BURNING DRAIN-T1LE.
In the burning of drain-tile, as in the burning of sewer-pipe, it is essential that the tile should be thoroughly dry ; the drier the tile the better the success to be attained. The time, fuel, and other items of cost, which have to be expended for the thorough drying of the tile in the kiln, might just as well be saved, if possible, by utilizing the natural method of drying. The manner of setting the tile in the kiln is also an imporant item, and the method employed varies with the various kilns in use. When the Dutch or open-top kiln is employed, it is usual to set the small tile in the bottom of the kiln; the larger tile is then placed in the central tier, the smallest tile being placed in the upper portion of the kiln, and in no case should the tile be allowed to come in contact with the walls ; a space of about one inch and a half should be left open all around the side of the kiln. When the up-draft or crown-top kilns are employed for burning drain-tiles, the method of setting is similar to that which has just been described, although it is found from ex perience that better results are obtained if the tile of the largest diameter are set near the top. When the down-draft kiln is used for burning the drain-tile, it is desirable that the large tile should be set at the too, care being observed, however, not to place the larger tile at the points of extreme heat. And in kilns of this character it is desirable that, if there are any tiles which are not thoroughly dry, they should be set at the bottom of the kiln, so as to obviate the necessity of driving the water smoke from the damp tile through those which are dry.
The method of nesting the tile varies with different clays ; some clays will allow close nesting, while other clays require to to be nested very openly. No rule for nesting the tile can be laid down ; the best method to be employed can be developed only from thorough knowledge of the practical qualities of the clay to be burned. In order to avoid the cracking and loss from improper nesting, it is desirable that, where defects of this character occur, the cause should be thoroughly investigated and a memorandum made of the result upon the books at the works. If some such simple system as this could be adopted
in the various clay-works of the country, and the result of the practical experiences could be brought out at the conventions, or recorded in the pages of the journals devoted to the clay industry, great good would result to the trade in many of its branches.
In firing the tile care should be observed not to push the burning too rapidly ; only a light fire should at first be used in the fire-box ; then the heat should be raised very gradually, fuel being added in smallest quantities, as nothing is to be gained from pushing the burning of the tile in its early stages. The water-smoke must be driven off gradually, but surely, until at last none of it can be discerned mixed with the blue-black smoke which issues from the top of the flues or stack. Patience worketh wonders in burning drain-tile, as in burning all other classes of clay products. Of course the drier the tile the quicker the kiln may be burned off; but, as it is not possi ble to have all of the tile of a uniform degree of dryness, all the dry tile have to be held back until the moisture has been thoroughly driven from the damp tiles, otherwise crushing, cracking, and other losses will result. Even after the water smoke has been thoroughly driven off, it is desirable not to push the burning too rapidly; gradually increase the heat until the tile have been brought to nearly the melting-point, and at this temperature the heat should be maintained for two or three hours ; great caution, however, should be observed not to in crease the heat to the actual fluxing point, for in such a case the tile would run together and the kiln prove a loss. With some clays, however, it will be necessary to maintain the final heat all the way from four to eight hours. The kiln, when burned off, should remain closed for about twenty to twenty four hours, after which time it may be gradually opened and allowed to cool.