'IT NX ELS THROUGH HARD ROCK 107 



debris, two with picks and two with shovels, while on either 

 side and behind are as many men as space will permit The 

 stone is thrown either to the sides of the heading or into the 

 wagon, shoveling being greatly aided by the steel flooring, 

 which, before the explosion, hud been laid over the rails for 

 nearly 10 yds. down the tunnel to receive the falling rock. 

 These steel plates are taken up when cleared, and the wagon 

 is pushed forward until the drilling-machine can be brought up 

 again, leaving the remaining debris at the sides to be handled 

 at leisure during the next attack. The roof and side walls are, 

 of course, carefully examined with the pick, to discover and 

 detach any loose or hanging rock. The times taken for each 

 portion of the attack in this particular antigorio gneiss are as 

 follows: Bringing up and adjustment of drills, 20 mins. ; drill- 

 ing, between lj hr. and 2 hrs. ; charging and firing, 15 mins.; 

 clearing away debris, 2 hrs. ; or for one whole attack, between 

 4 hrs. and 5i hrs., resulting in an advance of 3 ft 9 in., or a 

 daily advance of nearly 18 ft 



Fnmi this it appears that the time spent in clearing away 

 the debris equals that taken up in drilling, and it is in this clear- 

 ing that a saving of time is likely to be effected rather than in 

 tin- process of drilling. Many schemes have been tried, such as 

 a mechanical plow for making a jKissage ; at Brigue, " marin- 

 age," or clearing by means of powerful high-pressure water-jets, 

 directed down the tunnel, was tried, but the idea is not yet 

 sufficiently developed. 



. \nothrr series of experiments has been tried at Brigue 

 with regard to the utilization of liquid air as an explosive 

 agent instead of dynamite ; and for this purpose a plant has lieen 

 laid down, consisting of one ammonia-compressor, two air-com- 

 pressors, and two refrigerators, furnishing ,' gallon of liquid 

 air per hour at an expenditure of 17 1 1. P. The system used is 

 that of Professor Linde, who himself directs the experiment*. 

 The great difficulty experienced is that of shortening the interval 

 of time that must elapse between the manufacture of the 



