176 ENGINEERING ON THE FARM 



poured off, after which the nitroglycerin is filtered and 

 washed. It is a colorless liquid which dissolves very slowly 

 in water. Nitroglycerin is sweet in taste and poisonous. 

 Medically it is used as a heart stimulant, but its greatest 

 value is in the manufacture of commercial dynamite. 



Fulminate of mercury. Fulminate of mercury is a 

 gray crystalline salt formed by the action of alcohol and 

 nitric acid on mercury nitrate. When dry this compound 

 can be exploded by a very slight blow or rise in temperature. 

 It is too sensitive to be used as a primary commercial 

 explosive, but the ease with which it can be fired makes it 

 valuable for use in very small quantities as a detonator for 

 other explosives. 



Dynamite. Dynamite is the explosive most frequently 

 used for blasting. It was invented by a Swedish chemist 

 named Noble in 1867. The object of its invention was to 

 overcome the disadvantages of nitroglycerin due to the 

 danger in storing and transporting. Dynamite provides 

 for the use of nitrogylcerin in a form which is compara- 

 tively safe and convenient. It is made by the absorption 

 of nitroglycerin in some porous substance called the base. 

 Three kinds of material are used for the base: An inert 

 base, one composed of an absorbing material which is itself 

 neither combustible nor explosive and serves only as stor- 

 age for the nitroglycerin; a combustible base, one composed 

 of an absorbing material which is combustible and adds 

 to the explosion the force generated by combustion; an 

 explosive base, one composed of material which is itself an 

 explosive and on the explosion of the nitroglycerin explodes 

 with it. The term active base is applied to both the com- 

 bustible and the explosive. Practically all dynamite of 

 the present day has an active base. 



Good dynamite has much the consistency of dark-brown 

 sugar. It varies in color, being brown, gray, white, yellow, 

 or red, according to the base used. It appears on the 

 market in cylinders, usually 8 inches long and from pi to 



