Analisou-se numericamente a validade do método de cálculo do pH que consiste em resolver urna das equações do segundo grau, obtidas por simplificação da eliminante completa, de modo a conservar apenas três termos consecutivos do polinómio, para os seguintes casos: mistura de ácido e de base não conjugados monopróticos, em proporções estequiométricas; partículas anfipróticas; mistura de ácido muito forte e ácido não muito forte; mistura de dois ácidos não muito fortes; mistura de duas bases.

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Determinámos as razões de distribuição e as percentagens de extracção do t 37Cs à temperatura de 25,0 °C ± 0,5 °C em função do pH (1,9 a 7,0) da fase aquosa e a dois valores da força iónica (0,5 e 1,0), quando o radionuclideo foi extraído por uma solução de tetrafenilborato de sódio em acetato de isoamilo. No final fazem-se considerações teóricas.

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Verifica-se por via espectrofotométrica que o álcool butilico terciário é um bom estabilizador do ácido p-silicomolíbdico. Com base nesta propriedade, estabelece-se um processo de avaliação de microgramas de sílica, com elevado grau de precisão.

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Preparation of semipermeable porous cellulose acetate membranes is described. These are used to study the ultrafiltration of aqueous solutions of polyethylene glycol (M. W. 15,000-20,000) flowing over the membrane at pressures of 0.05-0.5 MN/m2 (5-70 lb/in2) approximately. A model is proposed to describe solvent and solute transfer in the concentration boundary layer and through the membrane which enable transport coefficients to be determined. These give good predictions of product flux and its purity. Concentration polarisation at the membrane surface is found to be extremely high, surface concentrations approaching one hundred times those of the bulk solutions, because of the high fluxes through the membranes. This results in observed solute rejections (based on the bulk solution concentration) of 90-95 % although the intrinsic membrane rejection (based on concentration at the membrane surface) is 99.9 % approximately.

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This work was carried out as part of a study of the gas coolant purification system for the High Temperature Nuclear Power Reactor (Dragon Reactor). Carbon dioxide and water vapour occur as impurities in the coolant gas and this combined experimental and mathematical study is concerned with the adsorption of carbon dioxide from flows of nitrogen and helium by fixed beds of granular 4A and 5A molecular sieve adsorbents.

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Some factors related to the scale-up problems of processes for the two-phase mixed-acid nitration of hydrocarbons are discussed, with particular reference to the design of multipurpose plant. By placing some emphasis on the overall characteristics, the relevance of certain fundamental processes can be evaluated. It is demonstrated that the rate of reaction is the most important factor, and the related mechanisms are discussed in some detail. Particular attention is paid to the question of uncertainty in some of the parameters which are nevertheless important and how this can be taken account of in the design.

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Estimates of plant investment are needed at the predesign stage of a project for screening process and plant alternatives. A suitable method should produce estimates of acceptable accuracy from a minimum amount of design information and with a minimum of computation. This paper, after a brief review of earlier methods, describes how such a method can be structured. In applying it, the reference data as well as the method itself must be reliable. To ensure this, the reference data is best provided by the user from earlier plants in his same industry.

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O sistema, que vigora desde há cerca de 15 anos, de produção de gás de cidade para abastecimento de Lisboa tem originalidade bastante para que mereça referência um pouco desenvolvida.

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