In my last post, I showed you the legendary overturning experiment. And guess what occurred to me? That there is an even easier way to show the same thing. No gel pads! (BUT! And that is a BIG BUT! Melting of ice cubes in lukewarm water is NOT the process that drives the “real” overturning! For a slightly longer version of this post check this out).
So. Tank full of luke warm water. Red dye on one end. Spoiler alert: This is going to be the “warm” end.
Now. Ice cubes on the “cold” end. For convenience, they have been dyed blue so that the cold melt water is easily identifiable as cold.
A very easy way to get a nice stratification! And as you see in the video below, awesome internal waves on the interface, too.
And because I know you like a “behind the scenes”:
I took this picture sitting on my sofa. The experiment is set up on the tea table. The white background is a “Janosch” calendar from 15 years ago, clipped to the back of a chair. And that is how it is done! :-)
My new favorite thing is to put strawberries through a blender and then freeze small portions of that to eat as ice cream later. It is super yummy plus you never know what you’ll see when you open the lid!
Sometimes, you get long crystals like these:
Ice crystals on strawberry ice cream
And then other times, you get something completely different. Look at those circular shapes! Perhaps that’s where the UFO landed? You can’t really see it in the picture, but those disks come quite a bit higher than the rest of the ice.
Ice crystals on strawberry ice cream
In the bottom left corner, you see a smudge – that is where I pried off one of the disks to see what might have caused it. Turns out there is a cavity underneath. So somehow bubbles in the strawberry mash freeze out into those disks?
I am guessing that the ice cream in the second picture came from a batch that I beat harder than the one in the first picture, hence more bubbles. Or maybe the one in the first picture sat outside the freezer longer, so the bubbles had all reached the surface and popped before it went into the freezer? What do you guys think? Seems like I should really be carefully writing protocols next time I’m making ice cream! :-)
Because surely there is one more post in this topic? ;-)
For those of you who haven’t heard about the “melting ice cube” obsession of mine, please check out the links to other posts at the end of this post. For everybody else’s sake, let’s dive right in!
When Kristin and I ran the workshop at EMSEA14, a couple of people asked very interesting questions. One that I totally had to follow up on was this: What would happen if the ice cubes were forced to the bottom of the beakers? Of course we knew what theory said about this, but who cares? I still had to try.
If you have ever tried holding down ice cubes with straws…
…and we have a movie of this! :-)
…you might know that that is quite difficult. So this is the experimental setup I ended up with:
Ice cubes melting at the bottom of a fresh water and a salt water beaker
Zooming out a little bit, this is my fancy equipment:
The camera gets a white skirt over the tripod because the reflection of the tripod is seriously annoying
Zooming out a little more, this is the whole setup:
Chair on table in my winter garden, holding the white-ish oilcloth that serves as background. I should invest in a proper rod for the upper edge of the oil cloth, the current one has suffered a bit…
I know that some people want to try the experiment for themselves, so I’ll hide the rest of the experiment behind the cut, at least until Kristin tells me that she’s done it :-)
I had to do the complete series of experiments, of course…
The other day I mentioned that I had used salt from my kitchen for the “ice cubes melting in fresh and salt water” experiment, and that that salt was the super healthy one that was both iodized and containing folic acid. And what happened is that the experiment looked like I was using milk. Not what I had envisioned.
Ice cubes melting in fresh water (left) and in iodized-salt-with-folic-acid water (right)
Since I had often before used just regular table salt – which is usually iodized – I was intrigued by the opaqueness that seemed to be due to the addition of folic acid. Or was it? That I had never noticed the milky-ness of the salt water didn’t necessarily mean that it had not been milky before. So this is what the same experiment looks like if regular iodized table salt is used:
Ice cubes melting in fresh water (left) and in iodized-salt water (right). Turbulence in the freshwater beaker due to me stirring (don’t ask)
In the literature it is always recommended to use kosher salt for experiments. Kosher meaning in this context that the salt should be only NaCl with no other additions. I happened to have some at hand after having bought it for the “teaching oceanography” workshop in San Francisco last year (after the salt that I brought for the workshop didn’t make it to the US. Long story). So this is what that looks like:
Ice cubes melting in fresh water (left) and in kosher salt water (right)
In summary: Folic acid is what makes the salt water look opaque – but iodized salt is completely fine for tank experiments. I think it’s tiny air bubbles that cling to something folic acid-y, but I have no clue what is going on. I noticed that the dusty stuff settled down over night (so the top experiment here is a lot clearer than the experiment I ran with the same batch of water the day before), but even the next day the water wasn’t completely clear.
Anyway, now we know. And I came out of this series with more movies of ice cubes melting in fresh water and salt water!
Links to previous posts on the topic after the cut.
