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It is different in the second case, which is used especially for the more expensive colors, and those most difficult to procure, as well as in three operations peculiar to colored glasses, which consist, 1st, in making colored, or colorless, glass vessels with a foot of a different color; 2d, in making vessels with an interior very thin and very highly colored layer, and with an exterior of colorless glass, which may then be ground off in places without spoiling the uniformity of the tint; 3d, in forming the vessels in the opposite way, that is, an interior colorless layer, and an exterior more or less thick colored one, which is then ground off in places, so as to obtain a glass which presents all the shades of the color.

To obtain these results it is enough, in the first case, to solder the bottom of the vessel to a lump of colored glass fixed to the end of another tube, then to separate the first tube, and finish as usual; in the second case, the tube is dipped successively into pots of the colored and of the colorless glass; and in the third case, the operation is reversed.

As we have already said, there exist certain colored glasses which are not prepared in pots, but in rolls of very deep color, about 1.2 inch diameter, and a foot long. These are more fusible than the colorless glass, and are such that they melt at the temperature necessary for the complete fusion of 64 parts of colorless glass, and one of peroxide of manganese. When one of these rods is to be used, a piece of the proper size is broken off, fixed at the extremity of a tube, softened in the furnace, and worked as has been explained.

These preliminaries being settled, I pass to the description of the different matters which are used to color glass.

Ruby. The manufacture of this color, which is extremely difficult to prepare, and is employed only in roll, is still involved in some obscurity. All the establishments which I have visited obtain their color from the manufactory of M. Meyer, at Stubenbach, near BergReichenstein. According to a manufacturer of the Riesengebirge, the glass which they use for preparing the cakes of ruby color, (which bears the name of schmelze,) is composed of silica 500, minium 800, nitre 100, calcined potassa 100. A solution of gold is then prepared by treating 10 grammes of fine gold with 180 aqua regia, by the aid of heat; when all is dissolved the liquid is poured into a vessel holding about a quart, which is then filled up with aqua regia. It is then poured into a second graduated vessel, and five times its bulk of water added. When this is done, they mix intimately 512 of schmelze, 48 of prismatic borax, 3 oxide of tin, 3 oxide of antimony, reduced to very fine powders, and of the solution prepared as above.

The whole is then heated for 12 or 14 hours in an open crucible, placed in a glass furnace, and then suffered to cool in an annealing oven. When it is cool they break the crucible, and take out the color. It is not necessary to use closed crucibles, as some manufac

turers assert.

If more acid is used than is prescribed above, the crucible is attacked, but the color is more solid.

* The French gramme is equivalent to 15.438 grains troy.

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The purple of Cassius is only mechanically mixed in the glass, and if this be remelted it often becomes dull, and striæ are formed, which are nothing more than extremely fine particles of reduced gold. In certain cases the quantity of oxide of tin used in the above mixture must be from 2 to 4 parts. The first of these mixtures is used especially for large pieces which have to be worked a long time in the fire; the second, for small and delicate articles. Nevertheless, as the process does not always succeed, the greater part of the manufacturers prefer, as I have said, to buy the color ready made from other manufacturers, who devote themselves exclusively to this. The antimony appears, in this case, merely to give brilliancy to the glass without coloring it at all.

