SILVERING  AND  GILDING   OF  GLASS. 
451 
iodide  of  potassium,  and  adding  starch-paste  and  muriatic  acid, 
the  reactions  were  not  nearly  so  delicate  as  with  the  mother- 
liquors,  although  the  latter  contained  much  more  iodine  in  the 
form  of  iodides,  than  was  employed  in  his  experiments.  The 
mother-liquors  were  free  from  persalts  of  iron,  which  might  have 
caused  the  reaction  Qhem.  Gfaz.,  June  1,  1856,  from  Liehig's 
Annalen,  April  1856. 
ON  THE  SILVERING  AND  GILDING  OF  GLASS. 
By  J.  Liebig. 
Silvering  G-lass. — At  the  request  of  M.  von  Steinheil,  the 
author  has  made  some  experiments  to  discover  a  process  for  sil- 
vering glass  in  the  cold,  especially  with  a  view  to  the  production 
of  faultess  optical  mirrors.  The  silvering  fluid,  which  perfectly 
fulfils  the  desired  end,  is  an  ammoniacal  solution  of  nitrate  of 
silver  with  an  addition  of  caustic  potash  or  soda,  which,  when 
mixed  with  a  solution  of  sugar  of  milk  in  water  at  ordinary  tem- 
peratures, deposits  the  silver  on  the  surface  of  the  glass  in  the 
form  of  a  mirror. 
To  prepare  the  fluid,  10  grms.  of  fused  nitrate  of  silver  are 
dissolved  in  200  cub.  centims.  of  water,  and  a  sufficient  amount 
of  liquid  ammonia  is  added  to  produce  a  clear  solution.  This  is 
gradually  diluted  with  450  cub.  centims.  of  a  solution  of  potash 
of  spec.  grav.  1.05,  or  with  the  same  volume  of  a  solution  of 
soda  of  1.035.  On  the  addition  of  this,  a  blackish-brown  pre- 
cipitate is  usually  produced,  which  must  be  at  once  dissolved  by 
a  fresh  addition  of  liquid  ammonia.  The  mixture  is  diluted  with 
so  much  water  as  to  bring  it  to  1450  cub.  centims.  A  dilute 
solution  of  nitrate  of  silver  is  then  dropped  in  until  the  produc- 
tion of  a  strong  gray  precipitate  (not  turbidity),  when  the  mix- 
ture is  brought  to  1500  cub.  centims.  by  the  addition  of  water. 
Each  cubic  centimetre  thus  contains  a  little  more  than  6.66 
milligrms.  of  nitrate  of  silver,  or  4.18  milligrms.  of  silver.  To 
produce  a  clean  mirror,  the  fluid  should  contain  no  free  ammonia, 
but  this  must  be  completely  saturated  with  oxide  of  silver.  For 
this  purpose  some  of  the  solution  of  silver  may  be  kept  back  and 
added  at  the  end ;  and  in  this  case  1  cub.  centim.  of  the  solution 
contains  rather  less  than  4.18  milligrms.  of  silver. 
