Sciencemadness Discussion Board

Rubber stoppers, or Glass Joints?

SimplyChem - 27-3-2014 at 17:26

Hello All :)
I am a bit new to chemistry, but am looking to purchase a distillation apparatus to distill some nitric acid and things of the like.

(I will post a photo of the apparatus I have been looking at. Seems good enough for a beginner like me )

After reading that someone's rubber stopper melted, I am debating on whether or not to purchase a rubber stopper to fit my boiling flask, or a glass joint. (70 degrees?)

Also, I don't want to risk getting glassware stuck together, as I don't really want to pay $30 for some Corning grease.
Anyway, experiences and input would be greatly appreciated.

- A fellow noob.

Chemosynthesis - 27-3-2014 at 17:29

I always use glass. For most hobby activities, vaseline is actually a decent substitute for greasing your joints.

TheChemiKid - 27-3-2014 at 17:30

Buy a glass joint. Nitric Acid will completely destroy any plastic or rubber. The glass may be more expensive, but it will serve you in the long run.

SimplyChem - 27-3-2014 at 17:33

Thanks for the input! I had thought Vaseline would work :D
Haha, just hoping it doesn't react with anything. That would be an unpleasant surprise. :)

Its just a shame most glassware I see online is so expensive.
Seems a bit much for what it is.
this "Distillation Adapter, 75° 3-way, 24/29" I have been looking at is 20 dollars!

HeYBrO - 27-3-2014 at 17:59

try ebay. type the size joint you want and a plethora of kits should appear. Ask Dr.Bob, he is a member here who sells second hand glassware that is in immaculate condition (most is new intact) and his prices cannot be matched. It is a sticky thread in the reagents and equipment thread. Have fun!

SimplyChem - 27-3-2014 at 18:07

Thanks! :D

thebean - 27-3-2014 at 18:17

Use glass joints. Also someone said that vaseline makes good lube. It's decent but I prefer silicon plumber's lube. It's more heat resistant.

Steam - 27-3-2014 at 18:40

If you really want to get fancy you can shell out the extra $7.50 and purchase a thing of dow highvac grease! ;)

thesmug - 27-3-2014 at 19:55

Quote: Originally posted by Steam  
If you really want to get fancy you can shell out the extra $7.50 and purchase a thing of dow highvac grease! ;)

Wow! Where does one find this so cheaply? Also to OP, based on what you've said, I think you're buying from Homesciencetools, correct? I have their standard organic chemistry glassware kit and it's very good quality and extremely useful for many procedures, however it is extremely expensive. I would suggest you get something with similar or identical parts as a starting point (though I don't think you probably need a fractionating column). Of course buy it from somewhere cheaper.

ParadoxChem126 - 27-3-2014 at 20:09

Teflon tape can also be used to seal ground joints. In some ways, it is better than grease because it does not usually dissolve in solvents. Grease can sometimes dissolve in the reaction solvent and contaminate the product.
Quote: Originally posted by SimplyChem  
Also, I don't want to risk getting glassware stuck together, as I don't really want to pay $30 for some Corning grease.


Ground joints can usually be separated by applying a little heat from a hot air gun. The heat causes the outer joint to expand slightly, allowing the inner one to be pulled out.

I agree that you should invest in a ground glass apparatus. They are much more versatile and convenient than traditional rubber stopper setups.

Zyklon-A - 27-3-2014 at 20:26

Petrolium jelly will melt with very little heat. Get all glass.

thesmug - 27-3-2014 at 20:33

Quote: Originally posted by Zyklonb  
Petrolium jelly will melt with very little heat. Get all glass.

I think he was asking about sealing said glass joints. Still a very good point, though.

Zyklon-A - 28-3-2014 at 05:28

Yeah, I know. I guess a very thin coat might not be affected even if it is above it's melting point.
It will also vaporize slowly above it's melting point.

Chemosynthesis - 28-3-2014 at 06:03

Quote: Originally posted by Zyklonb  
Yeah, I know. I guess a very thin coat might not be affected even if it is above it's melting point.
It will also vaporize slowly above it's melting point.

Definitely not ideal, but it's an old trick from Kubrick, iirc.

MrHomeScientist - 28-3-2014 at 06:27

I use silicon "faucet grease" from the plumber's section (I can't remember the actual name - it comes in a little round grey plastic container). I'm wary of using teflon tape, because if you don't wrap it just right the seal can be compromised. They do make teflon sleeves specifically for ground glass joints that sound very nice, but are quite expensive.

If you're reluctant about splurging on expensive grease, just remember that one tube of grease will last you forever!

hissingnoise - 28-3-2014 at 06:36

And there's always Glindemann?

Funkerman23 - 28-3-2014 at 06:52

Quote: Originally posted by hissingnoise  
And there's always Glindemann?

A great solution, were it not for the main seller of said rings. According to the homepage linked, its sold by Sigma. Not really an option for us amateurs unless a new seller emerges.

[Edited on 28-3-2014 by Funkerman23]

Chemosynthesis - 28-3-2014 at 23:56

Obviously your mikeage may vary, but I generally only even use grease when applying vacuum, inert atmosphere, and sometimes drying tubes anyway. Perhaps the seldom prolonged alkaline reaction, but I have been able to avoid joint seizing with prompt and routine cleaning. I keep forgetting about those Teflon sleeves and tape since I never worked in a lab that used them on anything I did.

More on rubber... it can not only melt, but react. The ability to drill holes or make slits in them is what makes them most useful, in my opinion. Additionally, old rubber loses some of its plasticity for a variety of reasons (ex. leaching and perhaps UV polymerization) over time. Properly respected glass should last you a long time.

*FWOOSH* - 29-3-2014 at 09:27

NEVER use rubber on vacuum setups, I've had a stopper get pulled so tightly into a joint under simple aspirator vacuum that it actually SHATTERED a piece of glassware :mad:

Chemosynthesis - 29-3-2014 at 10:13

Quote: Originally posted by *FWOOSH*  
NEVER use rubber on vacuum setups, I've had a stopper get pulled so tightly into a joint under simple aspirator vacuum that it actually SHATTERED a piece of glassware :mad:

Excellent advice. I hadn't even thought of that... however, I would add the caveat that you may use rubber stoppers in vacuum if there is some kind of pressure release hole drilled in, such as having two holes to link a thick walled flask in series while serving as a water/vacuum trap.