A very interesting piece of specialized equipment used in high explosive mining manufactured by the Atlas Powder Company of Wilmington, Delaware. Notice the dovetailing enclosure to protect the mechanism.

Unlike many tools and machines used in mining, the dynamite blasting machine, also called an exploder or blasting box is well known. Anyone who has watched cartoons is familiar with this machine.

The exploder uses a small magneto-electric machine, which is really a dynamo, to generate an electrical current to set off blasting caps that in turn ignite dynamite or other high explosives. A dynamo is another name for a generator, especially one for producing direct current.

In the early days of hard rock mining in the west, black powder was the explosive used. It is a mixture of sulfur, saltpeter (potassium nitrate), and charcoal and the ratio of these three determined the explosive characteristics. Blasting powder has less saltpeter and more sulfur than gun powder.

Front view of the
Atlas Blasting Machine.

Then came nitroglycerin, which was first used in the west by the Central Pacific Railroad in the Sierra passes. It is five times as powerful as black powder and was much better at pulling rock, but was very unstable. It was very dangerous to manufacture and to handle and its danger made it less attractive to miners than black powder.

It was not until after 1867, when Alfred Nobel received patents for dynamite and blasting caps that black powder became used less. Nobel found that a chalky earth, kieselguhr, would absorb a great deal of the highly unstable nitroglycerin. This mixture was packed into cylinders made of waxed paper and later plastics. These cylinders were called cartridges and were very stable, requiring a shock rather than a flame to set them off. It was the blasting cap that provided the shock. Cartridges generally contained fulminate of mercury due to cost and stability and were set off by fuse and caps or by electric blasting caps.

The first satisfactory electrical blasting machine was invented by H. Julius Smith, an American in 1878. It consisted of a gear-type arrangement of rack bar and pinion that operated an armature to generate electricity. A pinion is a small gear with teeth that fit into those of a larger gear or those of a rack, which is the case here. When the rack bar was pushed down rapidly, it revolved the pinion and armature with enough speed to generate the desired current. The armature is the rotating part of the dynamo, consisting essentially of wire wound around an iron core and where the current interacts with a magnetic field to produce torque. This current was released into the external, or cap, circuit when the rack bar struck a brass spring in the bottom of the machine. Smith's blasting machine was improved and made in a range of capabilities.

Rear view of the
Atlas Blasting Machine.

Since the electric blasting cap was considered safer, quicker, more efficient, more certain and cheaper, it came into widespread use. It was the exploder that played an important part in making this possible.