Sciencemadness Discussion Board - Is my boiling flask OK?

Is my boiling flask OK?

ManyInterests - 5-5-2021 at 20:06

I've recently received the glassware I need and the heating mantel/stirrer for some more advanced distillation and mixing. I cleaned them up and rinsed them with soap and water to get all the glue up and let them dry thoroughly from the inside and out.

But I do see two stains or so on the interior of my boiling flask. I am not sure if they are just water stains or something else. I plan on doing some distillation with sulfuric acid and fuming nitric acid so I need to make absolutely sure my glassware is fine before I do it. I realize how dangerous these chemicals are and the last thing I need is boiling hot acid bursting all over the place (I read the thread of life after detonation and it is terrifying. I have no interest in such a thing happening to me). I attached the photos below. Please tell me if they are fine or I should return it and order another boiling flask.

The brand is GG-17. I got it off Aliexpress. The reason why I chose that glass is because I saw several videos of NileRed using this brand in his sulfuric acid purification video (he did also use a Pyrex boiling flask for one method) and I figure if it is good enough for NileRed, it is good enough for me.

I did some research on this forum about the safety of glassware for distilling dangerous chemicals like sulfuric acid. From what I understand Chinese glassware is thicker than European/American glassware but it is not necessarily better against inorganic compounds.

I plan on making a big safety question dump to get all the safety questions answered before I do any dangerous distillations. My first distillation will be purifying alcohol (as a solvent. I do need some 95% ethanol) which I assume is much safer than sulfuric acid distillation!

[Edited on 6-5-2021 by ManyInterests]

Fyndium - 5-5-2021 at 22:59

Sulfuric acid distillation needs heat of way over 400C which can only be reached with few molten salt and metal baths or direct flame, which puts significant strain. I would use sacrificial flask, that is of no tragedy if it happens to crack. Boiling sulfuric acid will eat through everything upon contact, so best not to do it on your best and newest worktable. If I were paranoid and could not do it outdoors or an expendable surface, I would possibly get a sand vat beneath the flask.

But the GG17 and other stuff that deschem and others sell have been good quality so far. All of my glassware, with few exceptions from past times, are theirs. Only few minor imperfections.

Those stains are, if the flask is new, residues from grinding the glass joints. They should vanish with decent cleaning, but as the grinding materials are made of acid-base resistant(mostly) material, it may need mechanical attention to clean.

unionised - 5-5-2021 at 23:55

Quote: Originally posted by Fyndium

I would use sacrificial flask, that is of no tragedy if it happens to crack. .

Spilling boiling sulphuric acid is a tragedy.
It's easy enough to replace a flask, so that's not going to be the big problem.
Use the best flask you have because it has the least chance of breaking.

Keras - 6-5-2021 at 00:09

Call me an uppity snob or a stuck-up idiot, but I wouldn't risk my equipment and/or my health (boiling sulphuric acid burns) using Chinese glassware. Really. Draw a few more bucks out of your pocket and get prime glassware for that kind of thing.

You probably won’t distill sulphuric acid, as it boils above 330 °C, temperature at which it spontaneously decomposes into sulphur trioxide and water. What I advise you to do is heat your flask up to 200 °C. Hot sulphuric acid will oxidise almost everything it has been mixed with into water and carbon dioxide, so you’ll end up with pure acid. More diluted that you want, maybe, but almost pure. If you want to concentrate it, I'd even recommend generating sulphur trioxide and dissolving it into your acid, rather than trying to distill the latter. Both are dangerous, but at least sulphur trioxide is a gas, and it is visible.

Fyndium - 6-5-2021 at 00:44

I'm yet to see an issue with Chinese. I've used them for vacuum distillations multiple times. And yes, I've vacced sulfuric acid too, I built a blast shield around the boiler from thick plexi and plywood just in case of implosion. In this matter, I don't have best or worst flasks, they all seem to work equally, the smaller ones only lack the volume of the bigger ones.

For the perspective, distilling sulfuric acid as a first experiment is a bit hardcore IMO, if this is the case.

