1915] 



on Gaseous Explosions 



277 



centimetres within the wall of the vessel (4 inches), and D one 

 centimetre within the wall of the end (0*4 inches). The pressure 

 rise in the vessel and the temperature rise at the three thermometers 

 were measured ; the pressure by an optical indicator and the tempera- 

 tures bj the movement of galvanometer needles — all recorded photo- 

 graphically on a rotating drum. By this ingenious arrangement it is 

 possible to find the position on the rising pressure line when the 

 flame reaches the points D and C. 



Referring to Fig. 6, the spark is passed at the zero point on the 

 upper scale of the drum. The zero of pressure is shown on the 

 right-hand side. The spark passes at zero, and for some considerable 



Fig. 7. — Hopkinson Explosion Vessel. 



time, although the indication of the thermometer B shows a rapid 

 increase of temperature by departing from the line B, yet the rise of 

 pressure on the pressure line A is very small. It is obvious from the 

 nature of the line that the rate is rapidly increasing for about ' 22 

 second from the passage of the spark. It then diminishes, and the 

 rise proceeds more and more slowly until maximum pressure is 

 attained' at ()• 26 second. At 0'22 second the vessel is very nearly 

 filled with flame, and just over * 23 second a very sudden rise of 

 temperature occurs at the thermometer B. This indicates that the 

 flame has reached that thermometer, and so the vessel is then com- 

 pletely filled. The pressure, however, rises considerably after that. 

 Prof. Hopkinson considers that the vessel is entirely filled with flame 



