Random
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Beginner's question about test tubes
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?
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Saerynide
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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.
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watson.fawkes
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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.
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bbartlog
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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.
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Random
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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 
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Saerynide
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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  I didnt wrap it in foil because then I wouldnt be able to see the contents.
[Edited on 3/7/2011 by Saerynide]
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Bot0nist
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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
Safety first!
[Edited on 7-3-2011 by Bot0nist]
[Edited on 7-3-2011 by Bot0nist]
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Random
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Safety is of course first of all
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 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.
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Bot0nist
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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.
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White Yeti
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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.
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redox
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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.
My quite small but growing Youtube Channel: http://www.youtube.com/user/RealChemLabs
Newest video: Synthesis of Chloroform
The difference between chemists and chemical engineers: Chemists use test tubes, chemical engineers use buckets. |
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