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Author: Subject: Correct position of thermometer in Claisen adapter
Bezaleel
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[*] posted on 25-3-2021 at 14:50
Correct position of thermometer in Claisen adapter


The supplier I bought from, indicated that this (see photo) should be the correct position of the thermometer bulb, but to me it feels as if the region in the green circle would be a more correct position. (On the simple adapter, I always put the bulb before the middle of the outlet to the condenser, but with the ground joints I cannot adjust its position.)

Any thoughts?

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Fyndium
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[*] posted on 25-3-2021 at 14:55


It's a matter of degree or less, but the bottom should be at takeoff level.

I torched one thermowell shorter myself to match the depth.
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Bezaleel
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[*] posted on 25-3-2021 at 15:19


Thanks, Fyndium. Just to make sure I understand you correctly, you say that the bottom should be where I drew the green line, right? So it should ideally be a cm higher than where it is now?

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RustyShackleford
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[*] posted on 25-3-2021 at 15:33


I usually place it so its just below the line like it is in the image you posted. I dont think it matters if its below the line (by like 1-2cm, but above can be inaccurate with low flow rate.

[Edited on 25-3-2021 by RustyShackleford]
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Sulaiman
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[*] posted on 25-3-2021 at 19:01


I agree with your supplier,
and you should 'calibrate' your thermometer in the position that you will use it,
distill water and, if practical, a pure sample of your target liquid.

'Ideally' the thermometer should be in contact with the vapour over its specified immersion depth,
and the adapter should be thermally insulated to reduce any temperature gradients.
This is rarely practical so in-situ calibration and consistent location is recommended.




CAUTION : Hobby Chemist, not Professional or even Amateur
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Fyndium
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[*] posted on 26-3-2021 at 01:10


What is said above is what I agree with.

The very specific position is not super-accurate, unless you are measuring tenths or hundreds of a degree differences, as long as the head is well immersed in the vapors and is at least somewhat in line with the takeoff, it will give correct readings.

For more accurate measurements, like said, you will have to calibrate the thermometer and calculate the barometric pressure, your elevation, and such things. When I distilled ethanol, I got consistent high readouts and did everything else, after I calculated the barometric pressure difference and it was absolutely just on point at azeotrope. 1010bar barometric pressure can cause one % difference, which makes 78.2C show up as 78.9C.
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[*] posted on 26-3-2021 at 11:20


I did some tests here:
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
I found, that when the flask was almost empty, the vapor was further heated above boiling point very likely by hot flask walls.
e.g. I recorded 106 C for boiling water
so not only the thermometer bulb position is important but also the fulness / emptiness of the flask, whether the pot with hot oil is covered by Al foil, how much hotter bath is used, whether the level of the liquid in distilling flask is above the level of oil bath or already below and how deep below (so bigger glass area is heated above boiling point) etc




If there is a heaven, it seems not to be materially based. Does chemistry exist there and if yes, how does it look like? Are there good souls well supplied with laboratory equipment, glass, chemicals and information?
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Bezaleel
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[*] posted on 26-3-2021 at 16:23


Thank you all for your responses! This gives me a very clear idea on what to take into consideration when reading off my thermometer and setting up a proper distillation. I already recognise a lot of the things you have pointed out - thanks for your explanations.

@Fyndium @Sulaiman, so far my applications do not require very high accuracy, but I wanted to make sure I do not introduce any unnecessary error by wrong positioning.

@Fery, thanks for the link. A very nice read about your pineapple ester also.
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