[Edit: Using my mom’s iodized, but not folic acid containing, table salt leads to milky water, too. So there you have it. I have no clue what is going on!]
I can’t let go of this experiment. Last time I posted about it, someone (Hallo Papa!) complained about the background and how I should set a timer and a ruler next to the beakers for scale. The background and timer I did something about, but the ruler I forgot. Oh well, at least there is room for improvement still, right?
I always find it fascinating to see how differently the ice melts in fresh water and salt water. Below you see how convection has completely mixed the fresh water with the melt water, whereas the melt water forms a layer on the salt water. You can even still distinguish horizontal currents in there!
The beakers after ice cubes have melted in fresh water (left) and salt water (right)
For everybody who still enjoys watching the experiment: Here is a movie. Top one as time lapse, bottom one in real time, all 8 minutes of it. Enjoy!
The links to the “melting ice cubes” series after the cut.
As I mentioned before, Kristin Richter and I are running the workshop “Conducting oceanographic experiments in a conventional classroom anywhere” at the European Marine Science Educator’s Association Meeting in Gothenburg, Sweden. There is quite an active Twitter crowd around, so you can follow the storyfied meeting or look out for #EMSEA14 on Twitter.
Our workshop has been represented quite well there, too, so I’ll just post a couple of my own pictures here.
Final preparations: Kristin is mixing salt water
Watching intently the melting ice. As my former boss would say: It’s like watching paint dry.
Except that it is really fascinating and that there are so many things to discuss!
Kristin and I took turns presenting the workshops, which was great. Plus it was really nice to have two instructors walking around, talking to the groups, instead of just one.
Kristin talking about using our favorite experiment to practice applying the scientific method.
Plus there are a lot of post dealing with the exact same experiment after the cut below. And there are two more posts on this exact experiment coming up that are scheduled already, one tomorrow, the other one in two weeks time. And thanks to a very nice family of participants I already have plenty of ideas of how to modify this experiment in the future!
[edit: There finally is a picture of me in the workshop, too, to show that I actually did contribute and not just leave it all to Kristin:
So I did actually do something, too, and not just take pictures. Plus did you notice how there is a EMSEA sign on the podium? There were signs on the doors, too, both on the inside and outside, so one of them was visible even when the door was wide open. Such good thinking of the organizers! Gothenburg University does have a seriously impressive infrastructure in any case: Tables and chairs on wheels so the whole room could easily be modified to suit our needs. Awesome.]
Or why you should pay attention to the kind of salt you use for your experiments.
The melting ice cubes in salt and fresh water is one of my favorites that I haven’t written about in a long time, even though (or possibly: because) I wrote a whole series about it last year (see links at the end of this post).
Now that the EMSEA14 conference is almost upon us and Kristin and I busy preparing our workshop, I thought I’d run the experiment again and – for a change – take the time to finally know how much time to schedule for running the experiment. This is the experiment that I have run most often of all in all kinds of classes, but there you go… Usually I have more time than just 30 minutes, and there is so much other content I want to cover in that workshop!
There are a couple of things that I learned running this experiment again.
It takes at least 10 minutes to run the experiment. My water was slightly colder than usual room temperature, my ice cubes slightly smaller, though. And those 10 minutes are only the time the ice takes to melt, not the time it takes to hand out the materials and have the groups settle down.
There is a reason it is always recommended to use kosher salt for these kind of experiments. Look at the picture from one of the old posts in comparison to the ones from today: The iodized salt containing folic acid I had in my kitchen dissolves into really milky water. I really should have walked the two extra meters to get the good salt from my oceanography supplies in the other room!
Ice cubes melting in fresh water (left) and salt water (right) – old experiment
Ice cubes melting in fresh water (left) and salt water (right) – experiment today
Some food dyes are the devil. My whole kitchen is red. Plus the ice cubes didn’t freeze nicely (for a post on ice cubes freezing from salt water click here), the ice chipped when I tried to get the cubes out of the ice cube tray. I definitely can’t have that mess at a workshop. So here is another argument for using non-dyed ice cubes! The more important argument being that you think more if the cubes are not dyed and you don’t immediately see the explanation…
But it is always a fun experiment to run, and there are always new things to spot. Watch the video below and see for yourself! (Explanations on the weird phenomena coming up in a future post!)
Geli, Torge, and all you other ice people – do you know what this is?
Browsing pictures on my phone, I came across the pictures below that I took a while back in Bergen. What you see in the picture below is a photo taken down at the flat surface of a picnic bench. Each individual ice needle is about 1 cm high measured from the wooden surface of the bench. I only saw the crystals on that one bench that one day, but not on any other surface.
