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but they would especially call attention to the articles of Mr. Graves, on account of their apparent excellence, and the low price at which they can be afforded."

In conclusion, the committee recommend the following awards: No. 551, to Messrs. Farr, Powers & Weightman, for their admirable display of commercial chemicals, A Silver Medal. No. 536, Smith & Hodgson, for a beautiful display of chemical A Certificate of Honorable Mention.

preparations, No. 518, to Alex. H. Campbell, for the excellence of his prepared spermaceti, A Certificate of Honorable Mention. No. 549, to Eugene Roussell, for the best perfumery,

A Certificate of Honorable Mention.

No. 528, to H. P. & W. C. Taylor, for their transparent soap,

A Certificate of Honorable Mention.
No. 564, to J. R. Graves, for very beautiful and cheap soaps,
A Certificate of Honorable Mention.

MECHANICS, PHYSICS, AND CHEMISTRY.

Notice of the Manufacture of Glass in Bohemia. By M. L. P. DEBETTE. [Annales des Mines, 4th series, volume iv, page 553; December, 1843.]

TRANSLATED FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.

Of Glass in General.-Every transparent, or, at least, translucent. substance, which is brittle at ordinary temperatures, becomes soft and ductile, and finally melts, at a high temperature, and of which, when cold, the fracture presents a peculiar, well defined lustre, known as the vitreous lustre and the vitreous fracture, is called, in the most general sense of the word, glass. Many acids, such as the phosphoric and boracic, as well as many silicates, phosphates, borates, arseniates, fluorides, and some metallic chlorides, such as those of lead and silver, different mixtures of these bodies with each other, and with other substances, among which the alkalies and the earths hold the first place, give glasses by their fusion. That which in the arts is more especially meant by the term glass, is a compound of silica, potassa, or soda, or both together, and of lime and oxide of lead alone, or mixed. This compound gives, by fusion, an amorphous and transparent mass, which is not soluble in water, nor in any acid except the hydro-fluoric.

History. According to Pliny, the discovery of glass is due to some Phoenician travelers, who having, by accident, used a block of natron, (the native salt of soda,) in arranging their fire in the desert, saw, with astonishment, the two substances combine by fusion, and give a glass; but this fact cannot be admitted, the temperature required being far higher than could be obtained under such circumstances. M. Handicquer de Blancourt, one of the oldest French writers upon the VOL. IX, 3RD SERIES. No. 2.-FEBRUARY, 1845.

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subject of glass, carries the invention back as far as Tubal-Cain, because he having discovered the art of working metals, by fusion, must have obtained slags analogous to glass.

At all events, it is certain that the discovery is very ancient, for it is mentioned in the Holy Scriptures, first, in the Book of Job, chapter xxviii, verse 17, where it is written,-"The gold and the crystal* cannot equal it," &c. And secondly, in the Book of Proverbs, chapter xxiii, verse 31,-"Look not thou upon the wine when it is red; when it giveth this color in the cup,t" &c. Aristotle, in a work written in the year 384 B. C., speaks of glass, and seeks to explain its transparence. Fourteen years later, in 370, Theophrastus mentions the glass works situated at the mouth of the river Belus; which is nothing astonishing, for the Phoenicians were the most skilful in the arts of all the people of antiquity, and had, so to speak, the necessary sand and soda under their hands.

The Egyptians were also, from the most remote antiquity, acquainted with the art of making clear and colored glasses, of cutting and of gilding them, as is proved by the glass dresses found upon several mummies from the catacombs of Thebes and Memphis. At a later period, under the Emperors, glass works were erected near Alexandria, which became very celebrated, and filled Italy with their productions.

The Romans were acquainted with glass more than two centuries before Christ; but it was as late as the reign of Nero, that the first glass works was established at Rome; and even then they made only poor drinking glasses. The fine glasses were still so dear at this time, that the Emperor Nero paid more than four thousand francs of our money (eight hundred dollars,) for two handsome glass cups. Under Alexander Severus, A. D. 210, the number of glass workers had so much increased at Rome, that it was thought proper to assign to them a particular quarter of the city.

