■  ™De°c%9o.arm'}         Vulcanization  of  India-rubber.  619 
temperature  and  firm  at  high  temperatures,  whilst  the  latter  becomes 
hard  and  quite  plastic  respectively  at  those  temperatures. 
JJJIn  making  cloth  for  water-proof  garments  another  method  is  em- 
ployed for  vulcanizing  the  rubber,  viz.,  by  wetting  its  surface  with 
a  mixture  of  somewhere  about  5  to  10  parts  of  chloride  of  sulphur 
dissolved  in  100  parts  of  bisulphide  of  carbon,  and  then  heating  the 
fabric  gently  to  evaporate  away  the  excess  of  these  substances.  The 
rubber-covered  cloth  cannot  be  heated  to  a  high  temperature  like 
the  rubber  alone,  because  the  heat  would  be  liable  to  injure  the 
cotton,  silk  or  wool  of  the  fabric,  or  destroy  or  injure  the  colors. 
The  bisulphide  of  carbon  softens  and  penetrates  the  fine  layer  of 
rubber,  carrying  with  it  the  chloride  of  sulphur  dissolved  in  it,  and 
it  is  generally  supposed  that  the  chloride  of  sulphur  breaks  up  the 
sulphur  combining  with  the  rubber,  producing  vulcanization,  and 
the  chlorine  combining  with  the  hydrogen  producing  hydrochloric 
acid,  which  is  liberated.  This  reaction  is  clearly  not  the  correct 
one,  and  it  is  probable  that  the  reverse  is  more  in  accordance  with 
the  facts — viz.,  that  the  chlorine  of  the  sulphur  chloride  combines 
with  the  rubber,  producing  vulcanization,  leaving  the  sulphur  in  the 
free  state  or  only  partially  in  combination  with  the  rubber,  because 
in  rubber  vulcanized  by  the  cold  process  I  have  found  free  sulphur 
to  be  present. 
From  a  piece  of  rubber-covered  cloth  I  separated  the  rubber  and 
submitted  it  to  analysis  by  mixing  it  thoroughly  in  small  pieces 
with  pure  sodium  carbonate  and  igniting,  then  dissolving  the  whole 
in  water,  and  adding  to  it  peroxide  of  hydrogen  previously  treated 
with  excess  of  barium  chloride  (to  separate  sulphuric  acid  or 
sulphates.)  The  peroxide  ensures  the  conversion  of  the  lower  oxides 
of  sulphur  into  sulphuric  acid,  whilst  the  excess  of  barium  chlorides 
precipitates  the  sulphuric  acid  in  the  solution,  which  is  then  weighed 
as  barium  sulphate. 
Another  portion  of  the  made-up  solution  was  neutralized  and  the 
chlorine  present  titrated.  The  rubber  previous  to  ignition,  as  above 
described,  had  been  well  boiled  in  water  and  dried  to  separate  any 
hydrochloric  acid  which  might  be  present,  but  only  a  faint  trace  of 
chlorine  compound  could  be  thus  separated  from  the  rubber. 
The  total  sulphur  present  in  the  rubber  amounted  to  2-6o,and  the 
total  chlorine  to  6-31  per  cent. 
The  yellow-colored  sulphur  protochloride  is  best  adapted  for  vul- 
