548 
Crystalline  Constituents  of 
/  Am.  Jour.  Pharm. 
\       Dec.  1875. 
A  review  of  these  numbers  is  sufficient  in  my  opinion  to  convince 
anyone  that  it  is  impossible  to  distinguish  by  quantitative  analysis  the 
aloin  of  Barbadoes  from  that  of  Socotrine  or  Zanzibar  aloes. 
The  only  difficulty  encountered  in  this  table  of  results  occurs  in 
Stenhouse's  analysis  of  the  brominated  derivatives. 
On  referring  to  his  paper,  however,  I  found  that  this  compound  had 
been  prepared  by  adding  the  bromine  water  to  the  solution  of  the  aloin. 
Now  the  experiments  I  have  described  in  a  preceding  paragraph  indi- 
cate, I  think  conclusively,  that  the  substance  obtained  in  this  way  is  not 
pure,  that  it  is  in  fact  contaminated  with  aloin,  from  which  it  differs  so 
slightly  as  regards  its  solubility  in  spirit  of  wine  that  the  two  substances 
cannot  be  completely  separated  by  re-crystallization  from  that  solvent. 
The  only  way  of  avoiding  this  contamination  is  to  bring  the  aloin  at 
once  into  contact  with  an  excess  of  bromine,  and  this  is  best  effected 
by  reversing  the  process  of  precipitation  by  pouring  the  solution  of 
aloin  into  the  bromine  water. 
The  conclusion,  then,  to  which  these  experiments  lead  us  is  that  these 
two  crystalline  bodies  which  I  have  called  barbaloin  and  zanaloin  are 
isomeric  when  in  the  anhydrous  state.  This  conclusion  is  supported 
by  all  that  we  know  of  their  botanical  origin  and  physical  character- 
istics, as  well  as  their  chemical  properties.  The  two  bodies  resemble 
each  other  in  appearance  and  in  taste,  and  though  zanaloin  is  slightly 
paler  in  color  and  a  little  more  soluble,  there  is  no  marked  difference 
in  these  respects.  It  may  be  observed,  however,  that  zanaloin  and  its 
derivatives  contain  a  larger  amount  of  water  of  crystallization  than 
barbaloin.  As  to  qualitative  tests  there  is  but  one  in  the  action  of 
which  any  differences  can  be  perceived  in  operating  on  the  two  bodies, . 
and  that  is  nitric  acid.  With  barbaloin,  nitric  acid  gives  an  instant 
coloration  which  fades  quickly  to  orange  red.  Zanaloin,  on  the  con- 
trary, moistened  with  the  same  liquid,  gives  no  immediate  coloration, 
but  on  the  application  of  heat,  an  intense  orange  red  is  developed. 
They  both  give  chrysammic  acid  under  the  prolonged  action  of  nitric 
acid  and  both  yield  crystallizable  chloro-  and  bromo-  substitution  de- 
rivatives which  resemble  each  other  very  closely. 
Socaloin  is  believed,  and  with  great  probability,  to  be  identical  with 
zanaloin.  Zanzibar  aloes  is  but  a  variety  of  socotrine,  and  the  quali- 
tative reactions  of  the  two  agree  in  every  respect.  But  as  yet  no  quan- 
titative analyses  of  socaloin  have  been  published. 
Nataloin  is  evidently  widely  separated  from  the  rest  of  these  crystal- 
