match. A list of companies that sell North American and European joints are listed in Appendix C.

The Stopper Plug. There are two types of ground stoppers: reagent bottle stoppers and flask stoppers. They have the same 1:10 taper as the joints previously mentioned, however, they are listed by only one number based on their width measurement (see Fig. 3.7). Both stopper types have a flattened disk above the ground section for easy holding. Because the term "pennyhead stoppers" can refer to either reagent or flask stoppers, a complete description of the stopper you want is important for complete identification.

Reagent bottle stoppers are essentially the same size as midlength joints, although their lengths are somewhat shorter. A size 14 stopper is the same size as a 14/20 joint, and it can fit into a 14/20 female joint (see Table 3.2). Do not expect a stopper plug to maintain a vacuum, however, unless the stopper is hollow. The thinner walls of a hollow stopper will adjust to temperature changes better than a solid plug, so there is less chance for the members to become separated due to the expansion or contraction of the glass. In addition, only hollow stoppers are ground to the standards required for vacuum components.

Flask stoppers come in widths (sizes) that are different from other joints and stoppers; therefore, flask stoppers are not interchangeable with joints or stoppers (see Table 3.2).

3.1.2 Ball-and-Socket Joints

Ball-and-socket joints are typically used when the union between apparatus pieces is not linear. Ball-and-socket joints have a different type of measurement system

The two numbers for standard ball joints "vp " stand for A, the outside diameter (O.D.) of the ground area, and B, the inside diameter (I.D.) of the tube connected to the ball joint.

The smaller the "B" number, the more ground surface area (and therefore greater vacuum potential). The greater the "B" number, the greater the possible angle of joint rotation while still permitting acceptable gass flow (see illustration below).

Note the small opening that is left with a minor rotation of an 18/7 ball-and-socket joint.

Fig. 3.8 Ball-and-socket joints.

than standard taper joints (see Fig. 3.8). They cannot be used for significant (e.g., > 10'3 torr) vacuums, and they should not be relied upon for static vacuum environments.

Ball-and-socket joints must be held together with either a metal spring type of clamp (like a clothespin) or a semirigid plastic clamp. Because ball-and-socket joints cannot be used without one or the other type of clamp, be sure to include the right-size clamp when ordering apparatus that have ball-and-socket parts, if they are not otherwise supplied.

The clamp size required for ball-and-socket joints is identified from the outer diameter measurement. Thus, a size 18 clamp is used for either an 18/7 or an 18/9 size O-ring joint.

3.1.3 The O-Ring Joint

The O-ring joint (see Fig. 3.9) has no ground sections, and as opposed to other joint types, both members of an O-ring joint are identical. For sealing, O-ring joints require placing an O-ring, made from some polymer material (see Sec. 1.4), between the joint members, which are held together by the same type of "clothespin" clamp used with ball-and-socket joints.*

Because clamp identification numbers are derived from their relationship with ball-and-socket joints, there is no relationship between which size clamp should be used with which O-ring joint. There is no one-to-one relationship with O-ring joints and ball-and-socket joints; one clamp size is likely to fit several different

"The one-piece plastic clamp used with ball-and-socket joints will not work with O-ring joints.

size O-rings joints. Table 3.3 provides the recommended O-ring and clamp sizes for respective O-ring joints. Like ball-and-socket joints, be sure to order the appropriate size clamp when ordering apparatus with O-ring connections.

O-ring joints can easily be used with vacuum systems (<10~7 torr) and are particularly useful for quick-release connection. Occasionally it is necessary to leave a thin film of stopcock grease on an O-ring's surface to either help the vacuum capabilities of the joint, or to protect the O-ring's surface from the effects of a solvent.

3.1.4 Hybrids and Alternative Joints

A hybrid O-ring/ball joint (see Fig. 3.10) is available. This joint has the vacuum capabilities of the O-ring joint along with the variable angle abilities of a ball-and- socket joint. Typically, the socket side of an O-ring joint is ground and an O-ring cannot achieve as good a vacuum as it could against a non-ground surface. Because of this, some manufacturers are supplying unground sockets for use with O-ring ball joints. Regardless of the type of socket used, because this design does not require stopcock grease, it can be used in conditions where a connection

The size of the O-ring has no direct relationship to the size of the O-ring joint.

O-ring joints are measured by only one measurement: the I.D. of the passageway through the joint in mm (the I.D. of the tube connected to the joint is sometimes a bit larger than the "A" measurement).

Fig. 3.9 The O-ring joint.

(a)

Area that is likely to hold up liquids.

Fig. 3.10 The O-ring ball joint without the O-ring in place (a), and the hold-up it can create (b).

would otherwise be impossible. Unfortunately, there may be liquid holdup within such a joint.

