00:00:00 Hello, I am Harry Sello. It is my pleasure to introduce Tempest in a Test Tube, a television show which made its debut August 24th, 1955, on KQED Channel 9, the educational station for the San Francisco Bay Area.

00:00:22 Tempest was a series of 53 half-hour shows pioneering a new approach in which I, as lecture demonstrator, gave live, unrehearsed presentations of a series of chemical experiments.

00:00:36 These were designed to illustrate basic, simple chemical principles.

00:00:42 The purpose was to stimulate an interest in chemistry by teenage students and by adults.

00:00:49 The talks and experiments had to be entertaining, educational, and simple.

00:00:55 Spontaneity and liveliness were key to the approach.

00:00:59 All the experiments used in the shows were designed and constructed by members of the California section of the American Chemical Society.

00:01:08 The participants were employed by the Shell Development Company, Emeryville, and by Chevron Research, Richmond.

00:01:16 A grant of $52,000 from the Ford Foundation and National Educational Television permitted the filming of the first 24 shows of the series.

00:01:27 The management for the ACS consisted of Alan Nixon, section chair, Fred Strauss, TV committee chair, myself as first emcee, and Aubrey McClellan, second emcee.

00:01:41 We four constitute the core of the present committee.

00:01:46 The series was extremely popular then with KQED viewers of all ages.

00:01:54 The senior chemist committee of the California section today is determined to revive TEMPEST for the benefit of elementary schools, high schools, adult education classes,

00:02:07 ACS local sections, historical archives, TV stations, and similar organizations.

00:02:14 We believe in chemistry as a second language.

00:02:19 While basic principles have not changed, practices have.

00:02:24 Forty-five years ago, such simple chemical demonstrations were not treated with the degree of safety considerations that they are today.

00:02:34 Today, even such simple demonstrations would be carried out with the proper regard for safety glasses, shields, protective gloves, laboratory coats, and visible fire extinguishers.

00:02:49 The principle of safety first would be explicitly present as part and parcel of a modern TEMPEST in a test tube.

00:03:03 The principle of safety first would be explicitly present as part and parcel of a modern TEMPEST in a test tube.

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00:03:53 TEMPEST in a test tube, a series of experiments designed to explain the mysteries of chemistry and the laws that govern it.

00:04:03 Produced by KQED San Francisco, in cooperation with the California section of the American Chemical Society, for the Educational Television and Radio Center.

00:04:26 And now let's go to our laboratory and meet Dr. Harry Sello.

00:04:32 Hello. The title of this talk is Evaporation and Humidity.

00:04:39 Before we start the actual experiments and talking about them, I would like to set one up, which will take a little bit of time, so that we can look at it later in the show.

00:04:51 Here I have a glass U-tube, inverted U-tube, in one end of which has been placed a little bit of a colored, a dark liquid.

00:05:06 Attached to this side is a thermometer. The other side of the tube is empty.

00:05:11 This tube was then evacuated, or emptied, of all its air. Contains only the vapor which goes along with this liquid.

00:05:32 Now, I'll mark the level of the liquid in this side of the U-tube with a nice big black mark. Just about there.

00:05:45 And the thermometer, which reads about 20, it says here, 26 degrees centigrade, will also be marked.

00:06:03 Now, 26 degrees centigrade and the level of the liquid marked in the tube.

00:06:09 Now, I'll put a little bit of ice in the beaker here. That is, in the beaker, not around it, as much as possible. Mix that up with a little bit of salt.

00:06:23 A mixture of ice and salt is an excellent mixture for getting a low temperature, something below zero degrees centigrade.

00:06:31 Break it up a little bit. A little more ice. And a little more salt.

00:06:51 If you haven't seen this mixture used before, ice freezes or melts at zero degrees centigrade. Water freezes, ice melts. But when mixed with a little bit of salt, it will go down to a much lower temperature.

00:07:04 There, that's just about enough. Now, leave that here for a little while and proceed on with the other experiments.

00:07:16 The title of the talk, then, is Evaporation and Humidity. Let me do a rather profound experiment.

00:07:30 Light the candle. That's not the experiment yet. Here's a little piece of white cardboard bent in the form of a tray, a little paper tray.

