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Liquid Castile Soap: Olive Oil Boiled with Caustic Potash
Potash makes a soft soap where soda makes a hard one, and soft soap dissolves easily, so an olive-oil potash soap thinned with water is liquid castile soap. The boiling follows the soft-soap practice Andrew Ure described in 1839: oil and caustic potash lye added by turns and boiled gently until the paste turns clear.
The picture: Norwegian green soap (grønnsåpe), another soft soap of fat and potash lye.
Intermediate
Half a day
Instructions
1
1
Make two lyes
Make two lyes
Dissolve caustic potash in water to make a weak lye (hydrometer 1.05) and a strong one (1.20). Add the potash to the water, not the water to the potash.
Materials for this step:
Potassium Hydroxide190 g
Water1 literTools needed:
Balance Scale
Hydrometer
Glass Beaker
Chemical Splash Goggles
Rubber Gloves2
2
Oil and weak lye
Oil and weak lye
Heat part of the olive oil to nearly 100 °C, stir in some weak lye and bring it to the boil. Add more oil and weak lye by turns until all the oil is in.
Materials for this step:
Olive Oil1 kgTools needed:
Iron Kettle
Hot Plate
Wooden SpoonChemical Splash GogglesRubber Gloves3
3
Boil gently with strong lye
Boil gently with strong lye
Keep it at the gentlest boil, adding a little strong lye now and then. The froth settles, the paste turns clear and thickens.
Tools needed:
Iron KettleHot PlateWooden SpoonChemical Splash GogglesRubber Gloves4
4
Test on a glass plate
Test on a glass plate
Cool a dab on a sheet of glass. It is done when it is clear, not milky, and a thin opaque ring forms round its edge (Ure: the soap has its "strength"). Then take it off the heat.
Tools needed:
Glass SheetWooden Spoon5
5
Thin it with water
Thin it with water
Dissolve the soft soap paste in hot water, about three parts water to one of paste (our choice; add less for a thicker soap), and bottle it.
Materials for this step:
Water3 litersTools needed:
Iron KettleHot Plate
Pump Bottle (PET)6
6
Potash for the oil
Potash for the oil
Loading Jupyter Notebook...
7
7
Limits
Limits
The boiling and the glass-plate test are Ure's; the quantities, the hot plate and the dilution are ours. Caustic potash lye burns skin and eyes.
Materials
3- 190 gPlaceholder
- 4 litersPlaceholder
- 1 kgPlaceholder
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