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Glycerin from Candle-Works Sweet Water: Cap's Process
The sweet water washed out of lime soap in the stearin candle works holds the fat's glycerin, with lime and fatty traces. Cap's process, given in Muspratt's Chemistry (1860), turns it into glycerin: the lime is thrown down as sulfate with sulfuric acid, the liquor is boiled down out of contact with the air, neutralised with chalk, filtered, cleared with bone black and concentrated to a colourless syrup of about 51° Twaddell.
Advanced
Several days
Instructions
1
1
Boil down the sweet water
Boil down the sweet water
Reduce the glycerin water drawn off from the lime soap by evaporation over a fire.
Materials for this step:
Glycerin Water1 as required
Bituminous Coal1 as requiredTools needed:
Evaporating Pan
Brick Furnace2
2
Find how much lime it holds
Find how much lime it holds
Measure out a known volume, precipitate its lime with oxalate of ammonia, collect the precipitate, dry it, burn it and weigh it. From that, work out how much sulfuric acid will just combine with all the lime.
Tools needed:
Ammonium Oxalate
Filter Paper
Clay Crucible - Refractory
Balance Scale3
3
Throw the lime down with sulfuric acid
Throw the lime down with sulfuric acid
Add that amount of sulfuric acid. Sulfate of lime falls. Let it settle and decant the clear liquid into another vessel.
Materials for this step:
Sulfuric Acid1 as requiredTools needed:
Vat
Chemical Splash Goggles
Rubber Gloves4
4
Boil it out of contact with air, to 14° Twaddell
Boil it out of contact with air, to 14° Twaddell
Boil the liquid in a covered vessel, kept stirred, so the air cannot reach it. The boiling drives off volatile fatty impurities and the liquid loses colour and smell. At 14° Twaddell let it cool: more sulfate of lime falls.
Materials for this step:
Bituminous Coal1 as requiredTools needed:
Vat
Wooden PaddleBrick Furnace
Hydrometer5
5
Neutralise any excess acid with chalk
Neutralise any excess acid with chalk
Test with litmus. If the liquid is acid, add powdered chalk or limestone a little at a time until it is neutral.
Materials for this step:
Calcium Carbonate - Crushed Limestone1 as requiredTools needed:
Litmus PaperWooden Paddle6
6
Boil on to 37.5° and filter
Boil on to 37.5° and filter
Boil again out of contact with air, stirring actively, to 37.5° Twaddell. Collect the sulfate and carbonate of lime on a filter.
Materials for this step:
Bituminous Coal1 as requiredTools needed:
VatWooden PaddleBrick FurnaceHydrometer
Strainer7
7
Reduce to 49°, filtering again if needed
Reduce to 49°, filtering again if needed
Evaporate the filtrate, keeping it well agitated, until on cooling it marks 49° Twaddell. If more sulfate of lime falls, filter again.
Materials for this step:
Bituminous Coal1 as requiredTools needed:
Evaporating PanBrick FurnaceHydrometerStrainer8
8
Clear it through bone black
Clear it through bone black
Pass it through washed animal charcoal (bone black) to take out the tinge. It comes through as a colourless solution of about 45° Twaddell.
Tools needed:
Bone BlackStrainer9
9
Concentrate to 51° Twaddell
Concentrate to 51° Twaddell
Concentrate it carefully, driving off about a quarter of its weight of water, until the syrupy liquid reads 51.2° Twaddell. Store it closed.
Materials for this step:
Bituminous Coal1 as requiredTools needed:
Evaporating PanBrick FurnaceHydrometer10
10
Cap's readings as specific gravity
Cap's readings as specific gravity
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11
11
Troubleshooting
Troubleshooting
Glycerin troubleshooting.
Flow
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12
History and honest limits
History and honest limits
Muspratt (1860) gives Cap's process alongside the older lead-plaster method (olive oil and litharge, the lead removed with hydrogen sulfide). He quotes Wilson that Cap's glycerin, though better than the old product, is not absolutely pure. Bone black is used here as a filter that clears the colour; it is not part of the glycerin. The Twaddell-to-specific-gravity conversion is the standard definition of the scale.
Materials
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Tools Required
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