( 349 ) 



For ;i imiiilior of years tli(> ()|)iiii()ii lias gained ,i!;i-()iiii(l in dillerenl 

 ([uartcrs, (luil the pliotoclieiincal reaclion wonld be quite analogous 

 to the lliernioehemieal one at a niiicli higlier lemperatni-e ol' the 

 system; that, therefore, the liglit (diielly increases in a liigh degree 

 the "tein|)eratui'e" in the system of the reacting substances, vvliich 

 would explain the great reaction-velocity and tiie small temperature- 

 coefficient thei-eof, etc. 



()|)posed to this view in a certain sense is another theoi'y, lately 

 defended es|)ecially by Bancroft, in which the great analogy between 

 the photochemical reaction and the processes, occurring in the electi-o- 

 Ij'sis at the cathode or the anode is pointed out. In particular, the 

 analogy with cathodic reductions occupies the first place. It cannot 

 be denied that the comparison is, in many cases, strikingly correct. 

 The decomposition-form of ferric-trichloroacetate might serve in a 

 certain sense as an argument in favour of this theory, if the electro- 

 lysis of the acid actually proceeded in the sense of Kolbl's synthesis. 



The following may ser\e to prove also the incorrectness of this 

 pres um[)t ion. 



^9. If a dilute (N/jJ aqueous solution of trichloroacetic acid is 

 electrolysed between platinum electrodes, a current of about 0,05 anq). 

 and 5 volts being used, the only result is an evolution of 0.^ at the 

 anode and double the volume of H^ at the cathode. Yet, a little 

 C4 may be detected towards the end at the anode besides some 

 67'-ions in the liquid itself ^). 



Afterwards a N/., solution was taken and submitted to electrolysis, 

 a current of 0,17 amp. and 8 volts being used. At the commencement 

 most of the gas is being evolved at the negative pole; the potential, 

 however, slowly falls to 7,6 volts and after an hour the proportion 

 between the volumes of the two gases has undergone but little 

 modification. After four hours, however, both volumes have become 

 e(jual; at the anode the evolution of the gas becomes more and 

 more rapid whilst at the cathode a more and more retarded evolu- 

 tion lakes place. The li([uid itself gets rich 'u\ CY'-ions, owing to 

 which the resistance gets less and the intensity of the current a little 

 greater. After another 37, hours, the volume of gas at the positive 

 pole is already much larger than that at the negative one, and con- 



^) This fact has always escaped notice in experiments on the determination of 

 the electrolytic dissociation constant of trichloroacetic acid. It is very much the 

 question, whether the well-known extraordinarily large value of K for this acid, as 

 deduced fiom Ostwald's experiments, is nol to he attributed in part, to the pre- 

 sence of HCi in llie solutions. 



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