Am.  Jour.  Pharm. ) 
April,  1884.  | 
Logwood  as  a  Test  for  Metals. 
215 
1  in  100)  by  maceration  and  to  note  how  much  of  this  is  required  to 
produce  a  distinct  rose  color  in  100  cc.  of  distilled  water  rendered 
faintly  alkaline  with  ammonium  carbonate,  or  in  100  cc.  of  hard  water 
free  from  metals. 
This  quantity  of  logwood  solution  is  next  added  to  100  cc.  of  the 
water  under  examination,  and  the  two  tubes  compared.  If  a  rose 
color  is  developed,  metals  are  absent,  while  a  blue  color  indicates  their 
presence. 
More  logwood  may  afterwards  be  added  to  each  tube  and  the  pro- 
gressive differences  noted,  the  blue  color  increasing  in  depth,  or  to  a 
precipitate  if  much  lead  be  present. 
By  adding  sufficient  lead  solution  of  known  strength  to  the  pure 
water,  so  as  to  imitate  the  color  in  the  second  tube,  as  in  Nesslerizing, 
an  approximate  idea  of  the  amount  of  lead  may  be  obtained,  when  it 
is  known  that  no  other  metal  is  present ;  but  I  have  not  considered  the 
reaction  worth  experiment  in  this  direction,  because  the  exact  compari- 
son is  somewhat  difficult  and  can  hardly  reach  scientific  accuracy. 
The  presence  of  free  acids  interferes  with  the  reaction,  and  these,  if 
present,  must  therefore  be  carefully  neutralized  and  a  slight  excess  of 
alkali  added.  Free  carbonic  acid  gas  should  be  removed  by  boiling, 
but  I  have  never  met  with  drinking  water  that  required  such  treatment. 
A  variety  of  applications  of  this  test  will  suggest  themselves.  Some 
years  ago  I  recommended  a  convenient  means  of  testing  glycerin  for 
lead  and  other  metals,  by  adding  the  glycerin  to  water  colored  red 
with  logwood.  Soda  water  may  be  examined  by  boiling  to  free  from 
C02  and  adding  the  logwood.  Lemonade  by  adding  a  slight  excess  ot 
pure  alkaline  carbonate  and  boiling.  The  mineral  and  vegetable  acids 
may  be  examined  by  neutralizing  carefully  and  adding  the  solution  to 
water  colored  red  with  logwood. 
My  attention  was  first  attracted  to  this  test  by  observing  that  distilled 
water  stored  in  a  metal  cistern  when  used  to  dilute  a  logwood  tincture 
turned  it  to  a  dirty  greenish  color,  and  when  this  was  mixed  with  tap 
water  it  turned  blue.  On  examining  the  distilled  water  by  the  ordinary 
method,  with  SH2,  the  presence  of  lead  was  detected,  it  having  been 
dissolved  from  the  solder  used  in  the  joints  and  in  fixing  the  tap.  As 
I  have  since  met  with  this  same  condition  of  storage  and  impurity  I 
think  it  would  be  well  for  those  who  store  distilled  water  in  such  a 
manner  to  ascertain  the  absence  of  lead  before  using  it. — Pharm.  Jour, 
and  Trans.,  March  8,  1884,  p.  717. 
