WORKS, PUBLIC. 



771 



driven by air compressed by water-engines, and 

 led to the face of the headings by cast-iron pipes, 

 in this way not only supplying the power re- 

 quisite to drive the drills, but, either by the 

 exhaust or an open jet, when the drills are not 

 running, air for most of the ventilation. 



The following table shows the monthly ad- 

 vance, in metres, made during 1868 : 



This gives an average advance of 110 me- 

 tres per month, or 53.20 on the Italian side, 

 and 56.80 on the French ; and at this rate of 

 progress the time necessary for the completion 

 of the tunnel would be 28 months, or about 

 April, 1871, and for opening the railway about 

 six months more, or in less than three years 

 from the present time. The following table 

 shows the yearly progress, in metres, that has 

 been made with these works since their com- 

 mencement in 1857 : 



The work is done by contract, but at the ex- 

 pense of the Italian and French Governments. 

 In imitation, the State of 

 Massachusetts is afford- 

 ing aid in the construc- 

 tion of a tunnel through 

 the Hoosac Mountain. It 

 has been prosecuted for 

 many years, under vari- 

 ous political and engi- 

 neering difficulties, but is 

 now fairly under contract 

 with a fair chance of be- 

 ing completed some 



in 1874. The amount expended thus far has 

 been about $3,000,000, and contract for comple- 

 tion, $4,592,000, a total of $7,592,000. The fol- 

 lowing is the present condition of the work, as 

 taken from the report of the engineer in charge : 

 "At the east end the total distance penetrated 

 is 5,282 feet, or 2 feet over a mile. Of the first 

 half of this distance, a length of 810 feet is en- 

 tirely completed, and the remaining length con- 

 tains unfinished excavation only to an amount 

 equalling the contents of less than 300 mining 

 feet of full-size tunnel. In the succeeding 

 half mile driven as a heading, the quantity re- 

 moved constitutes about the cubic contents 

 of the tunnel. At the central shaft, depth al- 

 ready sunk, 583 feet. Kemaining to reach 

 grade, 447 feet. At the west shaft and west 

 end workings, a total continuous distance ol 

 4,056 feet has been opened. Of this distance 

 821 feet had been excavated and lined with 

 brick arching up to November 1st, and of the 

 remainder a quantity equal to about of full- 

 size excavation had already been removed. 

 The whole length of tunnel, exclusive of acces- 

 sory structures required at west end, is 25,031 

 feet." At the east end, machine drilling, in 

 general principle similar to that at Mont 

 Oenis, has been need for some years. ' During 

 the present year, "in addition to the repairs of 

 the old machinery, two new surface wheels, 

 with a four-cylinder compressor for earth, have 

 been set up in complete working order, both 

 of these compressors being intended to furnish 

 air at the ordinary power pressure of 50 pounds, 

 for driving the pneumatic drills. The appara- 

 tus for power is thus increased to nearly three- 

 fold its former capacity." Experiments have 

 been made with nitro-glycerine. " Its superior- 

 ity over powder ordinarily used in blasting, as 

 demonstrated by our own experience, may be 

 briefly expressed in the following items : Less 

 number of holes drilled in proportion to area 01 

 face carried forward. Estimated saving, 33 per 

 cent. Greater depth of holes permissible as depth 

 for glycerine 42", for blasting-powder 30". 

 More complete avail of the full depth of hole 

 drilled. The greatly superior explosive power 

 of the nitroglycerine rarely fails to take out 

 the rock to the full depth of the hole. Powder 

 often comes short of this." 



The above works can only be considered 

 among the most important, but private capital 

 and public aid have been liberally given during 

 the last few years to almost any enterprise 



