Just so you know: I’m mainly writing this story and sharing these pictures for my students from 3F. (Guys, you can skip this next paragraph). As a bit of an explanation to my other readers: I think most articles about me say I’m a biology teacher and my students also know me as the Dutch teacher. I’ve been asked more than once (by complete strangers online as well as my own students) what kind of teacher I actually am, since I’m now also teaching music again – and English. It’s complicated. For the sake of it, let’s just assume I’m a woman of many talents, okay?
Class 3F knows me as their English teacher. One of their English teachers actually, as I’m sharing them with my lovely colleague Inge. As you also may know, I’m still studying English. Therefore Inge sometimes visits my classes (to give me tips) and I visit hers. On one such occasion, Inge did an exercise with 3F for which they had to listen to a recording. It was about a girl who had participated in her school’s science fair. She explained how she had made stalagmites and stalactites. Our students had to put the images about this story in the correct order.
I took the above picture from their workbook, while they were correcting their answers. They didn’t have to do anything else with it, but I wanted to know if this actually worked. Whenever you get the chance to do fun experiments, you should take it, right? (I just realised my curiosity is probably the result of my parents raising me the way Neil deGrasse Tyson promotes, but that aside). I promised our students I would set it up to see if we could make our own stalagmites and stalactites. Spoiler alert: you sort of can! They’re not impressive, but they might be, with a little tweaking of the setup.
I started out with the materials in the picture above: an old baking dish, two plastic cups filled with warm water and a lot of baking soda and some thread with a paperclip on each end. I know ‘a lot of’ isn’t very scientific, but I forgot how much was needed (and I couldn’t find this experiment online, surprisingly). I started with three tablespoons of baking soda in each cup and I added two more later. You can see in this third picture that I was trying to solve the problem of the thread not hanging loosely downwards enough in the second picture, by adding another paperclip.
I figured it might get in the way of a possible stalactite though, so I removed it again. I also thought I should use thinner thread, which I could wind up better. Then I put everything in the carton box, where the cups would be further apart. This was the right position for the thread and I was also still able to move the whole experiment, if needed. (I later put it on the heating to see how evaporating the water quicker would influence the result). I put an old little plate under the thread, for the stalagmite to develop on.
Sure enough, the water climbed the thread from the cups and started dripping from the centre of the thread. I then quickly realised that the plate wasn’t flat enough. It had a sort of bump in the middle, so the water flowed to the edges of the plate, leaving curved paths. I wanted it to stay more in the middle, so I used the orange lid of a plastic cup. (Yes I was quite caught up in this). I took a couple of pictures while it kept dripping. And a couple more, to try and capture the moment the drop would leave the thread!
So it worked, but I thought it didn’t work fast enough. I changed back to a thicker thread, which could handle more water. It sure did! Meanwhile, a few crystals formed on the orange lid. I removed the lid again eventually though, because the water was now flowing so fast that the lid would soon be floating. The next morning, both the cups were half empty and the baking dish which I had put back again to deal with all the water, contained about 2 centimetres of it. You can see this water as it reflects the left cup in one of the pictures below.
I decided I had had enough fun adjusting this arrangement in trying to create stalagmites and stalactites from baking soda in my kitchen. I left it a few days to see how more evaporation would make it look like and you can see that result in the last picture. You can click this one to enlarge it and focus on the tiny stalactite (the dried up drop of water and baking soda). You can also see the thread is hard from where it left the cups. There isn’t a lot of water left in the cups and the white crystals on the orange lid were very powder like.
Lastly, there isn’t any liquid left in the baking plate. The transparent parts may look like there’s still fluid, but when you look closer you can see it’s solid. The little stalagmite ‘bumps’ also have crystal spots on them. So it kind of worked. It may look like a mess at first sight, but I can advise anyone to do try this at home. Just put everything in the sink when you’re done and pour hot water on it to clean it up. Of course, if anyone reading this manages to make more impressive stalagmites and stalactites: please feel free to show me your results!