126 



FUELS 



or condensers. The most remote tube would contain gasoline ; 

 the next, naphtha; the next, benzine; the next, kerosene; 

 and so on. 



When petroleum is heated to a very high temperature, heavier 

 oils vaporize and pass off and condense. From these oils, lubri- 

 cating oil, vaseline, and paraffin wax are obtained. 



Gas as a fuel. The most convenient fuel is gas. There is 

 no waste to gas and there is no removal of ashes ; it is available 



at a moment's notice and 

 requires less attention 

 than any other fuel (Fig. 

 52). For steady use, it is 

 more expensive than coal, 

 and the thrifty house- 

 keeper who does not wish 

 to economize her own 

 labors would not use gas 

 for laundry work where 

 the washing and ironing 

 is an all-day affair. In 

 summer, when comfort as 

 well as economy is to be 

 considered, the gas range 

 is almost indispensable. In practically all of the modern hotels, 

 cooking is done entirely with gas, thereby saving labor and 

 prolonged hot fires. 



Most of the gas that is used for cooking and for illumination 

 is made from the distillation of soft coal. In our study of coals 

 we saw that the decomposition of vegetable matter was far from 

 complete in soft coal and that it contains more volatile matter 

 than hard coal. These volatile gases are driven off from soft 

 coal by heating in closed clay-lined retorts from which air is 

 excluded. When the coal is heated to 1200 C. or more, cer- 





FIG. 52. Gas range. 



