Gelatin diffusion through

Imagine that you are a member of a research team trying to find out how the rate of diffusion through gelatin depends on the relative molecular mass (M ) of a drug. 

WA Strickland, Jr., M Moss. Water vapor sorption and diffusion through hard gelatin capsules. J Pharm Sci 51 1002-1005, 1962. 

In the most brilliant period of his career, Graham had demonstrated that certain polymers, including many gums, were unable to diffuse through certain gelatinous substances, membranes, and paper. He called the materials incapable of permeating a membrane "colloids", and reported that they could be obtained in a state free from diffusable "crystalloid materials" by this technique (20). 

Here c is the amount of moisture at time t, cq, the amounts of moisture at time zero and infinity, respectively, h the thickness of the gelatin film, and D is the diffusion coefficient of moisture through gelatin. 

The salt can be encompassed in a gel based on gelatin, agar, or polyvinyl alcohol, which is then brought into contact with the textile fiber loaded with the drug. The salt will diffuse through the gel and fiber, and thus release the drug. 

You have been given five coloured powders of dyes, labelled A to E, to test. These have relative molecular masses of 486,534,686,792 and 886, respectively. You are also provided with a stopclock/watch and a ruler with a millimetre scale. You can also use any other common laboratory apparatus needed to complete the investigation. The diffusion is a slow process and the team carry out some trial runs to get a rough idea how quickly the dyes diffuse through the gelatin. They decide to monitorthe experiment for 72 hours. 

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