Chemical glassware and accessories. Cookware for special purposes ()

Laboratory glassware is distinguished by its diversity. It is used in the process of conducting analyzes in various fields. A huge number of variations of the containers presented allows you to use the most suitable variety in each case.

Existing types of flasks can be classified according to some criteria. This allows you to delve deeper into their application and significance for analysis. Varieties of laboratory glassware deserve special attention.

general characteristics

Most commonly used in laboratory studies glass flasks. They allow you to perform many different operations and chemical reactions. A rather large expense item for any laboratory is precisely the container.

Since most flasks are made of glass, they can break. Today there are many different types of flasks. They may be exposed to temperatures or chemicals. Therefore, the material from which laboratory glassware is made must withstand such loads.

Flask configuration can be very unusual. This is necessary in order to conduct a full as well as analysis of the required substances. Most often, these containers have a wide base and a narrow neck. Some of them may be equipped with a cork.

Varieties of form

In laboratory studies, flat-bottomed and round bottom flask. These are the most commonly used types of containers. Flat-bottomed varieties can be placed on a flat surface. Their purpose is very varied.

The round-bottom flasks are held in a rack. This is very convenient if the container needs to be heated. For some reactions, this speeds up the process. Therefore, the round-bottom flask is most often made from heat-resistant glass due to this application feature.

Also, both presented varieties of laboratory glassware are used to store various substances. Sometimes, in very rare cases, sharp-bottomed varieties of containers are used in the course of laboratory analysis.

The use of flasks and their configuration

Very varied. They depend on the application. The Kjeldahl flask is pear-shaped. It is most often used in the device of the same name for the determination of nitrogen. This flask may have a glass stopper.

A Wurtz flask is used to distill various substances. In its design there is a discharge tube.

The Claisen flask has two necks, the diameter of which is the same along the entire length. A tube is connected to one of them, designed to remove steam. The other end communicates the dishes with the refrigerator. This variety is used for distillation and distillation at normal pressure.

The Bunsen flask is used in filtration processes. Its walls are very strong and thick. At the top there is a special process. It approaches the vacuum line. For experiments under reduced pressure conditions, this variety is ideal.

Erlenmeyer flask

Considering the existing types of flasks, it is impossible not to pay attention to another form of laboratory glassware. The name of this container is given in honor of its creator - the German chemist Erlenmeyer. This is a conical container that has a flat bottom. Its neck is characterized by a cylindrical shape.

This flask has divisions that allow you to determine the volume of liquid inside. A unique feature of this type of container is an insert made of special glass. This is a kind of notebook. On it, the chemist can make the necessary notes.

The neck, if necessary, can be closed with a stopper. The conical shape promotes high-quality hashing of contents. The narrow neck prevents spillage. The evaporation process in such a container is slower.

The flask of the presented type is used when carrying out titration, cultivation of pure cultures or heating. If the flask has divisions on the body, they are not heated. Such dishes allow you to measure the amount of the content of the substance.

A few more features

The types of flasks used can also be divided into groups depending on the type of neck. They are simple (for a rubber stopper), as well as with a cylindrical or conical section.

Depending on the type of material from which the cookware is made, it can be heat-resistant or plain. By purpose, the flasks can be divided into volumetric containers, receivers and reactors.

The volume of laboratory glassware is also quite diverse. Their capacity can be from 100 ml to 10 liters. There are flasks of even larger volume. When working with such containers, it is imperative to follow safety rules. Each type of equipment presented must be used strictly for its intended purpose. Otherwise, you can break the flask or harm your body.

Chemical beakers are low or high cylinders with a spout (Fig. 16, a) or without it (Fig. 16, c), flat-bottomed or round-bottomed (Fig. 16, d). They are made from different types of glass and porcelain, as well as polymeric materials. They are thin-walled and thick-walled, dimensional (see Fig. 16, a) and simple. Glasses made of fluoroplast-4 (Fig. 16, b) are used in work with highly aggressive substances, and polyethylene or polypropylene glasses are used for experiments involving hydrofluoric acid. If it is required to maintain a certain temperature during the reaction or when filtering the precipitate, then glasses with a thermostatic jacket are used (Fig. 16, e). Synthesis of substances weighing up to 1 kg is carried out in reactor beakers with a ground lid, which has several tubes for inserting the stirrer axis, refrigerator tubes and a separating funnel and other devices into the beaker.

