3.9 | 4.53 | 920447.4 || 8.9 | 6.90 | 1556658.9 4.0 | 4.67 | 1055551.4 || 9.0 | 7.00 | 1579199.3 4.3 | 4.81 | 1086135.4 || 9.3 | 7.10 | 1601759.2 4.6 | 4.95 | 1116718.7 || 9.6 | 7.20 | 1624319.1 4.9 | 5.08 | 1146047.4 || 9.9 | 7.29 | 1644622.1 5.0 | 5.22 | 1177631.3 || 10.0 | 7.38 | 1664927.1 ==================================================================== HOW WATER ENTERS THE TILES. How water enters the tiles, is a question which all persons unaccustomed to the operation of tile-draining usually ask at the outset. In brief, it may be answered, that it enters both at the joints and through the pores of the burnt clay, but mostly at the joints. Mr. Parkes expresses the opinion, based upon careful observation, that five hundred times as much water enters at the crevices as through the pores of the tiles! If this be so, we may as well, for all practical purposes, regard the water as all entering at the joints. In several experiments which we have attempted, we have found the quantity of water that enters through the pores to be quite too small to be of much practical account. Tiles differ so much in porosity, that it is difficult to make experiments that can be satisfactory--soft-burnt tiles being, like pale bricks, quite pervious, and hard-burnt tiles being nearly or quite impervious. The amount of pressure upon the clay in moulding also affects the density and porosity of tiles.