- •Contents
- •Foreword
- •Preface
- •1 Materials in the Lab
- •2 Measurement
- •3 Joints, Stopcocks, and Glass Tubing
- •4 Cleaning Glassware
- •5 Compressed Gases
- •6 High and Low Temperature
- •7 Vacuum Systems
- •8 The Gas-Oxygen Torch
- •APPENDIX
- •Appendix A Preparing Drawings for a Technician
- •Index
- •Foreword
- •Preface
- •For the Second Edition
- •Please note:
- •1 Materials in the Lab
- •1.1 Glass
- •1.1.1 Introduction
- •1.1.2 Structural Properties of Glass
- •1.1.3 Phase Separation
- •1.1.4 Devitrification
- •1.1.5 Different Types of Glass Used in the Lab
- •1.1.6 Grading Glass and Graded Seals
- •1.1.7 Separating Glass by Type
- •1.1.9 Stress in Glass
- •1.1.11 Tempered Glass
- •1.1.13 Limiting Broken Glass in the Lab
- •1.1.14 Storing Glass
- •1.1.15 Marking Glass
- •1.1.16 Consumer's Guide to Purchasing Laboratory Glassware
- •1.2 Flexible Tubing
- •1.2.1 Introduction
- •1.2.2 Physical Properties of Flexible Tubing
- •1.3 Corks, Rubber Stoppers, and Enclosures
- •1.3.1 Corks
- •1.3.2 Rubber Stoppers
- •1.3.3 Preholed Stoppers
- •1.3.4 Inserting Glass Tubing into Stoppers
- •1.3.5 Removing Glass from Stoppers and Flexible Tubing
- •1.3.6 Film Enclosures
- •1.4 O-Rings
- •1.4.2 Chemical Resistance of O-Ring Material
- •1.4.3 O-Ring Sizes
- •2 Measurement
- •2.1 Measurement: The Basics
- •2.1.1 Uniformity, Reliability, and Accuracy
- •2.1.2 History of the Metric System
- •2.1.3 The Base Units
- •2.1.4 The Use of Prefixes in the Metric System
- •2.1.5 Measurement Rules
- •2.2 Length
- •2.2.1 The Ruler
- •2.2.2 How to Measure Length
- •2.2.3 The Caliper
- •2.2.4 The Micrometer
- •2.3 Volume
- •2.3.1 The Concepts of Volume Measurement
- •2.3.2 Background of Volume Standards
- •2.3.4 Materials of Volumetric Construction #1 Plastic
- •2.3.5 Materials of Volumetric Construction #2 Glass
- •2.3.6 Reading Volumetric Ware
- •2.3.7 General Practices of Volumetric Ware Use
- •2.3.8 Calibrations, Calibration, and Accuracy
- •2.3.9 Correcting Volumetric Readings
- •2.3.10 Volumetric Flasks
- •2.3.11 Graduated Cylinders
- •2.3.12 Pipettes
- •2.3.13 Burettes
- •2.3.14 Types of Burettes
- •2.3.15 Care and Use of Burettes
- •2.4 Weight and Mass
- •2.4.1 Tools for Weighing
- •2.4.2 Weight Versus Mass Versus Density
- •2.4.3 Air Buoyancy
- •2.4.5 Balance Location
- •2.4.6 Balance Reading
- •2.4.7 The Spring Balance
- •2.4.8 The Lever Arm Balance
- •2.4.9 Beam Balances
- •2.4.10 Analytical Balances
- •2.4.11 The Top-Loading Balance
- •2.4.12 Balance Verification
- •2.4.13 Calibration Weights
- •2.5 Temperature
- •2.5.1 TheNature of Temperature Measurement
- •2.5.2 The Physics of Temperature-Taking
- •2.5.3 Expansion-Based Thermometers
- •2.5.4 Linear Expansion Thermometers
- •2.5.5 Volumetric Expansion Thermometers
- •2.5.7 Thermometer Calibration
- •2.5.8 Thermometer Lag
- •2.5.9 Air Bubbles in Liquid Columns
- •2.5.10 Pressure Expansion Thermometers
- •2.5.11 Thermocouples
- •2.5.12 Resistance Thermometers
- •3.1 Joints and Connections
- •3.1.1 Standard Taper Joints
- •3.1.2 Ball-and-Socket Joints
- •3.1.3 The O-Ring Joint
- •3.1.4 Hybrids and Alternative Joints
- •3.1.5 Special Connectors
- •3.2 Stopcocks and Valves
- •3.2.1 Glass Stopcocks
- •3.2.2 Teflon Stopcocks
- •3.2.3 Rotary Valves
- •3.2.4 Stopcock Design Variations
- •3.3.1 Storage and Use of Stopcocks and Joints
- •3.3.2 Preparation for Use
- •3.3.3 Types of Greases
- •3.3.4 The Teflon Sleeve
- •3.3.5 Applying Grease to Stopcocks and Joints
- •3.3.6 Preventing Glass Stopcocks and Joints from Sticking or Breaking on a Working System
- •3.3.7 Unsticking Joints and Stopcocks
- •3.3.8 Leaking Stopcocks and Joints
- •3.3.9 What to Do About Leaks in Stopcocks and Joints
- •3.3.10 General Tips
- •3.4 Glass Tubing
- •3.4.1 The Basics of Glass Tubing
- •3.4.2 Calculating the Inside Diameter (I.D.)
