SHEATHING APPARATUS. 371 



used ; they were not the means of saving 1 any life ; on the con- 

 trary, some of the rescue party lost their lives. A Royal Com- 

 mission was appointed in England to enquire into certain mat- 

 ters connected with the safety of mines, and, among other 

 things, went into the question of breathing" apparatus. In. 

 their first report, issued in 1907, the commissioners came to 

 the conclusion that there was not really any thoroughly suit- 

 able breathing apparatus so far brought to their notice, though 

 some of them were considered capable of being made effective. 

 They classified existing forms of breathing appliances into one 

 of the following four types : 



"(i.) The first and simplest consists of a helmet through 

 which a constant current of air is driven from a pump or com- 

 pressed air pipe connected with the helmet by a long length 

 of hose. This form of apparatus, which is similar in principle 

 to the ordinary diver's helmet, is very useful when the wearer 

 has only a short distance to go from the fresh air supply, as 

 for instance, in many operations connected with underground 

 fires, but would evidently be of little use in rescue work after 

 explosions. About two cubic feet of air per minute are required 

 during work." 



"(ii.) In the second type (including the "Shamrock," "Im- 

 proved Fleuss," "Draeger," "Weg," and other apparatus), the 

 wearer breathes into and out of a bag provided with such 

 arrangements that the carbon dioxide in the expired air is 

 absorbed, and that highly-compressed oxygen from a steel 

 cylinder replaces that which is absorbed by the wearer. In 

 the three first-mentioned appliances the rate of supply of oxy- 

 gen from the cylinder is constant, and equal to about the 

 maximum rate of consumption during hard work. This affords 

 .a certainty of there being sufficient oxygen at all times, but 

 necessitates much waste. In the "Weg" apparatus there is 

 an ingenious contrivance by which the rate of supply of oxy- 

 gen adapts itself to the rate of consumption, so that waste is 

 avoided." 



"(iii.) In the third type ("Pneumatogen" apparatus) the 

 expired air is passed through a cylinder containing superoxide 

 of sodium and potassium. This not only absorbs the carbon 

 -dioxide, but also liberates at the same time sufficient oxygen to 

 make up what has been absorbed by the wearer. This appara- 

 tus is much lighter than the others, and thus presents obvious 

 advantages. Unfortunately, however, some serious attendant 

 disadvantages have not as yet been overcome." 



"(iv.) In the fourth type ("Aerolith" apparatus), the 

 wearer is afforded a supply of air by the evaporation of "liquid 

 .air." The apparatus is light and comfortable, but its use 

 would entail arrangements for making liquid air and maintain- 

 ing a constant supply to each place where the apparatus was 



