[Illustration: FIG. 4 shows a well-designed arrangement of hoods, duct, and fan, in the packing of white lead, and the filter-bags for collecting the dust so removed. An additional safeguard is introduced, as the casks stand upon grids through which a down-draught is maintained by connecting the space underneath with the exhaust system. (Drawing supplied by the Sturtevant Engineering Company, Limited, London.)] Processes such as colour-dusting, aerographing, ware-cleaning, enamel-brushing, and the like, are best carried out at benches under hoods with glass tops. Air will enter from in front, and carry the dust or spray away into the exhaust duct placed at the back of the bench. [Illustration: FIG. 5 shows a pan mill with edge runners fitted with casing (partially open). The casing is connected to a powerful fan, and branch ducts with telescopic terminal sections control the dust in scooping out from the barrel, in feeding into the mill, and at the point where the ground material is discharged.] =Collection of Dust.=--Frequently no heed is paid to the collection of the dust. Sometimes a dust chamber is arranged to intercept it on the far side of the fan, or attempt is made to blow the dust into a tank of water. The fine dust of which we are speaking cannot be satisfactorily collected by either of these methods, nor even by a cyclone separator, so useful for the collection of many kinds of dust. In lead works generally, the dust removed by the fan is best collected in filter-bags made of some porous fabric. Various efficient filters constructed on these lines by Messrs. Henry Simon, Ltd.; Messrs. Beth and Co., Ltd.; and the Sturtevant Engineering Company, Ltd., are on the market. [Illustration: FIG. 6 shows an arrangement of piping with balanced telescopic joints fitted to a Sirocco dust fan for removal of dust, in an electric accumulator works, when scooping out litharge from a cask into the receptacle prior to emptying the weighed quantity into the mixing machine, also under a hood connected with the exhaust system. (Illustration supplied by Davidson and Company, Limited, Belfast.)] In collecting the dust, care must be taken to provide an adequate outlet for the spent air, so as to prevent creation of a source of friction in front which might destroy the effectiveness of the installation. [Illustration: FIG. 7.--EXHAUST VENTILATION ON THE PATENT “PENTARCOMB” PRINCIPLE APPLIED TO LINOTYPE AND MONOTYPE MACHINES IN PRINTING WORKS, AS INSTALLED BY THE ZEPHYR VENTILATING COMPANY, BRISTOL. P, Patent “pentarcomb” for equalizing exhaust; V, patent “pentarcomb” for general ventilation; D, main and branch ducts; F, fan; U, upcast from fan; M, hoods over metal-pots of monotype machines, constructed to raise and lower, and swing out and in with metal-pot; L, hoods over metal-pots of linotype machines, constructed to raise and lower.