PIPES FOR IRRIGATION PURPOSES. 



115 



and toughened, in which state it is placed by machinery 

 into the pipe molds and subjedled to a pressure of at 

 least 350 pounds to the square inch. After being 

 pressed the lengths are allowed a week or longer to 

 dry, when they are removed to the kiln, stacked verti- 

 cally with the spigot ends down, kiln-burned for four 

 or more days, and, when properly burned, very grad- 

 ually and slowly cooled. The glassy coating which 

 modern clay pipes possess is due to the 

 sprinkling of salt over the heated pipe 

 in the kiln at the close of the burning. 

 Owing to the application of common 

 salt and to the high temperature used 

 in burning, common clay pipe is now 

 termed salt-glazed vitrified pipe. Fig. 

 24 shows a joint of vitrified pipe. In 

 laying this kind of pipe the joints are 

 fitted in the collars, and these are made 

 to rest on solid ground or are placed 

 upon blocks of stone or wood. The 

 lengths are usually two feet and the 

 pipe is calculated to stand the pressure of a dray team 

 with heavy load passing over it. A common sort of 

 clay or cement pipe is made the same as the vitrified, 

 but is not glazed and is not so lasting. To make this 

 pipe porous, sawdust is mixed with the clay and is 

 burned out during the baking process. 



The matters which principally require attention in 

 vitrified and cement pipes are leaks at joints, removing 

 roots from the inside of pipes, replacing cracked pipes 

 and doing the necessary earthwork, with the addition 

 of replacing worn-out pipes in the case of *the latter. 



FIG. 24. 

 VITRIFIED PIPE. 



