482 REPORTS ON THE STATE OF SCIENCE. 



(B) Ethylene and Oxygen in Varying Proportions, fired at 10° and 760 mm. 



Mixture . C 2 H 4 +0 3 C 2 H 4 +20 2 C 2 H.,+30 2 * C,H 4 +40 2 C 2 H 4 +G0 2 



Rate in metres 1 2 5Q7 2 581 2 36g 2 24? 2 ng 



per sec. J ' 



* Compare this with the 2,413 metres per sec. observed for C 2 H 4 +20 2 +N 2 . 



(C) Acetylene and Oxygen in Varying Proportions, fired at 10° and 7(30 mm. 



Mixture . C 2 H 2 + 2 C 2 H 2 +H0 2 C 2 H 2 +2J0 2 * 



Rate in metres 1 2 2 716 2 3gl 



per sec. J ' ' 



* Compare this with the 2,414 metres per sec. observed for C 2 H 2 +H0 2 +N 2 . 



Section III. — The Pressures produced by Gaseous Explosions. 



Many investigators, from the time of Bunsen 's well-known experi- 

 ments in 1867 onwards, have measured the pressures produced in 

 gaseous explosions, with doubtless considerable success so far as what 

 may be termed the mean effective pressures are concerned. As the 

 subject is at present engaging the attention of a Committee appointed 

 by the Association in 1907 any lengthy reference to it in this report 

 may seem superfluous. Nevertheless, if only for the sake of complete- 

 ness, a brief resume' of our present knowledge may not be out of place. 

 The explosion vessel employed by Bunsen was a stout glass tube 

 8'15 cm. long, 1*7 cm. internal diameter, and of 18 c.c capacity. It was 

 closed by a suitable valve, the load on which could be adjusted until it 

 was just lifted when the explosive mixture was fired by means of a 

 powerful spark passed along the axis of the tube. Bunsen considered 

 that the combustion would occur under adiabatic and ' constant volume ' 

 conditions, and he identified the rate of ignition of a particular mixture 

 with that of the completion of chemical change. In calculating from his 

 results the corresponding flame temperatures he assumed the constancy 

 of the specific heats of steam and carton dioxide. Finding that the pres- 

 sures recorded in the cases of electrolytic gas and of a mixture of carbon 

 monoxide and oxygen in their combining proportions (namely, 9'5 and 

 lO'l atmospheres respectively) were somewhat less than one-half of 

 those theoretically required on the above assumptions, he concluded 

 that in each case combustion had proceeded per saltum, owing to the 

 supposed theoretical flame temperatures exceeding the limits at which 

 steam and carbon dioxide respectively are completely dissociated. 

 The problem was again attacked independently by Mallard and Le 

 Ohatelier in 1883, l and by Berthelot and Vieille in 1885. 2 The last- 

 named fired various gaseous mixtures at atmospheric pressure in a 

 spherical iron bomb, measuring the effective pressures by the movement 

 of a light piston working against a spring in a tube attached to the bomb. 

 In order to gain some information respecting the possible cooling influ- 

 ence of the walls upon the effective pressures recorded, three bombs of 

 different capacities— namely, A of 300 c.c, B of 1,500 c.c, and C 

 of 4,000 c.c — were employed. The results, expressed in each case as 

 atmospheres in excess of the atmospheric pressure, were as follows: — 



' Annalts des Mines, Sec. viii., vol. 4. 2 Ann. Chim. Phys. [vi.], 4, 13. 