According to the director of one of the glass works in the neighborhood of those of Bohemia, a very beautiful ruby color may be obtained in the following way:-Dissolve by heat one gramme (15.4 grains troy,) of fine gold in an aqua regia composed as follows,-12 grammes nitric acid, 12 grammes muriatic acid, and 1 gramme sal ammoniac. Again, dissolve by heat 1 gramme of tin, in an aqua regia composed of 20 grammes nitric acid, and 6 muriatic acid; then pour the two solutions into a large vessel containing already 500 grammes of clear water, and mix them intimately by agitating the vessel after corking it. The red precipitate of purple of Cassius, which forms, is washed and dried with care. A peculiar glass is then prepared by mixing together 40 parts of very pure quartz pulverized, 16 parts of nitre, S parts of borax, 1 part of white arsenic, 1 part of cream of tartar, finely pulverized and sifted through silk; and a greater, or less, quantity of the purple of cassius, according as you want a more, or less, deep color. This mixture is introduced into a clay crucible made expressly, not glazed, and of about the capacity of 5 quarts, or else in an ordinary glass pot, then heated in a glass furnace, or in a small furnace made expressly for it, taking care to stir the materials continually until they have attained a dull red heat. The crucible is then covered, and the heat continued for some time. When the mass is perfectly melted, and gives no more bubbles, the crucible is removed, and after suffering it to cool for 4 or 5 hours in a cellar, it is broken, and the glass obtained separated with care from the impurities which it may contain; it is then ground and sifted. If now there be melted together in a small crucible placed in the glass furnace, the following mixture:128 parts of pure quartz pulverized, 64 parts of nitre, 3 parts of borax, and 3 parts of white arsenic; and the glass thus obtained poured into cold water, then ground, and passed through a sieve, then mixed with the colored glass prepared as above, and melted in a glass crucible, a glass will be obtained, which, worked up into articles of a thickness not exceeding 0.16 to 0.2 inch, takes a beautiful ruby color when exposed to the smoke obtained from burning fir, or that of alder.

Bohemian Ruby-Red-They prepare besides, in Bohemia, a peculiar ruby color, which is also employed in cakes, and has received the name of Bohemian Ruby. It is prepared by melting together quartz powdered and fritted 100, minium 150, potassa fritted 30, borax fritted 20, sulphuret of antimony 5, peroxide of manganese 5, ful

minating gold rubbed in with oil of turpentine 5. If a little more fulminating gold is used a magnificent ruby color is obtained.

Fulminating gold is obtained by precipitating the solution of gold in aqua regia by ammonia, and stirring the liquid for some time. The precipitate is then collected upon a filter, and washed rapidly with water boiled, and rendered slightly ammoniacal, then dried at a very low temperature. There is thus obtained a powder of a deep brownish yellow, very explosive, and of which the manipulation requires great precaution.

Ancient Red called Kirschroth (cherry red.)-This color is generally employed in cake; it is procured by the use of sub-oxide of copper, which is kept in the state of sub-oxide by the addition of an equal quantity of protoxide of tin. When it is desired to pass the color to a fiery red, a little oxide of iron is added. The proportion of oxide of tin must then be reduced, and it may entirely disappear, as in a very beautiful antique red glass, found at Caprea, in the villa of the emperor Tiberius, the analysis of which gave,

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Sometimes the glass is merely colored with the oxide of copper, and then after the articles are finished they are smoked, which gives them a deep red color.

Blue. The azure blue color is obtained by the oxide of copper alone, cobalt blue by the oxide of cobalt, or smalts.

Amethystine Violet.-This color is obtained by the oxide of manganese, mixed with a little nitre.

Yellow. There are five distinct yellows which are prepared as follows:

1. Topaz Yellow.-Prepared with charcoal dust.

2. Antimony Yellow.-Prepared with a mixture of glass of antimony and minium.

3. Orange Yellow.-Prepared with glass of antimony, minium, and a little oxide of iron.

4. A peculiar Yellow.-Very expensive, which is prepared with chloride of silver, and is only applied in a very thin layer, as a sort of enamel, the glass must then be smoked, in order to make the color appear.

5. Greenish Yellow.-Which produces a fine effect in day light, but which appears of a dirty yellowish white by the light of a lamp, or candle. This yellow is prepared with the yellow oxide of uranium of commerce, but since this last contains traces of iron, the yellow glass obtained presents almost always a light green tint upon its edges.

Green.--There are four distinct greens:

1. Grass Green.-Which is obtained by the oxide of chrome, or a mixture of glass of antimony and oxide of cobalt.

2. Bottle Green.-Prepared with protoxide of iron.

3. Ancient Emerald Green.-Prepared with oxide of copper mixed with a small quantity of finery cinders.

4. Modern Emerald Geeen.-This color, which is far more beautiful than the preceding, is prepared with a mixture of oxides of nickel and uranium.

Black-Is prepared with peroxide of manganese, oxide of copper, oxide of cobalt, in equal parts; or else with a mixture of finery cinders, peroxide of iron, oxide of copper, or cobalt.

Hyacinth.-The hyacinthine color is obtained with a large quantity of red oxide of iron, and the oxide of nickel.

