Synopsis.Experimental methods for measuring the mechanical properties of concentrated polymer solutions and other viscoelastic systems under periodically varyiny stresses are reviewed. These include direct measurements of stress and strain, measurements of response at resonance frequencies determined by the inertia of the apparatus, propagation of waves in extended media, and measurements of resonance vibrations. The conditions for the suitability of each method are discussed, and equations for the interrelation of the various quantities measured are given. Examples are shown to illustrate the fitting of experimental data to the calculated behavior of mechanical models, in order to obtain frequency-independent mechanical constants which can be interpreted in terms of molecular behavior.It may be equally well represented by a frequency-dependent capacity in parallel with a frequencydependent resistance, the frequency variation of these units following certain simple relations (Debye, Polar Molecules, 1923). The latter model facilitates interpretation of the phenomenon in terms of orientation of dipoles, while the former leads to interpretation in terms of a heterogeneous system of two dielectric solids. notation is regretted, but it is hoped that the present notation, which has been chosen with care, will serve better for a variety of experimental methods and a variety of mechanical models.

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In calculating elastic constants of viscoelastic media from transverse wave propagation, it has been customary heretofore to assume a plane disturbance in a medium of infinite extent. Equations have now been derived for conditions which approach much more closely the experimental arrangement, namely, propagation from a finite source plate in a rectangular cell, and representative numerical calculations have been made. The new theory shows that the finite dimensions of cell and source should have very little influence on the wave-length as determined from observations of strain double refraction, but the attenuation should be perceptibly different from that of the plane wave case. Experimental data confirm these conclusions. Nevertheless, the simple plane theory is adequate within present experimental error for the majority of cases. Only in certain specified ranges of mechanical consistency will it be necessary to apply corrections taking into account the sizes of the cell and source.

The addition of non-ionic surface active compounds to solutions of a variety of anionic detergents has been shown to enhance foam stability. The effectiveness of such compounds depends strongly on the detergent. It is found that detergents increase in "susceptibility to foam stabilization" in the order (1) branched alkylbenzene sulfonates, (2) n-alkylbenzene sulfonates, (3) secondary alkyl sulfates, (4) 2-re-alkane sulfonates and (5) primary alkyl sulfates. This is also the order of increasing surface tension of the detergents (without additives) at concentrations greater than the critical micelle concentration (CMC). The polar aliphatic additives with straight hydrocarbon chains of 8-14 carbon atoms were the more effective foam-stabilizers and among these effectiveness increased in the order (1) primary alcohols, (2) glycerol ethers, (3) sulfolanyl ethers, (4) amides, and (5) N-polar substituted amides. This order is, in general, the order of increasing surface activity and CMC-depressing activity. Monolayer compositions calculated from surface tension and CMC measurements show that in the mixed monolayer there is negligible specific interaction between detergent and additive molecules, and that increasing foam stability in a series of detergent-additive pairs corresponds to an increasing mole fraction of additive in the adsorbed monolayer. The most stable foams were found with detergent-additive pairs having 60-90% of additive in the adsorbed monolayers. The requirements for preferential adsorption of additives are the same as found for foam stability: solutions of the detergent (without additive) should have a high surface tension, the additive should give water a low surface tension, and should depress the CMC of the detergent. The mechanism of CMC depression by additives is discussed, and the importance of the distribution of additive between sites on the surface of a micelle and elsewhere in a detergent solution is pointed out.

Sedimentation-equilibrium studies are made of the moleoular weights of bovine ,B.laotoglobulins A, B, and C at pH 7·5. The order of dissooiation of dimer to monomer is A> B ~ C. The dissooiation oonstant (Kd) for A and B is 0·6 X 10-4 and 0·08x 10-4 mole 1-1 at 20°C, respeotively. The oonditions ohosen for these measurements are based on sedimentation velooity studies in the pH range 6-9. There is no ohange in sedimentation velooity behaviour following different times of standing at 20°C for pH < 7·5. The sedimentation patterns exhibit a single peak with some trailing on the solvent side. At low oonoentrations the plot of weight average sedimentation coefficient (,~) versus concentration (0) is in aocord with that of a rapidly dissociating system of monomer-dimer type. There are time-dependent aggregations above pH 8. Effects of changes in ionic strength and addition of methanol are considered.Using several values of K d , .9 versus 0 ourves are oaloulated by the method of Gilbert (1963) and oompared with the present experimental ourves and also those of Zimmerman, Barlow, and Klotz (1970). The agreement between theory and experiment is only moderate.