Sciencemadness Discussion Board

Beginner's question about test tubes

Random - 6-3-2011 at 03:27

I am thinking about doing some experiments (heating urea and carboxylic acid to make amide). While that needs molten urea which could be at 150 degrees celsius, I am scared if the test tube could be broken somehow by heat as I wouldn't want to be sprayed by the molten hot liquid inside.

I would heat the test tube with a candle. Now, could a test tube easily break or maybe even I could make something for protection of myself so I would be safe?

Saerynide - 6-3-2011 at 04:01

150 C should most definately be fine if your test tube is boro. If its soda lime, it should still be ok, just definately do not put it on a cold surface (ie, steel counter top) when it's still very hot. Always point the test tube away from yourself and everyone else including animals.

watson.fawkes - 6-3-2011 at 09:56

Quote: Originally posted by Random  
I would heat the test tube with a candle. Now, could a test tube easily break or maybe even I could make something for protection of myself so I would be safe?
It's not heat itself, but thermal gradients, that break glass. Reduce thermal gradients by slow and even heating, heat baths, etc. For this purpose, you might try wrapping the tube with Al foil to create a more isothermal surface.

Also, do a test first with an inert and non-flammable material.

bbartlog - 6-3-2011 at 10:12

Candle is not a great heat source as it will tend to deposit carbon black on items placed in the flame (will make it hard to see what is going on in the test tube). There's a reason people use alcohol burners.
And don't worry about a test tube heated to 150C. Anything sold under that name should be able to take that much heat.

Random - 6-3-2011 at 12:00

Well, I am not sure which type of glass it is, I bought them in the pharmacy store. I know that about candle, it will deposit carbon, but it's still cheaper than alcohol so I will use it just because of this. Maybe wrapping the test tube in al foil could also protect me from hot liquids if it would explode, I should try that.

Thanks for the answers :)

Saerynide - 7-3-2011 at 05:30

Ah those test tubes. They should be fine. I've even put those over a gas stove flame (very carefully) 8 years ago. I was afraid it would break on me and spray me with hot liquid, so I fashioned a holder to keep it several arm lengths away using an unbent coat hanger :D I didnt wrap it in foil because then I wouldnt be able to see the contents.

[Edited on 3/7/2011 by Saerynide]

Bot0nist - 7-3-2011 at 08:10

I melt KNO<sub>3</sub> (334c) in my cheap test tubes from India to do the old oxidizing carbon trick, and I have never had so much as a crack. I have even boiled it at ~400c with no trouble at all. If its boro then don't worry.

Still, use common sense and were gloves, goggles/face shield, and a good lab apron or protective clothing.

Also, you can make a little DIY alcohol lamp with 70% isopropanol and some cotton shoelace if your crafty. Much better than a candle for low temp operations

:D Safety first! :D

[Edited on 7-3-2011 by Bot0nist]

[Edited on 7-3-2011 by Bot0nist]

Random - 16-3-2011 at 11:34

Safety is of course first of all :D

Maybe I'll make some simple face shield just to be sure my face will be fine if it explodes, though, now you remind me of something in golden book of chemistry experiments.

Those hanger wires, I could make a test tube stand out of aluminium wire, put a candle under it, light it and go away. If it breaks, I won't be near that :D Just I need to see how I will make holder, that test tubes always fall out, maybe some toilet paper or something else soft between the test tube and wire to hold it.

Bot0nist - 16-3-2011 at 11:56

Some all purpose clamps are cheap if you have the means to start setting up a little lab. I think unitednuclear.com has some pretty nice little starter kits for cheap that has many of the 'student grade' apparatuses that you may need.. Some members here will tell you to avoid them, but I haven't had any trouble with them at all.

<a href="http://www.youtube.com/watch?v=Y3Jxhbg0k4c">Here</a> is a good video of the KNO<sub>3</sub> carbon trick.

White Yeti - 29-7-2011 at 06:27

In this case, since the reagents are relatively unreactive, I would experiment with other reaction vessel materials. I am personally not fond of glass when it comes to dry distillation and high temperature reactions. In that situation, I would take that anodized aluminium reaction vessel I just so happen to have and use it instead. Also, why use a test tube? The solidified contents of the tube will be a pain to remove. Of course, if you use an open container, make sure to place some kind of blast shield between you and the vessel.

redox - 29-7-2011 at 06:43

I have found test tubes to be extremely robust when it comes to extreme heating. I regularly heatblast test tubes with a very powerful propane torch to heat small samples. Nevertheless, I keep a acrylic sash in between me and the sample, but I have never had a break.