McClelland and Gill — Self- Ignition of Ether- Air Mixtures. 119 



ignition temperature found by Alilaire and the temperature we measure in the 

 shortest tube in which we found it most satisfactory to obtain iajnition. 



Discussion of Results. 



1. With the type of apparatus employed we have found that when the 

 explosion-tube is about 3 feet in length, or longer, a temperature of 190° C, or 

 higlier, may occur Hear the end of the tube. It has been found (Alilaire) by 

 other methods that a temperature of 190^ C. is sufficient to ignite an ether-air 

 mixture. We may therefore conclude that the ignition observed in these 

 experiments is simply due to the rise of temperature produced. 



2. We may now consider how the high temperature is produced in the 

 explosioii-tube, the distribution of temperature along the tube, and the way 

 the temperature produced depends on the dimensions of the apparatus. 

 When the tap is opened the inrush of air, etc., from the reservoir reaches a 

 high velocity, approximately equal to the velocity of sound. A stream of gas 

 travels down to the further end of the explosion-tube, and the reflected stream 



meets the dii'ect stream, with the result that the translational energy is quickly ^^^^iTn inatftj?^ 

 changed into heat, the maximum generation of heat taking place near the closed - _ ^«„^ 



end of the tube. We can from these considerations understand the distribl- "'"'^ ^ ''" 

 tion of temperature along the tube as shown on the curves. "Vi's -■* 



The effect of the plug of cotton wool at the end of the tube in preventing 

 ignition results from the way it militates against the formation of the reflected 

 stream. The influence of the pressure of the residual gas in the tube before 

 the inrush takes place is also clear. The pressure in the explosion-tube might 

 be varied considerably without having much influence on the velocity of 

 efflux from the reservoir ; but, on the other hand, an increase of the amount 

 of gas in the tube would cause the heat produced when the velocity of the 

 stream of inrushiug gas is destroyed to be more evenly distributed along the 

 tube. It is not clear why the temperature generated near the further end of 

 the explosion-tube depends to such an extent on the length of the tube. With 

 the apparatus described, ignition does not take place unless the explosion- 

 tube is at least about 3 feet in length ; and curve 1 shows how different is 

 the maximum temperature in the air experiments when the length of the 

 tube is increased to 6 feet or more. The velocity of the inrushing stream will 

 increase to some extent when it enters and travels down the wide tube; the 

 fall of pressure in the jet will be accompanied by an increase of velocity. 

 Whether this is the only factor accounting for the effect due to the length of 

 the explosion-tube is a matter worthy of further consideration. Further 

 work in this and other points of interest is in contemplation. These 

 experiments were carried out in the Laboratory of University College, Dublin. 



SOIENT. PBOC. K.D.S., VOL. XVI., NO. XI. Q 



