BORING 



447 



\nfig. 185, and consists of a cylindrical shell or barrel p of cast-iron, about 8 feet 



long and a little smaller in diameter than the size of the borehole. At the bottom is 



a clack A opening upwards, somewhat similar to that in ordinary pumps ; but its 



seating, instead of being fastened to the cylinder p, is in an 



annular frame c, which is held up against the bottom of the 185 



cylinder by a rod D passing up to a wrought-iron bridge E at 



the top, where it is secured by a cotter F. Inside the cylinder 



works a bucket u, similar to that of a common lift-pump, having 



an india-rubber disc valve on the top side ; and the rod D of 



the bottom clack passes freely through the bucket. The rod 



o of the bucket itself is formed like a long link in a chain, and 



by this link the pump is suspended. The bottom clack A is 



made with an india-rubber disc which opens sufficiently to 



allow the water and smaller particles of stone to enter the 



cylinder ; and in order to enable the pieces of broken rock to 



bo brought up as large as possible, the entire clack is free to 



rise bodily about 6 inches from the annular frame c, as shown 



in fig. 1 85, thereby affording ample space for large pieces of rock 



to enter the cylinder when drawn in by the upstroke of the 



bucket. 



The general working of the boring machine is as follows : 

 The boring head is hooked on to the end of the rope, and lowered 

 to the bottom of the borehole, the rope is then secured by a 

 clamp to prevent it from being drawn off the winding drum. 

 Steam is admitted to the percussion cylinder, and the boring 

 bar kept at work until it has broken up a certain quantity of 

 material in the borehole. After this operation, the steam is 

 shut off, the rope undamped, and the boring head withdrawn. 

 The shell -pump is next lowered down by the rope, and the 

 debris pumped into it by lowering and raising the buckets in 

 the pump about three times, by means of the windkig engine, 

 while the pump barrel rests upon the bottom of the borehole. 

 These operations are repeated every fifteen or twenty minutes. 



Three men are required to work the machine and sharpen the 

 implements. 



Cost of Boring. It will be understood that the advantage 

 of putting down boreholes, as compared with wells or shafts 

 of large diameter, consists not only in the general convenience 

 in the small size, but also in the relative cost, which may be 

 said to vary according to the area of the perforation, but in an 

 uneven ratio. 



The cost of boring shallow holes is naturally much less per 

 foot than the rate of charge for borings at a considerable 

 depth. The general cost of boring by hand or by lever may 

 be taken as follows : 



First 30 feet . 

 Second 30 . 

 Third 30 . 

 Fourth 30 . 



Is. per foot. 

 2s. 



4s. 



And so on, adding Is. per foot for each additional 30 feet. 



In very hard strata the cost of boring may be taken at 50 per cent, more than the 

 above prices. 



The cost of boring by the ' Diamond ' machinery amounts to no less than 13s. 6d. per 

 foot for the first 100 feet, and for each additional 100 feet 7s. 6d. per foot is added. 

 The ' Diamond ' machinery, however, is capable in hard strata in a day of twelve hours 

 of boring a distance of 50 feet, whereas by hand boring, the average speed in similar 

 rocks cannot be taken at more than 10 feet per day. This refers to a depth of, say 

 200 feet, but in the ordinary system of boring with rods, whether by hand or 

 machinery, where the rods have to be disconnected and the d&bris has to be drawn 

 from great depths, an important element has to be considered. Whilst the weight of 

 the apparatus, consequent upon an increased depth, tends to augment the speed of 

 boring, the drawing, disconnecting, and connecting of great lengths of rods for the 

 purpose of clearing the hole, takes at a depth of about 250 feet really more time than 

 is occupied in the actual boring, and at great depths these processes absorb no less 

 than |ths of the total working time. This serious difficulty is obviated in two systems 



