148 SEWER DESIGN 



gallons per mile for the two places, respectively, or 122 and 

 136 gallons per square yard. It is absurd, however, as Mr. 

 Folwell himself points out, to expect that such leakage as this 

 is reasonable, and it only serves to illustrate what large flows 

 may occur through badly built brickwork. 



If the sewer is of vitrified pipe, ground-water enters the 

 pipe through the joints, and the amount to be expected depends, 

 assuming perfect workmanship, on the kind of cement, depth 

 of joint, and other details of construction of the joint. In 

 Vol. XIII, p. 71, of the Journal of the Association of Engineer- 

 ing Societies, are given the results of some tests by Freeman 

 C. Coffin, C. E., made to investigate this very point. His 

 results are given as follows: 



" In the standard form of pipe-socket, with well-made 

 joints of either Portland cement, neat or i : i, or of Rosendale 

 cement i : i, with over-filled joints, the leakage would not be 

 serious, probably not exceeding 1000 gallons per mile per day, 

 with the level of the ground-water from 2 to 8 feet over the pipe. 



" In pipe with deep sockets the tests indicate that if the 

 joints are well made the leakage will be about as follows: In 

 Rosendale cement neat it will be very large, perhaps over 

 100,000 gallons per mile per day. In Rosendale cement mixed 

 with sand i : i the leakage would not exceed 700 to 800 gallons 

 per mile per day. In Rosendale i : 2 it would approximate 

 1000 or 1200 gallons per day; with Portland cement neat, 

 about 150 gallons per day; with Portland i : i, about 500 or 

 600 gallons." 



The sockets of these pipes were very small to reduce the 

 area of cement as much as possible, and Mr. Coffin thinks 

 that even with the best intentions the difficulty of filling these 

 joints in a trench would be insurmountable, and he therefore 

 gives the figures above as representing only what can be done 

 in a laboratory experiment. 



In the discussion of the above conclusions, Mr. Coffin says 

 that it would seem that Portland cement, either neat or mixed 

 i : i, or Rosendale i : i, would make work that was suffi- 



