- •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
Stopcocks and Valves 3.2 |
189 |
Plastic cap with internal threads
External threads on end of —. glass barrel
Build up of the glass wall
Fig. 3.22 The rotary valve operates by rotating a plastic cap. The rotational motion of the cap is translated into linear motion on the Teflon shaft. When the shaft is inserted all the way into the glass barrel, the tip of the shaft pushes against a buildup of glass and stops fluid motion. The O-rings on the shaft prevent leaks past the cap.
becomes worn round, or a groove is worn into the threaded section of the plug. Either of these effects causes the washer to not rotate with the plug and is the same as switching the positions of the black and white washer. Replace the washer or plug if either are worn.
3.2.3 Rotary Valves
Standard Teflon stopcocks cannot be used for any vacuum work. A completely different design from those discussed thus far is required for a Teflon vacuum stopcock. This design is shown in Fig. 3.22 and is called a rotary Teflon valve. It is called a valve instead of a stopcock because its operation and design is similar to those of a metal designed valve.
There are many designs of rotary valves: Some have externally threaded glass barrels, others have internally threaded barrels; some have exposed O-rings, others have covered O-rings, and some have no replaceable O-rings. Regardless, they all work with the same operational technique. Rotating cap motion translates into vertical motion on a central shaft, which rides up and down to open or close a pathway.
When closing a metal valve, it is customary to rotate the valve until it cannot be rotated anymore. Then you must give it a final twist to make sure it is closed tight. This extra twist should never be done with glass rotary valves. These valves cannot withstand the same forces as metal valves, nor is it necessary to use such force on a glass rotary valve. Glass is likely to break if too much torque is applied to the cap. Fortunately, because you can see through glass, it is easily possible to see if the shaft is closed against the barrel. This closed position is shown in Fig. 3.23 on the walls of the barrel with a "wet" mark.
190 |
Joints, Stopcocks, and Glass Tubing |
You can see when the rotary valve is
The Teflon shaft with and without
closed when you can see the "wet" mark on
an O-ring on the end.
the wall of the barrel.
Fig. 3.23 The rotary valve plug with and without an O-ring on the end on the left, and the shaft showing "wet" marks on the right.
Both Fig. 3.22 and Fig. 3.23 show O-rings on the Teflon shaft. Some manufacturers cover these O-rings with Teflon so that the rotary valve can be used with solvents that might otherwise destroy the O-ring. Others have "fins" that sweep in front of the O-ring to prevent solvents from contacting the O-ring.
Although all vacuum rotary valves have O-rings along the side of the shaft, some have O-rings at the end as shown in Fig. 3.23. This design has advantages as it provides a better quality seal without over tightening. The reason is simple: The same force applied over a small area will have a greater pounds-per-square-inch pressure than that applied over a large area.* With an O-ring at the end, it is possible to obtain much more force without having to bear down on the barrel and risk breaking the stopcock.
All Teflon stopcocks and valves must remain free of particulate contamination so the surface will not be scratched or damaged. Any abrasions, or distortions, of the central shaft are likely to be leak sources. In addition, do not place any filled container closed with a Teflon stopcock (or valve) in a refrigerator. Just as Teflon expands in heated environments, it contracts in cooled environments. Thus, what was a good seal at room temperature may leak in a cold environment. Do not try to compensate for the cold temperature by overtightening the shaft for two rea-
Fig. 3.24 General designs for rotary valves.
'This amount is analogous to the pressure exerted by spiked heels vs. running shoes on a sidewalk.
Stopcocks and Valves 3.2 |
191 |
Open
Fig. 3.25 Inlet Valve Chem Cap™. The Inlet Valve Chem Cap™ is from Chemglass Co. Inc., Vineland, N.J. 08360. Reproduced with permission.
sons: One, it probably will not prevent a leak, and two, when it is removed from the cold environment, its expansion may break the apparatus.
Although the specific design of a valve varies between manufacturers, rotary Teflon valves are almost always a variation of the inline and right-angle designs shown in Fig. 3.24. Although the rotary design may be restrictive, it has provided new possibilities for valve design such as the Inlet Valve Chem Cap™ (shown in Fig. 3.25), which is designed for medium vacuum system use (up to approximately 10"4 torr). The Chem Cap™ does not have a second or third arm as is customary with just about all other stopcocks because the transmission of gas is through the Teflon shaft itself. This stopcock can be used in place of a standard glass vacuum stopcock for grease free operations where a standard Teflon stopcock could not be used because of its inability to maintain a vacuum.
