IceHomer (Newbee)
07-01-03 23:17
No 443838
      Clamp cracked condenser  Bookmark   

So enough messing around with ghetto-ware. I decided to get the proper labware. Easily and inexpensively enough, I obtained, among other essentials, a reflux condenser and boiling flask. So far so good.

But my inexperience showed through (yet again) when attempting to set up the apparatus on a ring stand. The only clamps available were a buret and a three-fingered clamp. Not knowing how much to tighten the thumb-screws, the condenser sprung cracks at the top and bottom ends (just above and below both ST joints) due to (guess it) over-tightening. I literally screwed the condenser, but to what extent is the query of this post.

I've got another condenser (of a different type) on the way, but lack of funds means it will not replace the cracked one soon enough. Can I still use my condenser for a reaction in the meantime, I wonder?

The cracks are only on the water-jacket (outside) part, except for a small one located (unfortunately) just below the very first inner condenser bulb. In order to determine how bad the cracks were, I blew lightly into the top joint whilst covering the bottom end with my hand. A chunk of glass flew out in between the condenser top and joint. I don't think that should be a problem, since the gas will not reach that far up (theoretically).

Speaking with a guy at a lab supply shop, I was told that it should do fine if I epoxy and/or duct-tape the cracked parts. The heat from the reflux will not be much more than 100C, but I don't know how well Pyrex-type glass holds up in this condition when the glass has already been compromised.

My main concern is that the inner bulb crack will give way, letting tap water flood the reaction flask. I realize now, after reading Zubrick, that I should have clamped the bottom at the neck of the flask. (But if I did that at the time, I probably would have broken the flask's neck.)

I haven't yet attempted a "dry run", but will try that soon before the big show. I suppose I'll have the new condenser on hand prior to doing the real thing, but regardless, does anyone have any tips?

Just another reason why newbees should at least take an intro course to organic chemistry before messing around without any real experience.

Drug use carries a monkey-back guarantee.
 
 
 
 
    hCiLdOdUeDn
(Hive Addict)
07-01-03 23:22
No 443841
      Dont try it.  Bookmark   

Hot vapors from the reaction touching the cool cracked glass from the cold water running through the condensor, will crack the condensor even further and may eventually flood the flask with condensor water.

I wouldnt reccomend it. Just sit back and chill, while waiting for your new condensor to come in.
 
 
 
 
    nitrous351
(Hive Bee)
07-02-03 01:49
No 443864
      I agree  Bookmark   

... with hidden cloud. Cracked glassware is usually trash. Wait for your new condenser to come, then do the reaction. SOunds like you need to learn to clamp though....you only need it tight enough so that the glass can't fall from the clamp's grip. If you tightened it so much that you broke it, you tightened it waaaay too much! You'll get the hang of it though. Remember when rigging a setup to build it like a house. Start with the foundation first. In a distillation/reflux setup, start with your boiling flask. If you're using a heating mantle, start with the mantle. With heating mantles, make sure you use an iron ring so you can drop the heat if the rxn gets out of hand. Work your way out from the boiling flask. Clamp everything loosely til you know it's how you want it. Then tighten everything down (not too tight!), but you have to make sure that your ground glass joints still line up. If you're doing vacuum distillation, don't forget silicon high vacuum grease. good luck peace

D.A.R.E. = Drugs Are Really Exciting
 
 
 
 
    xboXer
(Hive Bee)
07-03-03 06:27
No 444133
      go and buy  Bookmark   

now that you have the 411 on the glass, take the clamps you have (any/all) get some vinyl tube that will fit the clamp fingers snugly, and "pad" your rigging ware. Also cut 1/2 to 1" pcs., slit them lengthwise, and slip them on your rings. (that support funnels) try to avoid ANY metal to glass contact! Vinyl is an excellent medium to use as it has major friction coefficient w/glass, so even slightly loose if the glass in the clamp is angled, it won't slide out. Finally the "tink-a-link" clink of glass and clamp is reduced to a bare minimum, which is a plus when the walls have ears....blush

P.S. make a condenser ala' Dwarfer if the need is immediate...
It is ghetto, but only if you do a shitty job making it cool

Karma? Karma is on Murphy's payroll. Nothing improper, it's freelance.