How and from what is chalk made. Research project "Production of colored crayons at home Buy school chalk wholesale and retail

Everyone has known white and colored crayons since childhood. The appearance in Russian schools of modern boards, on which you can write with special markers and felt-tip pens, has led to a sharp decrease in the production of school chalk. However, crayon manufacturers are trying to find new distribution channels.

There are two main types of school chalk: lumpy and pressed. The natural chalk used to make school crayons comes from quarries or is extracted from rock. This raw material is absolutely safe, non-toxic and does not contain impurities. The pressed chalk is based on calcium sulfate, which is obtained from gypsum. For the manufacture of school chalk of a certain shape, starch and limestone are used. Lump natural chalk almost entirely consists of calcium carbonate. For the production of school chalk, sorted natural chalk is used.

Colored crayons are produced using a similar technology, with the only difference being that various dyes are added to the mass during the production process. The manufacture of chalk for drawing and writing on boards and on asphalt includes several main steps: grinding raw materials, settling heavy impurities, drying on a grate, adding a sticky substance, and molding.

For the manufacture of the highest quality crayons, elutriated chalk (or, as it is also called, melted) is used. To prepare elutriated chalk, natural chalk is broken into pieces, sorted, impurities removed, and then ground with water on millstones. The resulting mass is settled, as a result of which heavy impurities (sand, stones) are deposited at the bottom of the tank. Then the liquid with a purer raw material is passed into the second, and then into the third vat until all impurities are at the bottom of the container and are removed. The remaining chalk solution is left for several hours to settle, after which the water is drained, and the remaining mass is transferred to boxes with perforated walls, which are covered with a cloth. Then the mass is dried on grates. If the chalk crumbles during drying, then a small amount of dextrin solution or glue is added to it. Recently, the so-called non-crumbling crayons without dust have become increasingly popular. They are made using a special technology using casein. The main difference between such crayons and ordinary crayons is that they do not stain hands and clothes when used.

Colored crayons must also have a certain hardness. However, when dyes are added to the chalk mass after drying, the chalk becomes too crumbly. Therefore, in the manufacture of colored chalk, chalk powder is mixed with a certain amount of mineral paints to obtain the desired shade and kneaded in an aqueous solution of wood glue, gum arabic or dextrin. In principle, any mineral paint can be used, but keep in mind that when mixed with chalk, some colors are distorted (for example, cormorant, Prussian blue and chrome yellow). Colored crayons can be used not only for drawing on the asphalt (in this case they must be very hard), but also for writing on the board. To give the crayons more softness, soapy water, oil or wax are added to them. The finished and dried crayons are dipped in oil, which improves their color and makes them more soft. A mixture of chalk, dye and binder is laid out on a flat surface, which is previously covered with several sheets of paper. Paper absorbs a large amount of moisture, as a result of which the chalky mass acquires a thick consistency. When the mass becomes thick enough, a piece the size of a nut is taken from it, and then it is rolled into a cylinder. At the last stage of molding, the cylinder is rolled with a smooth plank to give it a smooth surface. Finished crayons are laid out on boards, covered with paper and dried at room temperature.

This technology, due to the large amount of manual labor, is considered quite expensive. To reduce the cost of production, crayons are made from a mixture of light clay, water and chalk, to which a dye is then added - ultramarine (for blue crayons), mummy and cinnabar (for red crayons), ocher (for yellow crayons), etc. The whole mass is evenly mixed and it is transferred to special wooden or metal forms, previously lubricated with fat. After molding, the pieces of chalk are removed from the molds and left to dry in the air or in a poorly heated room.

In addition, crayons can be made by grinding elutriated chalk with burnt gypsum (which does not set when wet) and steatite. Then mineral paint is added to the mixture, and it is kneaded with a weak solution of dextrin. The mass is placed on filter cloths to remove excess moisture. The dried mass is cut into prisms of the desired size and left on gypsum plates to dry, from time to time turning them over to the other side.

The degree of drying of the chalk and its composition determine the hardness of the product. Harder chalk is used for drawing on pavement, medium-hard chalk is for writing on blackboards, and softer chalk is used for tailoring.

