VOLUME 33, NO. 3, MARCH, 1956
a
A PHOSPHINE FIRE FLASK CLYDE R. DILLARD Morgan State College, Baltimore, Maryland
[EDITOR'S NOTE: This experiment involves a fire bamrd and should be carried out with esuti~n.1
A FLASK which spouts flame with no visible means of ignition provides a dramatic climax to a demonstration of chemical magic. The device works on the principle of displacement of phosphine gas which is spontaneously inflammable in air. The flask is shown in the figure. It consists of a one-liter Florence flask A, fitted with a two-hole rubber stopper into which are inserted a length of 12-mm. O.D. glass tubing, B, and a gooseneck C made of 7-mm. O.D. tubing. The demonstration is prepared as follows: The flask including the tube and gooseneck is filled with water. Care must be taken that no air bubbles are trapped in the tubes or between the stopper and the neck of the flask. The flask is then inverted into a pneumatic trough half filled with water. Phosphine, pH3, is prepared by heating a few pieces of white phosphorous with 40 per cent NaOH.' The generator is fitted with a delivery tube which dips below the surface of the water in the pneumatic FRET, PAULR., "College Chemistry," Prentioe-Hall, Ino., New York, 1952, p. 356.
trough. When the gas from the delivery tube begins to ignite spontaneously a t the surface of the water, the tube B is placed over the delivery tube and the flask is two-thirds filled with PH, by the displacement of water. A finger is placed over the end of tube B, and the flask is quickly set upright. Since the tube B now dips below the surface of the water left in the flask and the gooseneck is filled with water, the phosphine is safely out of contact with the air and the flask can be transported to the demonstration table. When water is poured int o the flask through tube B, the PH, is displaced and ' bubbles out through the gooseneck, bursting into flame as i t meets the atmosphere. Since the ignition is actually due to the presence of a small amount of P2H4which is unstable, the flask must be freshly prepared no more than three hours before the demonstration. -