Fig. 16. Chemical beakers: measuring beakers with a spout (a), fluoroplastic (b), with a polished upper edge (c), thick-walled (d), with a thermostatic jacket (e), a beaker-reactor with a ground lid (e) and a beaker for "Washing of precipitation by decantation (w)

In such vessels (Fig. 16, f) it is possible to maintain a vacuum or a slight overpressure. It is convenient to wash the sediments by decantation using glasses with a side recess (Fig. 16, g). From such a glass, inclined towards the side recess, only the liquid is drained, and the sediment is collected along the recess, which does not allow sediment particles to be washed out by the last portion of the liquid.

Thick-walled glasses without a spout made of Pyrex glass (see Fig. 16, c) with a polished upper edge are used in demonstration experiments, for steam or hot-air sterilization of products, installation of galvanic cells ("battery glasses"). A glass with a round bottom (see Fig. 16, d) with a polished upper edge, it can serve as a bell.

It is impossible to heat chemical beakers on an open flame of a gas burner because of their possible cracking. It is imperative to place an asbestos mesh under the glass (see Fig. 14, a) or use liquid baths for heating, electric tiles with a ceramic top.

The flasks are round-bottomed, flat-bottomed, conical, sharp-bottomed, pear-shaped, with a different number of necks and processes, with and without thin sections, with a thermostatically controlled jacket and a lower descent, and other designs. The capacity of the flasks can vary from 10 ml to 10 l, and the heat resistance can reach 800-1000 °C.

The flasks are designed for preparative and analytical work.

Various types of round-bottom flasks are shown in fig. 17. Depending on the complexity, the flasks can have from one to four necks for equipping them with stirrers, refrigerators, dispensers, valves for connecting to a vacuum system or for supplying gas, etc.

Pear-shaped flasks (Fig. 17, d) are necessary when, during the distillation of a liquid, the vapor should not overheat at the end of the process. The heated surface of such a flask does not decrease with a decrease in the liquid mirror. The Kjeldahl flask (Fig. 17, e) has a long neck and a pear-shaped lower part. It is used to determine nitrogen and is made of pyrex glass. (Kjeldal Johan Gustav Christopher (1849-1900) - Danish chemist) He proposed a method for determining nitrogen and a flask for this experiment in 1883.

Walter flasks (Fig. 17, f) and Keller (Fig. 17, g) have a wide neck for introducing various devices into the vessels through a rubber stopper or without it.

Rice. 17. Round-bottomed flasks: one- (a), two- (b) and three-necked (c), pear-shaped (d), Kjeldahl (e), Walther (f) and Keller (g)

Rice. 18. Round-bottom flasks for special applications: with a bottom bleeder and a shut-off valve (a), with a pocket for a thermometer (b), with a liquid bath (c), with a glass bottom filter (d), with a side branch tap (e) and with thermostatic jacket (e)

(Walter Alexander Petrovich (1817-1889) - Russian anatomist and physiologist. Keller Boris Alexandrovich (1874-1945) - Russian botanist-ecologist)

By special order, firms can produce more complex round-bottom flasks (Fig. 18). A flask with a bottom descent having a stopcock (Fig. 18, a) is used in experiments in which several immiscible liquid phases are formed. A flask with a side pocket (Fig. 18, b) For a thermometer or thermocouple, it is used in preparative work with a strictly controlled and regulated temperature.

A flask with a lower jacket (Fig. 18, c), which functions as an oil bath, is recommended for very many syntheses. This does not require a special heater, the temperature of the reaction medium in the flask is always constant and is determined by the boiling temperature of the liquid in the jacket, which has a side connection of a reflux condenser (see section 8.4). The boiling point of the liquid is chosen in accordance with the operating conditions (Table 18). A flask with a glass bottom filter is a multifunctional device. It allows, after the reaction, to separate the liquid phase from the solid and is equipped with a lower pressure valve. The designs of the remaining flasks (e, f) are clear in Fig. eighteen.

