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.

00:00:20 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.

00:00:35 These were designed to illustrate basic, simple chemical principles.

00:00:41 The purpose was to stimulate an interest in chemistry by teenage students and by adults.

00:00:48 The talks and experiments had to be entertaining, educational, and simple.

00:00:54 Spontaneity and liveliness were key to the approach.

00:00:58 All the experiments used in the shows were designed and constructed by members of the California section of the American Chemical Society.

00:01:07 The participants were employed by the Shell Development Company, Emeryville, and by Chevron Research, Richmond.

00:01:15 A grant of $52,000 from the Ford Foundation and National Educational Television permitted the filming of the first 24 shows of the series.

00:01:26 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.

00:01:40 We four constitute the core of the present committee.

00:01:45 The series was extremely popular then with KQED viewers of all ages.

00:01:53 The senior chemist committee of the California section today is determined to revive Tempest for the benefit of elementary schools,

00:02:03 high schools, adult education classes, ACS local sections, historical archives, TV stations, and similar organizations.

00:02:13 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.

00:02:33 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.

00:02:48 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.

00:03:13 The principle of safety first would be explicitly present as part and parcel of a modern Tempest in a test tube.

00:03:23 Tempest in a test tube.

00:03:50 A series of experiments designed to explain the mysteries of chemistry and the laws that govern it.

00:03:58 Produced by KQED San Francisco.

00:04:07 In cooperation with the California section of the American Chemical Society.

00:04:16 For the Educational Television and Radio Center.

00:04:22 And now let's go to our laboratory and meet Dr. Harry Sello.

00:04:27 Hello.

00:04:30 I'd like to start an experiment using a rather strange kind of garden.

00:04:37 Here's a jar full of liquid.

00:04:40 Let me throw a few seeds into this little garden.

00:04:55 That's one kind.

00:04:57 Here's another.

00:05:03 Take a little bit here.

00:05:11 Third.

00:05:23 And finally, a little more.

00:05:26 Let's see, I've just used this one.

00:05:28 Oh, here's one I missed.

00:05:34 Did I get any of this in it?

00:05:36 I guess I did, but I see there isn't enough in there, so I'll put some more in.

00:05:42 There, the garden is well seeded.

00:05:45 Will it grow?

00:05:47 Let's go on, give this a chance to develop, and we'll come back and look at it later.

00:05:53 The materials I used as seeds in this garden, the chemist calls crystals.

00:05:58 And that is the topic of this particular talk, crystals and glass.

00:06:05 Now, all substance in nature exists in three forms.

00:06:10 As a gas, a liquid, or a solid.

00:06:14 It is of the solids that we will learn a little bit today.

00:06:20 I had a lot to say about gases and liquids in previous talks.

00:06:24 But now we'll learn a little bit more about the solid state.

00:06:28 Specifically, we'll begin with crystals.

00:06:30 The word crystal is a means, ice-like, or having a structure like ice.

00:06:38 Usually has in it the meaning of clearness.

00:06:43 However, I would like to use the chemist's definition of crystal.

00:06:48 A crystal is a solid whose atoms, or molecules, or ions, the individual particles,

00:06:58 are arranged in a regular arrangement, and the solid has a definite form.

00:07:04 Here's a sample of some crystals.

00:07:07 The first is a very common one, table salt or sodium chloride.

00:07:11 This is actually just a powdery-like material.

00:07:16 If you looked at it with a magnifying glass, a rather strong microscope,

00:07:19 you'd see little cubes, perfect little cubes.

00:07:23 Here is another kind of crystal, sodium thiosulfate.

00:07:26 The photographer knows this as hypo.

00:07:28 It also has a regular kind of structure.

00:07:31 Sugar is still another kind of crystal.

00:07:34 And here is one which has much appeal to the fairer sex, a garnet.

00:07:40 A particular form of crystal which has 12 sides to it.

00:07:44 That is, a nice garnet will have 12 sides.

00:07:48 So the chemist then uses this as an example of a crystal.

