washing soda 
noun [mass noun]
Sodium carbonate, used dissolved in water for washing and cleaning.To get grease out of clothes, Andrew suggested dissolving washing soda in hot water and soaking the garment for half an hour....
- Dissolve one cup of washing soda in a litre of hot water and add the soap solution, mixing well.
- If approved disinfectants are unavailable washing soda, mixed with water at a rate of 50 grams per litre, is the next best alternative.