SCIENCE OF COMMON THINGS. 67 



Dry wood swells in water. Solution of substances. Liquids and gases. 



The pores of the sponge constitute minute tubes in 

 which the water rises by capillary attraction. 



409 Why does dry wood, immersed in water, swell 1 



Because the water enters the pores of wood by capil- 

 lary attraction, and forces the particles further apart 

 from each other. 



41 Why does sugar or salt give a flavor to water f 



Because the sugar or salt (being separated into very 

 minute particles) floats about the water, and mixes 

 with it intimately. 



411 Why does hot water dissolve sugar and salt more readily than cold 

 water f 



Because the heat of the water assists its solvent ac- 

 tion, and opens for the water a passage through the 

 particles of the substance. 



CHAPTEK IT. 



THE GENERAL PROPERTIES OF AERIFORM OR GASEOUS 

 BODIES. 



413 What is the difference between a liquid and a gas? 



The distinction between liquids and those more elas- 

 tic fluids which w r e term air, gas, vapor, steam, etc., 

 depends principally on heat and pressure. Thus, wa- 

 ter, according to the addition or subtraction of heat, 

 may exist as a solid, ice ; as a liquid, w r ater ; or as a 

 vapor, steam. 



413 Under what pressure of the atmosphere is water converted into 

 steam ? 



Tinder the ordinary pressure of the atmosphere, wa- 

 ter is converted into steam at 212 degrees, Fahrenheit's 

 thermometer ; if this pressure is increased, it requires 



