Washing Soda is chemically Sodium Carbonate.
. It is white in color and is alkaline in nature when mixed with water.
It reduces the hardness of water - if one gets hard water at home from the bore well. It removes stains - oil, grease, wax etc..
When some white powder (scales) like substance sticks strongly to the walls and edges of a tea pot, boiler etc., it can be removed by washing soda.
It is also used in municipal water supply ponds to reduce chlorine effect and increase alkalinity.