In the middle ages, Venice distinguished itself by its glass works, which, in 1291, were transferred to the peninsula of Murano, the name of which soon became famous. In this place, it is said, the first blown glass was made.

At this period Bohemia was the most skilful and the richest country in Germany, to which it gave its emperors. Its relations and commerce with Venice and Italy soon introduced into it the art of glass making, and the extreme purity of the raw materials, which are met with in abundance in the mountains which form a girdle around this country, soon assigned to it, in this art, a superiority and reputation which have been maintained to this time.

Traveling, in 1842, through Bohemia, I visited with interest the most renowned manufactures of glass and crystal, and especially the various groups of the Böhmerwaldgebirge. The beauty of the productions of these workshops, and the veil which still covers their pro

*The word which in our version is translated 'crystal,' is rendered in the Vulgate 'vitrum,' glass.-TRANS.

Here again the word rendered 'cup,' in the English, is given as 'vitrum,' or glass, in the Vulgate.-TRANS.

cesses of manufacture, have induced me to publish here the few observations which it has been in my power to make.

The extent of the work compels me to divide it into fifteen chapters, in which I shall treat successively

Chapter I. Of the composition and properties of glass.

Chapter II. Of the choice and preparation of the raw material. Chapter III. Of the glass works of Bohemia generally.

Chapter IV. Of the manufacture of table glass, (verre de gobeletterie) and that of the fine glass called Bohemian crystal. Chapter V. Of the manufacture of bottle glass.

Chapter VI. Of the manufacture of window glass.

Chapter VII. Of some particular articles made of glass.
Chapter VIII. Of colored glass.

Chapter IX. Of opalescent glass.

Chapter X.-Of hyalite.

Chapter XI. Of the manufacture of enamelled cast vessels.
Chapter XII.

Of the art of cutting glass.

Chapter XIII-Of the art of gilding, silvering, platinizing, and incrusting glass.

Chapter XIV. Of the manufacture of mirrors.

Chapter XV. A general statistical view of the glass works of Bohemia.

CHAPTER I.-The Composition and Properties of Glass.

Glasses are silicates which must contain at least fifty per cent. of silica; the more there is of it, the more perfect, unalterable, hard, and infusible is the glass. The hardest, most beautiful, and most perfect glass is found in nature in the state of pure silica in rock crystal; but as this is fusible only at the highest temperatures which can be produced in our laboratories, such as those produced by employing Newmann's blowpipe, or by the aid of a galvanic, or electrical, battery, it is impossible to procure it artificially. To render silica fusible, certain fluxes must be added; these fluxes are potassa, soda, lime, and oxide of lead.

Silica fuses very well with the alkalies, but the resulting glass is rapidly changed by absorbing moisture from the air. To prevent this alteration, it is always necessary, in the manufacture of glass, to introduce a certain quantity of lime, or of oxide of lead.

In the following table is given the analysis of a certain number of Bohemian glasses, which will indicate their composition with preci

sion.

This is one of the thousand European modifications of Hare's compound oxyhydrogen blowpipe, every one of which is as inferior in power, as in simplicity, to the original.-TRANS.

[blocks in formation]

101.2 98.1 100. 100. 100. 100.5 100. 99.2

(1) Bohemian glass from Neufeld; (M. Gras,) its composition is represented nearly, by the formula Ca.S+ (Al.F)S5+ (K.Mg.Mn)S.* (2) A fine table glass from Neuwelt, (M. Berthier;) it is exceedingly beautiful, and is prepared, according to M. Perdonnet, with a mixture of 100 quartz, 50 caustic lime, 75 carbonate of potassa, and a very small quantity of nitre, arsenious acid, and oxide of manganese. The presence of arsenic cannot be detected by analysis. The composition of this glass is expressed by the formula C.S+(KN)S6.

