loveoforganic - 13-3-2010 at 10:46
I was thinking of taking a test tube and deforming the lip of it with a torch so that it's narrower. I'd then add sample (probably a small amount of
bromine) and seal it off with the torch. Am I going to be making a dangerous pressure situation by doing so? I feel like any partial vacuum I made
with the torch would be quickly compensated for by bromine vapor. Thoughts?
Thanks!
1281371269 - 13-3-2010 at 12:12
Maybe you could cool the bottom of the test tube in an ice bath while you heated the top? I don't think the vacuum would be an issue. We did an
experiment in a physics lesson in which electricity was passed through various gases encased in glass tubes. One of these was mercury - kept as a gas
by the low pressure inside the glass. It was a fairly thin tube, so it seems glass can withstand fairly large pressure differentials.
loveoforganic - 13-3-2010 at 14:12
Yes, I was definitely planning on keeping the sample chilled while heating the top. Just tried to do a demo run with an empty tube and it looks like
I definitely need mapp gas - propane messed with the borosilicate a bit, but not nearly enough for me to mold it as desired.
Thanks 
UnintentionalChaos - 13-3-2010 at 14:25
I have no problems ampouling with a cheap plumbing torch. I use two pairs of lockjaw pliers with folded aluminum foil as cushioning to hold the test
tube. Then, rotate in the flame about an inch from the top and gently pull the two halves away from each other to make a neck. Add the sample in, dip
the bottom end in an ice-salt bath and then reapply flame to the neck. pull it sideways and fold it over on itself, then "wrap" it around the stub.
Nobody said it would be the prettiest thing ever, but it's airtight.
MagicJigPipe - 13-3-2010 at 20:59
Propane is definitely adequate for working with glass. In some cases MAPP may be detrimental depending on what you are doing exactly (and how skilled
you are). With propane there is more room for error (heats up slower...)
I used to keep both around just in case. Also a MAPP/O2 "setup" I found at Home Depot is useful for small welding jobs (the O2 runs out very
quickly... I wonder if I could put O2 into one of those Medical E cylinders to use with the welding; probably not worth it I suppose).
loveoforganic - 14-3-2010 at 00:16
Propane worked fine. On your assurances, I gave it another go and I just needed more patience. I'm used to the speed of working with mapp in lab.
Also, the value of a test run is priceless. I added some food dyed water to the test tube to give it a hint of realism, and as I sealed, a drop of
water stuck in there somehow boiled and shot gas into the contained water, which erupted through a tiny hole. Lucky that the test tube didn't
explode. Even luckier I wasn't using bromine yet.
So for anyone reading this, don't let your sample touch where you're sealing in the first place, and if you do, boil that crap off before sealing.
Thanks for all the help.
Skyjumper - 14-3-2010 at 11:10
Chill the bromine in ice water bath. even better, freeze it (freezes at -7 c) then seal it. That's not necessary for iodine, and impossible for
chlorine (or, impractical).
watson.fawkes - 14-3-2010 at 13:13
Here's a page on sealing glass ampules at the ASGS site. I note two items relative to the current discussion. One, the ampules are pre-necked at the point they
will later be sealed. Two, the process assumes that the interior of the ampule is at negative pressure relative to the outside by means of vacuum.
This allows the neck to collapse with just heat applied; there's no need to move the ampule until the seal is complete and it's time to tip off.
Also, pay attention to annealing, as discussed on that page.