The glass is an inorganic, transparent, rigid, non-crystalline, and versatile material made up of a mixture of metal oxides fused at high temperatures. The glassware is widely known across the globe for its three significant properties: transparency, stability and inertness, and malleability. The transparent nature of the glass enables the user to observe a reaction taking place within. The stability and inertness prevent the glass from reacting to the chemicals used in the laboratory. The malleable glass offers the creation of new designs and shapes of the apparatus and repair if broken.

Years of development and practice have yielded the present nature, composition, and structure of the glass, as well as the shapes and designs made from it. Wall thickness, angles, dimensions, and height-to-width ratios are varied to meet the specific challenges and needs of the laboratory practices. Each laboratory glassware is designed according to the function it is going to perform.

Different types of glass possess different properties depending on their chemical composition and preparation. Out of the physical and chemical properties of the glass, the expansion properties (the amount of size increase upon temperature increase, refractive index (how light passes through the glass), viscosity (the ability to remain consistent and integrated as temperature increases), and dielectric properties (electrical resistance) are of particular interest to the laboratory scientists.

There is no single melting or boiling point for glass. The glass tends to maintain its physical shape after it begins to soften at high temperatures. However, on the temperatures above the softening point, the glass sags under its weight because of the external forces such as gravity. The glass surface gradually loses its form as the temperature continues to rise. Then, on further higher temperatures the internal forces, such as surface tension, cause sharp corners on the glass to round, and the glass starts “beading up” on itself. Eventually, the glass collects into a thick, liquid puddle. The viscosity of the glass has an inverse relation with temperature. As the hotter a glass “liquid” gets, the less viscous it becomes. In fact, the high viscosity of the glass puddle prevents crystallization. The high viscosity of the glass beyond the crystallization temperature inhibits atomic mobility and prevents the atoms from clinging together to make crystals. Different properties of the glass on varying temperatures should be considered before manufacturing and handling the glassware to get desirable properties and functions

Different types of glass and their properties are discussed below:

Borosilicate Glass

Borosilicate glass possess extraordinary physical and chemical properties that enable using of this glass not only for the production of laboratory glassware but also for various others purposes including pharmacy (vials), medicine (glass syringes), production of brilliant lighting unit, various branches of the textile industry (fingers) and in other practices where higher temperature and chemical resistance are preferable.

Composition

Physical Properties

Chemical Properties

Borosilicate glass is inert to all materials except hydrofluoric acid, phosphoric acid, and hot caustic solutions. Also, the borosilicate is non-reactive with water and acids. Only a minimal amount of monovalent ions may be released into the surrounding medium at the beginning of the water or acid impact. A non-porous layer of silica gel is created on the glass surface gradually after water exposure. This layer inhibits the surrounding medium to influence the glass further. Only hydrofluoric acid and hot phosphoric acid can impact the borosilicate glass since both acids prevent the creation of the silica gel layer on the glass surface. Increasing temperature and concentration increases the alkali’s impact on the glass. Scales from the volumetric glass can be removed by surface etching.

Soda-lime Glass

Soda-lime glass is also known for its excellent chemical and physical properties. The products that resist the impact of chemical medium and temperature differences momentarily and limitedly are mostly manufactured of the soda-lime glass. Lower energy demand and longer working times make the soda-lime glass the most inexpensive type of glass to manufacture laboratory glassware. Also, it can be recycled easily. Usually, the soda-lime glass is used to make pipettes.

Composition

Physical Properties

Chemical Properties

The Soda-lime glass is not as resistant as Borosilicate glass. However, it shows some hydrolytic resistance.

Neutral Glass

Chemical Composition

Physical Properties

Chemical Properties

There are three major categories of glass used in the laboratory. These categories include soft glass, hard glass, and high-temperature and UV-transmission glass.

