Then (_W_{a}_ - _W_{w}_)gives the weight of the water displaced. And (_W_{a}_ - _W_{l}_) gives the weight of the liquid displaced. Hence, (_W_{a}_ - _W_{l}_)/(_W_{a}_ - _W_{w}_) equals the specific gravity of the liquid. Important Topics 1. Definitions of density and specific gravity. 2. Methods of finding density: (a) regular solids; (b) irregular solids; (c) solids lighter than water; (d) liquids by hydrometer; (e) liquids by loss of weight. Exercises _Note._--Consider that 1 cu. ft. of water weighs 62.4 lbs. Consider that 1 ccm. of water weighs 1 g. 1. What is meant by the statement that a block of wood has a specific gravity of 0.6? 2. Considering that the density of the human body is the same as that of water, what is the volume of a 125-lb. boy? Of a 250-lb. man? Of a 62.4-lb. boy? What is the volume of your body? 3. How is the weight of large ships found? Give an example. 4. Mention three cases where determinations of density are important. 5. A body weighs 40 g. in air, 15 g. in water, 5 g. in an acid. Find (a) the density of the body; (b) its volume; (c) density of the acid. 6. If the specific gravity of a horse is 1, what is the volume of a horse weighing 500 kg.? Of one weighing 1248 lbs.? 7. A weighted wooden box sinks to a depth of 20 cm. in water and 24 cm. in alcohol, and to a depth of 18 cm. in brine. What is the density of the alcohol and of the brine? 8. A glass stopper weighs in the air 25 g., in water 15 g., in oil 18 g. Find the density and volume of the stopper. Find the density of the oil. 9. What would a cubic foot of wood weigh if the specific gravity were 0.5.? 10. The specific gravity of aluminum is 2.7. Find the weight of a cubic foot of it. 11. A block of wood weighs 40 g. A piece of lead appears to weigh 70 g. in water. Both together appear to weigh 60 g. in water. Find the density of the wood. 12. A stone weighs 30 g. in air, 22 g. in water, and 20 g. in salt water. Find the density of the salt water. 13. Will iron sink in mercury? Why? 14. A submarine boat weighing 200 tons must have what volume in order to float? 15. Find the weight of 2 cu. ft. of copper from its density. 16. What is the weight in water of a mass whose specific gravity is 3.3 and whose weight is 50 kg.? 17. A block of granite weighs 1656 lbs.; its volume is 10 cu. ft., what is its density? 18. If the specific gravity of hard coal is 1.75 how would you determine how many tons of coal a bin would hold? 19. A hollow copper ball weighs 2 kg. What must be its volume to enable it to just float in water? 20. A mass having a volume of 100 ccm. and a specific gravity of 2.67 is fastened to 200 ccm. of wood, specific gravity 0.55. What will the combination weigh in water? 21. A block weighing 4 oz. in air is tied to a sinker which appears to weigh 14 oz. in water. Both together appear to weigh 6 oz. in water. What is the specific gravity of the block? CHAPTER IV MECHANICS OF GASES (1) WEIGHT AND PRESSURE OF THE AIR