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other earths, for the potters use without any addition; but the white and finer clays mostly require dilution with silex (flint-sand) in some form or other, which may be done to a considerable extent, without doing away the plasticity requisite for working.
“ The most important circumstances in clay for the purpose of making pottery, are these : plasticity, contractility, solidity, and compactness, for drying colours and fusibility. The colour of the earth is also of essential importance in the fiper pottery; but this part of the manufactory is always, and properly, a secret. The whitest looking clays do not always burn white: there is in Staffordshire, at the foot of a range of hills, overlooking the potteries, a stratum of clay, equal apparently in whiteness and texture to the Devonshire clays, but it cannot be used in the finest departments of the many. factory, because it acquires a cream colour in burning, which no art can correct.
“ We have defined porcelain to be a species of pottery ware, composed of an earthy mixture, which resists complete fusion in a very considerable heat, but has been brought by a less heat than its melting point, to a state of incipient fusion, and is thereby rendered extremely hard, sonorous, and semi-transparent, and possessing a semi-conchoidal splenetery fracture, approaching to the vitreous, which is completely conchoidai. This last is quite a distinctive character between porcelain and pottery, for the fracture of pottery is extremely granular; and hence porcelain may be considered as a substance of a middle nature between pottery and glass.
“ From this circumstance, it appears probable, that no chemical action takes place in pottery, till it arrives at the state of porcelain. The most perfect and beautiful porce- . lains of Japan in China, are composed of two distinct earths; one in which silex predominates, and which melts in a strong heat; and another which is infusible per SE, or by itself : and by the union of these two earths, a porcelain is produced which scarcely vitrifies at the utmost furnace heat, which art can excite. Of the beautiful European porcelains, which have been made in imitation of the original, it does not ap-pear, that
of them unite all its excellencies. The infu. sibility of the Nankin and Japan china, which is not affected by the intense heat of a wind furnace, is not to be met with: in the finer porcelains of Europe.”
EDWARD. “I think that is of very little consequence; and while we can produce the beautiful Worcester, Colebrookdale, and Swansea porcelain, the Chinese may keep their dragon and uncouthly ornamented China.''
DR.WALKER.-.“ You would then rather have a beautiful set of painted Worcester porcelain, than a real set of Nankin.”
Edward_" Iwould indeed, Sir. I have yet one question to ask you. You said alumine was one of the original earths. What are the others ?."
Dr. WALKER.--- Notwithstanding the varied appearance of the earth under our feet, and of the mountainous parts whose diversified strata present to our view substances of every texture and every shade, the whole is composed of only nine primitive earths ; and as three of these occur but seldom, the variety which is produced by the other six become more remarkable. To give a still greater variety to the works of nature, these earths are endowed with an affinity for acids and metallic oxydes, whence arise the spars, gems, and precious stones of every colour and every species. These nine earths are silica, alumina, lime; barytes, magnesia, strontian, yttria, glucino, and zirconia. Five of these are particularly useful. Lime is the basis of all mortars and cements ; silica, or silex, is a necessary ingredient in earthenware and glass ; barytes is employed in chemical laboratories as a re-agent, and for the formation of salts; magnesia being the basis of several salts, is of great use in medicine; and alumina, by a due mixture with silex, is capable of forming vessels for chemists, that will resist the action of the most concentrated acids, and it is the material of which bricks are formed."
Our travellers experienced much amusement from the inspection of the porcelain work; but the various processes in the formation of this beautiful article, would be but little un. derstood by description, and we shall therefore not attempt so dificult and discouraging a task.
Having strolled over the field on which the celebrated battle of Worcester was fought, so fatal to the interests of Charles II., they returned to their inn where they were to pass the night. After dinner having seated themselves. comfortably by the fire-side, “ Now tell me, Edward,” said the Doctor, " what is the cause of the steam round that bottle of wine which is just placed on the table.”
EDWARD." I cannot tell
the cause, Sir, although I have often observed, that when a decanter containing any thing cold is brought into a warm room, it is always covered with dew."
Dr.WALKER.-“ Well then, I will explain it to you: but this explanation will lead me first of all to define the word Caloric, which would be scientifically applied in the description of this phenomenon. The word caloric is synonymous with fire, or that substance which produces the sensation we call heat, but reverts the sensation itself, or the effect produced by fire. Animal heat is preserved chiefly by the inspiration of atmospheric air. If the hand be put upon a hot body, part of the caloric leaves the hot body and enters the hand; this produces the sensation of heat. On the con. trary, if the hand be put upon a cold body, part of the ca. loric contained in the hand, leaves the hand to unite with the cold body ; this produces the sensation of cold. Caloric comes to us from the sun, at the rate of 200,000 miles in a second of a minute. It may also be procured by combustion, percussion, friction, the mixture of different substances, and by means of electricity and galvanism. The absorption of the atmosphere by caloric, cannot be better seen than in the example before us. The bottle being colder than the surrounding air, absorbs caloric from it, and the moisture which that air held in solution, becomes visible, and forms the dew which is deposited on the bottle.”
