16 



SCIENCE 



[N. S. Vol. XXV. No. 627 



charges, loads have grown larger, likewise 

 the speed at which they are hoisted. Loads 

 of nearly seven tons are being raised on 

 some of the inclines at speeds up to 40 

 miles per hour. 



A considerable item in the hoisting 

 charges is the cost of maintenance of the 

 skip road, the expense per ton for this pur- 

 pose increasing with the length of the shaft. 

 The usual skip road is carried on heavy 

 timbers which are placed transversely along 

 the foot, and support large stringers to 

 which the rails are spiked. The expense 

 of maintenance of this road for great 

 depths is such that some of the mines are 

 substituting for it a road consisting of a 

 rail attached to a concrete stringer which 

 is borne directly on the rock of the foot- 

 wall. 



The stringer proper is about 13^ inches 

 wide by 14 inches high. Beneath it and 

 supporting it is a mass of concrete 16 

 inches to 18 inches wide extending to the 

 rock. The depth of this supporting mass 

 varies considerably, depending on the ir- 

 regularities of the rock face to which it is 

 attached. It ranges all the way from 4 

 inches to 2^ feet, and there is no reason 

 why these limits might not occasionaUy be 

 exceeded. The stringer and supporting 

 mass are structurally one piece, being 

 molded together. The stringer portion is 

 reinforced by means of a 1^-inch steel cable 

 passing longitudinally through its interior. 

 The rail is attached by bolts which are 

 spaced three feet apart, and hold it by 

 means of clips which grasp the rail flange. 

 The bolts pass through the stringer into a 

 rectangular opening about three by four 

 inches in section, which passes quite 

 through the concrete, and affords access to 

 the lower end of the bolt. 



In building the road a form of plank is 

 constructed having the cross section of the 

 stringer, and a length of 15 feet. To its 

 lower side are nailed the cores for the bolt 



openings just mentioned. The top is left 

 open. From one to three of these forms 

 are supported in place underground by 

 suitable means, and to the sides are nailed 

 boards extending downward to the rock. 

 These make the form for the supporting 

 part underneath the stringer proper. When 

 all is firmly secured the rock face is thor- 

 ougly washed, and the concrete is filled in, 

 beginning at the lower end. The mixture 

 used is one part Portland cement, three of 

 sand and five of crushed rock, and it is 

 tightly rammed in place. As the filling 

 proceeds the top of the form, or the cover, 

 is completed by nailing on short pieces of 

 plank. In the roads which have been built 

 at a slope of 70° the structure is anchored 

 to the footwall by heavy bolts spaced 8 

 feet apart. When the concrete has hard- 

 ened sufficiently the form is removed and 

 the rail is bolted in place. The road is 

 then complete. 



The first of these roads has been opera- 

 ting some three years, and has proved so 

 satisfactory that the others have followed. 

 Expectation regarding cost of maintenance 

 has been fully realized, and, in addition, it 

 has been found that the original cost of the 

 road is less than that of wooden construc- 

 tion. Its disadvantages seem to be con- 

 fined to the fact that, due to the unyielding 

 nature of the support, the effect of a blow 

 must be absorbed between wheels and rail, 

 resulting in a perceptibly greater deteriora- 

 tion of both. However, this is far more 

 than compensated by the decreased cost in 

 other directions and the fireproof character 

 of the road. 



In the effort to counteract the increased 

 costs due to great depth the economical 

 generation, distribution and use of power 

 have naturally received large attention. 

 The long period of operation necessary 

 makes it worth while to expend large 

 amounts of money in installing machinery 

 of large capacity and high economy. The 



