[Catalist] Repairing and maintaining alcohol thermometers for student labs: A CONSTAWA Investigation sponsored by Modern Teaching Aids

[Caroline Lucas]

Thank you Leon for taking the time to then communicate this with us! I have learnt something valuable through your interaaction with someone at CONSTAWA! I have now repaired 3 of our thermometers that were destined for the bin!!


Kind regards,

Caroline Lucas
Science technician
Cornerstone Christian College

08 9754 1144
http://www.cornerstone.education<http://www.cornerstone.education/>

[https://docs.google.com/a/cornerstone.education/uc?id=0B_MT-t5rzA43bnJfNGRkSThxYWM&export=download]

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________________________________
From: Catalist <catalist-bounces at lists.stawa.net> on behalf of Leon Harris <leon at quoll.com>
Sent: Thursday, July 15, 2021 3:19 AM
To: Catalist <catalist at lists.stawa.net>
Subject: [Catalist] Repairing and maintaining alcohol thermometers for student labs: A CONSTAWA Investigation sponsored by Modern Teaching Aids


Greetings all,

Yesterdays CONSTAWA was, as usual, excellent and as usual provided many stimulating conversations.


During one of these Frank De Rooy, of Modern Teaching Aids fame was showing me some glass alcohol thermometers where the column of alcohol had broken and the upper portion of alcohol was close to the top.

[Stuffed        Thermometer]

We normally regard these as hopelessly broken, but they are not.

This post aims to do two things:

1. show you how to prevent this type of damage

2. Show you how to fix it, as it is a common issue in lower school labs.


Part 1: how to prevent column breakage in the thermometer.

Always store your thermometers vertical position. Cut a 35cm length of 90mm pvc pipe, cut out a piece of sponge to place in the bottom, and glue a 90mm end cap to it. Secure it so it can't fall over (eg by putting in a cardboard box packed with newspaper, or any other technique you fancy) and keep your thermometers upright in this. The sponge in the bottom is to protect the bulb end of the thermometer. When students return thermometers from labs, have them return them to vertical containers.


Part 2: how to fix it.

Fixing thermometers takes a little time and care. The principle you need to keep in mind is that you must always have a significant volume of air in the thermometer, or the bulb will shatter.

The first task is to break up the liquid at the top (ill call this the top line from here on) . To do this you will need to drop the thermometer onto a plastic surface, such as a lunchbox turned upside down, repeatedly. The goal is to change a top line that looks like this ________ into one which looks like this - - --- -   - - . When you drop the thermometer onto this surface, small droplets of the top line are separate from the rest. Because the thermometer is vertical, these droplets move downwards under the influence of gravity, and become closer to the main mass of coloured liquid. You can see a person doing this step here: https://youtu.be/Be9BsV7KvfA

Once you have broken up the top line and have as much air between it as you can get, you can start to try to join the alcohol together.

Repeat this next step cautiously. You will need to do it several times if you are to avoid having your thermometer bub explode. To do this you need a low powered bunsen safety flame. You wave the bulb of the thermometer through the hot air above the safety flame (not the flame itself). You want to heat the thermometer as slowly as you can, and you MUST MAKE SURE THAT THERE IS ALWAYS AIR SPACE in the thermometer. Normally there is a little bulb in the top of the thermometer. As soon as you cannot see air space, the thermometer will shatter. As soon as you have heated the thermometer as much as you can, let it cool. If there are still droplets of alcohol that are separated, try tapping them a bit until the column breaks up, and then repeat the heating step.

I hope this helps with a common problem in our schools.

I thank Frank de Rooy and MTA for two samples of hopelessly damaged thermometers, one of which I destroyed to confirm my idea about incompressibility of fluids and broken thermometers.

I note in passing that such types of collaboration are one reason why face to face pd is essential, and will never be fully replaced by Zoom.


Have fun all,

Leon Harris


(Ps: apologies for the image, I shrunk it to 62Kb so as not to more space than a signatures logo)


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