Chap. 9] SEISMIC METHODS 487 



It is unfortunately true for much of the seismic work that famiUarity 

 breeds contempt. The most frequent offense is the storing or transporting 

 of blasting caps with the dynamite, despite repeated warnings by powder 

 companies. Accidents have happened in seismic work. Although remark- 

 ably few in number, they were probably more frequent in the days of re- 

 fraction shooting, owing to the greater quantities of explosives and greater 

 distances involved. 



Considerable progress has been made in recent years in solving the prob- 

 lem of storing explosives for seismic parties. Portable magazines have 

 been constructed. Two types are available, one on a two- and the other 

 on a four-wheel chassis. The body is electrically welded steel of a capacity 

 of about one ton. The housing is well ventilated, protected by locks 

 against theft, and coated with aluminum paint (see Fig. 9-24). Since it 

 is illegal to carry dynamite in a trailer or in a car towing a trailer, the dyna- 

 mite may be transported in one vehi- 

 cle, the trailer towed by another, and 

 the d3aiamite transferred on location. 

 Separate steel boxes for caps are also 

 available. These may be chained to a 

 tree in the field. 



Inflammahility. Straight nitrogly- 

 cerine dynamites are most easily 

 ignited, but all other grades are of low 

 inflammability. Explosives should be 

 well protected against fire. 



Experience collected with various 

 types of explosives in seismic work in 



,1 • i. e J. 1 -J- Texas Body and Trailer Co. 



this country for over twelve years mdi- 



cates that the fiO ner oent ammonia Fig. 9-24. Portable dynamite magazine. 



gelatins, especially the high-velocity types developed for seismic applica- 

 tions, are the most satisfactory. Dynamites for seismic work are manu- 

 factured by the Du Pont Powder Company, the Hercules Powder Com- 

 pany, and the Atlas Powder Company. The most popular sizes are: 

 ^-pound sticks, Ij x 8 inches; 1-pound sticks, 2x6 inches; 2^-pound sticks, 

 2 x 16 inches; 5-pound sticks, 3 x 12 inches; and 70-pound sticks, 8 x 24 

 inches (for swamp work). 



For setting off the charge, electric blasting caps are used exclusively 

 (Fig. 9-25). These consist of a metal container, two insulated leg wires 

 sealed with a waterproof compound and with sulfur on top, a pressed charge 

 at the lower end of the cap, and a primer charge at the ends of the leg 

 wires where they are connected by a bridge wire. The fusion of this wire 

 detonates the cap. The bridge wire is made of an 80-20 platinum-iridium 

 alloy and is 0.00125 inch in diameter. The priming charge surrounding 