From Worcester our travellers proceeded to Kidderminster, where they stopped one day in order to view the carpet manufactory in that place.
“ The first carpet made in England,” said Doctor Walker, “ was manufactured under the direction of Anthony Dufoysy, who was brought from France by Lord Pembroke, the present earl's grandfather. The manufacturers of Wilton, about twenty years ago, obtained a patent, which among other particulars, specified, that the carpets should be made with bobbin and anchor. Some persons, however, at Kidderminster, having obtained an insight into the process of the manufactory, procured some looms on the same principle, with this trifling difference, that they were worked with bobbins and balls, instead of anchors, and thus they eluded the infringement of the patent. The carpets at Axminster are woven in one entire piece; and although the genuine Turkey and Persian carpets are most valued, yet the imita
tions of them by English manufacturers, are brought to great perfection, they are so far improved as to be little inferior to the far-famed 'Parisian manufacture : English carpets are indeed, superior to those of foreign countries in beauty of colours, and neatness and taste in the patterns."
From Kiddermister they proceeded to Stourbridge, cele.brated in particular for its glass manufactory. On their way thither, the conversation turned upon the formation and origin of this beautiful article.
THE MAKING OF GLASS,
* Glass,” said Dr. Walker, “ is, strictly speaking, a chemical substance : you know the discovery of glass is at: tributed to chance."
EDWARD. “ Yes: some Phænecean merchants, as Pliny relates, having been driven by a storm at sea to the mouth of the river. Belus, kindled a fire on the shore, in order to dress their food. They were greatly surprised after their meal was finished, at observing a transparent substance round the spot where their fire had been lighted."
DR.WALKER." True : but you have not said what com. posed the shining transparent substance. It was a mixture of the herb pali, and the silicious particles, or sand on the shore, the glittering nature of which was peculiarly adapted for composing this useful and beautiful material. Certainly the first glass-houses mentioned in history were those at Tyre. The word glass is formed of the Latin glastum, a plant; called by the Greeks istatis ; by the Romans vitrum ; by the Ancient Britons, guadorn ; and by the English, woord. The ancient writers make frequent mention of this plant, as one from which the Britons dyed their bodies blue, and hence the fictitious matter of which we are speaking, obtained the name of glass, as having always somewhat of this blueishness in it. There was a plate of glass found amidst the ruins of Herculaneun), and this place you know was destroyed so long ago.as the year 80. As to the use to, which this plate was applied, that is not ascertained, al.
though the most probable speculation refers to its application as a mirror. Before the Romans invaded Britain, glasshouses had been erected in this country, as well as in Gaul, Spain, and Italy. In many parts of the country glass amulets have been found, called by the Britons glieneu reigreedh,. or glass adders; these were probably used by the Druids as amulets, or charms. In the time of Tiberius, we hear of glass being made among the Romans; and by the time of Nero, the art liad arrived at a considerable degree of perfection; for the glass bowls rivalled those of porcelain in value, and equalled the cups of crystal in their transparency. The venerable Bede mentions, that glass-makers came into England in the year 674, under the protection of the Abbot Benedict, who were employed in glazing the church and monastery of Weremouth. Other authors say, they were brought over by Wilfrid, bishop of Worcester, much about the same time. In the year 1180, glass windows became very general, but previous to this period glass was considered as an extraordinary mark of magnificence. Venice for many years excelled all Europe in the fineness of its glasses ; and in the thirteenth century the Venetians were the only people that had the secret of making crystal looking-glasses.
“.The glass manufacture was first set up in England in the year 1557, at Crutched Friars, and at the Savoy the fine fint glass was first manufactured. Glass plates for looking. glasses were not made in this country until the year 1673, at Lambeth, by the encouragement of the then Duke of Buckingham, who brought over some Venetian artists for that purpose.
The French soon learnt the art, and cast plates of an immense size.
“Thus much, Edward, for its origin, and the time in which it was discovered. Now for its properties.
" Glass is one of the most elastic bodies in nature. If the force with which glass bells strike each other be reckoned, sixteen, that wherewith they recede by virtue of their elas.: ticity, will be nearly fifteen.
“ When glass is suddenly.cooled, it becomes exceeding brittle; and this brittleness is sometimes attended with very surprising phenomena. Hollow. bells made of annealed (suddenly cooled) glass, with a small hole in them, will fly to pieces by the heat of the hand only, if the hole by which the internal and external air-communicate, be stopped with a finger, Lately however, some vessels made of such an,