﻿0. 
  Bancs 
  — 
  Solution 
  of 
  Vulcanized 
  India 
  Rubber. 
  367 
  

  

  long 
  standing 
  in 
  sealed 
  vessels 
  a 
  gradual 
  thickening 
  of 
  the 
  

   liquid 
  with 
  final 
  coagulation 
  seems 
  to 
  be 
  the 
  invariable 
  result. 
  

   Thus 
  there 
  must 
  be 
  a 
  gradual 
  growing 
  together 
  of 
  the 
  indi- 
  

   vidual 
  particles, 
  until 
  tinally 
  the 
  whole 
  solution 
  forms 
  one 
  co- 
  

   herent 
  gelatinous 
  mass. 
  

  

  To 
  summarize 
  : 
  Suppose 
  the 
  coherence 
  of 
  rubber 
  to 
  be 
  due 
  

   to 
  (cohesive) 
  affinities, 
  capable 
  of 
  being 
  saturated 
  like 
  ordinary- 
  

   affinities. 
  Then 
  in 
  case 
  of 
  impregnation 
  with 
  a 
  solvent, 
  a 
  part 
  

   of 
  these 
  combine 
  with 
  the 
  similar 
  affinities 
  of 
  the 
  solvent. 
  

   The 
  result 
  is 
  the 
  decided 
  decrease 
  of 
  tenacity 
  (observed). 
  To 
  

   liquefy 
  the 
  impregnated 
  sample, 
  the 
  residual 
  cohesive 
  forces 
  of 
  

   the 
  rubber 
  must 
  be 
  withdrawn, 
  and 
  this 
  can 
  be 
  done 
  by 
  heat. 
  

   The 
  liquid 
  so 
  obtained, 
  I 
  do 
  not 
  conceive 
  to 
  be 
  a 
  true 
  solution, 
  

   but 
  rather 
  a 
  suspension 
  of 
  particles, 
  the 
  exceeding 
  fineness 
  of 
  

   which 
  is 
  determined 
  by 
  conditions 
  discussed 
  elsewhere.* 
  Dif- 
  

   fusion 
  is 
  thus 
  an 
  excessively 
  slow 
  process, 
  and 
  hence 
  the 
  liquid 
  

   on 
  cooling 
  need 
  not 
  become 
  solid 
  again. 
  In 
  proportion 
  as 
  

   the 
  individual 
  particles 
  unite 
  however, 
  coagulation 
  gradually 
  

   sets 
  in, 
  and 
  its 
  structure 
  is 
  probably 
  that 
  of 
  a 
  fine 
  sponge 
  hold- 
  

   ing 
  solvent 
  in 
  its 
  interstices. 
  If 
  the 
  coagulated 
  solution 
  be 
  

   reheated 
  (under 
  pressure), 
  a 
  thin 
  viscid 
  solution 
  is 
  again 
  ob- 
  

   tained, 
  which 
  in 
  its 
  turn 
  coagulates. 
  

  

  19. 
  Behavior 
  of 
  reagents. 
  — 
  The 
  frequent 
  occurrence 
  of 
  

   gaseous 
  products 
  in 
  the 
  above 
  experiments 
  made 
  special 
  ex- 
  

   periments 
  on 
  the 
  decomposition 
  of 
  reagents 
  necessary. 
  Benzol 
  

   and 
  gasolene 
  were 
  found 
  stable 
  at 
  210°, 
  and 
  often 
  above 
  this 
  

   temperature, 
  both 
  in 
  the 
  presence 
  of 
  water, 
  or 
  of 
  sulphur. 
  

   §21. 
  Carbon 
  disulphide, 
  however, 
  in 
  addition 
  to 
  relatively 
  

   slight 
  decompositions 
  producible 
  by 
  sodium, 
  or 
  mercury, 
  or 
  

   copper 
  (§17), 
  at 
  210°, 
  is 
  doubly 
  decomposed 
  by 
  water 
  at 
  this 
  

   temperature, 
  with 
  the 
  evolution 
  of 
  much 
  gas, 
  presumably 
  H 
  2 
  S 
  

   and 
  C0 
  2 
  . 
  CS 
  2 
  remains 
  stable 
  in 
  the 
  presence 
  of 
  zinc 
  white 
  (a 
  

   common 
  rubber 
  pigment), 
  or 
  of 
  sulphur, 
  or 
  of 
  bright 
  steel, 
  at 
  

   210°. 
  §17. 
  Hence 
  a 
  thread 
  of 
  mercury 
  to 
  shut 
  off 
  the 
  ex- 
  

   perimental 
  tubes, 
  § 
  2, 
  is 
  generally 
  objectionable, 
  as 
  is 
  also 
  a 
  

   thread 
  of 
  water 
  in 
  case 
  of 
  CS 
  2 
  . 
  Moreover 
  the 
  absence 
  of 
  gase- 
  

   ous 
  reaction 
  in 
  case 
  of 
  mixed 
  solvents, 
  § 
  16, 
  is 
  to 
  be 
  attributed 
  

   to 
  the 
  fact 
  that 
  CS 
  2 
  and 
  the 
  water 
  are 
  intentionally 
  separated 
  

   by 
  layers 
  of 
  benzol 
  or 
  gasolene. 
  

  

  An 
  interesting 
  question 
  is 
  suggested 
  here, 
  as 
  to 
  whether 
  it 
  

   be 
  possible 
  to 
  express 
  affinity 
  on 
  a 
  scale 
  of 
  temperatures. 
  Let 
  

   it 
  be 
  required 
  to 
  determine 
  the 
  affinity 
  of 
  a 
  metal 
  for 
  sulphur. 
  

   At 
  ordinary 
  temperatures 
  not 
  even 
  sodium 
  decomposes 
  CS 
  2 
  , 
  

   whereas 
  such 
  decomposition 
  occurs 
  if 
  the 
  temperature 
  be 
  suffi- 
  

   ciently 
  high. 
  Hence 
  the 
  temperature 
  at 
  which 
  the 
  decompo- 
  

   sition 
  definitely 
  sets 
  in 
  (for 
  copper 
  sooner 
  than 
  for 
  iron, 
  etc.) 
  is 
  

  

  * 
  Barus: 
  this 
  Journal, 
  xxxvii. 
  pp. 
  126-128, 
  1889. 
  

  

  