EXCAVATING MACHINHs AND ROCK DRILLS 27 



and each manufacturer usually makes a number of grades to 

 which he gives special names. Dynamite for railway work* 

 tunneling, and mining con tains about 50 of nitroglycerine; for 

 quarrying about 35 ^ and for blasting soft rocks about 80 ^. 

 It is sold in cylindrical cartridges covered with pajH-r. 



Storage of Explosives. In driving tunnels through rock 

 large quantities of explosives must be used, and it is m i nrmrjr 

 to have some safe place for storing them. In many States 

 there are special laws governing the transportation and storage 

 of explosives ; where there is no regulation by law the engineer 

 should take suitable precautions of his own devising. It is 

 best to build a special house or hut in one of the most con. 

 cealed portions of the work and away from the tunnel, and 

 protect it with a lightning-rod and from fire. Strict orders 

 should be given to the watchman in charge not to allow perx-ns 

 inside with lamps or fire in any form, and smoking should !* 

 prohibited. The use of hammers for opening the 1- 

 should be prohibited; and dynamite, gunpowder, and fulminate 

 of mercury should not l>e stored together in the same room. 

 A quantity of dynamite for two or three days' consumption 

 may be stored near the entrance of the tunnel in a locked |M.\, 

 the keys of which are kept by the foreman of the work. 

 When dynamite has been fro/en the engineer should provide 

 some arrangement by which it may be heated to a tcmjM-raturo 

 not exceeding 120 F., and absolutely forbid it U-ing thawed 

 out on a stove or by an open fire. 



Fuses. When gunpowder is used in tunneling it is ignited 

 by the Bliekford match. This match, or fuse as it is more 

 commonly called, consists of a small rope of yarn or cotton 

 having as a core a small continuous thread of fine gunjxnvder. 

 To protect the outside of the fuse from moisture it IB coated 

 with tar or some other impervious substance. These fuses are 

 so well made that they burn very uniformly at the rnto of 

 about 1 ft in 20 seconds, hence the moment o/ explosion can 

 be pretty accurately fixed beforehand. Bliekford matches 