Various types of flat-bottomed flasks are shown in fig. They, like round-bottomed ones, can have several necks for thermostatic jackets (Fig. 19, d, e). The advantage of such flasks is their stable position on the laboratory table.

Narrow-bottom flasks (Fig. 20) can have from one to three necks. They are used in those cases when, during the distillation of a liquid, it is necessary to leave a small volume of it or remove the solution of the liquid phase completely, concentrating the dry residue in the narrow part of the flask.

Ordinary conical flasks (Fig. 21, a) are called Erlenmeyer flasks.

Rice. 19. Flat-bottomed flasks: one (a), three- (b) and four-necked (c) with thermostatic jackets (e)

Rice. 20. Narrow-bottom flasks: one- (a), two- (b) and three-necked (c)

They have, as a rule, a flat bottom, but their neck can be equipped with a polished stopper (Fig. 21, b) and even have a spherical section (Fig. 21, d), which makes it possible to rotate the tubes of various purposes inserted into the flask at the desired angle. Flasks that do not have a polished neck are closed with caps (Fig. 21, e), which make it possible to rotate the flask to mix its contents without the danger of splashing. The main field of application of Erlenmeyer flasks is titrimetric methods of analysis. If the analyzed liquid is strongly colored and it is difficult to establish the equivalence point, then Frey flasks (Fig. 21, c) with a bottom protrusion are used in volumetric analysis, which makes it possible to more accurately determine the moment of change in the color of the solution in a thinner layer of liquid. (Erlenmeyer Richard August Karl (1825- 1909) is a German organic chemist who, in 1859, proposed the design of the flask that was named after him.)

Thick-walled conical flasks with a side tube are called Bunsen flasks (Fig. 22). These flasks are designed for vacuum filtration.

Fig. 22. Bunsen flasks: ordinary (a), with a three-way valve (b) and with a lower descent (c)

Rice. 23. Flasks for the distillation of liquids: Wurtz (a), with a saber-shaped process (b), Vigre (c) and Favorsky (d)

The wall thickness of the flasks is 3.0-8.0 mm, which makes it possible to withstand the maximum residual pressure of not more than 10 Torr or 1400 Pa. The capacity of the flasks ranges from 100 ml to 5.0 liters. During filtration, the flasks should be covered with a towel or a fine nylon or metal mesh to avoid their rupture, which is usually accompanied by the scattering of glass fragments. Therefore, before work, the Bunsen flask must be carefully examined. If bubbles or surface scratches are found in the glass, it is not suitable for vacuum filtration.

When filtering large amounts of liquid, flasks with a lower tube (Fig. 22, c) are used to drain the filtrate. In this case, before draining, the water jet pump is turned off and air is let into the flask. To remove the filtrate without turning off the vacuum, Bunsen flasks with a three-way stopcock are used (Fig. 22, b).

For the distillation of liquids, flasks of various designs are used. The simplest of them are Wurtz flasks - round-bottom flasks with a side branch (Fig. 23, a), to which a refrigerator is attached. For liquids with a high boiling point, the reed should be located closer to the spherical part of the flask. Low-boiling liquids are distilled in Wurtz flasks with a branch located closer to the open end of the throat. In this case, less liquid splashes enter the distillate.

Charles Adolphe Wurtz (1817-1884) - French chemist, president of the Paris Academy of Sciences.

Rice. 24. Flasks for the distillation of liquids: Claisen (a), Arbuzov (b, c) and Stout and Schuette (d)

A narrow-necked flask with an internal neck diameter of 16 ± 1 mm, a capacity of 100 ml and a neck height of 150 mm with a side process like a Wurtz flask, but located almost in the center of the neck of the flask, was called the Engler flask. It is used for distillation of oil in order to determine the yield of oil fractions.

(Engler Karl Ostwald Victor (1842-1925) - German organic chemist, proposed the theory of the origin of oil from animal fat.)

Flasks with a saber-shaped process (Fig. 23, b) are used for the distillation or sublimation of easily solidifying and easily condensing substances. temporarily with an air cooler and a condensate or desublimate receiver.

