370  COLLODION  FOR  PROTECTING  SILVER  WARES. 
of  common  salt  are  added,  and  the  precipitate  thereby  caused  is 
collected,  after  24  hours,  on  a  filter,  and  the  latter  washed  with 
a  solution  of  common  salt ;  to  the  filtrate,  ammonia  is  added, 
and  the  fluid  left  standing  again  for  24  hours  ;  the  crystals 
which  have  separated  are  collected,  re-dissolved  in  acetic  acid, 
and  precipitated  with  ammonia;  the  precipitate  so  obtained  is 
washed,  dried,  and  weighed  ;  its  weight  should  not  be  less  than 
1  gramme. — Lond.  Chem.  News,  April  9,  1869,  from  Zeitschr. 
f.  Anal.  Chem. 
COLLODION  FOR  PROTECTING  SILVER  WARES. 
The  loss  of  silver  which  results  from  the  impregnation  of  our 
atmosphere  with  sulphur  compounds,  especially  where  gas  is 
burned,  is  very  great.  It  has  been  said  that  many  thousands  of 
pounds'  worth  go  down  our  sewers  annually  in  the  form  of  dirt 
from  plate  cleaning,  and  the  loss  of  one  large  house  on  Cornhill 
from  this  source  has  been  described  to  us  as  serious.  Silver- 
smiths may,  then,  thank  one  of  their  confraternity — Herr  Strol- 
berger,  of  Munich — -for  a  happy  thought.  He  seems  to  have 
tried  various  plans  to  save  his  silver,  if  possible.  He  covered 
his  goods  with  a  clear  white  varnish,  but  found  that  it  soon 
turned  yellow  in  the  window,  and  spoilt  the  look  of  his  wares. 
Then  he  tried  water  glass  (solution  of  silicate  of  potash),  but 
this  did  not  answer.  He  tried  some  other  solutions,  to  no  pur- 
pose ;  but  at  last  he  hit  upon  the  expedient  of  doing  his  goods 
over  with  a  thin  coating  of  collodion,  which  he  finds  to  answer 
perfectly.  No  more  loss  of  silver,  and  no  longer  incessant 
labor  in  keeping  it  clean.  The  plan  he  adopts  is  this : — He  first 
warms  the  articles  to  be  coated,  and  then  pays  them  carefully 
-over  with  a  thinnish  collodion  diluted  with  alcohol,  using  a  wide, 
soft  brush  for  the  purpose.  Generally,  he  says,  it  is  not  ad- 
visable to  do  them  over  more  than  once.  Silver  goods,  he  tells 
us,  protected  in  this  way,  have  been  exposed  in  his  window  more 
than  a  year,  and  are  as  bright  as  ever,  while  others  unprotected  « 
have  become  perfectly  black  in  a  few  months. — Che^n,  News, 
June,  1869,  from  Mechanic  §  Magazine. 
