- 
Am.  Jour.  Pharm.  > 
Dec,  1890. 
}         Vulcanization  of  India-rubber.  621 
rape  oil,  and  some  left  untreated :  these  were  put  into  an  incubator 
at  1500  F.  for  a  few  days,  when  it  was  found  that  the  oil-treated 
rubber  was  quite  soft  and  rotten,  whilst  the  other  two  had 
remained  sound ;  after  a  few  days  more,  the  original  rubber  threads 
had  become  quite  rotten,  whilst  the  threads  smeared  with  the  oily 
part  of  the  vulcanized  oil  remained  quite  sound. 
The  first  and  second  samples  of  rubber  substitute  were  examined 
for  soluble  chlorides  or  hydrochloric  acid,  by  boiling  in  water  ;  the 
first  gave  018  per  cent,  of  chlorine  soluble  in  water,  and  the  second 
0  05  per  cent. 
It  has  been  known  for  some  time  that  copper  salts  exert  a  most 
injurious  influence  on  india-rubber;  copper  salts  are  sometimes  used 
in  dyeing  cloths  which  are  afterwards  employed  for  water-proofing 
with  india-rubber,  and  it  seems  quite  astonishing  what  a  small 
amount  of  copper  is  required  to  harden  and  destroy  the  rubber,  and 
the  destructive  effect  of  copper  is  further  enhanced  if  the  cloth  con- 
tains oily  matters  in  which  the  copper  has  dissolved. 
As  an  example,  here  is  a  piece  of  cloth  alleged  to  have  damaged 
the  thin  coating  of  india-rubber  on  it :  I  found  it  to  contain  copper, 
and  with  a  view  of  demonstrating  this  point,  I  took  one  piece  in  its 
original  condition ;  to  the  end  of  this  I  pasted  a  similar  piece  of  the 
cloth  from  which  the  oily  and  greasy  matters  had  been  removed  by 
ether,  and  to  the  end  of  this  again  I  pasted  another  piece  of  the  same 
cloth  from  which  I  had  removed  both  oily  and  greasy  matters  and 
copper ;  these  three  pieces  joined  end  to  end  into  one  were  then 
coated  in  the  usual  way  with  india-rubber,  and  then  hung  in  an 
incubator  at  1500  F. ;  in  the  course  of  a  few  days  the  rubber  on  the 
original  cloth  had  become  soft,  and  it  then  hardened  and  became 
rotten  and  useless;  the  second  piece  from  which  the  greasy  matters 
had  been  removed  then  became  quite  hard  and  rotten,  whilst  the 
part  from  which  both  greasy  matters  and  copper  had  been  removed 
has  remained  in  a  perfectly  elastic  and  good  condition. 
Professor  Dewar  observed  accidentally  that  metallic  copper  when 
heated  to  the  temperature  of  boiling  water  in  contact  with  the  rubber 
exerted  a  destructive  effect  upon  it.  With  a  view  of  finding  whether 
this  was  due  to  the  copper  per  se  or  to  its  power  of  conducting  heat 
more  rapidly  to  the  rubber,  I  laid  a  sheet  of  rubber  on  a  plate  of 
glass  and  on  it  placed  four  clean  discs,  one  of  copper,  one  of  platinum, 
one  of  zinc,  and  one  of  silver;  after  a  few  days  in  an  incubator  at 
