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 rnain 

 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 off 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 satisfactory. 



TABLE I. 



TABLE II. 



