Am.  Jour.  Pharm. 
Feb.,  1884. 
Action  of  Acids  on  Lead  and  Tin. 
115 
ACTION  OF  CERTAIN  VEGETABLE  ACIDS  ON  LEAD 
AND  TIN. 
By  F.  P.  Hall. 
Taking  into  consideration  the  large  quantities  of  tinned  food  which 
are  constantly  being  consumed,  the  author  has  thought  it  expedient  to 
study  the  action  of  various  organic  acids  on  the  materials  which  are 
exposed  in  the  interior  of  the  cans,  viz.,  tin  and  lead.  The  present 
paper  contains  the  results  of  experiments  on  this  subject,  and  also 
investigations  on  the  quality  of  tin  plate  and  tin  foil  used  as  covers  for 
food  products. 
The  first  series  of  experiments  were  conducted  to  determine  quanti- 
tatively the  action  of  the  more  common  vegetable  acids  on  the  metals 
in  question,  all  previous  quantitative  work  in  this  direction  having 
been  made  with  acetic  acid  only.  First  of  all,  in  order  to  test  the 
effect  of  alloying  on  the  corrosion  of  the  metals,  the  amount  of  tin 
dissolved,  when  pure,  was  compared  with  the  amount  dissolved  under 
the  same  conditions  from  an  alloy  exposing  the  same  surface  of  the 
metals  in  question.  This  was  effected  by  proportioning  the  size  of  the 
plates  of  pure  metals  according  to  the  composition  of  the  alloy. 
Three  alloys  were  made,  taking  into  consideration  the  specific  gravities 
of  the  metals,  one  with  equal  parts  of  each  metal,  one  with  excess  of 
tin,  and  one  with  excess  of  lead.  The  metals  were  fused,  well  mixed 
together,  cast  into  thin  sheets  in  iron  moulds,  rolled  into  thin  strips, 
and  cut  into  pieces  \  inch  wide  and  12  inches  long,  thus  exposing 
one-fifth  of  a  square  foot  surface.  The  tin  and  lead  strips  were  of 
the  same  width,  but  varied  in  length  for  the  reason  stated  above. 
The  acetic  acid  solution  employed  contained  5*75  per  cent,  of  acid,  the 
solutions  of  tartaric  and  citric  acids  were  made  to  an  equal  degree  of 
acidity.  After  an  exposure  of  two  weeks  to  the  action  of  the  acids  at 
25°-35°,  all  the  metals  were  found  to  be  tarnished  more  or  less,  the 
tin  more  so  than  the  lead;  two  of  the  alloys  were  sprinkled  with 
small  black  crystals  of  lead ;  the  smallest  pieces  of  lead  in  tartaric 
acid  were  covered  with  transparent  crystals  of  lead  tartrate.  The 
solutions  containing  tin  were  yellowish,  whilst  those  with  lead  were 
clear  and  colorless.  The  pieces  of  tin  were  covered  with  a  dusty 
powder.  The  strips  of  metals  were  taken  out,  washed,  dried,  and 
weighed.     The  solutions  were  precipitated  with  hydrogen  sulphide. 
