SCIENCE OF COMMON THINGS. 65 



Iron ships. Movement Of stores in water. Capillary attraction. 



SOT* Why does not a vessel constructed of iron sink, as the iron is much 

 heavier than the water ? 



Because the vessel is constructed in a concave form, 

 and is thus rendered buoyant. Every substance be- 

 comes lighter in water, in proportion to the amount of 

 water displaced. This is a law of nature: if it dis- 

 places less water than its weight in air, it sinks; if 

 more, it floats. The ship, being concave, displaces a 

 greater weight of water than the weight of the iron of 

 which it is composed in the air. 



A thick piece of iron, weighing half an ounce, loses in water nearly 

 one-eighth jf its weight ; but if it is hammered out into a plate or vessel, 

 of such a size that it occupies eight times as much space as before, it then 

 loses its whole weight in water, and will float, sinking just to the brim. 

 If made twice as large, it will displace one ounce of water, consequently, 

 twice its own weight ; it will then sink to the middle, and can be loaded 

 with half an ounce weight before sinking entirely. 



398 Why are stones, gravel, and sand so easily moved by waves and 

 currents ? 



Because the moving water has only to overcome 

 about half the weight of the stone. 



399 Why can a stone which, on land, requires the strength of two men 

 to lift it, be lifted and carried in water by one man f 



Because the water holds up the stone with a force 

 equal to the weight of the volume of water it displaces. 



CHAPTER III. 



CAPILLARY ATTRACTION. 



400 Why does water melt salt ? 



Because very minute particles of water insinuate 

 themselves into the pores of the salt by capillary at- 

 traction, and force the crystals apart from each other. 



401 Why does water melt sugar f 



Because very minute particles of water insinuate 



