314 Introduction to the Study of Science 



Fractional distillation. Fermented mixtures of alcohol and 

 water and other substances produced from grains, such as 

 barley, rye, and corn, or from fruits, such as berries and grapes, 

 are distilled in fractions, as alcohol and water, the alcohol 

 being separated from other substances. The distillation of 

 crude petroleum illustrates clearly the process of fractional 

 distillation. Petroleum contains many different substances 

 which have different boiling temperatures. The most volatile 

 substances, such as gasoline, naphtha and benzine, are among 

 the first to boil or vaporize, and separate from the rest. Gaso- 

 line boils at from 70 to 90 C., naphtha at 90 to 120, and ben- 

 zine at 120 to 150 C. The residue after distillation yields 

 among other substances lubricating oil, vaseline, mineral oil, 

 paraffin, and a carbon which is used in making electric carbons. 

 From liquid air oxygen and nitrogen are readily separated 

 from each other, because nitrogen vaporizes at a much lower 

 temperature than oxygen, and it is easily removed, leaving 

 practically pure oxygen as the residue. 



Boiling point of mixtures. Mixtures of two or more sub- 

 stances have a boiling point somewhere between the two ex- 

 tremes, as determined by the proportions of the individual 

 substances mixed. Sugar or salt or other solids of a similar 

 nature, when dissolved in water, raise the boiling point in 

 proportion to the amount of the solid substance in solution. 

 Pure water boils at 100 C. ; but all water except distilled 

 water has more or less of impurities in solution and requires 

 therefore a higher temperature for boiling. The boiling tem- 

 perature of liquid air, as may be seen in the table, is between 

 the boiling points of nitrogen and oxygen. 



SUMMARY 



Steam is produced from water by heat. 



Its temperature at ordinary pressure is the same as that of boiling 

 water, or 212F. 



Steam becomes visible or condenses when its temperature is re- 

 duced below the temperature of the boiling water. 



