526 FARM AND SCHOOL PROBLEMS. 



4. What is the weight of a cubic yard of gravel? 



5. Find the weight of 20 cubic ft. of oak? 



6. If a cubic foot of substance weights 1,030 ounces, what is its 

 specific gravity? 



7. What is the weight of a cubic yard of Anthacite coal ? 



8. How many cubic inches of silver will weigh as much as 10 cubic 

 inches of gold? 



9. How many cubic inches of lead will have to be fastened to a 

 cubic foot of cork so that the combined mass shall have the weight of a 

 cubic foot of water? 



10. A cubic foot of platinum is on the bottom of body of water, 

 100 feet deep; how many cubic feet of cork will be required to lift the 

 platinum to the surface? 



Specific Gravity of Soils. 



PER CUBIC FOOT. 



PROBLEMS. 



1. Find the weight of a cubic foot of each kind of soil named 

 in the above list and place weight at the right of the specific gravity. 

 (This will be a valuable table for reference in the study of soils.) 



2. How many times greater is the weight of a cu. ft. of water than 

 a cu. ft. of muck? Compare a cu. ft. of clean sand with a cu. ft. of 

 clay. Why is coarse sand heavier than clay loam? 



Abundance of Plant-food Elements in the Earth's Crust. 



One of the most abundant of plant foods is nitrogen which is 

 about 80 per cent, of the air. 



Among the eighty elements that are known to chemists are 

 those that are known to be of chief importance in the growth of 

 plants and animals. 