00:07:42 I'll put the candle underneath the cardboard. Maybe you can guess what will happen. It's already happening.

00:07:54 The paper is scorching. Or, if you want to be a little bit more scientific about it, the paper has reached its kindling temperature, the temperature at which it will burn, and it's just about ready to burst into flame.

00:08:07 There, smoking, scorching, and bursting into flame. I'll repeat the experiment, this time with the same kind of a card, only adding a little bit of water.

00:08:28 There. Now, maybe some of you can guess what's going to happen. But let's see what does happen.

00:08:42 It was rather easy for the dry paper to scorch. It didn't take but just a few seconds. But, by now, this second paper has been over the candle flame for about the same time that this one was, and it isn't burning yet.

00:08:58 So, already, there's been a difference made. Now, as I say, this is a very profound experiment. It looks obvious, you can guess the answer, but let's look a little bit more deeply into what it means.

00:09:12 There is now, rising from the level of the liquid in the little paper tray, some faint wisps of steam, little trails of steam, which are just becoming visible.

00:09:26 And, in the tray itself, there are forming little bubbles of steam, indicating that the water is just about starting to boil. But, note this important thing. The paper is not scorching.

00:09:40 Sure, you'll say, so what? This isn't a very big experiment. Anything that's wet won't burn, won't scorch. But, then, let's examine the reason why. There, now, it's boiling rather quickly. And some steam still rising. I'll leave that there just while we go through the explanation.

00:10:01 When a liquid boils, it changes into a vapor. Or, in the case of water, we call it steam. This process is called boiling. Or, if you wish to be a little bit more scientific, you may call it a rapid evaporation.

00:10:17 The liquid will evaporate. And, there is the word evaporate. This means a liquid changing into a vapor. Note the use of the word vapor in the center of the word evaporate.

00:10:30 However, there's another thing that goes along with this. In order to make a liquid evaporate, you have to apply heat. That means that, let me state it the other way around, in evaporating, or in boiling, the liquid takes up heat.

00:10:44 That's exactly what's happening here. The water is taking up the heat which would normally go in to burn the paper. Therefore, the paper does not scorch when the boiling or the rapid evaporation takes place.

00:10:57 So, then, the principle illustrated here is that evaporation, or boiling, is a cooling process. Let me take the candle away so that the paper, the water won't all evaporate away, and then burn the paper.

00:11:09 Let's look further at an example of this evaporation. Here's a rather simple gadget which makes it just nice and easy to handle. A cork into which are stuck two thermometers.

00:11:24 These are a peculiar kind of thermometer in the sense that it's not commonly seen. They're dial thermometers. A metal stem, all metal thermometer, with a metal stem and a metal face.

00:11:37 Right now, both of them read something like 27 degrees centigrade. One seems to be just a little bit different than the other. This is a natural difference in thermometers.

00:11:46 Both are stuck through a cork. Now, around one of the thermometers, I have wrapped a piece of cotton. Let me wet this piece of cotton. What was that temperature now? So, we make sure we check on it.

00:12:01 Just about 20. One is 25. The other is about 27. Anyway, they're fairly close together. Same little bit of water. I'll just wet this. Shucks, this is an easier way. Here, I'll just dunk the cotton right into the water.

00:12:22 Now, this water's been standing around on the table for some time, so it's about the same temperature as the thermometers, but let's check that to see. Yes, just about. Maybe this one got wet. Maybe the water was a little warm. It raised about another degree.

00:12:38 Well, they're pretty close. This one says 20, almost 25. This one says about 27 degrees. Now, wet cotton. I do the experiment. Throw a little bit of water around.

00:12:56 This is just to prove that a chemist does some work sometimes. He also gets a little bit wet, too. That won't be any change in the talk, maybe. I think I've shaken off about all the water now, extra water.

00:13:13 You can see why a dial thermometer was used now instead of a glass one. Let's take another look at these temperature readings. The thermometer that said 27 before is now down to 21.

00:13:30 Now, just putting the water around didn't change it. We saw that. What did change it? The fact that I was waving it around in air. And what was the process that took place?

