Coherent Identifier About this item: 20.500.12592/tz3tdf

Journal of the Indian Chemical Society March 1935




COMPOSITION OF PRUSSIAN AND TURNBULL' S BLUES 145 It is known quantitatively that in the case of solutions the fractions dl II of the intensity of light absorbed by the solution is proportional to its thickness or the number of dissolved molecules i.e.—di II= Ki.c.dD where D is the finite thickness of the layer and c the concentration of the solution. [...] The time of exposure for the solvent was therefore allowed one tenth of that of the solution so that the point where equal intensities would appear on the spectra of the solvent and solution it became evident that the intensity of light through the solution had been weakened to one-tenth and hence the formula K=cD could be applied to evaluate the results under correct condtions. [...] The shift of the absorption bands may be due to (i) the different proportion of Prussian and Turnbuil's blues formed in course of the reaction between the reactants iron and ferrocyanogen salts and (ii) also due to the difference in the size of the particles of Prussian and Turnbull's blues when they are freshly precipitated. [...] In these exothermal photochemical reactions the activation of the reacting molecules or their atomisation and the loosening of the binding forces of the molecules are produced by the absorbed light and the energy liberated in the chemical changes. [...] It is of interest to note that in the dark reaction in presence of an excess of potassium oxalate the rate of disappearance of iodine follows the unimolecular formula but in presence of ultraviolet visible or infra-red radiations the velocity of the disappearence of iodine is semimolecular.


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