THE STEAM TRACTOR 43 



the steam plowing engine of to-day is a creation of the twen- 

 tieth century. 



ESSENTIALS OF THE TRACTOR 



The steam tractor consists essentially of a boiler, engine, 

 traction gearing, and wheels, with all the necessary fittings 

 for carrying fuel and water, supplying these to the fire box 

 and boiler, respectively, controlling lubricating the engine, 

 and steering. Steam is generated in a boiler by the heat 

 produced in the fire box and admitted to a closed cylinder, 

 where it moves a piston. The piston rod drives a connecting 

 rod which in turn causes a crankshaft to revolve. The power 

 thus produced is transmitted by a belt to a machine requiring 

 rotary motion to operate it, or is transformed into linear pull 

 by a train of gears and the wheels which grip the ground. 

 In discussing the steam engine, only those principles and 

 devices employed on the leading plowing tractors will be 

 included. This eliminates much that might be said of station- 

 ary engines and of many traction engines which have been 

 designed primarily for threshing and only partially adapted 

 to the severe work of plowing. Some topics common to both 

 types of tractor are discussed more fully in the chapters devoted 

 to the gas tractor. 



GENERATOR OF FOWER 



Steam is generated in a boiler to which heat is applied on 

 one side of a metal surface, on the other side of which is water. 

 The expansion of water decreases its density and colder water 

 displaces it. The resulting circulation gives the entire mass 

 a uniform temperature. On reaching a certain temperature, 

 determined by the pressure upon the surface, the water boils 

 and steam is formed. This takes place at 212 F. under the 

 ordinary atmospheric pressure of 14.7 pounds per square 

 inch. At higher altitudes the boiling point will be reached 