For the production of white and colored crayons by such methods, complex expensive equipment is not required. The total cost of purchasing everything necessary for production will be about 50 thousand rubles. In addition, you will need a cardboard package for packaging ready-made crayons (white crayons are usually packed in large boxes of 100 pieces, and colored ones - in small boxes of 6-12 crayons). The total cost of organizing a small production of chalk is from 100 thousand rubles (including the purchase of raw materials). Finished products are supplied to stationery stores, children's art stores, specialized stores for schools, as well as directly to public educational institutions.

Nordopov Arkady

The paper deals with the manufacture of colored crayons from improvised materials: gypsum, starch, eggshells. Their qualities are being studied.

Download:

Preview:

MOU "Mogoytuy Secondary School No. 1 named after V.R. Glasko"

NPC for junior schoolchildren "I am a researcher"

Research work on the topic

"Production of colored crayons"

Completed by: Nordopov Arkady

2nd grade student

Head: Tsybikova A.V.

primary school teacher

town Mogoytuy

2017

Introduction
What is chalk?
The use of chalk.
Manufacturing technology of school chalk.
Practical part. Making colored crayons.
Conclusion.
Information sources.

Introduction

Each of us is well aware of the usual, unremarkable school chalk. And not only represents, but also held in his hands more than once during his studies. And how many truths were discovered with the help of a piece of chalk, how many discoveries were made! And until now, a school teacher, holding an inconspicuous, but at the same time irreplaceable piece of chalk, performs miracles. Is school chalk really irreplaceable? More and more people are talking and writing about the benefits of interactive whiteboards. But we still work at the school with chalk. Yes, and we draw with chalk on asphalt, fences, on the walls of houses with chalk.

At school, the teacher gives us chalk. At home, we ask our parents to buy chalk, but parents will not buy us chalk every day. And I was interested in the question: is it possible to make chalk yourself and from what?

Object of study: colored crayons.

Subject of study: chalk components: gypsum, starch, eggshell, glue, paints.

Hypothesis : there is an opinion that chalk can be made at home from improvised means.

Target: make crayons with your own hands at home

Tasks:

1) study the history of chalk;

2) learn about the technology of its manufacture and the use of chalk in human life;

3) make colored chalk at home;

4) test the manufactured chalk on asphalt;

5) summarize the results of the work.

Research methods:

study of information;
practical (chalk making);
observation;
generalization.

Practical significanceis to describe different ways of making colored chalk at home. And you can also offer your parents to save money on the purchase of colored crayons.

What is chalk?

Chalk - these are the smallest remains of shells, fragments of the skeletons of extinct marine animals. Chalk has been deposited in water bodies for millions of years. And when they became shallow, the limestones came to the surface.

Chalk - sedimentary rock of white color, soft and crumbly, insoluble in water. Occasionally, mollusk shells, skeletons of bryozoans, sea urchins, lilies, flint sponges, and corals are found in the chalk.

Chalk is a semi-hardened marine silt deposited at a depth of 30-500m or more.

Chalk belongs to very common substances of mineral origin in nature and therefore is well known. It is obtained, in addition, and artificially.

Chalk of natural origin often has a greyish-yellow hue. There is also completely gray chalk. The best grades of chalk (the purest) are almost snow-white in color, as they are composed of almost pure calcium carbonate. Side natural impurities that are part of the chalk are: clay, quartz, magnesium carbonate, carbon and iron oxide. These impurities in good grades of chalk do not exceed 4% of its composition. Carbon turns chalk gray, and iron oxide yellowish.

An artificial product is obtained by precipitation of solutions of lime with carbon dioxide. This chalk consists of pure calcium carbonate, in which 100 wt. hours of product accounts for 56 wt. including calcium oxide and 44 wt. hours of carbon dioxide. It has an impeccable white color, is extremely thin and covers well, but its price is much higher than a natural product.

3. Application of chalk

Chalk is used in agriculture (for liming the soil, feeding animals). Precipitated chalk is used in medicine (as a medicinal product), in perfumery (an integral part of tooth powders, pastes). In plastic art, chalk is used as a basis for gesso and other primers, as a component in the manufacture of artistic paints (for example, pastels). White chalk and black chalk (the so-called Italian pencil) are used as drawing materials. In industry, chalk is used for the production of cement and lime, as a filler for rubber, plastics, paints and varnishes, for the production of soda, glass, sugar refining; making school crayons.

