( 346 ) 



wa« also deposited. After a long 'search it was found thai (he cause 

 of the reaction could not l)c traced to the different kinds of glass 

 used, but was directly connected with the presence of free oxygen 

 above the surface of the liquid. This prevents the separation of 

 hexachloroethane, but on tlie oilier hand, causes the formation of C'/., , 

 HCl, and Fe./),. Iji this and in other cases — as will be shown 

 afterwards more in detail — it has been proved that trichloroacetic 

 acid in aqueous solutions acts in a remarkable manner as an oxygen- 

 carrier, and that the free acid itself is oxidised with elinr'nation 

 of free chlorine. Such can be proved by the catalytic oxidation of 

 »//i-solution by air if (X'U . COJi is present; a reaction which also 

 takes place in the dark with measurable velocity. Further by the 

 auto-oxidation of 21s.- and 4N.-acid solutions, if they are kept in 

 contact with air; by the auto-oxidation of fei-iic-chloride-solutions, 

 which all begin to get charged with (V-ions etc. 



These oxidation phenomena explain why, from a solution pi-epared 

 from 240 grams of crystallised bariumhydroxide -}- 250 grams of 

 trichloroacetic acid and decomposed with 100 grams of anhydrous ferric 

 sulphate, after seven months, a quantity of hexachloroethane was 

 obtained which amounted to only 427o of the theoretical yield. In the 

 solution was still found, by titration, 0,118 gram-atom of chlorine as 

 ion ; besides about 25 grams of free trichloroacetic acid, which were 

 obtained by direct extraction and then identified. The solution gave 

 all the rccxctions for ft'rrou.-<-\o\\ besides these for the /Vryvr-ion. As 

 these reactions had taken place in three open bottles the cause must 

 be attributed to the action of the air. In the study of the photo- 

 chemical deconq)Osition it is, therefore, necessary to carefidhj exclude 

 every trace of free oxygen. 



§ 6. Light absorption. A solution of 16 grams of ferric salt in 

 100 grams of the liquid exhibits iji a layer of 10 cm. thickness the 

 complete absorption of the visible violet, of the blue and of about 

 ^j^ of the green in the visible spectrum. If then to the solution are 

 added 16 grams of trichloroacetic acid, the now colourless solution 

 has a much smaller absorption-power ; still, with a 10 cm. thick 

 layer, about 7s of t'^^ visible \iolet also disappeared. 



The solution was now placed in four troughs which were covered 

 with glass plates as monochromatic as possible ; yellow, green, red 

 and blue '). As might have been expected, no action whatever was 

 observed, even after several weeks, in the red and yellow troughs ; 

 on the other hand, after a short time, action occurred in the blue 



1) From ScHOTT & Gen, Jena. 



