HETTON COLLIERY. 



297 



required distance apart, and the top tier was crossed by others 

 -at right angles, leaving a square opening at the centre of the 

 shaft for the free passage of the sinking bucket. These balks 

 were decked over, and on the decking were placed the bags of 

 .sand, until the desired weight for the time being was obtained. 

 Safety chocks were built up to prevent the cylinder from slip- 

 ping down suddenly while the divers were working at the 

 bottom of the pit: (a) are guides to assist the cylinders to 

 .sink down vertically. Dining the process of sinking the 

 cylinder, when the resistance of the strata was sufficient to 

 balance the loading, a 400gal. tank was fixed at the surface, 

 from which a pipe led down to the bottom of the shaft, as the 

 water was baled from the shaft, it was discharged into the 



Fig. 192. Trepan Side Elevation. 



Fig. 193. Trepan Plan. 



-lank, and returning through the pipe acted with sufficient 

 force to stir up the sand. This caused sand on the outside 

 of the cylinder to have a downward movement, and by disturb- 

 ing the equilibrium, caused a further sinking of the' tubbing. 

 In spite of the care taken to make the cylinder sink vertically, 

 when at a depth of 60ft., it was found to be 18in. from the 

 perpendicular, so the work of re-adjusting was performed by 

 securing the edge of the lower end to a powerful screw by 

 means of chains, and this was supplemented by shores kept 

 tightly wedged to the lower side. Water was then led down 

 from the 400gal. tank to stir up the sand, and in a short 

 *ime the cylinder was restored to a perpendicular position. 



