The Trial of the Pyx is an annual trial conducted in Britain. Unlike other trials, in this case there is no person on trial, rather the quality of the British coinage is the subject of a two-months long scrutiny.
The Trial of the Pyx is ceremonial, and no longer of a real necessity. Coins are selected randomly throughout the year, and placed in bags. The bags are brought to the trial in chests. The type of chest used is called a pyx, hence the name.