Technologies for the manufacture of school crayons

There are several ways to make school crayons.

extrusion method.With this method, wet chalk in the form of thin sausages comes from a machine that looks like a meat grinder. Sausages are stacked on a baking sheet, cut and dried in ovens. The crayons are round in shape. The technological feature of these crayons is that their “binding” occurs due to glue (most often PVA), which is not entirely safe for the health of children (as you know, white chalk is literally eaten, both by children and adults). But this chalk is soft, pleasant to the touch, practically does not stain hands.
casting method . Cast white chalk is absolutely safe for health, as its binder is gypsum in very small quantities.

Cast chalk is made using a mold, which is a container with cells in the shape of an elongated cube. In the mixer, the chalk powder is thoroughly mixed with gypsum (white chalk), as well as with dyes (color). The quality of the chalk directly depends on the quality of the powder - it should not contain solid particles of gypsum or sand, which then scratch the board when writing.

The resulting powder is poured into a barrel, where it is manually diluted with water. The mixture is poured into the matrices and remains there for some time - the water gradually evaporates, the reaction of binding the molecular structure of chalk and gypsum occurs.

Then the matrix is turned over onto a special lattice tray and “removed” from the crayons. After that, the matrices are washed in a special soapy solution - raw crayons will be easier to lag behind. The pallet is placed in a drying cabinet, the chalk is kept there for a certain time, then the finished crayons are sent to the packaging shop. The packaging is done by hand.

elutriation. For the best varieties of various crayons, the so-called elutriated chalk is used (in trade it is called melted chalk). To prepare elutriated chalk, natural chalk is used. It is broken into pieces, sorted, discarded of all impurities and then ground with water on millstones. The resulting mass is settled, and heavy impurities (sand, stones) will settle to the bottom. The liquid, containing the already purer material, is passed into the second tank, then into the third, until all impurities have settled to the bottom and have been removed. Then the mass is allowed to settle in a vat for a rather long time, the water is drained, and the remaining mass is transferred to boxes with perforated walls covered with linen. Next, the mass is dried on sieves, and if, after drying, the chalk crumbles very much, then a little dextrin solution or glue is added.

Practical part. Making colored crayons

Chalk making is a simple and inexpensive undertaking that you can do at home using things you will almost certainly find on hand. Add some paints and get colored crayons with which you can draw.

1 way

Gather everything you need.In addition to the ingredients for making chalk, you also need to find a mold. Search around or head to your nearest hobby store to collect the following items:

Gypsum. You can buy a large pack of cast from almost any hobby store. You will need 1/2 cup of gypsum per batch of chalk.
Gouache paint.
Wax paper (or rub the paper yourself with a candle). You need her to lay out the chalk molds for her. Without paper, the chalk will stick to them.
Something that you will use as a form. You can use cardboard tubing from toilet paper or paper towels, plastic ice cube trays (only if you don't intend to use them anymore), or any tubes or cardboard molds.
Insulating tape or tape. You need to cover the bottom of the tube you will be using as a mold to keep the mixture inside.

Prepare the forms.Line the molds with waxed paper, glossy side up. If you are using tubes, seal one end with tape to keep the chalk mixture inside.

Pour the paint into the bowl.You need 2 tbsp. spoons of paint on a batch of chalk. Measure the paint into a bowl, one bowl - one color. You can mix paints to get new colors; for example, mix red chalk with yellow to make orange, or blue and yellow to make green. Make sure the total amount of paint per bowl is about 2 tbsp. spoons.

Add plaster. Pour 1/2 cup plaster of paris into each bowl. Stir the mixture thoroughly so that all the ingredients are completely combined and there are no lumps left.

Add a drop of liquid dish soap.So the chalk will be better washed. Just stir 1-2 drops into each mixing bowl.

Pour the chalk into molds.Using a spoon, spoon the mixture into individual molds, one color per each mold. Fill the molds as hard as you like - the chalk mixture will not expand when it dries. Cover the molds with waxed paper when you're done.

Let the chalk dry.Move the chalk to a dry place so that the moisture evaporates from it. The chalk is ready for use after it dries completely.

2 way

1. Collect all the ingredients.This method of making chalk includes only natural products that you can find in any store if you suddenly don’t have them on hand. Assemble the following items in preparation for your chalk making project:

Eggshell.
Flour. It will make the mixture thicker and make the chalk fluffier.
Food coloring. Suitable for both liquid dye and gel.
Forms. Use toilet paper tubes or ice cube trays, or any other shape you like.
Wax paper. You will need it in order to lay out the forms for her.
Duct tape.