00:13:40 Well, by waving it around, causing a little breeze to blow across the wet cotton, I made a little bit of water evaporate, change from a liquid into a vapor.

00:13:50 I've already mentioned and shown that this is a cooling process. Well, where did the heat come from that it took to evaporate the water on the cotton?

00:14:00 It came from the surrounding air, for one thing, and also from the thermometer itself. And it cooled the thermometer down. Notice that waving around didn't change the dry thermometer at all.

00:14:12 The wet thermometer, the one with the cotton on it, did get cooler. Let's see what's going on right this minute. It's still even a little cooler than it was before, just about 20 degrees.

00:14:24 Now, what's the point of all of this? We've shown that there's a difference in temperature when a thermometer is a wet one made to circulate around in air compared to a dry one.

00:14:35 There's a difference between a wet thermometer and a dry one. The difference is a measure of the amount of evaporation that took place.

00:14:42 But there's one further point here. When a substance evaporates, a liquid evaporates, it changes into a vapor, and the vapor goes into the surrounding air.

00:14:52 But supposing now that there is already a lot of water vapor in the surrounding air, like there is in a place where it just wants to rain, just about ready to rain.

00:15:02 Then, I'd like to put forth the question, what happens when you do this experiment in such an atmosphere where there is already a lot of water vapor in the air?

00:15:11 The answer is that not much water will escape from the wet bulb thermometer because the air is already filled with almost as much water as it can hold.

00:15:23 Therefore, there will not be much difference in temperature. So then, we can not only say that a difference in temperature measures the amount of evaporation, it measures one more thing.

00:15:33 It's a measure of how much air, how much moisture there is in the air around us. And the amount of moisture that's in the air around us, we give the name humidity.

00:15:45 Humidity. When the region is of a high humidity, there is a lot of water vapor in the air. When it's a low humidity, the place is relatively dry.

00:15:54 So, this then is a wet bulb and dry bulb thermometer, which illustrates that you can measure humidity. This is a pretty crude one.

00:16:04 Right over here in the next little demonstration, I have what is actually used for measuring humidity. The same kind of a thermometer, but just a little more elegant.

00:16:16 Well, it's not a sword. It's just a pair of thermometers in a brass case. Here are two, not dial thermometers or metal ones, but glass stem thermometers this time.

00:16:28 Both fixed right to a shield so that they don't roll off. Around one of the thermometers is a little bit of a cotton wick, which is the same as the cotton we had there. It's actually a little cloth wick.

00:16:41 I will dip the cotton in the water or this little cloth wick into the water, squeeze off the extra water. Now, one says 78 degrees Fahrenheit. The other says the same thing, 78 degrees Fahrenheit.

00:16:58 Notice that these thermometers are already more accurate than the ones I showed you there. The temperatures are the same. They both say 78 degrees Fahrenheit.

00:17:06 By the way, you see that on the centigrade scale, this was just about 25 degrees centigrade, illustrating the two different temperature scales.

00:17:14 Now, there's a neat little handle attached to this so that all you have to do is, in an easy way, just stand here and make light talk while the humidity is measured.

00:17:26 You see, a weatherman who uses this kind of thing is already a lot smarter than a chemist. He has a nice little handy gadget. He doesn't knock his arm off first.

00:17:39 Now, let us take a reading. 67 degrees on the wet bulb thermometer, but only still just about 78 degrees on the dry bulb thermometer.

00:17:56 Again, the difference in temperature is a measure of the humidity in the room. By the way, this instrument has a name. It measures humidity or moisture, and we call it a hygrometer, hygro meter.

00:18:13 Let's take a look at the next experiment. Well, for this, I'll need my little eyedropper and some of this liquid.

00:18:28 Here is a glass bulb with a stopcock at either end, shutoff valves. Attached to this glass bulb is a glass tube reaching down into a little container full of dyed water.

00:18:47 I'll shut this stopcock, leaving this one open. Nothing in the bulb but just some air. Around the bulb is wrapped a piece of blotter paper.

00:18:55 Take a little bit of this liquid and pour it out here on the blotter paper. Keep your eye on the glass tube, which reaches down into the dyed water.

00:19:18 Now, this is pretty wet so far with this liquid. It's been draining down around the sides here. Let's blow on it a little bit.

