114 IRRIGATION FARMING. 



lap is riveted. This is dipped in asphalt, but it cannot 

 have the intermediate lamina- of asphalt, which is the 

 main advantage of the laminated over the single sheet- 

 iron pipe. Both these descriptions of pipes are jointed 

 end to end, an inner sleeve being fixed in the shop. 

 In laying, the end is dipped in hot asphalt and an 

 outer sleeve is also dipped and pressed on by a clamp 

 over the joint until the asphalt is set. Bends and 

 branches are of cast iron, as in the ordinary sheet-iron 

 pipe, and the joints are made with cement. 



Steel Pipe. — Owing to freight charges cast-iron 

 pipe is pracftically barred in the western countries, and 

 the steel pipe is fast superseding it as well as all forms 

 of iron pipe. The present price of steel is rather less 

 than that of iron, and since steel suitable for this class 

 of work is twenty per cent stronger than the best 

 wrought-iron there is no good reason why this large 

 saving in cost should not be made. The claim that 

 wet soil corrodes steel more rapidly than it does iron 

 does not seem to be substantiated by experience. Since 

 there are so many grades of steel and there is so great 

 variety in the methods of produdlion, it is necessary in 

 order to secure a uniform suitable produdt that the 

 specifications be unusually specific and stringeni, that 

 the material be inspe<5led at the mills, and that the ap- 

 propriate tests be made in order to obtain the desired 

 grade. Steel pipe is made up substantially in the 

 same way as described under foregoing headings. 



Vitrified Clay Pipe. — The materials employed 

 and the mode of manuf adluring clay pipe do not differ 

 essentially from those of pressed brick. Suitable clay 

 mixed with loam is first ground dry, then moistened 



