Section III, 1919 [211], Trans. R.S.C. 



The Combustibility of Mixtures of Hydrogen and Heliujn 



By John Satterly, D.Sc, M.A., F.R.S.C, 

 and E. F. Burton, Ph.D., F.R.S.C. 



(Read May Meeting, 1919.) 



These experiments were performed at the request of the British 

 Admiralty in November and December of 1917. In connection with 

 the use of heHum in balloons it is of interest and importance to find 

 out how far the helium may be diluted with hydrogen before the 

 mixture becomes combustible. The addition of hydrogen to helium 

 increases the bouyancy. It also lessens the cost so that it pays on 

 both accounts to add hydrogen until the limit for safety is reached. 



In the following experiments the helium was obtained from natural 

 gas by the well-known methods of getting rid of all other ingredients 

 by condensation with liquid air and absorption by cocoanut charcoal. 

 The hydrogen was obtained from water by electrolysis, using pyro- 

 gallol to take out any oxygen that had diffused over to the hydrogen 

 side of the voltmeter, and phosphoric pentoxide to dry it. The quanti- 

 ties of gases used in the experiments' were measured in an apparatus 

 devised by the late Dr. T. G. Brodie. In it, a Travers' siphon com- 

 municates to a chamber or pipette where the volume can be adjusted 

 by mercury to be exactly 10 cc. and the pressure of the gas at that 

 instant can be read off by a mercury column in a barometer tube. 

 More gas can be passed in the mercury adjusted and the new pressure 

 read. The increase of pressure bears to the first pressure the same 

 ratio as the volume of gas passed into the volume of gas already in 

 the apparatus. 



In the first set of experiments the helium was passed into the 

 pipette and the pressure read, then a certain quantity of hydrogen 

 was passed in and the pressure again read. Then the mixture was 

 expelled through the Travers' siphon, a white hot platinum spiral 

 (heated electrically) being held in position just above the jet. We 

 looked for a flame as the gases issued into the air. The following 

 readings were obtained: 



