Washing soda (sodium carbonate, anhydrous)
A harder bar that unmoulds sooner.
Opens the calculator’s starter recipe with this additive in it. No source gives a dose to fill in, so enter your own.
What it is
Washing soda is sodium carbonate, sold for laundry: its solutions are strongly alkaline, pH 11.4 at 1 %. This is the anhydrous powder; soda crystals, the hydrated form, are 62.9 % water.
PubChem (HSDB) primary source, Wholesale Supplies Plus supplier or guide, Simmons & Appleton primary source
How much
No source gives a dose for soap: enter your own.
When and how
- Usually: in the water, before the lye.
- Also used: after the cook.
- Weigh it dry and dissolve it in the recipe’s own water: no extra water.
Wholesale Supplies Plus supplier or guide, Simmons & Appleton primary source
What it does to the recipe
- It changes neither the lye nor the water: it is only weight in the bar.
Simmons & Appleton primary source, PubChem (HSDB) primary source
Worth knowing
- It cannot turn oils into soap and uses up no lye, so the lye and the superfat stay as calculated. Simmons & Appleton primary source, PubChem (HSDB) primary source
- Caution: Too much can bloom on the surface as a white powder. Simmons & Appleton primary source
- Its usual job is laundry soap, mixed with grated soap rather than made into the bar. Soap Queen supplier or guide, Wholesale Supplies Plus supplier or guide
- Soda crystals, the hydrated form, are 62.9 % water, so a gram of them carries far less sodium carbonate than a gram of the powder. Simmons & Appleton primary source
- Caution: The dust irritates if breathed in. Soap Queen supplier or guide
Spoons and drops
- 1 tsp ≈ 4.02 g (2.91–5.13 g)
- 1 tbsp ≈ 12.1 g (8.72–15.4 g)
- 1 cup ≈ 193 g (140–246 g)
PubChem (HSDB) primary source
INCI name
Sodium Carbonate
- CAS number
- 497-19-8
- EC number
- 207-838-8
Guides that discuss it
Sources
W. H. Simmons and H. A. Appleton, The Handbook of Soap Manufacture (1908): the carbonates of soda or potash "cannot be used in the actual saponification of a neutral fat", only of free fatty acids; in "liquoring", "soda crystals," which, containing 62.9 per cent. of water", are added to hot soap, where "this addition gives firmness and tends to increase the detergent qualities"; a soda ash solution "stiffens and hardens soap, and the addition, which must not be excessive, or efflorescence will occur"; "Strong soda ash solution with a firm soap will result in a brittle product".
Hazardous Substances Data Bank, sodium carbonate (HSDB 5018), via PubChem: "At 25 °C, the pH of 1, 5 and 10 wt% sodium carbonate solutions are 11.37, 11.58 and 11.70"; "Bulk density: 0.59-1.04 g/mL"; the decahydrate "readily effloresces on exposure to air". Carbonate has no acidic hydrogen left, so it takes no hydroxide.
Wholesale Supplies Plus, sodium carbonate: "Dissolve sodium carbonate in warm water and add it to your laundry soap recipe as directed ... Use only at recommended levels, as too much can make the mixture overly alkaline and harsh on fabrics or skin."
Soap Queen, laundry soap: "2 cups Washing Soda", "1/2 cup Citric Acid" and "2-3 cups Cold Process Soap (finely shredded)"; "Washing soda can cause skin irritation ... It can also irritate the nose and throat".