00:07:52 Here is a sample of what a crystal might look like,

00:07:56 the arrangement of the atoms in a crystal.

00:07:59 The little one, you see, is the unit structure.

00:08:04 I'll just pull one of the atoms off.

00:08:06 You can see then, according to this model, that there's an atom in the center,

00:08:10 and this is surrounded by other ones on the outside.

00:08:14 A regular arrangement.

00:08:16 If I were to take this and to repeat it in many, many structures,

00:08:19 many, many units, I would have built up one like this,

00:08:22 and this could go on into many sizes.

00:08:27 Large sizes of crystals or small ones, as the case may be.

00:08:31 How do you form crystals?

00:08:32 How is it possible to make them?

00:08:34 Let's go on in the next experiment and see if we can illustrate

00:08:37 one way in which crystals are made.

00:08:42 I have two solutions in these flasks, two different solutions.

00:08:46 Let's see if we can get this experiment going.

00:08:54 On the end of this rod, I have some crystals of sodium acetate,

00:08:58 a particular kind of salt.

00:09:01 I didn't even have to dip the sodium acetate into the jar, into the flask.

00:09:07 A few crystals must have fallen off as soon as I held it over.

00:09:10 The start was crystallization, and there it's taking place.

00:09:15 Spreading down through the flask until it fills it up completely.

00:09:23 The liquid was a supersaturated solution.

00:09:27 I'll define that word in just a moment.

00:09:30 When it was ready to crystallize, when I just came near it,

00:09:33 and that was a surprise rather, when I just came near it

00:09:36 so that a few crystals could fall off the sodium acetate on the rod,

00:09:39 the crystallization started.

00:09:41 It was a sort of a delicate balance, ready to go, and it certainly did.

00:09:44 Let's try the next one.

00:09:46 Maybe we'll be just as lucky with this one.

00:09:50 This is a supersaturated solution of hypo or sodium thiosulfate.

00:09:56 To do this one, I'll just drop in a seed crystal of hypo.

00:10:02 Let's see what happens, if anything.

00:10:05 There, it has fallen in.

00:10:08 There's a crystal lying in the bottom.

00:10:12 Nothing visible taking place at the moment.

00:10:15 The crystal seems to be dissolving a bit.

00:10:17 Let's drop in a few more.

00:10:20 Crystallization is a rather tricky phenomenon.

00:10:24 That is, it's not easy to do when you want to do.

00:10:27 It happens sometimes when you don't want it,

00:10:29 and when you do want it, it just won't start.

00:10:33 There are a few crystals in the hypo.

00:10:35 Let me try.

00:10:37 I think they're beginning to crystallize here a little bit.

00:10:40 Let me try a bit of technique here to stir it.

00:10:43 Maybe this will start.

00:10:51 Yes, there are some crystals beginning to form on the bottom, but very slowly.

00:10:56 Let's just stir it a bit with the rod, scratching the...

00:11:03 There they go.

00:11:04 That's all it needed was a little bit of stirring with the rod.

00:11:07 Here are some crystals on the end of the rod.

00:11:09 And now this solution is filling up with solid sodium thiosulfate,

00:11:15 crystallizing out of the supersaturated solution.

00:11:22 Supersaturated solution, that's quite a mouthful.

00:11:25 Before we can define supersaturated, let's talk about saturated.

00:11:30 A solution is saturated when enough solid is placed, dissolved in the liquid,

00:11:38 until the addition of a little bit more of solid no longer dissolves.

00:11:43 This is a saturated solution.

00:11:45 Now, in some cases, if it's done very carefully, this saturated solution can be warmed up

00:11:52 so that this excess bit of solid, which previously wouldn't dissolve,

00:11:56 will now dissolve at the higher temperature.

00:11:59 Then, if this is cooled back down very slowly to the original temperature,

00:12:03 where it was started, quite often, if this is done carefully,

00:12:07 that excess bit of solid that didn't want to dissolve at first stays in solution.

00:12:12 This is what happened here.

