ear ing ▁mixture ▁of ▁min er als , ▁which ▁was ▁in ▁turn ▁named ▁after ▁the ▁Greek ▁myth ological ▁character , ▁ Κ ά δ μ ος ▁Cad mus , ▁the ▁founder ▁of ▁The bes . ▁St rom ey er ▁eventually ▁isolated ▁cad m ium ▁metal ▁by ▁ro ast ing ▁and ▁reduction ▁of ▁the ▁sul f ide . ▁ ▁In ▁ 1 9 2 7 , ▁the ▁International ▁Conference ▁on ▁We ights ▁and ▁Me asures ▁re defined ▁the ▁meter ▁in ▁terms ▁of ▁a ▁red ▁cad m ium ▁spectral ▁line ▁( 1 ▁m ▁= ▁ 1 , 5 5 3 , 1 6 4 . 1 3 ▁w avel ength s ). ▁This ▁definition ▁has ▁since ▁been ▁changed ▁( see ▁k rypt on ). ▁At ▁the ▁same ▁time , ▁the ▁International ▁Pro totype ▁Meter ▁was ▁used ▁as ▁standard ▁for ▁the ▁length ▁of ▁a ▁meter ▁until ▁ 1 9 6 0 , ▁when ▁at ▁the ▁General ▁Conference ▁on ▁We ights ▁and ▁Me asures ▁the ▁meter ▁was ▁defined ▁in ▁terms ▁of ▁the ▁orange - red ▁emission ▁line ▁in ▁the ▁elect romagnet ic ▁spectrum ▁of ▁the ▁k rypt on - 8 6 ▁atom ▁in ▁vac u um . ▁ ▁Mercur y ▁ ▁Mercur y ▁has ▁been ▁found ▁in ▁Egypt ian ▁tomb s ▁which ▁have ▁been ▁dated ▁back ▁to ▁ 1 5 0 0 ▁BC , ▁where ▁mer cur y ▁was ▁used ▁in ▁cos met ics . ▁It ▁was ▁also ▁used ▁by ▁the ▁ancient ▁Chinese ▁who ▁believed ▁it ▁would ▁improve ▁and ▁prolong ▁health . ▁By ▁ 5 0 0