The kilns in use in America and Europe vary very much in shape. M. Brongniart gives representations of three--that for common pottery (Fig. 26), that for hard pottery (Fig. 27), and that for porcelain (Fig. 28). Those used in England often take the shape of a low, vaulted chamber, with the fire at one end, the chimney at the other, and the firing chamber between. In the United States, the usual shape for both earthen-ware and stone-ware is conical, not unlike a ball-cartridge. The common pottery kiln is divided, by means of baked plates, into cells, in which the wares are placed. The length of time during which they are kept in the furnace varies according to the nature of the ware. It may be twenty-four hours or, as in the case of fine stone-ware, several days. For some wares, seggars are used in place of the open cells; and the arrangement of the seggars may be seen in the porcelain kiln. When, in the case of non-vitrifying earthen-ware, a combination of firing and glazing in one operation is not practicable, the ware is kept at a white-heat for about thirty-six hours; and on the kiln cooling, the pieces then known as “biscuit” are removed for glazing. This operation consists of dipping it into the glaze, composed as previously mentioned, ground to a powder, and mixed with water until of the right consistency. The second firing melts the glaze, and covers the surface with a thin, transparent coating. The Italian potters gradually increased the heat for four hours, and allowed the ware to remain at a white-heat for twelve hours, and then to cool. Porcelain is fired according to its composition. For English porcelain, the first firing lasts about fifty hours; the second firing, after the glaze is applied, lasts about twenty hours or less, at a lower temperature. Soft-paste or artificial French porcelain takes from eighty to a hundred hours for the first, and thirty for the second, firing. The greatest caution is demanded in placing the pieces in the seggars and in regulating the heat. The chief peculiarity about the making of porcelain is that the glaze fluxes with the paste, and forms, with it, a translucent whole. [Illustration: Fig. 29.--Broome’s Improved Porcelain or Parian Kiln. A, ash-pit; G, grate; F F, flues; B B, bags for the flames; D, door for filling the kiln; E, damper, or draught regulator; S S S, spy-holes for watching, or trials while burning.] Mr. Isaac Broome, of Trenton, has invented a new kiln, of which an engraving is here given (Fig. 29). An equal distribution and perfect regulation of the heat are the features which commend it to attention.