2. Prepare forms.Line your chosen shapes with waxed paper, glossy side up. If you are using cardboard tubes, tape one end.

3. Grind eggshells.Make sure they are completely dry before doing this. Use a mortar and pestle or a bowl and the back of a spoon to grind the shells into a fine powder. Make sure not a single large piece of shell is left; the mixture must be absolutely homogeneous.

1. Prepare the ingredients.A simple chalk recipe consists of two things: starch and water in equal proportions. Use food coloring to make more than one color. You can use toilet paper or paper towel tubes or other small containers as molds.

The main component of chalk is calcium carbonate (CaCO3) - one of the forms of limestone. Limestone deposits are formed from coccoliths - a shell of tiny flagellar plates created from the decayed skeletons of plankton. For the manufacture of pastel crayons, calcium sulfate (CaSO4) is taken as the basis, which is extracted from the evaporite mineral, which is formed from the salts of ocean water.

Chalk and dehydrated gypsum have similar properties. Pastel crayons also contain clay and oils, which bind the ingredients and make the color last. Thanks to this composition, the crayons have a velvety structure, glide smoothly over the surface and do not crumble. Although special attention is paid to the purification of impurities in production, some of them still remain. The main ones are: silicon, aluminum, iron, phosphorus and sulfur. In smaller quantities, manganese, copper, titanium, sodium oxide, potassium oxide, fluorine, arsenic and strontium are present.

Chalk production process

A limestone quarry is being developed for the production of chalk; it is usually open source. The limestone is then crushed and ground together with water in a ball crusher (a rotating steel drum inside which water is sprayed). At this stage, foreign impurities are washed out of the limestone, and a pure powder remains.

The extraction of gypsum is exactly the same as that of limestone. The difference is that the gypsum must be dehydrated to produce calcium sulfate. This takes place in a special chamber where gypsum is heated to a temperature of 116-121 degrees Celsius. When boiling, 12 to 15 percent of its mass is evaporated. Next, the gypsum is heated to 204 degrees and in this form it is taken out of the chamber. Then the mass is placed in a vibrating screen, where large particles are screened out. After that, the powder is washed again, dried, packed in bags and sent to the chalk manufacturer.

In the crayon factory, the chalk or calcium sulfate is ground again. For the production of school crayons, water is added to the mass and brought to the consistency of clay. Then the mass is stamped and cut into bars about 60 cm long, which are placed in a special mold, five pieces each. This form is sent to the oven, where the mass is kept for four days at a temperature of 85 degrees Celsius. Then the hardened crayons are cut into bars 80 mm long. For the manufacture of colored crayons, the pigments are mixed with the base in a dry form, and only after that water is added and the production cycle described above begins.

Choosing the best wax crayon recipe: a review of 5 videos and an article

Igor, good afternoon. We write you an answer in the form of a review article. Those guys who ordered molds for making crayons from us were politely refused the recipe for crayons, so we decided to conduct our own candle investigation)))

Go:

Making wax crayons

2. #5 How to make colored crayons at home

How to make colored crayons at home

Music in video:

Scady - Use Shazam

Axlance & Luka Krajina - Dreams (MI77ER Remix)

Caleb Mak

3. DIY wax crayons. Mom's school. TSV

4. How it's made \ Wax crayons

5. Crayola wax crayons ("What it's made of")

I hope it was useful, Sergey Mauser

International Festival "Stars of the New Age" - 2013

Natural sciences (from 11 to 13 years old)

"Assessment of the quality of school chalk"

MAOU lyceum №82 Chelyabinsk

Scientific adviser:

geography teacher of the highest category.

Introduction 2

I. The history of chalk and its location in nature 3

II. The chemical composition of chalk and its scope 4

III. School chalk production 5

Practical part

IV. Main indicators of chalk quality 6

V. Qualitative analysis of school chalk 7

VI. Making school crayons at home 8

VII. Sociological survey of students of the 5th class of the MAOU lyceum No. 82 9

VIII. Findings 11

IX. References 12

X. Applications 13

Introduction

For hundreds of years, people have been using chalk for various purposes. In school from the first to the eleventh grade, we use chalk to write on the boards, of course, we see the inscription on the packaging is non-toxic, made from environmentally friendly products, safe, but we encounter a few problems when using it. I decided to independently find out the composition of chalk, its scope and determine the quality of school chalk.

