FARM DRAINAGE. 187 



666. How many acres will a 10-inch main drain when 

 laid upon a grade of 2 inches per 100 feet, using the half- 

 inch standard? 



Process : 



D = discharge of the tile (Table I). 



R = square root of grade (Table II). 



S = standard. 



A = area in acres to be drained. 



A = D X R X S. 



A = 2.05 X -40 X 48 = 39 acres. 



667. How many acres will a 10-Inch main drain when 

 laid upon a grade of 3 inches per 100 feet, using the half- 

 inch standard ? The quarter-inch standard ? 



668. How many acres will a 6-inch main drain when 

 laid on a grade of 3 inches per 100 feet, using the quarter- 

 inch standard? The half-inch? 



669. How many acres will a 6-inch main drain when 

 laid on a grade of 6 inches per 100 feet using the quarter- 

 inch standard ? The half-inch ? 



670. How many acres will a 6-inch main drain when 

 laid on a grade of 9 inches per 100 feet, using the half- 

 inch standard ? The inch ? 



671. How many acres will a 6-inch main drain when 

 laid on a grade of 12 inches per 100 feet, using the half- 

 inch standard? The quarter-inch? 



672. How many acres will a 4-inch main drain when 

 laid on a grade of 6 inches per 100 feet, using the half- 

 inch standard? The quarter-inch? The inch? 



673. How large a main should be used on a grade of 

 6 inches per 100 feet to drain 230 acres, using the quarter- 

 inch standard? The inch? 



674. How large a main should be used laid on a grade 



