jgourlay
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Thinking about sulphur crystals, and other crystals
Wanted to get your thoughts on a method for getting crystals from sulphur and other solids with relatively low boiling points.
1. Dump stuff in long tall "test tube" of significant thickness. "cork it" on the bottom (so "bottom" of tube is sticking up)
2. Hook to vacuum pump and give it a good suck.
3. "Cork" contains heating element assembly that is inert to the liquid whatever. Set thermostat to "simmer"
4. Column is sufficiently insulated (temperature controlled?) so that the top of the tube is a few degrees below melting point.
5. Let this bad boy run for a month or three.
Recognizing also that the "top" would need a pressure gauge and relief valve. And maybe packed with quartz wool as a substrate?
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DJF90
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Woelen has a nice easy preparation of sulfur crystals on his website.
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not_important
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Note that sulphur transforms from the rhombic to the monoclinic form above 95.6 C, and v.v. Thus your condenser conditions are important, too warm
and the crystals will slowly crumble away at room temperature.
Easier to use an actual long & large test tube, heat the lower region externally with resistance wire or heater element plus insulation, and
letair cooling do its work. Pulling a vacuum is fine, under decent vac you'll not need to get anywhere near the normal boiling point. Takes longer
to get decent size crystals, perhaps, but not as troublesome as heating near the BP.
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Wizzard
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I use toluene 
I set up a test tube filled with relatively pure sulfur, attach an airtight tube (i use just regular plastic but it gets eaten away slowly) to a
larger vessel filled with toluene so that the tubes are now filled but held above and horizontal to the vessel- I then cover in tin foil (semi-air
tight) and put a small 1W heating element on the test tube. Temp gradients across the vessels carries sulfur in toluene to be deposited in the cooler,
large vessel. Voila! Give it a few days, or weeks depending on crystal size wanted. Slower yeilds better crystals, of course.
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jgourlay
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Thanks all!
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jgourlay
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wizzard, does that work for iodine also?
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nezza
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Toluene is a good solvent for recrystallising sulphur. I have attached a picture of sulphur recrystallised this way.
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