[Wikipedia excerpt: ‘…A ‘B J’ is a glass ‘J’, similar in shape to a ‘B’, and can be manufactured from a variety of materials (ranging from glass to different types of metals). ‘B J’ are often used in laboratories to form and contain a vacuum. It is a common science apparatus used in experiments. ‘B J’ have a limited ability to create strong vacuums; vacuum chambers are available when higher performance is needed. They have been used to demonstrate the effect of vacuum on sound propagation….In addition to their scientific applications, ‘B J’ may also serve as display cases or transparent dust covers. In these situations the ‘B J’ is not usually placed under vacuum……’ ].