Relevance: Today, very serious requirements are imposed on school chalk, so it is considered an environmentally friendly and safe product. However, in the process of use, school chalk begins to dust, dirty hands, cause an unpleasant sensation on the respiratory system of the student's body.

Hypothesis: School chalk can have a negative impact on the health of students.

Goal of the work: To determine the composition of school chalk used in Lyceum No. 82 in Chelyabinsk and find out its features of influence on the student's body.

Tasks:

Study the geographical location of chalk in nature and its composition

Consider the method of producing school chalk

· Examine chalk samples and find out compliance with the main indicators of chalk quality.

· To find out with the help of a sociological survey whether contact with chalk has a harmful effect on the body of students.

Subject of study: school chalk 3 samples.

Object of study: Respondents of the 5th grade of Lyceum No. 82, 32 people.

Research methods:

Theoretical: comparison method, analysis, generalization.

Practical: research-conducting chemical experiments.

Equipment and reagents: samples of school chalk (three types), acetic acid, test tubes, alcohol solution, iodine solution, distilled water, spirit lamp.

I.The history of chalk and its location in nature

Not everyone knows that in the beginning, chalk was a living organism. In the waters of the ocean there are various types of tiny plants and animals. One of them is a single-celled creature called "furaminifera" with a lime shell. As they die, they sink to the ocean floor. Over time, they form a thick layer of these shells. Of course, this takes millions of years. Gradually, this layer cements and turns into soft calcium carbonate, which we call chalk.1

But there is another way to deposit. Like salt and gypsum, which are deposited on the bottom of the seas, lakes, lagoons, due to the evaporation of water. From the subject of geography, we know that various changes took place on the earth. So the seas dried up and receded, turned into dry land. A striking example of this is the English Channel. The layers of chalk, which were on the seabed, were raised above the surface of the sea. The loosest areas were eroded away, leaving high chalk cliffs. In various parts of the world, chalk lies far from the sea, where once there was a sea. An example of this is the states of Kansas, Arkansas, Texas in the USA. But the best chalk comes from England.2

The extraction and processing of chalk does not cause serious environmental disturbances. Chalk reserves are practically unlimited in many European countries, countries of the former CIS and the Russian Federation. A powerful chalk belt stretches across the entire European continent, including the north of France, the southern part of Britain, Poland, passes through Ukraine and shifts to Asia-Syria and the Libyan desert. Chalk reserves are unevenly distributed over the territories: about 50% of the reserves of high-quality chalk without harmful impurities, with a high content of limestone and magnesium are concentrated in the Russian Federation, about 33% in Ukraine and 12% in Belarus.

There are not large deposits in Kazakhstan, Lithuania and Georgia. The total balance reserves of chalk in the Russian Federation are estimated at 3,300 million tons with unlimited forecast reserves. The Belgorod region has unlimited resources of chalk, in total 29 chalk deposits with total reserves of 1000 million tons have been explored. The largest chalk deposits are Lebedyanskoye, Stoilenskoye and Logovskoye.

The production of high-quality chalk grades is concentrated in Russia primarily at chalk plants in the Belgorod region, as well as in the Bryansk region, large deposits: Fokinsky, with a content of 75% chalk and 25% clay, are considered natural.

Cretaceous steep slopes Suponeva on the right bank of the river. The gums exposed a series of sandy chalk of the Turanian age (Late Cretaceous), which contains a large number of shell remains.

1-Arkady Likum. Everything about everything. Volume 1. Popular encyclopedia for children. From Moscow. 19p.

bivalve mollusks-inoterams.

The famous gradation of chalk by hardness-softness was developed at Algem. Chalk becomes hard from gypsum busting, and soft from prolonged drying or the use of very high temperatures.

Now it is difficult to imagine that before all the produced chalk was the same. For example: hard chalk is used to draw on any rough surface, while soft or medium-soft chalk is used on boards, fabric or furniture.

