The next patent, dated March 1831, is the invention of Mr. G. W. Turner, of Bermondsey, Surrey, which consists, first, in the construction of a new species of sieves for separating the lumps and coarse parts of the pulp from the finer portion, that the latter only be employed in the fabrication of the paper; and secondly, in a peculiar mode of applying the sieves, so as to supersede the use of, and form an improved substitute for the vat and the hog. Mr. Turner describes several forms of sieves in his specification, slightly varied, but partaking of the same characteristic features. That to which he appears to give a preference is of a circular form, and consists of a series of concentric rings of thin metal, previously bent into a right angle, but placed with a flat side upwards, like the letter L reversed, thus, T T T; they are arranged in concentric circles, leaving between each annular crevices about the fiftieth of an inch wide, and are fastened by screws, or solder, to radial arms underneath, proceeding from a central block to a peripheral band, which is about 8 inches deep, and 3 feet in diameter. The manner in which the sieves are used we will now explain.
Upon the top of a square vat or cistern is fixed a framed standard, supporting in plummer blocks, at its upper extremity, the axis of a vibrating beam; to each end of this beam is suspended, by a rod or spindle, one of the sieves just described, the bottoms of which lie, when at rest, upon the surface of the pulp in the vat. The rods, or spindles, are jointed to the beam, to allow of their moving vertically by its vibration, which is effected by a rod connected to a revolving crank, the latter imparting sufficient motion to the sieves to cause their bottoms to be alternately lifted out of the pulp an inch or two, and then plunged underneath it. To this action of the sieves is added that of a rotatory motion, communicated to them from the first mover by means of pulleys fixed on their rods or spindles, which pass through centre holes in the standard frame, and are provided with swivel joints between the links that connect them to the beam, and thus admits of a rotative as well as a vibratory action, at the same time, which tends to dislodge any gross particles that may stick in the interstices of the sieves, and, at the same time, to disturb and agitate the whole contents of the vat.
The pulp, thus reduced to a smooth and homogeneous state, flows over a wide lip in the vat, directly on to the endless web or mould, and thus supersedes the necessity of the "hog."
In 1832 Mr. John Dickenson took out a patent for the same important object, that of obtaining a perfectly uniform and smooth pulp, in order that the paper produced therefrom might be of a firm and even texture; the process we proceed to describe, with reference to the figures on page 254. a a a, Fig. 1, represents a section of a vat containing the pulp, which is to be regulated by a waste; at b is a false bottom; c c is a rotatory cylinder, through which that portion only of the pulp that is to be made into paper passes; the knots, grit, etc. being prevented from entering by the wires which envelope the periphery of the cylinder. These wires are arranged spirally by a continuous coil, in the manner of a squirrel cage, but so close together as to leave only the one hundred and fifteenth part of an inch space between them. The wire recommended for this purpose is to be drawn of the figure represented in Fig. 2, the narrow underneath side d being fixed next to the cylinder, where it is to be fastened by rivets to the longitudinal bars ee, leaving the uniform space between the coils as before mentioned, which may, of course, be easily performed by a gauge.
The spaces through which the pulp must pass are, therefore, longitudinal slits, two or three inches long, and only the one hundred and fifteenth part of an inch wide. The ends of the cylinder are closed, except at the axes of rotation, which are formed of large tubes; through these the fine pulp received into the cylinder flows off to the mould on which the paper is formed. As there would be a continual liability of the fine interstices of the cylinders becoming clogged, unless some means were adopted to prevent it, Mr. Dickenson employs what is technically termed a float (though it does not possess that precise character), which, by an up-and-down motion, agitates the liquid, and, by changing the course of the current through the wires, throws off whatever has accumulated on the outside of them. This float is a close vessel of strong copper, of nearly the length of the cylinder (four feet), and of the sectional figure seen at f f; an horizontal bar passes throughout the lower part of this vessel, and also through the tubular axes of the cylinder, beyond the plummer boxes, in which the latter turn, where the horizontal bar is fastened to a vertical bar h at each end, that are connected to a lever i, whose fulcrum is at k.
At l is a double cam, put in motion by a gear, in connexion with the wheel that actuates the rotatory cylinder; every revolution of the cam lifts the lever i twice by means of the wipers mm, and, through the medium of h, the copper floatff also, about l 1/4 inch each time; and the "float" being somewhat heavier than the fluid in which it is immersed, falls immediately afterwards, producing the required agitation. A second improvement under this patent, consists in the knives usually employed in the transverse cutting of the endless sheets of paper; these are usually two straight-edged blades, one of which being fixed, and the proper length of paper drawn over it, the other descends and divides the sheet by a similar action to that of shears. In lieu of the upper moving knife with a straight-edge, Mr. Dickenson employs one of an angular form, represented at n, Fig. 3, which is brought into contact with the lower fixed one, shown at a.