72 LAND DRAINAGE 



jected in burning. The heat is sufficient partially to 

 fuse or melt the material, and thus to render the walls 

 stronger and much more impervious to water. Vitrified 

 tile, like other kinds, when placed above the frost line, 

 may become filled with water which, in freezing, expands 

 and shatters them. At present, vitrified tile is made not 

 only round, as is the common clay tile, but also in hex- 

 agonal shape. It is a question whether hexagonal shapes 

 are desirable, for reasons which will appear when the 

 discussion of the laying of tile is taken up. Note com- 

 ments in paragraph 109. 



107. Cement tile. Within the past few years the 

 manufacture of cement tile has become common, and 

 numerous machines are to be secured on the market for 

 their manufacture. 



108. Difficulties with cement tile. While much is 

 claimed for the efficiency and durability of cement tile, 

 it has not yet been proved that they may be used suc- 

 cessfully even on upland soils. On lowland and muck 

 soils, numerous cases have been observed of their failure 

 to endure. Several instances have come to the writer's 

 attention where, within three months after laying in com- 

 mon muck soils, the cement tile were found to have seri- 

 ously crumbled and, in many cases, to have collapsed. 

 This may have been due to improper mixing. It did 

 not appear to be due to a lack of richness in cement. The 

 uniformity with which cement tile in muck soil crumbled 

 on the upper surface seemed to indicate that the crumbling 

 was not a mere matter of accident, but rather an indication 

 of the presence of a solvent in the downward moving 

 soil-water. A number of instances are reported in which 

 cement tile have shown a similar crumbling in loam and 

 sandy soils. Patten and Musselman, of the Michigan 



