Oct. 26, 1882] 



NA TURE 



637 



that, a- far as our experiments gc — and we have now tried a 

 large number of different leaves — although there are apparent 

 exceptions, this particular substance we cal ^chlorophyll exists in 

 all green leaves. 



If thinner and thinner strata, or more and more dilute solu- 

 tions of the same thickness be examined, the fainter bands are 

 seen gradually to fade out, and what is of importance, the 

 dominant band, the last to disappear, thins nut to a band from 

 670 to 660. 



Passing over a large number of experiments on other points, 

 We shall limit our present communication as far as possible to an 

 account of the action of acids and alkalis on this so-called 

 chlorophyll. 



It is a body exceedingly sensitive to the action of acids. If 

 for instance a mere trace of hydrochloric acid gas be introduced 

 into the air of a test-tube containing a chlorophyll-solution, on 

 shaking the tube, the 628 band will be found to have moved 

 slightly towards the blue, and the next band to have become 

 fainter. This action of the acid, specially with resard to the 

 628 band, is very remarkable; the addition of acid gradually 

 causes this band to move bodily towards the blue, till it reaches 

 611 — 599. So constant and complete is this action, that the 

 of the band is an indication up to a certain amount of 

 the quantity of acid present. On adding a little more hydro- 

 chloric acid gas to the air of the test tube, and again shaking, 

 this second band will be found to have moved from 615 to 596, 

 the 589 — 573 band will have disappeared, and the other band at 

 545 — 532 will remain unmoved, but will have become much 



darker. On still further increasing the amount of acid, the 

 second band comes to 611 — 589, and now a new band appears 

 from £73 — 55S, and the band at 545 — 532 has also again in- 

 creased in intensity. Further, the blue end of the spectrum has 

 considerably opened. This spectrum, Fig. 3, is permanent, for 

 on adding more acid, even a large amount of liquid acid, no 

 further alteration takes place. The action of hydrochloric acid 

 on chlorophyll appears then to be very definite, and is well 

 shown by the two drawings, Figs. 2 and 3, which represent two 

 well-marked stages ; in the first the movement of the 628 band 

 and the disappearance of the 589 band, the other two bands re- 

 maining unaltered in position ; in the second (Fig. 3) the 62S 

 band has moved to its furthest extent, and a new band has ap- 

 peared at 573 — 558, the most and least refrangible of the four 

 bands remaining still unaltered in position. 



We have described in detail these spectra, for they have great 

 interest and importance, owing to the fact that these change* do 

 not arise from the formation of any chlorine-compound, but are 

 produced by the action of the hydrochloric acid simply as no 

 acid. Substitute any strong acid, sulphuric, nitric, &c, for the 

 hydrochloric acid, and exactly the same changes will occur. 

 U*e a w eak acid, an organic acid, such as tartaric, citric, oxalic, 

 &c, aid the action does not go beyond the first stage (Fig. 2). 

 Carbonic acid is without action on the chlorophyll. 



There is also another way in which the same changes may he 

 brought about without the presence of acid, namely, by the 

 application of heat. If, for instance, the solution of chlorophyll 

 be evaporated to dryness on a water-lath at a temperature of 8o° 



B 



Fig. I. 

 ., 2. 





3. 



., 5. 



. 6. 



or above, then on redissolution it will be found to have changed 

 and to give no longer the original, but the second spectrum. Let 

 the evaporation take place at ordinary temperatures in a current 

 of air, or under the air-pump, then, on at once red;ssolving the 

 residue, no change will have occurred ; if, however, after the 

 evaporation, the dry mass be kept for a short time, it will 

 change even at ordinary temperatures. Further, if the alcoholic 

 solution be diluted with water, and then boiled, the body giving 

 spectrum No. 2 is formed ; and the addition of certain salts, such 

 as mercuric chloride, ferric chloride, &c, causes a similar 

 change. Alum precipitates the colouring matter, and if the 

 precipitate be collected, washed, and dried at ordinary tempera- 

 lures, and again dissolved, it will give the second spectrum. On 

 the other hand, basic acetate of lead precipi'.ates the chloropjhyll 

 unchanged. 



Acids, heat, metallic solutions, all action the chlorophyll, and 

 all give rise to an identical spectrum, and therefore, we con- 

 clude, to the same body. Further, it is of interest to note the 

 identity of these processes with those used to coagulate albumin, 

 and consequently the probability that the change in both cases is 

 of a similar character. 



Since these changes are produced by processes and reagents 

 which differ so materially, we are bound to conclude that the 

 change is a molecular, not a chemical one. In these cases the 

 least refrangible band does not alter, for if the solution be 

 diluted, it always thins down to a band from 670 to 660; the 

 other three bands, on the contrary, all change, the 628 — 607 

 moving towards the blue, the 589—573 band disappearing, and 

 the 544—531 band becoming very much darker. In fact, 

 although a shadow7 indication of this last band is constantly 

 visible in the normal solution, it is often so small in amount that 



it should be regarded rather as an accidental impurity than as a 

 necessary part of the normal spectrum. Again, the essential 

 and characteristic distinction between the two spectra, Figs. 2 

 and 3, is the presence in the latter of the band at 573 — 558. 

 This hand, as far as we know, is produced solely by the presence 

 of a strong acid in considerable excess, and all specimens of 

 chlorophyll, either normal or not, yield it on the addition of 

 hydrochloric, nitric, or sulphuric acid. 



There is obviously a considerable resemblance between these 

 three spectra, but at present, notwithstanding the beautiful work 

 of Abney and Festing, we can hardly deduce from these indica- 

 tions alone the nature and relationship between these bodies ; 

 but from the processes used for obtaining them, there can, we 

 think, be little or no doubt that they are simply molecular modi- 

 fications of the original chlorophyll, and we propose at present 

 to designate them as o and /3-chlorophyll. 



With regard to the different purifying processes that have been 

 used for obtaining chlorophyll from leaves, &c, in some cases 

 the normal chlorophyll has been extracted ; in others the leaves 

 have first been dried at steam— heat, or the alcoholic solution 

 has been boiled, and it is the a-chlorophyll that has been ob- 

 tained. We have tried several of these processes, and, efficacious 

 as they undoubtedly are in removing many, if not all, of the 

 numerous bodies existing in more or less intimate connection 

 with the chlorophyll, still they appear to produce really no 

 change in the spectrum. With regard to general absorption, no 

 doubt they do produce marked effects, specially at the blue end 

 of the spec' ram ; this is well seen in the methods of purification 

 recommended by Conrad. He obtained, as he believed, a sepa- 

 tation of chlorophyll into a green and a yellow body by means 

 of benzene. Observation shows, however, that the band-giving 



