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 consumption 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 prevent the overheating of the kiln, in which case the sulphur would become 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 increased 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 calcarone 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 consists 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 completely 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
