214 
Logwood  as  a  Test  for  Metals. 
Am.  .lour.  Pharm. 
Apvil,  1884. 
the  author  proposes  a  -colorimetric  method,  based  on  the  potassium 
cyanide  reaction.  The  ethereal  residue  is  diluted  to  10  cc.  with  a 
little  ammonia,  5  or  ten  drops  of  a  10  per  cent,  potassium  cyanide 
solution  added,  and  the  liquid,  after  heating  it  to  80°,  is  diluted  to 
100  cc.  with  dilute  ammonia.  The  color  produced  is  compared  with 
that  given  by  a  certain  quantity  of  a  standard  solution  of  picric  acid, 
100  cc.  of  which  contain  0*1  gram  of  pure  picric  acid,  the  operation 
being  conducted  in  the  same  way. — Jour.  Chem.  Soc,  Feb.,  1884; 
Arch.  Phar.,  (3)  xxi,  190. 
NOTE  ON  LOGWOOD  AS  A  TEST  FOR  METALS.1 
By  Arthur  Weddell. 
For  some  years  past  I  have  been  accustomed  to  examine  potable 
waters  for  metallic  impurities  by  means  of  the  alteration  produced  in 
the  coloring  matter  of  logwood,  and  as  it  furnishes  a  delicate  and  con- 
venient means  of  detecting  their  presence  I  have  thought  it  worth 
bringing  before  this  Society.  When  logwood  is  digested  with  alcohol 
an  extract  of  a  rich  yellow  color  results,  and  this  color  is  not  changed  on 
dilution  with  a  pure,  freshly  distilled  water.  When  added  to  ordinary 
samples  of  water,  which  contain  calcium  carbonate  in  solution,  the 
yellow  color  is  changed  to  a  beautiful  rose  red,  or  if  a  metal  be  present 
to  blue. 
These  changes  are  accounted  for  in  the  following  manner:  Hema- 
toxylin, the  ordinary  coloring  matter  of  logwood,  is  converted  by 
oxygen,  especially  in  the  presence  of  alkalies,  into  an  oxidized  product 
known  as  hsematein,  which  gives  a  blue  precipitate  with  salts  of  iron, 
lead,  copper  and  many  other  metals,  or  if  the  solution  be  extremely 
dilute,  a  blue  coloration  only.  This  reaction  is  so  delicate  that  1  part  of 
lead  in  100,000  parts  of  water  is  easily  detected,  and  with  care  1  part 
in  200,000. 
These  changes  do  not  occur  in  aciel  solutions.  The  method  of  u^ing 
the  test  is  extremely  simple  and  consists  in  the  addition  of  a  few  drops 
of  a  very  dilute  tincture  of  logwood  to  the  sample  under  examination, 
care  being  taken  that  the  quantity  added  is  not  too  great,  as  a  trace  jf 
metal  may  be  thus  overlooked,  owing  to  the  difficulty  of  observing  the 
change  of  color  in  presence  of  a  large  excess  of  red  coloring  matter. 
My  own  practice  is  to  prepare  an  alcohol  extract  of  logwood  (strength 
1  Read  at  an  Evening  Meeting  of  the  Pharmaceutical  Society,  March  5, 
1884. 
