SULPHUR AND ITS EXTRACTION. 



491 



manner in which it is heated from the top and back toward the front 

 and bottom, imitating, to a certain degree, the manner in which the 

 heating of an ordinary calcarone proceeds, with this difference, that 

 the heat is better utilized in the kiln, and therefore with less con- 

 sumption of sulphur as fuel. 



When the wall that closes the front opening, F, begins to heat, 

 and the kiln is ready for running, a small hole is made with a pointed 

 instrument, so as to allow the melted sulphur to flow off into wooden 

 molds. The horizontal flue or condensing chamber, H, should have 

 a sloping floor, and, when the temperature in it reaches the melting- 

 point of sulphur, the flowers that have been deposited on the sides are 

 liquefied, and run off. Toward the end of the operation it will be 

 found prudent to close all the dampers as well as the hole, N, to pre- 

 vent the overheating of the kiln, in which case the sulphur would be- 

 come thick, and difficult to run off, and the yield would consequently 

 be lessened. 



The first cost of the structure is slight, as the materials necessary 

 are usually at hand. The yield, too, is much increased ; but, on the 

 other hand, the extra cost in charging, discharging, and attendance, 

 as compared with the ordinary calcarone, make a large hole in the in- 

 creased returns. 



It will require little reflection to see that only a small quantity of 

 the finely pulverized mineral, necessarily produced in the operations 

 of mining and breaking down the ore, could be dealt with in the cal- 

 carone ,• consequently, for a long time the bulk of this portion of the 

 ore was simply thrown away, though it often assayed seventy per cent 





Fig. 4. 



of sulphur. The doppione was one of the earliest successful structures 

 designed to remedy this state of things. As shown in Fig. 4, it con- 

 sists of a set (generally six) of cast-iron pots, holding about thirty to 

 forty gallons each, arranged in a gallery furnace, e, so as to be com- 

 pletely enveloped by the heated vapors from a fire beneath. Each pot, 

 a, communicates by a long arm, b, with a cooling condenser, c, for the 



