A stopcock is a valve used to restrict or isolate the flow of a liquid or gas through a pipe. In Great Britain a stopcock, is used to prevent flow of water into a domestic water system. Laboratory glassware items sometimes have plug valves with conically-tapered plugs called stopcocks. When fused with the glassware, the valve bodies are made of glass. Otherwise, they can be made of an inert plastic such as Teflon. The plugs can be made of a similar plastic or glass. When the plug is made of glass, the handle and plug are fused together in one piece out of glass. When glass is used for both the stopcock body and the plug, the contacting surfaces between them are special ground glass surfaces often with stopcock grease in between. Special glass stopcocks are made for vacuum applications, such as in use with vacuum manifolds. They often have hollow plugs and glass tubing for the passageways across the side of the hollow plug. The valve body at the end opposite the handle is closed off, but the hollow plug is open at that end. This way, vacuum in the stopcock keeps the conical plug drawn into the conical seat in the body. Stopcock grease is always used in high vacuum applications to make the stopcock air-tight.

Stoppers is a truncated conical piece of rubber or cork used to close off a glass tube, piece of laboratory glassware, a wine bottle or barrel and containers with orifices. A rubber stopper is also called a rubber bung, and a cork stopper is called cork. Ground glass stoppers are commonly used with laboratory glassware, mainly because of their nonreactivity. They come in many forms such as cork, rubber and plastic film that stretches over the opening.

The storage containers are designed to prevent the deterioration of the plutonium, the formation of plutonium hydrides and oxides. Therefore, the existence of these compounds will alert us that the containers are failing in some way. These compounds are also indicators that pyrophoric plutonium compounds may be forming. Because it is extremely important to avoid fires in the storage vault and the spread of fine plutonium powders formed during a fire, the detection of the hydrides and oxides is crucial. Fortunately, the hydrides and oxides are very easy to detect radio graphically because they are powders with about 60% the density of plutonium.