obtained  approximately  pure  by  the  solution  ot  crude  rubber  in 
benzine,  allowing  the  insoluble  matter  to  settle  out.  and  subse- 
quently precipitating  the  rubber  from  the  dear  solution  bv  the 
addition  of  alcohol. 
When  pure  it  is  practically  colourless  and  is  cousiderablv  lighter 
than  water. 
It  is  quite  insoluble  in  water  and  alcohol,  which  however  are 
absorbed  to  some  extent  bv  the  rubber  which  swells  up  in  conse- 
quence. In  turpentine,  petroleum  spirit,  carbon  bisulphide,  ben- 
zole, and  chloroform,  rubber  can  be  dissolved:  the  ease  with  which 
the  solution  is  effected  depending  largely  upon  the  phvsical  con- 
dition and  historv  of  the  sample.  Strictly  speaking  these  solutions 
of  rubber  are  solutions  of  the  splvents  in  the  rubber  rather  than 
solutions  of  the  rubber  in  the  liquids.  This  property  of  forming 
solutions  with  certain  liqu’ds  may  be  of  practical  use  as  a rough 
test  for  the  purity  of  rubber  when  ready  for  the  market,  and  mav 
be  used  to  detect  any  mechanical  impurities  such  as  dirt  and  frag- 
ments of  bark.  It  is  however,  seldom,  if  ever,  that  Para  rubber 
can  be  prepared  which  will  give  a clear  solution  in  these  solvents, 
and  this  is  owing  to  an  impurity  which  is  associated  with  the  rub- 
ber from  the  first  and  which  is  quite  insoluble  in  the  rubber  solvent 
although  swelling  up  and  becoming  quite  conspicuous.  This  sub- 
stance, which  formerly  was  regarded  as  an  insoluble  form  of  India 
rubber  itself,  has  been  .shewn  by  Weber  to  be  quite  distinct  in 
character  but  never  to  be  present  in  more  than  a comparatively 
insigniticant  amount.  If  the-  rubber  be  masticated,  that  is.  mecha- 
nically kneaded  and  worked,  before  attempting  to  bring  it  into 
solution,  this  impurity  ceases  to  appear  in  the  solution  owing  to 
the  state  of  minute  division  into  which  it  has  been  brought  by  the 
mechanical  treatment,  but  though  not  apparent,  it  is  actually  pre- 
sent just  as  before.  If  a dilute  solution  of  crude  rubber  in  benzole, 
one  part  of  rubber  to  forty  of  benzole,  be  allowed  to  stand  fo- 
several  weeks  all  this  gelatinous  bulky  insoluble  residue  subsides 
into  a thin  film  at  the  bottom  of  the  vessel  and  the  quantity  is  then 
clearly  seen  to  be  quite  insignificant.  To  eft'ect  this  solution  of 
crude  dried  rubber  in  benzole  or  other  solvent,  is  a simple  experi- 
ment which  should  be  made  by  all  interested  in  the  preparation 
of  rubber — the  rubber  strips  should  be  put  in  a bottle  with  about 
forty  times  its  weight  of  benzole,  tightly  stoppered  anJ  shaken  at 
intervals.  The  rubber  will  be  apparently  in  complete  solution  in 
two  days  and  the  nature  of  the  insoluble  residue  can  be  conve- 
niently studied.  The  action  of  heat  upon  crude  India  rubber  is 
well  marked:- the  heating  results  in  a decrease  of  the  elasticity 
with  marked  increase-of  the  stickiness  of  the  rubber,  as  long  as  the 
heat  is  quite  moderate  and  not  much  above  loo^C.:  this  result  is 
largely  to  be  attributed  to  the  presence  of  resin  and  gums  winch 
exist  as  impurity  in  the  rubber.  The  resins  are,  in  the  case  ot 
Para  rubber,  of  low  melting  point,  and  thougli  the  percen  ag'  i> 
small,  not  usually  more  than  3*5  %,  yet  the  effect  ot  tins  small 
amount  is  most  markeJ.  I his  lias  an  important  bearing  on  the 