To be Continued.

On the Chemical Reactions produced by bodies which intervene only by contact. By E. MITSCHERLICH, (Ann. de Ch.)

TRANSLATED FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.

Whatever length of time hydrogen and oxygen gases may be left in a state of mixture with each other, they never combine, even in the presence of such bodies as sulphuric acid, potash, or lime, which have a great affinity for water, and which, it would seem, ought to provoke its formation. If, however, metallic platina be immersed in a mixture of these gases, their combination is instantly produced on the surface of the metal.

We may mix these gases in the proportions which constitute water, and in a very short time the hydrogen and oxygen are so distinctly diffused, that each molecule of the one finds itself in presence of a molecule of the other; and since the molecules of gaseous bodies possess an excessive mobility, and as their cohesion is not an obstacle to their combination, as in the case of solid and liquid bodies; and since also we may suppose that the affinity of hydrogen and oxygen in water is equivalent to a pressure of many thousand atmospheres, it must be at once admitted that besides the ordinary forces (raisons) which oppose chemical combination, there is another which prevents the combination of hydrogen and oxygen by neutralizing their natural affinity.

Some bodies in a state of solution act among themselves in the same manner as hydrogen and oxygen, with regard to platina. We may abandon, for a long time, an aqueous solution of cane sugar without perceiving any alteration in it; but if we add to it dilute sulphuric acid, the sugar, without combining with the sulphuric acid, solidifies a portion of water, and is transformed into glucose. The decomposition of gaseous ammonia by incandescent copper, is one of the (not very numerous) examples in which the decomposition of a gaseous body is promoted by a solid body: we have, on the contrary,

numerous examples of decompositions of this kind among liquid and solid bodies, which undergo themselves no change during the reaction; the decomposition, for example, of the binoxide of hydrogen under the influence of various bodies,-the decomposition of chlorate of potash by the oxide of copper, and other fixed bases.

Before we undertake to ascertain why certain chemical reactions take place under the influence of bodies which interfere with each other only by their presence, we must seek to give an account of the manner with which bodies that do not combine chemically, act upon each other when placed in immediate contact.

We may show with the greatest facility the attraction which a solid exerts upon a gaseous body, by employing the first in a condition in which it presents the greatest possible surface under the smallest volume, as in very thin leaves, or better, in impalpable powder. Charcoal, and many substances of difficult fusibility, like platina, which may be obtained in a state of extreme tenuity, are very suitable for these experiments.

I have calculated, in the first volume of my Traité de Chimie, the amount of surface in one cubic inch, divided into little cubes ofàðõ of an inch on each side, by two series of perpendicular sections. It would be equal to 100 square feet, without estimating the extent of the interstices

If any substance be brought to such a state of tenuity that we may suppose it reduced to its atom, or, at least, to a degree of known approximation, we may then calculate the surface which it would represent.

The estimate may furnish the value of the greatest diameter of an atom of a chemical compound, when the latter is obtainable in the condition of thin plates, or of vesicules, by the colors which they present ;-thus the diameter of an atom of water must be, at most, 100% of an inch, according to the color which appears at the thinnest portion of a soap bubble.

In reducing a dilute solution of chloride of platina, by means of carbonate of soda, and formic or tartaric acid;-or in decomposing very dilute sulphate of platina by weak alcohol, the metallic platina obtained in either case must be in the state of molecules, since the molecules, at the moment of reduction, are separated by water, which necessarily prevents their agglomeration.

A volume of one cubic inch filled with globules, which we will suppose, for the sake of facility, to have only 10000000 of an inch diameter, but placed in such a manner that the lines passing through their centres be perpendicular, or parallel, to each other, will present a surface of 218,166 square feet. In any other position the surface would be still greater if the globules touched each other. It is possible that platina black has a surface as considerable.

Wood charcoal is the most convenient substance for studying the action of large surfaces on gases, and the experiments of De Saussure, are, on this account, very important. Vegetable fibre does not melt when properly heated, so that the charcoal resulting from its calcination, still preserves the form of the fibre, as we may readily convince VOL. IX, 3RD SERIES. No. 5.-MARCH, 1845.

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