STONE, ARTIFICIAL

for statuary and other decorations of architecture, has been made for several years with singular succe at Berlin, by Mr. Feilner. His materials are nearly the same with those of English pottery; and the plastic ma is fashioned either in moulds, or by hand. His kilns, which are peculiar in form, and economical in fuel, deserve to be generally known. Figs. 1069. and 1070. represent his round kiln; fig. 1069. being an oblique section in the line A , B , C , of fig. 1070. , which is a ground plan in the line D , a , b , E , of fig. 1069. The inner circular space c , covered with the elliptical arch, is filled with the figures to be baked, set upon brick supports. The hearth is a few feet above the ground; and there are steps before the door d , for the workmen to mount by, in charging the kiln. The fire is applied on the four sides under the hearth. The flame of each pa es along the straight flues f i , f i , and f k . In the second annular flue g , g , as also in the third l , l , the flame of each fire is kept apart, being separated from the adjoining, by the stones h and m . In the fourth flue n , the flames again come together, as also in o , and ascend by the middle opening. Besides this large orifice, there are several small holes, p , p , in the hearth over the above flues, to lead the flames from the other points into contact with the various articles. There are also channels q , q , in the sides, enclosed by thin walls r , to promote the equable distribution of the heat; and these are placed right over the first fire-flues e . The partitions r , are perforated with many holes, through which, as well as from their tops, the flame may be directed inwards and downwards; s are the vents for carrying off the flames into the upper space u , which is usually left empty. These vents can be closed by iron damper-plates, pushed in through the side-slits of the dome. t , t , are peep-holes, for observing the state of ignition in the furnace; but they are most commonly bricked up. Fig. 1071. is a vertical section, and fig. 1072. a plan, of an excellent kiln for baking clay to a stony consistence, for the above purpose, or for burning fire-bricks. A , is the lower; B , the middle; C , the upper kiln; and D , the hood, terminating in the chimney E . a , a , is the ash-pit; b , b , the vault for raking out the ashes; it is covered with an iron door c . d , is the peep-hole, filled with a clay stopper; e , is the fireplace; f , f , a vent in the middle of each arch; g , g , flues at the sides of the arches, situated between the two fireplaces; h , i , k , are apertures for introducing the articles to be baked; l , a grate for the fire in the uppermost kiln; m , the ash-pit; n , the fire-door; o , openings through which the flames of a second fire are thrown in. At first, only the ground kiln A , is fired, with cleft billets of pine-wood, introduced at the opening e ; when this is finished, the second is fired; and then the third, in like manner. This kiln is very like the porcelain kiln of Sèvres, and is employed in many places for baking stoneware. Mr. Keene obtained a patent, about a year ago, for making a factitious stone-paste in the following way:—He di olves one pound of alum in a gallon of water, and in this solution he soaks 84 pounds of gypsum calcined in small lumps. He exposes these lumps in the open air for about eight days, till they become apparently dry, and then calcines them in an oven at a dull-red heat. The waste heat of a coke oven is well adapted for this purpose. (See Pitcoal, coking of .) These lumps, being ground and sifted, afford a fine powder, which, when made up into a paste with the proper quantity of water, forms the petrifying ground. The ma soon concretes, and after being brushed over with a thin layer of the petrifying paste, may be polished with pumice, ., in the usual way. It then affords a body of great compactne and durability. If half a pound of copperas be added to the solution of the alum, the gypsum paste, treated as above, has a fine cream or yellow colour. This stone stands the weather well.