Fig. 13.
The arrangement shown in [Fig. 13], in which the disintegrator is mounted on a dust-proof cast-iron collector, has been found very suitable for colour works of various kinds (aniline, lead, mineral and other colours), particularly on account of the suppression of dust; whilst the automatic charging worm greatly increases the capacity as compared with charging by hand.
Levigation
The effect of levigation is based on the circumstance that bodies of greater density than water remain longer in suspension in that medium in proportion as the fineness of their particles increases. This treatment consequently enables the finer portions of a substance to be mechanically separated from the coarser. Levigation is extensively practised in colour works because it furnishes powder of finer grain than can be obtained by even the most careful grinding.
The appliances used for levigation may be of a very simple character, consisting only of several tubs or tanks, mounted in such a way that the liquid contained in one can be run off into the one next below. With this primitive plant, the material to be levigated is stirred up in the water in the uppermost tub and left to settle until the coarsest particles may be assumed to have settled down, whereupon the turbid water is drawn off into another tub, in which it is left to settle completely. When the clear liquid has been carefully drawn off, a fine sludge is left in the bottom of the tub, consisting of the fine particles of material mixed with water.
When a particularly fine powder is required, a single levigation does not always suffice, but the liquid in the second tub must be left to settle for a short time only, and then run into a third for complete subsidence.
Fig. 14.
A well-designed levigator for treating large quantities of powder is illustrated in [Fig. 14]. A stirrer R, driven by cone gearing, is arranged in a wooden or stone vat G. The levigating water enters close to the bottom of the vat, through the pipe W. When G is half full of water, the stirrer is set running, and the substance to be levigated is added. After a while, the water laden with the levigated powder begins to run off at A into the long narrow trough T1 provided, at the opposite end from A, with a number of perforations through which the water runs into the trough T2. From this it escapes through the perforations into the trough T3 and thence successively into T4 and T5, finally discharging into the large tank S.
The coarsest and heaviest of the water-borne particles deposit in the trough T1 finer particles settling down in T2, and so on in succession, until the water reaching the tank S contains only the very finest of all in suspension, these taking a long time to settle down to the bottom. The deposit in the upper troughs can be returned to the vat, whilst that in the lower ones will be fine enough to dry as it is. The residue in the vat is discharged through Z when the operation is finished.