AMERICAN INSTITUTE. 641 



4tli. The flow through them will also be the maximum, in con- 

 sequence of their smooth internal surface and uniform diameter, 

 and they will be less liable to be obstructed by collections of 

 sediment, or other matters which may find their way into them 

 with the water. 



5th. In consequence of greater perfection of form, the space for 

 lead in the joints may be reduced to the minimum thickness, and by 

 that means considerable saving effected in the cost of laying them. 



The quality of the metal used in the manufacture of pipes for 

 conveying water, is perhaps a matter of even more importance 

 than the mode of casting them; for if an improper kind of iron 

 is sekcted, no amount of skill on the part of the founder will 

 produce strong and durable castings. 



In order to produce sound, strong and durable pipes, it is 

 requisite that the iron from which they are made should be as 

 free as possible from the unreduced oxide, lime, silex and other 

 impurities, which are always present, in greater or less quantities, 

 in crude iron, as it flows from the blast furnaeej and also from 

 the excess of carbon which very rich pig iron contains. Of the 

 latter, according to a late writer on the manufacture of iron, 

 (Truran,) as much as eight per cent, by weight, is sometimes 

 found, or nearly thirty per cent, of the bulk; and if to this be 

 added the two or three per cent, by weight, of unreduced oxides 

 and earths, it will appear, that about one-third of the bulk of 

 such kinds of iron is composed of matters which inj ure its quality, 

 rendering it weak, porous and liable to rapid destruction by 

 oxidation. When water pipes are cast from iron of this quality, 

 (as is often done at blast furnaces,) and subjected to proof by 

 hydraulic pressure, they are generally found so porous, that if 

 they do not burst in the proof, the water finds its way through 

 the whole thickness of the metal.* 



* The writer onee saw four twelve inch f)ipes proved at the corporation yard, in New- 

 York, which had been sent there bj a blast furnace proprietor, in New-Jersey. They 

 were selected specimens of a lot which he had manufactured and desired to sell to the 

 corporation. They were proved at the ordinary pressure of 300 pounds per square inch, 

 »nd three out of the four failed in the proof. In this case, an examination of the broken 

 pipes showed that their failure was caused, partly, by the poor quality of the iron, which 

 contained an excess of carbon and unreduced oxide, and earths, and partly from the fact 

 ihait they were cast horizontally, in green sand moulds. 



[Am. Inst.] 41 



