Am.  Jour.  Pharm. ) 
April,  1911.  j 
The  Response  of  Gums. 
177 
by  the  pentoses  (xylose)  and  hexoses  (dextrose,  levulose)  ;  of  the 
disac  char  ides,  maltose  and  lactose  give  the  reaction,  but  not  sac- 
charose. Mucin  is  also  said  to  respond  positive.  Of  the  polysac- 
charides, glycogen  and  dextrin  are  practically  negative,  but  may 
react  after  prolonged  heating,  which  presumably  decomposes  them. 
Starch  is  negative;  so  also  is  inosit. 
All  aldehydes  which  I  have  tried  react  positive  (acetaldehyde, 
paraldehyde,  formaldehyde,  benzaldehyde  and  cinnamic  aldehyde). 
In  all  the  preceding  instances,  the  substances  which  give  positive 
results  reduce  Fehling's  solution,  and  those  which  react  negatively 
to  Moore's  test  also  fail  to  reduce  the  copper. 
On  applying  these  tests  to  a  number  of  gums  and  similar  sub- 
stances, I  found  a  somewhat  different  behavior,  which  I  have  not 
seen  recorded:  These  gums  {acacia,  tragacanth,  and  cherry  gum), 
as  also,  agar,  cetraria,  and  chondriis,  give  a  golden  or  brownish- 
yellow  color  on  heating  with  sodium  hydroxide  solution ;  but  they 
do  not  reduce  Fehling's  solution  even  on  prolonged  heating. 
As  many  of  these  may  contain  reducing  sugar,  they  must  be 
thoroughly  washed  (sometimes  for  several  days).  Even  then  there 
might  be  a  suspicion  that  Moore's  test  is  more  delicate  than  Fehl- 
ing's, but  I  have  convinced  myself  that  a  dextrose  solution  which 
gives  the  Moore's  test  much  more  faintly  than  the  agar  solution, 
nevertheless  gives  a  very  plain  precipitate  with  Fehling's  test.  With 
the  difficulty  soluble  gums,  the  Moore's  reaction  can  be  best  observed 
by  heating  the  soaked  substance  directly  with  the  reagent.  I  have 
appHed  the  same  technic  to  the  Fehling's  test,  using  one  part  of 
Solution  A  to  three  parts  of  Solution  B.  The  results  were  nega- 
tive, except  with  occasional  specimens,  which  were  presumably  not 
sufficiently  washed. 
In  the  case  of  cetraria  and  cherry  gum,  the  Moore's  reaction  was 
applied  separately  to  the  portions  soluble  and  insoluble  in  water. 
The  insoluble  residue  gave  negative  results.  Cornstarch  and 
glycogen  did  not  give  the  Moore's  reaction. 
After  heating  with  dilute  acids  (which  converts  gums  into 
hexoses  and  dextroses)  all  these  substances  reduced  the  Fehling's 
solution. 
