I can imagine now that the last class of the week on a Friday afternoon is not one for which teachers have any particular fondness, despite the promise of freedom that lies after the final bell. For my seventy-year-old self, the weekend was the light at the end of the very long tunnel that was double chemistry. The Friday I remember so vividly was in winter the light was already fading and it would be dark before I got home. It always seemed that the best and brightest part of the day was wasted in school until introduced me to the alkali metals.