ON  THE  PREPARATION  OF  COPAL  VARNISH. 
343 
by  Freudenvoll  in  his  treatise  on  the  preparation  of  varnishes. 
According  to  him,  4  oz.  of  West  Indian  copal  are  dissolved  in  a 
mixture  of 
4  oz.  oil  of  turpentine,  and 
6  oz.  alcohol  of  spec.  grav.  0-813 ; 
or  a  mixture  of 
4  oz.  sulphuric  ether, 
4  oz.  oil  of  turpentine,  and 
4  oz.  alcohol  of  spec.  grav.  0-851. 
When  engaged  in  testing  this  process,  which  gave  very  good 
results,  the  author  found  a  small  variation,  which  he  describes 
as  follows,  particularly  efficacious  : — 
Two  sorts  of  copal  occur  in  commerce,  the  East  and  West  In- 
dian. The  former  is  usually  in  small,  irregular,  rounded  pieces, 
with  a  finely  verrucose  surface,  the  resemblance  of  which  to  the 
skin  of  a  goose  has  obtained  for  it  the  name  of  "  goose  copal." 
It  is  of  a  somewhat  yellow  color,  and  is  preferred  for  the  manufac- 
ture of  oily  copal  varnish,  because  it  acquires  less  color  by  fusion 
than  the  West  Indian.  The  latter  does  not  possess  a  warty  sur- 
face ;  it  is  very  pale  in  color,  often  nearly  colorless,  *md  occurs 
in  large  irregular  fragments,  partly  with  a  rounded  surface  and 
partly  with  a  shelly  fracture. 
West  Indian  copal  can  only  be  employed  in  the  following  so- 
lution, the  East  Indian  forming  only  gelatinous  lumps,  but  never 
a  solution.    The  solvent  is  a  mixture  of 
60  parts  by  weight  of  alcohol  of  spec.  grav.  0*813, 
10  parts  by  weight  of  sulphuric  ether, 
40  parts  by  weight  of  oil  of  turpentine, 
in  which  60  parts  of  copal  are  to  be  dissolved  for  the  production 
of  a  varnish  of  an  oleaginous  consistence.    Solution  takes  place 
even  in  the  cold,  without  any  previous  gelatinous  swelling  of  the 
copal ;  but  it  is  effected  much  more  rapidly  with  the  assistance 
of  a  gentle  heat.    As,  however,  single  pieces  are  often  found  in 
the  West  Indian  copal,  which,  instead  of  dissolving,  only  swell 
up  in  the  fluid,  by  which  the  rest  of  the  solution  is  spoiled,  it  is 
advisable  to  select  only  the  large  and  perfectly  clear  pieces  for 
the  purpose  of  varnish  making,  and  to  test  each  first  of  all  as  to 
its  solubility.    This  little  trouble  is  richly  repaid  by  the  certainty 
of  the  result. 