Test tubes. Test tubes are glass tubes sealed at one end in such a way that a rounded bottom is formed. They are intended for preliminary testing of samples. Test tubes are of various sizes, thin-walled and thick-walled, made of different types of glass (fusible and refractory), simple, graduated, centrifuge, etc. They can be heated directly in a burner flame, in a water bath. It is most convenient to work with such an amount of liquid that its total volume does not exceed half the volume of the test tube. In this case, to mix the liquid, take the test tube with the thumb and forefinger of the left hand near the upper open part and support it with the middle finger. Then, with the index finger of the right hand, oblique blows are struck at the bottom of the test tube.

If, nevertheless, the liquid occupies a volume of more than half of the test tube, mixing is carried out with a glass rod, lowering and raising it. Do not mix the contents of the test tube by closing the latter with your finger and shaking vigorously.

Test tubes are stored in special racks.

Funnels chemical. Glass funnels are mainly used for filtering and pouring liquids. They come in various sizes and diameters. Ordinary funnels have a smooth inner wall, but to facilitate filtering, the inner surface is sometimes made ribbed. While working with the funnel, it is fixed in the foot of the tripod, inserted into the ring attached to the tripod or into the neck of the flask in the latter case between the neck of the vessel and the funnel, there must be a gap that is formed if you put a piece of paper at the point of contact of the funnel and throat. Even better, make a triangle out of wire, put it on the neck of the flask and insert the funnel into the triangle.

When pouring liquids, the liquid level in the funnel should be 10-15 mm below the edge of the funnel; do not fill the funnel to the brim, as even with a slight inclination, the liquid from the funnel may splash out.

Chemical glasses. Chemical beakers come in various shapes: wide and low, as well as high and narrow, with or without a spout, of various capacities (from 25 ml up to 1-2 l).

Glasses are made from different types of glass. Chemical thin-walled glasses made of ordinary glass are not recommended to be heated on a bare flame without an asbestos mesh; when heated, they should be used in a water, air, sand or oil bath,

Flat-bottom and round-bottom flasks. A hot flask should not be placed on cold metal objects or a table covered with tiles. It is best to put asbestos cardboard under the flask. Round bottom flasks are used for distillation, boiling, and various reactions when heated. In this case, the neck of the flask is freely fixed in the leg of the tripod. The foot is best wrapped with asbestos cord. A ring is placed under the bottom of the flask, on which a sand, oil or water bath is placed. If heating is carried out with a burner, then an asbestos mesh or sheet asbestos is placed on the ring under the flask, and the bottom of the flask should only slightly touch the surface of the sheet. Round-bottom flasks cannot stand on the table, so rubber, asbestos or wooden rings are used as stands for them. Metal rings can be used as coasters only by wrapping them with an asbestos cord. Flasks made of ordinary chemical glass, especially flat-bottomed ones, cannot be heated on a bare flame.

Only flasks made of special types of glass, such as Pyrex glass, can withstand heating with a naked flame.

Flasks conical (Erlenmeyer).

A conical flask is a flat-bottomed conical vessel. Its shape makes it possible to touch any place on the walls with a glass rod and thus easily remove adhering precipitation particles. In addition, due to its shape, it is possible to quickly mix the contents of the flask with circular movements, which is very important in titration, which is why these flasks are used mainly in titration. Conical flasks come in various sizes, with and without a spout. For some work with volatile compounds, conical flasks with a ground-in stopper are used.

Crystallizers. Glass flat-bottomed cups with thin or thick walls, various capacities and diameters. They are used in the recrystallization of various substances, and sometimes evaporation is also carried out in them. Crystallizers cannot be heated on a naked flame. Depending on the work done in them, they are heated in a water, sand or air bath.

Most often in chemical laboratories, glass and porcelain dishes are used, shown in Fig. 12.

measuring utensils

In laboratory work, the following volumetric utensils are usually used: flasks, pipettes, burettes, beakers.

