The retorts of the prisoners were notable.
These distilling vessels are called retorts if they are supported only at the ends, and the furnace using them is termed a Belgian furnace.
In the Belgian process the reduction and distillation are carried out in cylindrical or elliptical retorts of fire-clay, from 3 ft.
Some fortysix or more retorts, arranged in parallel horizontal rows, are heated in one furnace.
The furnaces are square and open in front, to allow the outlet ends of the retorts to project; they are grouped together by fours; and their several chimneys are within the same enclosure.
