COMPOSITION OF MATTER 7 



be seen) and only a few have any color. Air is a 

 gas, as is also steam, hydrogen, oxygen, chlorine, and 

 others. Many gases which cannot be seen may be dis- 

 covered by their odor ; as coal gas, illuminating gas, 

 ammonia, etc. 



Vapor is a name given to such gases as easily change 

 to liquids ; as steam. True steam is invisible, the 

 white cloud that we call steam being made of tiny 

 drops of water. At the spout of a kettle we sometimes 

 notice a seemingly vacant space (Fig. 2) where there is 

 really steam; in a moment this steam has cooled into 

 drops. Smoke is not a gas, but is a mass of solid 

 particles. 



9. Changes of State. In general, substances change 

 from solids to liquids and from liquids to gases upon 

 being heated. For some kinds of matter great heat is 

 necessary. 



Experiment 2. Gently heat small quantities of ice, wax, par- 

 affin, sugar, or butter, and note the changes which take place. 



Experiment 3. Fit 

 a stopper into a test 

 tube, and through the 

 stopper run a glass 

 tube, as in Fig. 3. 

 Into the test tube put 

 a small quantity of 

 water, alcohol, ether, 

 or benzine. Dip the 



open end of the glass FlG 3 



tube under water and 



gently heat the liquid in the test tube. Note carefully and explain 

 all that you see. Be sure to apply only slow heat and use caution 

 with volatile liquids. 