Ice crystals growing on a picnic bench
I’ve googled a little to figure out how these crystals formed, since they don’t look like either ice flowers or ice needles or any other ice crystal that I am used to seeing. However, I haven’t found anything yet.
The picture below is a close-up of some of the crystals and even though it looks like the picture has a very bad resolution and like you can see individual pixels, that is not the case. That impression is caused by the weird shapes of the ice crystals.
Close-up of some of the ice crystals
Geli, Torge, anyone – do you know what these crystals are and how they form? Or do you have any idea where I could find out more?
P.S.: People who don’t understand why it’s awesome to have a camera on your phone either never had one or don’t have a blog.
Today I’m excited to bring to you a guest post from Innsbruck, Austria, written by my friend Kristin Richter. Kristin ran the oceanography lab in Bergen before I took over, and she is a total enabler when it comes to deciding between playing with water, ice and food dye, or doing “real” work. Plus she always has awesome ideas of what else one could try for fun experiences. We just submitted an abstract for a conference together, so keep your fingers crossed for us – you might be able to come see us give a workshop on experiments in oceanography teaching pretty soon! But now, over to Kristin.
A little while ago, I made an interesting experience while presenting some science to students and the general public on the “Day of Alpine Science” in Innsbruck using hands-on experiments. Actually, my task was to talk about glaciers but being a physical oceanographer I felt like I was on thin ice. Well, glaciers, I thought, hmmm … ice, melting ice, going into the sea, … sea, … sea ice! And I remembered how Mirjam once showed a nice experiment to me and some friends about melting ice in fresh and salt water. And suddenly I was all excited about the idea.
To at least mention the glaciers, I planned to fill two big food boxes with water, have ice float (and melt) in one of the tanks and put ice on top of a big stone (Greenland) in another tank filled with water to show the different impact of melting land ice and sea ice on sea level. Since melting the ice would take a while (especially on a chilly morning outside in early April) I would have enough time to present the “actual” experiment – coloured ice cubes melting in two cups of water – one with freshwater, and the other one with salt water.
Melting ice. A comparison of sea ice and glaciers melting’s impact on sea level, ice cubes melting in fresh and salt water on the right. Photo by “Forschungsschwerpunkt Alpiner Raum”, University of Innsbruck.
As we expected many groups with many students, I needed a lot of ice. I told the organizers so (“I need a lot of ice, you know, frozen water”) and they said no problem, they will turn on their cooling chamber. The day before, I went there and put tons of water into little cups and ice cube bags into the chamber to freeze over night.The next morning – some hundreds of students had already arrived and were welcomed in the courtyard – I went to get some ice for the first group. I opened the cooling chamber,… and froze instantly. Not so very much because of the cold temperature but because I was met by lots of ice cube bags and little cups with… water. Like in LIQUID WATER! Cold liquid water, yeah, but still LIQUID! Arrrghhhh, my class was about to begin in a few minutes and I had NO ICE. “Ah, yes”, volunteered the friendly caretaker, “come to think of it, it is just a cooling chamber!”I started panicking, until a colleague pointed out the Sacher Cafe (this is Austria after all) and their ice machine across the road. I never really appreciated ice machines, but that one along with the friendly staff saved the day. Luckily, I brought some colored ice cubes from at home – so I was all set to start.
And the station was a big success, the students were all interested, asked many questions and were excited about the colored melt water sinking and not sinking. :-) I even managed to “steal” some students from the neighboring station of my dear meteorology colleagues. That was something I was particularly proud of as they could offer a weather station, lots of fun instruments to play with and a projector to show all of their fancy data on a big screen. (Actually, I also abandoned my station for a while to check out their weather balloon.)
Anyway, I had a lot of fun that day and could definitely relate to Mirjams enthusiasm for this kind of teaching. I can’t wait for the next opportunity to share some of those simple yet cool experiments with interested students. I will bring my own ice though!
Is there an equation of state for hypersaline water at very cold temperatures?
A friend of mine is looking to calculate changes in density of a hypersaline Antarctic lake from summer to winter. Apparently, this lake is about 10 times saltier than the ocean and often cools down to -17C at the bottom.
My own spontaneous answer was that I am not aware of such an equation of state, and that I doubt that there is a lot of empirical data in that property range. Plus from talking to Dead Sea researchers while working on double diffusion, I know that measuring salinities that are that high is not at all easy – the constancy of composition of sea water breaks down (at least in the Dead Sea) which has consequences for the measurement methods that can be used, and in any case CTDs aren’t calibrated for those salinities. But I am hoping that the collective wisdom of my readers will come up with a better answer.
So, dear readers. Do you know of an equation of state that applies to that range of properties, or do you have any other comments on the issue? Please leave a comment below or get in touch with me! That would a) really help my friend, and b) help satisfy my curiosity :-)