Remember that in the lecture we talk about diffusion. Diffusion is how the molecules from one place, they would be able to move over to another place, based on the concentration difference, and they need to act through some sort of, like a medium. Now, we want to do a demonstration and tell you. How the medium, whether the temperature is high or low or whether its viscosity is high or low is going to affect the diffusion rate. So we do this by the following setting. On your left hand side we have a glass of water, which is room temperature. Relatively cold. The other side you'll see the steam coming out of it. It is a glass of hot water. Temperature roughly around like maybe 18, 19 degree. So we're going to put in some dye, and ask how long does it for the dye to diffuse throughout the entire glass of water. So let's take a look at it. This is the hot water. And this is the cold water. Let's pay attention to it, and see actually how fast they become totally homogenized, to have the red color fully distributed in the entire glass. You may notice that on the left hand side where the water is cold, sometimes you find that the dye they simply they are stagnant, they are not moving at all based on the very slow Brownian movement, they are simply moving a little bit, but then they are not really mix very well. But if you look at the right hand side you may recognize that you can't see the dye at all, basically they are almost like a mix up in a homogenized solution form. So what it tells you is that, on the right hand side, because of the high temperature, in fact the dye molecule, they would be able to move around very effectively. And so therefore they diffuse very well, but on the left hand side you find that with cold water at low temperature, diffusion occur much, much more slowly. In the second experiment, we're trying to demonstrate the effect of viscosity. Essentially the experiment is identical, but let's look at what we do. We have two glasses in front of us, again. On the right hand side, we are going to put in some starch solution. They are much more viscous. Here it goes. You say that they are a little bit turbid. Okay, done. And on the left hand side, we are going to put in water. This is just tap water. So, basically in terms of viscosity, they are not as viscous. So, we do the same experiment again. Now, what we do is that we are going to put in one drop of the dye. Let's look at it, one drop. And let's look at it, one drop. Now clearly, you can start, see the difference. On the left hand side, it's just the water with relatively low viscosity, and you'll find that the dye start to move around a little bit. As effectively as what you saw a moment ago. But if you look at your right hand side, look at what happen. So this is a very viscous starch solution, and you'll find the dye is at the top, and it's not moving at all, basically, they have a hard time defusing over distance. Let me remind you, in fact. Diffusion still occur, but it's much much more slowly if we stay here for long enough you will find that, the dye would start go into the solution, but then it will never be at the rate as fast as the one in the water. So combine both together basically it tells you the same concept again. High temperature with a very high rate of diffusion. High viscosity, they block diffusion very effectively. So in the future, when you're cooking something and you want to have certain dye being mixed up with the food, think about the viscosity and the temperature. The same thing when you're thinking about aroma, how something smell. If you have a medium which is of low viscosity, actually they would be able to diffuse much faster, and also you can increase the temperature by heating up a little bit, they always smell better.