_Dangers and Prevention._--Dust arises in unheading the casks from the displacement of air following the scooping or shovelling out of the lead, in filling the pails, and in discharging the lead into the mill. All points should, and can, be adequately protected by locally applied exhaust ventilation at each one of the points enumerated. A telescopic arrangement of the branch duct in connection with the barrel enables dust generated in scooping out to be removed as the contents of the barrel get lower and lower (see Fig. 15). [Illustration: FIG. 15.[A]] [A] FIG. 15 shows the arrangement for preventing dust at every point where it is produced in a factory where dry colours are ground, sifted, and packed on a large scale. On the upper floor, the chamber is shown in which the contents of a cask are tipped down a shoot leading in the one case to the burr stone mill on the left, and in the other into the Blackstone sifters. Exhaust is arranged at two levels to catch the dust arising from the displacement of air. After grinding in the closed-in burr stone mill, a hood and duct is arranged over the point where the material is discharged into the barrel. Similarly, the casing of the two Blackstone sifters is connected with the exhaust fan, and also the cover of the barrel into which the ground material falls. Inside the edge-runner (the door of which is shown open) a negative pressure is maintained, and one branch duct controls the dust in the scooping out of the material from the barrel, while another is connected to the cover of the receptacle into which the ground material is discharged. Tapering of the ducts, tangential entry of branches, fan-box, and collecting filters, are all shown. In the factory in question there are four edge-runners, three burr stone mills, and two Blackstone sifters. Altogether exhaust ventilation is applied at twenty-five points. (Drawing kindly supplied by the Sturtevant Engineering Company, Limited, London.)