186 
NOTES  ON  MATERIA  MEDICA. 
immediately  begins  to  decompose,  is  quickly  strained  through 
linen,  and  an  excess  of  baryta  water  added  to  the  clear  filtrate. 
By  this,  the  hydrated  peroxide  of  barium  is  precipitated  in  shin- 
ing plates,  which  are  insoluble  in  water,  and  can  be  washed  by 
decantation.  In  order  to  be  certain  that  all  the  peroxide  is  pre- 
cipitated, a  small  portion  of  the  liquid  may  be  filtered  and  tested 
with  a  dilute  solution  of  the  bichromate  of  potassa.  (In  case 
peroxide  of  barium  is  still  present,  the  addition  of  this  reagent 
causes  a  blue  coloration  of  the  perchromic  acid. — Wittstein.) 
The  washed  precipitate  is  to  be  collected  on  a  filter,  pressed 
between  filtering  paper,  and  dried  under  an  air  pump,  by  which 
all  the  water  of  crystallization  can  be  removed.  The  dried  per- 
oxide then  has  the  form  of  a  white,  fine  powder,  similar  to  mag- 
nesia, and  the  formula  BaOa  ;  is  anhydrous,  is  contaminated  by 
a  trace  (at  the  greatest)  of  carbonate  of  baryta,  and  is  entirely 
stable.—  Vierteljh.  Ph.,  xiv.  p.  80.  G.  J.  S. 
NOTES  ON  MATERIA  MEDICA. 
By  Prof.  Archer. 
1.  Notes  on  a  New  Species  of  Gall  from  China,  with  refer- 
ences to  other  unusual  Commercial  Grails. 
Since  the  greatly  increased  demand  for  gallic  acid,  which  has 
been  caused  by  the  requirements  of  photographic  chemistry, 
much  interest  has  been  felt  in  obtaining  galls  from  various  parts 
of  the  world  from  which  to  procure  that  acid.  One  of  the  first 
new  products  of  this  class  was  the  Chinese  gall,  described  by 
Dr.  Pereira  in  the  "Pharmaceutical  Journal,"  vol.  iv.  p.  384, 
1844,  under  the  name  of  Woo-pei-tsze.  These  have  now  become 
regular  articles  of  commerce,  and  so  also  has  a  similar  one  ob- 
tained in  Japan,  rather  smaller,  but  apparently  produced  on  the 
same  tree,  or  a  closely-allied  species.  Mr.  Daniel  Hanbury, 
who  has  carefully  examined  the  Chinese  galls,  is  of  opinion  that 
they  are  produced  on  Rhus  semi-alata,  and  Mr.  Doubleday,  the 
entomologist,  has  shown  that  they  are  caused  by  an  aphis,  and 
not  by  a  cynips,  as  in  the  case  of  most  other  galls  with  which  we 
are  acquainted. 
