32 CARBON ASSIMILATION [ch. 



then cuiitiiius in solution jihytochlorin e, the derivative of chlorophyll a. The phyto- 

 chlorin e gives to the ether an olive-green colour. 



The ether layer remaining in the funnel, after the separation of the gi-een-l)lue acid 

 layer, is now extracted with 10 c.c. of 12 "/q hydrochloric acid (sp. gr. 1 -06 i.e. 38-1 c.c. 

 strong acid: 61-9 c.c. water). The green acid solution so obtained is diluted with 

 water and shaken with ether which then becomes coloured red and contains phyto- 

 rhodin g, the derivative of chlorophyll h. 



If the phyllins are acted upon by mineral acids, they lose their 

 magnesium in the same way as the chlorophyllins, and the series of 

 substances obtained in this way are termed porphyrins. Thus aetiophyllin 

 will give aetioporphyrin CaiH36N4 (see Scheme 1, p. 34). 



The derivatives of chlorophyll which are free from magnesium, .such 

 as phaeophytin, phytochlorin, phytorhodin, the various porphyrins, etc. 

 combine readily with the acetates of some metals such as copper, zinc 

 and iron, and they form intensely coloured, stable compounds. The change 

 of colour is so noticeable that the smallest traces of certain metals can 

 be detected in this way.. Hence it is very difficult to prepare the 

 magnesium- free chlorophyll unless the reagents are perfectly pure and 

 all contact with certain metals is avoided. 



Expt. 25. Substitution of copper for magnesium in cMorophyll. 2 c.c. of an ether 

 solution of chlorophyll are shaken with a little 20 "/o hydrochloric acid (sp. gr. MO 

 i.e. 62-4 c.c. strong acid: 37-6 c.c. water), and then washed with water in a separating 

 . funnel. In this way is produced in ether solution the magnesium-free chlorophyll 

 derivative, phaeophytin. The solution is evaporated down on a water-bath, and the 

 residue dissolved in 5 c.c. of alcohol. The solution is olive-green in colour. This is 

 heated and a grain of copper acetate or zinc acetate is added. The colour changes 

 back to a brilliant green, but without fluorescence (if all the chlorophyll has been 

 converted into phaeophytin). 



From the results of these recent investigations, it is now possible to 

 write formulae for the two chlorophylls as follows : 



chlorophyll a (C^aHsoO N4Mg) (COOCH,) (COOC20H30) 

 chlorophyll h (QaHgsOaN^Mg) (COOCH,,) (COOC20H39) 



from which it will be seen that the phytol component amounts to one- 

 third of the weight of the chlorophyll. 



From the analyses of chlorophylls from different plants, it was found 

 that the phytol content varied, and plants which yielded little phytol 

 most readily produced "crystalline chlorophyll," a form of the pigment 

 which has been known for some considerable time to previous workers. 

 The Cow Parsnip {Heracleum Sphondylium), Hedge Woundwort (Stachys 

 sylvatica) and Hemp-nettle (Galeopsis Tetrahit) are plants which readily 

 giv6 crystalline chlorophyll. In this connexion it has been suggested 



