146 THE OLIVER PLOW BOOK 



The plaster wears away rapidly and the farmer is 

 obliged to recoat his mouldboard often sometimes 

 as often as every night. Considering that Texas 

 farmers have different sizes and shapes of plow bottoms, 

 it is plainly evident that the shape of the bottom does 

 not control its scouring qualities. The revolving disk 

 is the only type of steel plow at the present time that is 

 regarded as handling this soil successfully, but the disk 

 plow does not scour in these soils, showing that the ad- 

 hesive force of the steel disk and the earth is greater than 

 the cohesive force of the earth and also that the co- 

 hesive force between the two is greater than the adhesive 

 force of the earth particles. 



If it is a question of constant pressure of the soil 

 against the mouldboard, it is necessary, then, in the design 

 of a mouldboard to shape it to interfere as little as 

 possible with the crumbling of sticky soils when turning 

 them over. 



It is far from easy to design a plow bottom that will 

 always do these things satisfactorily. The Texas illus- 

 tration must be regarded as conclusive evidence that 

 the shape of the mouldboard is not the only factor to be 

 taken into consideration. The material from which the 

 mouldboard is made and the way it is made often have 

 more to do with the success of the bottom than its shape. 

 Very frequently a mouldboard that from all standpoints 

 of theory should do a better job than another type of 

 bottom does the poorer quality of work simply because 

 the mouldboard fails to scour. 



Another side in scouring that is little known and has 

 received but spasmodic attention is the effect of heat 

 upon metal mouldboards. 



