84 Schunck . — The Chemistry of Chlorophyll. 
acetate of copper or acetate of zinc. This reaction, lately re- 
discovered by Tschirch and by myself, is characteristic of 
Fremy’s phyllocyanin, with which Filhol’s ‘ matiere noire 
crystallisable ’ must therefore have been identical. 
Every one who has worked at the chemistry of plants must 
have observed the peculiar change of colour which takes 
place when fresh green leaves are treated with dilute acids. 
As the acid penetrates into the interior of the leaves the 
bright green colour changes to olive, at the same time losing 
greatly in intensity. This change is due, in the opinion of 
most observers, to the decomposition of the chlorophyll by 
the acid. When acidified leaves are extracted with boiling 
alcohol a greenish-yellow solution is obtained, which only a 
colour-blind person could mistake for an extract of fresh 
leaves with its lovely green colour. The solution no longer 
shows the absorption-spectrum of chlorophyll, but that of 
so-called ‘acid chlorophyll/ which is characterised by the 
appearance of two very dark bands at the more refrangible 
end in addition to those at the other end of the chlorophyll- 
spectrum, the latter being at the same time slightly altered 
as regards position and relative intensity. It is the presence 
of free acid in some leaves, such as those of the vine and 
Virginian creeper, that prevents our seeing the normal chloro- 
phyll-spectrum in the extracts of such leaves ; the acid re-acts 
on and changes the chlorophyll during the process of ex- 
traction, a change w r hich according to Russell and Lapraik 
may be prevented by adding calcium carbonate to the bruised 
leaves before extraction with alcohol and ether. The car- 
bonate of soda which cooks are in the habit of adding to 
green vegetables before boiling has the effect of preventing 
the discoloration which would otherwise take place in con- 
sequence of the presence of free acid in the leaves. 
Those who take a special interest in the subject should 
refer to the able and elaborate memoir entitled { A Spectro- 
scopic Study of Chlorophyll by Dr. Russell and Mr. Lapraik 1 / 
Journal of the Chemical Society, XLI. 334. 