00:19:36 Nice hot breath blowing on the liquid, which, by the way, is acetone. Acetone is a compound composed of carbon, hydrogen, and oxygen, an organic compound.

00:19:47 As many uses, it's used in paint solvents, lacquers, and finishes. It's also the main ingredient in fingernail polish remover, for those of you that are interested.

00:19:58 We're making use of another property of acetone in this particular experiment, the fact that acetone evaporates rather easily or has a low boiling point.

00:20:08 There. Note that the level of the liquid, which was down here at the surface of the little beaker before, has now come up about two or three inches.

00:20:20 All we did was sprinkle a little acetone on the blotter paper and blew on it. Just exactly what happened.

00:20:30 As I say, there's nothing but air in the flask, in this little tube. The acetone evaporates rather readily, and we've mentioned that evaporation is a cooling process.

00:20:41 In evaporating, the acetone cooled the air in the tube, causing it to contract. A gas will lower its volume, will shrink when it's cooled.

00:20:51 In order to make up for the shrinkage, some water rose up in the tube to take care of the amount which the acetone cooled, or the gas, and in turn the gas contracted.

00:21:05 Therefore, again we've shown that evaporation is certainly a cooling process. Cause the air to shrink.

00:21:15 Well, we've made a big point about the fact that acetone, or liquids like acetone, can evaporate rather readily, and that evaporation is a cooling process.

00:21:25 Remember that the definition of evaporation, or when a liquid evaporates, we mean that it changes from a liquid into a vapor.

00:21:33 However, there is another event that happens in the same way as evaporation, which is not quite the same, but takes place under the same type of conditions.

00:21:50 Well, let's look at the next experiment just to see.

00:21:54 Here I have a flask which contains a little bit of lime water. Now, for those of you who have seen the previous show, one of the previous shows, lime water has the property that when carbon dioxide reaches it, it turns milky.

00:22:12 Let's just perform that little experiment. Here I have a flask containing a few pieces of carbon dioxide. Throw into this little dish.

00:22:27 So, there is a fog rising from the pieces of carbon dioxide. This fog is actually not carbon dioxide, but water vapor. A small way of showing that there is water vapor in the air around us.

00:22:42 The carbon dioxide cools the air around it. The water vapor in the air condenses, causing the fog. But this is not exactly the point of the experiment. Let's just add a couple of more pieces. I see that isn't quite enough.

00:22:58 The carbon dioxide here is a solid, dry ice, familiarly known. Now, if I just tip my little flask over and proceed to just suck through some of the air immediately above the carbon dioxide into the lime water, let's see what happens.

00:23:29 Now, the lime water is starting to turn milky. This means that there must be carbon dioxide coming into the lime water. However, none of the solid pieces have disappeared. They're still there, just as we put them in.

00:23:48 So, that means that gaseous carbon dioxide has escaped from the solid carbon dioxide and was drawn over into the flask. So, here we have a slightly different kind of evaporation, if you will.

00:24:02 I don't like to call it an evaporation because we have another word for it. The word is sublimation. Sublimation means to change directly from a solid to a gas without going through an intervening liquid condition.

00:24:19 The carbon dioxide is a solid. It gave off carbon dioxide gas. I suppose you could call it vapor. It's more correct to call it gas in this case. It gave off this gas, which was then drawn into the flask.

00:24:33 So, the change of solid carbon dioxide into gaseous carbon dioxide without seeing anything like liquid carbon dioxide at all is called sublimation, the direct change.

00:24:46 Let's look at just another example of this very thing.

00:25:00 Turn this hot plate on to heat.

00:25:04 Here's another solid, a very common one, the solid iodine. Iodine is one of the elements that the chemist knows. In its natural state, it is a sort of black, purplish solid, just as I have here.

00:25:24 Put some in the beaker, black solid, and lower the beaker into the warm water.

00:25:33 Now, I'll take this same dish that I used to hold the carbon dioxide and now use the other property of the carbon dioxide, namely the fact that it's cold, put it right on this iodine as a lid.