Soft Glass

The soft glasses are physically softer than other glasses as they abrade more easily. Besides, these glasses tend to maintain their soft working properties over a higher temperature range. The most common type of soft glass is the soda-lime glass. The soda-lime glass is a mixture of carbonate of sodium or sodium oxide (Na2O), and calcium oxide (CaO) or magnesium oxide (MgO). Because of its lower energy demands (lower melting temperatures) and longer working times, it is the most inexpensive type of glass to manufacture laboratory glassware. The quality of a soft glass is based on the proportions of its constituent materials. Typically, 8% to 12% lime (by weight) and 12% to 17% soda (by weight) are used to make the soft glass. Too high lime concentration levels may cause devitrification during the manufacturing process. On the other hand, too low lime concentration can subject the glass to natural weathering and water attack. In addition to the soda-lime glass, sodium silicate and lead glass are examples of soft glass.

The significant disadvantage of using the soft glass for laboratory glassware is that any apparatus made with these glass types are essentially non-repairable. Also, the laboratory apparatus made of soft glass is likely to shatter when the flame of a gas-oxygen torch touches them as their thermal coefficients of expansion are relatively high.

Hard Glass

Hard glass has given the name of “hard” because of its ability to resist abrasion impact over three times the level of soft glass. Also, it sets at a higher temperature and, gets “harder” faster. Because of the lower thermal coefficients of expansion of the hard glass they can withstand much greater thermal shocks than the soft glasses. Besides, the hard glasses are chemically resistant to alkaline solutions and many other chemicals. Borosilicate glass is the most common example of hard glass.

The High-Temperature and UV-Transmission Glass

The high-temperature and UV-transmission glasses are commonly known as “quartz” in the laboratory. The quartz glass is popular in the laboratory because of its outstanding thermal and UV-transmission abilities. Unlike other glasses that deform and melt at temperatures more than 1200°C, quartz glass maintains a rigid shape. Besides, because of the extremely low thermal coefficient of expansion (approximately 5.0 x 10″7 Acm/cm/°C), it can withstand thermal shock that would likely smash all other glasses. Quartz glass transmits the broadest spectrum of light frequencies as compared to other glass types.

Beakers

A beaker is a cylindrical glass vessel used for holding liquids, storage, mixing, and transferring various solutions. The glass beaker is a multipurpose piece that is widely used in the laboratory to carry out a chemical reaction, measure liquids, heat the solutions or liquids over a Bunsen burners flame or to collect them in a titration experiment. Uniform wall thickness of our beakers makes them ideal for heating applications with easy-to-read scale and large labeling field for easy marking. Increased glass content strengthens the beakers with great mechanical stability. The reinforced rim increases shock resistance and reduces the risk of breakage.

Flasks

Volumetric flasks are employed to measure precise volumes of liquids to make standard solutions or weigh for density calibrations. The volumetric flasks aid in quantitative laboratory work. Made of low expansion coefficient and chemically resistant borosilicate; our volumetric flask is an optimum combination of resistance and readability. Volumetric flasks can be capped to prevent material in the flask from evaporating as well as to maintain the material’s purity.

Procedure

The proper procedure of filling and using the volumetric flask is as follows:

1. Transfer the liquid to be measured into the flask with the help of a pipette The instrument used for liquid transfer should supply a steady stream against the wall, about a centimeter above the calibration line. One should not splash the liquid. The tip of the pipette or a burette may touch the wall of the flask.
2. After reaching the level below the calibration line, cap the container and let the liquid drain from the walls of the flask.
3. Fill the flask as required. If the calibration line is crossed, a pasture pipette can be used to draw out the excess fluid. Make sure that the surface tension in the tip of the pipette is sufficient to draw out the fluid. Once completed, cap the flask.

Method for the gravimetric purpose:

1. Properly clean and dry the flask.
2. Using the physical balance weigh the flask, its cap, and any other materials that may interfere with the final weighing.
3. Note the liquid’s temperature and the room’s barometric pressure and humidity, if accurate readings are required.
4. Carefully transfer the liquid to be measured into the flask using a pipette or a burette.
5. When the level is just below the calibration line, put the cap on the container and let the liquid drain from the walls of the container.
6. Weigh the filled flask.
7. If Step 3 was performed, repeat it to verify the readings.
8. Deduct the empty flask weight from the filled flask weight.

