Photoelectric methods of measuring the velocity of rapid reactions - II—A simple apparatus for rapid p h and other changes requiring 200 cc or more of each reagent

In the course of their work on the velocity constants of the CO2 + H2O ⇌ H2CO3 reaction, Brinkman, Margaria, and Roughton (1933) made some colorimetric observations on rapid ph changes with the aid of a photoelectric modification of the Hartridge-Roughton apparatus, designed by the writer and his assistant, A. Secker. Fortunately no appreciable lag was caused by the ph indicators themselves, for controls showed that their intrinsic time of response is less than 0·001 second, whereas the half-periods of the processes studied were 0·01 second and upwards. No details of construction were given in the 1933 paper, and only minimum details of operation. Since, however, the apparatus can be quickly assembled, is simple yet accurate to work with, uses only moderate amounts of fluid (200 cc or more), and can obviously be applied to many other colour changes besides those of ph indicators, it has been thought fit to describe it more fully here. Construction of Apparatus In their early spectroscopic work on rapid reactions, Hartridge and Roughton kept their observation tube fixed, and moved the light-source and the spectroscope to the several points of the tube, at which analysis of the streaming fluid was required. In photoelectric recording of the colour of the streaming fluid, it is better to align the light source and the photoelectric cell in fixed position, and to move the observation tube relatively thereto, by attaching it, together with the mixing-chamber, to an adjustable platform, by means of which any desired part of the observation tube can be brought into the path of the beam of light illuminating the photoelectric cell.