00:12:14 I warmed up a saturated solution.

00:12:17 It all dissolved, the salt dissolved completely, this excess bit.

00:12:20 And then I cooled them both down very carefully.

00:12:23 It's now a delicate balance, just ready to crystallize.

00:12:26 All it needs is a start.

00:12:28 The start is either stirring, throwing in a seed crystal, scratching with the stirring rod.

00:12:35 And the result is the formation of these little regularly spaced crystals

00:12:39 of the type that I showed you in the samples.

00:12:42 By the way, these solutions are quite warm.

00:12:45 They were cool to begin with, now they're quite warm.

00:12:47 The process of crystallization liberates heat.

00:12:50 Now, I'd like to point out that this all occurred rather quickly and at a rather sharp point.

00:12:56 This is one of the ways of recognizing a crystal,

00:13:00 that is, its melting point or its crystallization point.

00:13:04 If you were to heat a solid crystal to melt it,

00:13:08 you would reach a certain temperature.

00:13:10 Well, up to a certain temperature, nothing would happen.

00:13:12 The crystal would just get a little warmer.

00:13:14 Then all of a sudden, at one sharp temperature, the whole thing would melt.

00:13:18 We'll have a demonstration of that a little later.

00:13:21 The whole thing would melt, you'd have a sharp melting point.

00:13:23 And this is what I've listed, one of the points I've listed on the board here,

00:13:26 as the properties of a crystal.

00:13:28 A regular arrangement of atoms, we talked about that.

00:13:31 It has a definite form.

00:13:32 It may be cubic, it may be six-sided, it may be twelve-sided.

00:13:36 It also has a sharp melting point.

00:13:39 These are the properties which identify a crystal.

00:13:42 It may also be made up of atoms, a collection of atoms, or molecules,

00:13:46 or of ions, depending on the kind that it is.

00:13:49 And we'll see the pictures of the formation of a crystal in the next experiment.

00:13:54 Using a slide projector, let's take a close look at the formation of a crystal.

00:14:00 Now, to see this better, I should move these flasks out of the way.

00:14:13 Here's a glass slide on which I'll put a crystal or two.

00:14:19 Of this material, which is acetamide, an organic compound.

00:14:25 We'll talk more about organic compounds in a later talk.

00:14:30 Let me just sprinkle a little bit of this on,

00:14:32 and warm it up on the hot plate so that these crystals will melt.

00:14:39 There they go, starting to melt on the hot plate.

00:14:42 I'll just put a little bit more on here.

00:14:47 They're smoking because some of them have become overheated.

00:14:54 Pretty hot.

00:14:56 Put that down and spread this acetamide around on the slide.

00:15:05 Now, let me slide this quickly into the projector.

00:15:11 To see this, we'll have to turn the lights off.

00:15:13 Let's see, where's the switch? Ah.

00:15:16 Here it is.

00:15:18 On, off.

00:15:20 Lights off, please.

00:15:22 Thank you.

00:15:24 I'll put the projector on.

00:15:29 There are the little bubbles or little globules of molten acetamide.

00:15:37 As they cool off, crystals will form.

00:15:43 Some of these little bubbles are bigger than others.

00:15:55 Let's see if I can move this in a little closer.

00:16:05 There.

00:16:08 Now, there we go.

00:16:11 Still kind of warm.

00:16:13 The slide hasn't cooled off enough to form these crystals,

00:16:16 but it should form momentarily.

00:16:21 Maybe blowing it will help a little bit here.

00:16:26 The heat from the projector, you see, makes this melting.

00:16:30 It keeps this in a molten form, makes it crystallize only very slowly.

00:16:34 There they go.

00:16:35 In the upper corner, upper right-hand corner, crystallization is starting.

00:16:40 The slow growth of the needle-like crystals toward the center of the slide.

00:16:47 Maybe moving this back, actually, will be a little bit better.

00:16:54 There, kind of magnifies them a little bit better.

00:17:00 Look at that.

00:17:03 There, kind of magnifies them a little bit better.

