Efficient heat radiation and cooling to avoid high temperature. (6) Simplicity, durability and strength and tight joints in every part.

The position of the apparatus when in use is shown by the side and rear views in the Fig. 18. For the better protection of the parts from injury, in the mine, a cover is provided as a

shield. The general arrangement of the parts is shown by the Fig. 19 in which the several elements are numbered to correspond to their description in the text.

Circulation in the Apparatus.-Oxygen from the bottle (1) in which it is compressed to 135 atmospheres, passes through the closing valve (2) to the reducing valve (3); thence, under normal pressure, by rubber tube connection, it passes through

a metal tube surrounded by a cooler; through an admission valve into another metal tube inclosed in cooler, being then discharged into the exhalation side of the cooler where it meets the exhaled air and passes downward with it into the regenerator; then upward into the inhalation side of the cooler, where

it enters the breathing bag in the cooler. From the breathing bag the air passes through an inhalation valve and enters the lungs, from which it is discharged through the exhalation tube into the exhalation side of the cooler.

Testing Gibbs Apparatus.-The following series of tests of the Gibbs breathing apparatus are recommended by its manufacturers:

1. Oxygen bottle should be charged to 135 atmospheres. The oxygen cylinder being tested under water for leaks, with main valve both open and closed. The cylinder is first tested with valve closed, then cap is placed on cylinder and tested with valve open. Connect oxygen bottle to reducing valve, using wrench in order to make tight connections.

2. Examine seals of regenerators in order to see that they are not broken. Connect regenerator to cooler, being sure that gaskets are in place between the connections. Screw down screws by hand and tighten with screw driver.

3. Lift breathing bag from bumper on admission valve, then turn on main oxygen valve.

Observe mica inhalation valve-if admission valve leaks the mica inhalation valve will raise and let oxygen escape.

Turn pressure tube valve on and observe the number of atmospheres indicated by the pressure gage. Pressure gage valve should always be left open. Squeeze bellows of reducing valve in order to open seat over orifice; this approximately increases the pressure to five pounds in rubber tube and metal tube. Safety valve will whistle at the above pressure if working properly. Try all connections from oxygen bottle to cooler for leaks by using brush and soap suds. Turn off main oxygen valve.

4. Blow into exhalation valve and observe air returning by way of inhalation valve, showing circulation of air through exhalation side of cooler, regenerator, inhalation side of cooler, and breathing bag. Next, close inhalation valve either by cupping hand over valve or by special connection, then blow into exhalation valve until bag is fully inflated. Exhalation valve seat and mica should make an air tight connection, keeping bag fully inflated. Test all connections for leaks, using brush and soap suds.

5. Connect mouthpiece to cooler, seeing that gaskets are in place. Inflate breathing bag and test mouthpiece connections for leaks, using brush and soap suds. Try release valve and saliva pumps for leaks.

6. After apparatus has been tested and adjusted to wearer, before adjusting noseclip, it is essential that the wearer turn on main oxygen valve, inhale from apparatus, exhale into open air several times before readjusting the clip. In this way a high percentage of oxygen and a low percentage of nitrogen will be contained in breathing apparatus. While inhaling from the apparatus the wearer will observe whether the whole apparatus is functioning properly. After noseclip is adjusted, the wearer is ready for a preliminary test in room filled with fumes. After remaining in room for five (5) minutes and no leaks being observed, the wearer can feel assured that his apparatus is in good working condition for doing work in poisonous gases and irrespirable air.

7. Under no circumstances should grease or oil be used on apparatus parts.

The Paul Breathing Apparatus.-This type of apparatus was designed by James W. Paul, long in charge of the minerescue work, as engineer of the Federal Bureau of Mines, at Pittsburgh, Penn. The apparatus is manufactured by the old Draeger. Company, now known as the American Atmos Corporation, Mr. Paul having disposed of his right and title in the apparatus to that company.

One of the highly essential improvements of the Paul apparatus, which is modeled chiefly after the Gibbs, is the combination of the self-adjusting oxygen-feed valve with a low-pressure oxygen-control valve, at the intake of the circulatory system. This device regulates the supply of oxygen and proportions it to the rate of consumption, which varies with the work performed by the wearer. Also, a pressure slightly in excess of 1 cm. of water column is automatically maintained in the system and minimizes the liability of an outside poisonous atmosphere penetrating within the apparatus.

BUREAU OF MINES

The Federal Bureau of Mines recommends that the circulation in breathing apparatus be under positive pressure throughout and that the apparatus be equipped with mouthpiece and noseclip and provided with a by-pass valve. The helmet, for mining use, is objectionable and dangerous, not only because of the difficulty of obtaining a perfectly airtight joint around the, face, but also because it is easily dislodged and greatly cuts down the range of vision. Also, the large dead-air space in the helmet permits an excessive accumulation of carbon dioxide.

The injector used in some types of breathing apparatus is complicated and liable to be out of order when needed. Any slight particle is sufficient to choke the orifice and cut off the supply of oxygen. The use of the injector also involves a negative pressure, which would cause an inflow of the surrounding atmosphere into the apparatus should there be any leak in the joints or tube connections.

Permissible Breathing Apparatus.-Owing to the grave importance of securing safe types of mining appliances manufactured in this country, an act of Congress (37 Stat., 681), approved Feb. 25, 1913, authorized the director of the Bureau of Mines to prescribe rules and regulations for testing such appliances as may be submitted to the bureau for that purpose.

Acting under this authority the Federal Bureau of Mines has prepared and published, Mar. 5, 1919, "Schedule 13," defining the requirements necessary to establish a list of socalled "Permissible" self-contained, mine-rescue, breathing apparatus. Following are the more important specifications contained in that schedule.

Definition. The Bureau of Mines considers a self-contained minerescue breathing apparatus to be permissible for use in irrespirable and poisonous gases if all the details of construction and materials are the same in all respects as those of the self-contained mine-rescue breathing apparatus that met the requirements and passed the tests for safety, practicability and efficiency made by the bureau and hereinafter described. Conditions of Testing.-The conditions under which the Bureau of Mines will examine and test self-contained mine-rescue breathing apparatus to establish their permissibility are as follows:

1. The examination, inspection, and test shall be made at the experiment station of the Bureau of Mines at Pittsburgh, Pa.

2. Applications for inspection, examination, and test shall be made to the Director, Bureau of Mines, Washington, D. C., and shall be accompanied by a complete written description of the self-contained mine-rescue breathing apparatus including the regenerator, and a set of drawings showing full details of construction of both the regenerator and the apparatus.

3. The applicant submitting the self-contained mine-rescue breathing apparatus for inspection, examination, and test will be required to furnish the apparatus in duplicate, which shall be sent prepaid to the minesafety engineer, Bureau of Mines, 4800 Forbes Street, Pittsburgh, Penn. In the event of the apparatus successfully passing all of the Bureau of Mines tests and requirements hereinafter specified, one set will be retained by the Bureau of Mines as a laboratory exhibit and the other set will be returned to the owner. In the event that an apparatus does not pass all of the bureau's tests or requirements, both sets will be returned to the owner.

4. Each self-contained mine-rescue breathing apparatus shall have marked on it in a distinct manner the name of the manufacturer and the name, letter, or number by which the type is designated for trade pur