blow that breaks the bulb may or may not break the filament. The result in either case may be briefly explained as follows: 1. If the filament is broken and its parts do not shortcircuit the current ignition of the gas is not likely to occur. If the broken parts, however, fall across each other in such manner as to again close the circuit their burning out in the air will generally ignite any gas present. 2. If the filament remains intact when the bulb is broken. it will burn out more or less rapidly, according to the manner of fracture and consequent inrush of air and gas. A small hole due to the breaking of the tip may admit the air so slowly that the gas is consumed without explosive violence. In that case there may occur a slight explosion within the bulb, which is not broken but only pierced. This feeble explosion, however, may not be communicated to the outside gas. Prevention of Mine Explosions. No means has yet been devised that will insure absolute freedom from mine explosions. But the tendency to explosion and the frequency of these occurrences can and has been greatly reduced by studying their causes and adopting measures to remove them. The following points are of chief importance: 1. Effective mine regulations and discipline. 2. Operation in accordance with the state mining law. 3. Enforcing by suitable penalties all mine regulations. 4. Thorough frequent inspection by competent men. 5. Education and training of all men employed in any capacity in the mine, in respect to the proper performance of their duties, the dangers to which they are exposed and the mining law and mine regulations in force. 6. Eternal vigilance of mine officials and a regard for safety greater than the desire for increasing the daily output of the mine. 7. Coöperation of employers and employed in increasing the safety of mine work. 8. Coöperation of all coal companies in respect to mining requirements. Aside from the above general outline there is the necessity for each company to study carefully the conditions existing in its own mines, and to adopt a system of inspection and methods of ventilating the mine and mining and hauling the coal that will produce the best results and insure the greatest freedom from accumulations of gas and dust on the roads and in the workings. Immunity from explosion can only be secured by removing the cause. SECTION V MINE RESCUE WORK AND APPLIANCES PRELIMINARY, ENTERING A MINE AFTER EXPLOSION, FIRST- PRELIMINARY Entering a Mine after an Explosion.-Prompt action and intelligent and effective measures are necessary for the rescue of any possible survivors of a mine explosion. The nature of the work and the great risk incurred in its undertaking demand that it shall be performed by the most experienced of the volunteers, of whom there is never any lack. Immediately after an explosion in a mine, the following procedure is important: 1. Call for volunteers and from them choose those who are more experienced and familiar with the mine and the work to be performed. 2. At the same time, observe the mine entrances and judge of the probable effect of the explosion in the mine; examine the ventilating apparatus and have any necessary repairs made at once. 3. Collect the necessary safety lamps, tools, timber, canvas, brattice boards, nails, etc. Caged canaries or mice should also be provided, and two or more sets of breathing apparatus should make up the equipment. 4. Divide the rescuers into three parties, as follows: (b) Repair gang and rescuers; (c) Supply gang to render every possible assistance. Organize each party under a competent leader who shall be in absolute control while underground. 5. Enter the mine at the earliest possible moment-the apparatus men proceeding first and keeping from 100 to 200 yd. in the lead of the others, who must not advance ahead of the air. 6. Each section of the mine should be explored by the apparatus men to discover any possible fire therein, before restoring the circulation in that section. As quickly as any survivors are found they must be promptly removed to fresh air and the proper restoratives applied. At the surface, physicians should be in attendance and ambulances provided for the prompt removal of those brought out of the mine. Suggestions on First-aid to Explosion Victims.-Those trained in first-aid work are the ones who should assume charge and have absolute control of the care of any survivors as quickly as found, until the arrival of a physician. The following brief suggestions are important: 1. Be calm and quiet; act promptly but not in a hurry; keep cool and observe closely every symptom and condition. 2. Remove promptly but carefully to fresh air. 3. Do everything possible to stop bleeding. 4. Examine for broken bones before moving far. 5. Use aromatic spirits of ammonia if stimulant is needed. 6. If overcome by gas, give artificial respiration. 7. If unconscious, loosen clothing, warm and stimulate by rubbing the limbs; give no stimulant if face is flushed and pulse strong, but sprinkle cold water on face and chest. If the body and limbs are cold, use warm applications; keep the patient covered with blanket or other coverings; apply smelling salts or spirits of ammonia cautiously to the nostrils. BREATHING APPARATUS Principle of Breathing Apparatus.-The principle of all breathing apparatus is that the wearer breathes the same air over and over again, the carbon dioxide exhaled in the breath being absorbed after each expiration while, at the same time, the requisite amount of oxygen is restored, thus rendering the expired air pure and fit to be again inhaled. Action in Respiration. In the act of inhalation, the air enriched with oxygen passes from the breathing bag in the bottom of the cooler, up through the latter and is drawn through the inhalation valve and tube into the lungs. In exhalations, the air, deprived of some of its oxygen and containing from 2 to 4 per cent. of carbon dioxide, depending on the amount of the exertion, is discharged through the exhalation tube and valve into the exhalation side of the cooler where it meets the oxygen supply, as previously stated, and passes into the regenerator where it is to give up its carbon dioxide, by contact with the absorbent caustic soda. Requirements in Respiration. The average full capacity of the lungs of an adult person is about 300 cu. in. This volume, however, is never utilized in the act of breathing; that is to say, all of the air contained in the lungs is never exhaled or the lungs would collapse, which would be fatal. There is a certain volume of residual air, about 100 cu. in., that remains in the lungs after a deep expiration. In the ordinary act of breathing, the average person expires only about 20 or 30 cu. in. of air at a single breath. This has been called "tidal air." In the performance of work or when undergoing any extra exertion, a larger quantity of air is expelled from the lungs at each breath and a corresponding quantity again inhaled. The ordinary rate of respiration is 16 breaths per minute when a person is at rest, making the volume inhaled, from 300 to 500 cu. in. per min. When making violent exertion in the performance of work, breathing is more rapid and a much larger volume of air is respired. This quantity will vary with the person and the exertion made or the work performed. When doing strenuous work a man may inhale 200 cu. in. of air at a single breath. Approximately, the volume of carbon dioxide exhaled is equal to that of the oxygen breathed into the lungs, the ratio of carbon dioxide to oxygen being slightly less when the person |