Am$elZ'im1rm'}  Detection  of  Minute  Quantities  of  Lead.  475 
ence  of  copper  and  iron.  There  are  certain  temperance  drinks,  such 
as  lemonade  and  soda  water,  which,  in  the  process  of  manufacture, 
are  liable  to  contain  at  least  these  three  metallic  impurities.  In  the 
case  of  lemonade,  the  lead  occurs  partly  in  the  tartaric  acid  used, 
and  partly  comes  from  the  use,  perhaps  one  ought  to  say  abuse,  of 
lead  pipes  for  transferring  the  charged  solutions ;  and  the  copper 
comes  from  the  copper  cylinders  (although  tin-lined)  in  which  the 
drink  is  charged  with  carbonic  acid.  Hence  the  difficulty  arises  of 
detectinga  highly  poisonous  metal  like  lead,  in  the  presence  of  a  mildly 
poisonous  metal  like  copper,  and  a  non-poisonous  metal  like  iron.  The 
most  delicate  reaction  for  both  lead  and  copper  is,  I  believe, the  precipi- 
tation as  sulphides,  either  by  sulphuretted  hydrogen  or  ammonium 
sulphide.  The  amounts  present  can,  of  course,  be  estimated  colori- 
metrically  by  comparison  with  known  quantities.  I  find  the 
sulphide  reaction  far  more  delicate  in  the  case  of  copper  than  the 
ferro-cyanide  reaction.  I  do  not  think  the  hundredth  of  a  grain  of 
copper  in  a  gallon  of  liquid  could  be  detected  by  means  of  the  ferro- 
cyanide  reaction  without  concentration,  but  ammonium  sulphide 
would  easily  detect  it.  The  objection  to  this  reagent  is  that  it  does 
not  distinguish  between  lead  and  copper.  To  effect  this  distinction 
I  simply  make  use  of  the  well-known  fact  that  sulphide  of  copper  is 
soluble  in  cyanide  of  potassium,  whereas  sulphide  of  lead  is  not. 
To  perform  a  determination : — Place  a  measured  quantity  of  lemon- 
ade, or  other  liquid,  in  a  cylinder  or  white  basin.  Add  a  few  cc.  of 
ammonia  and  a  little  cyanide  of  potassium,  then  add  a  minute 
quantity  of  ammonium  sulphide.  Down  comes  the  lead,  but  not 
the  copper.  Then  imitate  the  color  .by  known  quantities  of  lead 
precipitated  under  similar  conditions.  Iron  does  not  at  all  interfere 
with  the  test.  If  an  iron  salt  is  added  to  lemonade,  for  instance, 
and  made  alkaline  with  ammonia,  the  iron  is  kept  in  solution  by  the 
tartaric,  acid,  and  on  addition  of  cyanide  of  potassium  is  converted 
into  a  ferro  or  ferri-cyanide,  not  precipitable  by  ammonium  sulphide. 
In  the  case  of  liquids  not  containing  tartartic  acid,  it  is  easy  enough 
to  add  a  little  in  the  event  of  iron  being  present. —  The  Analyst, 
August,  1892,  p.  142. 
Santonin  has  been  recommended  in  enuresis  caused  by  irritation  of  the 
vesical  sphincter,  in  doses  of  X  t°  XA  grain,  given  with  sugar. — Quarterly 
Therap.  Rev.,  July,  1892. 
