542 ANNUAL EEPORT SMITHSONIAN INSTITUTIOlSr, 1916. 



barrier are all held in position near the roof. When the explosion 

 operates the barrier, however, the shelves fall to the positions shown, 

 and much of the dust is discharged into the entry. 



The door barrier consists of rock-dust compartments on both sides 

 and above a mine door, the barrier being held in place by the frame 

 of the door. If an explosion blows the frame out of position the 

 entire barrier collapses and a large amount of dust is discharged 

 into the air. 



The rock-dust stopping consists of two vertical rows of shelves, 

 one on each side of a stopping or wall, loaded with rock dust. In 

 the event of an explosion the overturning of these sets of shelves, 

 or the force of the explosion through the shelves causes the forma- 

 tion of a dense dust cloud that cools the flame, 



KOCK-DUST BLOWER. 



Plate 5, figure 1, shows a rather crude type of rock-dust blower, 

 with a chamber into which the dust can be fed from a hopper. 



Plate 5, figure 2, shows the dust being discharged through a hose. 

 This blower is used to blow a thick cloud of dust into the air current, 

 by whicii it is carried for considerable distances, when it settles down 

 as a mantle over whatever coal dust there may be in the mine road or 

 entry, and renders the coal dust much less likely to assist the propa- 

 gation of an explosion. The machine is particularly useful in carry- 

 ing the dust into entries that are accessible only with difficulty. 



IMPROVED MINE-GAS DETECTOR. 



Although the electric safety lamp, as compared with flame safety 

 lamps, is much safer in gaseous mines, not alone because it will not 

 under any conditions ignite the gas present, but because it gives 

 a better illumination than the flame safety lamps, it does not take the 

 place of the flame safety lamp in one of the latter's most important 

 fimctions, namely, that of testing for the presence of dangerous 

 gases. 



There has long been a demand for some sort of an indicator or 

 detector with which the presence of inflammable gas could be deter- 

 mined more accurately than with a safety lamp. Such an indicator, 

 called the Burrell gas detector, has been developed by one of the 

 chemists of the bureau. For determining the presence of inflammable 

 gases it has an advantage over a flame safety lamp because its use 

 eliminates any error due to defects of vision, and anyone can 

 easily determine the exact amount of gas present. Thus the detector 

 not only makes unnecessary the use of the flame safety lamp but 

 enables the proportion of gas present to be determined to within 0.1 

 per cent. The flame safety lamp enables the miner to estimate only 

 roughly the amount of gas present. 



