450 



THE ESSENTIALS OF AGRICULTURE 



of water available as well as upon the head, or distance through 

 which the water is allowed to fall. The reliability of this form 

 of power is affected by drought, by floods, and by ice in the 

 water supply. 



589. Fuel as a source of power. The greatest source of 

 mechanical power is fuel. The fuels most commonly used for 



power generation are coal, wood, pe- 

 troleum oil, and natural gas. These 

 fuels, when burned, give up heat 

 which is utilized in changing water 

 into steam or in heating the air. 

 The steam or the air is then allowed 

 to expand in a motor cylinder, push- 

 ing against the piston and thus doing 

 the work. 



590. The steam power plant. To 

 produce mechanical power by means 

 of a steam engine (Fig. 225), the fuel 

 must be burned in a furnace outside 

 the engine cylinder. The furnace is a 

 chamber arranged with a grate, if coal 

 or wood is burned, and with burners, 

 when oil or gas is used. This furnace 

 must be connected with a chimney, to 

 produce draft and carry off the gases. 

 The heat developed by the burn- 

 ing of the fuel in the furnace is 

 utilized by the changing of water 

 into steam in a closed cylindrical vessel called a boiler. 



In connection with modern farming the steam power plant is 

 used mainly on traction engines. 



591. The oil engine on the farm. Of all farm motors, the 

 oil engine using gasoline or the heavier oils has the greatest 

 field of usefulness. Such an engine is portable and can be 

 used for various farm and household purposes, such as pump- 

 ing water and driving cream separators, churns, pumps, ice-cream 



FIG. 224. A simple type of 

 water motor 



The water striking the vanes, or 

 cups, produces rotation of the 

 wheel. Such a water motor can be 

 constructed by inserting between 

 two wooden disks a number of 

 buckets made like V-shaped 

 troughs, and putting a wooden or 

 metal shaft at the center of the 

 disks, for the purpose of transmit- 

 ting the power developed by the 

 rotation of the wheel 



