The balance-beam is continued beyond the point where the piston is connected with it, and it goes to meet the blocks placed to check the force of the blow given by the descent of the tool. The guides of the piston-head are attached to the part of the machinery that acts in this manner; but at Passy, Kind made the balance-beam work upon two free plummer-blocks, or blocks having no permanent cover, that they might be more easily moved whenever it was necessary to displace the beam, for the purpose of taking up or letting down the rods, or for changing the tools; for the balance-beam was always immediately over the centre of the tools, and it therefore had to be displaced every time that the latter were required to be changed. This was effected by allowing the beam to slide horizontally, so as to leave the mouth of the pit open. The counter-check, above mentioned, likewise prevented the piston from striking the cylinder cover with too great a force, when it was brought back by the weight of the tools to its original position. The operation of raising and lowering the rods, or of changing the tools, was performed at Passy by a separate steam-engine, and the shell was discharged into a special truck, moving upon a railway expressly laid for this purpose in the great tower erected over the excavation. All these arrangements were in fact made with the extreme attention to the details of the various parts of the work which characterizes the proceedings of foreign engineers, and conduces so much to their success.

The beating, or comminution of the rock, was usually effected at Passy at the rate of from fifteen strokes to twenty strokes a minute. The rate of descent, of course, differed in a marked manner, according to the nature of the rock operated upon; but, generally speaking, the trepan was worked for the space of about eight hours at a time, after which it was withdrawn, and the shell let down in order to remove the débris. The average number of men employed in the gang, besides the foreman, or the superintendent of the well, was about fourteen: they consisted of a smith and hammerman, whose duty it was to keep the tools in order; and two shifts of men entrusted with the excavation, namely, an engine-driver and stoker, a chief workman, or sub-foreman, and three assistants. The total time employed in sinking the shafts executed upon this system in the North of France, where it has been applied without meeting with the accidents encountered in the Passy well, was found to be susceptible of being divided in the following manner: from 25 per cent. to 56 per cent. was employed in manœuvring the trepan; from 11 per cent. to 141⁄2 per cent. in raising and lowering the tools; from 19 per cent. to 21 per cent. in removing the materials detached from the rocks, and cleaning out the bottom of the excavation; and from 8 per cent. to 101⁄2 per cent. was lost, owing to the stoppage of the engines, or to the accidents from broken tools, or to other causes always attending these operations. In the well of Passy there was, of course, a considerable difference in the proportions of the time employed in the various details of the work; and the long period occupied in obviating the effects of the slips which took place in the clays, both in the basement beds of the Paris basin and in the subcretaceous strata, would render any comparison derived from that well of little value; but it would appear that, until the great accident occurred, the various operations went on precisely as Kind had calculated upon.

Kind-Chaudron System.

Fig. 110.

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In the year 1872 Emerson Bainbridge, C.E., drew attention to the Kind-Chaudron system of sinking mine shafts through water-bearing strata, without the use of pumping machinery, in a paper read before the Institute of Civil Engineers. As the operation is almost identical with that which would have to be carried through in the case of a well sunk through an upper series of water-bearing strata, of minor importance or of impure quality, past rock and into the lower water strata, as for instance through tertiaries and chalk into the lower greensand, the following extract from Bainbridge’s paper may be read with interest.

In the first place, it may be desirable to describe briefly the system of sinking hitherto pursued in passing through strata yielding large quantities of water. The most important sinkings of this character have been carried out in the county of Durham, to the east of the point at which the Permian overlie the carboniferous rocks. In this district there is a thin bed of sand between the Permian rock and the coal measures. Towards this bed the feeders of water are generally found to increase, and in the sand there is usually a large reservoir of water. The mode of sinking will be understood by reference to [Fig. 110]. Whilst sinking in hard rock, it has ordinarily been the custom to place iron curbs, or cribs, wherever a bed of stone appeared to form a natural barrier between two distinct feeders of water. Thus it has frequently happened that important feeders have been tubbed back, rendering much less pumping power necessary than would have been required had all the feeders been allowed to accumulate in the shaft. As will be seen by [Fig. 110], the number of wedging cribs employed is no less than thirteen in 250 feet. The cribs forming the foundation of each set of tubbing are generally much more massive and costly than the segments of tubbing.