FIG. TOO. STEEL SUBSOIL BAR 



Useful for making holes in shale or very tough hardpan. It can be made by 

 any blacksmith from \ l / 2 steel. It is driven in by means of a 16-pound maul. If it 

 sticks, it may be withdrawn by looping a stout chain a few times around it near 

 the ground, and prying it with a rail or crowbar passed through the loop of 

 the chain. 



Principles of Blasting 



When dynamite explodes, that is, when the small mass of dynamite 

 is changed into a very large volume of hot gases, these gases exert a 

 strong pushing force equally in every direction because they require a 

 much larger space than the dynamite which produced them. If the 

 dynamite is shut up in a space just large enough to hold it, that is, if it is 

 closely confined before it is exploded, the gases in escaping to the open 

 force out and carry along with them the material which shuts them in. 



These gases, pressing equally in every direction, will escape prin- 

 cipally where there is the least pressure to hold them in, that is, along the 

 lines of least resistance, and will force out the material confining them 

 more in that direction than in any other. If the back pressure holding 

 them in is about the same over the top and on all sides, then they will 

 carry with them, or break up as they escape, a large amount of the 

 material which shuts them in, but if one place in the earth or rock around 

 them is much weaker than all of the rest then the pressure will force 

 through there and the gases will escape without doing as much work as 

 they should. 



It must be remembered then that in order to have a charge of 

 dynamite do good work it must be so placed that the holding-in pressure 

 is as nearly as possible the same on top and all sides of it. If a charge of 

 dynamite explodes properly the change into gases is almost instan- 

 taneous, although some time is always required and some kinds of dyna- 

 mite explode or "detonate" as it is often called more rapidly than 

 others. 



Sometimes a charge of dynamite explodes imperfectly or may even 

 burn partly or entirely. When only part of the charge explodes so little 

 work may be accomplished that it will have to be done over again. The 

 gases given off by burning dynamite are quite different from those of 

 properly exploded dynamite and are often very poisonous. Imperfect 

 detonation is usually caused by the use of weak detonators or dynamite 

 that is insensitive because of being frozen or chilled. 



Chilled or frozen dynamite will rarely do good work. The other 

 principal causes of poor results in blasting are insufficient tamping or the 

 improper location of the charge. Poor results may also be due to too 

 large or too small a charge or to the use of the wrong strength or wrong 

 kind of dynamite. 



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