ON THE ACTION OF LIGHT ON THE IIYDRACIDS OF THE HALOGENS. 59 



Second Report of the Committee, consistinrj of Dr. Russell {Chair- 

 man), Dr. A. KicnAiiDSON {Secretary), Captain Ahxp:v, and Pro- 

 fessors W. N. Hartley and W. Ramsay, appointed for the 

 investigation of the action of Light on the Hydracids of the 

 Halogens in presence of Oxygen. {Drawn xvp by Dr. A. 

 Richardson.) 



An extended series of experiments has been made during the past year on 

 the following lines : — 



Solutions of chlorine water were mixed with equal volumes of dilute 

 hydrochloric acid of strengths varying between "029 per cent, and 1'44 

 per cent. ; these solutions were exposed in sealed tubes to sunlight. 



After seven days (August 17 to August 24) the free and combined 

 chlorine contained in the liquids was estimated. A glance at the following 

 table will show that the addition of even a small percentage of hj^dro- 

 chloric acid exerts a very material influence on the stability of the 

 chlorine water. A parallel series of experiments was made with hydro- 

 chloric acid of the same strength as that used in the previous experiments, 

 free chlorine being absent ; these solutions were exposed in presence of 

 free oxygen for a similar period. It was found tliat no chlorine was 

 liberated from the acid, but that on increasing the strength of the acid 

 to 15 per cent, a trace of chlorine was set free, whilst a 30 per cent, 

 solution gave 1"01 per cent, free chlorine. On comparing these two 

 sets of experiments it is seen that the oxygen liberated by the decom- 

 position of water by chlorine decomposes hydrochloric acid present in 

 the solution, whereby free chlorine is restored to the liquid, although the 

 same strength of acid is stable under the influence of light in free oxygen, 



HydrocJdoric Acid and Chlorine Water exposed to Light for seven days, 



August 17-24. 



Further, it was noticed tliat the rate at which chlorine water was 

 decomposed was unaltered, whether oxygen or an inert gas like carbon 

 dioxide occupied the space above the solution. 



The action of ozone on gaseous hydrogen chloride has been studied. 

 Tubes of about 300 mms. in length -were filled with a mixture of equal 

 parts of hydrogen chloride and oxygen containing ozone, and exposed to 

 light. 



A rough estimate of the relative rates of decomposition of the gas in 

 the different tubes was obtained by observing the colour of the gas ; as 

 seen by looking through the length of the tube against a white back- 