(3) Old Bohemian glass (M. Dumas;) its formula is (Al.C.K)S*. (4) Crown glass of German manufacture (M. Dumas;) its composition is expressed by the formula (K.C)S.

(5) Glass for mirrors (M. Dumas;) it is represented by the formula (N.ALC)S.

(6) Another glass for mirrors (M. Dumas;) its formula lies between B.SS, and B.S.

(7) White table glass from Silberberg near Gratzen; its composition is exactly expressed by the formula 2(K. Ca)S5+ (Al.F)S5.

(S) Mirror glass from Neu-Hurkenthal, for the manufacture of cast mirrors. It shows a greenish tint in section, and softens at a gentle heat. Its composition is nearly represented by the formula (Al.F) S3+6(K.C.M)S3, or more simply (K.C.Al)S3.

I shall give the composition of the mixtures which are introduced into the pots, when I come to describe the manufacture of each kind of glass.

Properties of Glass, Transparence, Colorlessness.-Transparence, and colorlessness are the first properties of glass; to obtain them, the materials must be employed extremely pure, and the least possible flux added; an excess of potassa gives to glass a greenish tint; soda and its salts gives it a yellow tint, and lime renders it milky. A very small quantity of the sulphate of potassa, or soda, gives it a yellowish, or blackish, brown green; iron colors it strongly bottle green, and an excess of the manganese employed to remove the coloration due to oxide of iron, gives it a bluish tint, which becomes a decided violet by the action of the solar light. If the minium employed in the manufacture of crystal contains a little copper, which very often happens,

The reader will remember that these are mineralogical, and not chemical, symbols; hence the letters signify the oxides, or acids, and not the elementary bases, as they would in chemistry.-TRANS.

the crystal takes a slight emerald green tint; this, however, is not to be feared in Bohemia, where there is but a single establishment which makes lead glass.

Charcoal colors glass of a topaz yellow, more, or less, dark, and sometimes reaching a purple, so that it is impossible to obtain a perfectly colorless glass in furnaces which smoke, or in those which are heated by turf, lignite, or bituminous coal; and in these cases it is necessary to employ covered crucibles, as is done in the manufactory of crystal at Choisy le-Roi; it is also necessary, on this account, when in the fabrication of glass the alkaline carbonates are replaced by sulphate of soda, to add, in the crucibles a little (about one-thirteenth,) less of carbon than would be necessary to reduce the sulphate completely, and even thus but common glass is obtained by this process, since the slight excess of sulphate of soda, which must be left, gives a blackish brown tint.

Hardness, Elasticity.-The Bohemian glass is within certain limits perfectly elastic, and very sonorous; when well made it is sufficiently hard to strike fire with steel, and is scratched with difficulty. The lead glasses, on the other hand, have but little hardness, and less in proportion as they contain more oxide of lead; besides which they rapidly lose their brilliancy by use.

Fusibility, Cooling, Annealing, Devitrification.-All glass is more, or less, fusible; when it is softened by the action of heat, it may be worked with the greatest ease, and may be drawn out into threads as fine as those of the cocoon of the silk worm. Glass, when it is submitted to rapid cooling, becomes very fragile, and presents several remarkable phenomena, among which I will cite as an example Prince Rupert's drops. Glass supports variations of temperatures better in proportion as it has been more slowly cooled; thus when they have been but slightly annealed, or not at all, their fragility may be considerably diminished by annealing them in water, or, better, in boiling oil.

All glass exposed during a longer, or shorter, time to a heat sufficiently elevated, loses its transparency, and becomes extremely hard, and much less brittle than before. There takes place a phenomenon precisely similar to that which we see taking place every day by the slow cooling of the slags of our smelting furnaces, and especially in volcanic lavas. Glass with a soda base is more fusible and less hard than that whose base is potassa.

Density. Below is given the densities of several glasses without lead:

[blocks in formation]

1830, 66

10*

2.396

3.782

2.642

2.892

2.506

2.488

2.551

2.563

Action of Atmospheric and Chemical Agents.-The harder and

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