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AGRICULTURAL ENGINEERING 



the furrow slice of tough sod gradually; second, the general- 

 purpose plow, to be used for general plowing in stubble and 

 light sod; and, third, the stubble plow, with an abrupt mold- 

 board for pulverizing the soil, used only in old ground. 

 Among these three classes there are numberless shapes of 

 plows difficult to classify. 



^ 



Fis 



108. The three principal types of plows, showing in order the 

 stubble, the general purpose, and the prairie breaker plows. 



Construction. The moldboard may be made of soft- 

 center steel or chilled iron; but the latter is used but very 

 little in the Middle West, where the soil is of such a character 

 that the hard-tempered surface of the soft-centered steel is 

 required to scour properly. Certain localities are furnished 

 with plows with common cast-steel moldboards; but they 

 can not be used where many rocks are encountered, in 

 which case a soft share, at least, must be provided. The 

 wearing properties of the soft-centered steel share is secured 

 through its hardness; but to secure hardness a certain 



amount of brittleness 

 must remain, even with a 

 soft center to the metal. 

 Adjusting the Walk- 

 ing Plow. The walk- 

 ing plow must have its 

 point turned down 

 slightly in order to cause the plow to take to the ground. 

 This gives what is called ' 'suction' ' to the plow, and is 

 resisted by the upward pull of the draft. It is imperative 

 that the suction be sufficient, and quite as important that 



Fig. 109. A steel beam walking plow of 

 the general-purpose type. 



