Amscpturi87h9ann }  Analysis  of  Caoutchouc.  46 1 
6071  to  15*3,  and  in  three  samples  the  percentage  of  calcium  carbon- 
ate was  II*  1,  30*29  (mean  of  three  analyses)  and  30*44  (mean  of 
two). 
The  action  of  certain  acids  on  the  caoutchouc  was  attended  with 
(1)  the  distension  of  the  material ;  (2)  appearance  of  small  elevations 
on  the  surface  ;  and  (3)  crimping  of  the  edges.  These  effects  are  due 
to  the  absorption  of  acid  by  the  material,  the  solvent  action  on  the 
mineral  matter,  and  in  some  cases  on  the  caoutchouc,  the  softening  of 
the  material  whereby  the  acid  enters  the  pores  more  readily,  and  the 
small  elevations  are  due  to  superficial  distension. 
Sulphuric  acid,  spec.  grav.  1*828,  decomposes  the  material  in  a  few 
hours  ;  when  diluted  with  an  equal  volume  of  water,  it  dissolves  out 
the  zinc  oxide  pretty  freely,  except  from  those  samples  containing 
considerable  quantities  of  calcium  carbonate  ;  it  slightly  impairs  the 
elasticity,  and  does  not  produce  crimping.  When  diluted  with  19 
times  its  volume  of  water,  it  dissolves  appreciable  quantities  of  zinc 
oxide. 
Hydrochloric  acid,  sp.  gr.  1*154,  dissolves  out  considerable  quanti- 
ties of  zinc,  in  some  cases  gas  being  evolved.  After  some  time  the 
caoutchouc  assumes  a  red  color,  and  becomes  decidedly  crimped,  and 
sulphur  separates  out.  Heated  with  four  times  its  volume  of  water  it 
produces  slight  crimping. 
Nitric  acid,  sp.  gr.  1  "374,. decomposes  caoutchouc  rapidly  ;  when  the 
acid  is  diluted  with  4  volumes  of  water,  decomposition  proceeds  more 
slowly,  with  slight  crimping.  When  diluted  with  9  volumes  of  water, 
the  acid  merely  dissolves  the  metallic  oxide,  producing  crimping. 
Acetic  Acid. — 63  to  64  per  cent,  anhydrous  acid  has  very  little  action 
on  pure  vulcanized  india-rubber,  but  when  it  contains  mineral  matter^ 
this  is  rapidly  dissolved  by  the  strong  acid,  the  mass  becoming  distended 
and  slightly  crimped  at  the  edges.  The  distension  is  greater  when 
dilute  acid  is  employed,  for  although  it  is  produced  more  rapidly  by  the 
stronger  acid,  yet  for  this  reason  it  is  sooner  arrested.  The  edges  soon 
become  crimped,  which  effect,  if  the  acid  is  very  dilute,  is  visible  oraly 
on  examination  with  a  lens,  by  the  aid  of  which  it  is  possible  to  detect 
1  part  of  anhydrous  acid  in  3,000  parts  of  water  by  the  crimping  of 
the  edges. 
It  is  possible  that  formic  acid  will  exert  a  similar  action. — Jour. 
Cbem.  Socn  July,  1879,  ^rom  Ghent.  News. 
