4 Professor Dixon and Mr. Harker on 



cyanogen and oxygen the rate of propagation of the com- 

 bustion is diminished by the addition of vapour-water to 

 the dry gases. The burning of cyanogen, at all events as far 

 as the initial combustion to carbonic oxide is concerned, 

 seems to be independent of the presence of water ; whereas 

 the combustion of carbonic oxide to carbonic acid seems 

 to depend upon the presence of water- vapour. A measure- 

 ment of the rate of explosion of hydrogen and chlorine, 

 firstly in the dry state, and, secondly, when saturated 

 with water-vapour seemed, therefore, likely to answer the 

 question. 



A knowledge of the velocity of the explosion-wave in 

 hydrogen and chlorine is also of great theoretical interest 

 in view of Berthelot's conclusions regarding the nature of 

 explosions : for hydrogen and chlorine combine without 

 condensation, and the gas formed approximates to a perfect 

 gas. 



The gas used in the experiments was made by the 

 method so minutely studied by Bunsen and Roscoe, namely, 

 the electrolysis of hydrochloric acid. The acid used (of 

 specific gravity about i'2o) was partly saturated with chlorine 

 gas, to save the long preliminary electrolytic saturation 

 otherwise necessary. The electrolytic cell was of glass and 

 contained about 3 litres of acid. It was provided with two 

 carbon electrodes, about 10 mm. thick, cemented by paraffin 

 into glass tubes, which dipped below the level of the liquid. 

 The upper ends of these tubes were filled with mercury, 

 making contacts for the battery wires. The delivery tube 

 contained a series of bulbs holding about 5 cc. of water. 

 This retained the greater part of the hydrochloric acid 

 carried over by the chlorine and hydrogen. From this the 

 gas was conducted through a Winckler worm, a series of 

 bulbs, and finally a large U-tube, all filled with boiled 

 sulphuric acid. Attached to the U-tube was a threeway 

 tap, one limb of which led to the explosion tube, and the 



