'^'"rik,'"i88L''°''}  ^etulw  empyr.  and  Tinct  RuscL  55 
stopi^ed  in  the  tubes  by  oil^  and  no  capillar}^  attraction  whatever  takes 
place  in  the  fibrous  structure  itself.  After  the  cotton  has  been  rendered 
absorbent  the  fibres  will  absorb  ^vater  throughout  their  Avhole  struc- 
turCj  and  the  collapsed  fibres  will  distend. 
Hence^  absorbent  cotton  is  cotton  entirely  freed  from  all  matter  that 
will  obstruct  capillary  attraction. 
OLEUM  BETUL.E  EMPYREUMATICUM  and  TINCTURA 
RUSCL 
By  the  Editor. 
Three  correspondents  in  New  York  have  favored  us  with  the  infor- 
mation that  Tinctwra  rusci  is  not  a  tincture  of  the  obsolete  butcher's 
broom,  as  we  suggested  on  page  33  of  the  January  number,  but  that  it 
is  an  alcoholic  solution  of  birch  oil,  or  rather  birch  tar,  which  is  largely 
manufactured  in  Russia  and  Poland,  from  birch  bark,  by  a  process  of 
descending  distillation  similar  to  that  employed  in- the  preparation  of 
ordinary  tar.  This  birch  tar  resembles  wood  tar  in  appearance,  but 
has  a  peculiar  penetrating  odor,  and  is  used  in  the  manufacture  of 
Russia  leather,  which  owes  to  it  its  peculiar  odor.  Its  common  name 
is  degutt  or  dagget,  and  it  was  formerly  employed  in  medicine  and  in 
veterinary  practice  under  the  following  names  and  synonyms  :  Oleum 
hetulinum,  s.  rusci,  s.  russioum,  s.  moscoviticum,  s.  lithauinicvm. 
Birch  tar.  contains,  probably,  the  j)rincipal  constituents  of  common 
wood  tar.  By  distillation,  A.  Sobrero,  in  1842,  obtained  a  brown  oily 
liquid,  of  a  strong  odor,  lighter  than  water,  and  of  an  acid  reaction. 
On  fractionating  this  product  near  100°C.  a  pale  yellow  oil  was 
obtained  having  an  agreeable  odor,  resembling  that  of  turpentine  and 
birch  bark,  and  an  acid  reaction.  After  treatment  with  potassa  and 
lime  water  it  was  again  rectified,  and  had  then  a  more  agreeable  smell, 
like  birch  bark.  Its  composition  was  found  to  be  C^qHig-  It  dissolves 
in  alcohol  and  ether,  and  is  a  solvent  for  resins.  Between  — 16°  aiid 
— 17°C.  (about  2°F.)  it  congeals  partly;  its  boiling  point  is  156°C. 
This  is  the  only  analysis  of  birch  tar  with  which  we  are  acquainted  ; 
the  principle  to  which  the  strong  odor  of  birch  tar  is  due  does  not 
appear  to  have  been  chemically  examined. 
Recently,  birch  tar  has  been  to  some  extent  prescribed  in.  New  York 
in  the  form  of  tinctara  rusci  and  pomatum  ruscij  occasionally  simply 
