( 647 ) 



It was to be expected tliat the «iecomposition of the diphenyliodoiihim- 

 salt would lake place at temperaliii-es cousiderahly below the iiieltiiig- 

 poiiit, and this its actually the case. 



1. Beforehand, however, it was deemed desirable to study the 

 behaviour of the iodide towards ligiit as in the study of the velocity 

 of trajisforiuation account had to be taken of a j)ossibly existing 

 sensitiveness to light ^), 



I have found that in the case of the iodide the transformation 

 is cansed by exposure to light -) ; whilst it remains quite intact when 

 kept in the (hirk for 2'/, months. It was to l)e expected that the 

 source of the light ^vould aftect the transformation. The following 

 results were obtained : 



Electric Arc-Light : after 1 hour titro: 26.6''/„ J, convei-ted about 14.5"/^ 



The decomposition of the iodide is therefore most rapidly effected 

 l)y the arc-light. 



2. If now the solid iodide was exposed to temperatures consider- 

 ably below its mellingpoint a more or less slow conversion seemed 

 to take i)lace. Whei-eas !"/„ at most was decomposed at 90^ after 

 3 hours, about 36"/,, had disai)i)eared at 100° after 13 houis, whilst 

 after heating at 123'' for 37^ hours only 5"/„ was left undecom[H)sed. 

 This shows that the decomi)osition of the solid substance already 

 takes place even at temperatures considerably below the melti]igpoint. 

 This also applies to the solid chloride which ho\ve\er is moi'e 

 stable than the iodide. 



Several series of ex])eriments were now made with (he solid iodide 



1) The (|nanlitative estimation of iodonium haloid and lialogen-honzene in the 

 presence of each olher is simply dune by titration with AgNO;. ; the first wlieii 

 introduced into water yields one of llic iudogpn atoms as ion whilst iodo- or 

 chloiobenzene does not react with AgXO.j. 



For «liplirnyliodoninm-iodide was foimd. according to (."..vniis &2.\ and (1^2. P'/,, J, 

 calculated (^2.^'%: i»y titration 31.0 and :51.1"o -1- The cldoridi» gav»- on lilralion 

 11.15% CI, calculated 11.2%. 



') V. Meyer states that it turns yellow on exposure to light. 



