Author Topic: Yes you just stick your thermometer threw the...  (Read 3850 times)

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icexool

  • Guest
Yes you just stick your thermometer threw the...
« on: October 10, 2004, 01:40:00 PM »
Yes you just stick your thermometer threw the hole, and then you can insert it in a distilling setup for example.

embezzler

  • Guest
make sure you
« Reply #1 on: October 10, 2004, 02:25:00 PM »
put the thermometer in far enough to ensure that the distillate (or any other procedure you are carrying out) condenses on the thermometer to get an accurate reading .................the bulb should be where the horizontal part of number 11 meets the vertical part for distillation.


thallium

  • Guest
Thanks, but...
« Reply #2 on: October 10, 2004, 02:44:00 PM »
...there is no hole to put the thermometer thru. I guess its called a thermometer pocket, se pic below. Until I get some dry ice or a proper teflon adapter; how do I use this?




biotechdude

  • Guest
caliberate and masterbate
« Reply #3 on: October 10, 2004, 06:33:00 PM »
there is no hole to put the thermometer thru. I guess its called a thermometer pocket

U may wish to make a snug fit using alfoil.  Realistically though; u will experience a small temperature difference between the distillate temperature and the thermometer reading.  To caliberate this difference, distill a solution of known boiling point (eg water) and realise the temp difference.  It may only bee a few `C, but it's worth the effort for clean product.

moo

  • Guest
I've read that when inserting a thermometer to
« Reply #4 on: October 10, 2004, 08:00:00 PM »
I've read that when inserting a thermometer to a thermowell, a bit of heating bath oil is poured to the thermowell to conduct heat from the thermowell walls to the thermometer bulb.


r2e3

  • Guest
the appropriate fitting
« Reply #5 on: October 11, 2004, 08:30:00 PM »
will be really cheap - esp 2nd hand.

i would recommend buying one but it does really come down to the efficiency of your vacuum source. if it's nice and steady, it is handy knowing exactly what temp you different distillates come over in your own rig. otherwise, the variation will be masked by the conductance throught the glass me thinks.
I have to say i have never seen that type of adaption.

memeep

  • Guest
Thermometer pockets
« Reply #6 on: October 11, 2004, 09:07:00 PM »
Have a few of those. The glass is eggshell thin (well..almost) so I don't know if oil is actually necessary. I've never bothered using any and they work fine.


Rhodium

  • Guest
air does not conduct heat as good as oil
« Reply #7 on: October 12, 2004, 01:11:00 AM »
The glass is eggshell thin (well..almost) so I don't know if oil is actually necessary.

The thickness of the glass is not an issue, it is the low thermal conductivity of the air between the thermowell walls and the thermometer bulb.

I've never bothered using any and they work fine.

If you haven't compared the temperature reading with and without oil filling of the thermowell, then how do you know you are getting an accurate temperature readout?


indole_amine

  • Guest
hmm
« Reply #8 on: October 12, 2004, 03:10:00 AM »
Maybe he distills H2O at 100°C with his setup/micro-thermowell without oil filling? Would be proof enough, if you ask me...  ;)


indole_amine

MargaretThatcher

  • Guest
Maybe someone can test it
« Reply #9 on: October 12, 2004, 03:17:00 AM »
Adding oil increases conductivity but also increases the thermal mass. I'd have thought the main problem is thermal lag rather than accuracy. Maybe someone can try.


indole_amine

  • Guest
?
« Reply #10 on: October 12, 2004, 04:01:00 AM »
You mean it warms up too slowly to allow for accurate measurement? I don't think the 2-3 seconds delay will make a big difference in terms of proper fraction separation, if you meant that...


indole_amine

MargaretThatcher

  • Guest
Yes, time-lag
« Reply #11 on: October 12, 2004, 04:11:00 AM »
A couple of seconds is OK, but if it takes 15 seconds, that would affect yields. A thermometer alone takes a few seconds to reach equilibrium. Does anyone know the effect of a pocket and whether to use oil?


memeep

  • Guest
>The thickness of the glass is not an ...
« Reply #12 on: October 12, 2004, 08:34:00 PM »
>The thickness of the glass is not an issue, it is the low thermal conductivity of the air between the thermowell walls and the thermometer bulb.


Well yes, but the bulb of the thermometer is actually in contact with the glass as well. The thermometer is just set in...there is no collar on these pockets. My own are much longer (3 sizes which I use for measuring temp. of contents of reaction flask) and narrower at the base than the one shown which looks more like a test-tube.
 
>If you haven't compared the temperature reading with and without oil filling of the thermowell, then how do you know you are getting an accurate temperature readout

The use of oil didn't even enter my mind until moo mentioned it therefore I had no reason to perform such an experiment. I do however know the temp readings are within acceptable margins of error (lag is another question).


indole_amine

  • Guest
lag is neglectible
« Reply #13 on: October 12, 2004, 08:48:00 PM »
Forget the lag - if the thermometer is in contact with the pocket side walls, and I suspect that the pocket is made of rather thin glass too, there will be max. 2-3 seconds delay in showing the actual temp.

15 seconds lag is impossible under these circumstances IMO, but of course a real ground glass distillation thermometer is far better in terms of accuracy and non-delayed measurement.

