Growing crystals is not just fun. Crystallization is a very common process in chemistry, rarely any production can do without it. But, of course, crystals are not grown in factories for the sake of beauty. There the task, you understand, is somewhat different. But if at the same time it turns out beautifully - is it bad?

And sometimes it really is beautiful. For example, when artificial bright red rubies are grown. And not just for jewelry. In wrist watches, very hard rubies play, for example, the role of supports for rotating parts. And now they have learned to grow synthetic diamonds, the hardest crystals in the world ...

I hope you will not be upset when you learn that we will not be able to grow rubies, diamonds, or other precious stones. But what we can do is also, believe me, quite beautiful.

We will obtain all crystals from saturated solutions, that is, from those in which so much substance is dissolved that it no longer dissolves. We will heat the water, then it will contain more substance. You know that sugar dissolves better and faster in hot tea than in cold tap water.

Prepare the solution as follows: pour the substance in portions into hot (but not boiling) water and stir with a glass or wooden stick until completely dissolved. As soon as the substance ceases to dissolve, this means that at a given temperature the solution is saturated. Then, when it cools, when the water begins to gradually evaporate from it, the "excess" substance will fall out in the form of crystals.

I advise you to start with a simpler substance - with table salt and granulated sugar. In two thin glasses, prepare hot saturated solutions. Put a stick or pencil on top, around which a thread is wrapped. Attach some small load to the free end of the thread, at least a button, so that the thread straightens out and hangs vertically in the solution, without reaching a little to the bottom. Leave the glass alone for two or three days. You will see that the thread is overgrown with crystals: sugar in one vessel, salt in the other.

Repeat these experiments with other substances: ammonia, calcium chloride, sodium thiosulfate, washing (soda ash), borax from a pharmacy, bitter salt (magnesium sulfate), copper sulfate, saltpeter. Carefully examine each time the crystals formed: many of them will be of different shapes. Some look like cubes, others look like needles, others look like bizarre polyhedrons. It is more convenient to look at small crystals through a magnifying glass.

Now let's complicate the experiment a little. Let's try to crystallize some substance about which you certainly know that it forms crystals well in different ways. You can take any salt from the above list, or you can supplement this list based on the results of your own observations.

By heating the water and adding the substance, prepare, as before, a hot saturated solution. But don't put a thread in it. Pour cold tap water into a bowl or saucepan (a few ice cubes from the freezer will not interfere), put a glass of solution in it. A lot of small crystals will fall out very quickly. They are so small that they look like powder.

Now you know: to get small crystals, you need to cool the solution quickly. And you can assume that for large crystals it is desirable to cool the solution more slowly. Quite right!

Prepare a new portion of the saturated solution. (However, if there is no use for small crystals, you can simply heat them again with the cooled solution - it will become saturated again.) Be that as it may, this time do not allow the solution to cool quickly. To do this, cover the vessel with cotton wool or wrap it in an old towel. And even better - pour the liquid into a thermos, close it with a cork and leave it for a day or two. Do not forget only after that in the most thorough way, and more than once, wash the thermos to a full shine with a soda solution or special dishwashing detergents.

On slow cooling, much larger crystals will fall to the bottom of the vessel. Sometimes they turn out neat, sometimes they are connected to one another, forming bizarre splices. If they are too fused, then prepare a new solution, taking more water or less salt.

One more warning. The substances you work with may not be very pure. If there is dirt in the solution, it must be filtered immediately after heating. Insert a piece of cotton wool into the spout of the funnel and pour the solution prepared by you through the funnel into another vessel. I advise you to rinse the funnel with boiling water so that the solution, in contact with it, does not cool down. Otherwise, crystallization may begin right in the spout...

You can show large crystals that have fallen to the bottom to relatives and friends, or you can, if you have enough patience, grow even larger, simply exceptionally beautiful crystals of the same table salt, or copper sulfate, or saltpeter. Wonderful crystals are obtained from alum. They are sometimes sold in photo shops, they are also in pharmacies - hemostatic pencils are made from alum. There are different alums, this is a whole group of salts; which ones you can buy doesn't matter, and if you buy different ones, it's only for the best.

So, collect the crystals that have settled to the bottom during slow cooling, dry them on a napkin or on a sheet of blotting paper and put them in bottles with tightly closed stoppers. Do not pour saturated solutions - in them you will grow beautiful large crystals. In order not to confuse the solutions, if you have several of them, make labels and stick them to the jars.