Method for making a definite solution:

1. Properly clean the flask and dry it.
2. Transfer the pre-calculated concentrated liquid into the flask using a pipette or a burette. Do not splash.
3. Add distilled water to the flask up to the calibration line using a pipette, a burette, or any other device that can supply a steady stream against the wall about a centimeter above the calibration line trying to rinse any of the concentrated liquid remaining on the flask’s neck. Cap the container after reaching up to the calibration line and let the liquid drain from the walls of the container.
4. Complete the filling process using step 3 again. Try not to cross the calibration line because any excess liquid may dilute the required concentration.

To empty the volumetric flask, follow the following procedure:

Incline the flask slowly to provide a steady stream of liquid from the spout. Continue inclining until the flask is vertical and hold it for half a minute to empty the flask fully. Wipe the drop at the tip of the flask with the wall of the receiving container. Make sure not to remove the flask in a vertical position.

Glass Bottles

The Glass bottles provide the handlers with an extraordinary mechanical strength which prevents them from breaking and cracking. They offer a vast and diverse range of applications. The bottles improve handling, sample identification, and ease of use. Also, the bottles and accessories help to make laboratory work more comfortable, safer, and more economical. We provide a diverse range of laboratory bottles to enable the experimenters to perform various research manipulations in them. The glass bottle range includes:

• Wide mouth polycarbonate bottle
• PETG media bottle
• Polycarbonate storage bottle (round and square)

The bottles are provided with reusable screw caps. The grooves and ridges on the screw caps are optimized to provide the user with more efficient and more comfortable tightening or removal, especially with gloved hands. The optimized cap sealing system ensures a liquid-tight seal. The bottles are marked with highly durable white ceramic. White markings on the bottles improve visibility and volume reading even for darker solutions.

Graduated Cylinder

A graduated cylinder is a relatively narrow glass cylinder, manufactured from chemically resistant borosilicate glass, explicitly used for measuring a liquid’s volume. Generally graduated cylinders are not used for high-quality volumetric work. The tolerance and resistance of graduated cylinders are considerably higher than that of the volumetric flasks. Our graduated cylinders provide increased mechanical strength to avoid breakage and cracking. Measurements on the graduated cylinders are taken by viewing the lower meniscus at the eye-level (the lowest point of the convex dip in the cylinder).

To fill a graduated cylinder following protocol should be followed:

1. Clean and dry the cylinder before filling.
2. Transfer the liquid to be measured into the cylinder with the help of a pipette, burette, or any other laboratory instrument in a steady stream. Do not splash.
3. Stop filling when the calibration line is achieved for a few minutes and let the liquid drain from the walls of the container.
4. Draw out the excess fluid by using a pipette if the calibration line is crossed. While pipetting out the excess liquid, make sure that the surface tension in the tip of the pipette is sufficient.
5. Cover the cylinder to prevent evaporation or contamination.

To empty a filled graduated cylinder follow the following protocol:

1. Incline the cylinder gradually to pour out a steady stream of liquid of the spout. Do not splash.
2. Keep inclining until the cylinder is vertical and hold it for about half a minute.
3. To empty the cylinder touch the drop at the tip of the spout to the wall of the receiving container.
4. Do not remove the cylinder vertically.

Pipettes

A pipette is a volumetric instrument used to transfer small amounts of liquid. The liquid to be transferred is drawn into one end of a glass cylinder by squeezing the rubber ball at the opposite end or by sucking. The glass pipette is marked with white ceramic to allow the accurate transfer of the required volume.

Types of Pipettes

There are three types of volumetric pipettes: volumetric transfer, measuring, and serological. Because of volume gradations, the serological pipettes can dispense varying volume of liquids. While using the serological pipette, do not include the tip region in the volume measurements. These pipettes are graduated with white ceramic along their sides. Do not drain or blow out the measuring pipettes when delivering a solution because the extra volume in the tip is not part of the pipette’s calculated volume. The volumetric pipettes are designed to dispense one specified volume of liquid, whereas the measuring pipette is calibrated to dispense different volumes. Unlike the serological pipette, both of these pipettes are designed to include the tip region in their entire dispensed volumes.

