Measurements have been made of the extent of adsorption from aqueous solutions by gold of some long-chain pyridinium bromides and sodium sulphates. Electrokinetic properties of gold in these solutions have also been investigated by microelectrophoresis. The degree of adsorption of the cationic surface-active agents was greater than that of the anionic compounds and a congruent function of reduced concentration within a homologous series of compounds. The isotherms exhibit a two-step character which, from the electrophoretic data, may be interpreted in terms of a two-layer adsorption mechanism. Specific adsorption of surfactant anions in the primary layer is postulated and it is suggested that the electrophoretic data allow conclusions to be drawn regarding the modes of orientation of surfactant ions in the adsorbed layers.

The extent of adsorptioii by gold from aqueous solutions of a series of long-chain ammonium bromides has been measured and electrokinetic properties of gold in these solutions studied by microelectrophoresis. Froth flotation of gold particles has been studied in solutions of long-chain ammonium bromides, of long-chain pyridinium bromides and of the anionic compounds sodium cetyl sulphate and sodium dodecyl sulphate. In part 1, conclusions were drawn from adsorption and electrophoretic data regarding the modes of orientation of surfactant ions in the adsorbed layers ; specific adsorption of surfactant anions but not of cations was postulated. The relative efficiencies of flotation reported here support those conclusions.We acknowledge, with thanks, the support of the S . R.C. in the award of a maintenance allowance to B.D.S.

The anhydrous salts of the long chain fatty acids are known to pass through a number of \\,ell-dehned mesomorphic forms between the true crystalline solid and the isotropic liquid. The nature of some of these mesomorphic forms has been investigated by a study of their optical properties, electrical conductivity, density, and viscosity. 111 this paper, results obtained by an optical method are presented for phase transition temperatures of the alkali metal stearates and a number of s o d i~~~n stearates having substituents in the hydrocarbon chain.

Electrostatic agglomeration can be induced in suspensions of glass beads in organic liquid media. The stability of the agglomerates is markedly dependent on temperature. The influence of surface roughness and the presence of small quantities of water on the interparticle interaction is discussed. Assuming a simple model the observed relationship between yield value and particle size for systems containing the same concentration of solid phase is derived. INTRODUCTIONThe behavior of suspensions of solids in liquid media is of considerable importance owing to the numerous practical applications of systems of this type which exhibit non-Newtonian behavior. Basically, the behavior of such a system is determined by the interparticle interaction, which is, in turn, determined by the nature and composition of the supporting medium. Suspensions of inert solids in organic liquids have been investigated by a number of workers (5, 12) and the presence of small amounts of water as an immiscible liquid has recently been shown to be of profound importance (9, 10).Eggleton and Puddington (4) investigated the effect of temperature on suspensions of glass beads in toluene containing various amounts of water. Although the suspensions containing large amounts of water behaved as expected, showing a minimum yield value below the freezing point of water, the anhydrous suspension and that containing 0.1% water showed an unexpected and steady increase in sedimentation volume and yield value as the temperature was lowered to -60' C. This work is concerned with a further investigation of this phenomenon and a consideration of other factors involved in systems of this type.

A reaction calorimeter has been used to measure heats of interaction between hydroxyapatite and a number of ionic species in solution. The technique has demonstrated substantial differences in heat output between fluoride and monofluorophosphate when interacting with hydroxyapatite. It was also possible to detect competition in reaction systems and thereby obtain information regarding reaction mechanisms.