From the crystals of each variety, find the most attractive (not necessarily the most even), tie it with a thin silk or nylon thread, for example from an old stocking, and lower it into a solution of the appropriate salt. You can wind the thread around a pencil, placed on the edges of the jar, and cover the top with a paper lid so that dust does not get into the jar. Do not forget to poke a few holes in the lid so that the water can evaporate from the jar. If it is more convenient for you, then tie a thread to a match, and thread the match through one of the holes in the paper cover. The weight is not great, and the match will withstand.

Keep the jars in which crystals grow in some secluded place, away from drafts. Say, behind the glass of a sideboard or bookcase. Keep an eye on the level of the solution and, if a lot of water evaporates, add a portion of fresh saturated solution. The crystal must be entirely in the liquid at all times.

Be patient. It will take several days before the crystals increase noticeably and close the threads that bind them. Perhaps ugly growths will appear on the crystals. They can be removed by scraping with a razor and lightly rubbing with a damp cloth. In two or three weeks, the crystals will grow so much that they can be demonstrated. And you can wait, if, of course, you have the patience. And two months to wait, and six months ...

If you have several types of alum, it will be interesting to prepare saturated solutions of each and alternately, once a week, transfer the thread with the crystal from one solution to another. Then you get a multilayer crystal.

The growth of the crystal can be controlled by taking it out of the jar from time to time and tweaking it. Remove unnecessary outgrowths; if you want some line to stop growing, smear it with Vaseline; it is necessary that it starts growing again, remove the vaseline with a cotton swab moistened with acetone. If, however, we take fused or branched crystals from the very beginning, we get a crystalline cluster (it is called a druse).

But please note: when you decide to remove a druze or large crystal from the solution, don't forget to coat it immediately with colorless furniture polish or nail polish. Otherwise, very soon, after a few days, the crystals will begin to erode, and all your work will go down the drain.

Our final experience with the crystals will indeed be like a miracle. Let's grow copper crystals. Not copper sulfate (you already did this), but real metallic copper.

Without knowing it, you once made a similar experiment - when you lowered an iron nail into a solution of vitriol. But the red crystals that covered the nail were so small that they seemed like a solid film to you. And in general, as you already know, growing small crystals is not a trick. Well, let's grow big. But for this it is necessary to somehow slow down the reaction of iron with copper sulphate. We'll slow her down with table salt.

At the bottom of the jar, put a little blue vitriol and fill it with fine table salt, preferably the "Extra" variety. Cut out a circle from a blotting paper of such a size that it touches the walls of the jar, and close the vitriol with salt with it. Place a slightly smaller iron circle on the paper. How to cut it out, figure it out yourself, just don't forget to wipe it with sandpaper and wash it well before the experiment. Pour a saturated solution of table salt into the jar, let it completely cover the iron circle. Leave the jar alone for about a week. Then remove the circle and look: red copper crystals have grown in the jar.

Perhaps you would like to keep them? In this case, take it out, rinse it with water, transfer it to a small bottle and fill it with pharmaceutical hydrochloric acid (or vinegar). Close the bottle with a stopper, and the crystals will last for a long time.

Working with crystals is unhurried, and while the crystals are growing, you can set up other instructive experiments. For example, with gelatin.

Yellowish gelatin powder is sold in grocery stores. Combining with water, this substance forms a jelly, more or less dense. For this reason, various tasty things are prepared with the help of gelatin - from aspic fish to sweet jelly. By the way, jelly in this case is not the name of the dish, but a completely scientific word that denotes such frozen, semi-liquid, semi-solid solutions.

Where, besides cooking, is gelatin jelly used? Yes, at least on film. The emulsion of almost any photographic film is made on the basis of gelatin with the addition of substances that are sensitive to light. The jelly adheres very strongly to the film, freezes on it, and it is transparent and transmits light rays.

You can check how sticky gelatin jelly is. Drop an incomplete tablespoon of gelatin (about 10 g) into a quarter cup of cold water and leave for an hour or two so that the powder has time to swell properly. Pour the mixture into a small saucepan. There is nothing dangerous in this, because gelatin is a food product. Heat the mixture over low heat, make sure that it does not boil in any case! Stir the contents of the saucepan until the gelatin is completely dissolved. (Even better, though more troublesome, is to heat in a water bath, that is, put the vessel with the mixture in another, larger vessel into which water is poured. It should be hot, but not scalding, about 50 ° C.)

When you get a homogeneous transparent solution, pour some of it onto a clean piece of glass or unnecessary ceramic tiles. And the other part - on plastic wrap, at least on a transparent bag in which bread is kept so that it does not stale. Let the solution dry. And try to tear it off the glass or the tiles. You probably won't be able to...