00:17:08 Look at the feather-like growth of the crystals.

00:17:11 Notice that they grow out almost like snowflakes.

00:17:14 Well, if anyone has ever seen snowflakes,

00:17:17 they'll recognize those as being crystals of ice.

00:17:20 Water, in solidifying, forms a crystal.

00:17:24 And particular patterns, regular form, sharp melting point,

00:17:28 just like this acetamide is.

00:17:30 The reason the acetamide was chosen is because

00:17:33 it will form a crystal quickly at room temperature.

00:17:37 Now it's about finished its formation,

00:17:39 and we see there that the slide is about half covered with the crystalline acetamide.

00:17:46 A very beautiful pattern, indeed.

00:17:50 I'll turn the slide projector off.

00:17:51 I believe we'll have to have the lights now.

00:17:53 Let me turn them on.

00:17:56 Lights, please.

00:17:58 Thank you.

00:18:01 Let's go on, then, and look at a peculiar property of one type of crystal.

00:18:05 We've seen about the melting, about the crystallization, and so forth.

00:18:11 Let me show you a rather interesting property of a kind of crystal.

00:18:22 I have the description of this crystal on this piece of paper.

00:18:26 It doesn't look like there's much on it,

00:18:28 but let's warm up this piece of paper by holding it over the hot plate.

00:18:37 The writing is beginning to appear.

00:18:42 Now, I'll just hold it flat over the hot plate to get the heat closer to it,

00:18:46 so this will develop a little more quickly.

00:18:49 The writing is almost all visible now.

00:18:51 Here it is.

00:18:53 Meet cobaltus chloride.

00:18:56 Cobaltus chloride is the name of the crystal that was used

00:18:59 to show this kind of invisible writing.

00:19:02 Cobaltus chloride forms a type of crystal known as a hydrate.

00:19:06 That hydrate is a type of crystalline acetamide.

00:19:09 It's a type of crystalline acetamide.

00:19:11 It's a type of crystalline acetamide.

00:19:14 Cobaltus chloride forms a type of crystal known as a hydrate.

00:19:17 That means in the solid material itself,

00:19:20 there is some water built right into the crystal.

00:19:23 If you dissolve this crystal in water,

00:19:25 you can form a kind of a light pink solution.

00:19:28 You can write with the solution just like you would with ink,

00:19:31 except that it's invisible,

00:19:33 because the cobaltus chloride hydrate is invisible.

00:19:39 Now, when I heated it,

00:19:42 I drove off this water that's built right into the crystal,

00:19:45 and that made it a dark color.

00:19:47 It dehydrated the crystal, we say, made it appear.

00:19:51 To make this writing disappear,

00:19:53 I just have to make a hydrate of it again that is wet.

00:19:56 The cobaltus chloride and the writing should disappear.

00:19:59 Let's do just that.

00:20:02 I'll do that by blotting it with this damp sponge,

00:20:06 converting the cobaltus chloride back to a hydrate form.

00:20:13 Actually, it's warm enough around the hot plate here

00:20:16 that as soon as I stop blotting it,

00:20:18 the writing will form again.

00:20:20 There it is, disappeared.

00:20:22 And again, of course, if I were to heat it,

00:20:24 why, that would, the writing would appear.

00:20:27 I got it good and wet, so it would take a little heating to do this.

00:20:30 I'll just heat up a center portion of it

00:20:32 to show that this writing will come back again.

00:20:34 I've washed it all off.

00:20:36 There it is, starting to appear.

00:20:38 So you could write a letter in this type of ink,

00:20:40 and your friends, the one who received the letter,

00:20:43 could just wet it, dry it rather than get the writing to appear,

00:20:47 but this might disappear while the letter was being sent.

00:20:50 So this is another form of crystal.

00:20:52 Let's go on and look at the other solid material

00:20:55 about which I wanted to speak.

00:20:57 Remember I said we would talk about solids,

00:20:59 and there would be two kinds, crystals and glass.

