Storm Glass

Long ago, people believed that they could use a Storm Glass to predict the weather up to several days in advance simply by looking at the condition of the solution in the jar and matching it to a corresponding weather condition (as shown in the picture; jar conditions on the left, cooresponding weather on the right). After about 200 years we've learned that the state of the jar has more to do with the temperature than anything else. As the ambient temperature rises, the crystals in the solution dissolve and disappear. As the temperature falls, the solution crystalizes, creating snow flakes that slowly fall and pockets of crystals that twinkle in the light. While the accuracy of this jar is debatable, they are a lot of fun to play with and watch as they ebb and flow with the weather.

The Storm Glass is made up of a few basic chemicals and pieces.

2.5 g of Potassium Nitrate

2.5 g of Ammonium Chloride

10 g of Camphor

33 mL of Distilled Water

40 mL of Ethanol

I managed to get all of these chemicals from my college's chemistry department, however they can all be bought online or at various stores. A quick google search of each one shows what they are typically used in and where you can buy them. A few things to note are...

The camphor must be in solid form. A lot of places like to sell it as a liquid, but it will only work if you buy the solid kind.

The purer the ethanol the better. Laboratory grade, which is what I used, is 99% ethanol. You can buy it in a diluted form from home improvement stores, but I can't guarantee that it will work as well.

I'm not sure if the purity of the potassium nitrate and ammonium chloride matters, but that might be worth investigating.

The camphor is the chemical that dissolves or crystalizes depending on the temperature, and is ultimately the most important ingredient. The reason you need ethanol is because camphor doesn't dissolve in water, so roughly half of the solution needs to be some kind of alcohol. The other two dry ingredients will dissolve just fine in water. The dry ingredients will take up about 13 mL of space in whichever bottle you choose, so make sure to account for that!

The other things you will need are

Some kind of bottle with an air tight lid (Mine was 750 mL)

One beaker or similar sized container

A graduated cylinder or something similar to measure the liquids

A pot to mix everything in

A stirring rod

A funnel

An electric heat source

I do not recommend using an open flame for heat, unless you enjoy being violently burned by ethanol

A fair warning: This step will emit a good amount of smelly fumes, so I recommend doing this somewhere where you don't mind the smell lingering for a while.

Begin by mixing your potassium nitrate, ammonium chloride and distilled water into your beaker-like container. Stir until all of the powder has dissolved, then set that aside.

Next, pour the ethanol into the pot and add the camphor. Both of these ingredients have a strong aroma, so avoid sticking your nose in it. Stir until the camphor has dissolved.

Move your pot over your heat source and set it to a medium-high temp. Slowly add the water mix to the camphor-ethanol solution in the pot. The solution should go from clear to cloudy once the two mixes meet, which indicates that you're moving in the right direction.

Cover the pot with a lid to avoid evaporating all of the ethanol out, then let it heat up until all of the cloudy substance has dissolved. Depending on how much you're making, this could take anywhere from 10 to 20 minutes. Avoid opening the pot so that as much of the ethanol remains in the pot as possible.

Once the solution has dissolved completely, remove the lid and slowly transfer it to the bottle you chose. This is where the funnel (and possibly some gloves) will come in useful, depending on how big the opening of you bottle it. Fill the bottle up a little over 3/4 of the way, making sure to leave some empty space towards the top. The solution is obviously hot and is emitting a lot of fumes that aren't fun to inhale, so try not to put your face over the pot.

Once the solution begins to cool, the camphor mix will begin to crystalize and fall throughout the jar. The solution will crystalize in a lot of places all over the jar, and the crystals will fall throughout the jar over time. You can shake it up like a snow globe and watch as they settle back down again.

Since this is a relatively simple project, there are lots of things you can do to make it more presentable. I laser cut a weather guide onto some plywood to act as a backdrop for the glass. I also programmed an Arduino to convert temperature to color on an LED. Of course, the LED also has a multicolor party program, which is what can be seen in some of the pictures above.

Some interesting expansions to this project that I haven't done would be to build an apparatus that allowed you to control the temperature of the jar directly. This could be with fans and a hot plate, or something similar. Dying the solution a different color would also add some effect. I would also be interested to see how changing some of the chemical amounts affected the sensitivity of the solution. Right now it takes a fairly large change in temperature to really make the jar change states, which makes it difficult to see it's full power inside. I know that this reaction is fairly flexible, so varying the chemical amounts might lead to something interesting.