No wonder: gelatin of a worse grade, not as carefully as for food, peeled, is called wood glue. Although there are many more modern adhesives now, carpentry is still in use, and not only with carpenters: rarely can it be compared with its adhesive power.

Now let's deal with that film of gelatin, which is frozen on a plastic bag. Since it almost does not stick to polyethylene, then carefully remove a thin sheet and, trying not to tear, cut out the silhouette of a fish from it. Place the fish on blotting paper and breathe gently. The fish will immediately begin to squirm and curl up. From your breath, the film is moistened, absorbs a little water, but only on one side, on the outside. This is where she bends. Why not focus?

With a thick gelatin solution, experiments can also be done in test tubes (or in vials), but this requires a more liquid jelly. If you still have a gelatin solution from previous experiments, then carefully, preferably in hot water, heat it up, dilute it four times with water, stir well and warm it up so that the solution becomes homogeneous. If you are going to prepare the solution again, then take about two grams of gelatin for a quarter glass of water, that is, about half a teaspoon. Remember not to boil!

Pour the hot solution into two vials. When it hardens (to speed up, you can put the bubbles in the refrigerator), in the middle of the bubble, with a quick and careful movement, insert the tweezers into which the potassium permanganate crystal is clamped. Slightly open the tweezers and take them out just as quickly, trying not to tear the jelly. In another vial, add a crystal of copper sulphate. Gelatin slows down their dissolution, and for several hours in a row you can observe a very interesting picture: a colored ball will grow around the crystal.

Perhaps this experience will not work the first time. However, it is worth practicing so that it eventually succeeds.

Pour the same hot gelatin solution into two other vials. Before it hardens, add a little phenolphthalein solution to one vial, and a little washing soda solution to the other. When a jelly is formed, then with tweezers, as before, insert a lump of soda ash into the middle of the first bubble, and a grain of phenolphthalein into the middle of the second. In both cases, a crimson color will slowly spread through the thickened solution. But from a grain of phenolphthalein, it will move more slowly. The explanation is this: phenolphthalein molecules are much larger than soda molecules, and therefore they move more slowly.

The next experiment with gelatin jelly will be a little more complicated. It will require not two, but three substances: citric acid, potassium dichromate and silver nitrate. With citric acid, everything is simple. As for the other two substances, potassium dichromate, also known as potassium dichromate, is found in photographic stores, and silver nitrate is found in a pharmacy. This nitrate has another, perhaps more famous name - "lapis". Please note that for our experiments it is not necessary to have pure silver nitrate. A lapis pencil sold in a pharmacy will also work (it is used to cauterize the skin). The tip of this pencil consists mainly of the same nitrate, and the impurities that it contains will not interfere with us.

Again, as you already did, prepare a solution of gelatin - at the rate of half a teaspoon to a quarter cup of water. Let me remind you that in no case should the solution be boiled. While the gelatin solution is still hot, pour about 10 cm3 of water into two clean bottles (this is where the beaker comes in handy). In the first bottle, dissolve about half a gram of potassium bichromate, in the second - the same amount of citric acid * If you do not have scales, take these substances on the tip of a spoon, no special accuracy is required.

Now add to the gelatin solution about a tenth, that is, about 1 cm3, of the contents of the first bottle (potassium bichromate solution) and half as much as the second solution (citric acid). While the mixture has not cooled, pour some of it onto a clean glass plate and leave for a while so that the solution turns into a jelly. And when this happens, drop one, but a large drop of a solution of silver nitrate (lapis) into the very middle. This solution should be strong enough, so don't take too much water for it. Let it be about three times more than lapis.

As in many other experiments with jelly, then you will have to be patient: after all, in thickened solutions, the reactions do not go quickly. But, as you probably expect, they do not go quite normally, ..

Your expectations will come true. In the jelly, a red ring will appear around the drop. Some time later, the next colored ring will appear, after it, at some distance, the third, fourth ... Each ring is separated from the next by a layer of colorless jelly. In the middle, near the drop, red circles are closely spaced, one to the other, and the farther from the center, the rarer and paler they are.

Such rings in jellies are called Liesegang rings, after the German chemist who discovered them. In our case, these rings are formed by reddish crystals of silver bichromate - a substance that is formed by the interaction of potassium bichromate (in the jelly) and silver nitrate (in a drop). And citric acid helped us slightly increase the rate of this reaction.

But if so, then, apparently, citric acid can somehow affect the nature of the rings formed? Quite right. Try varying the amount of citric acid added to the jelly, and you will find that when there is more acid, the rings are less frequent, and vice versa.