00:21:02 Now we'll say something about glass.

00:21:05 I've differentiated between the two.

00:21:08 The housewife may not like this

00:21:10 because she talks about her crystalware

00:21:14 and glass as the same thing.

00:21:17 Well, this may be all right in the home,

00:21:19 but strictly speaking, the definition of crystal

00:21:21 does not refer to a glass.

00:21:23 The reason that word has been used for glass

00:21:26 is that glass is ice-like,

00:21:28 and the word crystal means ice-like.

00:21:30 But what are the properties of a glass

00:21:32 as different from that of a crystal,

00:21:34 both being solids?

00:21:36 Let's take a look.

00:21:39 Here's a piece of glass commonly called soft glass.

00:21:43 There's nothing soft about it, actually.

00:21:45 It's quite hard.

00:21:49 Well, look what happens when I heat it.

00:21:52 Hold it in the flame of the burner,

00:21:55 rotating it to heat it evenly.

00:21:59 Let's make it a good hot flame here.

00:22:06 There it is, good and hot.

00:22:16 Notice that as I heat it, it softens.

00:22:18 This is the key point, and you can bend glass by heating it.

00:22:22 There it is bent.

00:22:24 This is a characteristic of glass that's not true of the crystal.

00:22:27 It doesn't have a sharp melting point.

00:22:29 It has, rather, a softening point,

00:22:31 and not even a point,

00:22:32 a sort of a spread of temperatures at which it will soften.

00:22:35 Let's put this down.

00:22:37 Let me show you the properties of two kinds of glass.

00:22:39 Here I have a piece of soft glass and another kind of glass.

00:22:42 I'll just heat both of them in the flame.

00:22:45 This time, their ends.

00:22:50 Get them warm, rotate them both.

00:22:57 There, I think they ought to be warm enough now,

00:22:59 and I'll rapidly quench them by dumping them into water.

00:23:03 Well, let's see.

00:23:04 This one didn't work so well.

00:23:05 They both broke.

00:23:07 Ah, they should have.

00:23:08 They're both soft glass.

00:23:10 Chose the wrong one.

00:23:12 Here's the other one I wanted to show.

00:23:13 I'll get this one hot.

00:23:16 Didn't read my tags.

00:23:19 This one is hot now.

00:23:24 You heard the quench, meaning it's hot,

00:23:26 and you'll notice it didn't crack

00:23:28 while the soft glass frosted and broke.

00:23:31 There it is, all snowy-like and broken.

00:23:33 I'll lay it down here.

00:23:35 The heat-resistant glass is what we commonly call Pyrex glass.

00:23:39 It has been treated to make it heat-resistant,

00:23:41 that treating being incorporating some minerals in the glass.

00:23:46 Let's look at another peculiar property of this glass here.

00:23:50 Here's a little glass balloon-shaped flask,

00:23:54 which is quite hard.

00:23:58 Doesn't want to break.

00:23:59 It's quite thick.

00:24:01 Interesting-looking little flask.

00:24:03 Now, I'll pick up this piece of solid material I have here,

00:24:07 which is in itself a crystal.

00:24:09 Well, here it is out here.

00:24:10 These are a collection of them.

00:24:11 These are little silicon carbide crystals,

00:24:15 commonly called carborundum,

00:24:17 a very hard material with sharp edges.

00:24:20 To do this, I think I'd better wear my safety glasses.

00:24:24 Now, I'll take one of these silicon carbide crystals

00:24:27 and very gingerly slide it inside this flask.

00:24:32 Now, watch what happens as I invert this,

00:24:35 turn it up, rather.

00:24:37 Now, I'll swirl it.

00:24:43 Shake it up a little bit more.

00:24:46 There it goes.

00:24:47 Broke into many pieces.

00:24:49 Let's try that one again.

00:24:51 Here's another sample of the same thing.

00:24:53 Quite hard.

00:24:56 I'll put another silicon carbide crystal in

00:25:00 and let it fall.

00:25:04 Let's swirl it this time.

