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. Rock 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- 