You must have left the gelatin solution, as well as the potassium dichromate solution. In this case, combine them in the same proportion, but do not add citric acid. Fill a tall vial or test tube with a warm solution about three-quarters and leave for several hours, and best of all for a day. In the resulting jelly, drop a few drops of silver nitrate solution, but only diluted two or three times compared to the previous experience. Close the vial with a cork, and under it, so that the solution does not evaporate, put a cotton swab moistened with water.

If you leave the test tube for several days in a dark place, then Liesegang rings will appear in it, as in the previous experiment. Only this time they will be located along the height of the test tube, and in the upper part, closer to the drop, the rings will be thicker and redder.

Did you pay attention to the warning that it is better to keep the test tube in a dark place? Please do not neglect this advice: experiments with Liesegang rings work best when they are not placed in a bright light. And preferably in a cool room. In any case, the temperature in the room where you are going to do these experiments should not be higher than 20°C.

And for some experiments with gelatin, hard frost is needed. Properly prepared jelly allows you to get ice patterns, like on glass in winter, and not only get them, but also keep them warm (which, unfortunately, is not possible with real frosty patterns on glass).

This time the ratio of gelatin and water is as follows: 5 g of powder (about a teaspoon) to a quarter cup of water (about 50 g). The cooking method is the same. Pour the warm solution onto a glass plate and immediately place in the freezer. If it's winter outside, then, of course, you can put the record out in the cold. After two or three days, bring it into the room and let it thaw slowly. The ice, as you understand, will disappear, but the imprints of frosty patterns will remain.

But maybe you are more interested in getting fingerprints, like in detective stories about detectives and criminals? Well, it's not such a difficult problem. Of course, the investigators have better equipment, they find the weakest prints, barely noticeable. But they also have a responsibility. And for the show, improvised means are also quite suitable: a candle, a plate and talc powder from a pharmacy.

A candle and a plate are needed in order to prepare soot. Hold a cold plate over a lit candle. She will be covered in soot. Scrape off the black residue from the plate onto a sheet of waxed paper, parchment, or plastic wrap. Repeat several times. When there is a noticeable amount of soot - say, a quarter of a teaspoon - mix it with an equal amount of talcum powder.

Now leave an imprint: breathe on some finger and press it to a sheet of white paper. So far, nothing is visible on the sheet. Sprinkle this place with black mixture. Shake a piece of paper so that the mixture covers well the area where you pressed your finger; You can very carefully draw several times with a soft squirrel brush. Pour the rest of the mixture back onto parchment or polyethylene. If everything was done carefully, a clear fingerprint will remain on the paper.

See if your other fingerprints look like him. Look at what different people's fingerprints look like (ask them to press their fingers against the paper). Do you understand now why fingerprints at a crime scene reveal a criminal? Among them, no two are the same, just as there are no two completely identical faces.

You can check whether this method is suitable for detecting prints on newspapers and magazines, on cardboard and plastic boxes, on glass. In the latter case, use some kind of glass, preferably of no value. When you prepare a mixture of soot and talc, take more talc, about double the amount. After sprinkling the surface of the glass with the mixture and shaking off the residue, slightly heat the glass over the candle - the prints will become more noticeable.

It remains only to explain what is the matter here. Whether we like it or not, we always have some fat on our skin. It is secreted by the subcutaneous sebaceous glands. Whatever we touch, we leave an imperceptible trace on everything. And the mixture you prepared sticks well to fat. Thanks to the black soot, it makes the print visible.

But, perhaps, even more surprisingly, the mark remains even if there was no fat on the surface. Absolutely clean surfaces in nature, probably, do not exist at all. They can, of course, be created artificially (if not perfectly clean, then close to ideal), but in natural conditions on every object, even on one that seems very clean to us, it is full of dirt.

Where does this dirt come from? From contact with other substances and objects. Finger grease is only one of the possible contaminations, although it is very common. And even if the object, as it seems to us, did not come into contact with anything, it does not matter - it is in constant contact with air. And in the air there are dust particles visible to the naked eye, and dirt particles so small that they can only be seen with a microscope, and even such that even a microscope cannot be seen. And there are tiny droplets of liquid that are in the air in the form of vapor and mist...

That is why thousands and millions of particles of various substances are deposited on the surface of each object. Adsorption takes place (of course, you already remember this word), and we can easily detect it in a very simple experiment.

