12 



BULLETIN 347, U. S. DEPARTMENT OF AGRICULTURE. 



has a small cone set in it, which fits snugly into a concentric electro- 

 magnet, and this is attached to the lower side of a crosshead (M) 



ff M£T*C TVm£[ 



Fig. 6.— Details of grinding lap. 



which slides freely on the guide rod (J). This crosshead is provided 

 with a slot in its rear side through which a sprocket chain (S) passes, 

 and this sprocket chain is supported on the sprocket wheels, which 



