480 JR. W. Wood, Jr. — Combustion of Gas Jets. 



visible. At a very low pressure, too small to be accurately 

 measured by the manometer (say about 0*l cm ), the column of 

 gas rose unbroken like the smoke of an extinguished candle 

 (fi.g. 1 A), and a burning match applied to the top of the column 

 would ignite the jet, the flame running down to the orifice and 

 burning quietly there. On blowing out the flame and increas- 

 ing the pressure a little, the column broke into a fan at a 

 definite height (v, iig. 1 b). Below this point, the regular out- 

 line was preserved, but above it the gas diverged rapidly in 

 whirling masses. To ignite the jet permanently, it was now 

 necessary to apply flame below the point Y. If applied above, 

 the gas beyond the match burnt with a roaring blue flame, which 

 went out the instant the match was withdrawn, or if the ve- 

 locity was not too great, hung for a few moments in mid-air. 

 The point Y, where the divergence commences, is evidently 

 the point where air is being mixed with the gas. Increasing 

 the pressure brings the point nearer and nearer the orifice, 

 until finally there is scarcely a trace of the unbroken column. 



Let us now consider why it is necessary to bring the flame 

 below Y in order to ignite the jet permanently. Above this 

 point there is a mixture of gas and air, which is moving at a 

 rate considerably greater than 18 inches per second, conse- 

 quently the flame is carried up by the jet faster than it can 

 run down. Below the point Y we have a stream of undiluted 

 gas, down which the flame will travel rapidly enough to keep 

 the jet permanently lighted, for then the gas above Y will be 

 kept lighted by the flame below. What we should expect 

 would be a quiet cylindrical yellow flame below Y, and a 

 roaring, flaring, blue flame above, but this is not what happens. 

 On bringing the match below the point of divergence, the 

 burning mass above ceases to flare, and the whole subsides into 

 a quiet tapering yellow flame. The pressure may be increased 

 some centimeters before the tip begins to flare and burn with 

 a blue flame. The reason for this is not very obvious. Ignit- 

 ing the jet appears to bind it together and prevent entrance of 

 air. 



With an ordinary four-foot bat -wing burner the best flame 

 was given by a pressure of about l*3 cms of mercury. A pressure 

 f 2 cms gave a quiet flame, but there were lateral horns at the 

 bottom. At 6 cms the luminosity was greatly diminished, wide 

 horns formed, and radiating streaks appeared in the blue part. 

 At 12 cms the luminosity was nearly gone, and a dark arch of 

 unconsumed gas appeared above the orifice, fig. 3. A pressure 

 of 20 cms widened this arch, and rendered the flame non- 

 luminous. At 25 cms the flame blew itself out. 



These experiments were repeated with ether vapor, the 

 pressure being derived by boiling the fluid. Owing to the 