00:25:07 There it goes.

00:25:08 Broke into four different pieces.

00:25:11 This shows you one of the characteristics of poorly made glass.

00:25:14 This is very thick glass.

00:25:16 It's been made by starting with molten glass

00:25:19 and quenching it rapidly,

00:25:21 but not so rapidly that it would break.

00:25:23 When it's done this way,

00:25:25 the glass is under a tremendous strain.

00:25:27 It has on its surface a sort of a skin,

00:25:30 very much like the skin of a balloon.

00:25:32 You can squeeze it and pound on it, it won't break.

00:25:34 But once you puncture this skin,

00:25:36 all the stress is relieved and the glass will shatter.

00:25:39 This is exactly what happened.

00:25:41 Now, this glass is thick.

00:25:43 A mark of poor glass is usually thick glass.

00:25:45 Well, not all poor glass is thick.

00:25:47 If it's thick, it has to be made very carefully to be good glass.

00:25:50 Now, what I'd like to say here is this.

00:25:53 Glass is a solid,

00:25:55 but it's not a crystal.

00:25:57 You see, a crystal has a regular form,

00:25:59 regularly spaced atoms or molecules or ions,

00:26:02 whatever they happen to be.

00:26:03 In the glass, these little particles,

00:26:05 the molecules are not regularly spaced.

00:26:08 They're arranged every which way,

00:26:10 so glass does not have a sharp melting point.

00:26:12 It has a softening point.

00:26:14 Actually, if you were ever to put,

00:26:16 if you were to put a bottle of,

00:26:18 made of glass on a shelf

00:26:20 and let it stand there for about 20 years or 30 years,

00:26:22 over a long period of time,

00:26:24 this glass would slowly flow,

00:26:27 indicating that it's not really a solid,

00:26:29 but a very thick, viscous liquid.

00:26:32 Try this sometime.

00:26:35 Put a bottle on a shelf, come back to it 20 years later

00:26:37 and see if it has changed its shape.

00:26:38 It generally will change a little bit.

00:26:40 Glass is really a super-cooled liquid.

00:26:44 Super-cool is the new term being introduced here.

00:26:47 It is a liquid, but not yet crystalline.

00:26:50 Let's go on and look at the chemical garden

00:26:52 and see what has developed.

00:26:54 In the meantime, I think I'd better turn the burner off first.

00:27:02 The chemical garden has grown quite a bit.

00:27:05 The solution I used was sodium silicate,

00:27:08 commonly called water glass.

00:27:11 This is a commercial solution.

00:27:12 It's used in the preserving of eggs, for one thing.

00:27:16 Into this water glass solution,

00:27:18 that is the sodium silicate in water,

00:27:21 I threw in three different crystals.

00:27:23 I threw in ferric chloride.

00:27:25 These are the dark streamers.

00:27:27 I threw in magnesium sulfate.

00:27:29 These are the light ones which have formed near the bottom.

00:27:32 And I threw in a little bit of copper sulfate.

00:27:35 These are the sort of grayish streamers

00:27:38 that are slow to form.

00:27:40 They formed only little ones.

00:27:41 Ferric chloride has grown quite a bit.

00:27:43 Let's throw a ferric chloride crystal in right now.

00:27:49 And in a short time,

00:27:51 it would do the same thing that the others have done.

00:27:54 The growth of this chemical garden

00:27:56 is due to the formation of a peculiar kind of crystal itself.

00:28:00 Let me illustrate this on the board.

00:28:04 Here's our garden, or aquarium, if you will,

00:28:08 with the sodium silicate in it.

00:28:10 Liquid.

00:28:12 I threw in a piece of ferric chloride, let's say.

00:28:16 Sulfuric chloride.

00:28:18 What happens is it dissolves in the sodium silicate.

00:28:21 At the same time that it dissolves,

00:28:23 it reacts with the sodium silicate,

00:28:25 and a new compound is formed.

00:28:27 This compound is ferric silicate.

00:28:30 And it forms a skin.