Take a small mirror (you can also use the one that your family uses, because nothing bad will happen to it). Wipe the mirror very carefully with a clean cloth so that no visible traces of dirt remain on it. On the mirror, we will try to "translate" the drawing from some metal flat plate. You can scratch with a file on an iron plate a simpler drawing or a few letters; and if you don’t feel like messing around, then just take a copper coin.

On a clean mirror, carefully place the plate with the pattern; no need to press it, let it lie freely. A minute later, very carefully so that the mirror and the plate do not move relative to each other, lift the plate and look at the mirror. I can not see anything? Well, just like when fingerprints appear on the surface, we have a latent image that needs to be developed. After all, we know for sure that the molecules of various substances that were on the surface of the metal and polluted it, probably passed to the mirror, and not just anywhere, but in those places where the metal came into direct contact with the glass. But how do you find them?

With my own breath. Breathe on the mirror several times, and you will see the imprint of the pattern that was on the metal plate. Most likely, this print will be weak, but it will be there anyway.

In experiments with lime water, when you breathed into the water through a tube, you found out that there is always carbon dioxide in the exhaled air. Now it's time to say that moisture is necessarily present in it. Actually, everyone saw her - in the cold, steam escapes from the mouth. The water that is in the air that you breathe out instantly cools in the cold and turns into tiny cold droplets, like those droplets that make up fog, as well as clouds. This is how invisible water vapor becomes visible.

It was this moisture from your breath that showed an imprint on the mirror. On clean glass and on dirt particles, it is deposited in different ways. The cleaner the surface, the easier water droplets settle on it, and moisture almost does not linger on contaminated areas. So the invisible image becomes visible. What you managed to see on the mirror is drawn, one might say, with water from your exhalation.

Hurry up to see the picture, because very soon it will disappear. Well, you can breathe on him again, then again and again. But for some reason, each time the print becomes more and more faded.

If it were in open space or in a deep vacuum, that is, in a space from which almost all the air was pumped out, then nothing would have happened to the surface of the mirror. But in the air, more and more particles are deposited on it, all kinds of extraneous molecules, which gradually cloud the picture and make it almost indistinguishable.

If you want the picture to be more distinct from the very beginning, wipe the mirror thoroughly with a dry woolen or synthetic cloth before the experiment. And not so much to make it cleaner, but to electrify.

Even in antiquity, it was noticed that when various surfaces are rubbed, electric charges arise on them. Try running a plastic comb through your hair a few times or rubbing it against wool or fur, and then bring the comb to the paper, torn into small pieces. Paper scraps will immediately stick to such an electrified comb. Glass also becomes electrified when it is rubbed with a cloth, and the electricity that accumulates on its surface, albeit very weak, helps pollutant molecules to move faster to the mirror. And then, when you breathe on the mirror, the same electrical forces attract and hold water droplets.

In the last chapter of this book there are many experiments with electricity, but they will need batteries or the simplest accumulators. And now, continuing the topic, let's put one more experiment with electrified particles.

Break a simple pencil, remove the lead from it and finely grind it to make a powder. To it, add a little (literally a drop or two) of a mixture of household lubricating oil, which is used to lubricate, say, bicycles and sewing machines, with an equal amount of gasoline for lighters. Although you need very little gasoline, do not forget that it is very flammable, and make sure that there are no open flames nearby.

You will get a black graphite-oil-gasoline slurry. Rub it for several minutes, because when rubbing, two useful processes take place at once: firstly, the graphite particles become smaller and smaller, and secondly, they are charged by friction, and this will be very useful to us in the experiment.

When you have finished grinding, dilute the slurry with a new portion of the mixture of lubricating oil and gasoline, but now take much more mixture and with even more attention make sure that there is no fire nearby. Dilute the gruel to such a state that the mixture in the vial or in the test tube seems almost transparent. Stir it again, and then take a comb or a glass rod, a plexiglass ruler, etc. in your hand. Rub such a plastic or glass object on a woolen or synthetic fabric so that it becomes electrified. This will happen faster if you slightly lubricate it with any machine oil - you can use the same one from which you prepared the mixture for diluting graphite powder.

Bring a stick or comb to a vessel with a transparent-looking liquid. When you do this, then the particles of graphite, which are also electrified by friction, will begin to move towards your hand. Again, rub the stick or comb, bring it to the vessel - and do this five or six times. Then pour out the liquid. In the vessel where it was, just opposite the place to which you brought the wand or comb, there was a clear black imprint on the glass.

Such an experiment works well not only with graphite, but also with other substances, for example, with ordinary table salt. It also needs to be rubbed well with a mixture of oil and gasoline; then the experiment is set in the same way as with graphite slurry. Since table salt is white, after the experiment, it goes without saying that a white imprint will remain on the glass.

