CHEMISTRY. 27 



same gravity or weight, owing to difference in density : thus 

 lead weighs about twelve times as much as cork, bulk for 

 bulk, that is, it contains twelve times as much matter, and 

 hence it has twelve times the gravitating force. 



What this gravitating force is, has not been determined ; all 

 we know in relation to it is, its effects. Specific gravity, de- 

 notes the weight of any body, compared with some other body 

 of equal bulk, which is taken as a standard and is reckoned at 

 unity. Water is taken as the standard of specific gravity for 

 solids and fluids, while atmospheric ah- is the standard from 

 which the weight of the gases is estimated. 



DENSITY. 



By density, is understood, the compactness of bodies, or the 

 number of ultimate particles contained in a given bulk : bodies 

 which contain the most particles are most dense, that is, their 

 particles are in the closest proximity to each other. Rarity, or 

 porosity is opposed to density. Density does not depend upon 

 the peculiar kind of matter of which a body is composed, but 

 only upon the proximity of its particles. This is apparent, 

 from the fact that the lava ejected from volcanoes, if cooled 

 on the surface of the earth, produces a stone sufficiently light 

 and porous to float upon water, while if cooled under great 

 pressure at a distance below the surface, it forms a dense 

 heavy rock like granite. 



ELASTICITY. 



Elasticity is the property in bodies, which causes them to 

 resume their original form and bulk, after being bent, com- 

 pressed or condensed. Most solid and hard bodies possess 

 this quality in some degree : glass, ice, ivory, <fec. are elastic 

 solids : india-rubber is an exceedingly elastic body, while wet 

 clay is entirely destitute of this property. The gases are far 

 the most elastic of all bodies. 