00:28:32 I'll just draw a little skin on the outside of the crystal.

00:28:35 That skin sort of holds back

00:28:38 the solution of more ferric chloride,

00:28:40 but it's only a thin skin, rather porous.

00:28:42 So more ferric chloride can get through these little pores.

00:28:45 As soon as a little bit more gets through,

00:28:47 more ferric silicate is formed by reaction,

00:28:50 and another layer of skin appears.

00:28:53 And this process goes on and on and on in all directions,

00:28:57 and sort of grows in the form of a tree.

00:29:00 The same thing happened with the magnesium sulfate,

00:29:03 which I used.

00:29:04 It formed magnesium silicate

00:29:06 and formed little membranes which were porous,

00:29:08 through which the salt could leak and grow.

00:29:12 And the same thing happened to the copper sulfate.

00:29:14 So we have here a neat way of forming what looks like a tree

00:29:19 or plants growing right up in the solution.

00:29:22 Now this, if it weren't disturbed,

00:29:24 could stay for a long time,

00:29:25 and eventually would fill up the flask in all directions

00:29:29 until all the ferric chloride or all the magnesium sulfate

00:29:32 or so would be consumed.

00:29:34 But the interesting part is that

00:29:36 the crystal of the particular silicate is formed

00:29:39 starting with the original crystal,

00:29:41 either of ferric chloride or one of the others.

00:29:44 Chemical garden,

00:29:45 due to the insoluble nature of the silicate that is formed.

00:29:49 Well, let's summarize all this talk

00:29:51 and see just what we've learned.

00:29:53 We've talked about the solid form of matter,

00:29:56 realizing that all matter is either a gas, a liquid, or a solid.

00:30:00 We talked about the solid.

00:30:01 There were two kinds of solids, crystals and glass.

00:30:04 A crystal was a solid in which the atoms,

00:30:08 if there are atoms in the crystal,

00:30:09 or molecules or ions were regularly spaced,

00:30:13 had a regular arrangement and a definite form.

00:30:16 When they were heated, they formed,

00:30:19 they had a sharp melting point.

00:30:20 That is, they reached a certain temperature

00:30:21 where they melted immediately, clean and sharp.

00:30:25 We went on to look at how such a crystal could be formed

00:30:29 from a supersaturated solution.

00:30:32 We took sodium thiosulfate, which is hypo,

00:30:35 photographer's hypo,

00:30:36 and we caused crystals of hypo to be formed.

00:30:39 We did the same with sodium acetate.

00:30:41 Then by using a slide projector,

00:30:42 we could look at the formation of individual clusters of crystals.

00:30:47 Finally, we went on,

00:30:49 well, these individual clusters, by the way, were acetamide.

00:30:52 I might as well write that one down.

00:30:55 It's a particular compound.

00:30:58 Acetamide.

00:30:59 Some might call it acetamide.

00:31:01 Choose your own pronunciation.

00:31:03 It's an organic compound having a high melting point.

00:31:06 We then went on to look at the second form of a solid.

00:31:10 We talked about crystals and we talked about a glass.

00:31:12 Glass is not a crystal.

00:31:14 What the housewife calls a crystal,

00:31:16 well, that's a peculiar use of the word.

00:31:19 Glass does not have a definite form

00:31:22 or regularly spaced atoms or molecules.

00:31:24 They're all throughout.

00:31:26 It has a softening point.

00:31:27 It can be heated and softened

00:31:28 and then finally softened a little bit more

00:31:30 and a little bit more until it becomes a liquid,

00:31:32 but never a clean, sharp melting point.

00:31:35 We showed that we could bend the glass.

00:31:37 Pyrex glass is heat-resistant glass.

00:31:39 It didn't break when heated and quenched.

00:31:41 Finally, we looked at some glass which was strained

00:31:43 and we broke it by throwing in a silicon carbide crystal.

00:31:46 This constituted crystals and glass.

00:31:49 Thank you.

00:31:51 ♪

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00:32:35 This is National Educational Television.