Amocturi8P9?.arm-}      Copper  in  Preserved  Vegetables.  491 
the  standard  iodine  must  be  added  to  each  flask.  The  iodine  is 
allowed  to  react  for  five  minutes,  then  to  each  flask  4  cc.  of  the  nor- 
mal sulphuric  acid  is  added  to  neutralize  the  sodium  carbonate, 
and  10  cc.  of  the  sodium  thiosulphate  solution  is  added  to  reduce 
the  excess  of  iodine  present.  A  few  drops  of  starch  paste  are  now 
added  to  each  flask,  and  the  excess  of  thiosulphate  determined  with 
the  iodine  solution.  The  number  of  cc.  of  iodine  required  to  titrate 
the  thiosulphate  in  flask  1  represents  the  amount  of  iodine  which 
has  entered  into  combination  with  the  sodium  carbonate,  the  starch, 
and  other  errors  which  may  be  inherent  to  the  titration  ;  the  amount 
of  iodine  used  by  flask  2  represents  that  absorbed  by  the  solution 
of  tannin  ==  0-005  gram  plus  the  amount  absorbed  in  the  blank 
experiment ;  the  iodine  used  by  flask  3  represents  that  which  was 
absorbed  by  the  tannin  of  the  hops  plus  the  amount  absorbed  in  the 
blank  experiment.  From  these  figures,  the  amount  of  tannin  in  the 
hops  may  be  readily  calculated. 
COPPER  IN  PRESERVED  VEGETABLES. 
At  the  meeting  of  the  Bavarian  Society  of  Applied  Chemistry, 
held  last  month  in  Augsburg,  the  subject  of  the  presence  of  copper 
in  preserved  vegetables  was  the  subject  of  a  long  discussion,  which 
is  epitomized  in  the  Chemiker  Zeitung,  as  follows  : 
The  discussion  was  preceded  by  a  paper  from  Herr  Mayrhofer,  of 
Mayence,  in  which  the  author  stated  as  the  result  of  his  experience 
that  in  nearly  all  preserved  vegetables  copper  is  present,  sometimes 
derived  from  the  vessels  used  in  their  preparation,  sometimes  added 
directly  in  the  form  of  sulphate.  In  the  case  of  fruits  boiled  with 
sugar  the  juice  contains  on  an  average  4  to  9  milligrams  of  copper 
to  the  kilogram  of  juice,  derived  entirely  from  the  copper  vessels, 
which  are  found  in  practice  to  be  better  suited  for  boiling  products 
of  this  kind  than  vessels  of  any  other  material.  The  green  pre- 
serves met  with  in  commerce  vary  in  the  amount  of  copper  they 
contain  between  26  and  36  milligrams  per  kilogram ;  in  once  case 
76  milligrams  per  kilogram  was  found.  In  these  green  preserves 
the  copper  is  partly  derived  from  copper  vessels  and  partly  added  as 
sulphate.  Preserves  of  this  kind  show  after  heating  and  sterilizing 
a  green  color,  comparable  to  that  of  the  fresh  vegetable,  whilst 
without  the  copper  they  take  a  brownish  or  yellowish  color  that 
