MODE I. ALUM ROCK. 245 



" The blasted stones are calcined in furnaces, 

 which have an inverted conical form. They are 

 in the open fields close together, surrounded and 

 separated by a covering of turf and mould. The 

 upper diameter is about eight feet. They are 

 filled at the bottom with wood, and then heaped 

 with alum-stone, which appears above the fur- 

 naces as an accumulated cone, nine or ten feet 

 high, which is nearly answering to the 'epth of 

 the furnace. Then fire is set to the wood by a 

 square vent near the bottom, and the whole is 

 burnt down in about three hours' time ; which 

 is, as they told me, the requisite time for burn- 

 ing : after which the heated stones are carried 

 to the boiling-house, distant about one Italian 

 mile from the quarries. Here they are put into 

 large pits, or square wooden reservoirs, half sunk 

 into the ground; where they are steeped in a 

 convenient quantity of water, which, after suffi- 

 cient dissolution of the alum, is by troughs con- 

 veyed into the alum- house, and in large square 

 wooden settlers, that the dregs may settle at the 

 bottom. This done, the clear lixivium is poured 

 into brass pans, and, after sufficient boiling, con- 

 veyed into wooden coolers, on whose sides the 

 alum crystallises white and reddish. Before the 

 inspissated brine be conveyed into the cooler, 

 they stop it for some time in the troughs, in 