During production, chalk powder is thoroughly mixed with gypsum (white chalk), as well as with dyes (color). The quality of the chalk depends on the quality of the powder, for example, it should not contain solid particles of gypsum or sand, which then scratch the board when writing. The resulting powder is poured into a barrel, where it is manually diluted with water. The mixture is poured into the matrices and remains there for a while, then the water gradually evaporates, a chemical reaction occurs to bind the molecular structure of chalk and gypsum. Then the matrix is turned over onto a special lattice tray and “removed” from the crayons. After that, the matrices are washed in a special soapy solution, since raw crayons will be easier to lag behind. The pallet is placed in a drying cabinet, the chalk is kept there for a certain time, then the finished crayons are sent to the packaging shop. Packaging is done by hand, good manufacturers have a low percentage of defects. The crayons that have split during the removal of the matrix are immediately removed by the workers. Over-dried or under-dried crayons are selected by packers, "under-dried" chalk is returned for drying, over-dried - into production waste .6

IV. The main indicators of the quality of chalk.

The main indicators of the quality of chalk include:

Obvious

Crumbles

· Dirty hands

Purity (white)

・Hard inclusions

Non-obvious

No traces of PVA glue

Use of purified water

The quality of dyes

To consider the obvious indicators of the quality of the chalk, let's take 3 samples of chalk:

A sample of 1-chalk from the Algem company, Moscow (this chalk is used by students in my class at the lessons near the blackboard)

Sample 2-chalk company "Elikont", Belgorod

Sample 3-chalk firm "Pegasus", Klin

According to the indicators, of the three samples, samples No. 1 are the highest quality ones with good color, low flowability, soiling.

Sample color, medium flowability.

Sample No. 3 - high flowability, high soiling.



Flowability (can be determined on black fabric)
Markost	Small
The presence of solid inclusions
Has a shape	Bar with rounded edges	Square bar	Square bar

V. Qualitative analysis of school chalk.

The main component of chalk is calcium carbonate (CaCO3). Natural chalk does not contain any other components. In the manufacture of crayons, binders are added to the chalk powder, such as starch or gypsum.

To find out what binders were used to make chalk, a qualitative analysis is carried out.

Experiment No. 1. To determine calcium carbonate in chalk (CaCO3).

Grind a piece of chalk in a mortar to a powder.

Pour crushed chalk into a test tube with a glass rod.

Add a few drops of acetic acid to the test tube.

We observe the reaction (hissing), carbon dioxide is released.

We bring a burning torch, the fire goes out, carbon dioxide does not support combustion.

Conclusion:

Calcium carbonate (CaCO3) interacts with acetic acid, carbon dioxide (CO2) is released, all chalk samples contain calcium carbonate (CaCO3), since carbon dioxide (CO2) is actively released when acid is added.

Experiment No. 2. To determine gypsum in chalk.

In a test tube with crushed chalk, add warm water, shake vigorously, add a few drops of acetic acid. (The acid will dissolve calcium carbonate, but gypsum will not)

There is no test tube, the solution is white and there is a small sediment at the bottom

Test tube gray foam does not settle for a long time

Test tube No. 3 - gray solution, does not settle

Conclusion:

Samples No. 2 and No. 3 contain a large amount of gypsum, sample e.

Experiment No. 3. Determination of starch content.

We will detect starch with the help of an alcohol solution of iodine. 2-3 drops of iodine solution were applied to the studied pieces of chalk. The color and iodine color should change to blue if starch is present in the samples.

Sample No. 1		Conclusion (is there starch or not?)
No blue coloration	No starch
Sample #2	No blue staining, but the color is close to purple	There is no starch, but another substance similar to PVA glue is probably added
Sample #3	No blue coloration	No starch

I want to know what is present in sample No. 2, I take PVA glue, add 3 drops of iodine and the resulting color is close to the color in sample No. 2. It is possible that PVA glue was added to the chalk sample No. 2 during production.

VIMaking school crayons at home.

After I got acquainted with the material on making school chalk, I wanted to try making chalk myself. It turns out that this is not a difficult process, the main thing is to be patient and take into account the correct dosage.

I needed:

Chalk powder, gypsum powder (alabaster), starch, mortar and glass spoon, beaker, ice molds, scales with technical weights (from the chemistry room in the school laboratory), rubber gloves.

From the beginning I am trying to make a shaped chalk with the addition of gypsum:

1. You need to weigh 12g. Chalk powder and 18g. Gypsum powder

3. Add a little purified water (Luxe water) to the mortar and mix quickly to get a mass similar to sour cream, since gypsum can quickly harden.

Now we are trying to make school chalk with the addition of starch.

