This image has 3 'round bottom flask with flat bottom'. Can I use these to do refluxes
& distillations?Heptylene - 24-4-2019 at 01:40
Nice colors! As long as they are borosilicate you should be fine, chemplayer has used flat bottom flask if I recall correctly. Don't put them under
vacuum though.DrP - 24-4-2019 at 02:12
I guess a light reduction in pressure wouldn't hurt to lower the BP. (?)
I feel that you'd get better heating on a hotplate from a flat bottom.
I had a distillation kit once where the bulb was pear shaped. Was one single piece of glass from the bulb through column to the pipe out, which, had a
quick fit glass joint for a collection vessel to be added to it. I don't think the shape of the bulb has any bearing on the distillation other than
ease of heating and strength for vacuum as noted above. DavidJR - 24-4-2019 at 02:35
Yes, you can use them. I also use them under vacuum, as well as erlenmeyers, and never had any issue at all.Sulaiman - 24-4-2019 at 02:58
Yes, you can use a flat-bottomed (Florentine) flask for distillations etc.
You will need something equivalent to a cork/rubber bung with hole, glass tubing etc.
For many liquids you will need to protect the bung from corrosion.
Cork bungs are easily damaged, rubber bungs can be surprisingly expensive.
If you are going to use bungs and tubing then a Florentine flask is better than an RBF as it can sit on a hotplate or rest on a work surface stably,
RBFs fall over and spill without a support system (e.g. cork rings) and are only really required if vacuum is anticipated.
If you are on a really tight budget then a Florentine flask, bung, glass tubing etc. is a good option.
Ground joint glassware is sexier and more useful but of course the startup cost is higher.
Assuming that you will eventually use ground joint glassware,
think ahead when buying for your immediate needs,
e.g. a ground joint flask is a little more expensive than a plain flask,
but a ground joint flask can work with bungs now and with ground joint glassware in future.
The same applies to funnels, condensers etc.
P.S. (after reading earlier replies) Erlenmeyer (conical) flasks are to me better than Florentine flasks,
they are more stable (especially useful for small filtrations) and have a larger heating area,
I feel comfortable subjecting my conical flask with side arm, for use with a Buchner funnel, to vacuum - because it is designed for that, it is called
a vacuum flask.
(some are very thick, some are bulbous etc.)
I would not use my normal thin glass Erlenmeyers with vacuum,
others may be lucky, but 15 psi (one kilogramme weight per cm2) multiplied by the flat area is too much stress for my liking.
[Edited on 25-4-2019 by Sulaiman]Dr.Bob - 28-4-2019 at 19:05
Realistically, if you want to distill something (or even reflux most organics), you will want to use glass jointed flasks. I even have some Pyrex
flat bottom flasks like this, so if you want a few, I would give you some to try (if you pay the postage), since you asked about them, but they are
only really safe for non-flammable solvents or if you create a really good seal to the next step. But rubber stoppers don't last long in
distillations. These could also work for simple refluxes or heating of solutions, but making a condenser work well without a joint is tough.
Note, thicker glassware will withstand vacuum better, but heating thicker glassware requires very gentle heat, as the difference in temp from inside
to outside is large, so heating must be very gentle.
fusso - 29-4-2019 at 06:19
Sorry, I should've said that I was referring to flat bottoms with ground joints.Dr.Bob - 30-4-2019 at 17:58
Just realized that you are in asia, so shipping would be prohibitive. But flat bottoms with joints can be used for any normal heating, and
reactions, they would even work OK in most heating mantles as well, I suspect. I try not to use them under vacuum, but they likely would be OK. I
have used them a few times, and they are handy for not needing cork rings when handing on the bench, but otherwise not that special. I have always
used either heating mantles or oil/water baths for heating, so round works fine for that. Mr. Rogers - 30-4-2019 at 20:29
Messing with corks and glass tubing like that you're just going to end up stabbing yourself.fusso - 1-5-2019 at 06:01
Messing with corks and glass tubing like that you're just going to end up stabbing yourself.
Back in the mists of time I wouldn't even have known that ground glass joints existed, let alone been able to afford one - all my chemistry was glass
tubing and bungs and incompetent though I am I never managed to injure myself
I'd obviously rather use ground glass joints but tubing and bungs isn't dangerous if you do it properly with care - it's like suggesting that I
shouldn't use a knife to eat my steak because I might stab myself!
