Test for zinc
Cobalticyanide paper (Rinnmanns test for Zn) can be used as a chemical indicator for zinc. 4 g of K3Co(CN)6 and 1 g of KClO3 is dissolved on 100 ml of water. Paper is dipped in the solution and dried at 100 °C. One drop of the sample is dropped onto the dry paper and heated. A green disc indicates the presence of zinc. History
Ancient use
The Charaka Samhita, thought to have been written between 300 and 500 AD, mentions a metal which, when oxidized, produces pushpanjan, thought to be zinc oxide. Zinc mines at Zawar, near Udaipur in India, have been active since the Mauryan period (c.  322 and 187 BCE). The smelting of metallic zinc here, however, appears to have begun around the 12th century AD. One estimate is that this location produced an estimated million tonnes of metallic zinc and zinc oxide from the 12th to 16th centuries. Another estimate gives a total production of 60,000 tonnes of metallic zinc over this period. The Rasaratna Samuccaya, written in approximately the 13th century AD, mentions two types of zinc-containing ores: one used for metal extraction and another used for medicinal purposes. Various isolated examples of the use of impure zinc in ancient times have been discovered. Zinc ores were used to make the zinc–copper alloy brass thousands of years prior to the discovery of zinc as a separate element.
2
          
          
            ZnSO
            
              4
            
            
              
            
          
          +
          2
          
          
            H
            
              2
            
            
              
            
          
          O
          ⟶
          2
          
          Zn
          +
          
            O
            
              2
            
            
              
            
          
          +
          2
          
          
            H
            
              2
            
            
              
            
          
          
            SO
            
              4
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2ZnSO4 + 2H2O -> 2Zn + O2 + 2H2SO4}}}
  The sulfuric acid is regenerated and recycled to the leaching step.