Tests 



119 



be strengthened somewhat by anchored bearings, but at the center 

 of the pipe a shearing stress is developed which might induce failure 

 under some extreme conditions. This shearing stress will be a 

 mathematical average in value between the unit tension and the 

 unit compression, both being considered as positive and will be a 

 maximum on an angle of 45 degrees. In all the tests at the City- 

 Water Works no pipe was observed to fail while the jackscrew was 

 being turned in the effort to reduce the leakage past the gaskets. 



Fi^ 



Tl'SL specimens biukL-u in intni nul-in^ 



lilt- te.stiiig" machine. 



Nor were there any breaks which showed a failure in shear at the 

 midheight of the specimen. On a similar testing frame recently 

 three men attempted to break an 8-inch pipe by applying the utmost 

 pressure, but were unable to injure the pipe. 



The record of tests, excluding some that were rejected, is given 

 in Tables VIII and IX. The first of these two tables gives the pre- 

 liminary measurements and age of the test pieces, and the second 

 table gives the results of the tests. 



Examination of Table VIII proves that the wall thickness of 

 machine-made pipe is very uniform, the variation being less than 

 one-eighth inch. The thickness of hand-made pipe is uniform at the 



