Sciencemadness Discussion Board

Boiling chips

mericad193724 - 8-8-2006 at 19:07

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

BromicAcid - 8-8-2006 at 19:11

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.

Darkblade48 - 9-8-2006 at 03:04

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).

mericad193724 - 9-8-2006 at 04:36

how much is necessary if I were to use broken pottery...I can chip off a few pieces from the pots around the house:D. One tiny 1cmx1cm piece, a handful of sand-like pottery, or a teaspoon of really finely crushed pottery?

Mericad

Tacho - 9-8-2006 at 08:03

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.

not_important - 9-8-2006 at 08:33

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.

Eclectic - 9-8-2006 at 09:53

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]

unionised - 9-8-2006 at 10:15

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.

mericad193724 - 10-8-2006 at 12:26

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

pantone159 - 10-8-2006 at 13:34

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?


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.

neutrino - 10-8-2006 at 15:06

Are you using glazed or unglazed pottery? You want the porus unglazed stuff for boiling stones.

mericad193724 - 11-8-2006 at 08:54

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

neutrino - 11-8-2006 at 18:23

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.

The_Davster - 11-8-2006 at 19:00

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.

SpeedyDreamer - 11-8-2006 at 21:19

http://www.ecu.edu/glassblowing/gb.htm

Very imformative site on glassblowing.

DrP - 27-10-2006 at 00:59

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.