Page:Popular Science Monthly Volume 26.djvu/504

488 the care exercised in its construction; ten years is not an unusual period. The charging of the calcarone is a matter of primary importance, as on it depends the yield of sulphur. The largest pieces of ore are selected for the first layer, leaving interstices between them; the size of the lumps gradually diminishes as the height increases, care being taken to form the walls of the morto with calcareous stones, so as to insure a passage being maintained for the escape of the liquefied sulphur. In adding the finest portions on the top, narrow channels, about two feet apart, are left for the draught to carry the heat down. The whole is covered with a layer of the refuse from previous operations. This layer is more or less thick, according to the state of the weather, because, the calcarone being built in the open air, variations of temperature and wind influence the progress of the operation; consequently means have to be adopted to prevent an undue access of air rendering the combustion too rapid. For instance, during a sirocco (local hot wind) there is danger of the sulphur contained in the ore lying at the side facing the wind being completely converted into sulphurous acid, and thus lost. The employment of a roofed shed would prevent much of the waste occasioned by climatic causes.

When the charging is completed, the morto is closed by a stone slab, and tire is communicated to the mass by means of little bunches of dried herbs, dipped in sulphur, which are thrust into the vertical channels before mentioned. Some six or eight days afterward, a hole is pierced in the top of the morto, by means of an iron rod; later, a



second hole is made near the floor. By these two openings the sulphur escapes, and is collected in wooden buckets (gravite), shaped like a truncated cone, and holding about one hundred-weight of sulphur. These buckets cost over two shillings, and serve only for three or four castings without wanting repairs. The outflow of sulphur lasts for a fortnight or a month. Commonly, the calcarone is left to itself when once the mass has been ignited, but then the loss of sulphur is much more serious. To insure good results, many precautions have to be observed, mainly connected with the nice adjustment of the draught, so