To fill a measuring or serological pipette follow the following method:

1. Draw the solution to be transferred just above the volumetric level, then let the solution fall to the calibration mark.
2. Remove the pipette from where the fluid is drawn, and wipe the tip with a laboratory tissue to remove any excess solution drops from the outside of the pipette.
3. When dispensing the fluid from a measuring pipette, let the tip touch the side of the receiving container and let the fluid flow. If one is dispensing the liquid by hand, control the flow rate by placing the thumb on the end of the pipette. However, never let the thumb wander away from the end of the pipette because it will let the fluid flow uncontrollably.
4. Thoroughly drain the solution from the pipette.
5. Do not remove the tip with an upward or downward motion.

Burette

Burettes are specialized measuring instruments. To accurately dispense the liquid and to control the liquid outflow the burettes have attached pinch clamp, stopcock, or valve. The burettes are made out of standard, tolerant laboratory borosilicate glass to avoid breakage and cracking. We provide graduated burettes with white-enamel markings that increase visibility while using dark solutions as well as facilitate meniscus readings. A burette clamp or several three-fingered clamps are attached to the side of the burette when mounted in a vertical position as the single three-fingered clamp is likely to wobble or swing off vertically.

Procedure

1. Clean the burette by rinsing it with the same solution that is used for titration.
2. Fill the burette above the zero mark so that there is enough liquid to prime the stopcock or rotatory valve. Remove the air bubbles from the valves.
3. Pour the solution of the interest in the burette to set the zero point at eye level.
4. Wipe the drops from the tip.
5. Slowly open the stopcock and start the titration. Ensure that the burette tip is not touching the wall of the titration vessel. Make sure that the vessel rests on a stirrer to guarantee agitation of the titrated solution.
6. Close the valve as soon as the color change of the solution has occurred.
7. Read the volume of the dispensed solution.

Types of Burettes

There are four types of burettes.

• Mohr Burettes

Mohr burettes are the least accurate burettes. They do not have stopcocks at their tips; therefore flexible tubes with pinch clamps are used to control the flow of the liquid from the burette.

• Giessler Burettes

Giessler burette is commonly used in laboratory practices. It has a stopcock clamped at the tip. Some Giessler burettes have three-way stopcocks for easier filling. One way moving of the stopcock fills the burette and if it is turned 180° the burette empties.

• Automatic Burettes

For measurements, there is no arithmetic required. As they can be filled quickly and efficiently to precisely 0.00 mL, so the amount dispersed is determined simultaneously. Because of the accurate measurements, the errors due to arithmetic calculations are minimized. This type of burette is filled by intentionally overfilling the top which is enclosed and has drainage for collecting the overflow. The top portion of the automatic burette is not calibrated, so if less liquid is dispensed than is contained in this region, the amount removed cannot be determined.

• Dispensing Burette

The dispensing burette can carry up to one liter of liquid and is capable of fast and efficient liquid dispensing. Its accuracy is about ±0.5% of total volume.

Care and Use of Burettes

Burettes are more prone to chipping or cracking as they are seldom tip- or end-heat strengthened. In addition to the tip, the care of the stopcocks on a burette is equally essential. Check the stopcocks for jamming, leakage, and consistency of liquid flow. Glass stopcocks break easily so cautiously remove the plug of the burette’s stopcock, clean the plug and the barrel, and regrease it. Remove the grease from the stopcock if it is leaking and replace the plug. Tighten the plug firmly but do not rotate it.

Do not use silicon-based stopcock grease on burettes unless the nature of the chemicals requires it because silicon-based greases need constant cleaning and replacement to maintain their slippery nature. The silicon grease may be inexpensive in the short run, but the consequences are costly. Instead of the silicon grease, Teflon stopcock or rotatory valve can be used. Check the Teflon grease stopcocks for scratches periodically. Never store any solution in a burette.  Alkaline solutions may react with the glass and cause freezing of the glass stopcock so never store alkaline solutions in a burette. Also, an alkaline solution may react with the glass and create a rough surface that may scratch the Teflon plug.

When filling a burette, first remove any air bubbles in the tip region. If the bubble comes out while making a measurement, it may take the place of fluid that was recorded, but never leave the burette. To remove the bubble, overfill the burette, and open the stopcock fully to push the bubble out.

