Am.  Jour.  Pharm, 
May,  1888. 
Action  of  Water  on  Lead. 
251 
last  fractions  attacked  it  with  considerable  energy.  The  protecting 
influence  of  the  first  fractions  must  be  considered  as  due  to  their  con- 
taining a  relatively  large  quantity  of  carbonic  anhydride.  Distilled 
water,  which  was  vigorously  boiled  for  some  time  and  quickly  cooled 
in  contact  with  air,  was  found  to  contain  0*04  per  cent,  of  its  volume 
of  carbonic  anhydride,  0*236  per  cent,  of  its  volume  of  oxygen,  and 
0"514  per  cent,  of  its  volume  of  nitrogen.  The  rapid  absorption  of 
these  gases  explains  the  behavior  of  water  so  treated  towards  lead. 
Distilled  water,  quite  free  from  carbonic  anhydride  but  containing 
oxygen,  scarcely  acts  on  lead,  but  on  exposure  to  the  air  the  liquid 
becomes  cloudy,  owing  to  the  formation  of  a  white  precipitate. 
Samples  of  water  containing  different  amounts  of  carbonic  anhy- 
dride, but  an  invariable  quantity  of  oxygen,  behave  very  differently 
with  lead.  In  one  case,  when  the  oxygen  present  was  0*35  per  cent, 
of  the  volume  of  the  liquid,  and  a  saturated  solution  of  carbonic  anhy- 
dride was  added  until  the  water  contained  0*14  per  cent,  of  its  vol- 
ume, the  lead  was  appreciably  attacked.  On  increasing  the  carbonic 
anhydride  to  0*6  vol.  per  cent.,  the  attack  became  remarkably  ener- 
getic. With  1  vol.  per  cent,  the  action  was  considerably  weaker,  and 
when  the  carbonic  anhydride  was  increased  to  1*5  vol.  per  cent,  the 
lead  was  no  longer  visibly  corroded.  Water  containing  2,  2*5,  and  3 
vols,  per  cent,  of  carbonic  anhydride  was  equally  inactive.  Water 
containing  carbonic  anhydride  but  no  oxygen  is  practically  without 
action  on  lead,  when  atmospheric  air  is  excluded.  When  strips  of 
lead  are  immersed  for  eight  days  in  pure  distilled  water,  recently 
boiled  and  cooled  out  of  contact  with  the  air,  they  do  not  become 
tarnished.  Before  filtration,  however,  but  not  after,  the  water  gives  a 
considerable  reaction  with  hydrogen  sulphide.  Pure  water  evidently 
attacks  lead  with  formation  of  an  oxide.  Ordinary  distilled  water  in 
which  strips  of  lead  were  placed,  and  from  which  the  air  was  excluded, 
contained  a  maximum  quantity  of  lead  at  the  end  of  three  days,  after 
which  the  lead  was  by  degrees  thrown  out  of  solution.  This  is 
explained  by  supposing  that  water  containing  carbonic  anhydride  and 
oxygen  in  contact  with  lead  forms  lead  carbonate,  which  dissolves  in 
the  excess  of  the  gas  ;  but  as  more  lead  oxide  is  formed,  this  carbonic 
anhydride  is  absorbed,  and  all  the  lead  falls  out  of  solution  as  lead 
carbonate.  Distilled  water,  free  from  carbonic  anhydride,  to  which 
minute  quantities  of  ammonia  have  been  added,  attacks  lead,  but  is 
without  action  on  it  if  carbonic  anhydride  is  present. 
