The valve in the old form of mizer is subject to various accidents which interfere with the action of the tool; for instance, pieces of hard soil or rock often lodge between the valve and its seat, allowing the contents to run out whilst it is being raised through water. To remedy this defect the eminent well-sinker, Thomas Docwra, designed and introduced the improved mizer, shown of the usual dimensions in Figs. 31 to 36; [Fig. 31] being a plan at top, [Fig. 32] an elevation, [Fig. 33] a plan at bottom, [Fig. 35] a section, [Fig. 34] a plan of the stop a, and [Fig. 36] a plan of the valve. It consists of an iron cylinder, conical shaped at bottom, furnished with holes for the escape of water, and attached to a central shank by means of stays. The shank extends some 7 inches beyond the bottom, and ends in a point, while the upper part of the shank has an open slot, to form a box-joint, [Figs. 37 to 39], with the rods. The conical bottom of the mizer has a triangular-shaped opening; on the outside of this is fitted a strong iron cutter, and on the inside a properly-shaped valve, seen in section and plan in [Figs. 35 and 36]. When the mizer is attached to and turned by means of the boring rods, the débris, sand, or other soil to be removed, being turned up by the lip of the cutter, enters the cylinder, the valve, whilst the mizer is filling, resting against a stop. After the mizer is charged, which can be ascertained by placing a mark upon the last rod at surface and noting its progress downwards, the rods are reversed and turned once or twice in a backward direction; this forces the valve over the opening and retains the soil safely in the tool.
Figs. 41-43.
[Fig. 40] is a pot mizer occasionally used in such soils as clay mixed with pebbles; there is no valve, as the soil is forced upwards by the worm on the outside, and falls over the edge into the cone.
Figs. 44, 45.
Mizers are fastened to the rods by means of the box-joint, shown in [Figs. 37 to 39], as a screw-joint would come apart on reversing.
As many as five or six different sized mizers, ranging from 1 foot 6 inches to 9 feet in diameter, can be used successively, the smallest commencing the excavation, and the larger ones enlarging it until it is of the requisite size.