There are the clues I found:
1. somehow the red alcohol in the thermometer became un-continuous. there are gas between the red-alcohol.
2. the hot plate was cold although the knob is still on the right position. Restarted the hotplate returned the heat.
3. What is more, the mineral oil bath became darker than before.
4. although cooling water is running, half of the methanol was gone. (open container reaction)
My conclusion is the hot plate is bad. It heated up to a very high temperature sometime in the night! The high temperature exceeded the range of the thermometer and destroyed it. Also it darkened the mineral oil.
This hotplate is the same one I used for the other accident! SEE PIC!
the mechanism of controlling temp of this kind of hot plate is by a electromagnetic relay. I can hear the "click" sound when it started to heat. When the temp reached a preset value, the clicking sound became intense.
It is not reliable. Never use this kind of hotplate!
4 comments:
That's the kind I use, and they're pretty nice. They can take some abuse, but they do eventually give out. I have one on the brink of death right now--I'm not sure if it's actually in its death throes or if it's just acting up because the wiring to the temperature probe isn't well insulated.
I know there should be an external probe. But I don't have that.
Anyway, it should use its internal temperature probe when there is no external probe.
why the left knob is turned to far right? isn't it too much for refluxing methanol?
i usually use external probe for this stirred and never encountered any problem with temperature control.
the pic is not the "real" one, I got it from the web.
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