235 
of Chlorophyll. 
achromatic lens, and a direct-vision prism. After some time 
the leaf is treated with boiling alcohol to extract the colour- 
ing-matters, then with tincture of iodine ; the image of the 
spectrum of chlorophyll will then appear traced in starch 
iodide on the pale yellow ground of the leaf, the chlorophyll- 
band I being indicated by a well-defined line, those in the 
orange and yellow by an indistinct shading. 
Henri Jumelle 1 finds that chlorophyllic assimilation is 
always much feebler with trees having red or copper-coloured 
leaves than with trees of the same kind bearing green leaves. 
Thus the leaves of the copper beech and the purple sycamore 
assimilate six times less than those of the common beech 
or sycamore. This explains the fact familiar to horticulturists 
that the growth of trees with red foliage is much less rapid 
than that of trees of the same kind having green leaves. 
I shall now proceed to give a short account of such recently 
published memoirs as relate to the various derivatives of 
chlorophyll. 
Tschirch 2 prepares a substance which he calls c phyllocyanic 
acid ’ by making an alcoholic extract of grass, evaporating to 
dryness, and treating the residue with hydrochloric acid. It 
is evident from the mode of preparation that phyllocyanic 
acid is merely impure phyllocyanin. That it is an impure 
product may be inferred from the fact that it gives bright 
green compounds with copper and zinc, whereas it has been 
shown that phyllocyanin yields such compounds with metallic 
oxides only in the presence of organic acids. Tschirch 
prepares a normal solution of his phyllocyanic acid in alcohol 
(i : 100,000), and having obtained an alcoholic extract of a 
measured square area of a leaf, as exactly uniform as possible, 
to which a drop of hydrochloric acid has been added, and 
having diluted the extract until its absorption -spectrum 
coincides with that of the normal solution, he is able to 
estimate the quantity of chlorophyll contained in the leaf. 
In the paper on the chemistry of chlorophyll, published in 
this journal several years ago, I gave a general account of the 
1 Comptes Rendus, cxi. 382. 2 Chem. CentralbL 1889, p. 996. 
