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Caustic Potash (Potassium Hydroxide) from Potash and Slaked Lime, Ure 1839
Boiling potash with slaked lime makes it caustic: the lime takes the carbonic acid and falls as chalk, and potassium hydroxide stays in the water. Andrew Ure (1839) gives the method; it was the main way to make caustic potash until electrolysis took over late in the 19th century.
Intermediate
Half a day
Instructions
1
1
Dissolve and add lime
Dissolve and add lime
Dissolve the potash in six times its weight of water in an iron kettle. Stir in as much slaked lime as there was potash.
Materials for this step:
Potassium Carbonate (Potash)1 kg
Water6 liters
Calcium Hydroxide (Slaked Lime)1 kgTools needed:
Balance Scale
Iron Kettle
Chemical Splash Goggles
Face Shield
Rubber Gloves2
2
Boil an hour, then settle
Boil an hour, then settle
Boil for an hour. Cover it and let the chalk settle, out of contact with air: the lye takes carbonic acid back from the air.
Materials for this step:
Charcoal1 as requiredTools needed:
Iron Kettle
Charcoal FurnaceChemical Splash GogglesFace ShieldRubber Gloves3
3
Siphon off and boil down
Siphon off and boil down
Siphon the clear lye into the cleaned kettle and boil it down, covered except for a small steam hole, until it flows like oil, nearly red-hot.
Materials for this step:
Charcoal1 as requiredTools needed:
Siphon TubeIron KettleCharcoal FurnaceChemical Splash GogglesFace ShieldRubber Gloves4
4
Pour, cut and bottle
Pour, cut and bottle
Pour it onto a bright iron plate, cut it into pieces as soon as it sets and bottle it at once under a ground stopper: in air it soaks up water and carbonic acid.
Tools needed:
Iron Plate
Glass Bottles with StoppersChemical Splash GogglesFace ShieldRubber Gloves5
5
How much caustic potash
How much caustic potash
Loading Jupyter Notebook...
6
6
Limits
Limits
Ure's method; the kettle, the charcoal fire and the quantities in the notebook are ours. Caustic potash burns skin and eyes: Ure says never to touch it with the fingers.
Materials
4- Placeholder
- 6 litersPlaceholder
- Placeholder
- 1 as requiredPlaceholder
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