Sciencemadness Discussion Board

Glassware Questions...

FatPat005 - 5-2-2004 at 19:11

Hello all...
My name is Patrick Kelly and I have been reading the boards here for a long time and still know very little. I am a major newbie at this chemistry stuff although I have some experience from my simple high school chemisty classes that I have taken to date. I do have one question for you however that I was unable to find by searching the internet as I usually do. I have been doing some research on glassware and will probably be buying some here in the near future to get started with some simple experiments, but my question is this: All of the different flasks and such have different mouths on them, but for some purposes(distilling, etc,...) must be connected together. It is probably some very simple concept, but I am just unable to see how they can be connected. If you could please explain or link me to a site that might help clarify, it would be greatly appreciated...

Mumbles - 5-2-2004 at 19:41

There are two kinds of connecting glasware. Ground glass and not ground glass.

Ground glass will have a number with it. 24/40 is fairly common in the US. As for other sizes there are a little bit harder to find, in the US at least. A ground glass joint is like a puzzle. One male piece will fit into one female piece perfectly. Any two joints of the same size will fit together, well they should anyway.

Non ground glass flasks and such are said to have tooled mouths. They'll have a number that goes with this too. The number is the size of stopper that will fit into the mouth. Basically everything non ground glass will be concencted together by rubber stoppers and glass tubing.

vulture - 6-2-2004 at 07:04

In europe, 29/32 joints are the standard.

Make sure that the glassware you buy is all borosilicate glass. Joints of different types of glas will crack due to different expansion coefficients when heating them.

Mendeleev - 6-2-2004 at 20:18

I also had a glassware question that I posted on another forum, but seem to be getting no answer. Why is it that round bottom flasks are preffered to flat bottom flasks for distilling? I got to wondering this because all of the websites that sell ground glass equipment sell the flat bottom flasks, but if they sell a fully constructed ready to go apparatus then it is always round bottom. It seems less convenient to me as they have to have a heating mantle instead of a hot plate, and you can't use magnetic stirrers with them. I was wondering if maybe flat bottom flasks implode in vacuum distillation, but I do not know if this is true.

unionised - 7-2-2004 at 05:12

Flat bottomed flasks are likely to implode under vacuum.
I generally use a water bath or oil bath for heating stuff when I distill it and so a RB flask is no problem. I also usually find that the mag stirer works fine in RB flasks.

If the flask has more nekcs than you need the easiest thing to do is put stoppers in them. It's cheaper to get a 3 neck flask and 2 stoppers than to get 3 flasks, one of each with 1, 2 and 3 necks.

On the offchance that anyone cares, those numbers (like 29/32) are the diameter of the large end and the length of the ground cone in mm. The angle is a standard 1 in 10 taper.

Glad someone explained the taper protocol.(zinc shot)

Hermes_Trismegistus - 7-2-2004 at 07:53

I'd like to add something on the topic of baths. I've found oil baths to be messy and I always end up with a pernicious film in the form of a ring on the glassware.

and water does have such a low liquid range.

I used to use white sandbox sand, but it would invariably get everywhere. especially stuck to the silicone oil I seal the ground glass joints with. Just a grain or two would break the seal and make a gawdawful noise that make fingernails on a slate blackboard seem like wonderful muscic.

The only upside to the sand was never having to add boiling chips to anything.

What I have really gotten fond of using is ZINC SHOT. I get it in a jar at the Canadian Tire (you yanks'd get it at a hunters supply shop I guess) and it works wonders. It has a relatively low heat capacity and transmits heat better than you would think.

I think the best recommendation for zinc shot is that its lag time is miniscule in comparison to water or sand. In fact, the limiting factor is usually the container you use for the bath!

It's cheap and comes in a durable round carton with its own pouring spout. The one I buy, even has its own wide mouth funnel included!:)

vulture - 7-2-2004 at 08:10

A saturated Solution of CaCl2 boils at 178C which is very good for a water bath.

Hermes, zink melts at 419C, isn't that a little hot?

Also, the low heat capacity causes it to heat up fast, possibly too fast for the glass. Remember that the temperature difference between inside and outside of the flask should not exceed 30C, certainly under reduced pressure.

Organikum - 7-2-2004 at 08:49

I believe Hermes doesnt melt the zinc but uses it similar to a sandbath - where the sand also is not molten, isnt it?

If using a waterbath - or salt saturated water, it is a good idea to add some hard paraffine to the bath - this melts at about 50°C and forms a thin film on the surface preventing evaporation almost completely. I hate this sauna-touch waterbaths usually have....

Paraffine wax from candles works fine. Make sure to get paraffine and not stearine candles.

vulture - 7-2-2004 at 10:47

Doesn't that cause splattering?

huh ?

Organikum - 7-2-2004 at 13:25

Adding water to hot oil causes splattering.
Adding an small amount of an longchainhydrocarbon to hot water makes an film on the surface.

I found this in a paper on lab-practice from a german university - it sounded good, was tried and works well.

What do you think could splatter here?

