Cast: Bing and Bong, two people who like to talk about interesting topics.
Props: A cup of ice and a cup of water, a needle, some capillary tubes of various diameter.
Bing and Bong are sitting in a cafe on the left bank of Paris. They have just finished discussing the comparative merits of the philosophies of Gide and Sartre. Bing puts down a glass and sighs. Then looking carefully at Bong, Bing begins to speak.
Bing: Let's talk about something more interesting, Bong. I'm tired of this subject.
Bong: Good idea, Bing. How about something to do with biology. That's among the most interesting of subjects, I think you'll agree.
Bing: By all means, let it be biology. Why not, in fact, begin with the most important and interesting subject in all of biology.
Bong: [Somewhat embarrassed] You can't mean...
Bing: Of course -- water. What could be more important and interesting than that. Let's talk about water.
Bong: [Looking very doubtful] Water? What possibly could there be about water that is of interest to biology. I think you're all wet, Bing.
Bing: Not at all. Don't you realize that 75% of the surface of the earth is covered with water, that 45 to 95% of the weight of all active living things is water! What could be more vital. And the properties of water...well, were water not as it is, it is quite possible that there would be no life at all, not even in Paris.
Bong: I know a few things about water. It's made up of two atoms of hydrogen and one of oxygen, and its melting point is 0o and its boiling point is 100o. In fact, that is how the centigrade scale was set up with these properties of water as the reference points for the scale. In fact, water is one of those rare substances that can exist in all phases -- solid, liquid and gas -- within the range of temperatures on the earth.
Bing: There's far more to it than that, Bong. Take some of that ice in that cup and put it in your glass of water. [Bong does so.] What do you see?
Bong: Nothing. The ice is just floating there in that water like it always does.
Bing: Yes, but just because that is so commonplace an event doesn't make it any the less amazing. Most substances get continually more dense as their temperature is reduced. So if you put a solid piece of most materials in the liquid phase, the solid sinks. If you freeze a container of ethanol, it freezes from the bottom up because the solid ethanol is denser than the liquid. Not so with water. It gets denser as the temperature goes down until it reaches 4o, but that turns out to be as dense as it gets. Below that it becomes less dense again so that ice floats.
Bong: [Stands up, very much excited] Of course! I see now how important that is to living things. Think if ice sank. Ponds would freeze from the bottom up, and life in lakes where there is a cold winter would be impossible. But why is that -- why does it float?
Bing: I think it's because of the hydrogen bonding water undergoes. Water is a polar molecule. The electric charge on the molecule is not evenly distributed, so there is a positive and negative end to a water molecule. The hydrogens of neighboring water molecules are shared by the oxygens so that there is some structure even to liquid water. This hydrogen bonding imposes a crystalline structure to water in the solid phase that spreads the molecules out more, making them less dense. But this hydrogen bonding, now that I mention it, is responsible for some other properties of water too.
Bong: Yes, in fact, I can think of one already. Take that needle sitting there on the table and VERY carefully lay it on the surface of the water. If you do it carefully and gently enough you can get the needle to float on the surface of the liquid! [Bing gives it a try.] That's due to a property of water called "surface tension." The water molecules attract each other in hydrogen bonds so that they hold together forming a surface that will hold up a needle.
Bing: Yes, and I see that you have several little tubes lying on the table too. Dip those in water and you'll see water go up the tubes. Is there any relation between the diameter of the tube and how high the water moves? [Bong does this experiment and then proclaims...]
Bong: Yes, there IS a relationship. And it is [state the relation between the diameter of the tube and the height the water goes]. By the way, this is called "capillary action." It is very important in some biological processes as we will see.
Bing: I knew this would be more interesting than existentialism. And there is much more. One biologically very important property of water is its ability to absorb heat energy without increasing in temperature very much. This is called its "specific heat," and it's important for the temperature stability of many biological systems. In fact, I saw a performer once who boiled water in a paper container. This was possible because the water very efficiently carried away all the heat so that the paper never reached its burning point. Not only that, evaporating water absorbs an enormous amount of heat, so that makes possible a very efficient method of cooling for temperature regulation.
Bong: Well, Bing, this has been an interesting discussion after all, but now I think the floor show is about to begin. [Bing and Bong turn their attention to the front of the room.]
Donald Cronkite September 28, 1992