- •3.4.3 Sample Volume Calculations
- •4 Cleaning Glassware
- •4.1 The Clean Laboratory
- •4.1.1 Basic Cleaning Concepts
- •4.1.2 Safety
- •4.1.3 Removing Stopcock Grease
- •4.1.4 Soap and Water
- •4.1.5 Ultrasonic Cleaners
- •4.1.6 Organic Solvents
- •4.1.7 The Base Bath
- •4.1.8 Acids and Oxidizers
- •4.1.9 Chromic Acid
- •4.1.10 Hydrofluoric Acid
- •4.1.11 Extra Cleaning Tips
- •4.1.12 Additional Cleaning Problems and Solutions
- •4.1.13 Last Resort Cleaning Solutions
- •5 Compressed Gases
- •5.1 Compressed GasTanks
- •5.1.1 Types of Gases
- •5.1.2 The Dangers of Compressed Gas
- •5.1.3 CGA Fittings
- •5.1.4 Safety Aspects of Compressed Gas Tanks
- •5.1.5 Safety Practices Using Compressed Gases
- •5.1.6 In Case of Emergency
- •5.1.7 Gas Compatibility with Various Materials
- •5.2 The Regulator
- •5.2.1 The Parts of the Regulator
- •5.2.2 House Air Pressure System
- •5.2.4 How to Use Regulators Safely
- •5.2.6 How to Purchase a Regulator
- •6 High and Low Temperature
- •6.1 High Temperature
- •6.1.1 TheDynamics of Heat in the Lab
- •6.1.2 General Safety Precautions
- •6.1.3 Open Flames
- •6.1.4 Steam
- •6.1.5 Thermal Radiation
- •6.1.6 Transfer of Energy
- •6.1.7 Hot Air Guns
- •6.1.8 Electrical Resistance Heating
- •6.1.9 Alternatives to Heat
- •6.2 Low Temperature
- •6.2.1 TheDynamics of Cold in the Lab
- •6.2.2 Room Temperature Tap Water (=20°C)
- •6.2.8 Safety with Slush Baths
- •6.2.9 Containment of Cold Materials
- •6.2.10 Liquid (Cryogenic) Gas Tanks
- •7 Vacuum Systems
- •7.1 How to Destroy a Vacuum System
- •7.2.1 Preface
- •7.2.2 How to Use a Vacuum System
- •7.2.4 Pressure, Vacuum, and Force
- •7.2.5 Gases, Vapors, and the Gas Laws
- •7.2.6 Vapor Pressure
- •7.2.7 How to Make (and Maintain) a Vacuum
- •7.2.8 Gas Flow
- •7.2.9 Throughput and Pumping Speed
- •7.3 Pumps
- •7.3.1 The Purpose of Pumps
- •7.3.2 The Aspirator
- •7.3.3 Types and Features of Mechanical Pumps
- •7.3.4 Connection, Use, Maintenance, and Safety
- •7.3.5 Condensable Vapors
- •7.3.6 Traps for Pumps
- •7.3.7 Mechanical Pump Oils
- •7.3.8 The Various Mechanical Pump Oils
- •7.3.9 Storing Mechanical Pumps
- •7.3.11 Ultra-High Vacuum Levels Without Ultra-High
- •7.3.12 Diffusion Pumps
- •7.3.13 Attaching a Diffusion Pump to a Vacuum System
- •7.3.14 How to Use a Diffusion Pump
- •7.3.15 Diffusion Pump Limitations
- •7.3.17 Diffusion Pump Maintenance
- •7.3.18 Toepler Pumps
- •7.4 Traps
- •7.4.1 The Purpose and Functions of Traps
- •7.4.2 Types of Traps
- •7.4.3 Proper Use of Cold Traps
- •7.4.4 Maintenance of Cold Traps
- •7.4.5 Separation Traps
- •7.4.6 Liquid Traps
- •7.5 Vacuum Gauges
- •7.5.2 The Mechanical Gauge Family
- •7.5.4 The Liquid Gauge Family
- •7.5.5 The Manometer
- •7.5.6 The McLeod Gauge
