Some Photochemical Experiments with Pure Chlorophyll. 347 



(V) Allomerisation. Particularly in water-free media, chlorophyll fre- 

 quently undergoes a change, called by Willstatter allomerisation, which 

 consists of an alteration in the internal constitution of the chlorophyll 

 molecule. Unaltered chlorophyll on saponification with alkali gives a 

 brown colour, which, after a few minutes, changes back to green. Allomerised 

 chlorophyll does not give this "brown phase " on saponification. 



(c) The phytol group may have been attacked. This is likely to take 

 place if the chlorophyll is extracted from leaves rich in the enzyme 

 chlorophyllase. The substances formed by such an action on the phytol 

 group are most frequently the acid chlorophyllide, the presence of which 

 may be detected by extraction of the ether solution with N/100 KOH, 

 while the alkyl chlorophyllides, which possess strongly basic properties, are 

 extracted with a 22-per-cent. HC1 solution. 



(d) A further proof that the chlorophyll has remained unaltered is that, 

 on saponification with hot alkali, it shall give the dissociation products 

 " phytochlorin e " and " phytorhodin g." 



The Preparation and Properties of a Colloidal Solution of 



Chlorophyll. 



Earlier investigators have used either a true solution of chlorophyll or a 

 film of solid chlorophyll. A few investigators have used what they call an 

 " emulsion," by which must presumably be understood water containing solid 

 lumps of chlorophyll. In view of Willstatter's researches it is extremely 

 unlikely that any solvent which dissolves chlorophyll is present in sufficient 

 quantity in the leaf to give a true solution, nor is it at all likely that 

 chlorophyll is present as a solid layer. There is good reason therefore to 

 assume with Willstatter that chlorophyll is present in the leaf in the colloidal 

 condition. 



Chlorophyll in colloidal solution is an electronegative suspensoicl. In the- 

 preparation of a chlorophyll sol a method is used which is frequently employed 

 to obtain colloidal solutions, viz., the replacement of the solvent of a true' 

 solution of the substance by a medium in which the latter is insoluble, but 

 which is miscible with the solvent. Thus chlorophyll is soluble in methyl 

 alcohol, ethyl alcohol, acetone, and pyridin, but insoluble in water. A 

 colloidal solution can therefore be prepared by dissolving chlorophyll in any 

 one of these four solvents and mixing the solution so obtained with a large 

 volume of water. 



By using a colloidal solution with water as the dispersion medium one has 

 a definite system which can be reproduced at will. 



Further, in such a system, other substances (gaseous, liquid, or solid) can 



