6 3 8 



NA TURE 



[Oct. 26, 1882 



body, the chlorophyll, remains quite unchanged by the benzene, 

 but that certain bodies which absorb in the blue are insoluble in 

 this menstruum : hence the change in colour. 



Hydrochloric acid has apparently considerable power of de- 

 stroying certain of these blue-absorbing bodies, for on adding 

 this acid to an ordinary chlorophyll solution, blue rays come 

 through, where before the addition it was quite dark. This fact 

 has also this applicition : by means of it chlorophyll can be 

 obtained more free from blue-absorbing matter than in any other 

 way we are acquainted with. If to an alcoholic chlorophyll solu- 

 tion dilute hydrochloric acid be added, a precipitate is obtained, 

 and if this be washed, dried, and dissolved in ether or in a mix- 

 ture of alcohol and ether, it gives a solution which shows, not 

 only the bands of the a-modification, but also a band at the blue 

 end of the spectrum, which was before alluded to, quite dark 

 and distinct from 513 to 499. In all probability this band is 

 present in other cases, but is masked by general absorption. 



The action of alkalis on chlorophyll is quite as marked and as 

 characteristic as the action of acids. On adding either an alco- 

 holic or an a ^ueous solution of potash or soda to a chlorophyll 

 solution, two effects are produced : one is the fading out of all 

 except the least refrangible, the dominant band, and the other is 

 the spread of this band towards the blue, extending from 674 

 to 628. The action of alkali does not, however, stop here, for if 

 a considerable excess be present, another, and an exceedingly 

 interesting change sets in the dominant band now from 674 to 

 628 dividing into twodistinec bands, 1 one from 674 to 660, and 

 the other from 646 to 632 ; then if sufficient alkali be present, 

 the 674 to 628 band gradually becomes fainter and fainter, 

 and ultimately the one from 674 to 628 alone remains. 

 The same changes can be brought about with the o- and 

 )3-chlorophyll, but with far more difficulty. To change these 

 varieties the potash or soda must be stronger, and the con- 

 tact longer. With ammonia we believe we have broken this 

 band up, but in almost all cases ammonia is without action 

 on these modified chlorophylls, and it is quite clear that, as 

 regards the action of alkalis, the o- and /8-chlorophylls are far 

 more stable than normal chlorophyll. There are other and more 

 convenient methods for preparing this one-banded modification 

 of chlorophyll. One is to evaporate an alcoholic solution of 

 chlorophyll to dryness over a water-bath ; then treat the residue 

 with water, which washes out a soluble yellow subs'ance, varying 

 very much in amount with different samples of chlorophyll ; and 

 then evaporate the residue several times to dryness with a 

 mixture of equal parts of ammonia and water. Another method 

 is to act on the chlorophyll with a solution of copper sulphate ; 

 the precipitate formed is washed with water until all the co| per 

 is removed, then dried, and dissolved in alcohol and ether. 

 It gives a spectrum identical with that obtained by the 

 ammonia process, and like it the band is capable of being 

 split up into two bands. In the filtrate from the above 

 precipitate there is always much chlorophyll remaining, 

 but this, curiously enough, has also been modified, and 

 now gives only the one-band spectrum. When we first obtained 

 this one-banded substance, the position of this band appeared so 

 nearly to correspond with that of the dominant band in a strong 

 solution, that we were inclined to believe that we had really 

 separated the bodies giving the more refrangible bands, from 

 those which give the less refrangible ; but evidently this is not 

 the case ; neither does it now seem at all probable that such a 

 separation would be possible. 



We have used the term one-banded modification of the 

 chlorophyll, and are aware of the possible ambiguity that this 

 band can be split into two ; but this change is really brought 

 about only by the continued action of alkalis, for on simply 

 diluting the solution down even to the vanishing point of the 

 band, there is no indication of two bands being present. 



The solution of this one-banded substance is still of a beautiful 

 green colour, and is very remarkable for its stability ; neither a 

 trace nor an excess of acid of any kind produces any change in 

 its spectrum, and it may even be dissolved in strong sulphuric 

 acid and reprecipitated by water without alteration. 



If the action of caustic potash or soda be pushed to an extreme, 

 for instance if chlorophyll be heated with solid potash, then it is 

 apparently completely decomposed, the dominant band disap- 

 pearing, and two bands different in position from any of the 

 former ones being produced ; the*e are shown in Fig. 6. 



