Contributions to the Chemistry of Chlorophyll. 185- 



The compounds of phyllocyanin containing zinc are in some 

 respects not unlike chlorophyll itself, or rather the green constituent 

 of chlorophyll, and it was, therefore, natural to suppose that the 

 peculiar effects observed when zinc powder was made to act on 

 Hoppe-Seyler's chlorophyllan (impure phyllocyanin ?) were due to- 

 regenerated chlorophyll. The phyllocyanin zinc compounds, like 

 chlorophyll itself, yield bright green strongly fluorescent solutions • 

 they are easily decomposed by strong acids, and they are rapidly 

 changed under the combined influence of air and light. The absorp- 

 tion spectrum of the phyllocyanin zinc compounds consists like that 

 of chlorophyll of four bands, but the bands do not exactly coincide 

 with those of chlorophyll as regards position and relative intensity. 

 In making such comparisons it must not of course be forgotten that 

 what we in a general way call chlorophyll is a mixture, the com- 

 ponents of which have not hitherto been separated from one another 

 in a satisfactory manner. 



The various double compounds of phyllocyanin are not equally 

 susceptible to the influence of air and light ; they differ as much in this 

 respect, inter se, as do phyllocyanin and chlorophyll, the former being 

 a very stable body, the latter exceedingly unstable. The compounds 

 containing zinc are most easily changed, while those containing 

 copper are very permanent. These differences were clearly manifested 

 in an experiment of which the results were as follows : — A dilute 

 alcoholic solution of phyllocyanin was divided into four equal parts. 

 In one part the phyllocyanin was left uncombined ; in the second 

 part it was by the addition of acetic acid and zinc oxide and boiling 

 changed into phyllocyanin zinc acetate, while in the third and fourth 

 parts it was in like manner converted into phyllocyanin ferrous 

 acetate and phyllocyanin cupric acetate respectively. All four liquids 

 having been made equal in volume by the addition of alcohol where 

 required, were exposed from the end of July in loosely stoppered 

 cylinders to alternate sunlight and diffused daylight, an alcoholic 

 solution of chlorophyll of approximately the same intensity as the 

 phyllocyanin zinc acetate solution being placed in a fifth vessel at the 

 side. After three days' exposure the chlorophyll solution had 

 become nearly colourless, though it still showed bands due to ready- 

 formed phyllocyanin. After one week's exposure the phyllocyanin 

 zinc acetate solution had in like manner lost the greater part of its 

 green colour, retaining only a faint greenish-yellow tinge with a 

 slight fluorescence, and showing a faint band in the red. After a 

 fortnight's exposure the solution appeared nearly colourless, and the 

 band in the red could only be seen when the light passed through a 

 considerable thickness of liquid, while the other solutions were quite 

 unaltered as regards colour and absorption-bands. After a further 

 exposure of five weeks the phyllocyanin solution had become much 



