Potasium dichromate crystals, early 1920s.
© Science Museum / Science & Society Picture Library
This mas of red crystals was prepared in the early 1920s by Burroughs Wellcome (now part of Glaxo Wellcome). Potasium dichromate (K2Cr2O7) is used extensively in chemistry and in the chemical industry as an oxidising agent, for instance, to bleach waxes and in tanning. The substance shown here was not known to the ancient world, but was discovered by the French chemist Vauquelin in 1797 during the analysis of a mineral, which he later showed to contain a hitherto unknown metal. He named the element 'chromium', after the many colours of its compounds.