Mine Gases and Ventilation

Little was known of the aërial envelope that surrounds the earth, until the researches of Cavendish and Priestley in England and Lavoisier in France, in the latter part of the 18th century showed that air was not an element, as had been supposed, but a mechanical mixture of gases.

Up to this time, air and all combustible material was believed to contain a certain substance called "phlogiston," which escaped as flame when the substance was burned. Both Cavendish and Priestley held this phlogistic theory even after they discovered the complex nature of air. Hence, the name "dephlogisticated air" was applied to oxygen; while hydrogen was called "inflammable air" and carbon dioxide "fixed air."

It remained for Lavoisier to expose this fallacy by showing that no matter was lost, but the weight of the products of a combustion was equal to that of the combustibles burned. A large number of carefully made analyses showed a practically constant proportion of the two chief gases of which air is formed. This seemed to suggest that the oxygen and nitrogen of the air were chemically united, although the proportion of each gas did not correspond to its combining power

as determined by the analyses of well-known chemical compounds. The character of air as a mechanical mixture thus became definitely established.

Besides the two principal gases oxygen and nitrogen that constitute the air we breathe, there are other gases whose presence in the atmosphere is of much vital importance, although their proportion is small. Of these may be mentioned carbon dioxide, water vapor, ammonia, argon and

czone.

Carbon dioxide is most important, because of its toxic effect on the human system. This effect, it is stated on the highest authority, increases with the barometric pressure. Thus, for example, air containing but 1 per cent. carbon dioxide, at a pressure of 4, 5 or 6 atmospheres produces the same effect on the respiratory organs as air containing 4, 5 or 6 per cent. of the gas at a pressure of 1 atmosphere. In other words, the true gage of the effect of this gas in inspired air is the percentage of the gas multiplied by the number of atmospheres.

Water vapor present in the atmosphere breathed has a marked effect on the vital activities and the consequent development of physical energy in the body. In what manner the relative humidity of the inspired air operates to impair the physical force has not been fully explained; but experience has shown that a high degree of humidity in a warm atmosphere or climate has an extremely weakening effect on the human system.

The association of high humidity and temperature marks a comparatively large amount of water per unit volume of air and, to that extent, it may be assumed impairs the respiratory functions of the lungs. The result is to incapacitate men. exposed to such conditions and render them wholly or in part unfit to perform the required manual or mental labor. These effects are continually observed in the warm moist atmosphere of deep mine workings and other similar places.

The Respiratory System.-Respiration is the prime means of maintaining the vital action in animal organisms. Its objects are twofold: 1. The oxidation of the organic matter of the animal tissues with the resulting development of vital

energy. 2. The removal of the carbon dioxide produced in the process of oxidation. Both of these processes are performed through the medium of the blood.

The Circulation.-Under the action of the respiratory system, the blood flows from the heart into and through the arteries of the body, as water flows through a circulating pipe system under the action of a pump. The pulsations of the heart, corresponding to the strokes of the pump, force the blood through a complex system of arteries and veins to every portion of the body and limbs.

All the blood does not flow in a continuous circuit, but the arteries branch, forming separate channels leading to different parts of the body. The time required to complete a circuit and return to the heart is obviously widely different, varying from 20 or 30 sec. to one-fourth as many minutes. This is of interest in relation to the time required for poison entering the blood to be disseminated throughout the system.

Respiratory Action.-The action known as "breathing" originates, or, at least, is regulated by a nerve center at the base of the brain from which impulses are transmitted through the spinal column to the respiratory muscles. By this means air enters the air cells of the lungs and oxygen, absorbed therefrom by the red corpuscles (hæmoglobin) of the blood, is carried by the circulation to the tissues of the body, where it is consumed with the production of carbon dioxide. This gas is absorbed by the blood and carried back through the veins to the heart and lungs, where it gives up a portion of its gas, which enters the lungs and is expelled by each succeeding exhalation.

While air expired by a healthy adult, at rest, contains from 2 to 3 per cent. carbon dioxide, careful determinations show a constant production of 5.6 per cent. of this gas in the lungs when the person is at rest.

Quantity of Oxygen Consumed in Breathing.—A man at rest consumes 263 cm.3 of oxygen per min., or 263 × 0.06102 cu. in. per min. and exhales an equal volume of carbon dioxide. Air exhaled from the lungs contains 2.6 per cent. carbon dioxide, 18.3 per cent. oxygen, 79.1 per cent. nitrogen. In vio

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Mine Gases and Ventilation: Textbook for Students of Mining, Mining ...