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more infusible a glass is, the less is it alterable by the action of atmospheric and chemical agents, with the exception of hydrofluoric acid. Glass, which is too alkaline, attracts gradually the moisture of the air, and loses its lustre and polish. Many glasses are perceptibly attacked by a prolonged boiling with water, and a fortiori by acid and alkaline solutions; thus the bottle glass is frequently attacked by the tartar which is found in the wine. According to Guyton Morveau, all glass which is attacked by prolonged boiling with concentrated solutions of alum, common salt, sulphuric acid, or potassa, is of bad quality.

CHAPTER II. Of the Choice and Preparation of the Raw Material.

The silica which is employed in Bohemia in the manufacture of glass, is obtained by calcining crystaline quartz, and afterwards pounding it while dry. The quartz is sometimes found in veins in granite and gneiss, as at Neu-Hurkenthal; but it is more frequently met with, either under the form of rolled pebbles in the torrents of Böhmerwaldgebirge, or in fragments, more or less angular, scattered through the vegetable earth, which comes from the decomposition of the primitive rocks. It is evident that these fragments are the remains of the quartzose veins, which, presenting a greater resistance, have escaped the disintegration of the granite or gneiss which enclosed them, and which have been more or less rolled in their transportation.

Those of these fragments which appear to the eye exempt from metallic matters, are bought and sent to the glass works, at the mean price of 0.65 francs per 100 kil: (6.6 cts. per cwt.) These fragments are roughly assorted at the manufactory; those of smoky quartz, called topazkies by the inhabitants, are laid aside as the purest, and reserved for the manufacture of glass of the finest quality, or crystal.

The quartz is calcined, either in reverberatory furnaces or in furnaces of a peculiar form, shown in the plate which accompanies this notice.

When the quartz has been heated to a cherry red, it is withdrawn from the fire, and thrown immediately into a large and shallow tub, the water of which may be continually renewed by a stop-cock, and its heating thus prevented: the quartz thus calcined and cooled, is picked out by hand by women, who gain 0.4 francs (8 cents) for 12 hours work. The fragments which are too large and too hard, which have not been sufficiently calcined, are broken into pieces and thrown back into the furnace: the rest is broken up into small fragments, and those parts which are perfectly white, are alone employed in the manufacture of glass. All fragments which present the least trace of metallic oxides, (ordinarily oxide of iron) are separated with the greatest care, pulverized separately, and employed upon iron wheels in grinding the cut glass.

Upon an average, 0.07 steies of pine wood is consumed in calcining 100 kils. of quartz, (14 cubic feet per cwt.) The quartz, after being calcined and picked out, is then pounded while dry-the pestles are armed with cast-iron heads, the weight of which varies from 120 to

150 kil: (264 to 330 lbs. av.) their play is from.5 met. to.6 met., (1.64 to 1.99 ft.) and each of them falls into a hemispherical mortar, about 10 in. in diameter, cut in a large beam which extends throughout the length of the pounding machine. The use of iron and stone mortars had to be rejected on account of the fear that the head of the pestles might detach sufficient ferruginous particles to diminish perceptibly the purity of the glass.

The powder obtained from the pounding machine is sifted, and that which remains upon the sieve is pounded over. Each pestle of the pounding machine pulverizes in 12 hours 90 lbs. of quartz.

Potash. Almost all the Bohemian glass is potash-glass; because soda and its salts give to glass a sensible yellowish tint, and because the difference of the price of potash and soda is far less in Bohemia than in most of the countries in Europe. A small quantity of the potash used in Bohemia is made in that country; but the greater part is drawn from Hungary. There the Carpathians are covered by immense forests, the greater number of which are, in the present condition of things, unavailable, on account of the low price of fuel, and the difficulty of communication. They are, therefore, put to use by burning them standing, and withdrawing the common potash from their ashes by washing.

To obtain potash of the second quality, the preceding is treated cold by its own weight of water, then decanted; the decanted liquor evaporated to dryness, and the potash thus obtained, calcined at a heat high enough to frit it.

Finally, to obtain the finest potash, or that of the first quality, treat the potash of the second quality as before, using only one half of its weight of cold water.

