It has been remarked, that when soda and potash have been introduced, the colours scaled, so that they cannot be used

as fluxes. These alkalies, being vola

tilized, abandon the colours which cannot adhere to the glaze by themselves.

It has been observed, that other colours are likewise prepared, which being laid upon the general surface, are fused by the same fire as bakes the porcelain. These colours are but few, because there are few metallic oxides that can support such a fire without being volatilized or discoloured. Their solvent is the feldspar. As they incorporate with the glaze they never crack, and are more brilliant.

The third receptacle of metallic vitrifiable colours is glass without lead.

The application of these colours constitutes the art of painting upon glass; an art much practised in former ages, but which was, till lately, supposed to be lost, because out of fashion. It, however, too immediately depends on the art of painting on enamel and porcelain to be lost. Descriptions of the processes may be found in different books.

A book, entitled “L'Origine de l'art de la Peinture sur Verre," published at Paris in the year 1693, and "Le Traité de l'art de la Verriere," by Neri and Kunckel, seem to be the first works containing complete descriptions of this art. Those published since, even the great work of Leviel, which constitutes part of "Les Arts et Metiers," of the French academy, and of the " Encyclopédie Methodique," are only compilations from the two former works.

It is somewhat remarkable, that if we follow the processes exactly as they are described in these works, as our author has done with some of them, the colours of which they pretend to give the receipt, would never be fabricated. They only serve to show an able practitioner the method, and leave it to him to correct or make additions. This was found to be the case by Citizen Meraud, who was engaged to prepare them for the manufactory of Sévres. He was obliged to make the colours for painting on glass rather from his own experience, than from the instructions in the work just

mentioned.

The materials and fluxes which enter into the compositions of the colours for painting on glass are, in general, the same as those applied to porcelain. They Vary only in their proportions; but a great number of the colours used for VOL. V.

enamel and porcelain cannot be applied on glass; many of them, when seen by transmitted light, entirely change their aspect, and exhibit an obscure tint, which can be of no use when deprived of the white ground which throws them out. We shall point out these when we treat of the colours in particular. Those colours which can be used on this body sometimes change in the baking, and acquire a great transparency. They are generally beautiful only when placed between the eye and the light, and they answer the purpose intended in painting glass.

There is more difficulty in baking plates of coloured glass than is commonly thought. The bending of the piece and the alteration of the colours are to be avoided. All the treatises we have consulted recommend the use of gypsum. This method sometimes succeeded with Brougniart, but generally the glass became white, and cracked in all directions. It appears, that the glasses which are too alkaline, and which are far the most common in clear white glasses, are attacked by the hot sulphuric acid of the sulphate of lime. He was able with ease to bake much larger glasses than any before painted, by placing them on very smooth plates of earth or unglazed por

celain.

Concerning the several particular Colours.

After having collected the several phenomena which each class of vitrifiable colours offer, with regard to the bodies on which they are placed, we must shew the particular and most interesting phenomena, which every principal species of colours employed on tender porcelain, on glass, and in the fire that bakes the porcelain, present.

Concerning the Reds, Purples, and Violets, obtained from Gold.

The carmine-red is obtained from the purple precipitate of Cassius. It is mixed with about six parts of its flux, and this mixture is directly employed without being first fused. It is then of a dirty violet, but acquires the beautiful carmine by baking. It is however very delicate; a little too much heat or carbonated vapours easily spoil it; yet it is more beautiful when baked with charcoal than with wood.

This colour, and the purple, which dif

fers little from it, as well as the shades which are obtained from their mixture with other colours, really change in all porcelains, and in the hands of all operators. But this is the only one which changes on hard porcelain. It may be replaced by a substitution of rose-colour from iron, which does not change; so that by excluding from the pallet the carmine made from gold, and substituting the rose-coloured oxide of iron here spoken of, we have a pallet composed of colours, none of which are subject to any remarkable change. The rose-coloured oxide of iron has been long known, but was not employed on enamel, because it is then subject to considerable change. Or, perhaps, when the painters on enamel became painters on porcelain, they continued to work according to their ancient method.

It might be supposed, that by previous ly reducing the colour flamed carmine, already mixed with its solvent into a vitreous matter, the last tint would be obtained; but the fire which must be used to melt this vitreous mass destroys the red colour. Besides, it is found, that, to obtain this colour in perfec ion, it is necessary to pass it through the fire as little as possible.

The carmine of tender porcelain is made of fulminating gold, gently decomposed, and muriate of silver; there is no tin in it, which proves it is not necessary, for the fabrication of a purple colour, that the oxide of this last metal and that of gold should be combined.

