TILE DK A IN AGE 



35 



closely together and prevent the washing in of sand and 

 silt. Nos. 1 and 2 of the illustration on the cover page 

 show two badly formed tiles, while 3 and 4 are almost 

 perfect. 



In regard to the shape of tile there is a difference of 

 opinion. Makers of the six and eight-sided tiles claim 

 that they Avill lie in place better than the round. If the 

 bottom of the ditch is grooved, however, there is little 

 chance for the round tile to get out of place. One ad- 



FiG. 8. Showing lime pebbles and effects of frost on tile. 



vantage of the round tile is that if the ends do not fit 

 closely in one position it can be turned around any dis- 

 tance until a close fit is obtained. Another point to be 

 considered in favor of the round tile is its greater strength. 

 In making a tile six-sided, the thickness of the walls is 

 reduced nearly one half at the center of each side so that 

 its strength is proportionately diminished. As the result 

 of some crushing trials with round and six-sided tiles 

 selected with as nearly the same hardness as possible, it 



