Self-Dumping Buckets.—Before passing to a more minute description of grabs, one or two types of mechanical self-dumping buckets may be mentioned, one of which is illustrated in the Figure. These generally consist of a large tub with hinged bottom doors; such appliances were used at the Millwall Docks for unloading grain before the Duckham pneumatic elevator came into use. These tubs have the advantage of being light, as they hold 60 bushels of grain, or nearly 3 cub. yds., and weigh only 5 cwt. The bottom is divided into two halves which are hinged to an iron bar traversing the bottom of the tub, and the lower edge is so contracted as to form a truncated cone 6 in.