ArnMi?ch.  f895 rm' }    The  A pocynacece  in  Materia  Medica.  1 7 5 
paratively  few  are  the  products  utilized  or  of  commercial  importance. 
They  are,  for  the  most  part,  obtained  from  the  stems  of  climbing 
plants.  The  solidification  is  sometimes  allowed  to  take  place  naturally, 
but  generally  by  concentrating  by  exposure  to  the  sun  or  by  fire. 
Rapid  coagulation  has  the  advantage  of  preventing  from  the  begin- 
ning injurious  fermentation,  which  develops  disagreeable  odors  in  the 
caoutchouc  and  alterations,  and  yields  a  product  harder,  more  dense 
and  containing  less  water.  Coagulation  can  also  be  produced  by 
chemical  means,  as  by  acids  (sulphuric,  nitric,  tartaric  or  lemon 
juice,  etc.)  or  by  sodium  chloride,  sea-water,  alum,  etc.  Coagulation 
by  heat  is  usually  preferred,  and  during  the  operation  it  is  necessary 
to  strongly  compress  the  product. 
For  the  most  part  the  American  caoutchoucs  are  excellent  for 
industrial  purposes  ;  their  resistance,  their  toughness  and  their  con- 
siderable hardness  is  much  appreciated,  and  equatorial  America 
furnishes  alone  the  best  caoutchouc  for  all  the  rest  of  the  world. 
All  the  caoutchoucs  of  Mexico,  Central  America,  Columbia 
Guiana,  Ecuador,  and  likewise  a  large  part  of  that  from  Brazil,  are 
exclusively  furnished  by  Euphorbiceae  (Hevea,  Siphonia,  etc.)  or  by 
Urticacese  (Castilloa,  Cecropia,  etc.)  The  Hancornia  specicosa. 
Gomez  is,  with  one  or  two  closely  allied  species,  the  principal 
caoutchouc  yielding  Apocynaceae  of  America.  It  yields  the  varieties 
known  as  Pernambuco  caoutchouc,  Maranham  Caoutchouc,  and  Bahia 
Caouthouc  The  first  appears  in  plates  varying  in  thickness  from 
0*5  to  7  c.m.,  of  a  rose  color  and  an  efflorescence  of  alum  on 
the  surface.  Its  quality  is  very  inferior  to  that  of  Para  or  of  the 
Malay  caoutchoucs.  The  Maranham  Caoutchouc  is  deeper  in  color, 
like  wine-lees,  with  brown  marbling.  The  surface  is  smooth,  non- 
efflorescent,  harder  and  less  porous,  and  contains  less  water.  It  is 
probably  coagulated  by  sulphuric  acid.  The  Bahia  Caoutchouc  is 
said  to  be  produced  from  the  variety  minor  of  Hancornia.  It  is  rare 
and  of  but  little  value,  possessing  none  of  the  excellent  qualities. 
It  contains  much  water  and  foreign  substance  and  a  certain  quantity 
of  non-solidified  latex.  It  is  in  masses  or  large  plates,  rose-colored, 
and  is  probably  prepared  by  spontaneous  coagulation. 
The  caoutchoucs  of  Africa  are  furnished  almost  exclusively  by 
two  genera  of  Apocynacese,  the  Vahea  and  the  Landoljia,  which 
many  botanists  consider  under  one  genus.  A  few  Ficus  and  some 
Asclepiadeae  may  produce  a  little  of  the  gum  elastic,  but  generally 
