86 



IRRIGATION FARMlXi,. 



order to obtain the desired grade. Steel pipe is made up 

 substantially in the same way as described under fore- 

 going headings. 



Vitrified Clay Pipe. The materials employed 

 and the mode of manufacturing clay pipe do not differ 

 essentially from those of pressed brick. Suitable clay 

 mixed with loam is first ground dry, then moistened and 

 toughened, in which state it is placed by machinery into 

 the pipe molds and subjected 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 gradually and 

 slowly cooled. The glassy coating 

 which modern clay pipes possess is due 

 to the sprinkling of salt over the heak-d 

 pipe in the kiln at the close of the 

 burning. Owing to the application of 

 common salt and to the high tempera- 

 use( l i 11 burning, common clay pipe 

 1>11M is now termed salt glazed vitrified pipe. 



Figure 23 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 vitri- 

 fied 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 



