

Between normals. 



122 a 120 



54° 26 excellent 



122^120 



54° 17 " 



120^120 



50° 7 



jR. W. Wood, Jr. — Combustion of Gas Jets. 477 



Between normals. 

 100 a 111 64° 5 approximate. 

 Ill ,s 122 12° 3 

 122 ^ 122 28° 20 excellent. 



It is apparent from the foregoing tables that the crystals 

 under discussion do not differ essentially in crystalline habit 

 from those of the same species previously described by other 

 mineralogists. The slight differences in the recorded measure- 

 ments must be due to the imperfection of the surfaces from 

 which the light is reflected. Reflected images of the slit of 

 the goniometer have been frequently observed superimposed 

 upon each other, and differing in position by two and three 

 minutes. Errors arising from this source have been elim- 

 inated to a great extent in my tables of measurements by the 

 choice of the mean value of many observations. 



Chemical Laboratory of the U. S. Geological Survey, 

 Washington, D. C, Feb. 24th, 1891. 



Art. LYII. — Combustion of Gas Jets under Pressure; by 

 R. W. Wood, Jr. 



Any one who has watched a burning jet of ether vapor has 

 probably noticed that, as the pressure increases, the flame 

 gradually retreats from the orifice, hovering in mid-air, as it 

 were, and eventually goes out, if the pressure be carried beyond 

 a certain point. In endeavoring to discover the exact cause of 

 this, a number of rather curious phenomena were observed. 

 Different gases were experimented upon, and found to act in 

 very different ways, dependent apparently upon the relative 

 amounts of oxygen required for their combustion. 



The first experiments were made with coal gas, with pressures 

 varying from 0*5 to 25 cms of mercury. The gas was drawn 

 from a large reservoir, used for supplying an oxy-hydrogen 

 lantern, at a tension of about ten pounds to the inch, the pres- 

 sure at the jet being regulated by a stop-cock and measured by 

 an open U-form mercurial manometer. With an orifice l mm in 

 diameter, the following were the results obtained under varying 

 pressures. 



Pressure 0*5 cms — A quiet cylindrical flame, like a candle, 

 17 cms high (fig. 2 A). Pressure l cm — Flame 26 cms high. Pres- 

 sure 14 cm — Flame 33 cms high, still quiet and tapering to a fine 

 point ; this pressure gave the maximum illuminating power to 

 the flame. On increasing the pressure, the flame suddenly 

 shortened, diminished in luminosity, and vibrated considerably, 

 emitting a slight roaring sound which increased with the pres- 



Am. Jour. Sci. — Third Series, Vol. XLI, No. 246. — June, 1891. 

 32 



