concentrated and diluted solutions of chlorophyll. 87 



are quite well marked : there are very faint traces of the band 

 \ 565, and the general absorption has decreased very considerably. 

 In the dilute solution the band A, 565 is stronger, and the 

 band A, 538 is much weaker and more diffuse than the correspond- 

 ing band in the strong solution, and, in fact, it has almost dis- 

 appeared. In the dilute solution no band at X 508 appeared. 

 There is also a gradual creeping in of light on the more refrangible 

 side in the dilute solution when compared with the last series of 

 observations. The difference between the general absorption at 

 the beginning (1), and at the end of the observations (9), in the 

 dilute solutions is very small, whilst that of the strong solution is 

 very striking. 



Discussion of the results. 



As no effort was made to purify the chlorophyll, it is probable 

 that some vegetable acid was present : and, by the continued use 

 of the alcoholic solutions, a little of the spirit may have been 

 oxidised to acetic acid : for, at the end of the experiments, the 

 solutions were found to give a weak acid reaction with litmus 

 paper. In any case, the first series of photographs showed absorp- 

 tion spectra very similar to those described by Russell and 

 Lapraik (Jour. Ghem. Soc. vol. XLI. (1882), p. 334). Their solutions 

 were obtained by the action of very dilute acids on fairly pure 

 chlorophyll. Assuming, therefore, that the solutions used in these 

 experiments show absorption bands characteristic of chlorophyll 

 solutions in the presence of a very small amount of acid, some 

 explanation is necessary to account for the gradual changes in the 

 bands and the general absorption of two solutions containing equal 

 amounts of chlorophyll, one of which was diluted 719 times that of 

 the other. 



(1) The greater volume of the diluted solution might have 

 contained sufficient dissolved oxygen to oxidise the small quantity of 

 the dissolved chlorophyll. Against this argument is the fact that 

 although both solutions stood for several weeks in a well-lighted 

 room and with easy access of air, the changes in the strong solu- 

 tion were not in the same direction as those in the dilute solution. 

 It was the dilute solution which showed more general absorption 

 at the end of the experiments. If the primary cause of the changes 

 had been oxygen, the dilute solution might have been expected to 

 have undergone a greater change. 



(2) The changes might have been caused by the action of a 

 very weak acid analogous to that which occurs by the decomposi- 

 tion of sugars and glucosides, whereby complex molecules are broken 

 down into simpler ones ; but the same objection may be brought 

 against this explanation as against the last. 



VOL. XV. PT. II. 7 



