9-025-One-DimensionalDiffusion

One of the challenges in studying diffusion is that since this phenomenon occurs at the molecular level, while it is often ``easy'' to observe the diffusion process, it is usually difficult to directly measure concentration levels. As an example, one can illustrate one--dimensional diffusion by means of gases of different types such as ammonia and hydrogen chloride introduced into a long thin glass tube where each gas enters from opposite ends of the tube. When the gases meet in the tube, a white ring will appear at the point along the tube where they initially meet and mix. While this is an effective way to demonstrate one-dimensional diffusion, one cannot measure the concentration level of the gasses at any point along the tube at any given time.