An
OXY-HYDROGEN SOAP BUBBLE PIPE H. M. ULLMANN AND THOMAS H. HAZLEHURST, JR. Lehigh University, Bethlehem, Pennsylvania
A CONVENIENT and strikmg method of demonstrating the lightness of hydrogen and the explosive nature of an oxygen-hydrogen mixture is to blow soap bubbles containing these gases. The danger of using the hydrogen-oxygen mixture is considerable if it is necessary to have a reservoir of the mixture as a source. Besides the obvious and greatest dwger of igniting the bubble too soon and so allowing the flame to travel b a c p through the pipe to the reservoir, there is the lesser danger of detonating the mixture in the reservoir by exploding a particularly large bubble. Both dangers may be avoided by using a soap bubble pipe with two inlet tubes, one admitting hydrogen and the other oxygen. Such a pipe may be very simply constructed from a test-tube, a cork, and f ? two pieces of glass tubing. A two-inch H& section is cut from an ordinary 5" soft glass test-tube. The lip end of a test-tube is not the best shape for a bubble pipe but the other end of the section, well fire-polished, is satisfactory. A half-inch section of cork is cut to slide with some difficulty into the tube. Two pieces of small-bore glass tubmg are inserted so that the ends are made flush with the surface of the cork. Small tubing is used to minimize
back diffusion. The cork is then pushed through the large tube until the face of it i$not more than behind the bubble end of the pipe, as shown in the figure. The smaU-bore glass tubes are connected to sources of hydrogen and oxygen, respectively. Desk cylinders of the gases are very convenient sources. No mixing of the gases can occur except in the %" space a t the mouth of the pipe and this presents practically no danger. The worst mishhp possible is that the hydrogen may bum a t the mouth of the small tube, and i t may be readily extinguished by simply turning off the hydrogen before the heat of the flame can damage the pipe, wet as i t is. To get the proper mixture of hydrogen and oxygen (approximately 2 to 1) in orderto obtain bubbles which explode with maximum violence three devices may be used. The first and simplest is to adjust the valves on the gas tanks by trial and error until the reports of the explosions of trial bubbles are as loud as possible. Instead of this, bubble tubes containing water or mercury may be inserted and the valves adjusted until approximately two bubbles of hydrogen pass in a given time for one bubble of oxygen. The most accurate method is, of course, to use flowmeters, but the demonstration hardly warrants such complication of apparatus. The pipe as described has been used by freshman demonstrators without fire or accident.