Volumetric flasks(Fig. 3) are used to prepare solutions of a strictly defined concentration and to accurately measure the volumes of liquids, they are flat-bottomed flasks with a long and narrow neck, on which a thin line is applied. This mark shows the boundary of the liquid, which at a certain temperature occupies the volume indicated on the flask. The neck of the volumetric flask is made narrow, so a relatively small change in the volume of liquid in the flask is noticeably reflected in the position of the meniscus. Commonly used flasks are 50, 100, 250, 500 and 1000 ml.

Volumetric flasks usually have a ground glass stopper. In the non-working position, when storing an empty flask, a piece of clean filter paper should be placed between the stopper and the neck of the flask.

When filling a volumetric flask, the liquid is poured through a funnel inserted into the neck until its level is 1-2 mm below the ring line. Then the funnel is removed and with the help of a rinsing or pipette, the volume of liquid is brought dropwise until the meniscus merges with the line of the flask. The last drops must be added especially carefully so as not to add excess liquid. If the level of the poured liquid is even slightly above the annular line, the work should be repeated, that is, pour the liquid from the volumetric flask, wash it and fill it again with liquid until the meniscus exactly matches the line.

When filling a volumetric flask, the following rules must be observed:

1) the flask can only be held by the neck above the mark, but not by the ball, so as not to change the temperature of the liquid in the flask;

2) the liquid should be poured until the lower part of the concave meniscus merges with the ring line;

3) the flask must be held so that the line and the eye of the observer are at the same level.

Figure 1. Chemical glassware.

Figure 2. Chemical glassware.

If a solution of a solid substance is prepared in a volumetric flask, then the substance accurately weighed on a watch glass or in a weighing bottle is quantitatively transferred through a funnel to the flask. To do this, the watch glass or bottle is thoroughly washed over the funnel from the washing liquid used as a solvent. The flask is then filled approximately half way.

Rice. 3. Mer- Fig. 4. Pi- Fig. 5. Burettes

flask petka

volume and shake (without inverting the flask!). Only after the sample is completely dissolved and the liquid in the flask reaches a temperature of 20 °, the solvent is added to the desired volume, as indicated above, the flask is closed with a ground glass stopper and the contents are mixed by repeated inversion.

Solutions, especially alkaline solutions, cannot be stored in volumetric flasks for a long time, as they corrode glass. In such cases, the volume of the flask changes, the glass becomes thinner, and the flask quickly breaks down. Volumetric flasks should also not be heated, as this leads to a change in their volume.

Pipettes serve to accurately measure a certain volume of liquid and are glass cylindrical, drawn from above and below narrow tubes (Fig. 4, a - Mora pipette (designed to measure only a certain volume, if the pipette is 2 ml, then it can be used to measure only two milliliter)). At the top of the pipette there is a mark showing to what level it is necessary to fill the bottom of the pipette so that the liquid poured out of it has the volume indicated on the pipette. Most often use a pipette with a capacity of 10 or 20 ml. There are measuring pipettes that look like a narrow graduated tube (Fig. 4, b - a conventional graduated pipette). Pipettes are calibrated for free flow of liquid. You should not blow out or quickly squeeze out the liquid - in the first case, an excess volume will come out of the pipette, which should remain in its nose due to capillary forces, and in the second case, due to the leakage effect, the volume of the leaked liquid will be less than the standard one.

Burettes(Fig. 5) are designed to pour strictly defined volumes of liquid from them. They are long glass tubes on which a scale with divisions is applied. Most often, burettes with a capacity of 50 ml are used, graduated to tenths of a milliliter. There is a stopcock at the bottom of the burette. Sometimes there is no tap in the burettes, then a piece of rubber tube with a glass ball inside and a glass tube drawn at the bottom is put on the end of it. By pulling the rubber tube away from the ball with your fingers, you can drain the liquid from the burette. It is necessary to ensure that the retracted end of the tube is completely filled with the drained liquid.

The burette is filled with liquid a few millimeters above the zero line and a descending meniscus is placed on this line. Remove the drop remaining on the spout by touching the glass vessel. During pouring, do not touch the wall of the receiving vessel with the tip of the burette. The drop remaining on the spout after pouring is completed is added to the poured out volume by touching the inside of the receiving vessel. If the buret does not have a waiting time, it is not necessary to wait for the liquid remaining on the walls to drain. The pouring time should not exceed 45 s for 1 ml burettes, 100 s for 100 ml burettes.