Glass Test Tubes

A test tube is a thin glass vessel with a rounded bottom designed to hold small quantities of chemicals and feature a flared lip to make pouring easier. Test tubes can hold liquid or solid chemicals and can be used to contain small chemical reactions. The slimness of the test tube efficiently reduces the spread of any vapors that may be produced by the reaction. Also, a test tube allows the user to heat the sample on the flame.

Uses of Glass Culture Tubes

• The glass culture tubes are commonly used in chemistry labs to handle chemicals, especially for qualitative experiments and assays. Their round bottom and vertical sides reduce fluid and mass loss while pouring. Also, the round bottom makes it easier to wash out, and allow convenient monitoring of the contents.
• Test tubes are useful vessels for heating small amounts of liquids or solids on a Bunsen burner. Its neck usually holds the tube with a clamp or tongs. By slightly inclining the tube, the bottom can be heated to hundreds of degrees in the flame, while the neck remains relatively cold, allowing vapors to condense on its walls.
• A water-filled test tube and upturned tube in a water-filled beaker are used to capture gases in electrolysis.
• A test tube with a stopper can also be used for temporary storage of chemical or biological samples.
• In clinical medicine, air-removed, sterile test tubes are used for the collection and holding of physiological fluid samples such as blood, urine, pus, and synovial fluid.

Thermometers

A thermometer is a commonly used laboratory instrument to measure and show temperature with high accuracy. As the temperature ranges and conditions of a system can vary, a variety of materials have been incorporated into different types of thermometers.

Types of Thermometers

• Liquid-in-glass thermometer

The volume of the material is measured by the liquid-in-glass thermometers. As the volume of liquid increases with an increase in heat.

• Gas or vapor at constant volume

This type of thermometer measures the pressure change as the pressure of a gas increases with increase in temperature.

• Dilatometer (or bimetal coil)

It measures the length change of the metals. As heat rises, the length of one metal expands more than the length of the other metal.

• Platinum wire

It measures the electric resistance of the material as the electrical resistance of the wire increases with the temperature.

• Thermocouple

It measures the thermal electromotive force as the thermal electromotive force has a direct relation with the heat.

Parts of a Thermometer

1. Bulb

It is the storage area for the liquid. Size of the thermometer decides the size of the bulb.

2. Stem

The stem is the main shaft of the thermometer.

3. Capillary

The capillary is a channel carrying the liquid up the stem. The narrower the capillary, the higher the accuracy of the temperature measurement. Despite the accurate measurements because of the narrower capillary, the temperature readings are affected by the surface tension of the liquid and the glass of the thermometer.

4. Main scale

The scale provides with the temperature reading.

1. Immersion line

The immersion line sets the placement depth for partial-immersion thermometers.

2. Expansion chamber

The expanded region at the top of the capillary is designed to avoid excessive pressure build-up from the expanding liquid.

3. Contraction chamber

The contraction chamber is used to reduce the necessary length of a thermometer.

4. Auxiliary scale

It is required on thermometers lacking an IPTS (International Practical Temperature Scale) calibration point.

• Wear protective gloves, eye protection glasses, aprons, lab coats while handling with laboratory glassware.
• Avoid using cracked or broken glassware as it may cut.
• Use safety shields, nets or coatings to avoid broken glass from injuring the handler.
• Always check the glassware for damage or breakage even for small cracks or scratches as they may reduce the strength of the glassware.
• Use wire gauze when heating on flame or use medium heat when using a hot plate.
• Heat up and cool down the glassware gradually and slowly even when using Borosilicate glass which has a lower coefficient of expansion. The maximum working temperature for Borosilicate glass is 500°C; however, special precautions must be taken even when working above 150°C.
• Extra thick glassware is ideal for working under vacuum when higher mechanical strength is required; this glass is less heat resistant so do not heat it.
• Ordinary, thin-walled, laboratory glassware should not be subjected to pressure or vacuum.
• Do not lift the glassware by more fragile rims or side arms, instead lift the instruments by the body or neck.
• Lose the caps of the glass bottles while heating.
• Do not draw the solution by sucking through the pipette as it may intoxicate, burn, or injure the handler.
• Free the stuck jointed parts cautiously. Gently tap or rock the two sides of the joints to free them.
• Do not heat glassware over 420°C as it may cause stress in the glassware that eventually leads to breakage.