00:25:54 Already you can see what's happening. There is a purple vapor or gas appearing in the beaker. The iodine solid is now liberating or giving off a purple gas. The purple gas is iodine gaseous or iodine vapor.

00:26:09 This then is the process of sublimation, the change of iodine solid to iodine gas. No liquid iodine is visible. Let's leave that. Let it sit for a little while and see what has happened in just a few minutes.

00:26:24 In the meantime, let's go back and take a look at our previous experiment that was started at the beginning of the talk.

00:26:31 Now, very interesting indeed. Here was the previous level of the liquid. It has now dropped almost a full, oh, I'd say about an inch and a half, quite a bit, down to here where I have my new chalk mark. It's a little hard to see. I'll just mark it off.

00:26:52 So the level has dropped quite a bit. And the previous temperature, which was just about 26 degrees centigrade, where the previous mark was, now is about, I say about because I'm getting a little angle here and I can't see it directly, is 19 degrees centigrade.

00:27:11 It's clearly lower. It's almost six degrees down. So this side of the tube has both dropped in level and cooled off. Let's look at the other side.

00:27:24 Where did the liquid go? Here is where the liquid went. Wipe this off here to get rid of the ice and salt that's still on it.

00:27:44 Here is that inch and a half of liquid or so that was formerly on this side. There has been a transfer from this over to here. There is another fact which can be noticed.

00:27:56 While the liquid in the starting side is colored or darkened with a bit of a dye, the liquid on the ending side or on the finishing side is now colorless.

00:28:08 Why has that happened? For the following reason. The liquid in here, by the way, is acetone, the very same acetone that I used on the blotter to cool that tube before.

00:28:19 All the air has been taken out of this tube and it was sealed off when the experiment started. That is, we did this before we started the experiment.

00:28:27 Now, so there is nothing in the tube but liquid acetone and vapor acetone. See, a liquid evaporates. By chilling down this side, I caused the vapor, which came over to this side of the tube, to go through the reverse of evaporation.

00:28:43 It condensed and filled this side of the tube. Now, in evaporating, the acetone escaped from the dye that colored it. So here we have a way of purifying acetone, if we wanted to, by a type of distillation.

00:29:01 It's not really a distillation. It's a kind of a low-temperature evaporation. Well, the acetone evaporated, came over to this side where it was colorless and pure. At the same time, since it was evaporation, the temperature dropped, showing that evaporation is a cooling process.

00:29:18 Let's go back and look now at the iodine experiment, which showed the sublimation and see how far it has gone. Now, the beaker is quite full of purple fog. Maybe the talk is full of a little fog, too, but we hope that clears up with time.

00:29:41 The beaker is full of a purple fog. There's still solid in the bottom, and I think, if we're lucky, yes. Let me just empty out this dry ice. And on the cold surface of the glass can be seen these long, thin, paper-like, beautiful crystals of iodine shimmering in the light.

00:30:02 So we completely reversed the process. The solid iodine sublimated, or sublimed would be more correct, to gaseous iodine, which in turn collected on the cold surface of the cover on top. Well, let's summarize. What have we demonstrated?

00:30:19 We talked about evaporation and humidity. We illustrated, by means of the candle boiling the water in a little paper tray, we illustrated the fact that evaporation is a cooling process. This was made use of in a practical example to measure the humidity, which is the moisture content of the air around us.

00:30:44 The instrument used was a hygrometer, a device consisting of two thermometers with a wet and a dried bulb, which cools when the water on it evaporates, measures the humidity in the air.

00:30:57 Finally, we showed that a gas, air, for example, in a tube can contract when it's cooled by evaporation process, and a water level will rise to indicate that this happens. And added to that, we showed a process which was very similar to evaporation, but not quite the same, a process in which a solid changed directly to a vapor instead of a liquid changing directly to a vapor.

00:31:20 A solid changed directly to a vapor, indicating that this was sublimation. I would like to throw in one more little added fact. If you're ever uncomfortable on a hot day, you might have heard the expression, it ain't the heat, it's the humidity. Well, usually that's quite true. You can't perspire when there is a lot of water vapor in the air, hence you cannot cool yourself so that it ain't the heat truly, it's the humidity. Thank you.

00:32:20 This is National Educational Television.