PIPES FOR IRRIGATION PURPOSES. 



for the ordinary sheet-iron pipe. The inner shell is tele- 

 scoped into the outer shell while immersed in hot asphalt 

 especially prepared, giving a thickness between the sheets 

 one-sixteenth 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 01 the single sheet until the edges will lap with a 

 thickness of iron between them. The lap is riveted. 

 This is dipped in asphalt, but it cannot have the inter- 

 mediate 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 practically 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 cor- 

 rodes 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 a variety in the 

 ' methods of production, it is necessary in order to secure a 

 uniform suitable product that the specifications be unusu- 

 ally specific and stringent, that the material be inspected 

 at the mills, and that the appropriate tests be made in 



