HOT-AIR DRYING-HOUSES.--Mention has already been made of the existence of a system of drying in which hot air is forced into a drying-house by means of a powerful fan. Provided that the temperature of the hot air could be so regulated as not to exceed 100° F., there would be merit in the system. Such matter of regulation could be solved by having a duct in the main air passage, through which cool air could be admitted in such proportion as to modify the temperature of the hot air. As the process is worked at present, the temperature attained is often well above 100° F., and there is a danger of thin crepe placed in this house over-night being found upon the floor in the morning. Unless the crepe is prepared thick and cut into fairly short lengths, it will not bear its own weight at higher temperatures; and if it is made thick, drying is impracticably prolonged. It is probable that, with a temperature of 100° F., and a steady current of air, average thin crepe would dry in such a drying-house within six or seven days. This would be an improvement upon the usual rate of drying in most factories, although several ordinary drying-houses are known in which thin crepe will dry naturally in that period. SMOKE-HOUSES.--No discussion of theoretical considerations regarding the process of smoke-curing will be attempted here. We are concerned only with the necessity for supplying a demand for smoke-cured sheet rubber. Broadly, the process is akin to the smoke-curing of herrings, and the objects are much the same--viz., (1) drying, (2) preservation--except that while herrings are only dried partially, rubber should be dried perfectly. On a small scale a primitive smoke-house could be built easily and cheaply, and such a building might be fully as efficacious as the most elaborate and expensive installation. In the early days of estates it was not uncommon to see temporary smoke-houses constructed of wood, and roofed with "attaps" (palm leaves). Some of the best rubber in the market has come from wooden buildings, but naturally the risk of destruction by fire is considerable. For imperative reasons it may be sometimes found necessary to smoke rubber when the only available building is a single-storey one. As a temporary measure, the building may be converted into a smoke-house by placing the fires in pits sunk deeply into the ground, and effectively screened above by iron baffle plates. But it is not advisable that smoking be continued in such a single-storey building, as the best effects are not obtained, and the risk of fire is far too great.