270 
Alkaloidal  Assay  Work. 
Am.  Jour.  Pharm. 
June,  1900. 
Now,  a  very  white  sample  of  dextrin  is  liable  to  contain  a  large 
percentage  of  unconverted  starch,  which  would  be  insoluble  in 
water,  and  it  could  be  readily  detected  by  iodine  T.S. 
A  high  specific  rotatory  power  for  the  sample  of  material  and 
the  presence  of  unconverted  starch,  left  upon  treatment  with  water, 
would  be  indicative  of  the  presence  of  dextrin  in  the  sample  of 
powdered  acacia.  On  the  other  hand,  a  sample  of  dextrin  free 
from  insoluble  and  unconverted  starch  would  be  more  or  less  yel- 
low in  color.  A  sample  of  powdered  acacia  containing  such  an 
admixture  would  be  soluble  in  water,  and  while  starch  might  be 
absent,  the  presence  of  dextrin  or  similar  impurities  could  be  in- 
ferred from  the  specific  rotatory  power,  which  would  be  very  much 
higher  than  that  of  any  pure  acacia. 
The  amount  of  dextrin  or  similar  impurities  detected  by  the 
polariscope  may  be  calculated  in  the  following  manner : 
From  the  specific  rotatory  power  of  the  sample  examined  sub- 
tract the  specific  rotatory  power  of  the  pure  acacia  (viz.,  18),  and 
divide  the  result  obtained  by  the  increase  in  the  specific  rotatory 
power  made  by  1  per  cent,  of  dextrin. 
Example. — A  given  sample  of  powdered  acacia  has  a  specific 
rotatory  power  of  126.  What  is  the  percentage  of  dextrin  present 
as  detected  by  the  polariscope  ? 
126  —  18  =  108  ;  108  -r-  1*8  =  60  per  cent. 
The  increase  in  specific  rotatory  power  made  by  1  per  cent,  of 
dextrin  (viz.,  1-8)  is  obtained  in  the  following  manner: 
198  _  18  =  180;  180  -~  100  =  i-8. 
198  is  the  specific  rotatory  power  of  pure  dextrin.  > 
1 8  is  the  specific  rotatory  power  of  pure  acacia. 
RUSTING'S  TRAGACANTH  SCHEME  FOR  ALKALOIDAL 
ASSAY  WORK. 
BY  J.  B.  Nagei/voort. 
In  his  second  edition  of  "  Assay  of  Drugs,"  Dr.  Lyons  speaks 
admiringly  of  F.  A.  Thompson's  sawdust  "  wrinkle,"  a  feature  of 
assaying,  appealing  to  the  busy  druggist  by  its  simplicity,  who 
wants,  nevertheless,  to  verify  the  strength  of  his  fluid  extracts. 
