Various types of joints and stopcocks are available separately and come fused with a length of glass tubing, which a glassblower may use to fuse to another piece of glassware.
Two general types of ground glass joints are fairly commonly used: joints that are slightly conically-tapered and ball and socket joints (sometimes called spherical joints).
For either standard taper joints or ball-and-socket joints, inner and outer joints with the same numbers are made to fit together. When the joint sizes are different, ground glass adapters may be available (or made) to place in between to connect them. Special clips or pinch clamps, known as Keck clips, may be placed around the union of the joints to help keep them together.
Describing glassware can be complicated since manufactures provide conflicting names for glassware. For example ChemGlass calls a glass stopcock what Kontes calls a glass plug. Despite this it is clear there are two main types of valves used in laboratory glassware, the stopcock valve and the threaded plug valve. These and other terms used below are defined in detail since they are bound to conflict with different sources.
Stopcocks are often parts of laboratory glassware such as burettes, separatory funnels, Schlenk flasks, and columns used for column chromatography. The stopcock is a smooth tampered plug or rotor with a handle, which fits into a corresponding ground glass female joint. The stationary female joint is designed such that it joins two or more pieces of glass tubing. The stopcock has holes bored through it which allow the tubes attached to the female joint to be connected or separated with partial turns of the stopcock. Most stopcocks are solid pieces with linear bores although some are hollow with holes to simple holes that can line up the joints tubing. The stopcock is held together with the female joint with a metal spring, plastic plug retainer, a washer and nut system, or in some cases vacuum. Stopcocks plugs are generally made out of ground glass or an inert plastic like PTFE. The ground glass stopcocks are greased to create an airtight seal and prevent the glass from fusing. The plastic stopcocks are at most lightly oiled.
Stopcocks are generally available individually with some length of glass tubing at the ports so that they can be joined by a glass blower into custom apparatus at the point of use. This is especially common for the large glass manifolds used in high vacuum lines.
The more examples are featured in the gallery. This is a small sampling of stopcock valves many additional variation exist in both plug boring and joint assembly.
Threaded plug valves are used significantly in air-sensitive chemistry as well as when a vessel must be closed completely as in the case of Schlenk bombs. The construction of a threaded plug valve involves a plug with a threaded cap which are made so that they fit with the threading on a corresponding pieces of female glass. Screwing the plug in part way first engages one or more o-rings, made of rubber or plastic, near the plugs base which seals the female joint off from the outer atmosphere. Screwing the plug valve all the way in engages the plugs tip with a beveled constriction in the glass which provides a second seal. This seal separates the region beyond the bevel and the o-rings already mentioned.
With solid plugs a tube or area exists above and below the bevel and turning the plug controls access. In a number of cases its convent to fully remove a plug which can give access to the region beyond the bevel. Plugs are generally made of an inert plastic such as PTFE with and are attached to a threaded sleeve in such a way that the sleeve can been turned without spinning the plug. The contact with the bevel is made by an o-ring fitted to the tip of the plug or by the plug itself. There are a few examples where the plug in made of glass. In the case of glass plugs the joint contact is always a rubber o-ring but are still prone to shattering.
Not all plugs are solid. Some plugs are bored with a T-junction. In these systems the plug extends beyond the threaded sleeve and is designed to form an airtight fitting with glass tubing or hosing. The shaft of the plug is bored from beyond the threaded sleeve to a T-junction just before the bevel plug contact. When the plug is fully sealed region beyond the bevel is separated from the plug shaft as well as the bore which leads out of its shaft. When the plug bevel contact is released the two regions are exposed to each other. These valves have also be used as a grease free alternative to straight bored stopcocks common to Schlenk flasks. The high symmetry and concise design of these valves has also made them popular for capping NMR tubes. Such NMR tubes can be heated without the loss of solvent thanks to the valves gas tight seal. NMR tubes with T-bore plugs are widely known as J. Young NMR tubes named after the brand name of valves most commonly used for this purpose. Images of J. Young NMR tubes and a J. Young NMR tube adapter are in the gallery.
In a fritted glass filter, a disc or pane of fritted glass is used to filter out solid particles, precipitate, or residue from a fluid, similar to a piece of filter paper. The fluid can go through the pores in the fritted glass, but the frit will often stop a solid from going through. A fritted filter is often part of a glassware item, so fritted glass funnels and fritted glass crucibles are available.
Laboratory scale spargers, scrubbers, and gas-washing bottles are similar glassware items which may use a fritted glass piece fused to the tip of a gas-inlet tube. This fritted glass tip is placed inside the vessel with liquid inside during use such that the fritted tip is submerged in the liquid. To maximize surface area contact of the gas to the liquid, a gas stream is slowly blown into the vessel through the fritted glass tip so that it breaks up the gas into many tiny bubbles. The purpose of sparging is to saturate the enclosed liquid with the gas, often to displace another gaseous component. The purpose of a scrubber or gas-washing bottle is to scrub the gas such that the liquid absorbs one (or more) of the gaseous components to remove it from the gas stream, effectively purifying the gas stream.
If the glassware are still dirty, more caustic methods may be needed. This includes soaking the piece in a saturated solution of sodium or potassium hydroxide in an alcohol ("base bath"), followed by a dilute solution of hydrochloric acid ("acid bath") to neutralize the excess base. Sodium hydroxide cleans glass by dissolving a tiny layer of silica, to give soluble silicates.
Older methods involving aqua regia (for removing metals from frits), piranha solution and chromic acid (for removing organics) are generally considered unsafe because of possible explosions and the corrosive/toxic materials involved.
WIPO ASSIGNS PATENT TO WARATAH NZ FOR "PROTECTIVE ROUTING OF DELIMB CYLINDER HOSING" (NEW ZEALANDER INVENTORS)
Dec 22, 2010; GENEVA, Dec. 22 -- Publication No. WO/2010/143076 was published on Dec. 16. Title of the invention: "PROTECTIVE ROUTING OF DELIMB...
US Patent Issued to Waratah NZ on Aug. 6 for "Protective Routing of Delimb Cylinder Hosing" (New Zealander Inventors)
Aug 06, 2013; ALEXANDRIA, Va., Aug. 6 -- United States Patent no. 8,499,803, issued on Aug. 6, was assigned to Waratah NZ Ltd. (Tokoroa, New...