Mendeleev - 7-2-2004 at 14:47

So flat bottom flasks are more likely to implode under vacuum eh? Just how likely, is it a guarantee or just more probable that they will implode? If anyone has any good glassware sites please post them, here are my top four listed in order from best to less best:

1. http://www.chemglass.com/
2. http://www.unitedglasstech.com/
3. http://www.elementalscientific.net/
4. http://www.wilmad-labglass.com/

Also what is the purpose of having so many necks on flasks, two I can understand, but 3, 4, and 5? What is the purpose unless you have a complex process reactor like on www.chemglass.com? Should you in theory have such a five neck flask would you hook up the adapter/condenser to the middle neck or the outer necks. The reason I ask is that their largest flask the 22 liter five neck has four outer 24/40 necks and the center one is 45/50. They have 45/50 flasks, and adapters, but I could not find a 45/50 condenser, and I am trying to rig the largest possible still.

[Edited on 7-2-2004 by Mendeleev]

Mumbles - 7-2-2004 at 15:15

With 5 necks you can have 5 of the following at the same time.

Distilling
Addition
Gas inlet
Manual Stirrer
Reaction Temp
Gas bubbler

I had a few more, but they are slipping my mind as of now.

[Edited on 2-7-2004 by Mumbles]

Hmmm!

Hermes_Trismegistus - 7-2-2004 at 15:32

O Canada!

http://www.indigo.com/

http://www.fcsurplus.ca/shopping/shopdisplayproducts.asp?id=...

coming soon (er or later)
http://www.torontosurplus.com/


http://labsurplus.com/html/gla.html

(these guys are selling a stirring hotplate for 75$)

american
http://www.sciplus.com/category.cfm?subsection=4

http://www.macnanbio.com/

repairs and hard to find items...

http://www.medscitech.com/surplusglassware.htm

http://www.sciencestockroom.com/

others
http://www.spendloveresearch.org/XSPages/glassware.htm

aww screw it....look at em yerselves, they're like fleas on a dog's arse!
http://www.spacetransportation.org/Instruments_and_Supplies/...

Mendeleev - 7-2-2004 at 15:32

D'oh, I should have thought of that, I guess my knowledge of applied chemistry is not quite are good as I thouth, or maybe not good at all, but either way, I suppose that means that the distillation adapter, column can be attached to the outer neck. Thanks Hermes, some of those are pretty damn good! Yet upont closer inspection none of these sources are what you would call, comprehensive.

[Edited on 7-2-2004 by Mendeleev]

[Edited on 8-2-2004 by Mendeleev]

Hermes_Trismegistus - 7-2-2004 at 15:35

Quote:
Originally posted by Mumbles
With 5 necks you can have 5 of the following at the same time.

Distilling
Addition
Gas inlet
Manual Stirrer
Reaction Temp
Gas bubbler

I had a few more, but they are slipping my mind as of now.

[Edited on 2-7-2004 by Mumbles]


yessireebob, You also usually don't want to break a vacuum to change addition funnels while a reaction is proceeding. Not all synth's are one step-two reactant:P

Glassware Site

Taz - 7-3-2005 at 19:20

http://www.organicglassware.com/

Blind Angel - 7-3-2005 at 20:43

Kinda off topic, but for how much can i get a old used cheap heating mantle for 500 or 1000ml, i looked on ebay but they don't go lower than ~70$, am I too cheap or can I get a better deal by shopping more?
Also, what should be my next big purchase:
- 14/20 Micro Distillation Apparatus
- 2/3 Necked Flask
- Reflux/Friedrich condenser
- Soxhlet Separator
???
I'm mostly asking or reccurrance of the needed glassware than the immediate use. Also if someone could provide me a link to the use of a Soxhlet I would be very pleased, thx :)

Oh, and about Gas Mask, does old army one can be usefull or they're only decorative?

[Edited on 8-3-2005 by Blind Angel]

Magpie - 7-3-2005 at 21:09

Blind Angel I picked up a 500 mL mantle for $39 and a 100 mL mantle for $9. But I think I was lucky to get them that cheap.

For a big purchase I'm a real believer in a glassware kit. I have and like the 19/22 ST size but have to admit that the 24/40 seems more popular. The beauty of the kit is that it is all gg and can be rearranged in many different configurations depending on the application, i.e., distillation, steam distillation, fractional distillation, reaction w/reflux, etc.

I'm looking for a 45/50 Alihn condenser to go with my Soxhlet extractor. I've been waiting for a long time as the ebay prices are too high in my opinion. Fortunately I'm not obsessing about some experiment that needs it.

neutrino - 8-3-2005 at 03:16

$39? I got a used 500mL mantle for ~$10 on eBay. Strange, no one else seemed to want it.

Quince - 10-3-2005 at 01:41

I want to store concentrated HNO3 in an amber glass bottle with a ground glass stopper. However, I've read that ground glass joints should be lubricated. But what sort of grease will withstand that acid? Is silicon grease OK? I have the plumber's Teflon tape, but that's not very convenient as I'd have to rewind it every time I open the thing.

Magpie - 10-3-2005 at 15:36

I keep a very thin film of silicone stopcock grease on my gg organic kit connections. But I have never heard that reagent bottle gg stoppers should generally be lubed. It would make sense if you find that the joint isn't vapor tight or you are storing something that attacks glass like sodium hydroxide.