It is of the greatest importance that the trees which have furnished the potash, shall not have grown upon a metalliferous soil, that is a soil perceptibly charged with metallic oxides and salts, for we know that these substances are absorbed by the sap, and that we can even imitate artificially by this process, a great number of colored woods, by causing certain metallic solutions to be successfully absorbed by woods of analogous structure and tissue.

When this is the case, the potash which is obtained by washing the ashes of the trees, although it may appear very pure at first sight, contains almost always, a sufficient quantity of metallic oxides to color the glass perceptibly, which must cause it to be rejected in the manufacture of fine glass. This remark, and the recollection that the value of the Bohemian glass depends peculiarly upon its perfect colorlessness, have caused the adoption in this country, of a process of testing, altogether different from the alkalimetic processes employed in France, which give only the amount of alkali, without at all indicating the nature and proportion of the foreign and injurious materials which it may contain. This test, which is still farther facilitated by the small size of the glass-pots, which in Bohemia do not contain more thau from 120 to 200 lbs. of calcined and fritted materials, is performed by replacing in one of the pots in which fine glass is made, the potash ordinarily employed, by its weight of the potash to be tested, and

comparing the articles made with the glass obtained, with glasses of known composition, made once for all, by varying the quality and quantity of the alkali.

Thus, by the perfect whiteness, or by the more or less decided shade of color of the glass obtained, the nature and proportion of the metallic impurities, and even, approximately, the alkaline contents of the potash tested, are ascertained; and thus its commercial value can be directly obtained.

In the mines of the Böhmerwaldgebirge, the prices of the different kinds of potash, per cwt., are as follows:

For common potash, (third quality)

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$4 69

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Soda.-Soda is, as I have before remarked, but little employed in Bohemia, where it is used only in the manufacture of common window glass. Common soda costs $3.74 per cwt.

Sulphate of Soda.-The sulphate of soda, or glauber salts, is obtained in chemical works as a residue from the manufacture of nitric acid, by means of nitrate of soda and sulphuric acid, and it is employed only in certain glass works annexed to these establishments, (as at Gross-Lucka witz, near Chrudim,) where they make the bottleglass retorts and matrasses used in the works themselves. (1-13 of its weight of carbon must be added.)

Lime. The lime employed in the glass works of the Böhmerwaldgebirge, is obtained from a saccharoidal limestone, found both in Moravia and in Bohemia, (near Winterberg,) in beds enclosed in gneiss, which shews the same stratification; whilst in certain places, and especially near Winterberg, the granite upon which these beds rest, may be seen to send forth veins into them. This fact appears to demonstrate in a clear manner, that this limestone and gueiss, which are regarded as primitive by many German geologists, and among others by Professor Zippe, of Prague, are the effect of a metamorphosis due to the appearance of the granite, which has elevated the chain of the Böhmerwaldgebirge.

This saccharoidal limestone is perfectly white, and presents two extreme varieties; one of which, with broad plates and very transparent, imitates to deception, the most beautiful ancient statuary marble, (such as that of Paros,) while the other, with an extremely fine and close grain, has a greater analogy with the Carrara marble.

These limestones are calcined in the same furnaces which serve to burn the quartz, and are then suffered to slack spontaneously in the air, and care is taken to frit again the powder thus obtained, before placing it in the crucibles of the glass furnace. In the mixture, from 6 to 20 parts of calcined lime are introduced for 100 parts of silica..

Peroxide of Manganese.-The peroxide of manganese is but little employed in Bohemia, at least in the manufacture of fine glass: it serves to destroy the bottle-green color due to the protoxide of iron.

Arsenic. The arsenic is obtained in the state of arsenious acid, from the Erzgebirge and from the Riesengebirge, where it is obtained,

both as a principal product of the roasting of arsenical pyrites, and as an accessory product of the roasting of ores of tin and cobalt. It is much employed in Bohemia, especially in the manufacture of fine glass. It serves, first, to destroy the greenish tint due to a small quantity of the protoxide of iron; secondly, to destroy the topaz yellow color which the glass assumes if the furnace smokes, or if the wood in crackling should throw small sparks of charcoal into it; and thirdly, it serves to agitate the melted matter and assist the disengagement of bubbles.

