English: Design of a furnace for making iron from ironsand, developed by and patented in 1873, by Joel Wilson of Dover, New Jersey, USA. It was used at the Onehunga Ironworks in New Zealand from 1883 to 1887, at least. A mixture of the concentrated iron-sand and the reducing agent (fine coal) was loaded into one of the twelve retorts of the smelting furnace, where this mixture resided for about 24-hours, during which it was heated by flue gases from the puddling furnace. —The multiple retorts in each furnace allowed an essentially 'batch' process to be operated more or less continuously, another ingenious feature of Wilson's design.—When a gate-valve in the base of any retort was opened, a sticky mass of hot, reduced iron-sand was transferred (by gravity) into the 'balling' section of the furnace; here it was heated for about half an hour—again by puddling furnace flue gases—until a ball of 'sponge iron', about 18-inches in diameter, was created. This ball was then rolled across into the 'puddling' section of the furnace. The conventional 19th-century iron-making process of puddling then took place, resulting in a ball-shaped piece of puddled iron. The source of the image of this drawing is Page 225 of the Transactions of the Wellington Philosophical Society, in a paper "New Zealand Ironsands: an Historical Account of an Attempt to Smelt Ironsands at Onehunga in 1883" writtem by J.M.Chambers (communicated by Evan Parry, who presumably read it to the meeting).