Ultraviolet Absorption Coefficient Research Articles

PHYSICOCHEMICAL STUDIES OF LIGNINSULPHONATES: III. PROPERTIES OF FRACTIONS PREPARED BY SUCCESSIVE SULPHONATION OF PERIODATE LIGNIN

Periodate lignin was sulphonated in stages by a series of short bisulphite cooks. At each stage the soluble ligninsulphonate was removed and purified, and the residue was resulphonated. The 14 fractions thus obtained had constant methoxyl content and ultraviolet absorption coefficients. There was a gradual increase in the sulphur content as the integral reaction time increased, but 26% of the ligninsulphonate possessed a sulphur content of less than 3%. There was a marked increase in both the intrinsic viscosity and rate of solution with increase in reaction time. The mechanism of the sulphonation reaction is discussed in the light of these results.

The Determination of the Absorption Coefficient of Luminescent Microcrystals

The absorption and luminescence emission of single Zn-type microcrystals was investigated. A photoelectric microscope photometer was built which consists of a Zeiss microscope and a 931 A multiplier phototube. Evaluating the results of absorption measurements, neither a plane-parallel, nor a spherical crystal model furnished reliable results for the absorption coefficient. The application of an empirical model, based on the non-absorbed radiation (5 770 A) made possible the determination of the ultraviolet absorption coefficient by comparing the transmission of single microcrystals for different wavelengths. The method was experimentally checked on K2Cr2O7 crystals. The ultraviolet absorption coefficient of luminescent microcrystals may also be determined from the dependence of the light emission on the particle size. On etudie ici l'absorption et l'emission luminescente d'un microcristal simple de Zn-type. Un microphotometre photoelectrique a ete construit dans ce but, a partir d'un microscope Zeiss et d...

THE ULTRAVIOLET ABSORPTION OF SILVER BROMIDE

The photoelectric absorption process in solid insulators is discussed and contrasted with that for free atoms and ions. It is suggested that in substances of high dielectric constant the resultant screening of the field of the remaining positive hole due to the polarization of the material results in a reduction of the absorption coefficient at the spectral edge, and produces a maximum at higher energies. This effect is illustrated by a calculation of the ultraviolet absorption coefficient of silver bromide using as a model a bromine ion in a hole in a uniform dielectric. The calculated absorption coefficient is found to rise from the edge to a maximum at a wave length of about 850 Å.

Chemical Tests for Vitamins

AT a meeting of the Society of Public Analysts on November 1, a discussion was held on “The Chemical (as distinct from Physiological) Tests for Vitamins”. Mr. A. L. Bacharach, in opening the discussion, outlined the present state of knowledge of the chemistry of the individual vitamins, of which one, vitamin C, has been synthesised. Of the others, most is known about the constitution of calciferol (vitamin D) and vitamin A. He enumerated such chemical tests as have been used or suggested for the estimation of vitamins, of which the two most important are the Tillmans-Harris test for ascorbic acid (vitamin C) and the antimony trichloride test for vitamin A. Dr. Leslie Harris, discussing the most accurate methods of applying the antimony trichloride test for vitamin A, said that for quantitative work it is essential to saponify the oil, substances interfering with the production of the blue colour being removed by hydrolysis. For vitamin C a quantitative method based on the use of Tillman's indophenol indicator has been made more nearly specific by a preliminary removal of interfering reducing substances. Prof. J. C. Drummond directed attention to certain defects in the B.P. procedure for the antimony trichloride test. The colours should be matched at the period of maximum intensity, and reliable results can only be obtained with the unsaponifiable matter. Mr. Norman Evers showed that even the blue value of the unsaponifiable matter of cod liver oil might not be the true vitamin value. He pleaded for uniformity in the method of expressing results. Mr. S. K. Crews and Mr. S. J. Cox read a paper on the relationship between the Carr-Price value and 328 m[x absorption coefficient of preparations containing vitamin A. They showed that the purification of vitamin A products removes substances which inhibit the blue colour and that eventually the ratio of the Carr-Price blue colour value to the ultraviolet absorption coefficient rises and tends to become constant.