A hellbox is a receptacle where cast metal sorts

Sort (typesetting)

In typesetting by hand compositing, a sort is a piece of type representing a particular letter or symbol, cast from a matrix mould and assembled with other sorts bearing additional letters into lines of type to make up a forme from which a page is printed.-See also:* History of western typography*...

are thrown after printing. The job of sorting the type from the hellbox and putting it back into the job case

Movable type

Movable type is the system of printing and typography that uses movable components to reproduce the elements of a document ....

 was given to the apprentice, known as a printer's devil

Printer's devil

A printer's devil was an apprentice in a printing establishment who performed a number of tasks, such as mixing tubs of ink and fetching type...

. Later, when continuous casting or hot-metal typesetting machines such as the Linotype machine

Linotype machine

The Linotype typesetting machine is a "line casting" machine used in printing. The name of the machine comes from the fact that it produces an entire line of metal type at once, hence a line-o'-type, a significant improvement over manual typesetting....

 and Monotype became popular, the hellbox was used for storing discarded or broken type that were melted down and recast.