20 MECHANICS 



IMPENETRABILITY. 



Another property of matter is impenetrability , or 

 the inability of two portions to occupy the same space 

 at the same time. A nail driven into wood only 

 crowds the particles of wood asunder. Sugar will 

 dissolve in water, but the particles of the sugar only 

 pass in between those of the water. "Wood becomes 

 soaked with water by its entering the pores of the 

 wood. These pores are seen by means of a powerful 

 microscope, and are so small that one million have 

 been computed to exist m a space not larger than a 

 five-cent piece. 



INDESTRUCTIBILITY. 



Another property is indestructibility. Matter is 

 separated and changed in form from one body to an- 

 other, but never destroyed. When wood is burned in 

 the fire, it disappears ; but it is found that the smoke, 

 vapor, and ashes weigh as much as before, although in 

 a different form. The flashing of gunpowder appears 

 to destroy it wholly ; but if all the vapors and gases 

 are retained within a vessel, they are found to weigh 

 as much as the original soHd. Growing plants derive 

 all their weight from the soil and air ; they decay 

 again, and form the manure for new plants ; but none 

 of their particles are lost. They furnish food for ani- 

 mals, or are manufactured into different substances, 

 and, in all the changes they undergo, still retain their 

 existence. 