There are occasions when a solvent must remain in contact with a connection for several days and the connection must maintain a vacuum. Depending on the nature of the solvent, standard grease and most O-rings cannot be used in these situations.

An alternate solution to complications with long-term solvent contact with CDring polymers is the Solv-Seal joints by Andrews Glass Co. Inc. These joints seal together with a double-ringed Teflon seal (see Fig. 3.11) within a specially designed glass joint. Although there is a Viton O-ring within the Teflon sealing unit, the O-ring is used as backup protection. The primary containment for the material within the system is the Teflon.

3.1.5 Special Connectors

There are several special connectors that provide "demountable" connections between glass to glass, glass to metal, or metal to metal. These connectors provide many advantages over standard connections.

Swagelok® fittings (see Fig. 3.12) are used to connect metal tubes to metal tubes. These fittings, which provide permanent connections on metal tubing, are not meant for use on glass. These connectors have a pair of small metal ferrules (like a collar), one of these ferrules tightens around a metal tube as the Swagelok nut is tightened, while the other is a washer. The tightened ferrule is permanently attached to the metal tube and cannot be removed. It provides a leak-tight fit that can be used in high-vacuum or high-pressure conditions.

Fig. 3.11 Solv-Seal joints. The Solv-Seal joint, from the Lab Crest Product line, is made by Andrews Glass Co. Inc, reproduced with permission.

Fitting nut

J L-*v*v\^£sa_.

Fitting body

Front ferrule Back ferrule

Fig. 3.12 The Swagelok® fitting. The illustration of a Swagelok® Fitting is used with permission of Swagelok Co., Solon, Ohio 44139. The illustration was supplied by the Swagelok Co.

Swagelok fittings are made in a wide variety of styles, connections, and sizes. They are especially useful when connecting copper tubing for delivering nitrogen gas to various systems around a lab, or when making connections for extension tubes on metal high vacuum systems.

Cajon® Ultra-Torr® fittings are similar to Swagelok fittings except they are reusable and can be used on metal as well as glass and plastic (see Fig. 3.13). Instead of a metal ferrule, there is an O-ring that imparts a leak-tight seal. They are made in a wide variety of styles and sizes. Unlike Swagelok® fittings, Cajon Ultra-Torr fittings cannot be baked out for ultra high-vacuum work.

If you are going to connect a Cajon Ultra-Torr fitting to glass, first verify whether the fitting is metric or not. If the fitting is nonmetric, use the appropriate type of tubing. Medium and heavy wall tubing are both made in English sizes, but are identified in metric numbers (see Table 3.9 and Table 3.10). Because glass tubing has variations in O.D. tolerance (see Sec. 3.4.2), pretest the fitting before you commit yourself to any construction. This pretesting can be done by simply ensuring that the Ultra-Torr® tightening nut can slip over the tube. Because glass

Fitting nut

O-ring

Sleeve

Fig. 3.13 The Cajon® Ultra-Torr® fitting.This illustration of a Cajon® Ultra-Torr® Fitting is used with permission of Swagelok Co., Solon, Ohio 44139. The illustration was supplied by the Swagelok Co.

Fig. 3.14 Several generic designs of glass-threaded connections.

has no macroscopic compressional abilities, do not force a Cajon fitting onto glass. If it does not fit, select another piece of glass that does fit.

There is a glass variation of the Cajon fitting design available from several glass industry sources. These variations go under a variety of names (depending on the manufacturer), but are typically under the classification of glass-threaded connections (see Fig. 3.14). There are adapters made with a threaded connection on one end and either (a) a glass tube ready to be attached to some glass apparatus or (b) a standard tapered joint on the other, made out of glass or Teflon. These connectors can be used (for example) to support thermometers within a flask.

Glass-threaded connectors can be used for limited vacuum operations. However, there often is nothing to stop the inserted tube from being sucked in unless there is some step in the fitting or ridge on the tube. Cajon Ultra-Torr fittings typically have an internal step to prevent the inserted tube from being sucked in during vacuum operations. Because glass-threaded connections seldom have such an internal step, the glassware needs to be altered by adding a bulge (also called a maria) to the tube by a glassblower (see Fig. 3.15). Alternatively, a glassblower may be able to form (depending on the apparatus configuration) a step on the inside of a connector to prevent inward motion of an inserted tube (see Fig. 3.16).

The advantages of glass-threaded connections are that they allow easy connections to be made and, disassembled, require no grease.* Additionally, there is little, if any, chance of two pieces seizing. The disadvantages are that they may not

Maria

Tubing cannot move in anymore due to the maria.

Fig. 3.15 Internal motion of the inserted tube is blocked by the addition of a maria.