- •7.5.7 How to Read a McLeod Gauge
- •7.5.8 Bringing a McLeod Gauge to Vacuum Conditions
- •7.5.10 The Tipping McLeod Gauge
- •7.5.11 Condensable Vapors and the McLeod Gauge
- •7.5.12 Mercury Contamination from McLeod Gauges
- •7.5.13 Cleaning a McLeod Gauge
- •7.5.14 Thermocouple and Pirani Gauges
- •7.5.15 The Pirani Gauge
- •7.5.16 Cleaning Pirani Gauges
- •7.5.17 The Thermocouple Gauge
- •7.5.18 Cleaning Thermocouple Gauges
- •7.5.19 The lonization Gauge Family
- •7.5.20 The Hot-Cathode Ion Gauge
- •7.5.21 Cleaning Hot-Cathode Ion Gauges
- •7.5.24 The Momentum Transfer Gauge (MTG)
- •7.6 Leak Detection and Location
- •7.6.1 AllAbout Leaks
- •7.6.3 False Leaks
- •7.6.4 Real Leaks
- •7.6.5 Isolation to Find Leaks
- •7.6.6 Probe Gases and Liquids
- •7.6.7 The Tesla Coil
- •7.6.8 Soap Bubbles
- •7.6.9 Pirani or Thermocouple Gauges
- •7.6.10 Helium Leak Detection
- •7.6.11 Helium Leak Detection Techniques
- •7.6.13 Repairing Leaks
- •7.7 More Vacuum System Information
- •7.7.1 The Designs of Things
- •8 The Gas-Oxygen Torch
- •8.1.2 How to Light a Gas-Oxygen Torch
- •8.1.3 How to Prevent a Premix Torch from Popping
- •8.2.2 How to Tip-Off a Sample
- •8.2.3 How to Fire-Polish the End of a Glass Tube
- •8.2.4 Brazing and Silver Soldering
- •Appendix
- •A.2 Suggestions for Glassware Requests
- •B.1 Introduction
- •B.2 Polyolefins
- •B.3 Engineering Resins
- •B.4 Fluorocarbons
- •B.5 Chemical Resistance Chart
- •C.1 Chapter 1
- •C.4 Chapter 4
- •C.5 Chapter 5 & Chapter 6
- •C.6 Chapter 7
- •C.7 Chapter 8
- •D.1 Laboratory Safety
- •D.2 Chemical Safety
- •D.3 Chapter 1
- •D.4 Chapter 2
- •D.5 Chapter 3
- •D.6 Chapter 4
- •D.7 Chapter 5 and the Second Half of Chapter 6
- •D.8 Chapter 7
- •D.9 Chapter 8
- •Index
High and Low Temperature
6.1High Temperature
6.1.1TheDynamics of Heat in the Lab
Heat is used in thelaboratory for a variety of applications which include: speeding up chemical reactions, evaporating solvents, facilitating crystallization, softening or melting materials, anddistillation bybringing chemicals to their vapor points.
To get heat from one point to another, heat (thermal energy) is transferred by four processes: conduction, convection, radiation/absorption, transfer of energy, or some combination of the four.
1. Conduction is the transfer of heat from one body to another by molecules (or atoms) being in direct contact with other molecules (or atoms). This process is how hotcoffee heats a coffee cup.
2.Convection is the physical motion of material. An example of thisprocess would be hot air rising andcold air settling. Rigid materialscannot have convection.
3.Radiation/absorption is theresult of heat energy being transformed into radiant energy. This energy process gives us a sun tan.
