Rehydrating Dry Reference Electrodes Mast comhination electrodes use a silverlsilver chloride reference with potassium chloride electrolyte that is saturated with silver chloride. For the majority of acidhase pH determinations these are quite satisfactory, but in solutions containing protein the ion junction becomes plugged by silver-protein precipitate and the comhination electrode fails. In this case a double junction reference or a calomel reference must be used to avoid this failure. Faced with this situation and an emergency need, I intended to use a separate pH electrode with a calomel reference electrode. The unused calomel reference electrode had been on the shelf too long and even the mercurous chloridelmercury mixture within was completely dry and could not be wetted with the added potassium chloride solution. The electrode was salvaged by placing it in potassium chloride solution in a small beaker and then putting the beaker, electrode, and lead inside a vacuum desiccator. By application of a vacuum the trapped air in the HgzCldHg mixture was expanded and when the vacuum was released the electrolyte seeped in properly. This proved to be a rapid and effective means of restoring dried calomel el=-
Howard P. Willlams University of So~thernM ss~sslppl Hanyeso~rg.MS 39406
584
Journal of Chemical Education
