PHILOSOPHICAL TRANSACTIONS. 



I. On the Atomic Weight of Chlorine. 

 By EDWARD C. EDGAR, D.Sc., the University, Manchester. 



Communicated \>y Prof. H. B. DIXON, F.R.S. 



* 



Received and Read June 25, 1908. 



PART I. GENERAL. 



Six years ago Prof. DIXON and I began a research with the object of determining 

 directly the weight of chlorine which combines with the unit weight of hydrogen. 

 Our method was to burn a jet of hydrogen in an atmosphere of chlorine; hydrogen 

 being stored and weighed in palladium, the chlorine being condensed and weighed as 

 liquid. The figure we obtained for the combining weight of chlorine was appreciably 

 higher than that found indirectly by STAS, and still higher than that approved by the 

 International Committee on Atomic Weights. 



While this research was in progress, other determinations had been made bearing 

 on the relative weights of silver, chlorine and nitrogen, so that some modification in 

 the accepted values of one or more of these elements appeared inevitable. The direct 

 "joining up" of the two ends of the chain connecting hydrogen with chlorine thus 

 became a matter of immediate importance. Since the method of burning one gas in 

 an atmosphere of the other had been proved to be accurate within fairly narrow 

 limits, I was encouraged to continue the investigation, and to modify the apparatus 

 with a view to eliminate some of the possible sources of error in the former series of 

 experiments. 



The most important source of error lies in the weighing of the hydrogen. To 

 diminish this error the weight of hydrogen employed was doubled ; and since 

 Prof. DIXON and I found, when water was used to condense the hydrogen chloride 

 formed in the flame, that some of the water vapour was decomposed by the free 

 chlorine, I avoided this by burning a jet of chlorine in dry hydrogen, condensing the 

 hydrogen chloride as it was formed in a tube dipped into liquid air. In some of the 

 experiments the hydrogen chloride has been weighed. My experiments (concluded in 

 1907) agree closely with the results previously obtained in 1905. 



The method employed was briefly as follows : 



Hydrogen, made by the electrolysis of barium hydrate solution and dried by potash 

 and phosphorus pentoxide, was occluded and weighed in palladium contained in a 



VOL. CCIX. A 441. B 28.10.08 