Violet is likewise obtained from the purple oxide of gold. This colour proceeds from having a greater quantity of lead in the flux, and it is nearly of the same tint, whether crude or baked.

These three colours totally disappear in the strong fire necessary to bake porcelain.

Carmine and purple afforded, upon glass, only tints of dirty violet. The violet, on the contrary, has a beautiful effect, but is subject to change to blue.

Concerning the Red, Rose, and Brown

Colours, obtained from Iron.

These colours are made from red ozydated iron, prepared with nitric acid. The oxides are calcined still more by exposing them to the action of fire. If too much heated, they change to a

brown.

Their flux is composed of borax and minium in small quantity,

These are the oxides which afford the rose and red colours, which may be substituted instead of the same colours made from oxide of gold. If properly applied on hard porcelain, they never change. Brougman made roses with these colours, and there was no difference between the flower, before and after baking, except the brilliancy which colours naturally receive from fusion.

The colours may either be previously fused or not, at pleasure.

In a violent fire, they either partly disappear, or produce a dull and brickdust red colour, which is not at all agree. able.

Their composition is the same, either for tender porcelain or for glass. They do not change on the latter, but on the former they almost entirely disappear by the first fire; and they must be laid on very heavily, in order to have any part visible.

It is to the presence of lead in their glaze that this singular effect must be attributed. Brougman ascertained this by a very simple experiment. He placed this colour on window glass, and fired it very strongly, and it did not change. He then covered some parts of it with minium, and again exposed it to the fire. The colours totally disappeared in those places where the red oxide of lead had been applied. When this experiment was performed on a larger scale, in a closed vessel, a large quantity of oxy. gen gas was disengaged.

This observation seems clearly to prove the effect of oxydated lead as a discolourer of glass. We see that it does not operate, as has been supposed, by burning combustible impurities in the glass, but by dissolving, discolouring, and volatilizing the oxide of iron, which may affect its clearness.

Concerning the Yellows.

Yellows are colours which require much precaution in fabricating, on account of the lead they contain; which, sometimes, by approaching to the metallic state, produces black spots.

The yellows of hard and tender porcelain are the same. They are composed of oxide of lead, white oxide of antimony, and sand. Oxide of tin is sometimes added; and when it is required very lively, and resembling the colour of marigold, red oxide of iron is added, the very deep colour of which disappears during the previous fusion they undergo, on ac

count of the lead contained in this yellow. When these colours are once made, they do not change: they disappear almost entirely in the porcelain fireyellows.

These cannot be applied to glass; they are opaque and muddy. That employed by the ancient painters on glass is, on the contrary, beautifully transparent, very brilliant, and of a colour approaching gold. The processes they give indicate that it contains a mixture of silver; but when exactly followed they afford nothing satisfactory. Citizen Meraud succeeded in making it as beautiful as the ancient painters on glass, by employing muriate of silver, oxide of zinc, white clay, and the yellow oxide of iron. These colours are applied to glass simply ground, and without flux. The oxide of iron gives the yellow nearly the same tinge as it ought to have after the baking, and contributes, with the clay and oxide of zinc, to decompose the muriate of silver without disoxydating the silver itself. A powder remains after baking, which does not penetrate the glass, and may be easily cleared off.

This yellow when employed in greater quantities affords deeper shades, and produces a reddish colour.

Concerning the Blues.

These are known to be obtained from the oxide of cobalt; their preparation is known to every chemist. The superiority at Sévres, so justly reputed for the superiority of its blues, is owing merely to the care taken in its fabrication, and to the quality of the porcelain, which appears more proper to receive it, on account of the violent fire it can support.

Brougniart observed one fact respecting the oxide of cobalt, which is, perhaps, not known to every chemist. It is vola. tile in a violent heat; to this property must be attributed the bluish tint which the white (bordering upon blue) always receives. A white piece was purposely put in the same case next to a blue; the side of the white piece which was turned towards the blue became very bluish.

The blue of hard porcelain, prepared for what is called a blue ground by strong fire, is fused with feldspar; the solvent for tender porcelain is silex, potash, and lead; it is not volatilized like the preceding, because the fire is much inferior to that of the hard porcelain.

These colours, being previously fused, do not in the least change when applied.

The blues for glass are the same as for tender porcelain.

Concerning Greens.

The greens employed in painting are made with the green oxide of copper, or sometimes with a mixture of yellow and blue. They must be previously melted with their flux; without this precaution they would become black but they do not change after the first fusion.

