Am.  Jour.  Pharuj. 
March,  1«  9. 
Syrup  of  Hydriodic  Acid. 
127 
Some  authors  recommend  the  addition  of  glycerin  to  the  syrup, 
with  the  object  of  preventing  discoloration. 
One  writer  recommends  complete  substitution  of  glycerin  for  syrup. 
Glycerin  will,  however,  not  prevent  the  syrup  from  becoming  dis- 
colored, as  shown  in  numbers  of  specimens  prepared  by  the  writer. 
Other  acid  syrups,  to  which  glycerin  is  added  to  insure  greater 
stability,  will  show  similar  changes. 
The  addition  of  glycerin  to  syrup  of  hydriodic  acid  gives  rise  to 
another  objectionable  feature,  which,  if  found  true,  will  absolutely 
exclude  its  use. 
Hydriodic  acid  readily  forms  substitution  products  with  organic  hy- 
droxyl  compounds  with  formation  of  the  corresponding  iodide.  From 
the  triatomic  alcohol  glycerin  (C3H5(OH)3),  allyl  iodide  (C3H5I)  is 
produced  by  the  action  of  concentrated  hydriodic  acid.  If  a  glycerin 
substitute  for  the  official  syrup  is  prepared,  it  will  be  found,  that  a 
peculiar  leek-like  odor  is  developed.  Syrups  in  which  a  partial 
glycerin  substitution  is  made  show  a  like  result,  which  in  the  case 
of  syrups  prepared  with  sugar  alone  was  never  observed. 
To  further  investigate  this  point  would  form  an  interesting  sub- 
ject for  research. 
The  peculiar  odor  described,  noticeable  only  in  syrups  of  hydriodic 
acid  containing  glycerin,  make  the  presence  of  allyl  iodide  extremely 
probable. 
The  action  of  hydriodic  acid  upon  alcohols  may  also  be  used  as 
the  basis  for  objection  to  the  presence  of  ethylic  alcohol  in  the  syrup, 
as,  under  similar  conditions,  ethyl  iodide  may  perhaps  be  formed. 
No  physical  evidence  of  such  a  presence  is,  however,  found  either 
in  diluted  alcoholic  solutions  of  the  acid,  standing  for  about  one 
year  or  in  specimens  of  the  syrup,  containing  a  small  alcoholic  per- 
centage. 
With  the  object  of  preventing  discoloration  some  authors  suggest 
recent  preparations  by  diluting  a  concentrated  solution  of  hydriodic 
acid  with  simple  syrup. 
A  10  per  cent,  acid  solution  is  recommended,  and  a  commercial 
article. 
Experiments  conducted  by  the  writer  show  that  solutions  of  hy- 
driodic acid,  in  the  presence  of  hypophosphorous  acid,  keep  almost 
indefinitely  without  liberating  iodine. 
A  disadvantage  to  be  considered  is  the  liability  of  discoloration 
