232 Mr. M. Dunn on the Sinking of Preston Grange Engine Pit. 



wedging cribs were affixed at the top of the tub, and made water-tight by 

 wedging the space between the back part of the cribs and the solid rock ; 

 the whole fabric being kept firmly down by a range of strong stays against 

 the overhanging brow. In order to collect the straggling drippings of wa- 

 ter, and keep it from falling upon the sinkers, rings, or spiral excavations, 

 a few inches deep, were cut around the shaft, from whence it is con- 

 veyed, in boxes, downwards. 



As the pressure upon this tub was considerably greater than the for- 

 mer, the segments were prepared half inch thick, and found to be ade- 

 quately strong, for the tub when completed gave out scarcely any 

 leakage. The sinking was then carried on with little interruption till it 

 reached the depth of 36 fathoms, the pumps being also progressively 

 lowered down, when a third tub, of 4 fathoms long, was required to 

 shut off a similar feeder of water to the last mentioned. 



Up to this period the column of pumps had been hung on ropes, 

 strengthened by the application of five-fold sheaves, but it now became 

 desirable to establish them as a fixed set, 31 fathoms long, especially as 

 a seam of Coal, 2 feet thick, passing through the shaft at that place, of- 

 fered facilities for getting room made. 



The Coal and Stone were, therefore, excavated for the reception of 

 beams of timber, strong enough to bear the column (about 40 tons), to 

 which was attached a cistern, for receiving the waste water of the shaft, 

 as also that of the intended lower set ; and, in order to equalize the 

 working of the engine,* this, hitherto common, sucking pump was, by 

 the application of a separate working barrel, converted into a forcing 

 set, with iron rods, contrived to bestride the said working barrel, so 

 as to bring the lower column of pumps directly underneath the main 

 spear of the engine. 



Owing to the fixed arrangements of engine shaft, the clack door of 

 this forcing set was found to project so near to the side of the pit as to 

 obstruct the necessary handling of that part of the pumping apparatus ; 

 it therefore became necessary in the construction of the second tub, to 



* The beam at one motion raises the water up the forcing set to the surface, and, by tfie 

 other, the two lower sets deliver into their respective cisterns. 