We often use common salt and sodium chloride in our experiments. This is one of the most popular substances in chemistry, known to people since ancient times.

Perhaps you know that in the old days salt was highly valued and in some countries it was used as a substitute for money. Such a respectful attitude towards table salt was due to the fact that people were usually content with native salt, which is rare, at least in accessible places. Meanwhile, there are salt lakes in the world, the water in which is literally saturated with table salt. And there are seas and oceans, in the water of which millions of tons of sodium chloride are dissolved ...

It would seem that you take salt from sea water, there is more than enough of it on Earth ... That's how it is, but in addition to table salt, sodium chloride, other salts are dissolved in sea water, which we do not need, in any case, when we add salt to food. This is what we will test experimentally.

If you do not live by the sea, then you can do two things. Either ask someone who is going to the sea to bring you a bottle of sea water (and if you yourself go to the sea on vacation, then you don’t need to ask anyone), or - and this is probably easier - buy a package of sea salt at the pharmacy .

Dissolve a little salt in water so that the solution resembles ordinary sea water in strength, for which take thirty to fifty grams of sea salt per liter of water. The exact proportion is not important, and, in fact, it does not exist, because in different seas the salinity of the water is different.

It is possible that sea water made from dry salt will not be very clean; in this case, filter it through a clean cloth or paper filter. And then take a deep plate and a large bowl (or pan), into which pour ordinary tap water and set it to heat up. This large bowl (or saucepan) will serve as your water bath, in which you will evaporate the sea water.

So, putting a plate of sea water in a water bath, watch what happens. The first time, while the sea water has evaporated a little, there are no changes. But then, as it evaporates, salts dissolved in water begin to precipitate. In which order depends on the composition of the sea salt, but calcium sulfate always precipitates first. You probably know this substance, but under a different name: calcium sulfate is gypsum. It is very often used in construction, in art and in medicine, because gypsum has a remarkable ability to harden and turn into a white stone when combined with water.

When a white precipitate of gypsum appears at the bottom of the plate, it must be carefully removed from the water bath (I hope you understand that this must be done not with bare hands, but with a thick rag so as not to burn yourself). Once the liquid has cooled slightly, filter it through a clean cloth or filter paper and continue to evaporate the remaining clear solution. Soon after that, the very salt that we were trying to get, sodium chloride, will begin to precipitate.

Again, carefully, so as not to burn yourself, remove the plate and filter its contents. Air dry the white wet residue that remains on the filter, and you can heat the brine further. As it heats up, other salts will begin to precipitate out of it, primarily magnesium salts, which, as you probably remember, are among the hardness salts (like calcium salts). It is thanks to them that sea water is extremely hard, it is absolutely impossible to wash it with ordinary soap, it does not even foam.

The table salt that you got by evaporation is not good for food. To use such salt for food, additional purification is required, which most likely cannot be done at home. In industry, such salt, together with impurities, can be used quite well. If so, then you can use it for those chemical experiments in which common salt is involved.

Let's try to extract some substance containing magnesium from the remaining brine. To do this, mix the brine with lime water, and then a white precipitate will fall out. It is called magnesium hydroxide, it is a very useful substance for industry. And you can also extract iodine from the brine, but we won’t even start such an experiment, because we can’t do it. To get just one gram of iodine, you would have to evaporate about twenty tons of sea water ...

And one more way to extract table salt from sea water. Do you think the ice that floats in the seas in winter is fresh or salty? Let me tell you right now, it's fresh. Icebergs, even the largest ones, are also made entirely of pure fresh water. There are even projects on how to tow such icebergs to the coasts of Africa and South America, to deserts and arid steppes, melt them there and use the resulting water for drinking and washing ...

Ice in the sea is always fresh, that is, when ice forms, salts do not pass into it, but remain in the water. We will try to use this property to get table salt.

Put a little sea water in the freezer of the refrigerator; You can use ice molds for this. Since you took not tap water, but sea water, all of it will not turn into ice. Carefully separate the fresh ice from the brine. Since the ice now contains almost no salts, the brine, as you might guess, contains these salts in a much higher concentration than the original sea water.

As in the previous experiment, evaporate the brine in a water bath. But since its strength is much higher, salts will precipitate out of it much faster and in greater quantities.

The next miracle will also be instructive. You and I will get natural rubber. The same rubber from which tires, galoshes and balls are made.