If you perform distillation outdoors and use gas burner at inert ground, if the glass breaks, the acid just spills on the place, and as long as you and your gas bottle aren't in the vicinity, that's about it. You lose a flask, a gas burner and perhaps a stand and whatever it's on. Chances are small, though, as long as you don't perform any hasty actions, don't heat it at full blast and use air or hot water condenser and a secondary to cool down the condensate. People nitrate sensitive energetics here without a flick, but distilling sulfuric acid is a tragedy?

Keras - 6-5-2021 at 01:56

Quote: Originally posted by Fyndium

I'm yet to see an issue with Chinese.
[…]
For the perspective, distilling sulfuric acid as a first experiment is a bit hardcore IMO, if this is the case.
[…]
People nitrate sensitive energetics here without a flick, but distilling sulfuric acid is a tragedy?

I don’t pretend all Chinese flasks are bad. But I’m less confident in their quality. I happened once to order a three-way tap from China. It was cheap, but what I got was unusable: the hole in the teflon stopcock did not align properly with the inlet. I tried to enlarge the hole with a gimlet, but the whole thing cracked. I chucked it and swore never to order anything else from there.

Yeah, distilling sulphuric acid is rough. Using vac is a must, in my opinion, to reduce the thermal stress.

As for nitration, I mean as long as you stop at mono-nitrations (even di-nitrations), there’s hardly any danger of explosion. And since tri-nitrations require the use of fuming nitric acid and pretty high temperatures, it’s unlikely to happen by chance. Whereas a crack in a flask is all but predictable…

draculic acid69 - 6-5-2021 at 02:32

Ask yourself do U really "need" to distill your sulfuric acid?
It's a very risky unnecessary thing to do compared to the
other possibilities out there.

Fyndium - 6-5-2021 at 05:29

Quote: Originally posted by Keras

I happened once to order a three-way tap from China.
cheap,
unusable:
teflon stopcock did not align
the whole thing cracked.
I chucked it and swore never to order anything else from there.

I have received a lot of stuff from China that was not quite what I expected. My vacuum desiccator outlet is still broken, as it snapped clean off with very little force. Also, my 500mL fritted funnel snapped clean off the frit base when I was drying it. My stirplate was absolute garbage.

Still, vast majority of my stuff has been good.

Keras - 6-5-2021 at 06:35

Quote: Originally posted by Fyndium

You’re lucky, in that all the defective pieces were 'low-stake' devices – I mean it’s liking buying a car and finding that indicators, wipers and, say, A/C don’t work properly. But it could’ve happened to any object, RBF included (or say, the crankshaft in case of a car). That’s a risk I’m not willing to take.

[Edited on 6-5-2021 by Keras]

Sulaiman - 6-5-2021 at 08:24

I successfully used GG17 glass 1000ml rbf and 300mm air condenser (sold as a plain column) to distil sulphuric acid,
during a second run my generic (not GG17) Claisen adapter cracked but the rbf and column seem ok.

If you need but can't purchase conc. sulphuric acid then distillation is the best option
as no choking fumes are released and none of the acid is wasted
you get some dilute and some concentrated distilled acid
and a little concentrated acid left in the pot.

I used the open flame of a butane-powered mini-bbq grill
prepare for violent bumping and the rbf breaking
- consider anything less a bonus.

'need' is rather subjective given that amateur/hobby chemistry is not 'needed'.

ManyInterests - 16-5-2021 at 18:34

Thank you very much for your responses and your concerns. I think I am assured that my boiling flask will be OK for this task.

The main thing that I am worried about is the bumping that this will invariably cause. I have boiling chips that should help, and I will only be distilling/boiling very small quantities of sulfuric acid at a time. While I do have a 1 liter flask and I've seen videos where mishaps happen due to overfilling (and those are TERRIFYING) I will not do more than 25% capacity at a time.

I am still thinking whether or not to distill or to just boil it and kill power the instant the white fumes appear. The main thing that concerns me with that is I am afraid my setup might not be able to handle the bumping and it will dislodge my distillation setup. That is my biggest fear. I have a fractional distillation column that will go on top of my flask, then lead to a condenser column (it can have water pumped through it, but for sulfuric acid I was informed this is not a good idea) and numerous clamps to hold everything together. I only have one stand that is part of my mantel. So I will have to improvise by using the bars on my balcony as makeshift stands. The final joint does have vacuum capability, but I don't have a pump to make that work. Despite this, I am still worried about the bumping.

