The photosensitivity of diphenylamine-p-diazonium sulphate by the method of photometric curves

Abstract

The rate of a photochemical reaction is generally defined as the decrease in the number of molecules of a particular species with time and can be expressed by ‒ dn / dt = γ I A , where γ is the quantum efficiency and I A the intensity of the absorbed light in quanta per second. For thin layers of absorbing medium, i. e. layers in which the light intensity is not appreciably reduced, the value of I A is given by Beer’s and Lambert’s laws, I A = α clI ,

The spectral variation of the photosensitivity of visual purple

“…1-6) the variation in the ay values at A = 502 mp corresponds to the limits of accuracy set by the cumulative effect of the separate measure ments involved in each final result. The mean error of the final value for 502 m p,as determined from the table, is ± 0*1 4 x 10~17cm.2, but experi mental uncertainties raise this to about 0*6 x 10~17 cm.2 The reproducibility compares favourably with th a t obtained by Goodeve and Wood (1938) for the photosensitivity of a well-defined substance measured by the same method.…”

“…The method of photometric curves was recently applied successfully to the bleaching of a simple organic dyestuff by Goodeve and Wood (1938). They confirmed th at the photosensitivity does not depend on the amount of absorbing impurity present in the solution: the equations still hold even though only a small part of the sample consists of the photosensitive sub stance, the factor < f> providing adequate correction for the absorption of the light by the impurity.…”

“…For any photochemical process the expression ay gives a quantitative measure of the change occurring when a known amount of luminous energy is incident on the photosensitive substance (see Goodeve and Wood 1938). If, therefore, it is assumed th a t the photochemical bleaching of visual purple is the prim ary process of the act of vision (in man and all vertebrates) the 'photosensitivity must be taken as a basis for linking up the photochemical data on visual purple with the scotopic luminosity curve.…”