66 
THE  PRESENCE  OF  IODINE  IN  VARIOUS  PLANTS. 
pumice-stone  and  a  few  iron  filings  with  sufficient  water  to  cover 
them  ;  a  similar  jar  with  pumice-stone,  scrapings  of  clean  lead,  and 
solution  of  acetate  of  lead;  and  lastly,  a  condensing  worm  immersed 
in  a  freezing  mixture  and  attached  to  a  receiver.  Air,  under  a 
pressure  of  3  lbs.  per  square  inch,  was  allowed  to  traverse  this  ar- 
rangement for  four  hours.  It  was  then  taken  apart  and  examined. 
The  slips  of  paper  were  not  sensibly  altered.  The  condensers  con- 
tained a  small  quantity  of  liquid,  which  did  not  offer  the  slightest 
evidence  of  iodine  to  the  most  delicate  tests.  The  contents  of  the 
jar  containing  iron  filings  was  thrown  on  a  filter,  washed  with  cold 
water,  half  an  ounce  of  solution  of  pure  carbonate  of  potash  added, 
and  the  whole  evaporated  to  a  quarter  of  an  ounce  and  tested.  No 
iodine  was  present.  Lastly,  the  jar  with  lead  scrapings  was  search- 
ingly  tested  without  any  indication  whatever  of  iodine.  This  ex- 
periment proved  that  4000  cubic  feet  of  air  contained  no  appreci- 
able iodine. 
Mr.  Macadam  then  sought  for  iodine  in  rain-water,  and  in  several 
trials  with  three  gallons  each,  was  unable  to  detect  any  trace  of 
that  element,  even  from  rain-water  collected  for  him  at  the  Shet- 
land Islands  where  a  constant  marine  atmosphere  prevails.  He 
therefore  infers  that  even  if  the  atmosphere  of  the  ocean  does  con- 
tain iodine  carried  up  mechanically  in  saline  form  during  evapora- 
tion, it  must  be  in  quantity  too  minute  to  be  detected. 
The  author  now  recurs  to  the  existence  of  iodine  in  the  potash 
of  commerce  as  shown  in  his  first  experiment.  He  examined 
various  specimens  of  the  commercial  alkali  used  in  Edinburgh  and 
Glasgow,  which  were  derived  from  the  United  States,  and  Canada, 
and  found  that  they  all  afforded  iodine  when  examined.  Our  author 
infers  that  as  the  potashes  from  America  are  derived  from  the  ashes 
of  forest  trees,  that  iodine  must  pre-exist  in  these  trees,  a  belief 
rendered  much  more  probable,  when  he  was  able  to  detect  it  in 
charcoal  prepared  in  Scotland,  from  oak,  elm  and  ash. 
Mr.  Macadam  infers  that  the  proportion  of  iodine  in  forest 
trees  is  extremely  minute,because  the  weight  of  the  potash  they  yield 
is  small  compared  with  their  weight,  and  this  contains  only  a  very 
small  amount  of  iodine.  He  also  believes  that  succulent  marsh 
growing  plants  are  much  richer  in  this  element  than  trees. 
Mr.  Macadam  made  a  number  of  experiments  on  plants  growing 