To return now to the fact of different leaves giving different 



1 Chautard, as long ago as T836. mentions this : he naturally concludes 

 that it is the original dominant baud split up {Cornet, rend , lxxvi. 570). 



spectra ; for instance, when vine-leaves are treated with alcohol 

 and ether, the liquid gives strongly the o- not the normal spec- 

 trum. As is well known, the juices of the vine-leaf are very 

 acid : consequently during the extraction of the colouring- 

 matter, the acid has time and opportunity for action, and hence 

 the cause of what appears at first to be an anomaly. In the leaf 

 itself the chlorophyll is in the normal condition, for if to the 

 bruised leaf precipitated calcium carbonate or carbonate of soda 

 be added, together with the alcohol and ether, the filtered liquid 

 then gives, not the o- but the normal spectrum ; and even with- 

 out the addition of the calcium carbonate, on rapidly extracting 

 the colouring-matter from the leaf and examining it immediately, 

 the spectrum is normal. It is therefore evident that although 

 both chlorophyll and acid are present in the leaf, they are not 

 under such conditions that they can act on one another ; but 

 bring them into solution, and the change commences imme- 

 diately. 



Virginia creeper, Bigonia, and other leaves, act exactly like 

 the vine. The acid in the Bigonia can be entirely removed by 

 water, and if the colouring-matter be then extracted, it gives the 

 normal spectrum. 



The way we now generally adopt in extracting the chlorophyll 

 from leaves is to add with the alcohol and ether precipitated 

 calcium carbonate ; then, whether the juice of the leaf be very 

 acid or not, is a matter of indifference. We have already stated 

 that in all the different leaves which we have examined, the 

 chlorophyll has been found to lie in the normal condition. This 

 applies of course only to freshly-gathered leaves ; the chlorophyll 

 in gathered leaves gradually changes, and passes over the a- 

 modification, the time required for this change varying with the 

 leaf and with external circumstances ; whether the leaf be ex- 

 posed to light, or kept in the dark, does not appear to affect the 

 result. Pear leaves, after being gathered for threa weeks and 

 kept in a dry room, yielded both normal and a-chlorophyll; the 

 change apparently had just begun. The chlorophyll in some 

 vine leaves that had been gathered less than ten days had com- 

 pletely passed over to the a modification ; but similar leaves, 

 gathered at the same time and kept in water, gave only normal 

 chlorophyll. Remembering how easily the solid normal chloro- 

 phyll passes over to the a-modification, it is evidently not 

 necessary to suppose that the acid in the leaf is the cause of this 

 change. 



The chlorophyll having passed over to the a-modification, 

 remains with wonderful pertinacity in the dead leaf. Dead pear 

 leaves which had fallen from the tree seven months ago si ill gave 

 a brilliant spectrum of a-chlorophyll, and even an alcoholic and 

 ether extract of tobacco gives this spectrum. 



The solutions of chlorophyll obtained by the direct treatment 

 of leaves with alcohol and ether, contain a large number of 

 substances, and the chlorophyll, as well as the other bodies, 

 undergoes change on keeping. The length of time during which 

 these solutions retain their green colour varies very much ; 

 expose them to light, and the rapidity of the change is enor- 

 mously increased. If acid be present in the solution, the chloro- 

 phyll quickly passes over to the a-modification, and even if the 

 extract has been made with calcium carbonate present, the same 

 change occurs, only more slowly. These changes take place 

 even in the dark. Besides this change of the chlorophyll, other 

 and more complicated changes occur. Solutions from some 

 leaves can be kept in the dark apparently without change for 

 months, whereas others rapidly alter, and the chlorophyll dis- 

 appears from them. The extract from rhubarb, for instance, 

 very soon changes, the solution becoming of a tolerably bright 

 red colour, and the chlorophyll bands disappearing. This x> d 

 substance and the other products of decomposition from their 

 solutions do not give visible spectra, and the same remark 

 applies to at least the majority of the colouring matters in 

 flowers. If these green solutions be exposed to bght, they are, 

 without exception, rapidly decomposed, and lose ent rely their 

 green colour, becoming either red, yellow, or of some inter- 

 mediate shade. Brilliant sunshine in an hour or two will com- 

 pletely decompose all the chlorophyll in a dark green solution, 

 not even a vestige of the dominant band remaining. If a solu- 

 tion of the a-chlorophyll, dissolved in alcohol and ether, be 

 exposed to light, it is far more difficult of decomposition, and 

 will withstand its action for a few days. That this stability is 

 not due to the absence of certain substances in the solution of 

 the a-rnoftification, is shown by dissolving some of this modified 

 chlorophyll in a normal and readily decomposable solution, when 

 it will be found that, although there will be a change of colour 



