158 Dr. W. Eamsden. Separation of Solids in the [June 8, 



obtained from liquids containing as little as one part of dissolved or 

 suspended solid in 1,000,000 parts of water. 



3. The separated solids differ greatly from one another in the 

 rapidity and completeness of their re-solubility in the mother liquid, 

 and they are sometimes insoluble and " coagulated." 



4. They may have a delicate membranous, membrane-fibrous, or 

 fibrous structure, simulating that of various biological tissues, or they 

 may consist of particles lying loosely side by side (e.g., sulphur). 



5. The film of the free surface of all proteid solutions, and many of 

 the various solutions or suspensions which yield solid "mechanical 

 surface aggregates," exhibits a specially high viscosity not met with 

 in the bulk of the solution. This "special superficial viscosity" 

 develops at very different rates in different solutions, and attains very 

 different degrees of maximal intensity. In some solutions (<?.</., egg- 

 albumin, saponin) it develops with great rapidity ; in others (e.g., 

 serum-albumin, methyl-orange, ferric acetate, mastic, etc.) several 

 minutes or even hours may be necessary for any considerable develop- 

 ment. Evaporation hastens its development, but is not essential. 

 Slight convection currents have a powerful accelerating influence, but 

 are essential only when the suspended solid is indiffusible. The nature 

 of the gas in contact with the " solution " is a matter of indifference, 

 provided it be chemically inactive. 



6. In most cases the " special superficial viscosity " is accompanied 

 by a special superficial resistance to " shear." This is often so intense 

 that a magnetised needle floating on the solution is capable of rotating 

 the vessel containing the solution, if this be floated on water or sus- 

 pended by a fine thread and the needle be exposed to the attraction 

 of a magnet. 



7. The presence on a liquid of a thin coating of matter (even of 

 liquid) which diminishes the "surface energy " would account for some 

 "special superficial viscosity" (Marangoni), but would not account 

 for superficial resistance to " shear," unless the coating of matter were 

 solid or highly viscous and also coherent. 



8. Bubbles of solutions of egg-albumin, caseinogen and saponin 

 exhibit remarkable phenomena, which show that the bubble-film as 

 a whole is very imperfectly elastic and is covered with solid membranes. 

 Egg-albumin bubbles are deformed on collapse by the formation of 

 persistent folds of solid proteid in the bubble-film. Bubbles of pure 

 saponin solution, containing O'Ol per cent, or more of saponin, fall on 

 collapse into innumerable shimmering folds containing isolated curved 

 rods of solid saponin, although water is capable of dissolving at least 

 2500 times this amount. 



The collapsing bubble assumes extraordinary shapes, with sharp 

 angles (as observed by Plateau), and when a hanging bubble is broken, 

 a ragged curtain of bubble-film, which instantly becomes dull and 



