

 of ascertaining the precise cause of this phenomenon, has led me to the 

 discovery of an important, but hitherto unnoticed physical fact : 

 namely, that, quite apart from evaporation, solid or highly viscous 

 coatings are spontaneously, and more or less rapidly formed on the 

 free surfaces of all proteid solutions. 



By purely mechanical means these free-surface coatings can be heaped 

 up to form visible solid masses of proteid, which in some cases is not 

 only " de-soluted," but at the same time coagulated and rendered 

 permanently insoluble in the mother-liquid. 



By extending the range of my experiments, I have been led to the 

 further conclusion that similar coatings of solid or highly viscous matter 

 occur on the free surfaces of a large number of non-proteid colloid 

 solutions, of fine and coarse " suspensions," and of a few apparently 

 crystalloid solutions, and that they are formed also at the interfaces of 

 every pair of liquids which, without being of high viscosity, are capable 

 of forming persistent emulsions. 



The explanation of these spontaneous de-solutions of previously 

 dissolved matter at the free surfaces must be sought in the observation, 

 which I have found to hold good in all cases hitherto examined, that 

 the matter which accumulates possesses the property of lowering the 

 surface-tension, and, therefore, the " surface energy," of the free sur- 

 face of water. 



On dynamical grounds, the most stable arrangement of any solution, 



* " Physiologische Abtlieilung." pp. 517 534. 



