[mana]

Hi all
When I want to crystallize  a substance I have to prepare a saturated solution. I add a little solvent and heat the solid and then add more solvent to dissolve all the impure solid completely and then filter the undissolved impurities, but before filtration complete my pure solid is crystallized, I know I have to filter the hot solution, but I guess the concentration of my solution is high thus it crystallizes rapidly, how much solvent should I add to prevent this problem?

[Arkcon]

It depends on how much solid you have.  You may add a drop more, to let you work without it crystallizing.  You can chose a two solvent system for recrystallizing.  You can dissolve in an abundance of solvent, filter, then concentrate before cooling for crystallization.

[Babcock_Hall]

[reminiscence] Many years ago I saw a heating mantle that wrapped around a funnel, so that the glass funnel would stay hot during a hot filtration.  I could kick myself for not buying it. [/reminiscence]

This is my way of saying that I have never found a completely satisfactory technique, but perhaps one of the organic specialists will have a thought.

[wildfyr]

I use a heatgun and get the buchner funnel as hot as I reasonably can before filtering if I'm right on the edge like that. That does sound like a nifty piece of equipment Babcock.

OP, there is no prescribed amount you need to add, you will to solve it will by trial and error, or by better hot filtration technique like I described above. Can I suggest using a large Buchner funnel that is pre-heated? The large funnel will be able to keep its temperature longer and let the filtration go faster due to surface area.

[Corribus]

We used one of these.

http://www.wilmad-labglass.com/Products/LG-7110-108/

[wildfyr]

Cheap too! Only $800 a pop. I want one but can't justify that expense haha.