Science (DIY) Glass Bottle Thermometer- How It Works And Other Reflections

In Science class yesterday, we made a (DIY) glass bottle thermometer. Although I didn't succeed in it, I understand how it works and why it didn't work for my mine.

Materials to do the experiment:

• Tap water
• Food colouring
• Glass bottle
• Beaker
• Dropper
• Ruler
• Straw
• Clay
• Cooking oil
• Hot water
• Cold water
• Thermometer
• Marker

How to do the experiment:

1. Mix food colouring to tap water, and fill the glass bottle with the solution.
2. Place a straw into the bottle with about 4 cm in the water (at least 15 cm out of the water and not it should not touch the bottom of the bottle).
3. Air-seal the the bottle mouth (like the picture below)
4. Use a dropper to add more coloured water through the straw to the bottle, do it until you the water reaches 5 cm above the water in the bottle (actually 5 cm you can see, above the level of the clay).
5. Drop a drop of cooking oil to prevent water evaporating.
6. Place a real thermometer into a bowl of hot water, wait for the coloured water in the straw to reach its highest level and stopped moving. Now, check the temperature on the real thermometer and mark it on the straw, the spot where the water level in the straw is.
7. Do the same thing except in cold water.
8. Divide the two marks into 5 mm intervals, count the marks you have, and divide the difference of the two temperature by the number. Mark all the temperatures down.

How it works:
Its functions are just like the function in a real thermometer. When the water gets heat, the particles in the water has more the energy, they move around more and more violently, pushing each other away. At that time, the particles get pushed away, so they get further and further apart from each other. Hence, there is more and more space in between each of the water particles, and thus, the water expands. When the water expands, it naturally goes up the straw until it stops, or even until it flows out of the straw! The opposite thing happens when you put your (DIY) bottle thermometer into cold water. The water particles loses their energy and moves slower, they get close to each other eventually as they do not need space to move around anymore. As they get close, the water condenses, and it naturally goes down to a certain level.
The above is also the reason that a seal glass may explode when you put it in something hot. Especially when air particles move around more freely than solid particles. Air particles will need more space to move than solid particles need, relatively.
The above about the particles get far and close and the object expanding and condensing also explains why you put the lead hot water or the bottle in cold ice when you can't open the lead. It also explains how it works.

What are the uses of the different materials:

• The use of the food colouring is only to let you see the water level in the straw clearer.
• The use of the clay is to prevent air going in or water leaking and helps the DIY thermometer to be more accurate and the experiment to be more controlled.
• The cooking oil is really important because it prevents the water inside the bottle from evaporating when it absorbs heat. This help keeping the water in. Otherwise, the water level rises slower (than what it should be) because the water is getting away.

Why didn't the one I made work:
It is just that it is hard to get the mouth sealed, especially that the clay I was using was keep on drying up and cracking. That's it, it can probably get fixed with more time.

How can the DIY thermometer be improved:

• First of all, glass is not a poor conductor, so it might get bigger too in a short time. This may seriously affect the accuracy of the results. Although it may not because if the whole glass bottle is identical, where you marked your temperature has already included the expanding of the bottle, only if the glass bottle expand the same amount every time it gets the same heat (or condense when it gets cold).
• Secondly, the clay also expands, this one is a more serious one, because it allows air to go in the bottle so the water leaks, which is going to mess up the whole thing.