Proper cleaning of the laboratory glassware is essential before starting any experiment. Cleaning glassware is a multistep process. If soap and water can remove the contaminating material, at least two more steps are required: rinsing with water, followed by a distilled water rinse. Particulate matter on the glassware needs to be brushed or wiped off before the cleaning processes begin. Similarly, grease is removed by using organic solvents before salt deposit removal with water.

The fundamental principle of cleaning glassware is “like dissolves like,” as polar solutions dissolve polar and non-polar dissolve non-polar. For instance, oil cannot dissolve crystals, and water cannot clean grease. Lubricants containing chlorofluorocarbons need chlorofluorocarbon solvents for cleaning.

General recommendations for cleaning the glassware are;

• Clean the glass equipment as soon as possible to prevent the residues from hardening.
• Rinse or soak the laboratory glassware with an organic solvent to remove grease and then again rinse with water thoroughly.
• Clean the glass manually or in a washing machine.

Techniques for Glassware Cleaning

1. Manual Wash

Use soft sponges or other soft clothes or plastic core brushes with non-abrasive bristles to wash the glassware. Choose from the several detergent formulations offered by laboratory specialists for manual washing, depending on the residues to be washed out. Optimize the detergent formulations according to the requirement of the stains.

2. Washing Machine

Select the detergent formulations according to the residues to be eliminated. Optimize these formulations for typical laboratory residues. Use nonabrasive material to coat the glassware racks and support cupboards as it will prevent the glass from scratches or breakage because of the hard surface.

3. Specialized Cleaning Methods

• For Permanganate Stains

A mixture of 3% sulphuric acid and 3% hydrogen peroxide (equal volume) is used.

• For Iron Stains

A solution containing equal volumes of hydrochloric acid and water is used.

• For Bacteriological Material

Soak the glassware in a disinfectant solution or steam autoclave the glass equipment. After that clean it with a detergent.

Precautions while Cleaning the Glassware

• Do not clean the glassware with abrasive sponges.
• Do not use any detergents or cleaning solutions containing abrasive particles.
• Get rid of any hard objects like metal spatulas, stirring rods or brushes immediately since they can break the glass or scratch it.
• Do not use strong alkaline detergents as they may dissolve the glass and cause breakage.
• Do not wear jewelry or rings while cleaning the glassware.

Do not wet the volumetric glassware thoroughly since it is essential to preserve the meniscus. Therefore, perform the cleaning procedure to eliminate organic substances, especially grease, which may not allow a uniform wetting with distilled water. After the washing, rinse the materials thoroughly with distilled water. If glassware is to be dried, ethanol or acetone are recommended for rinsing. The drying process may be shortened by passing dry air through it. Make sure that the air is clean and free from oil, and the air compressor is equipped with appropriate filters. Also, do not remove any dirt by applying direct heat as it may cause the calibration of the volumetric glassware to be altered. Do not use abrasives on volumetric glassware as the scratches may deposit dirt or prevent proper drainage of liquid. Do not drain the solution in the pipette by mouth. Graduated lines in blue or white color which have been fused on the glass are quite resistant to alkalis and acids but are not as resilient as the glassware itself is, so avoid immersion in such solutions for extended periods.

Laboratory glassware is specially manufactured so it should be handled with extreme care and stored at the proper place after use. Keep it well away from shelf edges. Don’t let the instruments roll around in drawers (use drawer pads). Place glassware well back in hoods or on benches. Also, dispose of the broken glass in a rigid and puncture-resistant container.

1. C. Holloway, The Physical Properties of Glass, Wykeham Publications LTD, London, 1973, p. 205.
2. J. Austin, “Simple Removal of Buret Bubbles,” Journal of Chemical Education, 66, p. 514(1989).
3. Jacquelyn A. Wise, Liquid-in-Glass Thermometry, S. Government Printing Office, Washington, D.C., 1976, p. 23.
4. E. Stanworth, Physical Properties of Glass, Oxford University Press, London, 1953, p. 209.
5. W.A. Weyl, “Chemical Composition and Constitution of Glasses,” Proceedings of the Seventh Symposium of the American Scientific Glassblowers Society, pp. 16- 23 (1962).