The shaft P always revolves with the water-wheel; but transmits its motion to the shaft P′ only when the latter is thrown into geer 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 R, which is supported upon a cast-iron arch Q′, seen in profile in [fig. 900.]; its base is solidly fixed by four strong bolts. Four set screws above R, [fig. 900.], serve to set the shaft Q truly perpendicular: thus supported, and held securely at its lower end, in the step at R, [figs. 900.] and [908.], 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 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 manner, 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, [figs. 900.] and [908.], so as to glide past it pretty closely, without touching.
The speed of this large mill is eight revolutions in the minute. The turning hornstone describes a mean circumference of 1411⁄3 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 mixture out of the vessel, though its top is 6 inches under the lip of the tub o; an inconvenience 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 cwt., there would remain an effective weight of less than 1⁄2 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 cwt. of hard kaolin or felspar gravel, in 24 hours, into a proper pap.
To the preceding methodical account of the porcelain manufacture, I shall now subjoin some practical details relative to certain styles of work, with comparisons between the methods pursued in this country and upon the Continent, but chiefly by our jealous rivals the French.
The blue printed ware of England has been hitherto a hopeless object of emulation in France. M. Alexandre Brongniart, membre de l’Institut, and director of the Manufacture Royal de Sèvres, characterizes the French imitations of the Fayence fine, ou Anglaise, in the following terms: “Les défauts de cette poterie, qui tiennent à sa nature, sont de ne pouvoir aller sur le feu pour les usages domestiques, et d’avoir un vernis tendre, qui se laisse aisément entamer par les instruments d’acier et de fer. Mais lorsque cette poterie est mal fabriquée, ou fabriquée avec une économie mal entendue, ses défauts deviennent bien plus graves; son vernis jaunâtre et tendre tressaille souvent; il se laisse entamer ou user avec la plus grande facilité par les instruments de fer, ou par l’usage ordinaire. Les fissures que ce tressaillement ou ces rayures ouvrent dans le vernis permettent aux matières grasses de pénétrer dans le biscuit, que dans les poteries affectées de ce défaut, a presque toujours une texture lâche; les pièces se salissent, s’empuantissent, et se brisent même avec la plus grande facilité.”[42]
[42] Dict. Technologique, tom. xvii., article Poteries, p. 253.
What a glaze, to be scratched or grooved with soft iron; to fly off in scales, so as to let grease soak into the biscuit or body of the ware; to become foul, stink, and break with the utmost ease! The refuse crockery of the coarsest pottery works in the United Kingdom would hardly deserve such censure.
In the minutes of evidence of the Enquête Ministérielle, published in 1835, MM. de Saint Cricq and Lebeuf, large manufacturers of pottery-ware at Creil and Montereau, give a very gratifying account of the English stoneware manufacture. They declare that the English possess magnificent mines of potter’s clay, many leagues in extent; while those of the French are mere patches or pots. Besides, England, they say, having upwards of 200 potteries, can constantly employ a great many public flint-mills, and thereby obtain that indispensable material of the best quality, and at the lowest rate. “The mill erected by M. Brongniart, at Sèvres, does its work at twice the price of the English mills. The fuel costs in England one-fourth of what it does in France. The expense of a kiln-round, in the latter country, is 200 francs; while in the former it is not more than 60.” After a two-months tour among the English potteries, these gentlemen made the following additional observations to their first official statement:—