234 CHEMISTRY OF FARM PRACTICE 



tained in petroleum-ether to C2sH56 contained in paraffin. 

 Within recent years, petroleum in its unrefined con- 

 dition has come into use as a fuel for steamships and 

 for manufacturing purposes, competing successfully with 

 coal. 



183. Kerosene. This is the most commonly used source 

 of illumination in rural districts. Its use as a means of 

 temporary or quick heating is both economical and conve- 

 nient. Kerosene is a mixture of seven hydrocarbons ranging 

 from CioH22 to CieH^ with specific gravity varying accord- 

 ing to the grade of the oil, from 0.795 to 0.810. In the 

 trade kerosene oil is classed according to color and to the 

 temperature at which the oil gives off enough inflammable 

 vapor to produce a momentary flash when a flame is applied. 

 The grades of color are " Standard White " (pale yellow), 

 " Prime White " (straws) and " Water White " (colorless). 

 The flash tests required in different states of the United 

 States vary from 100 F. to 120 F. Water White oil with 

 flash-point of 150 F. is known as Head Light Oil. Low 

 flash-points in kerosenes indicate the presence of benzines 

 or naphthas whose inflammability makes the oil dangerous 

 for use in lamps. 



184. Gasoline. This is formed by the distillates of pe- 

 troleum that pass off at lower temperatures than that 

 required for kerosene. These are different grades of gaso- 

 lines, but those most used in automobile engines have dis- 

 tilling temperatures varying between 70 and 90 C. cor- 

 responding to hydrocarbons with the formulas CeHu and 

 CrHio. The volatility of gasoline enables it easily to be 

 converted into vapor which when it is mixed with air be- 

 comes highly explosive and therefore suitable for the internal 

 combustion demanded by engines of the automobile and 

 steam-launch type. 



185. Acetylene. When petroleum oil is " cracked " 

 by dropping upon plates heated to a high temperature, 

 among the decomposition products is Acetylene (C2Ho). 



