Section III. _Appliances for firing Blasting Charges._--Squibs. Safety Fuse. Electric Fuses. Cables. Detonators. Electric Firing- Machines 42
CHAPTER II. EXPLOSIVE AGENTS USED IN ROCK BLASTING.
Section I. _Phenomena accompanying an Explosion._--Nature of an Explosion. Heat liberated by an Explosion. Gases generated by an Explosion. Force developed by an Explosion 64
Section II. _Nature of Explosive Agents._--Mechanical Mixtures. Chemical Compounds 76
Section III. _Relative Strength of the common Explosive Agents._-- Force developed by Gunpowder. Relative Force developed by Gunpowder, Gun-cotton, and Nitro-Glycerine 88
Section IV. _Means of firing the common Explosive Agents._--Action of Heat. Detonation 92
Section V. _Some Properties of the common Explosive Agents._-- Gunpowder, Gun-cotton, Dynamite. Firing Temperatures 97
Section VI. _Some Varieties of the Nitro-Cellulose and the Nitro- Glycerine Compounds._--Nitrated Gun-cotton. Tonite, or Cotton- Powder. Schultze’s Powder. Lithofracteur. Brain’s Powder. Cellulose-Dynamite 103
CHAPTER III. THE PRINCIPLES OF ROCK BLASTING.
Line of least Resistance. Force required to cause Disruption. Conditions of Disruption. Example of a Heading. Economical Considerations. Tamping 106
CHAPTER IV. THE OPERATIONS OF ROCK BLASTING.
_Hand Boring._--Boring the Shot-holes. Charging the Shot-holes. Firing the Charges 128
_Machine Boring._--Boring the Shot-holes. Charging and Firing. Removing the dislodged Rock. Division of Labour 142
_Examples of Drivings._--The St. Gothard Tunnel. The Hoosac Tunnel. The Musconetcong Tunnel. Headings at Marihaye, Anzin, and Ronchamp 157
Preparation of the Charge. Boring under Water. Submarine Rocks. Obstructions in Water-courses 164
THE TOOLS, MACHINES, AND OTHER APPLIANCES USED IN BLASTING ROCKS.
_Drills._--The operations of blasting consist in boring suitable holes in the rock to be dislodged, in inserting a charge of some explosive compound into the lower portion of these holes, in filling up, sometimes, the remaining portion of the holes with suitable material, and in exploding the charge. The subjects which naturally first present themselves for consideration are: the nature, form, and construction of the tools, machines, and other appliances used. Of these tools, the “drill” or “borer” constitutes the chief. To understand clearly the action of the rock drill, we must consider the nature of the substance which has to be perforated. He who has examined the mineral constitution of rocks will have recognised the impossibility of _cutting_ them, using that term in its ordinary acceptation, inasmuch as the rock constituents are frequently harder than the material of the tools employed to penetrate them. As a rock cannot be cut, the only way of removing portions of it is to fracture or to disintegrate it by a blow delivered through the medium of a suitable instrument. Each blow so delivered may be made to chip off a small fragment, and by this means the rock may be gradually worn away. To effect this chipping, however, the instrument used must present only a small surface to the rock, in order to concentrate the force, and that surface must be bounded by inclined planes or wedge surfaces, to cause a lateral pressure upon the particles of rock in contact with them. In other words, the instrument must be provided with an edge similar to that possessed by an ordinary _cutting_ tool.