132 THE OLIVER PLOW BOOK 



surface soon exposes the center which is so soft that it 

 will not scour in any soil. 



Chilled plows are constructed by an entirely different 

 process. When the mouldboard is properly made it has 

 a flinty hardness that never has been duplicated in steel. 

 This hardness enables a chilled mouldboard to much 

 better withstand the scratching of sand, gravel, stones, 

 etc. As a matter of fact, there is no scratching that will 

 affect the scouring qualities of properly chilled metal. 



As a result the more a chilled mouldboard is operated 

 in sandy soil the smoother it becomes, and the higher 

 polish it takes. Long experience has shown that used 

 plows have a better polish than can possibly be put on 

 in the factory. This peculiarity of chilled metal 

 makes chilled plows scour better in all kinds of sandy, 

 gravelly, stony, heavy clay soils, and the silt loams that 

 contain silica, potash, lime, iron and aluminum oxide. 



The chill, as plowmakers call the term of hardening, 

 crystallizes the metal so that the grain is edgewise of the 

 mouldboard instead of lengthwise. This means that 

 the dirt in shedding passes over the ends of the crystals. 



The ends of the metal crystals furnish the surface for 

 scouring. For this reason chilled mouldboards are very 

 hard to wear out. They often wear twenty years. 

 Instances are known where they have worn fifty years. 

 Chilled mouldboards have been used until the edge has 

 been worn to the thinness of a piece of paper and sharp 

 enough for a keen cut knife. 



The thickness of a chilled mouldboard is about % to 

 }/2 of an inch. One-quarter of an inch of this entire 

 thickness is made of chilled metal, consequently, a 

 mouldboard will wear and scour until the entire thick- 

 ness of the chilled portion is worn away. When this is 



