mericad193724
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Boiling chips
I have had a problem with "bumping" when boiling liquids...I have a $20 electric hotplate used for cooking food and it gets pretty much red hot. When
I put beakers on it, they make weird sounds and start jumping at around 80C. I was boiling a Ferrous Sulfate solution when it started jumping more and
more so I grabbed it to take it off and it jumped again scaring me so I spilt the stuff all over and got some on me.
I now know that boiling chips can stop this from happening...I really don't want to order some so what can I use as a impromptu solution... searching
i found hints at sand, broken glass, pottery, and Internet says Teflon(not sure).
Any recommendations/suggestions???
Mericad
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BromicAcid
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Was there any precipiate in your ferrous sulfate solution that was boiling. When evaporating to dryness, if there is a large amount of solid that
begins settling out of the solution it leads to bumping where the beaker can literally jump off the hotplate. If there was no solid though boiling
chips will work. As you said there are lots of things that can work. The function is to act as a nucleation surface for the genesis of new bubbles
from the liquid. I personally use broken pyrex as I have an abundance of it although I have seen other things, expecially pottery, used in practice.
I believe the boiling stones that are availibe commercially are either a porus ceramic or obsidian glass, I think that I've seen both.
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Darkblade48
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In a pinch, I've used broken ceramic mugs as boiling chips (of course, I have great fun in smashing the cups into useable boiling chip sizes first).
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mericad193724
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how much is necessary if I were to use broken pottery...I can chip off a few pieces from the pots around the house . One tiny 1cmx1cm piece, a handful of sand-like pottery, or a teaspoon of really
finely crushed pottery?
Mericad
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Tacho
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About 5 pieces with the size of a grain of rice or corn should do it.
I strongly advise you to use porous ceramic. I am surprised that Bromic had good results using pyrex, it seemed to me that porosity was crucial.
Don't re-use boiling stones. Add new ones to each boiling, even if it's the same reaction.
Bromic is right, the worst bumping happens when you have solids settled at the bottom of the flask. Really dangerous bumps. It seems to me that your
solution may be 80ºC where your thermometer is, but higher temperatures are building up under the sediments.
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not_important
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Anything with sharp edges can provide nucleation points for boiling, broken glass does work. Porous meterials generally work better. This is oft
attributed to the air trapped in the porous material "bubbling out", the fact that if used in a vacuum distallation and at one point the vacuum is
released, which forces the liquid into the pores, the boiling chips will not work after vacuum is reapplied.
I think that what is happening is that the small air bubbles in the porous chips provide a space for the heated liquid to release vapour into. This
increases the size of the bubble, which eventally gets big enough to squirt some of itself out of the pore. It's easier to release vapour into an
existing bubble that to create a bubble in the liquid; however it is easier to form a bubble on a sharp point that it is on a smooth surface or in the
bulk liquid.
Some lab technique books talk about fusing poweder glass onto the inner surface of a flask, to give it a rough surface. It's a lot of trouble, I
can't see anyone going through it unless it did result in an improvement.
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Eclectic
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Chips carved from a chunk of Teflon wth a sharp knife work fairly well also. I think it's because of the unwettability and sharp edges.
[Edited on 9-8-2006 by Eclectic]
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unionised
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Depending on the stuff you are boiling you can get away with a splinter of wood with a bit of copper wire round it as a sinker.
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mericad193724
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I just tried pottery...no good I stopped the boiling before thinks started to get violent. Sounds(bumping) started at 50C. I am trying to isolate
Ascorbic acid from Vit.C tablets so I crushed them up and dissolved then in 300ml water. There is insoluble stuff on top and bottom. The sounds are
about every few seconds with a big one every ten. I tried sand and pottery and they didn't help. I am not evaporating to dryness, haven't even
evaporated 1ml. I am just trying to boil it do dissolve all the Vit.C
What is the diagnosis?
Mericad
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pantone159
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| Quote: | Originally posted by mericad193724
I am trying to isolate Ascorbic acid from Vit.C tablets so I crushed them up and dissolved then in 300ml water. There is insoluble stuff on top and
bottom. I am just trying to boil it do dissolve all the Vit.C
What is the diagnosis?
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Ascorbic acid dissolves easily, you shouldn't need to boil to dissolve it. Anything that doesn't go into solution with some stirring is insoluble
excipients.
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neutrino
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Are you using glazed or unglazed pottery? You want the porus unglazed stuff for boiling stones.
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mericad193724
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I am using unglazed pottery.
I don't want to start a whole new thread for this so I will ask here....
I am trying to make a T connector out of glass tubing. The tubing is about 15mm and I got it from a neon sign shop. Making the connector is not a
problem I seal one end, Blow a hole in the tube, make it wider and attach a second peace at a 45 degree angle (this is for my distillation apparatus).
The problem is when I let the tube cool by holding it in air for about 2 min it develops cracks which make the tube I just made useless. I have gone
through 5 of these. I only have 2 feet of tubing left so could someone give me a tip...I an using a propane torch to heat the tubes.
thanks
Mericad
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neutrino
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Working glass consists of heating the glass to soften it, working it while soft, and cooling it. Unfortunately this causes large internal strains in
the glass that make it <b>very</b> prone to cracking if you let it cool normally. This problem is almost universal in the world of
glassworking.*
The solution is called annealing. This consists of letting the glass cool very slowly so the internal strains can be eased.
There are several ways of annealing glass at home. The first is turning down the oxygen in your flame to coat the glass with a layer of soot and
manipulating the temperature of the glass with the aid of this soot layer. I don't know the specifics of this so you'll have to search around.
Another way is to heat the entire piece red hot and put it between two blankets of rock wool or to in a can of vermiculite (available as a soil
conditioner). This allows the glass to cool very slowly and ease internal tensions.
Unless you have access to an annealing oven (used by professional glassblowers), I think these are your best options. Still, search around and see
what you can find.
*The only types of glass that I know of that are exempt from this are quartz and high silica (Vycor-type) glasses, which have extremely low
coefficients of thermal expansion.
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The_Davster
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I can confirm about the quartz and Vycor glass tubing. I have dipped ampoules made of one of these types into cool water from white heat. No
cracking at all. Damn good stuff.
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SpeedyDreamer
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http://www.ecu.edu/glassblowing/gb.htm
Very imformative site on glassblowing.
I\'ve got friends in low places.....
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DrP
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back to anti bumping - when I used to purify monomer with small scale distillations, I had a problem with it boiling over and shooting through the
column. Putting some glass wool in the colomn itself helped this alot. instead of boiling over the liquid hit the wool and fell back into the vessel
rather than shooting over into the collecter. The distillation would take alittle longer though as some of the monomer would condense on the wool.
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