92 



Prof. F. Clowes. Application of a Hydrogen [Mar. 31, 



is : the difference is possibly due to the much smaller quantity of 

 oxygen required by the hydrogen flame for its combustion. 



Alcohol Lamps. — The possibility of producing large and distinct 

 "caps " when testing by means of an alcohol flame for low percent- 

 ages of " gas " in air was taken advantage of by Gr. Pieler in 1883 to 

 produce the most sensitive form of safety-lamp for gas-testing yet 

 invented. The Pieler lamp is a large Davy lamp, burning alcohol 

 from a circular wick, which yields a large flame, 30 mm. in height. 

 "When the lamp is used for testing, even the feeble light of this flame 

 is shielded from the eye, so as not to interfere with the perception of 

 the " cap." Experiments with this lamp in known percentage pro- 

 portions of " gas " and air have been described by several observers, 

 and their results were fully confirmed by a series carried out in the 

 test-chamber. The " caps " obtained were as follows : — 



0'25 per cent, of methane gave a 30 mm. cap. 

 0*5 „ . „ 65 „ 



0- 75 „ „ 75 „ 



1- 00 „ „ 90 



Indeed the flame of this lamp is so sensitive that when the propor- 

 tion of methane in the air reaches 1*75 per cent, the " cap " touches 

 the top of tne gauze of the lamp; and with a somewhat higher per- 

 centage of " gas," the enlarged " cap " completely fills the interior of 

 the gauze. 



Practical men, who have used this lamp, seem to feel some doubt 

 as to its perfect safety in the mine. But their main objection is 

 that the alcohol flame is non-luminous, and accordingly a second 

 lamp must be carried for lighting purposes when the Pieler lamp 

 is employed for gas-testing. 



Attempts have been made to obviate the inconvenience of carrying 

 two lamps, by constructing a safety-lamp with two reservoirs. One 

 of these would contain oil, and the other alcohol. Each would be 

 supplied with a wick in the ordinary way. By raising or lowering 

 one wick or the other, a luminous oil-flame for lighting purposes, or 

 a non-luminous alcohol-flame for gas-testing, should thus be obtained 

 at will within one and the same lamp : the flame being passed from one 

 wick to the other, as may be required. Practical difficulties arose in 

 the use of this composite lamp, which have prevented its adoption. 



Hydrogen Lamps. — Pieler was aware of the advantage secured by 

 employing a hydrogen flame for gas-testing. Owing to the difficulty, 

 however, of adapting a hydrogen supply to a portable safety-lamp, he 

 recommended that samples of air from the mine should be brought 

 to the surface, and tested by a hydrogen flame burning from a 



