USE OF CONCRETE PIPE IN IRRIGATION. 5 
cipal reasons for its extended use are its relative cheapness, dura- 
bility, strength, and general adaptability to irrigation requirements. 
An excellent quality of cement is made in scores of factories in the 
West and sold at relatively low prices, while the other ingredients 
of sand, gravel, rock-dust, and broken rock usually are found in 
close proximity to where the pipe is made. 
Fig. 1. — Form used in incasing riveted steel pipe with concrete. 
Concrete pipe is made both reinforced and plain, the former 
having more or less steel embedded in the concrete shell in order to 
increase its tensile strength. A few years ago plain concrete pipe 
was placed in the same class as vitrified clay pipe as regards tensile 
strength and limited to less than 15 feet head. This precaution was 
then necessary owing to the inferior quality of the pipe made, and 
failures were common even under less than 10-foot heads. In recent 
years a marked improvement has been produced by substituting a 
proper concrete mixture for the cement and sand formerly used and 
