726 
Standardization  of  Digitalis  Preparations.  {A™0^ 
standing  fifteen  minutes,  is  compared  with  the  color  chart,  noting 
the  values  for  experiment  B. 
The  colors  produced  in  this  process  (B)  are  much  darker  than 
in  process  A.  They  are  also  more  inclined  to  approach  a  reddish- 
brown  shade.  This  is  due  to  the  presence  of  all  the  glucosides  in  the 
residue,  and  probably  impurities,  such  as  traces  of  chlorophyll. 
This,  however,  is  immaterial,  as  it  is  the  "  density  "  of  the  color 
which  we  must  compare. 
The  correct  way  to  match  the  colors  is  to  examine  the  tubes  by 
direct  transmitted  light,  with  the  eyes  wide  open,  holding  a  piece  of 
white  paper  behind  them  at  an  angle  of  45  °.  Then  slightly  close  the 
eyes  and  look  at  the  color  chart. 
In  process  B,  should  the  value  compare  with  tubes  "  d  "  or  "  e," 
it  is  too  dense  to  be  judged  with  accuracy  on  the  first  color  chart. 
A  more  dilute  mixture  must  be  made.  This  is  accomplished  by 
taking  0.1  Cc.  only  of  the  acetic  glucosidal  solution  and  introducing 
it  into  4  Cc.  of  Frohde's  reagent,  allowing  to  stand  for  fifteen  min- 
utes, and  then  comparing  the  tubes  with  the  second  chart. 
The  value  may  thus  be  accurately  determined,  as  the  "  relative 
strength  "  values  on  Chart  2  are  strictly  comparable  with  those  on 
Chart  1,  the  colors  having  been  painted  directly  from  known  tubes 
and  the  "  relative  strength  "  values  worked  out  and  checked  by  ex- 
periment. 
The  result  from  Process  A  gives  water  soluble  glucosides  only. 
This  I  shall  call  the  "  Therapeutic  Value  "  of  the  tincture. 
The  result  from  B  gives  Total  Glucosides — viz.,  water  soluble 
glucosides,  saponin  and  digitoxin.  (The  residue  here  is  not  very 
pure,  but  this  does  not  greatly  affect  the  colorimetric  estimation, 
whereas  weighing  would  be  inaccurate.)  Subtracting  A  from  B  we 
get  the  "  Toxic  Value  "  of  the  tincture. 
We  can  therefore  compare  toxicity  by  means  of  the  ratio 
If  we  estimate  this  for  a  standard  tincture  and  for  an  unknown 
tincture,  and  compare  the  two  (using  "  relative  strength"  values) 
we  can  compare  the  toxicity  of  the  samples,  as  in  the  following 
example : — 
B  — A  . 
Toxic  Value 
i.e., 
Therapeutic  Value. 