Nitrate of Potassa.-Saltpetre, or nitrate of potassa, is employed in some of the establishments, together with white arsenic, to produce the same effects.

The pieces broken off in grinding, old broken glasses, glass which has been spilled upon the hearth of the furnace by an accidental fracture of the glass-pots, &c., are broken up, washed and classed according to their nature, their color and purity, and commonly employed in the manufacture of common glass. The pieces from making the fine glass alone, are used in the manufacture of white table glass.

Combustibles.-The combustible used in the glass works of Bohemia, is resinous wood, of which the prevailing species is the kiefer, (pinus sylvestris); this species is also the best for working glass, because it crackles least in the fire, and gives the most flame. The flanks and summits of all the mountains which form the chain of the Böhmerwald and Reisengebirge, are covered with forests of resinous woods. These forests are cut when of full growth, about every 80 or 100 years. The wood is cut during the summer, then in winter it is transported to the water courses which wind through the valleys, by means of slides made in the snow, and when these melt it is floated down to the glass works. The mean price when delivered at the establishments, throughout the whole of the Bömerwaldegebirge, is 23 cts. per cubic yard. The wood is completely dried and even slightly roasted before it is used, in cast iron boxes, heated externally by the flames which escape from the glass furnaces. I have seen but the five glass works of the Count de Buquoi, where this process has been abandoned for some fifteen years, and I do not know the motive of its disuse.

By the preliminary roasting of the wood, an economy of ten per cent. in the fuel is gained; and besides, the fire becomes much more easily regulated.

Clay for the Crucibles.-The clay employed in the manufacture of the crucibles, in the glass works to the east of the Bömerwaldgebirge, comes from Moravia; that employed in the glass works situated in the western part of that chain, is taken partly from the environs of Pilsen, in Bohemia, partly from the neighborhood of Nuremberg, in Franconia.

These clays are very white, very aluminous and but slightly adhesive; by calcination they lose nothing of their original whiteness. A specimen of the clay from Moravia, employed at Silberberg, in the manufacture of glass pots, gave by analysis, the following results:

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Which gives for its formula AS2+Aq., which represents Triklasite or Fahlunite. Except that this clay contains no combustible matter, it presents in its composition a very great analogy with the refractory clays of Stourbridge and Stannington, the analysis of which has been given by M. Play, (Annales des Mines, 4th series, vol.III, p. 646) in a very remarkable memoir upon the manufacture of steel in Yorkshire.

CHAPTER III. Of the Glass Works of Bohemia generally.

On the Situation and Composition of the Glass Works.-The principal thing to be considered in the location of glass works being the facility of procuring fuel, they seek as much as possible to establish them in the midst of forests, and upon the banks of a water course which will allow the floating of the wood to them, and upon which may be also established, at no great distance, the stamping machines, and the mills for cutting the glass, (schleifer mühle,) which are almost always driven by a water-wheel. The power of the stream of water is increased, when necessary, by putting it into communication, by means of sluice-gates, with the small pools which are met with in such quantity among the mountains. As the forests can be cut only about once in a century, it is often advantageous, after having cut off all the wood in the neighborhood of an establishment, to transfer it, for a certain time, to another place, where a supply can be more easily found, until this, in its turn, also becomes exhausted. This instability in the location of the greater part of the works, has, from motives of economy, led them to construct the buildings which enclose the furnaces entirely of wood; so that, at first sight, nothing is more miserable than the appearance of these works, which seem lost in the midst of endless forests, and which show themselves from afar off by the clouds of smoke which rise above the trees. It is only those works which are certain of what may be called an indefinite supply, such as those of MM. Meyer, situated near Moldau, which are, in part, constructed of stone.

The glass works of Bohemia are generally composed of two melting furnaces (schmelzöfen, or glasöfen,) one of which is in action, while the other is undergoing repair, so that one is always in activity.

When the establishment makes window glass, it has besides one or two furnaces (flattening kilns) to flatten the glass (strecköfen) which are placed under a separate shed attached to the works.

The store house for the raw materials is also attached to the works. The stamping machine and the furnaces for calcining the quartz and the lime, are also attached to the works whenever the stream is of sufficient power to allow it, but generally they are separate and placed at some distance either above, or below; the same arrangement is

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