They must not be treated with a violent fire, or they would totally disappear. The green grounds by strong heat are made with the oxides of cobalt and nickel, but it is only a brownish green.

The bluish greens, named sky-blue, formerly a colour very much in esteem, can only be used on tender porcelain ; they always scale off from hard porcelain, because there is potash in their composition. These greens cannot be used on glass, because they afford a dirty colour; it is necessary to put a yellow on one side, and a more or less pale blue on the other, in order to produce a green. This colour may likewise be fabricated, by mixing a blue with the yellow oxide of iron. Brougniart hoped to obtain a green from the oxide of chrome; and the experiments he made promised to be attended with success. The pure chromate of lead, fixed on porcelain by means of a strong fire, afforded him a very deep and very fixed blue, of considerable beauty.

Concerning Bistres and Brown Reds.

These are obtained by mixtures of dif ferent proportions of manganese, brown oxide of copper, and the oxide of iron, called umber. They are likewise previously fused in their solvents, so that they do not in the least change on tender porcelain, lead not having the same action on the oxide of manganese as it has on that of iron. This colour may be employed very well on glass.

The brown red, ground by strong heat, known by the name of fonds caille, are made in the same manner: feldspar is their flux. There is no titanium in their composition, though generally asserted in books. Titanium was not known at Sévres when Brougniart first came to that manufactory. He treated this singular metal in various ways, and never ob. tained any grounds but a slight obscure yellow, and very uncertain in its quality.

Concerning the Blacks.

Black colours are the most difficult to be obtained very beautiful. There is no metallic oxide, which, singly, affords a fine black. Manganese gives the best; iron, an opaque, dull, blistered black, which casily turns to red. The makers of colours have therefore combined several metallic oxides, which, singly, do not afford blacks, and they have obtained a very beautiful colour, but it is subject to scale and become dull.

The oxides are, those of manganese, the brown oxides of copper, and a little of that of cobalt. Grey is obtained by suppressing the quantity of copper and increasing the quantity of flux.

The Sevres manufactory is the only one which has as yet produced beautiful blacks with a strong fire. This is more owing to the quality of the biscuit, than to any peculiarity of process It is by a

mixture of blue with the oxides of manganese and iron that they make this very

brilliant black.

The blacks for opaque glass are made the same as for painting, by giving dif.

ferent doses of solvent.

After the display of the principles of fabricating each principal colour, it is clear, that by mixing these colours all possible shades may be obtained: and also that care in the preparation, choice of materials, and just proportions of doses, must exhibit very sensible differences to the experienced eye of a painter. A knowledge of the composition of colours does not give the requisite care and neatness in making them up.

On recapitulating the facts here just stated, in order to present them in a general view, we see, first, that amongst the colours usually employed for hard porcelain, one only is susceptible of change, namely, the carmine: and this may be replaced by the reds of iron, and then no colour changes

M. Brougniart presented to the Institute an unbaked head made in this manner, and a painting of two roses, the one baked, and the other in its first state. There was not any difference between them.

Secondly, That amongst the colours of soft porcelain and enamel, several change considerably, particularly the reds of iron and gold, with the yellows, greens, and browns. None have been substituted instead of them, this species of painting being almost abandoned.

Thirdly, That several of these colours

change likewise upon the glass by becoming perfectly transparent, particularly the yellows and violets.

Fourthly, That neither an additional calcination, nor an additional fusion, as has been suspected, will prevent them from changing: for this method alters the colours that change, and does nothing to the rest. The change which several colours undergo on tender porcelain, and on glass, does not therefore relate to the nature of their composition, but rather to that of the body on which they are placed. Consequently, by suppressing the carmine of gold from the colours of hard porcelain, we shall have a series of unchangeable colours.

ENARGEA, in botany, a genus of the Hexandria Monogynia class and order. Essential character: calyx none; petals six, oblong, ovate, concave, acute, three outer, three inner, green spotted; berry three-celled, with four or five globular seeds. There is but one species. viz. E. marginata, a native of Terra Del Fuego.

ENCALYPTA, in botany, a genus of the Cryptogamia Musci class and order. Capsule cylindrical; fringe simple, of sixteen linear erect distinct teeth; veil campanulate, inflated, lax. six species.

There are

ENCAUSTIC, the same with enamel ling and enamel. See ENAMELLING.

ENCAUSTIC painting, a method of painting made use of by the ancients, in which wax was employed to give a gloss to their colours, and to preserve them from the injuries of the air.

ENCHASING, or CHASING, the art of enriching and beautifying gold, silver, and other metal work, by some design, or figures represented thereon, in low relievo. See RELIEVO and SCULPTURE.

