Are chemical elements critical for the modern economy in dangerously short supply? It's a question that Justin Rowlatt poses a century and a half after the Russian chemist Dmitry Mendeleev published the original periodic table. Justin speaks to two chemists - Andrea Sella of University College London explains the significance of Mendeleev's scheme to the modern world, while David Cole-Hamilton talks us through an updated version of the table he has just published that highlights chemical elements that could run out within the next century unless we learn to make better use of them. However, perhaps we don't need to worry just yet, at least not for two of those red-flagged elements. Thomas Abraham-Jones describes how he happened across the world's biggest reserve of helium in the African savannah, while Rick Short of Indium Corporation explains why the metallic element his company is named after is in abundant supply, so long as you don't mind sifting an awful lot of dirt for it. (Picture: Manuscript of Mendeleev's first periodic system of elements; Credit: Science & Society Picture Library/SSPL/Getty Images)