Cliflon College Scientific Society. 37 



deep. In order to break down the clay fully, and amalgamate 

 it with the water, a long wooden instrument is used, formed with 

 a blade at one end and a cross handle at the othei", which is 

 moved violently about in the trough in all directions. In large 

 manufactories, where machinery takes the place of ordinary work- 

 men, the blunging is effected in the following manner : — The clay 

 is thrown into a cast-iron cylinder four feet deep and twenty 

 inches in diametei\ Through the centre of the cylinder runs an 

 upright shaft furnished with knives placed at right angles to the 

 shaft, but so arranged on it that their flat sides are in the plane 

 of a spiral thread, so that by the revolutions of the shaft the 

 knives perform the double office of cutting whatever stands in 

 their way and of forcing downwards the contents of the cylinder in 

 the manner of a screw. A second set of knives is inserted in the 

 interior surface of the cylinder, and these extend to the shaft in 

 the centre parallel to and corresponding with the revolving knives : 

 thus the two sets, the one active, the other passive, have the effect 

 of shears in cutting the clay into small pieces ; while this in its 

 reduced state is at the same time forced through an aperture at 

 the bottom of the cylinder and transferred to a vat for the pur- 

 pose of being mixed witia water : a process which this previous 

 dividing of the clay is found materially to facilitate. The vat 

 where this mixture is performed is likewise of a cylindric form, 

 its diameter being equal to four times its depth. In the centre 

 of this vat also a perpendicular shaft is inserted, furnished with 

 cross arms or radii, one below the other. These cross arms are 

 connected by upright staves, giving the appearance of two opposite 

 gates hung upon the central shaft. These revolve within the 

 cylinder ; and as they are partially immersed in the pulp, the con- 

 stant agitation mixes all the finer particles of clay with the water, 

 while stony particles of greater magnitude fall to and remain at 

 the bottom. The pulp, now mixed to the consistence of cream, is 

 passed off from the vat through a series of sieves of increasing 

 degrees of fineness, which are worked to and fro by machinery ; 

 thus a separation is effected between the grosser parts and that 

 portion which is fitted to enter the composition of the ware. 



The operation of throiving consists in shajjing such vessels as are 

 circular, and is performed upon a machine called a potter's lathe. 

 This is an upright shaft about the height of a common table, on the 

 top of which is fixed a circular piece of wood, the breadth being 

 sufficient to sujiport the widest vessel that may be required. The 

 bottom of the shaft runs in a step, and the upper part in a socket 

 a little below the circular board, so that the shaft and board turn 

 together. The shaft has a pulley fixed on it, by means of which 

 it is turned, a band passing round the pulley from a wheel placed 



