Index of content:
Volume 13, Issue 9, 01 September 1945
13(1945); http://dx.doi.org/10.1063/1.1724049View Description Hide Description
The rate of exchange of the C13isotope between carbon monoxide and carbon dioxide has been studied. It has been found to be a surface catalyzed reaction on quartz,gold, and silversurfaces. Within the limits of experimental error, which are rather large because of change of surface activity, the reaction is independent of pressure and composition of the gas mixture. The exchange is accelerated by hydrogen or water vapor. Oxygen produces a rapid initial exchange attributed to a chain process of oxidation of carbon monoxide, but is without effect on the subsequent exchange. Isotope exchange takes place with a velocity convenient for study around 900°C, and at this temperature the apparent energy of activation is about 100 kcal.
Several mechanisms for the exchange of C13 have been examined. One which is not entirely free of difficulties accounts for the experimental data. This assumes the presence of H and OH molecules (or other activated forms of H2 and H2O) on the surface with the condition that the total amounts of these molecules is constant.
13(1945); http://dx.doi.org/10.1063/1.1724050View Description Hide Description
When a cross‐linked polymer initially swelled to its equilibrium volume in pure solvent is transferred to a solution of a high polymer in the same solvent and at the same temperature, the gel deswells. A quantitative treatment of this effect is given in terms of the Flory‐Rehner theory of the thermodynamic properties of gels, and the Flory‐Huggins theory of thermodynamics of high polymer solutions. The extent of deswelling depends on the molecular weight and concentration of the solute, on the solvent‐polymer interactions, and on the degree of cross‐linking in the gel. It thus offers in principle a new method for determination of the number average molecular weight of the solute. Various calculations are presented to show the extent of deswelling under given conditions. Finally, some experimental data is offered to demonstrate determinations of molecular weights, using styrene‐divinyl‐benzene copolymergels and polystyrene solutions.
13(1945); http://dx.doi.org/10.1063/1.1724051View Description Hide Description
Experimental data are presented illustrating a specific case of amphipathic adsorption, namely, of gelatin to silver bromide. In this there is mutual coagulation of the silver hydrosol and protein, followed by peptization in excess of dissolved protein. The phenomena in their relation to the isoelectric point of the protein and the pH of the solution are interpreted in terms of a basically duplex polar: non‐polar structure in proteins, and of a resonance factor, involving both adsorbent and adsorbate, in similar cases.
- LETTER TO THE EDITOR
13(1945); http://dx.doi.org/10.1063/1.1724054View Description Hide Description