Measuring graduated cylinders and beakers(fig. 6) are used for rough measuring of liquids and come in various capacities: 5, 10, 25, 50, 100, 150, 250, 500, 1000 and 2000 ml. To measure the required volume of a transparent liquid, it is poured into a cylinder so that the lower part of the concave meniscus of the liquid surface is at the level of the division of the measuring cylinder, showing the given volume; the volume of opaque or somewhat colored liquids is determined by the upper meniscus.

When using cylinders, it must be remembered that the degree of accuracy of measuring volume depends on the diameter of the cylinder, namely, the wider the cylinder, the less accurate the measured volume. Do not use large cylinders to measure small volumes.

Usually measuring cylinders, especially large ones, are used in the preparation of solutions.

They are also used to measure volumes. beakers. They have a conical shape, which gives them great stability. Beakers are graduated only for infusion. Graduated cylinders and beakers must not be heated and it is also dangerous to pour hot liquids into them.

Rice. 6. Measuring cylinders and beakers

The main laboratory chemical glassware includes flasks, glasses, test tubes, cups, funnels, refrigerators, reflux condensers and other vessels of various designs. Most often, chemical glassware is made from glass of various grades. Such dishes are resistant to most chemicals, transparent, easy to clean.

Flasks, depending on their purpose, are made in various capacities and shapes.

a - round bottom; b - flat-bottomed; in - round-bottomed with two and three necks at an angle; g - conical (Erlenmeyer flask); d - Kjeldahl flask; e - pear-shaped; g - sharp-bottomed; h - round-bottom for distillation (Wurtz flask); and - sharp-bottomed for distillation (Claisen flask); to - Favorsky's flask; l - flask with a tube (Bunsen flask)

a - a glass; b - buks

Round bottom flasks are designed for high temperature, atmospheric distillation and vacuum applications. The use of round-bottom flasks with two or more necks makes it possible to simultaneously perform several operations during the synthesis: use a stirrer, refrigerator, thermometer, dropping funnel, etc.

Flat-bottom flasks are suitable only for operation at atmospheric pressure and for the storage of liquid substances. Conical flasks are widely used for crystallization because their shape provides a minimum evaporation surface.

Thick-walled conical flasks with a tube (Bunsen flasks) are used for vacuum filtration up to 1.33 kPa (10 mmHg) as filtrate receivers.

The beakers are intended for filtration, evaporation (at a temperature not exceeding 100 °C) and preparation of solutions in laboratory conditions, as well as for carrying out separate syntheses in which dense, hard-to-remove precipitates are formed from the flasks. Do not use beakers when working with low-boiling or flammable solvents.

Bottles, or glasses for weighing, are used for weighing and storing volatile, hygroscopic and easily oxidized substances in air.

Cups are used in evaporation, crystallization, sublimation, drying and other operations.

Test tubes are available in various capacities. Test tubes with a conical section and a drain tube are used for filtering small volumes of liquids under vacuum.

Glass laboratory equipment includes. also connecting elements (transitions, allonges, nozzles, closures), funnels (laboratory, separating,

a - cylindrical with a developed edge; b - cylindrical without limb; c- sharp-bottomed (centrifuge); g - with interchangeable conical sections; d - with a conical section and a drain tube

The connecting elements are intended for assembly on thin sections of various laboratory installations.

Funnels in a chemical laboratory are used for pouring, filtering, and separating liquids.

Laboratory funnels are used for pouring liquids into narrow-necked vessels and for filtering solutions through a paper pleated filter.

a - laboratory; b - filtering with a soldered glass filter; into dividing; g - drip with a side tube for pressure equalization.

Funnels with glass filters are usually used to filter aggressive liquids that destroy paper filters.

Dividing funnels are designed to separate immiscible liquids during extraction and purification of substances.

