METHOD  OF  HASTENING  FILTRATIONS 
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a  porous  vase  holding  the  alkaline  lixivium  and  the  metallic  zinc. 
Plunge  the  article  to  be  tinned  into  the  outer  vessel,  and  estab- 
lish communication  between  the  article  and  the  zinc  by  means  of 
a  conducting  wire.  To  revive  the  lixivium  after  it  has  become 
saturated  with  oxide  of  zinc,  precipitate  by  sulphide  of  sodium. 
True  Bronzing. — Iron,  cast  iron,  steel  and  other  metals  may 
be  covered  with  a  coating  of  alloy  of  copper  and  tin  (true  bronze) 
by  an  operation  effected  without  the  aid  of  heat. 
This  result  is  produced  by  adding  to  the  copper  bath  some 
stannate  of  soda,  or  a  solution  of  bichloride  of  tin,  previously 
treated  with  a  sufficient  quantity  of  soda ;  immersing  the  article 
in  contact  with  zinc  determines  the  deposition  of  bronze. 
Alkaline  Baths  Containing  other  Metals  Instead  of  Copper. — 
Tartro-alkaline  baths  containing,  for  instance,  cobalt  or  nickel, 
instead  of  copper,  form  no  adhering  metallic  deposit  in  presence 
of  zinc;  they  disengage  hydrogen.  Copper,  or  metals  previ-. 
ously  coppered,  if  heated,  become  covered  with  a  white  metallic- 
deposit,  consisting  of  an  alloy  of  zinc  and  cobalt,  zinc  and; 
nickel,  &c. — Lond.  Chem.  News,  Jan.  5,  1866,  from  Annales  de 
Chemie  et  de  Physique,  iv.,  374. 
METHOD  OF  HASTENING  FILTRATIONS. 
To  the  Editor  of  the  Chemical  News, 
Sir, — In  your  number  306  (vol.  xii.,  p.  180)  you  mention 
Dr.  Picard's  "  Way  of  Hastening  Filtrations  "  as  rather  an  in- 
jurious* one,  and,  therefore,  few  of  your  readers  will  have 
felt  inclined  to  consult  the  description  given  in  the  original 
paper.  I  happened  to  come  across  the  latter,  and  found  that 
the  author  himself  does  not  attribute  much  value  to  the 
method  you  described  with  a  few  words,  on  account  of  the 
complication  of  apparatus,  and  of  the  danger  of  breaking  the 
filter.  But  he  proceeds  to  propose  another  arrangement,  which 
obviates  both  these  drawbacks ;  and  since  I  have  found,  on 
trial  every  one  of  his  statements  to  be  correct,  I  venture  to 
*The  word  injurious,  we  must  state,  was  a  misprint  for  ingenious  
Ed.  C.  N. 
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