FARM WATER-WORKS 157 



sufficient, but if dependence is to be placed upon a windmill the 

 tank should be of a capacity to tide over a week of still weather. 



The amount of water required for each person on a farm, 

 including the water used for drinking, cooking and washing, is 

 commonly placed at 10 gallons, but, if water-closets and bath- 

 rooms have been installed, the amount is likely to be nearer 25 

 gallons. Each horse or cow consumes about 10 gallons, each pig 

 2 gallons and each sheep about I gallon. A large farm will 

 hardly get along with less than 500 gallons daily, while in some 

 cases the amount used reaches a total of several thousand gallons. 



Each foot of elevation above a water tap would give about 

 half a pound of pressure if it were not for the loss of head due to 

 pipe friction. This amounts to considerable in the case of moder- 

 ate flows through small pipes. For instance, water flowing at 

 the rate of 5 gallons a minute through a f-inch pipe (inside diam- 

 eter) loses 3! pounds of pressure (equivalent to a head of about 

 6 feet) for each 100 feet of pipe. A i-inch pipe loses about 

 0.8 pound, a i^-inch pipe i pound, and a 2-inch pipe ^V pound 

 of pressure for each 100 feet of pipe when the water is flowing at 

 the same rate. It is evident that pipe friction must be taken 

 carefully into account when the height of a tank intended for 

 supplying given buildings is to be determined. 



The makers' prices for wooden (cypress) tanks are approxi- 

 mately $5.50 for a tank of 175-gallon capacity, $12 for one of 600 

 gallons, $20 for 1000 gallons, and $28 for one holding 2000 gallons. 

 Steel tanks of the same capacity cost respectively about $5, $11, 

 $17 and $26. A 2O-foot steel tower to hold a zooo-gallon tank 

 will cost about $40, or, if 40 feet high, about $75. The tower for 

 a 25OO-gallon tank should cost about $65 if 20 feet high, or about 

 $125 if 40 feet high. The cost of pipes has been already indicated. 



Pneumatic or Pressure Tanks. -- These are vertical or hori- 

 zontal tanks of varying capacity, into which, after the outlets have 

 been closed, water is pumped from a well or other source of supply. 

 As the water rises the air is compressed, the pressure increasing 

 to i, 2 and 3 atmospheres as the air is compressed to |, $ and J 



