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Venetian Borax: Refining Tincal with Lime
Native borax, tincal, came to Europe from the dried lake shores of Tibet and India coated in an earthy, soapy fat. Venice, then the Dutch, refined it in secret: the refined salt was called Venetian borax. One of their methods is recorded by Knapp, as Muspratt gives it in 1860: soften the tincal with water and a little slaked lime, wash it clean, dissolve it hot with a little chloride of calcium to take out the last of the soap, then crystallise it in lead-lined wooden cones. Borax is the flux of brazing and soldering.
中级
Several days
说明
1
1
Weigh the tincal and the additions
Weigh the tincal and the additions
Weigh the tincal, about 1 per cent of its weight of slaked lime, and about 2 per cent of chloride of calcium (step 7 works it out for 10 kg).
此步骤所需材料：
天然硼砂（粗硼砂）10 公斤
熟石灰（氢氧化钙）100 克
氯化钙200 克所需工具：
等臂天平2
2
Soften it with water and lime
Soften it with water and lime
Soften the tincal in a small quantity of cold water in a wooden tub, and stir it about while adding the slaked lime little by little.
此步骤所需材料：
水1 as required所需工具：
箍木盆
木桨
化学防溅护目镜
橡胶手套3
3
Wash it several times
Wash it several times
Pour off the turbid lime-water. Let the impurities settle out of it, then pour the clear liquid back over the crystals. Repeat this several times; it takes away the greater part of the soapy crust.
所需工具：
箍木盆木桨4
4
Dissolve hot with chloride of calcium
Dissolve hot with chloride of calcium
Dissolve the washed crystals in hot water and add the chloride of calcium. It turns what soap remains into an insoluble lime soap (and common salt); strain that off.
此步骤所需材料：
水1 as required
木炭1 as required所需工具：
蒸发锅
木炭坩埚炉
滤网木桨化学防溅护目镜橡胶手套5
5
Boil down to 21 degrees Baumé
Boil down to 21 degrees Baumé
Evaporate the clear liquid to 21 degrees Baumé, a specific gravity of 1.17, checking with a hydrometer.
此步骤所需材料：
木炭1 as required所需工具：
蒸发锅木炭坩埚炉
比重计6
6
Crystallise in lead-lined cones
Crystallise in lead-lined cones
Run the liquor into wooden vessels lined with lead and shaped as short inverted cones, and let it crystallise. Any deposit collects in the narrow lower part and does not spoil the crystals. Knapp adds that a little tincal stirred in before this last crystallisation keeps the crystals from splitting and flying off the work when heated for soldering.
所需工具：
结晶槽
铅片7
7
Knapp's additions, per 10 kg
Knapp's additions, per 10 kg
正在加载 Jupyter 笔记本…
8
8
Powder it for flux
Powder it for flux
Take out the crystals, dry them and grind them in a mortar to a powder for use as flux. Keep it covered: in dry air borax slowly loses water and turns opaque on the surface.
所需工具：
研钵与研杵9
9
Troubleshooting
Troubleshooting
Borax refining troubleshooting.
Flow
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10
10
History and honest limits
History and honest limits
Muspratt (1860) gives Knapp's two known methods of the secret Venetian and Dutch refining; this is the lime method. The other washed the powdered tincal with caustic soda lye and added carbonate of soda. By Muspratt's time most borax was made instead from the boracic acid of Tuscany and carbonate of soda. Knapp's per cent figures do not say of what; we take them as per cent of the tincal. Grinding the crystals to powder is ours.
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