Am.  Jour.  Pharm., 
Dec,  1885. 
Chemistry  of  Rhubarb. 
G17 
the  same  kind  of  rhubarb  root  after  forty-eight  hours'  maceration  in 
water  (experiment  4).  But  whilst  the  colored  matter  obtained  in 
experiment  4  was,  after  drying,  of  a  golden  yellow  color,  showed  a 
^  granular  crystalline  condition  and  separated  readily  from  the  filter, 
that  obtained  in  this  subsequent  experiment  had,  after  drying,  a  more 
dirty  yellow  color,  adhered  closely  to  the  filter  and  the  horny  crystalline 
form  was  less  pronounced. 
In  this  case  a  small  quantity  of  amorphous  substance  still  clung  to 
the  coloring  matter,  due  probably  to  the  shorter  duration  of  the 
maceration  of  the  rhubarb  powder  with  water. 
6.  1*037  gram  of  rhubarb  No.  Hi  was  treated  with  water  as  in 
experiment  4,  and  then  upon  the  dried  residual  rhubarb  was  poured 
12  grams  of  light  petroleum  spirit,  which  upon  being  shaken  was 
immediately  colored  intensely  yellow.  After  eight  days'  maceration 
the  liquid  was  filtered  off,  more  petroleum  spirit  passed  through  the 
rhubarb  on  the  filter  and  the  filtrate  evaporated.  The  residue,  dried 
at  between  100°  and  105°C.,  amounted  to  O'OIS  gram  =  1-36  per 
cent,  of  dried  substance ;  it  consisted  of  chrysophanic  acid  and  fat. 
It  will  be  seen  that  here  the  yield  was  considerably  smaller  than  by 
the  process  followed  in  experiment  4,  and  this  is  explained  by  the 
fact  that  chrysophanic  acid  is  only  soluble  to  a  small  extent  in  light 
petroleum  spirit,  so  that  an  eight  days'  maceration  of  the  root  with 
twelve  times  its  weight  of  light  petroleum  spirit  only  partially 
exhausted  it.  When  the  residual  rhubarb  from  this  experiment  was 
treated  with  a  second  quantity  of  petroleum  spirit,  the  latter  after  a 
time  acquired  a  strong  yellow  color.  Light  petroleum  spirit  would 
seem,  therefore,  to  be  better  adapted  for  the  qualitative  than  for  the 
quantitative  determination  of  chrysophanic  acid  in  rhubarb. 
The  foregoing  experiments  make  us  acquainted  with  the  interesting 
fact  that  chrysophanic  acid  is  first  formed  in  rhubarb  root  upon  diges- 
tion of  the  latter  with  water ;  and  that  therefore  little  or  none  of  this 
acid  exists  preformed  in  the  more  important  kinds  of  rhubarb.  The 
formation  of  chrysophanic  acid  is  due  without  doubt  to  its  splitting 
off  from  the  mother  substance,  chrysophan,  effected  probably  by  a 
ferment-like  body,  which  is  soluble  in  water,  but  not  soluble  in  alco- 
hol ;  it  is  for  this  reason  that  an  alcoholic  extract  of  the  root  can  be 
•evaporated  without  decomposition,  because  while  chrysophan  will  be 
contained  in  it  the  body  causing  the  fermentation  will  not.  In  this 
way  also  it  is  explained  sufficiently  for  present  purposes  how  an 
