To  50  Ibs.  of  foreign  asphaltum,  melted  and  boiled  in  an
iron  vessel  for  three  or  four  hours,  add  16  Ibs.  of  red  lead
and  litharge  ground  to  a  fine  powder,  in  equal  proportions,
with  10  gals,  of  drying  linseed  oil,  and  bring  the  whole  to  a
nearly  boiling  temperature.  Melt,  in  a  second  vessel,  8  Ibs.
of  gum-anime1  ;  to  which  add  2  gals,  of  drying  linseed  oil  at
a  boiling  heat,  with  12  Ibs.  of  caoutchouc  partially  dissolved
in  coal-tar  naphtha.  Pour  the  contents  of  the  second  vessel
into  the  first,  and  boil  the  whole  gently,  until  the  varnish,
when  taken  up  between  two  spatulas,  is  found  to  be  tough
and  ropy.  This  composition,  when  quite  cold,  is  to  be  thinned
down  tor  use  with  from  30  to  35  gals,  of  spirits  of  turpentine,
or  of  coal  naphtha.
313.  It  is  recommended  that  the  iron  should  be  heated  be-
fore receiving  this  varnish,  and  that  it  should  be  applied  with
a  spatula,  or  a  flexible  slip  of  horn,  instead  of  the  ordinary
brush.
When  dry  and  hard,  it  is  stated  that  this  varnish  is  not
acted  upon  by  any  moderately  diluted  acid  or  alkali ;  and,
by  long  immersion  in  water,  it  does  not  form  a  partially  sol-
uble hydrate,  as  is  the  case  with  purely  resinous  varnishes
and  oil  paints.  It  can  with  difficulty  be  removed  by  a  sharp
pointed  tool  j  and  is  so  elastic,  that  a  plate  of  iron  covered


PAINTS   AND   VARNISH.  103

with  it  may  be  bent  several  times  before  it  will  become  de-
tached.