But I think the manufacturer of these pockets has thought a bit about it before designing them, so they should be rather well suited for temp,. measurement, don't you think?


indole_amine

moo

  • Guest
But we do not know how the manufacturer ...
« Reply #14 on: October 13, 2004, 01:04:00 AM »
They probably have, but we do not know how the manufacturer advises to use their product. They might even assume everyone knows there should be oil put in for what we know.

For what I know, air is much better insulator than oil.


LaBTop

  • Guest
If
« Reply #15 on: October 13, 2004, 02:56:00 PM »
that thingy's pocket bulb is eggshell thin, I should concider it only for distillations without vacuum applied.
And if you use it at all, be damn carefull when you insert a thermometer into it, so you don't cause a crack in the bottom.
 
Especially when you want to fill it with a suitable heat conducting fluid, think first what this specific fluid would do to your motherliquid boiling under it, when the bulb should burst.

The heat conducting fluid needs to be having a much higher boiling point than your motherfluid, or it will start to boil up and away out of the pocket during distilling.
Then it will also be of less harm if the pocket bulb bursts and the h.c.fluid hits the boiling motherfluid in the distillation flask, contrary to f.ex. an alcohol used, which would cause a nifty vulcano outburst through the broken thermopocket.

Using pure mercury as heat conducting fluid would be shear madness btw, if that perhaps came to anyones mind.

All in all, I would advice to only use it for atmospheric distillations of simple solvents, and not for oils with a high boiling point, far over 100°C, such as MDP2P etc., where a narrow boiling trajectory is of  great importance to your expected yield.

Use eventually silicone oil as the pocket filling. That has a very high boiling point. Or peanut oil.

Better stick to a ground glass-connector thermometer. They are not so overly expensive.
Most of the time you also need a ground connector fitting your wide neck progressing to the commercially available smaller ground-neck thermometers.

Btw, I always used a small diameter screwed glass connector on top which progresses to a wide ground connector, fitting in my flask necks, and a special high temp screw-on PPP thingy, with a silicone rubber ring in it, through which my long thermometers can be sticked through, so I can adjust, by screwing it's mutter tight, my thermometer bulb just into the boiling motherfluid in my distillation flasks. Works perfect for even the highests vacuums. And can be adjusted on the fly, when the fluid level in the flasks lowers, while it's distilling away. LT/


indole_amine

  • Guest
I know this kind of glassware...
« Reply #16 on: October 14, 2004, 10:00:00 AM »
"[...]my long thermometers can be sticked through, so I can adjust, by screwing it's mutter tight"

Yeah, and do you know how much of these thingys I already broke in my long chemistry career? Due to screwing up their mutters tight... >:(

"And can be adjusted on the fly, when the fluid level in the flasks lowers, while it's distilling away"

Not to mention the many long thermometers I broke during "on-the-fly" adjustments with said adaptors, due to tightly screwed-up mutters of course... ::)

But besides their fragility, they're indeed very useful, one can measure the reaction temperature and at a certain point start some distillation and simply raise the themometer to use it for steam temp. measurement. Indeed very useful. (but fragile!  :) )


indole_amine

LaBTop

  • Guest
ahh, a Gym-chemist.
« Reply #17 on: October 15, 2004, 12:04:00 AM »
Those inserts are very cheap, and therefor they should be changed often.
Also due to their deformation after too many high temperature distillations, they need to be exchanged.
And always use high vacuum silicone grease on all surfaces of the insert, inside and outside, this facilitates adjusting the thermometer immensely, and helps to keep your vacuum.
Also always grease the glass screw-thread. LT/


indole_amine

  • Guest
enlighted
« Reply #18 on: October 15, 2004, 02:06:00 AM »
D'oh - my varoius gym coaches never told me to grease those threads, too...

And the thought that the screw caps could become deformed is new to me, too - but another good explanation why I always broke them exactly the same way (and although being careful while stemming weights  ;) ).

But I personally can't really reconcile with the idea of greasing the inside of my still head (after all, it's that) thoroughly, and my dist. thermometer too. What if I distill for purity's sake? OK lab grade grease *should* be inert; but still will interfere with crystallizations for example if traces are present in your purified product.

I use them only for atmospherical or low-vac distillations, though - a standard 14/23 joint is unbeatable when it comes to sealing hermetically, and ground glass joint thermometers are therefore highly recommended for working uder vacuum.


indole_amine

Rhodium

  • Guest
High-vacuum silicone grease is not volatile
« Reply #19 on: October 15, 2004, 02:16:00 AM »
What if I distill for purity's sake?

High-vacuum silicone grease is not volatile at the temperatures used in normal distillations, hence it will not distill over into the purified product. Also, any greasing should be so thin anyway, that even if the thermometer would become coated, it wouldn't be more than a few milligrams on it.


indole_amine

  • Guest
not vaporized - rinsed!
« Reply #20 on: October 15, 2004, 03:16:00 AM »
I just meant the small amount that would be carried along by the already condensed vapors, for example if vacuum distilling amines..

But I don't use those thread fits at all when vacuum distilling.

(and I clean & dry the bulb of my (jointed) distilling thermometer, the inside of my still head, condenser, vacuum adaptor and receiving flask very thoroughly each time beforehand - maybe not really necessary, but it gives me the good feeling of having done everything possible to achieve high purity!  ;) )


indole_amine