302 THE GAS ENGINE 



above distillations are accomplished with steam, as the 

 steam distilled products are of better grade with less loss 

 and less danger of decomposition in the still. 



The tar left in the stills is removed and destructively 

 distilled, yielding hydrocarbons of much higher density and 

 greater viscosity ; some even being solid at ordinary tempera- 

 tures. By redistillation, washing with sulphuric acid and 

 caustic soda, and chilling and pressing, there are obtained 

 heavy oils used for lubricating — called lubricating and 

 paraffine oils — paraffine, vaseline, and coke. 



The very volatile products of low density are used for 

 solvents; intermediate products for fuel; kerosene for light- 

 ing purposes; lubricating oils for machinery; paraffine for 

 candles; vaseline for medicine; and coke for electric light 

 carbons. 



221. Gasoline. — Originally the name gasoline was applied 

 to a fraction whose density was somewhere between 90° 

 and 80° Be., but now the product sold under the name of 

 gasoline may be anything from 90° to 60° Be. Most of the 

 engine gasoline runs from 65° to 60° Be., 1 specific gravity 

 0.718 and 0.737, boiling point 120° to 150° C. It is a mixture 

 of hydrocarbons, having no constant composition. It is 

 possible to obtain any particular density by mixing light 

 and heavy fractions. The same result may be secured by 

 uniting a very light product with a very heavy one, or by 

 uniting two of more nearly equal densities. As a result the 

 mere specific gravity or Baume reading of a grade of gasoline 

 does not tell the purchaser just what he is getting. If a single 

 hydrocarbon liquid, having a density of 65° Be., is just suited 

 to a certain engine, a grade of material would not be as well 

 suited which consists of a mixture of very light hydrocarbon 

 with very heavy hydrocarbon, the resultant density of which 

 is 65° Be. The lighter material would vaporize too rapidly 

 and explode too easily, whereas the heavier portion would 

 vaporize very slowly or too slowly to make a proper explosive 

 mixture. In time it may be possible to buy gasoline, or 



1 Instead of saying "65° or 60° Be. gasoline" it is usually customary to 

 speak of it as "65 or 60 test" gasoline. 



