Schunck . — The Chemistry of Chlorophyll. 79 
base by the action of the alkali. The solutions of the acid 
have a pink or purple colour, and possess very peculiar optical 
properties. The substance is, however, of interest only to the 
chemist and the physicist, its connection with chlorophyll 
being remote. 
In his memoir on the change of refrangibility of light, Pro- 
fessor Stokes 1 alludes to what I presume he considered to be 
a derivative of chlorophyll, and which he calls ‘ modified 
chlorophyll/ the words he uses being as follows : ‘ This type 
was rather ideal than actual, being derived from a comparison 
of different cases until it seemed to be realised in the case of a 
fluid obtained by redissolving in alcohol a crust which had 
formed itself at the bottom of a test-tube containing leaf-green. 
The principle to which the peculiar absorption of such a fluid 
seems due may be called modified leaf-green. The fluid itself 
is not green, but olive-coloured, becoming red at great thick- 
nesses.’ Professor Stokes then proceeds to give an account of 
the absorption-spectrum of this substance, but has not, so far 
as I know, alluded to the matter again. The subject has, 
however, given rise to much discussion, opinions being divided 
as to what modified chlorophyll really is; some observers think- 
ing that it is chlorophyll slightly altered perhaps, not chemically 
changed, others that it is a product of the action of acids on 
chlorophyll. I mention it here because it seems to belong to 
the same class of bodies as Hoppe-Seylers chlorophyllan, the 
formation of which is due, or is supposed to be due, to the 
spontaneous decomposition of chlorophyll. 
To the same class belong probably several of the crystalline 
pigments observed by Borodin 2 on examining alcoholic ex- 
tracts of the leaves of various plants under the microscope. 
Most of the pigments described by him belong, however, to the 
class of yellow-colouring matters which are always found 
accompanying the chlorophyll of leaves, and of which so little 
is known. 
1 Philosophical Transactions for 1852, p. 487. 
2 Bulletin de l’Academie Imperiale des Sciences de St. Petersbourg, t. XXVII. 
pp. 328, 350. 1883. 
