Today I noticed that I was having stirring problems on my Glas Col 2L heated mantle with built in magnetic stirring. It uses the Glas Col Stir Controll II device to control magnetic stir speed. For those who are familiar, it has a button to reset the field when the stir bar gets stuck and “spins out”.
Well, I can’t get it to stir any more! Tried a couple different fresh stir bars in the lab and its just wobbling. Has anyone ever had one of these break on them? Seems strange. Looking for a quick fix. I might be able to borrow another mantle and stir control to see if that is indeed the problem. Very frustrating. Any reasonable work around to get distilling in the meantime without stirring? Boiling stones? I’d rather not but…
Does anyone have a 5l (or larger) heat stir mantle I can use for 2nd pass on a batch?
My Glas Col was set at 200c and read an internal temp of 323c! My 22l boiling flask cracked, so far the only replacement 22l is a week out (minimum) from now. Thank you
Yes, the Tc was inside the flask. I recently read @anon42519203 tek regarding the TC’s location better serving the process on the outside of the bf between the glass and mantle.
Yes, the best way to control a heater is with a sensor directly on heater. If you have a thermocouple inside the flask you are subject to overheating. This can push your magnet above the curie temp of both the magnet and the stirbar.
Tomorrow’s priority is to find a solution and run it. My bf replacement has a 1 week lead time from American Scientific. I need replacements on hand, lesson learned.
Boiling stones do not work for providing nucleation sites in vacuum distillation. The old school work around was to insert a bleeder tube into the boiling puddle through a side neck instead of a thermometer. The tip would be placed at the bottom of the puddle and a valve allows it to “leak” bubbles into the boiling puddle under vacuum. This eliminates the need for a stir bar. I have never needed this configuration so cut my bleeder tube into a length better suited for a steam injector. I repurpose my junk drawer.
Hmmm… Boiling chips do work under modest vacuum (50 torr) in 20 litre flasks based on previous experiences I’ve had… it must depend on absolute pressure.
Are there a better stir bar to use? I seem to demagnetize the bar by the end of every run, not sure if they are just cheap or if I’m doing something wrong…
You are heating the stir bar up to the point it loses its magnetism. Almost certainly your mantle is set too high for this process. I did the same to mine at first. Many small mantle manufacturers do not even offer a stir bar option because mantles can easily be set high enough to demagnetize the stir bar.
I would only be doing an internet search about degaussing to know because I only had an analog mantle. I would set it on nearly the highest setting. No matter what stir bar I used they all stopped being a magnet in one run. It was way too hot in hindsight but I don’t know the number.
American Scientific. I need replacements on hand, lesson learned.