26 TUNNELING 



Nitroglycerine. Nitroglycerine is one of the modern explo- 

 sives used as a substitute for gunpowder. It is a fluid pro- 

 duced by mixing glycerine with nitric and sulphuric acids ; it 

 freezes at +41 F., and burns very quietly, developing carbonic 

 acid, nitrogen, oxygen, and water. By percussion or by the 

 explosion of some substances, such as capsules of gunpowder 

 or fulminate of mercury, nitroglycerine produces a sudden 

 explosion in which about 1,250 volumes of gases are pro- 

 duced. The pressure of these gases has been calculated at 

 26,000 atmospheres, or 324,000 Ibs. per sq. in. Nitroglycerine 

 explodes very easily by percussion in its normal state, but with 

 great difficulty when frozen ; hence, in America, at the begin- 

 ning of its use, it was transported only in a frozen state. When 

 dirty, nitroglycerine undergoes a spontaneous decomposition 

 accompanied by the development of gases and the evolution 

 of heat, which, reaching 388 F., causes it to explode. Not- 

 withstanding the enormous pressures which nitroglycerine de- 

 velops, it is very seldom used in its liquid state, but is mixed 

 with a granular absorbent earth composed of the shells of 

 diatoms. The fluid undergoes no chemical change by being 

 absorbed, and explodes, freezes, and burns under the same con- 

 ditions as in the fluid state. 



Dynamite The credit of rendering nitroglycerine available 



for the purposes of the engineer by mixing it with a granular 

 absorbent is due to Albert Nobel of Stockholm, Sweden, who 

 named the new material dynamite. The nitroglycerine in 

 dynamite loses very little of its original explosive power, but 

 is very much less easily exploded by percussion, and can be 

 employed in horizontal as well as vertical holes, which was, of 

 course, not possible in its liquid state. Dynamite must contain 

 at least 50 % of nitroglycerine. Some manufacturers, instead of 

 diatomaceous earth, use other absorbents which develop gases 

 upon explosion and increase the force of the explosion. These 

 mixtures are classed under the general name of false dyna- 

 mites. A great many varieties of dynamite are manufactured, 



