120 Mr. R. W. Wood on tlte Duration of the 



independent of the temperature, and Wildermann's suppo- 

 sition has not been confirmed. The deviations of the values 

 for the dissociation-degree calculated by the two methods 

 still remain. 



In all probability the cause lies in the inexact determina- 

 tion of the freezing-point of dilute solutions. We know from 

 the investigations of Nernst and Abegg* that its exact deter- 

 mination is attended with great difficulty. 



XV. The Duration of the Flash of Exploding Oxyhydrogen. 

 ByU.W. WooDf. 



SOME time ago, in endeavouring to photograph the ex- 

 plosion-wave, if it may be so termed, of electrolytic gas 

 by means of the electric spark, I was struck with the fact that 

 the duration of the flash was exceedingly small. In many 

 cases I found that the glass bulbs, which were thinner than 

 paper, were photographed by the light of the incandescent 

 gas within before the walls had given way. The striations 

 on the glass were sharp and the outlines of the bulb were 

 perfectly distinct, the interior being quite filled with a bright 

 glow. 



I have recently repeated and enlarged somewhat on these 

 experiments with a view to determine the duration of the 

 flash. 



The bulbs were blown very thin, with a quill-like neck at 

 each end. They were filled with a mixture of oxygen and 

 hydrogen by means of an electrolytic apparatus, and two 

 copper wires were then sealed in with wax, with a gap of 

 perhaps half a millimetre between them. 



A pendulum, made by hanging a heavy lead ball on a fine 

 wire, was hung in front of the bulb, the copper wires of which 

 were connected with the terminals of a small inductorium. 



From the bottom of the ball projected a pin which came in 

 contact with a slip of platinum foil mounted edgewise before 

 the bulb, and the pendulum and foil were put in circuit with 

 the primary coil of the inductorium. This arrangement 

 insured the explosion of the bulb at the moment when the 

 pendulum passed its point of equilibrium, and by calculating 

 the velocity of the pin's head and measuring the amount of 

 blur of the photographic image the duration of the flash 

 could be approximately determined. The camera, provided 

 with a Zeiss lens of large aperture, was placed near enough 



* Zeitschr. fiir phvs. Chemie, xv. p, 681 (1894). 

 t Communicated by the Author. 



