Am.  Jour.  Phaim.  f 
April,  1884.  J 
Preparation  of  Pure  Chlorophyll. 
217 
but  not  chlorophyllan — are  nevertheless  totally  distinct  one  from  the 
other.1 
But  it  is  not  only  towards  concentrated  acids  that  chlorophyll  is  so 
sensitive,  for  it  is  quickly  decomposed  even  by  weak  acids,2  always 
with  formation  of  chlorophyllan.  The  constant  presence  of  vegetable 
acids  in  the  cells  of  the  leaf  explains,  therefore,  the  rapid  decomposi- 
tion of  chlorophyll  tinctures,  which,  as  may  be  shown  spectroscopi- 
cally,  takes  place  even  during  the*  preparation  of  the  solution,  and  goes 
-  on  till  the  whole  of  the  chlorophyll  is  converted  into  chlorophyllan, 
as  evidenced  by  the  change  of  color  of  the  liquid  from  green  to 
yellow.  Hence  all  attempts  to  obtain  the  coloring  matter  in  the  pure 
state  from  chlorophyll  solutions,  either  by  precipitation  with  saline 
solutions,  as  I  formerly  proposed  (loo.  cit.,  p.  181),  or  by  separation 
with  benzene,  carbon  sulphide,  etc.,  fail  in  their  object,  inasmuch  as 
the  coloring  matter  is  decomposed  by  the  accompanying  substances, 
even  during  the  process  of  extracting  it  from  the  leaves. 
Equally  unavailing  have  been  the  attempts  made  to  prepare  the 
pure  coloring  matter  by  saponification  of  chlorophyll  extracts.  Chau- 
tard,  ("  Compt.  rend.,"  [76],  570)  has  drawn  attention  to  the  differ- 
ences between  the  spectroscopic  characters  of  these  alkaline  solutions 
of  chlorophyll  and  those  of  chlorophyll  tincture.  I  myself  have  also 
further  studied  the  action  of  alkalis,  and  have  found  that  this  treat- 
ment always  yields  products  of  decomposition,  recognizable  as  such  by 
their  spectroscopic  characters. 
According  to  the  present  state  of  our  knowledge,  we  must  regard  as 
pure  chlorophyll  the  product  whose  absorption  spectrum  agrees  with 
that,  of  living  leaves,  as  regards  both  the  positions  of  the  individual 
bands  and  likewise  their  breadth  and  intensity.  Such  a  body  I  have 
obtained  by  a  reduction  of  chlorophyllan,  a  substance  easily  obtained 
in  the  crystalline  state  by  the  action  of  zinc  dust  on  alcoholic  solution 
of  chlorophyllan  at  the  heat  of  the  water-bath. 
[The  author  then  describes  the  absorption  spectra  of  this  emerald- 
green  body  and  of  living  leaves,  and  continues:] 
1  The  spectroscopic  behavior  of  those  two  bodies  shows,  t  herefore,  that  a 
body  may  undergo  chemical  alterations  not  recognizable  by  spectroscopic 
observation. 
2Conipare  also  Kraus,  "Zur  Kenntniss  der  Chlorophyllfarbstoffe  und 
ihrer  Verwandten."— -Stuttgart,  1872.  Sachsse,  "Die  FarbstofFe,  Kohlehy- 
drate  und  Proteinsuhstanzen. — Tjeipzig,  1877. 
