piece be placed in or on another in the seggar, and all must be so arranged that the heat will be equally applied to every part of each.

In some instances seggars are made having triangular holes in their sides, for the purpose of admitting prisms of the same form, which are inserted therein, horizontally, in order to support a greater number of pieces in a state of isolation within each case than could be accomplished by other means. The prisms thus used must be compounded of the same materials as the cases themselves. This course is not pursued except with common articles, and is adopted with the intention of economising the time, space, and fuel employed for baking them.

If the clay whereof they are composed be well chosen and carefully managed, the seggars may be placed from fifteen to twenty several times in the furnace before they are rendered useless.

Some art is required so to dispose the cases within the oven, with reference to their shape, size, and the objects they contain, that the heat shall be distributed as faithfully as possible, and that the sufficient baking of all the different-sized vessels shall be accomplished during the same time. The largest and coarsest pieces are usually placed on the floor of the oven, which must be previously covered with a layer of sand. If the heat be not faithfully distributed through the whole area, some pieces would be injured by excessive firing, while others would be inadequately baked. The bottoms of the seggars being flat, each, as it is placed upon another, forms a cover to that beneath, and the entrance of smoke is further prevented by placing a ring of soft clay on the upper rim of each case. In this manner the seggars are built one upon another, until they reach nearly to the top of the oven: the upper seggar in each pile is always empty. Each of these piles, as it stands, is called a bung; in building them up, intermediate spaces of about three inches must be left for the circulation of heated air throughout.

Although the privileges so long enjoyed by the royal manufactory at Sèvres, and which were accompanied by corresponding restrictions placed by the French government upon private establishments, must have been upon the whole prejudicial to the progress of the art in France, these regulations had yet in some respects a contrary tendency. Being secured in a great degree from the effects of competition from without, the directors of the royal works were enabled to prosecute experiments with regard to improvements in their utensils and processes, from the adoption of which they might otherwise have been deterred by considerations of expense. Suggestions appear to have been continually made, having such improvements for their object, by men who enjoyed the highest scientific reputations; and the success of plans thus proposed, conduced to the increasing celebrity of the establishment.

Among others, MM. de Montigny and Macquer contrived a form of furnace, which effected at the time of its adoption a very great advantage. In that previously used (and the construction of which had been copied from those employed in Saxony), the heat was so unequally distributed, that it was necessary to vary the composition of the porcelain so as to render it suitable to different parts of the furnace. The improvement here noticed occasioned the sufficient equalisation of heat throughout its area, and a great inconvenience was at once and completely remedied.

The arrangement whereby this important change was accomplished will be understood by a reference to the following figures, which describe the elevation, section, and plan of the kiln. The same letters are employed to denote similar parts in the different figures.

A is the interior area of the kiln. This is fourteen feet eight inches high, and eight feet three inches in diameter: the walls should be three feet thick. BBBB are four air-flues placed at equal distances in the circumference. CCCC are hearths one foot below the base of the kiln: the heat from these passes towards its

centre. DDDD are openings, eighteen inches square, for the reception of the fuel. These openings are pro

vided with mouth pieces of plate iron. E is a door-way in the side of the kiln: its sill is three feet above the Fig. 4. 7

ground; its width is two feet, and its height five feet six inches. This door is used for the introduction of the seggars within the kiln, after which it must be securely walled up. F is a square hole of which there are three in the entire circumference. These are de

signed for the introduction of trial pieces within the kiln : another similar opening is left when walling up the

Fig. 5.

B

A

BD

D B

door-way E. The whole of these are provided with clay stoppers which exactly fill the holes, and which have projections whereby they can be removed or replaced at pleasure. G is the chimney in the centre of the dome-shaped roof; it is of a conical form, eighteen inches diameter at the base, lessening to twelve inches at the top. HH represent four air-holes, placed over the openings F. These air-holes serve to divide the draught, and consequently to equalise the temperature of the kiln. I is a round iron plate, supported on four pillars of the same metal, and placed over the chimney to defend the opening.

When the firing has been sufficiently performed, no more fuel is added, and so soon as the smoke from that already upon the hearths has passed away, the mouth pieces are entirely closed to prevent the passage of air. Shortly after this, the chimney G and the air-holes H are also carefully closed, and the kiln is left, that the

cooling of its contents may go forward as slowly as possible.

Previously to the adoption of this improvement, the kiln employed for baking porcelain was always made of a rectangular form, having only one fire-place and one air-flue, which stood at the side opposite to that whereon the chimney was placed: an arrangement which rendered quite inevitable the before-mentioned inconvenience, arising from the unequal distribution of heat.

The extension of the art, and the consequent competition among the manufacturers in France since the return of peace, have compelled them to use the utmost economy in their various processes; so that, while the quality of their goods has been fully sustained, the prices have been importantly lowered. These savings have been partly realised through the increased skill of the workmen, but are more referrible to the smaller proportionate quantity of fuel consumed, which has arisen, not from any further improvement in the form of their kilns, but through a better arrangement in filling them, whereby they are now made to contain, at each baking, nearly one third more of pieces than was formerly customary.

The potter's oven is now always made of a cylindrical form, and very similar to the common kilns used for burning tiles, with the external appearance of which every one is familiarly acquainted. The drawing here given (fig. 6.) represents the "biscuit oven" now used in one of the extensive porcelain works carried on in the city of Worcester. The furnace mouths of the oven are placed at certain intervals around it; from these the fire and heated air pass into horizontal flues in the floor, and thence ascend through all the interstitial spaces between the bungs, until the surplus heat escapes through an aperture in the centre of the roof.

The Chinese subject the greatest part of their porcelain to only one firing, drying the pieces sufficiently in the air to prepare them for glazing. This plan they are able to pursue, because the nature of their materials is