186 



FARM ARITHMETIC. 



663. If the selling price of apples averaged during 

 that time 50 cents a bushel, what was the total value of 

 the crop on the undrained five acres ? 



664. The total value on the tiled five acres ? 



665. What is the percentage difference between the 

 tiled and untiled areas for the period of 20 years ? 



Size of tiles. The size of the tile to be used in a main 

 will depend on the fall, the area to be drained, and the 

 water delivered by sub-mains and laterals. To determine 

 the number of acres that a tile main of given size and 

 grade will drain, multiply the discharge in cubic feet per 

 second for a tile of the given size when laid on a one 

 per cent grade, by the square root of the per cent of the 

 grade in question, and this product by the proper con- 

 stant. This constant is 24 when it is desired that the 

 main shall be able to carry oflf in 24 hours an amount of 

 water equal to .a depth of one inch over the area drained ; 

 48, if one-half inch; 96, if one-fourth inch. This 

 constant is known as the standard. For most of the open 

 soils the one-fourth inch standard is used in practice, and 

 is found to be satisfactorv. 



Table I. 



Table II. 



