POTTERY 



610 



horizontal shaft, P, bears at one of its extremities a toothed wheel, usually mounted 

 upon the periphery of the great water- wheel (fig. 1658 shows this toothed wheel by a 

 dotted line) at its other end : p carries the fixed portion p of a coupling-box, similar 

 to the one just described as belonging to the little mill. On the prolongation of p, 

 there is a second shaft, P', which bears the moveable portion of that box, and an up- 

 right bevel wheel, p". Lastly, in figs. 1650 and 1658, there is shown the vertical 

 shaft Q, which carries at its upper end a large horizontal cast-iron wheel Q, not seen 

 in this view, because it is sunk within the upper surface of the turning hornstone, like 

 the clamp d,f, 'mfig. 1652. At the lower end of the shaft Q, there is the bevel wheel 

 Q", which receives motion from the wheel p", fiq. 1650. 



The shaft, p, always revolves with the water-wheel ; but transmits its motion to 

 the shaft p 7 only when the latter is thrown into gear with the coupling-box p', by 

 means of its forked lever. Then the bevel wheel p' turns round with the shaft p', 

 and communicates its rotation to the bevel wheel Q", which transmits it to the shaft Q, 

 and to the large cast-iron wheel, which is sunk into the upper surface of the revolving 

 hornstone. 



The shaft Q is supported and centred by a simple and solid adjustment ; at its lower 

 part, it rests in a step E, which is supported upon a cast-iron arch, Q.', seen in profile 

 inficf. 1650 ; its base is solidly fixed by four strong bolts. Four set-screws above E, 

 fig. 1650, serve to set the shaft Q truly perpendicular : thus supported, and held 

 securely at its lower end, in the step at n,figs. 1650 and 1658, it is embraced near the 

 upper end by a brass bush or collar, composed of two pieces, which may be drawn 

 closer together by means of a screw. This collar is set into the summit of a great 

 truncated cone of cast-iron, which rises within the tub through two-thirds of the 

 thickness of the hornstone bed ; having its base firmly fixed by bolts to the bottom of 

 the tub, and having a brass collet to secure its top. The iron cone is cased in wood. 

 When all these pieces are well adjusted and properly screwed up, the shaft Q revolves 

 without the least vacillation, and carries round with it the large iron wheel Q', cast 

 in one piece, and which consists of an outer rim, three arms or radii, and a strong 

 central nave, made fast by a key to the top of the shaft Q, and resting upon a shoulder 

 nicely turned to receive it. 



Upon each of the three 1658 



arms, there are adjusted, 

 with bolts, three upright 

 substantial bars of oak, 

 which descend vertically 

 through the body of the 

 revolving mill to within a 

 small distance of the bed- 

 stone ; and upon each of 

 the three arcs of that wheel- 

 ring, comprised between its 

 three strong arms, there 

 are adjusted, in like man- 

 ner, five similar uprights, 

 which fit into hollows cut 

 in the periphery of the 

 moving stone. They ought 

 to be cut to a level at their lower part, to suit the slope of the bottom of the tub o, 

 Jigs. 1650 and 1658, so as to glide past it pretty closely, without touching. 



The speed of this large mill is eight revolutions in the minute. The turning horn- 

 stone describes a mean circumference of 141^ inches (its diameter being 45 inches), 

 and.of course moves through about 100 feet per second. The tub, o, is 52 inches wide 

 at bottom, 56 at the surface of the sleeper block (which is 16 inches thick), and 64 at 

 top, inside measure. It sometimes happens that the millstone throws the pasty mix- 

 ture out of the vessel, though its top is 6 inches under the lip of the tub o ; an incon- 

 venience which can be obviated only by making the pap a little thicker ; that is, by 

 allowing only from 25 to 30 per cent, of water; then its density becomes nearly equal 

 to 2'00, while that of the millstones themselves is only 2'7 ; whence, supposing them 

 to weigh only 2 cwts., there would remain an effective weight of less than cwt. for 

 pressing upon the bottom and grinding the granular particles. This weight appears 

 to be somewhat too small to do much work in a short time ; and therefore it would be 

 better to increase the quantity of water, and put covers of some convenient form over 

 the tubs. It is estimated that this mill will grind nearly 5 cwts. of hard kaolin or 

 felspar gravel, in 24 hours, into a proper pap. 



