500 



Prof. F. Clowes. 



[Feb. 2, 



On comparing these cap-heights with those for the corresponding 

 percentages of methane, it will be seen that they somewhat exceed 

 the latter when the hydrogen flame is used, and are somewhat less 

 than the methane cap-heights when the oil flame is employed. It is 

 important to remember that this difference exists, if coal-gas is used 

 to represent firedamp in the test-chamber. 



Observation of Flame-caps in a Rapid Current of Air containing 

 Coal-gas, and in the presence of Coal-dust. 



The test-chamber was originally introduced as a convenient form 

 of apparatus for testing the delicacy of lamps. The chamber is far 

 less costly, and less troublesome in use, and far more economical of 

 the gases to be tested, than the forms of apparatus previously used for 

 the same purpose. 



Bat it has been frequently stated by practical mining men that the 

 examination of the flame-caps in the still air of the test-chamber 

 might lead to fallacious conclusions ; since the " gas," when tested for 

 in the mine, was contained in a rapidly moving air-current caused by 

 the ventilating fan ; and this movement of the air around the safety- 

 lamp might entirely alter the character of the flame-caps which were 

 seen with the same percentage of gas in still air. 



That any effect could be produced on the cap by the movement of 

 air seemed extremely unlikely, since no lamp is now considered safe 

 in the mine the flame of which is at all affected by the ordinary 

 ventilation current. 



But whilst working with air containing coal-gas, which was easily 

 obtainable in large quantity, the question was put to the test of 

 experiment in the apparatus represented in fig. 10. 



FIG. 10. 



A square wooden tube, 12 feet in length and 14 inches square in 

 section, had a fan, A, driven by a little electric motor, pushed into one 

 end of it. This fan, when in rotation, drove an air-current at the rate 

 of 300 feet per minute through the tube ; a pipe, B, supplying coal-gas 

 from the mains, fed the gas into the air current drawn by the fan. 



