572  ON  THE  EXAMINATION  OF  INDIGO. 
of  indigo  then  contain  —Ij1?— =6.21  grs.  of  available  coloring 
blue,  or  62.1  per  cent,  of  the  weight  of  the  crude  article.* 
Berzelius'  reduction  test,  for  the  same  indigo,  indicated  only 
12*81  per  ct. ;  nearly  four-fifths  of  the  color  had  consequently 
entered  into  an  insoluble  compound  with  lime  and  was  lost. 
The  author  claims  for  his  method,  therefore,  not  only  relative, 
but  absolute  results  in  determining  the  commercial  value  of  in- 
digo ;  he  likewise  thinks  it  advantageous  to  employ  for  dyeing, 
instead  of  sulphate  of  iron  and  lime,  impure  grape-sugar  and 
caustic  potassa,  which  might  be  cheaply  prepared  from  wood 
ashes  with  burned  lime.  The  higher  price  of  the  material  would 
be  more  than  fully  compensated  for  by  the  increased  yield  of 
the  pure  dyeing  matter. 
The  author  has  also  examined  the  products  of  decomposition 
of  grape-sugar.  The  deep  brown  liquid  remaining  after  pre- 
cipitating the  indigo  blue,  was  neutralized  by  potassa,  evaporated, 
freed  from  the  crystallizing  sulphate  of  potassa,  the  residue 
treated  with  strong  alcohol,  then  dissolved  in  water,  decomposed 
by  acetate  of  baryta,  and  filtered.  A  few  drops  of  solution  of 
sugar  of  lead,  precipitated  the  humus-like  substances  ;  the  fil- 
trate yielded  with  acetate  of  lead  a  voluminous  pale  yellow  pre- 
cipitate which  in  composition  agreed  with  Bo  decker  and  Struck- 
mann's  gallactinate  of  lead.  Basic  acetate  of  lead  now  pro- 
duced a  deep  yellow  precipitate,  which,  after  decomposition  by 
sulphuretted  hydrogen,  and  digestion  with  carbonate  of  baryta, 
yielded  a  salt,  corresponding  to  pectolactinate  of  baryta.  Bo« 
decker  and  Struckmann's  formula  (Ann.  d.  Chem.  und  Pharm. 
C.  265)  for  gallactinic  acid  is  C14  H3  07  +  2  HO,  and  for  pec- 
tolactinic  acid  C10  II6  O10  +  2  HO. 
Kiessling  states,  that  the  products  obtained  by  the  decompo- 
sition of  chloride  of  silver  by  grape-sugar  and  potassa  are  like- 
wise identical  with  these  acids. —  Wittstein's  Viertelj.  Sehrift 
viii.  325—331.)  j.  m.  m. 
*No  notice  is  here  taken  of  the  weight  of  impurities,  which  ought  to  be 
deducted  from  the  weight  of  the  whole  before  calculation ;  but  even  50 
per  ct.  impurities  would  not  influence  the  result  more  than  about  -2  per  ct.  of 
the  real  coloring  matter,  if  that  point  of  the  author's  directions  is  observed, 
to  decant  the  whole  clear  liquid,  so  as  to  leave  as  little  as  possible  behind. 
