USE OF CONCRETE PIPE IN IRRIGATION. 11 
distorted pipe. Such pipe is more difficult to lay, but if care is 
taken in laying it should be satisfactory. Some of the pipe that 
presents the most attractive appearance in the yard may be of poor 
quality on account of having been mixed too dry. 
The best grade of pipe for use against pressure should withstand 
a heavy blow with a hammer and should give a clear, ringing sound. 
The pipe should be dense when broken and be difficult to scratch with 
a knife. The best pipe can be thrown from a wagon to the ground 
without breaking, although this is not recommended except for a 
test. 
The best grades must also be made from materials that will pass 
the test for any good concrete work. As much hard, broken rock or 
gravel containing a high proportion of hard pebbles should be used 
as can be incorporated. High-pressure pipe often contains as much 
as 50 per cent rock and is made with 1 part of cement to 3 
parts of aggregate. Pipe for use under low pressures is often made 
of 1 part of cement to 5 parts of sand and rock. Some machines 
will not handle a large proportion of rock and with such more cement 
must be used to get the same grade of pipe. Machines are usually 
more reliable for compressing the concrete, and the product is liable 
to be more uniform. At the same time some of the most reliable pipe- 
making firms in the West are using hand-tamped methods, and guar- 
anteeing their product. 
Some farmers buy equipment for making hand-tamped pipe and 
make their own pipe. This practice is not to be encouraged as a 
rule, as experience is necessary if a reliable product is to be turned 
out. The saving in cost is small in many cases, and failures may 
make this method an expensive experiment. The safest thing for a 
farmer to do is to buy pipe from a reliable firm, have the same firm 
lay the pipe, and demand a guaranty that the pipe will conform to 
the specifications. 
It is not intended to discuss the best materials required for making 
concrete pipe, as this subject will be taken up in another bulletin. 
Briefly stated, however, the sand should be clean, the rock clean, hard, 
and durable, and the whole aggregate well graded. If gravel is used, 
the materials should be clean and hard, with a minimum amount of 
organic matter. The presence of clay or silt free from organic mat- 
ter in the gravel may not be harmful, and tends to make an imper- 
vious pipe if it is not present in too large quantities. Bock dust 
may be added with benefit to the pipe, while a certain proportion of 
lime will tend to make an impervious pipe. Soft or partially disin- 
tegrated rock or gravel is very harmful, especially if high-pressure 
pipe is desired. When possible, materials should be tested in the 
laboratory or test lengths of pipe made, which can be tested to fail- 
