44 WELLS'S NATURAL PHILOSOPHY. 



pearanco of the gold. The specific gravity of pure gold being 19, and of pure 

 silver 10, it is obvious tliat a mixture of the two -will have a specific gravity 

 less than pure gold, and greater than pure silver, the diflerence being propor- 

 tioned to the amount of adulteration. In the same way we can determine 

 whether cheap oils have been mixed with expensive oils, cheap and poor il- 

 luminating gas, with expensive and brilliant gas. In any case it enables U3 

 to ascertain the exact size or solid bulk of a mass, however irregular — evcQ 

 of a bundle of twigs.* 



PRACTICAL PROBLEMS RELATING TO SPECIFIC GRAVITY. 



1. The weight of a solid body is 200 grains, but its weight in water is only 150 grakis; 

 -what is the specific gravity of the body ? 



Solution: 50 grains = loss of weight in water; 200 grains (weight in air)-^50— 4, spe- 

 cific gravity required. 



2. A body weighed in the air 28 pounds, and in water 2-1 pounds ; what is its specific 

 gravity ? 



3. An irregular fragment of stone weighed in air 73 grains, but lost 30 upon being 

 weighed in water; what was the specific gravity of the stone? 



4. A piece of cork weighed in the air 4S grains, and a piece of brass 560 grains ; the 

 brass weighed in water 4S3 grains, and tts brass and cork when tied together weighed in 

 water 336 grains. What was the specific gravity of the cork ? 



5. How much more matter is there in a cubic foot of sea-water, than in a cubic foot of 

 fresh water ? 



6. Would a piece of steel sink or swim in melted copper? 



7. Wlien alcohol and whale-oil are put in the same vessel, which of these two sub- 

 stances will occupy the top, and which the bottom part of the vessel? 



8. If a cubic foot of water weigh 1,000 ounces, what will be the weight of a cubic foot 

 of lead ? 



9. What will be the weight of a cubic foot of cork, in ounces and in pounds 7 



• The attempt to ascertain whether a particular body had been adulterated led Archi- 

 medes, it is said, to the discovery of the principle of specific gravity. Iliero, King of 

 Syracuse, having bought a crown of gold, desired to know if it were formed of pure mctfll ; 

 and as the workmanship was costly, he wished to accomplish this without defacing it. 

 The problem was referred to Archimedes. The philosopher for some time was unable to 

 solve it, but being in the bath one day, he obseived that the water rose in the bath in ex- 

 act proportion to the bulk of his body beneath the surface of the water. He instantly per- 

 ceived that any other substance of equal siz3, would raise the water just as much, thongh 

 one of equal weight and loss size, or bulk, could not produce the same effect. Convinced 

 that he could, by the application of this principle, determine whether Hiero's crown had 

 been adulterated, and moved with admiration and delight, he is said to have leaped from 

 the water and rushed naked into the street, crying " Evpi7<fa ! EvpriKu !" " I have found it! 

 1 have found it !" In order to apply his theory to practice, he procured a mass of pure gold 

 and another of pure silver, each having the same weijxht as the crown ; then plunging the 

 three metallic bodies successively into a vessel quite filled with water, and having carefully 

 collected and weighed the quantity of liquid which was displaced in each instance, he 

 ascertained that the mass of pure gold, of the same weight as the c-own, displaced less 

 water than the crown ; the crown was, therefore, not pure gold. The mass of pure silver 

 of the same weight as the crown, displaced more waterthan the crown; the crown, there- 

 fore, was not pure silver, but a mixture of gold and silver. 