4.Transfer of energy is the mechanism of microwave ovens. Here, asan
electromagnetic wave passes matter, some of theenergy of the wave is transferred to the material. The extra energy is indicated by an increase in its heat.
There are sixways to heat materials in thelab: open flame, steam, thermal radiation, electromagnetic bombardment (microwave ovens) passive electrical resistance (such as hot air guns), and direct electrical resistance (such as hot plates). All of these heating methods (except thermal radiation) useconduction to heat the container holding thematerial to make thematerialhot.
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6.1.2 General Safety Precautions
General safety precautions are important when dealing with hot materials. Because heat increases the activity level of chemicals, the chemicals become more dangerous when heated (nitric acid is dangerous, hot nitric acid is very dangerous). When you add the fact that heated chemicals can splatter or be ejected from a container, the dangers are compounded. In addition, the heat source and heated containers can also be dangerous.
Standard safety equipment is a must: eye or face protection, thermal gloves, lab coat, and closed-toed shoes should all be worn. Tongs, tweezers, or test tube holders should be used to transport heated containers.
There are other dangers present with the act of heating materials. They include:
1.Toxic or dangerous gases, produced from the material(s) being heated.
2.Explosions, caused by pressure buildup of trapped gases.
3.Breakage and explosions, caused by faulty or damaged apparatus or heating devices.
4.Flash fires, caused by flammable fumes ignited by a spark or flame.
Because of these potential dangers, heating operations should be done within a fume hood. The windows of the fume hood should have tempered glass and/or plastic film coatings. The door of the fume hood should always be closed as low as possible, especially when in use. Place your hands underneath the door to work while protecting your face behind the window. However, do not use the fume hood door in place of eye protection—use both.
Unfortunately, a fume hood is not always available or practical. If you are unable to work in a fume hood but still require shielding, portable explosion shields are available and should be used.
Experiments or processes that use heat must constantly be monitored. If you need to leave the lab, even for a short time, be sure that someone else can monitor the operation in your absence. Problems such as chemicals boiling over, or the evaporation of materials from a container, can occur. In addition, water hoses that lead to condensers have a habit of slipping off or being turned off when no one is looking. To remedy this problem, the use of relays that turn off heat sources are recommended.
If you ever find a dry glass container on its heat source (the liquid within having boiled off), it is possible that the container may have developed thermal strain. In this condition, it is dangerous and likely to crack or break into pieces without any notice or warning. Unless you have the facilities to examine for strain or to properly anneal the potentially strained glassware, throw it away (see Sec. 1.1.13).
6.1.3 Open Flames
Period movies, such as those starring Sherlock Holmes, often showed an oil lamp that was always burning and always ready for heating a test tube. Contemporary
High Temperature 6.1 |
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movies now show a Bunsen, or Fisher, burner (see Fig. 6.1) in the lab, always burning and always ready for heating a test tube. If as a child you had a student chemistry kit, it probably came with an oil lamp. The mere fact that you had it burning away on your kitchen table was proof to your younger siblings that you were doing chemistry!
While it is true that a burning flame provides good images and great ambiance, it is not a very good source of heat. You will not see open flames burning away in a laboratory for effect or ambiance. If an open flame is used for heating solutions in the laboratory, it is always shut off after use.
Fortunately, the use of oil lamps is now neither common nor necessary. Although there are modern substitutes for oil lamps, such as Bunsen and Fisher burners, they are not the heating mechanism of choice because most heating is done by electric mantels and stirrer/hot plates. There are too many drawbacks associated with open-flame heat sources for them to be considered the heat source of choice. The problems associated with these burners include the following:
1.Open flames may provide a too-intense and localized source of heat.
2.Open flames may provide an ignition source for flammable gases or other combustible materials.
3.Open flames may fill a poorly vented room with carbon dioxide.
4.The tubing connecting the gas outlet to the burner can leak, emitting gas into the room.
5.Specific temperatures are hard to obtain and maintain, and it is simple to overheat materials.
6.It is simple for an open flame to heat things you do not want heated, causing injury or damage.
7.Lighting these burners in a fume hood can be very difficult. Although it is possible to ignite a burner with a striker (a flint and steel connected by a spring), it is not easy. An easier approach is with a disposable lighter. Probably the easiest technique for lighting a Bunsen burner in a fume hood is to have enough flexible tubing to take it out of the fume hood for lighting and, once lit, return it to its proper location.
