effect of liquid oxygen may be a disadvantage, as the breathing of air that is always cool may produce serious physiological complications if the wearer is exerting himself and consequently warm. Four types of this form of apparatus have been produced. The

FIGURE 16.-Fleuss-Davis apparatus, back view

Areophor, Areolith, the Brown-Mills, and the Rotherham, all manufactured in England. The latter two are used to a small extent in that country.

INTERNAL REGENERATION

as the source of oxygen and as the medium for absorbing the carbon dioxide exhaled. This method is attractive in theory, as sodium or potassium peroxide (Na,O, or K,O) plus water (HO) produce either sodium or potassium hydroxide (NaOH or KOH) and oxygen (02). However, in practice the method has a number of disadvantages, such as the great amount of heat produced and the foaming of the material and resultant blocking of the air ducts and tubes; also, when these chemicals are mixed with coal dust they are explosive.

CIRCULATION OF AIR THROUCH APPARATUS.

OXYGEN FROM CYLINDER PASSES THROUGH CLOSING VALVE INTO
REDUCING VALVE. THENCE THROUGH INSERTION RUBBER TUBE INTO INHALE
SIDE OF BREATHING BAC AT THE LEFT SIDE OF BODY.

WHILE INHALING. OXYCEN PASSES FROM THE BREATHING BAC INTO
THE COOLER, THENCE THROUGH INHALE TUBE PAST THE INHALE VALVE AT
THE MOUTHPIECE. TO THE MOUTH,

UPON EXHALING. OXYGEN AND CO2 PASS BY MEANS OF THE EX-
HALE VALVE AT THE MOUTHPIECE AND EXHALE TUBE. INTO THE EXHALE SOC
OF THE BREATHING BAC. WHENCE IT PASSES THROUGH THE RECENERATING
MATERIAL AT THE BOTTOM OF THE BAC.

THE RECENERATED SUPPLY PASSES TO THE FRONT OF THE BREATH-
INC BAC READY FOR THE NEXT INHALATION.

THE BY-PASS VALVE WILL SUPPLY OXYCEN TO THE WEARER ENTIRELY
INDEPENDENT OF THE MAIN CLOSING VALVE.

FIGURE 17.-Circulatory system and valve details of Fleuss-Davis apparatus

Two types of this form of apparatus the Pneumatogen designed in England and the Service devised in America-were completed, but they did not meet practical requirements and were therefore abandoned.

Since its introduction into America the development of the compressed-oxygen form of mine rescue apparatus has been extensive. The so-called "helmets" have been supplanted by apparatus of the mouthpiece types, and the set or fixed feed type of apparatus supplying the oxygen at a definite predetermined rate to the wearer has