Application of interferometry to reaction kinetics: hydrolysis of ethyl acetate

The use of multiple-beam interferometry has been extended to the study of the kinetics of the hydrolysis of ethyl acetate in acid solution. The rate of change of refractive index in the reacting solution is shown to be directly proportional to the disappearance of the reactants and the appearance of products. The rate of movement of fringes on a wedge interferometer was measured with a photomultiplier tube by recording the response of the tube on passage of a bright fringe. A continuous uniphase output gas laser was used as a light source. Extremely small refractive index changes, hence very small concentration changes, can be detected. Design characteristics of the cell are discussed.