156 Bulletin 86 



percentage of the pipe were light on the exterior, yellow on the 

 fracture, and were therefore much underburned. 



After these tests the author took steps to ascertain the practice 

 in other cities. The first city to use a percolation test was Brook- 

 lyn, and the reason there was that many of the sewer lines are be- 

 low groundwater level and the sewage has to be pumped into the 

 seas; therefore, if the pipe is pervious a considerable volume of 

 groundwater will have to be handled by the pumps. Kansas City 

 adopted the Brooklyn specification, although the reasons for using 

 it at Brooklyn did not exist at Kansas City. Furthermore, it was 

 found very early that any pipe which stands the internal pressure 

 test of 33 pounds per square inch will stand the percolation test of 

 10 pounds (no duration of time being stated), and hence the test 

 fell into disuse, although it was still retained in the specifications. 

 At the author's request, the city engineer of Kansas City on Decem- 

 ber 11, 1916, kindly tested six clay pipe for percolation. The sizes 

 ranged from 8-inch to 21-inch, and all six pipes withstood 15 pounds 

 for 5 minutes with "no percolation." It is evident that the pipe 

 clay of the Middle West is superior to that of California or that the 

 art of burning the pipe is better developed in the Middle West. 



It has been suggested* that the percolation test be replaced by 

 the test for absorption, that is, to ascertain not under v.'hat pressure 

 the pipe begins to sweat, but what proportion of the pipe is voids. 

 However, in the tests of sewer pipe at Tucson the pipe which 

 showed the least porosity was one which sweat freely and uni- 

 formly all over when tested for perviousness. Also no definite re- 

 lation between porosity and strength of clay pipe has been deter- 

 mined. The absorption test is easier to make than internal press- 

 ure and percolation tests, but since it fails of having a definite 

 significance, it would seem that in those cases where percolation 

 is of importance the percolation test should be retained. The speci- 

 fication requirements for percolation should be modified to fit the 

 actual conditions in each case. 



Sewer pipe is not subjected, ordinarily, to more than one or two 

 pounds pressure, and it is the common belief of engineers that 

 sewer pipe, either clay or cement, soon becomes sealed up and 

 covered with a slime. A slight percolation when the pipe is new 

 might result in a damp soil surrounding the pipe, but oxidation 

 would prevent any objectionable result, excepting in those cases 

 where the pipe is laid below or near the water table and in the 

 vicinity of domestic water supplies. 



•EnKln. News. Vol. 77. No. 8. Feb. 22. 1917. p. 329. 



