510 



Mr. DugaJd Clerk 



[Feb. 22 



at low temperatures. He generally found a deficit of about 50 per 

 cent., that is, the pressures were only half those which he expected. 

 He accounted for this by assuming that upon gaseous explosion the 

 dissociation temperature of steam and carbonic acid Avas exceeded, 

 and consequently chemical combination was arrested until tempera- 

 ture fell. Bunsen's apparatus was very crude, and could not have 

 been expected to give accurate results. The maximum pressures 

 must have far exceeded the pressures registered by his apparatus. 

 To register pressures so instantaneous as those given by hydrogen 

 and air or oxygen in such a small tube as Bunsen's, very light and 

 delicate apparatus would be required ; whereas he used long levers 

 with heavy weights. 



Messrs. Mallard and Le Chatelier, and Berthelot and Yieille, took 



Fig. 5. 



up the subject of gaseous explosions, and made experiments also with 

 numerous gases and oxygen, and coal gas and air. They used an 

 indicator instrument of a different type ; but even with their instru- 

 ment the records examined by me appear subject to very great 

 oscillations of pressure, apparently depending upon the period of the 

 indicators used. 



A few years later a series of experiments were made by me, in 

 1888, with the apparatus which I show in section. Here I used a 

 Richards indicator of the best construction known at that date, and 

 secured indications which were fairly reliable. I show a slide from 

 which you will see curves of explosion and cooling with coal gas 

 obtained by means of this apparatus. These experiments also showed 

 clearly that the whole of the heat present was not evolved at maxi- 

 mum temperature, assuming the gases to have their ordinary specific 

 heat at the high temperatures as well as low. Messrs. Mallard and 

 Le Chatelier, and Berthelot and Vieille, came to the conclusion that 



