70 



PUBLIC HEALTH CHEMISTRY 



methods care must be taken that the temperature and 

 pressure do not vary while the experiment is in progress. 

 Gases in Mines. The atmosphere in mines is liable to 

 become dangerously contaminated by noxious gases 

 issuing from the coal face, such as sudden discharges of 

 marsh gas from accumulations under pressure in the coal 

 measures (so-called " blowers "), by accumulation of dust 

 which may fire, and by the gases resulting from fires and 

 explosions. The following table gives the principal gases 

 found in mines, and their popular and other names. 



Miner's Name 



Composition 



Occurrence 



Remarks 



