Why are preservatives, including mercury compounds like thiomersal, added to vaccines? What is "invert sugar" and is it better for my teeth? How does is "aquamation" - the alkaline hydrolysis equivalent of a cremation - work? Is crude oil the same stuff everywhere, or does the composition vary? Can you clean your teeth with bicarbonate of soda? Why do knuckles crack? And what actually is "acidity". Join Dr Chris and Kieno Kammies for all the answers... Like this podcast? Please help us by supporting the Naked Scientists