118 



Scientific Proceedings, Royal Dublin Society. 



this way the maximum temperature reached by the thermal-junction could be 

 found. 



A careful determination of the maximum temperature was made in this 

 way when the junction was placed 2'5 cm. from the end of the explosion- 

 tube .3 feet long and 3 inches in diameter. The pressure of the air in the 

 tube was 2 cm., that of the air in the reservoir being atmospheric. About 

 3 feet is the shortest length of explosion-tube which was certain to give good 

 ignition. The junction was carefully calibrated over the range indicated by 

 the galvanometer deflections. 



The temperature reached by the air under these conditions varied 

 between 185° and lOS'^C. 



-X- 



(y 



'W 



<y 



Fig. 2. — Potentiometer arrangement by means of which the actnal temperature reached in 

 the explosion-tiihe was determined. 



From the results of the various temperature determinations we made, it 

 may be concluded that at a short distance from the closed end of the 

 explosion-tube, 3 feet long, a temperature as high as 190° C. may occur when 

 air at atmospheric pressure is allowed to rush in, the pressure of the residual 

 air in the tube being about 2 cm. of mercury. From our earlier experiments it 

 would follow that higher temperatures would be reached with longer 

 explosion-tubes. 



Assuming that when air is replaced by an ether-air mixture the tempera- 

 ture reached is not very different, we have to consider whether this rise of 

 temperature is sufficient to ignite the mixture. 



M. E. Alilaire (Comptes Eendus, tome elxviii. No. 14, Avril, 1919, p. 729) 

 has recently studied the ignition of ether-air mixtures, and has found it 

 possible to produce ignition at a temperature of 190° C. He states that with 

 modifications of his apparatus he is of opinion that ignition could be obtained 

 at even lower temperatures. The agreement is close between the lowest 



