24 THE THREE CONDITIONS OF MATTER. 



62. Test Questions. What is the one character- 

 istic difference between a solid and a liquid ? Between a 

 liquid and a gas ? Between a gas and a vapor ? Between 

 a fluid and a solid ? Into what two classes may these 

 three physical conditions of matter be divided, reference 

 being made only to ease or difficulty of a change of rela- 

 tive position of the molecules ? 



Note. Recent experiments with electric discharges in high vacu- 

 ums [ 290 ; 371 (31)] have yielded remarkable results which are 

 held, by some, to show the existence of a fourth condition of matter. 

 Formatter in this " ultra-gaseous " state, the name " Radiant mat- 

 ter " has been proposed. 



Recapitulation. To be reproduced, upon paper or 

 the blackboard, by each pupil. 



MATTER 



SOLIDS. 



Molecules change 

 their relative po- 

 sitions with diffi- 

 culty. 



FLUIDS. 



Molecules change 

 their relative po- 

 sitions easily. 



LIQUIDS, 



Molecules cling to- 

 gether feebly. 



AERIFORM BODIES. 

 Molecules tend to 

 separate. 



GASES ; ordinarily 

 aeriform. 



VAPORS ; ordinarily 

 liquid or solid. 



