Carbon Assimilation. 
1 7 
little 20% hydrochloric acid and then washed with water in a separat¬ 
ing funnel. In this way is produced in ether solution, a magnesium 
free chlorophyll derivative, phaeophytin. The solution is evaporated 
down on a water hath and the residue dissolved in 5 c.c. alcohol. 
Note the olive green colour of the solution. This is heated and a 
grain of copper acetate is added. The colour changes back to a 
brilliant green, but without the chlorophyll fluorescence. A copper 
compound of chlorophyll has been produced very similar to the 
magnesium compound, but much more stable. 
For spectroscopic examination of this substance, see Experi¬ 
ment 15. 
Phaeophytin combines very easily with salts of some metals to 
form intensely coloured stable compounds. Ferric salts give, even 
in the cold, a greenish blue solution with a weak fluorescence. 
Zinc acetate gives a blue green solution with strong fluorescence. 
Not only phaeophytin but all the chlorophyll derivatives devoid 
of magnesium, such as phaeophorbide, phytochlorin, phytorhodin 
and the various porphyrins behave similarly towards the salts of 
certain metals (copper, zinc and iron) and form complex compounds 
all very stable in acid and alkaline media. The formation of these 
complex compounds is accompanied by such noticeable changes in 
colour that even the smallest traces of certain metals can be 
discovered in this way. Hence it is very difficult to prepare the 
magnesium free chlorophyll derivatives absolutely pure, as even the 
zinc from the walls of glass vessels may disturb the molecule ; for 
the same reason spatulas of ignoble metals must not be used. 
Also solvents may disturb the molecules of these derivatives 
owing to the impurities in them. Thus ‘ pure ’ methyl alcohol often 
contains a small quantity of copper which would be sufficient to 
affect the magnesium free derivatives. Willstatter uses this 
property in order to test the purity of methyl alcohol as regards 
copper, by dissolving some phytochlorin e in the methyl alcohol. 
After standing for some time, the chlorophyll derivative is carried 
over into ether and the excess of phytochlorin removed by washing 
with 10% hydrochloric acid. As the copper compound of phyto¬ 
chlorin e is stable in presence of this strength of acid, it remains in 
the ether layer to which it gives an intense blue-green colouration. 
The spectrum of these derivatives is also quite distinct from 
the metal free substances and more like the chlorophyll spectrum. 
See Experiment 15,^b and c. 
