Am.  Jour.  Pharm. ) 
June,  1879.  j 
Chemical  Notes. 
thallium  chromate;  potassium  bichromate  precipitates  from  neutral 
solutions  a  mixture  of  thallium  chromate  and  bichromate,  and  from 
acid  solutions  exclusively  orange-yellow  thallium  bichromate.  The 
two  salts  have  the  formulas  Th2Cr04  and  Th2Cr207,  respectively. 
With  lithium  salts — The  lithium  chromate  and  bichromate  were  both 
obtained  by  adding  the  calculated  amounts  of  lithium  carbonate  to 
chromic  acid  solution,  and  allowing  the  solution  after  concentration  to 
stand  over  sulphuric  acid  until  the  crystals  separated  out.  Lithium 
chromate  forms  transparent  yellow  prisms  containing  two  molecules  of 
water  of  crystallization.  The  bichromate  forms  hard,  nearly  black 
plates,  which  show  a  red  color  on  the  edges.  These  crystals  also  con- 
tain two  molecules  of  water  of  crystallization.  The  results,  when 
summed  up,  seem  to  show  that  bichromates  are  only  formed  with 
monad  metals,  and  not  with  dyad  or  tetrad  elements. — 'Journal  fur  pr. 
Chem.,  19,  p.  36. 
Organic  Chemistry. —  Dr.  Erwin  von  Sommaruga  has  succeeded  in 
carrying  out  what  might  be  considered  a  difficult  undertaking,  viz.,  a 
determination  of  the  vapor  density  of  indigo.  The  formula  of  indigo  is 
frequently  written  C8H5NO,  while  the  formulas  of  many  of  its  deriva- 
tives demand  16  atoms  of  carbon  in  the  molecule.  Sommaruga  has 
now  shown  that  the  formula  of  indigo  must  be  taken  as  C16H10N2O2, 
instead  of  the  half  of  this.  Carefully  purified  and  sublimed  indigo  was 
taken,  and  Habermann's  modification  of  Dumas'  vapor-density  method 
was  used,  the  glass  globe  being  heated  in  sulphur  vapor,  and,  at  the 
same  time,  nearly  exhausted  of  air,  so  that  the  tension  was  only  30  to 
40  mm.  The  figure  gotten  for  the  vapor-density  was  9*45,  while  the 
formula  C10H16N2O2  demands  9  06,  and  C8H5NO  demands  4*53. — 
Annalen  der  Ch.  und  Ph.,  195,  p.  302. 
The  chemical  study  of  the  Quebracho -bark  has  engaged  several 
chemists  within  the  last  year.  These  results  have  been  transferred  in 
part  already  to  these  pages  (this  Journal,  1879,  PP-  I52  ana*  192)-  1° 
neither  of  these  articles,  however,  has  its  growing  importance  as  a  tan- 
ning material  been  alluded  co.  At  the  late  Paris  Exhibition  it  attracted 
considerable  attention  in  this  connection. 
According  to  Jean  ("  Bulletin  de  la  Societe  Chimique,"  1878,  No. 
28,  p.  6),  it  contains  157  per  cent,  of  a  tannic  acid,  which,  however, 
is  not  identical  with  querco  tannic  acid,  and  in  addition  2  8  per  cent,  of 
another  astringent  acid,  which  does  not  act  upon  the  animal  hide,  and 
which  behaves  with  reagents  like  gallic  acid. 
