Mercury polar organic liquids

Many examples exist of interfaces formed between two immiscible liquids. A well-known one is the interface between a long-chain hydrocarbon, for example, dodecane, and water, which is commonly known as the oil water interface. Dodecane and water are immiscible because the hydrocarbon phase is nonpolar. Liquid liquid interfaces are also formed between water and organic liquids with polar groups such as octanol and heptanoic acid, which also have rather long hydrocarbon chains. The polar liquid nitrobenzene, which has a relative permittivity of 35, is also immiscible with water. Another well-known system is the mercury polar liquid interface. This has been studied extensively, especially for aqueous electrolyte solutions. However, the mercury polar liquid interface is also an example of a metal solution interface which was considered in the previous section. The discussion here is limited to liquids with relative dielectric permittivities falling in the range 1-200, and systems which have poor conductivities as pure liquids. 

The RHgX compounds are crystalline solids whose properties depend on the nature of X. When X is an atom or group that can form covalent bonds to mercury, for example, Cl, Br, I, CN, SCN or OH, the compound is a covalent non-polar substance more soluble in organic liquids than in water. When X is S04 or N03, the substance is salt-like and presumably quite ionic, for instance, [RHg]+NOJ. Acetates behave as weak electrolytes. For iodides or thiocyanates, complex anions, e.g., RHglJ and RHglf-, may be formed. 

We now come to the question of the mechanism of the magnitude of surface tension and interfacial tension. The magnitudes of surface tensions of molten materials are much greater than for organic liquids. This can be observed in mercury with its ready breakup into drops. Hildebrand and Scott [3] have described the surface tension k of pure liquids and its relation to the solubility parameter of non polar liquids. They suggest the correlation... 

Evidence of attachment of an organic molecule to a metal surface by a particular group in the molecule is not only provided from surface tension data on the surface of liquid mercury but is also to be noted in the phenomenon of displacement of one liquid by another from a surface. The hydrocarbons adhere to metals much less tenaciously than molecules containing polar groups such as —COOH and —OH. Thus we find that a hydrocarbon may be removed from a metal surface by displacement with alcohol and also that the lubricating properties of a hydrocarbon are materially affected by the addition of hydrocarbon compounds containing polar groups (Hardy, Proc. Roy. 8oc. A, c. 650, 1922, A, ci. 487, 1923). 

---