No abstract

Errors in setting the wavelength scale of an ultra‐violet spectrophotometer cause an increase in the variance of extinctions measured on the slope of an absorption curve. For a given instrument and operator, the coefficient of variation of extinctions measured on a steep slope was ten times the normal value for zero slope. A method is described for obtaining reasonably precise estimates of (E/), where “S” refers to the displacement of the wavelength scale. The coefficient of variation bears a linear relationship to (E), which is relevant to the choice of wavelengths for Vierordt's method.

The shape of a titration curve contains useful information, which may be extracted in terms of orthogonal polynomial coefficients. In this way, it is possible to (i) distinguish a monobasic acid from a polybasic acid, having groups of closely similar strength; (ii) detect acid‐base impurities in acids and bases, and (iii) study medium effects. The choice of polynomial, range, number of points and experimental conditions are discussed. Using twelve point polynomials and equipment of modest performance, the Pi coefficient (for the central half of a monobasic acid titration curve) can be measured with a relative standard deviation of 0·58.

A number of low-pressure catalytic hydrogenators have been described in the literature, most of them being intended for use in the determination of structure, in which the hydrogen absorbed by small quantities of material must be measured with great accuracy1,2. However, such apparatus is quite unsuitable for normal laboratory-scale hydrogenations. The small number of hydrogenators intended for synthetic work vary from simple devices3,4,5,6 to those which are exceedingly complex7. The simpler designs are divisible into two groups; one kind will handle large volumes of hydrogen with ease and fair accuracy of measurement, but is somewhat inaccurate for quantities of 1 litre or less5,8. The other type is capable of dealing with small quantities with good accuracy, but requires too much refilling when large volumes are required3,4,6.