History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4.202

v1.c13.s2.t4.202

Till 1981 the exact details of the retort furnace was not known, but during the recent excavations Hegde et al. (1984) have unearthed a set of three furnaces intact with the bottom plate Fig.44 shows a sketch of the furnace assembly prepared by the excavators on the basis of the study of the furnace. As seen from the hearth of the furnace it consisted of four perforated bricks (55 mm thick) each containing 9 large holes (35 mm dia) to accommodate the condenser neck and 26 smaller holes plus 9 holes shared with neighbouring bricks for the passage of air into the furnace and for ash to drop through. These bricks were supported on a central peg and the side walls of the furnace. The square furnace was 660 mm by 69 mm at the base and curved at the top as shown in the sketch. A battery of such furnaces was constructed in a row and operated. The construction and operation of these furnaces has been described in detail by Hegde (1986) and Craddock et al. (1985) in a number of papers. The examination of the furnace remains by the British Museum Research Laboratory has established that the upper chamber of the furnace (Kosthi) was raised to the temperature of 1200 to 1300°C and maintained for 4 to 5 hours by burning wood or mixture of cow dung cakes and wood etc.