Another advantage of the rotary valve design is apparent when an extension from the end of the shaft is added and the valve becomes a needle valve. It can then permit fine control for the release or addition of materials (see Fig. 3.26).
Rotary Teflon valves have greater initial costs than comparable vacuum glass stopcocks. However, due to their lack of maintenance needs, as well as not requiring any stopcock grease, their long-term expense can be considerably less than that for standard vacuum stopcocks. However, because Teflon stopcocks or valves require a limited temperature environment, all glass stopcocks will always remain in demand.
3.2.4 Stopcock Design Variations
All of the above designs are called two-way stopcocks because there are two arms, or connections, to the stopcock. Two-way stopcocks typically are open/ close valves with no proper orientation. The exception for this statement are the stopcock designs shown in Figures 3.18, 3.19, and 3.20, which require a specific
Fig. 3.26 A close-up of the end of the Teflon shaft with a needle valve extension.
192 |
Joints, Stopcocks, and Glass Tubing |
Fig. 3.27 Different designs of the three way stopcock, with the barrel on the left and a side view or crosssection of the plug on the right.
orientation of the plug to the stopcock to evacuate the inside. There are no orientation requirements for rotary valves.
Stopcocks with three arms are called three-way stopcocks. Five of the most common three-way glass stopcock designs are shown in Fig. 3.27. Represented are the barrel and plug cross sections (or end views) of three-way stopcocks. The three-way stopcocks (a), (b), and (e) are available in solid plug, Teflon, and highvacuum designs. The (c) and (d) designs are exclusively for vacuum systems and are currently difficult to find. Because of their design, rotary valves can only have two arms. It is possible to creatively place two of them together in a three-way alignment, however. An example of a three-way rotary Teflon valve configuration is shown in Fig. 3.28.
3.3 Maintenance and Care of Joints,
Stopcocks, and Glassware
3.3.1 Storage and Use of Stopcocks and Joints
So much depends on the proper performance of stopcocks and joints that they should be treated with the same care, and consideration, as an optical lens. If your chemicals are stored in a volumetric flask, or held within a storage container by a
\J
Fig. 3.28 A three-way Teflon rotary valve.
Maintenance and Care of Joints, Stopcocks, and Glassware 3.3 |
193 |
stopcock, the material becomes worthless if you lose access to it because of a frozen stopper or stopcock.
Most occurrences of stuck stopcocks and joints can be prevented by proper storage, preparation (of the item to be used), application of grease (if required), and proper use. All of these points may seem obvious, but regrettably they are seldom executed. The greatest disasters I have seen from stuck stopcocks and joints occurred not from the original jammed piece, but rather from inexperienced attempts at separating the members, which often make it impossible to follow through on other separation approaches. For information on how to prevent joints and stopcocks from sticking, see Sec. 3.3.6. For a comprehensive list of stuck stopcock and joint separation techniques, see Sec. 3.3.7.
When putting items away for storage, the apparatus should be cleaned of all grease and then thoroughly cleaned so that all items are ready for use at all times. Glassware should never be stored dirty with the intent to clean a piece before use.* In addition, dried grease and dirt often cause stopcocks and joints to stick. Finally, apparatus should be stored with all pieces assembled (note precautions in Sec. 3.3.2 and Sec. 3.3.3).
Stopcocks. After a stopcock has cleaned, a small slip of paper (measuring about 6 mm by 50 mm) should be inserted between the plug and barrel to prevent jamming (see Fig. 3.30). You may remove solid plugs and store them separately, but this storage is generally not recommended as it may cause future problems. For example, many manufacturers guarantee that their plugs are interchangeable. If the plugs are not interchangeable, the hole of the plug will not align with the holes of the stopcock. However, not all manufacturers are as good as their claims. Regardless, plugs from one manufacturer seldom fit the barrels of another. If you have stopcocks from Kimble, Kontes, Corning, and Ace (to name a few) and do not wish to deal with trying to match plugs with barrels (and then try to match alignment, if necessary), store matched sets with a paper slip between the barrel and plug and be sure to match the plug and barrel with their respective code numbers.
Vacuum Stopcocks. Hollow plugs (with or without an open end) always indicate vacuum and should always be kept with their respective barrels. Vacuum stopcocks should never be stored with their plugs separated from their mated barrels. On the side of a plug and barrel is a numeric or an alphanumeric code that is used to match the two units. All high-vacuum stopcocks receive the final grind of the plug and barrel together, making them matched and individual. You should never cross-match high-vacuum stopcock parts, even if they seem to fit. If one or the other parts should be lost or broken, replace the entire unit. For storage, slip a
*It is always more difficult to clean glassware that has sat for a period of time than it is to clean glassware that is recently soiled.
