CHANGES IN STATE OF MATTER 



41 



the form of gases. Such gases are hydrogen, oxygen, 

 and carbon dioxide. 



Distillation. The fact that different liquids boil at 

 different temperatures is utilized in the separation of 

 various substances by means of a process known as 

 distillation. If a mixture of alcohol and water is heated 

 between 78C. and 100C. the alcohol will boil and 

 pass off as a vapor, while 

 the water will remain. If 

 the alcohol vapor is then 

 cooled, it will again become 

 a liquid. If the boiling 

 points of the two liquids lie 

 close together, as they do 

 in this case, repeated dis- 

 tillation is necessary. Even 

 then a complete separation 

 can not be obtained by dis- 

 tillation alone. 



Commerciallv. distillation 



Fig. 20. Distillation. The solu- 

 tion to be distilled is placed in 

 the flask. The steam passes 

 through the tube, is cooled, and 

 condenses in the test tube. Any 

 impurities present in the original 

 liquid are left in the flask. 



is a very important process. 

 When liquids contain dis- 

 solved solids, the liquids 

 can usually be distilled. Water can be freed from impur- 

 ities by it. If muddy water is boiled, the water 

 evaporates, or passes off in the form of steam, but the 

 impurities remain in the vessel in which the water is 

 being boiled. The steam can then be condensed and pure 

 water obtained. Water freed from impurities in this way 



