II. On supersaturated saline solutions. Part III. —On a relation between the surface-tension of liquids and the supersaturation of saline solutions

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 liquid 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-tensionb , be placed on the surface of another liquid A, with the surface-tension the drop will spread into a film, ifa >b +c (c being the tension of the common surface of the liquids A and B ); but if, on the contrary,a = <b +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,c has 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 flask above the solution, and the flask be inclined so as to bring a portion of the solution against such smear, the liquid 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.