132 SOILS 



mouldboard should be spiral. This most important 

 principle in the construction of the mouldboard was 

 first stated clearly in 1839 by two plow makers, 

 Samuel Witherow and David P.ierce. "The main 

 object is to pulverise the soil, and the only way in 

 which it can be effected is by bending a furrow-slice 

 on a curved surface forward so that it shall be 

 twisted, somewhat in the manner of a screw." 

 The more nearly spiral a mouldboard is, the more 

 completely will the soil be inverted, but it is not 

 pulverised to any extent. 



The extent to which the mouldboard pulverises 

 depends mostly on the steepness of its upward curve 

 and the abruptness of its outward curve; that is, 

 the upper or rear end is curved more sharply than 

 thelowerorforwardend. This "bold mouldboard," 

 as it is called, draws slightly harder and clogs a 

 little more than those having a more moderate curve, 

 but its much greater effectiveness in pulverising the 

 soil more than compensates for these objections. 

 The abrupt mouldboard is adapted for nearly all 

 plowing, except for the fall plowing of clayey soils 

 and for breaking new land, when a plow having a 

 long and gradually sloping mouldboard is more 

 effective. 



The Coulter, or cutter, may be in the form of a 

 knife or a rolling disk. The disk coulter is usually 

 more useful than the knife coulter, which clogs 

 easily. It is especiallv serviceable for plowing 

 under litter, as cornstalks and straw, which it rolls 

 down and cuts. The jointer, however, is now used 

 more for this purpose. 



The Jointer, or skim coulter, is a most service- 

 able attachment, especially when stubble, grass or 

 manure are to be turned under. When herbage 

 is plowed under without a jointer there is likely to 