The basis of any rubber is flexible, resilient rubber, capable of incredibly strong stretch and shrink, and then again take its former shape. Natural rubber is obtained from the juice of some plants, mainly the Brazilian hevea, which is specially grown for this purpose in hot regions, and not only in Brazil, but also in many countries of Asia and Africa. Hevea is an evergreen tree from the Euphorbiaceae family. Stop! There are a lot of milkweeds in the world; so is it possible to get rubber from other plants containing white milky juice?

It is possible, although such rubber will be worse in quality than that obtained from hevea. But in order to be convinced of this possibility and to get at least a drop of natural rubber on our own, we will set up a simple experiment with any available euphorbia plant.

If you decide to do this experience in the summer, then there is hardly a more affordable plant than the dandelion. However, instead of it, you can take any other plant with milky juice and test it for the presence of substances resembling rubber. And it will be even easier to use the leaves of ficus - a very common houseplant. In this case, you no longer have to wait for summer, because ficus, like Hevea Brazilian, is an evergreen plant. We will not destroy it, two or three leaves will be enough for us, and for a ficus this is not a great loss.

So, take a few dandelions or ficus leaves and squeeze the juice out of them as much as you can. Add a few drops of calcium chloride or ammonium chloride solution to the juice. Under the action of these substances, the shell, which is surrounded by rubber particles in the juice, will begin to collapse. And when such a shell is destroyed, nothing prevents the tiny particles that float in the juice from uniting, merging into larger particles.

Stir the mixture. Although the rubber particles in it have already begun to stick together, this is still invisible to the eye. Add some alcohol or cologne to the mixture. Droplets of rubber after this operation can be seen with the naked eye.

Separate the droplets floating in the liquid from the solution, for example, by straining them through gauze, and then dissolve in a few drops of gasoline. You have a solution of natural rubber.

Of course, we cannot make real rubber out of this rubber; frankly, even if it could, such rubber is unlikely to be durable. But you can easily verify the elasticity of the rubber extracted from the juice. Drop the benzene solution on the glass and wait until the solvent has evaporated. On the glass you will see a transparent, very thin film of dried rubber. Carefully separate it from the glass and see how it stretches and contracts. After such a test, there is no longer any doubt - this is really an elastic rubber.

Previously, hevea rubber was, in fact, the only elastic material, and all rubber was made from it. Now it has been noticeably replaced by synthetic rubbers, that is, those obtained at factories, synthesized artificially from other substances. A variety of synthetic materials - and not just rubber - in the world is becoming more and more. After all, the possibilities of nature are not unlimited. No doubt, wool is a wonderful material, but in order to dress all mankind in woolen dresses, sweaters and sweaters, it would be necessary to breed so many sheep that they might simply not have enough food. Cotton fabrics are also very good, but you can't give all the land for cotton, you have to grow wheat and potatoes, apples and apricots somewhere.

There are many such examples. Well, where is the exit? As for our clothes, the way out, of course, is that, along with cotton and wool, it is necessary to make artificial fibers. Of these, it is possible to prepare yarn and fabric, which is no worse than that made from natural materials. However, to be honest, today synthetic fabrics are somewhat inferior to natural ones. But not much. And let's not forget that people have been growing fibrous plants and raising sheep for many millennia, and the history of artificial fibers dates back at most a few decades. So the materials invented by chemists are still ahead ...

Let's learn how to make artificial fiber, and not just any, but silk. We will prepare it in almost the same way as in the factory, only in a slightly smaller quantity ...

The most famous man-made fibers similar to silk are viscose and acetate. But with the substances that we have at hand, such fibers probably cannot be obtained. But the very first (and quite good) fiber of this kind - copper-ammonia fiber - we, perhaps, will succeed.

Prepare copper ammonia solution. Dissolve five teaspoons of copper sulfate in a small amount of water, add a teaspoon of soda ash and stir. A new substance is formed in the flask - basic copper carbonate (basic - from the word "base"). Pour the solution into some clean tin, such as a washed tin can, and heat over low heat to evaporate the water. There will be sediment at the bottom. Carefully pour out the rest of the water from the jar, cool the sediment and transfer it to a piece of blotting paper - let it dry.

This powder is one component of the copper ammonia solution. And the second, as you might guess, is ammonia, the solution of which is called ammonia. However, pharmacy ammonia is rather weak for our purpose. Hardware stores sell a stronger, 25 percent ammonia solution. Keep in mind that it has a strong smell, after work (or even during work) ventilate the room. Or put the experience on the balcony. Ammonia you need quite a bit, 20 - 30 ml. If you have a beaker, then measure this amount, and if not, then take into account that a tablespoon contains approximately 20 ml of liquid.