1. You need to weigh 12g. Chalk powder and 18g. Starch powder.

2. Thoroughly mix the resulting mixture with a glass rod, then rub it so that there are no lumps.

3. Add a little purified water to the mortar and mix quickly to get a mass similar to sour cream.

4. Pour the resulting mass into an ice mold and dry for several days in a warm place.

It was noticeable that the color of the mass with the addition of starch differs in color from the mass with the addition of gypsum, and also the mass with the addition of gypsum quickly hardened, and the mass with the addition of starch only on the second day.

Mission accomplished. It turned out to be chalk! Chalk with gray plaster, very hard, writes well on the board, but not very bright, does not crumble. (Receiving 1 sample)

Chalk with starch, the color is almost white, but there is a grayish tint, it is soft, it crumbles in the hands, it is very dusty, but it writes brighter on the board than chalk with plaster, but I would not use such chalk in the lesson. (Getting 2 samples)

VII Csociological survey of students 5G 82 lyceum.

1. Are you satisfied with the chalk you write with in class?

2. Check which of the following do you experience after working with chalk?

A) dirty hands

B) causes dry skin

C) scratches the board or writes poorly

D) nothing

3. How do you feel on the respiratory system when working with chalk?

B) cough

B) sore throat

D) don't feel anything

I interviewed 32 students in my class and received the following results, which I calculated as a percentage (tables in the appendix).

Questionnaire analysis:

Based on a sociological survey, we can say that 22 students are satisfied with the quality of chalk, 10 students are not satisfied with the quality of chalk.

Scratches the board-21%

Dirty hands-41%

Causes dry skin-32%

Sore throat-17%

Sneeze-11%

Do not experience anything - 63% and 10%

Conclusion

Based on the conducted research, the following conclusions can be drawn:

· Not all chalk sold in stores is of good quality.

Chalk is of great practical importance, as it is used in various areas of our life.

· While examining crayons, I found out that they are composed of calcium carbonate (natural chalk), gypsum and starch, and possibly other adhesives (PVA glue).

・Qualitative analysis
The safest school chalk is sample No. 1 of the Algem company, it meets all GOST standards (this chalk is used in our lyceum).

· Sample No. 2 may have a negative effect on health, since chalk dust can cause allergic reactions, it is an allergen and it can cause an asthma attack.

Never taste school chalk.

Analyzing the questionnaires of students, I came to the conclusion that school chalk can, with constant contact, have negative health effects so that there are none:

· After handling chalk, wash your hands with emollient soap.

· Wash the chalk off the board with a damp cloth only.

Rinse the rag often and wipe the tray attached to the board.

· Use only good quality chalk.

Despite all the consequences of the impact of school chalk on the body, yet ordinary chalk and a blackboard are currently safer for health than marker boards, which emit esters and cause asthma attacks, and interactive whiteboards cause excessive eye strain.

I plan to continue my work, at the moment a questionnaire has been developed for a sociological survey of teachers of Lyceum No. 82 to find out what effect work with chalk has on the health of teachers.

Bibliography

1. Arkady Likum. Everything about everything. Volume 1. Popular encyclopedia for children. From Moscow. 19p.

2. Chalk/Science. Encyclopedic dictionary / comp. .-M. Great Russian Encyclopedia. 20s.

Other sources:

kraeved*****/82/100488/index. ht.

ru/publikatsii/marki-mela-i-in.

Application

https://pandia.ru/text/78/168/images/image002_11.png" width="624" height="527 src=">

https://pandia.ru/text/78/168/images/image004_10.png" width="624" height="794 src=">

Table of chalk grades and their purpose

Designation	body brand	Areas of use
MK-2 and MK-3	Lumpy	lime production
MD-1;MD-2;MM-3	crushed	Glass, ceramic and other industries.
MM-1;MM-2;MM-3		Glass, ceramic and other industries.
	Ground for animal nutrition	For feeding animals
	Ground for the production of animal feed	Feed production
	ground peeled	Paint, chemical and other industries
MMS-1;MMS-2	Ground separated	Cable, paint, rubber, polymer and other industries
	ground for chemical industry	Chemical industry
MTD-1;MTD-2;MTD-3;MTD-4	Fine	In the absence of MMC-1 and MMC-2 grades, finely dispersed chalk is used
MHO-1; MHO-2	Ground chemically cleaned	Perfumery, cosmetic, rubber, medical, food and other industries