THE FLOW OF WATER IN CONCRETE PIPE. 95 
method, are as stated by the author, namely, for from 12 to 24 inch 
pipes 71 = 0.011; from 26 to 48 inch pipe 71 = 0.0115; and for pipes over 
50 inches in diameter ti = 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, n=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 alwavs 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 
fine, 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 Kialto, San Bernardino 
County, Calif., which carried water from Lytle Creek. Attention was 
