252 
Action  of  Water  on  Lead. 
Am.  Jour.  Pharm. 
May,  1888. 
Lime  water,  through  which  a  current  of  air,  perfectly  free  from  car- 
;bonic  anhydride,  was  passed,  at  first  slowly  dissolved  lead,  but  this 
was  soon  again  thrown  out  of  solution  in  the  form  of  minute  crystals. 
The  solution  attained  a  maximum  after  13  hours,  and  then  decreased. 
Sodium  hydroxide  solution  behaved  in  a  similar  way.  In  the  absence 
of  oxygen,  neither  lime-water  nor  sodium  hydroxide  solution  attacked 
lead.  Lead  tubing,  buried  in  mortar,  and  kept  in  a  dry  room  for  a 
year  suffered  no  change,  but  when  the  mortar  was  occasionally  moist- 
ened with  pure  water,  corrosion  rapidly  took  place.  When  soapy 
water  or  an  alkaline  solution  of  lime  was  used  instead  of  pure 
water,  the  decomposition-products  consisted  to  some  extent  of  red 
lead. 
Ordinary  distilled  water,  to  which  a  small  quantity  of  sodium  car- 
bonate was  added,  dissolved  no  lead,  but  the  metal  became  slowly  cov- 
ered with  a  white,  compact  coating.  When  the  water  contained  oxy- 
gen but  no  carbonic  anhydride,  lead  was  found  in  solution  after  a  few 
Jiours.  A  trace  of  sodium  hydrogen  carbonate  added  to  distilled 
water  completely  prevented  the  dissolution  of  lead,  and  the  metal 
became  covered  with  a  protecting  crust.  Waters  containing  lead  in 
solution  were  found  to  be  freed  from  it  by  adding  sodium  carbonate. 
Pure  lead  carbonate  is  soluble  in  water  containing  carbonic  anhydride ; 
it  is  reprecipitated  by  boiling  the  solution  or  by  adding  hydrogen 
sodium  carbonate  to  it.  Evidently  lead  forms  an  acid  carbonate, 
which  is  soluble  in  water  but  possesses  little  stability.  Hydrogen  cal- 
cium carbonate  acts  in  precisely  the  same  way  as  hydrogen  sodium 
carbonate. 
Polished  strips  of  lead  immersed  in  a  saturated  solution  of  pure  cal- 
cium sulphate,  containing  oxygen,  become  covered  with  a  hard,  white 
coating,  but  no  lead  goes  into  solution.  In  the  absence  of  oxygen,  the 
metal  remains  perfectly  bright.  On  placing  lead  covered  with  the 
white  crust  formed  by  long  immersion  in  a  solution  of  calcic  sulphate, 
in  pure  distilled  water,  no  lead  went  into  solution  except  when  a  con- 
siderable quantity  of  carbonic  anhydride  was  present.  When  a  trace 
of  hydrogen  calcium  carbonate  was  added  to  the  solution,  in  no  case 
was  any  lead  dissolved.  The  coating  is  in  all  probability  a  basic  sul- 
phate of  lead. 
The  presence  of  minute  quantities  of  chlorides,  nitrates,  organic 
matter  and  ammonia  in  water,  did  not  influence  its  behavior  towards 
lead.    This  seems  to  depend  on  the  presence  of  oxygen  and  carbonic 
