Am.  jour,  pharm. )        Caramelization  in  Rk'Cis's  Test. 
April,  1910.  J 
153 
I  made  some  years  ago  upon  learning  of  the  explanation  of  the 
browning  of  syrup  of  ferrous  iodide.  The  results  simply  confirmed 
the  statements  of  W.  F.  Horn.  The  color  of  the  browned  syrup 
vanished  quite  suddenly  when  the  syrup  was  heated  to  boiling. 
Such  evanescence  is  not  a  quality  associated  with  the  fairly  per- 
manent color,  caramel. 
When  I  met  with  the  same  assumption  again  recently  in  connec- 
tion with  Rivas's  test,  I  undertook  further  experiments  that  I  shall 
describe. 
The  first  experiment 9  was  intended  to  determine  whether  or  not 
the  formation  of  a  brown  color  when  the  glucose  broth  is  heated 
with  sodium  hydroxide  is  dependent  on  the  presence  of  the  peptone, 
or  beef  extract  with  the  glucose  at  the  time  the  alkali  acts  on  it. 
Accordingly  5  c.c.  10  per  cent.  NaOH  was  heated  with  0.25  c.c. 
portions  of  (a)  a  1  per  cent,  glucose  nutrient  broth,  (b)  a  similar 
nutrient  broth  to  which  the  glucose  had  not  yet  been  added,  and 
(c)  a  1  per  cent,  solution  of  glucose  in  distilled  water.  The  color 
developed  in  both  tubes  containing  glucose,  but  not  in  the  tube  of 
plain  nutrient  broth.  Therefore  the  other  constituents  of  the  broth 
are  not  concerned  with  the  formation  of  the  yellow  and  brown 
colors. 
In  order  to  determine  to  how  great  an  extent  the  glucose  is 
involved  in  the  action  of  the  alkali,  45  c.c.  of  a  1  per  cent,  solution 
of  glucose  heated  with  5  c.c.  of  water,  and  45  c.c.  of  a  1  per  cent, 
solution  of  glucose  heated  with  5  c.c.  10  per  cent.  NaOH,  were 
examined  successively  in  the  polariscope.  The  effect  of  the  alkali, 
it  was  found,  was  to  destroy  completely  the  optical  activity  of  the 
glucose.    Evidently,  then,  all  of  the  glucose  is  affected  by  the  alkali. 
Upon  adding  sufficient  acid  to  the  browned  solutions  obtained 
by  heating  glucose  with  alkalies,  the  color  immediately  disappears.10 
This  evanescence  resembles  that  of  the  brown  color  in  the  syrup  of 
ferrous  iodide.  Is  the  glucose  restored  to  its  original  condition 
when  the  brown  color  is  destroyed  by  acids?  To  answer  this  ques- 
tion, 49  c.c.  of  the  browned  solution  described  above  was  treated 
with  1  c.c.  of  water,  and  another  49  c.c.  of  the  same  browned  solu- 
tion was  treated  with  1  c.c.  strong  sulphuric  acid,  and  the  resulting 
solutions  examined  in  the  polariscope.    Neither  tube  showed  the 
9  The  glucose  used  in  these  experiments  was  crystallized,  CP.,  monohy- 
drated  glucose. 
10  Cf.  West,  16c.  ext.,  p.  228. 