For those who've mentioned that I would need an open flame. I do have a 350 Watt heating mantle that is rated to go as high as 380 degrees Celsius. I don't think I need to put an open flame below it. I don't have the setup for that. But I do believe my mantle will provide sufficient heating power for that.

I have many more questions. I think I should prepare a large question list and dump it all in one go to avoid needlessly making threads.

ManyInterests - 19-10-2021 at 17:41

I was doing a search for something else before I popped by my old thread here. Just decided to give an update.

Seems like the boiling flask I got is a winner! No joke. I purified almost 2 liters of sulfuric with it without a hitch. Adding a good amount of boiling chips controlled the boil that it appeared to boil like water instead of having bumping. My first run I added a few chips and instead of a rolling boil it was steady before giving a rather cool looking eruption. Thankfully my setup for boiling H2SO4 kept me fully protected from all the dangerous fumes.

GG-17 appears to be a good brand at a good price.

teodor - 20-10-2021 at 02:37

I think bumping could be prevented by controlling the temperature of the heating media. For this reason, a (direct) flame is the worst source of heat. I've got a nice result using a heat gun (my model allows control of the air temperature with 10C step up to 650C). Adjusting the air temperature I've got a constant violent boiling. I am not sure my acid was more than 85% so probably it could be different with 95%. But I have the impression that heat gun or heating mantle don't cause bumping which I often have with many mixtures using other heat sources.
When I use the heat gun I apply the air stream from the side, so it prevents contacting of contents of the flask with the heating element in the case of the crack.

[Edited on 20-10-2021 by teodor]

monolithic - 20-10-2021 at 07:53

I realize the original post is 5+ months old, but my deschem round bottom flasks have that same weird ring on them. They're fine and still hold up to vacuum.

macckone - 20-10-2021 at 08:04

Using air heating for sulfuric acid is one way to reduce bumping as is not heating from the bottom.
sulphuric acid has a high density and a high boiling point both of which increase bumping.
I have apparatus specifically made for such procedures that is silica glass.
Custom made silica air condensor and silica flask was pretty pricey.
The air condensor feeds a regular condenser with a flexible fiberglass seal.
The fiberglass handles the differential expansion and seals well once it is soaked in sulfuric acid.
I use an alnico in glass stir bar. Curie Temp 800C.

ManyInterests - 18-5-2025 at 06:45

I decided to bump this up since I had an... interesting situation with a boiling flask.

I was distilling some nitric acid using sodium nitrate and sodium bisulfate. This is not the first time I did it. To be more accurate, this was the third time I was doing it with the same equipment. But then... this happened?

Look at the two pictures? I have no idea what happened there. Did my mantle get so hot that it annealed itself to the shape of the sulfate cake? I'm not sure why. I will in all likelihood need to replace my 2000ml flask (it is pricey, but thankfully not THAT pricey), but I wonder if I can keep using it? I'm going to do another distillation with it today, I washed it and dried it thoroughly, there are no leaks in it. I will definitely NOT be using it for boiling any more sulfuric acid, that's for sure!

So what could have caused this? And is it still safe? I guess my next distillation will tell. I need to take particular caution with it.

dettoo456 - 18-5-2025 at 07:07

Indeed, way too hot, and the NaHSO4 cake was probably insulating to heat the glass past its softening point. I’d trash it if I were you and look at any other glass you have from that supplier for stress marks.

If you have a diaphragm pump, I’d use that and a trap for any dry distillation. It lowers the temps needed dramatically and speeds up the process.

ManyInterests - 18-5-2025 at 07:59

Quote: Originally posted by dettoo456

Indeed, way too hot, and the NaHSO4 cake was probably insulating to heat the glass past its softening point. I’d trash it if I were you and look at any other glass you have from that supplier for stress marks.

If you have a diaphragm pump, I’d use that and a trap for any dry distillation. It lowers the temps needed dramatically and speeds up the process.

OK I think I understood why it fucked up on my third distillation and not the others.

