1873.] Comparative Vegetable Chromatology. 



453 



ciently so to enable me to determine many of its peculiarities. The best 

 method of obtaining it is to boil Ulva latissima first in water and then in 

 spirit. If this plant cannot be procured, the small green Algce so com- 

 mon on damp wood and stones may be used with advantage, and need 

 not be boiled in water. The deep green solution in alcohol should be 

 agitated with bisulphide of carbon, and a few drops of water added, if 

 requisite, to cause nearly all the green colouring-matter to be carried 

 down, and nearly all the xanthophylls to remain in solution. On removing 

 this and agitating the bisulphide with fresh spirit of wine of the usual 

 strength, taking care to have a considerable excess of the bisulphide pre- 

 sent, a large portion of the yellow chlorophyll and some of the blue are 

 dissolved. Removing this solution to another tube, adding a little water, 

 and separating the diluted alcohol, the precipitated bisulphide should be 

 evaporated to dryness at a gentle heat. On redissolving in benzole and 

 examining the spectrum of a properly diluted solution, it will be seen 

 that it differs in many important particulars from that of pure blue 

 chlorophyll. Besides bands exactly corresponding with those charac- 

 teristic of that substance, it has an independent dark and narrow band 

 in the red, and another much broader in the middle of the blue, as 

 though the solution were a mixture of blue chlorophyll with some other 

 substance* — a conclusion completely borne out by further examination, 

 since the same blue kind as that found in olive Algce occurs almost free 

 from this second substance in the residue left after repeated agitation 

 with spirit. Taking, then, a solution in benzole of blue chlorophyll, of 

 such a strength that the principal absorption-band in the red may exactly 

 correspond with that seen in the above-named mixture, and comparing 

 together the spectra side by side, it is easy to see what absorption-bands 

 are due to the other substance. Again, since blue chlorophyll is far more 

 easily decomposed by weak acids than the yellow, and yields a product 

 very slowly decomposed by light, we may take a mixed solution in which 

 the blue has undergone this change, and, by treating it in the manner 

 described above, may obtain a mixture of yellow chlorophyll and the pro- 

 duct of the action of acids on the blue. Dissolving this in benzole, and 

 taking a solution of the product of the action of acids on the pure blue, of 

 such a strength as to give the corresponding absorption-bands equal when 

 seen side by side, those due to the yellow chlorophyll can easily be distin- 

 guished ; and on exposing for a while to the direct rays of the sun, these 

 bands disappear, whilst those due to the product of the action of acids on 

 the blue kind remain just as in the specimen used for comparison. By these 

 means I have been able to prove that the spectrum of yellow chlorophyll 

 dissolved in benzole has a very dark and well-defined narrow band in the red, 

 further from the red end than that due to blue chlorophyll, and probably 

 another much fainter in the orange. There is also a broad and strong 



* See my paper "On Mixed Colouring-matters," Monthly Microscopical Journal, 

 vol. vi. p. 124. 



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