178 ENGINEERING ON THE FARM 



worthless. Powder does not give results unless it is thor- 

 oughly tamped, and this necessarily means the drilling or 

 boring of holes. Frequently a grade of dynamite can be 

 selected that will give results without tamping. Dynamite 

 may be stored and transported with comparative safety, 

 and sparks will not ignite it. 



Special explosives. Explosives are on the market under 

 various trade names. They differ somewhat in their chem- 

 ical composition from ordinary dynamite, some small 

 percentage of the ingredients being known only to the 

 manufacturer of each brand, but they accomplish practically 

 the same results and are handled in the same manner as 

 described for dynamite. 



The charge. In practical blasting the quantity of explo- 

 sive assembled in one complete unit is known as the charge. 

 This consists of the explosive proper with a suitable primer 

 for firing. The method of making up a charge is determined 

 by the nature of the explosive used : gunpowder is fired by a 

 spark, dynamite by detonation, nitroglycerin by concussion. 

 Safety fuse. A safety fuse (Fig. 157) is a core of very 

 fine gunpowder surrounded by yarn and lapped with tape. 

 The tape is waterproof and is dusted with powdered soap- 

 stone to prevent stickiness. The fuse may be single, double, 

 or triple tape, according to the amount of moisture resist- 

 ance required. Cheap hemp or cotton fuse is made for 

 work which is dry, and gutta-percha fuse for work which is 



submerged. A single or double tape 

 fuse is most satisfactory for ordinary 

 farm purposes. The object of the 

 fuse is to carry a spark of fire 

 directly into a black powder charge 

 Ne t mou; s I & d co Pontde or into the detonator when dynamite 

 Fig. isi. Coil of safety i s US ed. The powder core at the 



fuse . 



outer end of the fuse is lit with a match 

 and burns at a rate of 3 feet per minute. Safety fuse is 

 placed on the market in 50-foot coils, two coils in a package. 