Enchasing is practised only on hollow thin works, as watch-cases, cane-heads, tweezer-cases, or the like. It is performed by punching or driving out the metal, to form the figure from within side, so as to stand out prominent from the plane or surface of the metal. In order to this they provide a number of fine steel blocks, or puncheons, of divers sizes; and the design being drawn on the surface of the metal, they apply the inside upon the beads or tops of these blocks, directly under the lines or parts of the figures; then with a fine hammer, striking on the metal sustained by the block, the metal yields, and the block makes an indenture or cavity on the inside, corresponding to which there is a

prominence on the outside, which is to stand for that part of the figure.

Thus the workman proceeds to chase and finish all the parts, by successive application of the block and hanimer to the several parts of the design. And it is wonderful to consider with what beauty and justness, by this simple piece of me. chanism, the artist in this kind will represent foliages, grotesques, animals, histories, &c.

ENCHELIS, in natural history, a genus of the Vermes Infusoria. Worm invisible to the naked eye, very simple, cylindrical. There are fifteen species. An account of these may be found in Adams "On the Microscope."

ENCROACHMENT, in law, an unlawful gaining upon the rights or possessions of another. It is generally applied to the unlawful occupation of wastes and com

mons.

ENDEAVOUR, where one endeavours actually to commit felony, &c. he is punishable as for a misdemeanour; and an assault, with intent to rob, is punished by transportation. Statute 7 Geo. II. c. 21.

ENDECAGON, a plane geometrical figure of eleven sides and eleven angles. If each side of this figure be 1, its area will be 9.36563994 of the tangents of 737 degrees to the radius one.

ENDEMIC, or ENDEMICAL diseases, those to which the inhabitants of particular countries are subject more than others, on account of the air, water, situation, and manner of living.

ENDIVE, in botany, &c. broad-leaved succory. See CICHORIUM.

ENDOWMENT, in law, is the widow's portion; being a third part of all the freehold lands and tenements, of which her husband was seized at any time during the coverture. Of lands, not freehold, her portion varies, according to the custom in different places.

ENEMY, in law, an alien, or foreigner, who in a public capacity invades any country, and who cannot be punished as a traitor, but must be subjected to martial law. An alien residing in England, under the protection of the king's peace, may be dealt with as a traitor, because he owes a qualified allegiance.

ENFRANCHISEMENT, in law, the incorporating a person into any society or body politic; such as the enfranchisement, of one made a citizen of London or other city, or burgess of any town corporate, because he is made partaker of its liberties or franchises.

ENGINE, in mechanics, is a compound machine made of one or more mechanical powers, as levers, pullies, screws, &c. in order to raise, casi, or sustain any weight, or produce any effect, which could not be easily effected otherwise.

Engines are extremely numerous; some used in war, as the battering ram, balista, waggons, chariots, &c. others in trade and manufactures, as cranes, mills, presses, &c.; others to measure time, as clocks, watches, &c.; and others for the illustration of some branch of science, as the orrery, cometarium, and the like

In general, we may observe, concerning engines, that they consist of one, two, or more of the simple powers variously combined together; that in most of them the axis in peritrochio, the lever, and the screw, are the constituent parts; that in all a certain power is applied to produce an effect of much greater moment; and that the greatest effect or perfection is when it is set to work with four-ninths of that charge which is equivalent to the power, or will but just keep the machine in equilibrio

In all machines the power will just sustain the weight, when they are in the inverse ratio of their distances from the centre of motion.

ENGINE, fire, by Rowntree. We have selected an engine by this maker to give a drawing and description, as it is greatly superior to the common engine with two force pumps. As that kind of engine has so often been described by various authors, and its principles so essily comprehended from the description of a forcepump, we judge it unnecessary to give any drawing of it.

The fire engine by Rowntree is a double force-pump, of a peculiar construction, similar in its action to the beer engine, (described under that article,) but as it is on a much larger scale, its conPlate structions, are of course varied. Rowntree's engine, fig. 1 and 2, are two elevations at right angles to each other, of the external part of the engine mounted on four wheels. Fig. 3 and 4, are two sections, perpendicular to each other, of the body of the engine or pump: fig. 5 and 6, are parts of the engine. The same letters are used as far as they apply in all the figures, A, A, A, A; fig. 3 and 4, is a cast-iron cylinder truly bored; it is ten inches diameter and fifteen long, it has a flanch at each end, whereon to screw two covers, with stuffing boxes, a, a, in their centres, through which the spindle, B, B, of the engine passes, and being tight