In cases where there are no means of artificial drying, as Ett some old-fashioned works, the thick clay is at once transferred from the originEt1 settling pit to shallow depressions in the ground, called " pans." Ten or twelve of these, each holding from 40 to 50 tons, should be provided for each settling pit ; they measure from 20 to 40 ft. square, and 2 ft. deep, and are enclosed by granite walls, the interstices of which are rendered impervious by plugging with moss. The clay, filling two thirds of their depth, is here left exposed to the sun and wind, by which it is partially deprived of its moisture. In order to complete its desiccation, the clay is removed from the pans, after three or four months' exposure. A number of parallel incisions are made lengthwise in the clay, hy means of Et knife attached to a long handle ; tho strips are next divided transversely, by men with spades, who throw the blocks on to a board, upon which they are borne by women and. children to the sandy drying yard, where, in fine summer weather, they soon become dry. They are then collected, and piled away in sheds, under Et number of thatched gates or " reeders," or Etre placed in somo sheltered position, where air can circulate around them without their becoming wet from rain. When required, the blocks are scraped by women artned with hoes, before being despatched from the works. The transport is often effected in small casks, holding about half a ton. A few years since, a machine for drying china-clay was invented by a mechanical engineer, named Leopoldo Henrion, of Sampierdacena, neEtr Genoa. It is said that, by its use, the operation ean be effected in a few hours, at a relatively small cost.
Collins was first led to adopt his arrangement in consequence of the formation of the ground ; but he is inclined to recontmend it in most cases if practicable. Very large quantities of stone are required in the dry pits, tEtnks, Ste. Very often this is got, in part or entirely, in the process of exeavEtting the pits, Ste.; but if it cannot be so obtained, a. very serious expense will be incurred, in some instances amounting to several thousand pounds. The total cost of the works may even be doubled from this cause, if stone has to be fetched from a distance of several miles. Two modes of building with rough stone are adopted ; they ere known as " lime building," and " dry stone welling." The first needs no special remark, but the second is very ingenious and very effectual. The wall is built up double, with a batter of about / in., or 1 in. to the foot. Moss is placed between the joints of the wall, and the space between is filled in with sharp sand, the refuse of that or some other clay works. A small stream of water is then made to flow over the sand, which is well beaten in with rammers, or hy treading with the feet. This process is continued, a foot at tt tiMe, till the wall reaohes the required height, when it is either posed with rough stones set on edge, or turfed. A wall properly built, in the manner just described, is quite impervious to moisture, and will stand for fifty years or more. It is, where the proper kind of sand is abundant,
much cheaper than lime walling, and is always preferred for the walls of pits and tanks.
Where the bed of clay is situated on a hill-side, with plenty of space below, a tunnel is driven in from the bill-side or from the valley to the required depth, and a rise is put up as before. This rise is then divided off into two parts. In the smaller, a button-hole launder is placed as before, and packed around with clay ; but the larger is left open. A stream of water, obtained by pumping or otherwise, is made to run over the stope, and down the button-hole launder. -It then flows along a launder plEteed in the bottom of the level, until it makes its exit in the valley. It may then be purified, settled, and dried exactly as already described—the works being laid out at a lower level than the edit ; or, if the clear water is wanted to flow over the stope, or it is, for any reason, necessary to place the pits and tanks at a higher level than the stopes, the water is pumped up after partial or complete purification. The main difference in this mode of working is that, instead of pulling the sand and rubbish up over an incline, it may be tipped down the pass into waggons, run out through the level, and tipped over the hill-sides. In cases where water is abundant, it may even be washed out at night, thus saving the expense 'of trainrning. Of course, when the workings have reached their full depth, the rise and the launder are dispensed with, and the adit level communicates directly with the " bottoms." By this mode of working, a considerable economy may he effected, especially when it is not necessary to pump the clay water for settling or repeating.
Uses.—The first use to which china-day was applied was the manufacture of porcelain, and this is still popularly believed to be its sole application. This, however, is by no means the case, probably little more than one-third of the clay now produced is so employed. Large quantities are used by bleachers, for filling up the pores of calicoes as a dressing, and still larger quantities by paper-makers, to give "body " and weight to the paper, especially to printing papers. The manu factures of alum, sulphate of alumina, and ultramarine, consume very large quantities annually. Small quantities are taken by photographers, manufacturing chemists, and colour-makers, for a great variety of purposes ; and, if reports are to be believed, it has been devoted to the adulteration of flour and of artificial manures. Should low prices be maintained, its use will, no doubt, be still more largely extended, in directions as yet unsuspected. The use of china-clay in the sizing of calicoes and other goods appears to have a very objectionable feature, apart from the question of fraud, inasmuch as the dust created, and the materials used to make the clay adhere to the warps, are productive of serious illness in the weavers. For further information on this subject, the reader may refer to the Journal of the Society of Arts,' vol. xx., pp. 625, 690.