Because of the problems associated with open flames, various states regulate their use in labs. Some states even ban the use of open flames in any lab. Despite the problems associated with open flames, they are still used quite extensively in many labs because the advantages of open flames are as follows:
1.Fuel is inexpensive.
2.Equipment is inexpensive and easy to set up.
3.They are easy to operate.
When you have a general chemistry lab with 20 to 30 (or more) students, providing expensive equipment to all can be a sobering jolt to safety considerations.
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High and Low Temperature |
Hose |
Hose |
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connection |
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connection |
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Needle |
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valve |
Fig. 6.1 Bunsen and Fisher burners.
Therefore, as long as open flames will continue to be used, the following are some safety insights for their proper use.
A burner is connected to its gas source with either amber latex or vinyl tubing (Tygon). The advantage of amber latex tubing is that it has excellent memory of its original shape (See Resilience in Sec. 1.2.2). So, regardless of how long a hose is connected, the hose will always grip the hose connection it was originally slipped onto. Unfortunately, latex tubing ages over time and can easily burn. Both of these conditions, aging and burning, will eventually cause leaks in the tubing. If you use latex tubing, monitor it often for signs of age (cracking) or burns.
Never Look For Gas Leaks With a Match. Your nose will probably offer the first indication that you have a leak. Then, you can either listen for the hissing of the leak, while occasionally twisting and moving the tubing to arrange the leak region, or coat the tubing with a soapy solution and look for bubbles.
Vinyl tubing has poor memory and with time begins to conform to new shapes. With time, vinyl tubing can lose its grip on hose connections and may leak or be pulled off easily. There are two solutions to this problem. The best solution is to use a hose clamp. This clamp will provide a secure attachment of the hose to the gas outlet and allow for (relatively) easy removal. Alternatively, you can soften the tubing by placing the end in boiling water for a minute or so. This method will allow you to shove the tubing onto the hose connection sufficiently far that the chances of accidental removal or leakage are considerably diminished.
Vinyl tubing does not age and is fire-resistant. However, a hot object may melt through the tubing causing a leak. Fortunately, because the tubing does not burn, it therefore is unlikely to ignite a combustible gas.
Removing vinyl and amber latex tubing is best done with a razor blade. Do not pull vinyl tubing off because the torque is likely to break the hose connection off.
Needle valves on both Fisher and Bunsen burners are threaded right-handed. These valves are in reverse angles during use; that is, you observe the valves from the top. This orientation may confuse some people. Just remember that in use, you close a needle valve by rotating it CW, and open the valve by rotating it CCW.
High Temperature 6.1 |
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When first setting up a burner, close the needle valve all the way. Rotate the lab bench valve to the open position (checking for leaks in the tubing at this point is advised). Light a match (or get a striker ready) and open the burner's needle valve. Depending on the length of the tubing, you may need to wait a moment for the gas to travel to the burner (your nose is a good indicator of gas presence). Light the burner.
Once the flame has ignited, it needs to be "fine-tuned." By opening the valve you increase gas flow, and by closing the valve you decrease gas flow. By rotating the air gates on the side of the burner, you can also increase or decrease the amount of air that is allowed to premix with the gas to intensify the flame. When you open an air gate, more air is available to combine with the gas, thus producing a bluer and hotter flame. As a gate is closed, less air is available to the gas, producing a whiter ("yellower") and cooler flame.
Any flame that is predominantly white (or yellow) will smoke and deposit black (carbon) soot on any object that is placed over it. It is best to allow at least enough air in the gates to ensure a blue flame. A blue flame will not deposit soot. Additionally, a white (yellow) flame is not likely to have enough energy to accomplish any significant heating.
The main difference between the Fisher burner and the Bunsen burner is size and heat dispersion. When trying to heat a test tube in a Fisher burner, you are likely to overheat the material. Likewise, when trying to heat a two-liter flask with a Bunsen burner, you are likely to have a long wait. The exact demarcation line of which tool you should use for which type of heating job requires common sense and experience.
If you need to heat a test tube with a Bunsen burner, follow the following rules: 1. Be sure to hold the test tube with a proper test tube holder. Do not use
fingers, rags, tweezers, or pliers.
2.Hold the test tube at an angle off of vertical.
3.Do not "aim" the test tube at yourself or any other person. This positioning may be difficult in a crowded lab, but it is important. If the solu-
Fig. 6.2 Heating the whole bottom of a test tube.