Add a teaspoon of powder obtained from copper sulphate to the ammonia solution, close the vial with a rubber or plastic stopper and shake well. You will get a dark blue liquid. Pour it into two smaller vials, picking up a cork for each. Add regular cotton wool in portions to the first vial, close with a stopper and shake well. In the second, put small pieces of blotting paper in the same way. Wait for the solutions to become thick, like syrup. Such solutions are called spinning solutions, because fibers can be spun from them. But first, let's try to get the material in the form of flakes.

Pour some diluted vinegar into a glass. Drip into it slowly any of the spinning solutions prepared by you. The flakes will immediately fall out." In composition, they are exactly like the fiber that we want to prepare. In composition, but not in appearance ...

Let's do this: pour vinegar into a glass and add a drop of spinning solution. The drop will begin to sink to the bottom, thickening on the go and leaving a trail in the form of a thread. Try to pick it up with tweezers or a splinter, after training it succeeds; but it is even better to set up the experiment together, so that one drips the solution, and the other drags the thread.

We can make a good thread, smooth, even and shiny, with a medical syringe, Or with a needle from a syringe inserted tightly into a rubber tube. Take the spinning solution into a syringe (or into a rubber tube; close the free end of the tube with a wooden plug or a suitable stopper). Pour the vinegar into some kind of flat dish, say an old plate, and gently squeeze out the liquid by pressing the plunger of the syringe or squeezing the rubber tube. Ask a friend to grab the thread with tweezers and gently pull it through the vinegar in the plate. If you practice, you can even wind this thread on a spool.

At the factory, in principle, they do the same: they force the solution through very thin holes and dip it into a bath, where the fibers become hard, flexible and glossy, as it should be for silk fibers. Let it be artificial.

Now - an instructive experience from the field of photography. Perhaps you know that photosensitive emulsions that cover photographic film and photographic paper contain silver salts. These salts decompose under the action of light, and in this case crystals of metallic silver are formed; in this form, the silver is "painted" black. Here is a brief summary of the main principle of black and white photography.

You recently dealt with silver salt: when you experimented with jellies. Only you had lapis, silver nitrate, and it is not suitable for photography. Here you need, say, silver chloride. Getting it from nitrate is easier than a lung - just carry out a reaction with ordinary table salt, sodium chloride.

Prepare a solution of lapis and a solution of table salt. Before you mix them, remember that you must form a substance that is sensitive to light. And if so, then you need to mix in the dark (not necessarily in complete darkness, but in any case with good blackout). As soon as the solutions are combined, the desired silver chloride will precipitate - a white fine powder. Drain the solution and lay the precipitate in an even layer on a piece of blotting paper. Cover the layer of silver chloride on top with some other paper sheet with a pattern cut out on it or tracing paper, on which something is drawn or written in ink. Take this structure out into the sunlight for a few seconds or put it under a bright lamp. Those areas that were not covered will darken very quickly: black metallic silver stood out from the silver chloride in the light.

Such an image will be very fragile. If you want to save it, you will have to do the same as in a real photograph: first develop it in a developer solution (and then the illuminated places will become even darker, more distinct), and then fix it in a fixer solution (and then the silver chloride that not decomposed by light). Now you can take out the image even to the brightest light - nothing will be done with it. As with the most real black and white photography.

Finally - the shortest experience of the instructive. Short but effective.

Take half a glass of water, dissolve about half a teaspoon of sodium thiosulfate (hyposulfite), add five to six drops of vinegar and stir. Nothing happens. Don't rush, wait! After a few minutes, the solution will suddenly, by itself, become cloudy. How long will it take? It depends on how much hyposulfite you put in. But if so, why not make a chemical clock? Let's do. Prepare a hyposulfite solution - somewhat stronger than in the previous experiment (take either more powder or less water). Pour half of this solution into a vial, and dilute the rest with water to the previous volume. Pour half into the second vial, and what remains, again share with water. Half - in the third vial, mix the rest with water - and the fourth vial. All.

Place four vials in a row and quickly drop a few drops of vinegar into each. Put a watch with a second hand in front of you and mark the time. At regular intervals, the liquid in the bubbles will instantly become cloudy.

But what is the lesson in this beautiful experience? The fact that not all reactions, even with already known substances, take place in the same manner. And it is not without reason that before building a workshop in which some important and necessary substance will be prepared, chemists carefully study dozens and hundreds of reactions in flasks and test tubes for a long time, sometimes for years.

And this, I must say, is a very interesting occupation.

Author: Olgin O.M.

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