S06

CLOTH-BINDING.

occurs there ia a bed, or perhaps a vein of beds of granite, or rather of that feldspar rockcalled Pe-tun-tse, which exists here in every stage of decomposition. This Kaolin is gen-erally white, but sometimes a little yellowish, with hardly any mica. It is meager to thetouch, and some beds include large grains of quartz, called pebbly by the China manufac-turers. This variety, when ground, affords, without the addition of any fusible ingre-dient, a very transparent porcelain.

Near Bayonne. A Kaolin possessing the lamellated structure of feldspar, in manyplaces. The rock containing it is a graphic granite in every stage of decomposition.

In England, in the county of Cornwall . This Kaolin or China clay is very white, andmore unctuous to the touch than those upon the continent of Europe mentioned above.Like them it results from the decomposition of the feldspars and granites, occurring in themiddle of these rocks. Mr. Wedgewood found it to contain 60 of alumina or pure clay,and 40 of silica, in 100 parts.

Pure clay, the alumina of the chemist, is absolutely infusible; but when subjected tothe fire of a porcelain kiln, it contracts into about one half of its total bulk. It must,however, be heated very cautiously, otherwise it will decrepitate and fly in pieces, owingto the sudden expansion into steam of the water combined With its partidles, which isretained with a considerable attractive force. It possesses little plasticity, andconsequently affords a very short paste, which is apt to crack when kneaded into acake.

It is not only infusible by itself, but it will not dissolve in the fusible glasses; makingthem merely opaque. If either lime or silica be added separately to pure clay, in anyproportion, the mixture will not melt in the most violent furnace; but if alumina, lime,and silica be mixed together, the whole melts, and the more readily, the nearer the mix-ture approaches to the following proportions:—1 of alumina, 1 of lime, and 3 of sahd. Ifthe sand be increased to five parts, the compound becomes infusible. These interestingfacts show the reciprocal action of those earths which are mixed most commonly in naturewith alumina.

Iron in small quantity, but in a state not precisely determined,‘though probably of pro-toxyde, does not color the clays till they are subjected to a powerful heat. There arevery white clays, such as those of Montereau, which do not become red till calcined it 1the porcelain kiln ; the oxyde of iron contained in them, which colors them in that case,was previously imperceptible. It appears from- this circumstance, that the clays fit f° rmaking fine white stone ware, as also the Kaolins adapted to the manufacture of porce-lain, are very rare.

Iron, in larger proportion, usually colors the clays-green or slate-blue, before they havebeen heated. Such clays, exposed to the action of fire, become yellow or red accordingto the quantity of iron which they contain. When the iron is very abundant, it rendersthe clays fusible; but a little lime and silica must also be present for this effect. Theearthenware made with these ferruginous clays can bear but a moderate baking heat; Ris thick, porous, and possesses the advantage merely of cheapness, and of bearing consid'erable alternations of temperature without breaking.

Alumina and the very aluminous natural clays which possess most plasticity, are aP*to crack in drying, or to lose their shape. This very serious defect for the purposes of P ot "tery is rectified, in some-measure, by adding to that earth a certain quantity of sand orsilica. Thus, a compound is formed which possesses less attraction for water, and driesmore equably from the openness of its body. The principal causes of the distortionoiearthenware vessels, are the unequal thickness of their parts, and quicker desiccationupon one side than another. Hard burnt stone-ware ground to powder, and incorporate^with clay, answers still better than sand for counteracting the great and irregular contraction which natural pottery paste is apt to experience. Such ground biscuit is call®cement; and its grains interspersed through the ware, may be regarded as so many so1tions of continuity, which arrest the fissures. , y

The preceding observations point out the principles of those arts which employ cfor moulding by the wheel, and baking in a kiln. See Porcelain and Pottery.

CLOTH, MANUFACTURE OF. See Textile Fabrics, Weaving, Wool . .

CLOTH-BINDING. Nothing places in so striking a point of view the sup ertaste, judgment, and resources of London tradesmen over those of the rest of the w° r >as the extensive substitution which they have recently made of embossed silks acalicoes for leather in the binding of books. ' In old libraries, cloth-covered boa L.“indeed may occasionally be seen, but they have the meanest aspect, and are noto be compareiavith our modern cloth-binding, than the jupon of a trull, with the banedress of TaglSni. The silk or calico may be dyed of any shade which use or f» nc I"‘ tsrequire, impressed with gold or silver foil in every form, and variegated by ° rnaI f 0 fin relief, copied from the most beautiful productions in nature. This new styi ^binding is distinguished not more for its durability, elegance, and variety', than j ( j ieconomy and despatch with which it ushers the offspring of intellect into tne