I remember it well, Chemistry Practical - all Friday afternoon, qualitative analysis - we had access to the works, and a bit of unofficial chemistry was commonplace; take a penny, give it a quick dip in conc nitric acid then drop it into 10% mercuric chloride. 1961 long before Health & Safety  The dental amalgam was insoluble and of very little hazard to the patients. However both dentists and their nurses did suffer problems due to long term exposure of fumes from traces of spilt mercury An example of why Health & Safety was necessary What we often lack these days is intelligent interpretation of risk - so managers ban everything in case they are sued.  David