MINE SAFETY DEVICES MANNING. 537 



The apparatus, a self-contained unit, is carried wholly on the 

 back of the wearer, so that his arms are unimpeded by the customary 

 front breathing bag and its connections. 



An aluminum cover incloses the whole apparatus and protects it 

 from injury. 



A pump within the mouthpiece permits the removal of saliva as 

 fast as it is formed. 



The weight of the apparatus is only 30 pounds. Its general 

 appearance is shown in plate 1. 



The apparatus has satisfactorily passed severe tests. In use it 

 is expected to prove more satisfactory than any such device hitherto 

 available. Consequently, the United States will be independent of 

 foreign makers of breathing apparatus for its future supply. 



DEVELOPMENT OF PERMISSIBLE COAL-MINE EXPLOSIVES. 

 CHARACTER AND INCREASED USE OF PERMISSIBLE EXPLOSIVES. 



The risks arising in the handling, transportation, and use of ex- 

 plosives have been lessened by the introduction of improved explo- 

 sives for coal mines. In the past black powder was generall}^ used 

 in mines that were gaseous or contained dry coal dust, and many 

 great mine disasters resulted. The Bureau of Mines seeks to have 

 safer explosives used in dangerous mines, and to this end is testing 

 explosives to determine their permissibility for such use. Those pass- 

 ing the tests are termed permissible explosives, and their use is urged 

 in all mines containing gas and large quantities of bituminous coal 

 dust. In the year 1908 only 2,000,000 pounds of these permissible 

 explosives was used in such mines, wdiereas in 1915 the amount of 

 jiermissible explosives had grown to nearly 22,000,000 pounds. 



On October 1, 1916, 148 explosives had passed the required tests 

 and had been placed on the Bureau of Mines list of permissible 

 explosives. 



MISCELLANEOUS TESTS OF PERMISSIBLE EXPLOSR'ES. 



Other tests to which permissible exlplosives are subjected are as 

 follows : 



Samples of the explosives on the permissible list are frequentl)^ 

 collected for a chemical examination to determine whether they are 

 similar in all respects to the samples originally tested by the bureau. 



The products of combustion of explosives submitted for permis- 

 sibility are examined for poisonous gases, and no explosive is ad- 

 mitted to the permissible list which giA^es more than 158 liters (5.5 

 cubic feet) of poisonous gases from 1.1 pounds of explosive. 



All explosives are examined for liability of the ingredients to 

 exude from the containers. 



