"CREAM ON."
Ivan: You may think that after a long hard day of doing science experiment, we just want to sit back, relax, and may be enjoy a small aperitif. you may think that, but in fact, what we are going to do, is another science experiment. this time using this rather ominous looking dark liquid, so Nick, what is this liquid?
Mick: Well fortunately it is not too ominous, it is Tia Maria.
Ivan: Oh Tia Maria, is a Liqueur.
Mick: Exactly, it's Coffee based Liqueur, and it's quite viscous and thick.
Ivan: Smells very nice, and you are right, it is viscous, it kind of has a consistency of molasses, you could say, rather thick. So what does this have to do with the experiment?
Mick: Well, you are going to pour that into the plate here.
Ivan: Really?
Mick: You will, I am sorry about that.
Ivan: It looks like a bit of a waste, but I guess it is the science, so here we go. We will pour it into the plate, there we go.
Mick: This experiment looks well in the glass by itself, where you get a good view of what's happening if you use a plate.
Ivan: Oh we certainly have a good view, so we have got our Tia Maria, what happens now?
Mick: We are going to use another liquid.
Ivan: Okay, this does not look like a liqueur, doesn't smell like a liqueur.
Mick: No, that's cream, it is pouring cream, it a single cream or table cream.
Ivan: Table cream.
Mick: Double cream tends to be too thick, and it doesn't work with milk either, this is just about perfect.
Ivan: It is the in between cream.
Mick: It is the in between cream.
Ivan: Not too thick not too light.
Mick: You are going to pour very gently over the surface. You can do it like that, but more gently with the spoon, if you could.
Ivan: Alright, here we go.
Mick: Spoonful poured out on to that.
Ivan: Just I guess you just spoon it on top.
Mick: That's right.
Ivan: Here we go.
Mick: And very gently.
Ivan: Okay there it is.
Mick: Absolutely perfect.
Ivan: Okay, that looks interesting, shall I keep going?
Mick: Yeah, keep going.
Ivan: Okay, here we go.
Mick: Maybe another one after that as well.
Ivan: Okay.
Mick: And you can probably see already how this whole thing is going on.
Ivan: Oh yeah, I can actually, yeah.
Mick: There you go.
Ivan: Oh look at this.
Mick: There you could see somewhere along -- look at this one here.
Ivan: Oh my Gosh! Yeah, okay so this is what is see, it's is a very complicated, convoluted outline now, it is breaking up into all of these cells. If I look very closely, I see the cells are -- They are convecting they are rotating yeah. In fact they look like a little pulsing lips.
Mick: In fact, convection is exactly the right word, because although we usually think of convection as being in a hot liquid with different regions of temperature in the liquid. This is Solutal Convection, which takes place when two liquids of different densities are mixed, and this is a particular special version which gives an incredible patterns as you can see.
What's happening, is that the alcohol from the Tia Maria is pushing out through the cream, when it reaches the surface, it creates an area where the surface tension is reduced, so the rest of the surface, yanks above surface tension, because it is higher surface tension in the rest of the area, starts to pull the alcohol away.
Ivan: Okay, as far as I understand, you have got the cream sitting on top of the alcohol, the alcohol diffusing up through the cream, and the cream has a certain surface tension, like elastic bands on the surface. When that alcohol comes up through, it changes the surface tension and what the cream pulls back.
Mick: Yeah, the cream pulls back and pulls the alcohol away too.
Ivan: So more alcohol coming up and it is just going around and around, you can see those rolls.
Mick: Exactly.
Ivan: They are rolling and they are getting larger as we speak, they are just rolling and rolling and rolling. What is really impressive about this, is you can just see this amount of motion, it almost seems as we have got a hot plate under the plate, because it looks like --
Mick: You would think that was heating.
Ivan: And it looks like it is boiling, and you kind of wonder where is all this energy coming from, but it is not a chemical reaction it is not temperature.
Mick: No, it is Solutal Convection.
Ivan: Solutal Convection, that's just fantastic. Well Mick, thanks for telling us about this really nifty effect. If you would like to find out more about this and plenty of other science experiments that you can do around the house here is the book you need, 'How to Fossilise Your Hamster.'
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