This invention may also be applied, essentially in the manner described, to calcining-kilns, coke-ovens, or other analogous apparatus.

Fire-clay and terra-cotta clay are sometimes used to form columns, and often for the manufacture of hollow tiles for fire-proofing between iron floor and ceiling joists. When used for these purposes the clay should be fatty and plastic, with an idea to securing the necessary strength for the purposes for which the wares are to be employed.

In the United States Pension Office building now (1884) being constructed in the city of Washington, D. C., all the columns on the principal floor that support the galleries running entirely around the interior of the building, which is four hundred feet long by two hundred feet wide, are made of fire-clay, in separate sections, densely moulded and thoroughly burned. Each section of the column is circular, the thickness six inches and the diameters varying so as to taper from the bottom to the top. In the centre of each block or section there is a small circular hole about three inches in diameter, which allows good action for the heat while the block is in the kiln. The bottom section is carefully bedded in best Portland cement, and encircling it is a light cast-iron rim, forming the base of the column; each section is then laid level in Portland cement, and the hollow spaces in the centre of each block filled with a fine concrete made with Rosendale cement, which does not expand in setting. The surface of the column is then immediately smoothed over with Portland cement, which

is dampened with water once or twice a day, for several days, to prevent the too rapid drying of this slow setting cement.

The best cement for erecting or coating this kind of column is the one given at the end of Sec. I., Chapter VI. There is no danger from saltpetre if the cement is prepared as directed and with clean river sand.

When columns prepared in this way receive proper polychrome treatment, the effect in all classes of buildings is very pleasant, and can be made to form an attractive part of the design.

All medieval buildings were intended to be colored, and the color entered into and formed part of the original design, which in most cases has been lost from the practice of whitewashing them over, which so generally prevailed in the seventeenth and eighteenth centuries. Whenever this whitewash is removed carefully, the original coloring appears; but unfortunately, in getting off the whitewash, the original thin coat of fine plaster which formed the gesso or ground to paint upon, is removed in company with it.

In some instances the stone itself seems to have been painted upon, and the color mixed with wax varnish, which is impervious to moisture; and although these have been treated to repeated coats of the worse than senselessly applied whitewash, the coloring still reappears, seemingly in defiance of the ignorance which ordered its application.

At times the coloring was executed while the plaster was wet, in what is termed fresco painting, and thus became part of the plaster itself, and can be destroyed only by the destruction of the plastering.

As the style of carved ornaments changed, so did the style of coloring follow in company with it.

This may seem an out-of-the-way place to inject observations on the matter of artistic coloring, but as it is peculiarly applicable to the decoration of fire-clay columns and ceilings, liberty has been taken to sandwich it between these fire-clay productions, which are generally used only in such class of constructions as receive an artistic finish of this character.

Hollow tiles made of fire-clay are largely employed in fireproof construction for arches between floors, ceilings, and rafters; the pieces are so moulded as to form a perfectly keyed arch, and so laid as to break bonds or joints, when in place. They are much lighter than the brick arch and the usual mass of material used to weight the hause or haunch.

In order to give the plastering perfect hold, the ceiling face is roughly scratched before burning. With these tiles a level floor or ceiling can be obtained without furring or lathing; extra thickness of floors and consequent additional height of the building can also be saved. When made porous they absorb all dampness, which is carried off through the hollow spaces in the tile.

Hollow tiles can be used both for heating and for ventilating purposes; flues, ducts, chambers, etc., have been largely constructed with them in many of the United States Government buildings; and are now (1884) being largely employed in the reconstruction of the United States Patent Office building in Washington, D. C. The building was partially destroyed by fire September 24, 1877, since which time these tiles have been used for arches and sometimes for portions

in the reconstruction of the destroyed parts, and Congress has since ordered the remaining portions not touched by the flames to be taken out and made fire-proof, which is now being done.

These tiles have great elasticity to resist sudden impact, and an eight-inch tile arch with a span of five feet between beams will sustain, without deflection, more than 2000 pounds to the superficial foot of floor.

Some recent tests instituted by Gen. M. C. Meigs, now superintending the construction of the U. S. Pension Office building in Washington, as to the resistance of terra-cotta sheathing tiles to dead weight superimposed upon their surfaces, are of interest to builders in all sections of the country, and particularly so to those desiring a cool, non-conducting material for roofing and flooring. The tiles used in the Pension Office are to be covered with an external tunic of metalroofing, in order to protect them. They are of ordinary pattern, with three rectangular holes running longitudinally through them from end to end, thus insuring dryness, lightness, and atmospheric circulation. The dead weight was applied to the middle of the tiles that were tested, the edges being so supported as to leave a clear span of 22 inches. Tiles of pure clay sustained a weight of 2394 pounds before yielding, while those of mixed clay and sawdust gave way under a dead pressure of 1940 pounds-a resistance amply sufficient for the practical purposes of flooring material, to say nothing of roofing in either case. Indeed, the fire-proof flooring of the new Columbia College Law School-one of

the most elegant Gothic structures erected in New York during the last five years-is composed of tiles of the kind tested by Gen. Meigs, protected at the surface by a tesselated fabric of colored marbles. The tiles are all perforated longitudinally, thus adding to the ventilation resources of the building and obviating the dampness that seems to be unavoidable in floors of common brick, while at the same time securing a degree of resistance to heat that can hardly be predicted of ordinary brick and cement. The use of sawdust, one-third woody débris to two-thirds of clay, it appears, renders the tiles considerably lighter and more elastic, without to a sufficient degree impairing their availability for roofing or even for flooring, providing the protection from sharp percussion is adequate to the purpose; and the coolness of such roofs and floors in the hottest days in summer has also been verified by experience in several buildings in New York City.

The tiles which were tested as above stated were made by the Potomac Terra-Cotta Company of Washington, D. C.

Fig. 120 shows three views of hollow tile fire-proof floors; the first is a 6-inch form, between 6-inch light I beams, span 4 feet, concrete 2 inches thick on which is a tile floor.

The second is an 8-inch tile arch, between 10-inch I beams, span 5 feet, 2 x 4, furring strips are shown bedded in the concrete in case board floors should be desired.

The third view represents a 12-inch arch laid between 15-inch I beams, ready for either marble, tile, wood, or cement floor finish.

If uniformity in design is essential, the hollow tiles can