Physical and chemical properties: purple or purple equiaxed crystal system octahedral crystal, easy to make large particles crystal.The relative density was 1.826(25).Melting point is 89 .When heated to 100, 10 crystal water was lost, and when heated to 400, 12 crystal water was lost and turned into anhydrous substance.Soluble in water, dilute acid, insoluble in alcohol.Dissolved in water as a purple solution, heating to 70 when the green solution, cooling gradually purple.It is easy to absorb moisture and can be weathered in dry air.Molecular formula :KCr(SO4) 2-12h2o purpose: used as tanning agent, mordant and photographic fixing agent. Packing: in plastic woven bags lined with polythene polythene bags of 25kg net each.