Zum Verhalten von Polyamidcarbonsäuren aus Pyromellithsäuredianhydrid und Benziding in Lösung. I. Streulicht- und Viskositätsmessungen in Dimethylacetamid

Poly(amic acids) of M _w = 48000 to 434000 were prepared by Polycondensation of pyromellitic dianhydride (PMDA) and benzidine using different stoichiometric ratios of the monomers. The poly(amic acids) were investigated through light scattering and viscosity measurements in dimethylacetamide solutions. In solutions containing LiBr, the polyelectrolyte effects are completely supressed; it is therefore possible to determine the molecular weights, the end-to-end distances and the second virial coefficients. The viscosity equation for poly(amic acid) from PMDA and benzidine in LiBr-dimethylacetamide is as follows: [η] = 3,40 × 10^?2 × M _w^0,78 ml/g. The relatively high [η]-values or correspondingly the low coil densities indicate a loose coiling of the poly(amic acid) molecules. As it is shown by the comparison of the unperturbed dimensions of these poly(amic acids) with the corresponding Avalues of other polymers, the loose coiling of the poly(amic acid) molecules is caused not only through the strong solvation of the polymer molecules by the solvent, but also through the long and stiff benzidine-units in the chain. In LiBr-free dimethylacetamide the beginning dissoziation of the COOH-groups has been noticed through decrease in the intensity of the scattered rays with decreasing angles of observation in the region of small angles and low concentrations. This effect is interpreted by external interferences of the scattered rays, caused by a more regular distribution of the macromolecules in the solutions. The intramolecular interaction of the negative charges produced by the dissoziation of the COOH-groups causes in LiBr-free systems a certain widening of the coil, which is noticed on the higher [η]-values as compared to the systems containing LiBr. As shown by the increase in the optical anisotropy in solutions without LiBr, a change in the coil configuration on the dilution takes place in such a way that it leads to an increase in the ratio of the ellipsoid axis, eventually joined with a geometical widening of the coil.     

The mechanism of the adsorption of alkyl xanthate species on galena

Oxidation of galena produced thiosulphate and sulphate ions at the mineral surface but flotation activity, using isopropyl xanthate as collector, was found to depend on the concentration of thiosulphate ions at the surface. It is proposed that the thiosulphate ion reacts with di-isopropyl dixanthogen formed by oxidation of xanthate ion in solution. It was demonstrated that these species react in homogeneous solution to give xanthate and xanthogen-thiosulphate ions. The proposed surface reaction may account for the formation of a layer of adsorbed xanthate ions and for the surface redox potential being raised to a value where more xanthate ions can be chemisorbed and where dixanthogen is stable.     

Inflammation of the tail in swine. Slaughter-house findings during 1972, 1973, and 1974 (author's transl)

In the Public Salughter-House of Utrecht, a percentage increase in the number of pigs with inflammation of the tail, which had or had not healed, was observed during the period from 1972 to 1974 inclusive. The most common secondary symptoms of inflammation consisted in embolic pneumonia, osteomyelitis of the vertebrae and abscess formation in other parts of the body, particularly the semimebranosus muscles. Osteomyelitis was found to be the most common complication in pigs in which the inflammation of the tail had healed, whereas this usually consisted in embolic pneumonia in those cases in which the inflammation of the tail had not healed. The bacteriological examination carried out in accordance with the Meat Inspection Regulations was positive in 21.7 per cent, 13.5 per cent of the cases respectively in 1972, 1973 and 1974. Micro-organisms were isolated much more frequently from the kidney than they were from the spleen and meat. There was no relationship between the presence of inflammation of the tail and climatological conditions during the fattening period. The losses at slaughter from inflammation of the tail in the Netherlands are estimated at 3-4 million guilders per annum.     

Kinetics of absorption,equilibration (or distribution), and excretion of orally and intraperitoneally administered cholesterol in the rat

Resorption and metabolism of cholesterol administered intraperitoneally and per os have been described in the rat utilizing a technique of double isotopic labeling. Depending upon the route of administration, these parameters vary to a large degree. Alimentary cholesterol is progressively resorbed over a period of 10 hr, while the maximal blood level of cholesterol is attained after the 6th hr following intraperitoneal injection. On the other hand, cholesterol administered per os is more rapidly utilized in biliary acid synthesis than cholesterol administered intraperitoneally. In the range of concentrations utilized in this work (10–300 μg and 0.2–300 μg, respectively, administered to the rat, orally and intraperitoneally), the rate of cholesterol resorption remained constant.     

On the characteristics of the equations of motion for a bubbly flow and the related problem of critical flow

Summary For the study of transients in gas-liquid flows, the equations of the so-called separated flow model are inadequate, because they possess, in the general case where gas and liquid move at different velocities, complex characteristics. This paper is concerned with the equations of motion for bubbly flow. The equations are discussed with emphasis on the aspects of relative motion and the characteristics are calculated. It is found that all characteristics are real. The results are used to establish a relation between gas velocity, liquid velocity, void fraction and sound velocity at critical flow. This relation agrees very well with experimental data for these quantities as measured by Muir and Eichhorn in the throat of a converging-diverging nozzle.On leave of absence from Istituto di Fisica, Universitá Degli Studi, Milano, Italy.     

EUROPEAN BREWERY CONVENTION—HAZE AND FOAM GROUP AMINO ACID COMPOSITION OF THE BEER HAZE COMPONENTS RETAINED BY INORGANIC ADSORBENTS

The amino acid composition of the substances retained by bentonite, Stabifix and Stabiquick on addition to filtered Pilsner beers was determined by ion-exchange chromatography. The results indicate large differences between the 3 adsorbents. Stabifix is the most selective, for the amino acid composition of the adsorbed substances is very similar to that of the chill hazes of the E.B.C. The prolamin content is high. Bentonite adsorbs proportionally more salt-soluble proteins. Stabiquick, in agreement with its composition, is less selective than Stabifix, but adsorbs proportionally more prolamins than bentonite. The difference between the adsorbents was also confirmed by solubility measurements in the solvents most commonly used in this laboratory for the extraction of the prolamins. The desorption of the nitrogenous substances decreases from Stabifix to Stabiquick and from Stabiquick to bentonite. A comparison by Sephadex G-25 and G-50 chromatography of the beers before and after treatment indicated that in addition to the nitrogenous substances other components are retained by the adsorbents.     

On the use of superposition in the approximate solution of heat conduction problems

The use of convolution integrals and of the method of images, applied to approximate basic solutions, is investigated. The value of these techniques in deriving approximate solutions of heat conduction problems is discussed, and their accuracy, relative to both known exact solutions and other approximate ones, is assessed.