I had not put teflon tape to seal the thermoadapter that I inserted. This allowed to vent slightly (loss of yield, but safer for equipment).

Another thing is that I could have had a problem with the nitrate salt... the batch I used was old and may have had some impurities. The older purer stuff didn't cause this.

I am running a fourth distillation now. I will make sure that the temperature does not go above a certain amount. I will set it lower to maybe 130C

EDIT: I set the temp lower immediate (as of writing there is a distillation is in progress). to a max of 145C. It will not get hot enough to cause this again.

the flask is holding out quite fine, but I will be buying a new one because this is NOT a hobby you want to cheap out on.

[Edited on 18-5-2025 by ManyInterests]

[Edited on 18-5-2025 by ManyInterests]

ManyInterests - 18-5-2025 at 12:19

OK, I completed the distillation without a hitch. It can still work, but it must be taken VERY seriously in terms of security. That is, until I get my new 2000ml flask.

In the meantime, it would probably smart if I used my other 2000ml flat bottom three-necked flask. I got enough stoppers to seal the other two necks if needed.

Edit: Nope. It cannot be reused. I saw a crack. Thankfully it held out throughout thedistillation, but that is the last hurrah of this flask.

[Edited on 18-5-2025 by ManyInterests]

Precipitates - 19-5-2025 at 05:27

Quote: Originally posted by dettoo456

Look at any other glass you have from that supplier for stress marks.

This is probably the most important point for any glassware.

And I should probably be doing this more frequently - not that I do high temperature distillations.

just curious...

Sulaiman - 19-5-2025 at 20:55

Quote: Originally posted by ManyInterests

... is it still safe? I guess my next distillation will tell. I need to take particular caution with it.

what happened to the heating mantle liner ?
If the borosilicate rbf melted/softened,
why did the mantle survive ?
- it must have been at an even higher temperature.

Keras - 19-5-2025 at 22:01

In my opinion, this was not true borosilicate glass, but some other composition halfway between borosilicate and soda lime. That would explain why the glass softened at such low temp.

I’m super wary of the quality of Chinese glass. I would *never* use it for high temperature experiments. Even for vacuum filtration, I would be suspicious.

ManyInterests - 22-6-2025 at 04:43

OK, so I learned a lesson with using sodium bisulfate (and what an expensive lesson it is!), especially with using a short therometer adapter. Note this is mostly as a note to myself. Your experience may differ.

Never set the temperature to above 99C and increase it in graduations, this is because the heat of the flask below will always be mucher higher than the (mostly pure) nitric acid coming over). I did this twice so far with my new round bottom flask and no sign of any damage whatsoever.

On the other hand? NEVER DO IT WITH A FLAT BOTTOM FLASK. I just lost another nice flask, twice so far (a little over 100$ in losses! Ugh! The sodium bisulfate didn't cost me that much!) Since even with good temperature control, the bottom of the flask will get damaged. I saw some damage on it the first time and so I already wrote it off as aloss. I did it again and it survived, but the damage was more visible, I won't be using it a third time.

Edit: On a plus note: the nitric acid I have is of the finest quality. WFNA territory if a little red, but that can be cleared up quickly in the freezer in a bag of sodium bicarbonate

[Edited on 22-6-2025 by ManyInterests]

Dr.Bob - 22-6-2025 at 12:40

You fused the heating mantle or its cover to the flask, seen it happen before when people tried to use a heating mantle without a variac or other power controlled on a rbf. The marks line up with the heating elements in a mantle. Using vaccum will help this, or just using very slow heating via a power controller or variac.

Nitrox2 - 16-7-2025 at 08:42

Here is the rim of my 250mL Erlenmeyer

Yay, or nay?

Is there anything to look for that is more of a guarantee that there will be less or no imperfections? It says it is GG-17. It is also from China, However, I've had a lot of good, glassware from China Nanshin organic chemistry apparatus, back in the day. Ground glass set, didn't use it really, at all.

I remember looking at the little flasks they have on display at my JC in the bookstore, it did appear that a lot of these flasks did have seemingly minor imperfections, if looked at close enough.

[Edited on 7-16-25 by Nitrox2]