SCOURING TROUBLES 



145 



A never failing way to determine the soft spots in a mouldboard is to 

 take an old file and break it so that a sharp edge results. Run this 

 lightly over the mouldboard. The file will slide smoothly over the hard 

 parts. It will stick t the soft spots. Plow manufacturers are always 

 desirous of having their plows give satisfaction. After a little exper- 

 ience of this kind it will be easy to detect soft spots in mould boards from 

 their cloudy appearance. Soft spots never take the high polish that the 

 rest of the board does. 



The reason given for the success of the plaster of Paris 

 board is that the plaster wears away with the earth. 

 This demonstrates that the adhesive force between the 

 earth and the plaster is greater than the cohesive force 

 of the plaster. It also demonstrates that the cohesive 

 force of the earth is greater than that of the plaster of 

 Paris. 



