( 342 ) 



To sum up, we have been able to analyse tlie j)i"oc'ess of pliototropic 

 stimulation into the primary electro-physiological perception process 

 which causes the remarkable polar division of sensitiveness between 

 the apex and the base and by this means has become the actual 

 cause of the irreversibility of the phototropic curvature effect and 

 in addition, secondarily, the photochemical process which brings about 

 the curvature. Possibly we may be able to refer the decrease of the 

 phototropic curvatnre effect by means of greater quantities of energy, 

 as also rectipetality, to the origin of polarisation currents, to which 

 the polai' accumulations of ions in their turn give rise. 



Utrecht, September 1911. 



Chemistry. — " The photochemical transformations of Ferri-trichloro- 

 acctate solutions".. By Prof. F. AI, Jaeger. (Communicated by 

 Prof. V. Rombukgh). 



(Communicated in the meeting of September 30, 1911). 



§ 1. When carrying out some few yeai-s ago a series of investi- 

 gations relating to the photochemical transformations of certain 

 iron-salts by exposure to the light, 1 noticed that the almost 

 colourless solution, which forms, if fresldy precipitated ferric hydroxide 

 is shaken for some days, in the dark, with an excess of an a(|ueous 

 solution of trichloroacetic acid, — rapidly deposits, when exposed 

 to the light, a white crystalline substance; while, simultaneously, 

 a colourless gas collects in the closed limb of the U-tube employed. 

 Although a more fully detailed article on the many c[uestions which 

 present themseKes, will appear shortly, a few preliminary communi- 

 cations are already following here, regarding this remarkable photo- 

 chemical reaction. 



§ 2. Originally the solutions were prepared by shaking freshly 

 precipitated ferric hydroxide, after prolonged and complete washing, 

 in stoppered bottles with an aqueous solution of thrichloroacetic acid 

 for some days in the dark. The colourless solution may be kept 

 unaltered in the dark for an indetinite time; but when exposed to 

 daylight, it splits off, after some time, a white crystalline substance 

 with a peculiar odoui'. If an e.vcess of Fe„0^ is taken, the solution 

 obtained is orange-yellow, it is then not sensitive to light, but it 

 regains this property as soon as the solution is again rendered 

 colourless by addition of an excess of trichloroacetic acid. 