194 |
Joints, Stopcocks, and Glass Tubing |
Teflon flow
Locking Nut
Fig. 3.29 If the locking nut is left too tight, the Teflon will flow (over time) into the holes of the barrel.
piece of paper (about 6 mm x 50 mm) between the plug and barrel, then support the two parts together with a rubber band as shown in Fig. 3.30.
Teflon Stopcocks. Teflon stopcocks should never be stored with the locking nut tightened. Teflon flows under pressure, and such pressure could squeeze the plug up and into the holes of the barrel (see Fig. 3.29). Teflon plugs are tapered at a 1:5 ratio rather than the 1:10 ratio of glass stopcocks to help relieve some of these pressures.
If the barrel of a Teflon stopcock was designed too thin and the locking nut is left on too tight, any increase in temperature causing the Teflon to expand may cause the barrel to crack open into pieces.
The order of the washers on Teflon plug is important. As described in the previous section, after the plug is inserted in the barrel, the first piece to go on is the plastic washer, followed by the O-ring, which acts as a lock washer. The final piece to go onto the plug is the locking nut.
The hole through the plastic washer is not round; rather, it has a flat part on the hole (some manufactures use two parallel flat sections). This flat section matches a flat section on the threaded part of the Teflon plug and keeps the washer, O-ring, and locking nut as a unit to rotate with the plug when it is rotated. If this flat part wears round, the washer, O-ring, and locking nut do not rotate with the plug as it is turned. The result of this condition is that when the plug is rotated clockwise (CW), the locking nut (which is not rotating) tightens onto the plug. When the plug is rotated counterclockwise (CCW), the locking nut loosens from the plug. The occurrence of this phenomenon could be either just annoying or disastrous.
Teflon Rotary Valves. Teflon rotary valves should also be stored with the plug in place. The primary danger is to the plug which, if scratched, becomes worthless. The plug should be left screwed into the barrel, but never to the closed position. If the plug is screwed too tightly into the closed position, it is likely to place too much pressure on the threaded part of the Teflon, which, due to Teflon flow, will flatten out rendering the plug useless.
Round-Bottom Flasks, Pennyhead Stoppers, Plugs, and Other Loose Items.
Many items are stored in drawers and (as the drawer is opened and closed) can bang around. This situation applies especially to round-bottom flasks, which are hard to prevent from rolling around. When these flasks bang around, star cracks, or flaws for future fracture, are created. For round-bottom flasks, Erlenmeyer
Maintenance and Care of Joints, Stopcocks, and Glassware 3.3 |
195 |
|
Be sure to |
CTB135 ^JL ^Paper slip |
Be sure to |
|
||
match code #'s.
match code #'s.
Rubber band
Fig. 3.30 When storing a high-vacuum stopcock, use a rubber band to secure the plug onto its respective barrel.
flasks (on their sides), and other glass items that can roll, line the drawer with soft, irregular surface materials (like bubble pack), and, if possible, place cardboard dividers between the pieces. Finally, identify on the outside of the drawer what size flasks are stored within to limit the amount of opening and closing required.
Small, loose items, like pennyhead stoppers, should be stored by size and type in small boxes in a drawer. Occasionally you may have extra glass plugs from glass stopcocks (i.e., from broken burettes). These plugs also should be stored by size and type in small boxes in a drawer. Do not store Teflon stopcock plugs with glass stopcock plugs because the glass may scratch the Teflon leaving it worthless. Wrap Teflon plugs in a tissue and then mark the tissue with its contents to help protect the surface of the plug as well as let people know the tissue's contents.
Cold Traps and Apparatus. Items like cold traps should be stored as complete units to protect the inner tubes. A small slip of paper (measuring about 6 mm by 50 mm) should be inserted between the inner and outer joints to prevent jamming. If there are hooks, use a rubber band or springs to hold the parts together. If not, use masking tape to hold the parts together (see Fig. 3.31). Unfortunately, mask-
Insert a slip of paper to prevent the joints from
A sticking.
Use rubber bands, springs, or tape to hold cold traps together for storage.
Fig. 3.31 Proper storage of apparatus will not only protect the joints, but will also protect any internal glassware that could otherwise be broken.