the operator kneeling at his head grasps the wrists of both arms and proceeds to alternately swing the arms, first forward on the chest and then back to a position above the head, at the normal rate of breathing or, say 16 times a minute. In the forward movement, the arms are doubled at the elbow and pressed down firmly against the sides of the chest so as to compress the lungs and force out the gas therefrom. This is followed by the backward movement, which has the effect of expanding the lungs and inducing inhalation. These movements are continued alternately, first compressing the lungs and then expanding them in turn. While doing this, it is

important to secure the tongue and hold it forward in the mouth so that it will not impede the access of air to the lungs. A handkerchief covering the fingers will help to hold the tongue forward, or a clip must be used for that purpose.

The common method of resuscitation now most generally employed is that known as the "Schaefer method," or the "prone method" of resuscitation. By this method, the patient is laid prone on his face, except that the head is turned to one side to facilitate breathing. The operator, having made sure that the tongue is drawn forward in the mouth so as to give free access of air to the lungs, straddles the patient's thigh, as shown in Fig. 20, and rests the palms of his hands.

on the person's loins with the two thumbs together and the fingers reaching well down on each side, in a manner to bring pressure on the short ribs and across the small of the back.

In this position, the operator first swings forward so as to throw his weight on the patient's body compressing the lungs to drive out the gas or water they contain. Then, swinging backward, he gives opportunity for the expansion of the lungs, which induces the inhalation of fresh air. As in the Sylvester method, this forward and backward movement must be continued alternately, for a period of an hour or two, until there are signs of returning life or it is absolutely necessary that life is extinct. There are instances on record where the victim has been revived after several hours of hard work. It is often necessary for the operator to be relieved for a time by another, but the process must be continued without cessation, until a doctor gives it as his opinion that life has fled. In every case, send for a doctor while giving first-aid to the patient.

SECTION VI

THEORY OF VENTILATION

MINE VENTILATION-PROBLEMS-FLOW OF AIR IN AIRWAYS —VENTILATING PRESSURE, HOW PRODUCED AND MEASURED, THE WATER GAGE-VELOCITY OF AIR CURRENTS -QUANTITY OF AIR, REQUIREMENTS-WORK OR POWER ON THE AIR-EQUIVALENTS IN MEASUREMENT-EXAMPLES FOR PRACTICE-MINE AIRWAYS-SYMBOLS AND FORMULAS MINE POTENTIAL METHODS MEASUREMENT OF AIR CURRENTS-EXAMPLES FOR PRACTICE-TANDEM CIRCULATIONS-SPLITTING THE AIR CURRENT-NATURAL DIVISION OF AIR-EXAMPLES IN NATURAL DIVISIONPROPORTIONATE DIVISION OF AIR, REGULATORS SECONDSPLITTING THEORETICAL CONSIDERATIONS SPLITTING-PRACTICAL PROBLEM

ARY

MINE VENTILATION

IN

The ventilation of a mine, as the term implies, involves the supply and maintenance of a sufficient current of air throughout the mine to render the same healthful and safe.

Requirements of Ventilation.-The quantity of air in circulation must be sufficient to comply with the state mining law, and to dilute, render harmless and sweep away the gases that would otherwise accumulate in the mine. The air current must be conducted so as to sweep the entire working face and all void places with a moderate velocity sufficient to remove the gas without danger from the lamps or inconvenience to the workmen.

The Circulating System.-In order to circulate a current of air through a mine, it is necessary to provide two separate openings, one for the air to enter, called the "intake opening,' and the other for it to leave the mine, called the "return" or "discharge opening." Two distinct air passages or airways are also required, leading from these openings into the mine, in order to conduct the air current to and from the working

face. These are called, respectively, the "intake" and "return" airways. These openings and airways form a part of the circulating system in the mine, similar to the arteries and veins of the human body.

Kinds of Ventilation.-There are three different kinds of ventilation, in mining practice, known as "natural ventilation," "furnace ventilation" and mechanical or "fan ventilation," according to the agency employed for its production.

Natural Ventilation.-Ventilation is natural when it is produced by any natural agency, such as surface winds, falling water or the natural heat of the mine. The accompanying Fig. 21 illustrates the manner in which the natural heat of the mine produces a warm upcast air column, in either a drift mine or a shaft mine.

In the drift mine shown on the left, the warmer air column in the shaft only partly balances the cooler outside air. Above the level of the top of the shaft the two air columns are of equal temperature and equal weight, and, therefore, need not be considered since they balance each other. The same is true in the shaft mine shown on the right, whenever the two shafts have the same elevation at the surface.

Natural Ventilation in Slope Mines and Dip Workings.A similar condition in respect to the natural heat of the mine producing or modifying the circulation of the air, holds in all slope mines and dip workings, the same as in shafts and drifts. Whenever the mine temperature is much below or above that of the outside atmosphere, the difference in temperature makes the return air heavier or lighter than the

intake air; and the difference in weight of these two air columns destroys the equilibrium of the mine air and creates a current in the airways throughout the mine.

A considerable difference of temperature is often observed between the dip and rise air currents in particular sections of a mine. It is this difference in the temperatures of the intake and return currents that often makes dip workings harder to ventilate in summer than in winter. For the same reason, rise workings are frequently found to be more easily ventilated in the summer season.

Air Columns.-The term "air column," like water column, always refers to a vertical column. The air column, in ventilation, is an imaginary vertical column of air, of unit section (commonly, 1 sq. ft.) and of such height that its weight, in pounds, is equal to the pressure it measures (lb. per sq. ft.). The density of the air (wt. per cu. ft.) is either stated or understood, so that when the height of air column is given the pressure it indicates is readily calculated.

In mining practice, it is common to express ventilating pressure in feet of air column or, as we say, "head of air." Calling the weight of 1 cu. ft. of air w (lb.) and the head of air column h (ft.), the pressure p (lb. per sq. ft.) is calculated by the formula

=
Ρ wh

Or the air column corresponding to any given pressure is found by transposing this formula; thus,

Example. What is the head of air column corresponding to a ventilating pressure of 10 lb. per sq. ft., assuming a temperature of 60 deg. F. and a barometric pressure of 30 in.?

Solution. The weight of 1 cu. ft. of air, at the given temperature and pressure is