PIPES FOR IRRIGATION PURPOSES. 



113 



the same way, and some advantages are claimed for it 

 by manufacfturers. 



Laminated Iron Pipe. In California twenty 

 years ago the irrigators used plain sheet-iron pipes, 

 which soon corroded so badly that they were worn-out 

 completely and had to be taken up. The life of a 

 sheet-iron pipe depends on its coating, and without 

 some protection against oxidation the shell of the pipe 

 will soon be consumed by rust. Wrought-iron lami- 

 nated asphalted pipes are made of two shells of sheet 

 iron. These shells are made of one sheet of iron eight 



FIG. 23 — SPIRAL IRON PIPE. 



feet long, rolled and lapped one inch, and united by a 

 composition solder. They are half the thickness of 

 iron that would be necessary for the ordinary sheet- 

 iron pipe. The inner shell is telescoped into the outer 

 shell while immersed in hot asphalt especially pre- 

 pared, giving a thickness between the sheets one-six- 

 teenth of an inch or more if desired, thus making an 

 impassable barrier to corrosion from outside or inside. 

 The outside and inside coatings are also substantial. 

 This produces a solid shell eight feet long with an 

 inner surface free from all excrescences. The pipe is 

 also made double, of one sheet, by rolling a sheet that 

 is twice the width of the single sheet until the edges 

 will lap with a thickness of iron between them. The 



