454 
SILVERING  AND  GILDING  OF  GLASS. 
muriatic  acid,  adding  292  milligrms.  of  chloride  of  sodium  to  the 
solution  for  every  gramme  of  gold,  evaporating  to  dryness,  and 
heating  the  residue  until  all  free  acid  is  driven  off.  The  double 
salt  is  then  dissolved  in  water,  and  water  is  added  until  each  100 
cub.  centims.  of  fluid  contains  exactly  1  grm.  of  gold.  50  cub. 
centims.  of  this  solution  are  mixed  with  20  cub.  centims.  of  a 
solution  of  soda  of  spec.  grav.  1.035,  and  300  cub.  centims.  of 
water  in  a  glass  flask,  and  boiled  until  it  is  reduced  to  250  cub. 
centims.  ;  and  another  50  cub.  centims.  of  the  solution,  mixed 
with  20  cub.  centims.  of  the  same  solution  of  soda  and  230  cub. 
centims.  of  water,  are  kept  for  an  hour  in  boiling  water.  The 
two  fluids  are  then  mixed  together,  and  must  be  employed  in 
gilding  whilst  fresh. 
To  gild  the  inside  of  a  glass  vessel,  a  tenth  part  of  its  volume 
of  a  mixture  of  2  parts  of  alcohol  and  1  part  of  ether  is  poured 
into  it,  and  it  is  then  filled  up  with  the  hot  gold  solution.  The 
vessel  is  then  set  in  water,  the  temperature  of  which  must  not 
rise  above  176Q  F.  In  from  ten  to  fifteen  minutes  its  inner  sur- 
face is  covered  with  a  brilliant  golden  film,  and  the  vessel  is  re- 
moved from  the  water  when  its  walls  are  opake,  or  exhibit  a  deep 
green  color  by  transmitted  light. 
The  alkaline  solution  of  gold  is  of  course  always  reduced  by 
the  alcohol,  but  the  glass  only  acquires  its  brilliant  golden  coat 
when  the  fluid  is  of  such  a  nature  that  the  adhesion  of  the  gold 
to  the  glass  may  be  somewhat  stronger  than  that  to  the  water  ; 
in  the  former  case  the  gold  is  precipitated  only  on  the  glass,  in 
the  latter  only  in  the  fluid.  It  is  very  difficult  to  hit  this  point 
exactly,  and  the  smallest  error  in  the  mixture  renders  success 
impossible.  The  author  adds,  that  he  has  obtained  the  most 
beautiful  gilding  by  this  means,  whilst  in  other  cases  he  has  failed 
entirely,  without  being  able  to  discover  the  cause,  so  that  he  does 
not  think  this  method  will  be  of  general  application.  The  mix- 
ture will  only  act  whilst  fresh,  when  it  has  a  very  slight  yellowish 
tinge  ;  by  standing  it  becomes  colorless.  Alcohol  reduces  the 
gold  from  the  colorless  fluid  with  difficulty. — Ibid,  from  Liebig 's 
Annalen,  April  1856. 
