THE FLOW OF WATER IN CONCRETE PIPE. 95 



method, are as stated by the author, namely, for from 12 to 24 inch 

 pipes ^ = 0.011; from 26 to 48 inch pipe 71 = 0.0115; and for pipes over 

 50 inches in diameter n = 0.012. 



On the other hand, pipes made with a wet mix and laid with equal 

 care by using the brass-band device, or some other method for making 

 the joints smooth, should show better results, probably about as 

 follows : 



For pipes 12 to 24 inches in diameter, n=0.010 to n=0.0105. 



For pipes 26 to 48 inches in diameter, ?i=0.0105 to n=0.011. 



For pipes over 50 inches in diameter, n=0.011 to n=0.0115. 



In reference to the decrease of carrying capacity in concrete pipes, 

 after they are laid, the writer has formed the following opinions from 

 his own personal observations: 



First. There is no risk of interfering with the carrying capacity of 

 concrete pipes on account of roots entering them if they are properly 

 made and laid. There is no case of record where roots have entered 

 cement pipes, unless they were made without being properly tamped, 

 or the spaces in making field joints were not properly filled with 

 mortar. 



In this respect concrete pipes are different from vitrified-clay pipes, 

 from which it is very difficult to exclude the roots of certain trees. 

 This difference is due to the fact that it is not easy to cause proper 

 adhesion between cement mortar and vitrified clay, when making 

 field joints, while perfect adhesion between a concrete pipe section 

 section and the mortar used for making joints can always be had, so 

 as to eliminate all possibility of roots entering at the joints. 



Second. Some concrete pipes have become deteriorated through 

 scour, the surface having become pitted and rough. Several cases of 

 this kind have been observed by the writer in southern California. 



Such instances, however, are due to one of two things, either on 

 account of too little cement in the concrete from which the pipes were 

 made, or subjecting properly made pipes to unreasonable water 

 velocities, particularly when the water carries sand or silt. Proper 

 engineering will prevent anything of this kind, as every case where it 

 has been done is an instance of design and construction without 

 proper engineering advice. 



Third. It is possible, under many conditions, to have accretions 

 occur on the interior of concrete pipes, whereby their capacity will be 

 decreased. The most frequent cause of this is the deposition of 

 mineral carried by the water in solution, either in its pure form or 

 combined with silt and sand, carried by the water in suspension. 



As shown by the author, the most common mineral causing depo- 

 sition on the interior of concrete pipes in southern California is 

 bicarbonate of lime, and this will apply equally to any other locality 

 where waters contain bicarbonate of lime in solution. Unless the 

 water is very heavily impregnated with bicarbonate of lime and the 

 velocity in the pipe is rapid, the deposition is very slow and would 

 require a long time to make much change in the capacity of a pipe 

 line, unless the water also carries such matter as silt, sand, and fine 

 gravel in suspension. 



The writer has observed that the deposition of bicarbonate of lime 

 is much more rapid from water which is warm than from cold water. 

 This observation was made in connection with steel and iron pipes in 

 the domestic water system in the city of Bialto, San Bernardino 

 County, Calif., which carried water from Lytle Creek. Attention was 