Drip funnels are designed for controlled addition (adding) of liquid reagents during the synthesis. They are similar to separating funnels, but their different purpose predetermines some design features. Drip funnels usually have a longer outlet tube and a tap located under the tank itself. Their maximum capacity does not exceed 0.5 liters.

Desiccators are used for drying substances under vacuum and for storing hygroscopic substances.

Cups or glasses with substances to be dried are placed in the cells of porcelain inserts, and a substance is placed on the bottom of the desiccator - a moisture absorber.

a - vacuum desiccator; b - normal

Refrigerators laboratory glass apply to cooling and condensation of vapors.

Air coolers are used for boiling and distillation of high-boiling (ґklp > 160 °С) liquids. The cooling agent is the ambient air.

Water-cooled refrigerators differ from air-cooled refrigerators by the presence of a water jacket (the cooling agent is water). Water cooling is used to thicken vapors and distill substances with< 160 °С, причем в интервале 120-160 °С охлаждающим агентом служит непроточная, а ниже 120 °С - проточная вода.

The Liebig refrigerator is used to distill liquids.

Ball and spiral coolers are most applicable as return liquids for boiling liquids, as they have a large cooling surface.

Dephlegmators serve for more thorough separation of the fractions of the mixture during its fractional (fractional) distillation.

In laboratory practice, for work related to heating, porcelain dishes are used: glasses, evaporating cups, crucibles, boats, etc.

a - evaporating cup; b - Buechner funnel; c - crucible; g - mortar and pestle; d - spoon; e - glass; g - a boat for burning; h - spatula

For filtering and washing precipitates under vacuum, porcelain suction filters - Buchner funnels are used.

Mortars with pestles are designed for grinding and mixing solid and viscous substances.

To assemble and fix various devices in a chemical laboratory, tripods with sets of rings, holders (legs) and clamps are used.

To fix the test tubes, racks made of stainless steel, aluminum alloys or plastics, as well as manual holders, are used.

a - tripod; b - manual holders

The tightness of the connection of the components of laboratory instruments is achieved with the help of thin sections, as well as rubber or plastic plugs. Stoppers are selected by numbers that are equal to the inner diameter of the closed neck of the vessel or the opening of the tube.

The most universal and reliable way of sealing a laboratory instrument is to connect its individual parts with the help of conical sections by joining the outer surface of the core with the inner surface of the coupling.

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The round bottom flask 1 has the shape of a ball with a diameter of 90 mm at the bottom, and a cylinder with a height of 170 mm and an inner diameter of 45 mm at the top.

A 1 L round bottom flask is soldered to the bottom of a 500 ml Wurtz flask using a glass tube 25 cm long and 30 mm in diameter. The tube for the introduction of boron fluoride passes through the hole in the stopper that closes the upper flask and ends in the middle of the lower flask. The upper flask serves as a condenser in which aluminum chloride is trapped, carried away by the current of the resulting boron halide.

Round-bottom flasks (Fig. 59) are made from ordinary and special (for example, Jena) glass. Everything that has been said about the handling of flat-bottom flasks applies to round-bottom flasks; they are used in many jobs. Some round bottom flasks have a short but wide neck.

Round-bottomed flasks, as well as flat-bottomed ones, come in a wide variety of capacities; with and without a throat cut.

Round-bottom flasks are conveniently placed in stands made of wood.

A round bottom flask / sealed with a rubber stopper is reported as shown in fig. 477, with a glass tube 2 dipped into a vessel with mercury.

A round-bottom flask is chosen with such a capacity that the mixture of liquids to be distilled occupies no more than 2/3 of the volume of the flask.

Round bottom flasks are the most stable and cheapest of all glassware. They are used in distillation, for all reactions with heat, and for long operations such as extraction. The spherical shape of round-bottom flasks is also the best in terms of heating uniformity.

Round-bottom flasks are rarely used in school practice; they are mainly used in experiments for prolonged and intense heating, which is more common in organic chemistry. Their most popular capacity is 100 - 500 ml. Large flasks with a capacity of 500 - 1000 ml or more are needed in much smaller quantities.

Round-bottom flasks with a long neck are used for heating low-boiling liquids that spray easily. Wide-mouth round-bottom flasks are used for reflux distillation.