﻿382 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  nature 
  is 
  no 
  longer 
  to 
  be 
  expected, 
  it 
  is 
  in 
  order 
  to 
  take 
  account 
  of 
  

   any 
  rubber 
  bearers 
  that 
  may 
  be 
  encountered 
  in 
  regions 
  that 
  have 
  not 
  

   received 
  careful 
  explorations. 
  

  

  RUBBER 
  AND 
  NEAR-RUBBER 
  

  

  Two 
  very 
  different 
  meanings 
  are 
  carried 
  by 
  the 
  word 
  rubber 
  — 
  the 
  

   more 
  common 
  physical 
  meaning 
  of 
  a 
  highly 
  elastic 
  substance, 
  and 
  a 
  

   more 
  general 
  chemical 
  meaning, 
  admitting 
  as 
  rubber 
  all 
  the 
  sub- 
  

   stances 
  sufficiently 
  related 
  to 
  rubber 
  to 
  show 
  the 
  same 
  reactions 
  with 
  

   solvents 
  and 
  precipitants, 
  with 
  little 
  regard 
  to 
  the 
  factor 
  of 
  elasticity 
  

   which 
  seems 
  so 
  all-important 
  from 
  physical 
  and 
  mechanical 
  view- 
  

   points. 
  The 
  trees 
  or 
  plants 
  that 
  produce 
  fully 
  elastic, 
  high-grade 
  

   rubbers 
  are 
  relatively 
  few, 
  the 
  best 
  known 
  being 
  the 
  Para 
  rubber 
  

   tree, 
  the 
  Castilla 
  tree, 
  and 
  the 
  Assam 
  rubber 
  tree. 
  Several 
  others, 
  

   the 
  African 
  rubber 
  tree 
  (Funtumia) 
  , 
  the 
  African 
  rubber 
  vines 
  (Lan- 
  

   dolphia), 
  the 
  intisi 
  rubber 
  of 
  Madagascar 
  (Euphorbia 
  intisi), 
  the 
  

   Sapium, 
  or 
  virgin 
  rubbers 
  of 
  South 
  America, 
  and 
  the 
  Gryptostegia 
  

   vine 
  may 
  also 
  qualify 
  as 
  producers 
  of 
  real 
  rubbers. 
  To 
  be 
  reckoned 
  

   as 
  near-rubbers 
  are 
  gutta-percha, 
  balata, 
  chicle, 
  guayule, 
  goldenrods, 
  

   milkweeds, 
  and 
  many 
  other 
  rubberlike 
  gums, 
  some 
  of 
  them 
  of 
  distinct 
  

   industrial 
  and 
  commercial 
  value. 
  

  

  Some 
  of 
  the 
  near-rubbers, 
  like 
  some 
  of 
  the 
  synthetic 
  rubbers, 
  have 
  

   special 
  uses 
  which 
  they 
  may 
  serve 
  even 
  better 
  than 
  the 
  best 
  elastic 
  

   rubber. 
  Gutta-percha, 
  for 
  example, 
  had 
  developed' 
  many 
  special 
  

   uses 
  for 
  which 
  rubber 
  became 
  serviceable 
  after 
  being 
  vulcanized. 
  

   Making 
  rubber 
  more 
  like 
  gutta-percha 
  was 
  one 
  of 
  the 
  immediate 
  

   advantages 
  of 
  vulcanization, 
  rubber 
  being 
  much 
  cheaper. 
  Gutta- 
  

   percha 
  was 
  indispensable 
  to 
  the 
  early 
  discoveries 
  and 
  applications 
  

   of 
  electricity. 
  Insulating 
  the 
  first 
  Atlantic 
  cables 
  was 
  the 
  epoch- 
  

   making 
  contribution 
  of 
  gutta-percha. 
  If 
  rubber 
  had 
  not 
  arrived, 
  

   gutta-percha 
  doubtless 
  would 
  have 
  been 
  the 
  great 
  wonder-working 
  

   material, 
  and 
  all 
  the 
  other 
  nonelastic 
  or 
  slightly 
  elastic 
  gums 
  doubt- 
  

   less 
  would 
  have 
  had 
  relatively 
  greater 
  values 
  than 
  they 
  can 
  attain 
  in 
  

   competition 
  with 
  rubber. 
  Yet 
  each 
  of 
  these 
  substitute 
  substances 
  is 
  

   worthy 
  of 
  being 
  considered 
  from 
  the 
  standpoint 
  of 
  possible 
  use 
  and 
  

   potential 
  improvement. 
  The 
  advance 
  of 
  rubber 
  chemistry 
  may 
  make 
  

   it 
  possible 
  to 
  improve 
  the 
  quality 
  of 
  the 
  rubber 
  material 
  in 
  any 
  

   plant 
  by 
  simple 
  treatment 
  in 
  connection 
  with 
  the 
  processes 
  of 
  ex- 
  

   traction 
  or 
  of 
  manufacture. 
  

  

  RUBBER 
  WITHOUT 
  LATEX 
  

  

  Even 
  if 
  rubber 
  were 
  confined 
  to 
  plants 
  with 
  latex, 
  to 
  make 
  a 
  com- 
  

   plete 
  canvass 
  of 
  the 
  rubber 
  bearers 
  would 
  be 
  a 
  large 
  undertaking, 
  but 
  

   no 
  such 
  limit 
  can 
  be 
  set 
  to 
  the 
  plants 
  that 
  need 
  to 
  be 
  examined 
  to 
  

  

  