112 



Bulletin 86 



mud. A piece of tar paper was then placed around the outside but 

 was left open at the top. Heated asphalt was then poured into the 

 joint and allowed to harden there. The cost of these expansion 

 joints was about $1.70 for each joint. 



The cracks did not appear to come in the pipe for several hours 

 or a few days after water was admitted, and in some cases one or 

 two weeks elapsed before the cracks appeared. It was very desir- 

 able to ascertain more directly the relationship between the satura- 

 tion of the pipe line and the expansion, to determine what may be 



Fig. 22. — Increase in weight and expansion of two 14-inch cement pipes. 



called a saturation-time curve showing the rate of absorption from 

 the time of the immersion, and also an expansion-time curve show- 

 ing the rate of expansion beginning at the time of immersion. This 

 was studied by immersing two 14-inch pipe that were about one and 

 a half years old and had been exposed to the sunlight and wind dur- 

 ing all of this time, in consequence of which they were absolutely 

 dry. The pipes were provided with metal discs inlaid on the sur- 

 face 20 inches apart from each other, and the exact distance between 

 points on these discs was determined to the nearest five-thousandth 

 of an inch. After weighing, one of the pipes was immersed entirely 



