A™anu°ary  ^919"'  }  Examination  of  Commercial  Dextrin.  53 
The  error  is  thus  within  the  limit  aimed  at,  though  much  larger 
than  would  be  tolerable  for  purposes  of  careful  scientific  enquiry. 
Mixtures  of  unknown  composition  were  next  examined,  all  being 
ordinary  articles  of  commerce.  They  were:  (A)  "  Yellow  dextrin  "  ; 
(B)  "Soluble  starch";  (C)  "Soluble  gum"  (a  textile  dressing); 
(D)  "Treated  starch"  (believed  to  be  a  starch  which  had  been 
washed  with  dilute  acid).  Each  sample  was  examined  independ- 
ently by  two  analysts,  so  that  differences  in  the  result  of  duplicate 
analyses  display  all  the  error  which  can  arise  from  "  personal  equa- 
tion." The  results  obtained  were  as  follows :  Dextrin  gum  per  cent, 
in  (A)  99.90,  99.74;  (B)  11.60,  11.86;  (C)  24.00,  25.00;  (D)  17.00, 
15.72. 
If  dextrin  gum  is  determined  by  the  above  method  and  deter- 
minations are  also  made  of  ash  and  moisture,  the  starch  may  then  be 
estimated  by  difference.  Such  a  procedure  is  not  always  desirable, 
and  we  have  commenced  work  on  a  method  for  estimating  the  total 
starch  directly,  by  means  of  the  polarimeter,  after  hydrolysis.  The 
pressure  of  departmental  routine  has  prevented  the  completion  of 
our  experiments.  At  present  is  it  enough  to  say  that  we  have  found 
that  starch  which  has  been  precipitated  by  barium  hydroxide  is  some- 
what more  rapidly  hydrolyzed  by  hydrochloric  acid  than  when  not 
so  treated.  Whether  the  hydrolysis  is  complete  we  are  not  prepared! 
to  say,  but  we  find  that  under  our  experimental  conditions  (1000'  C. 
at  atmospheric  pressure)  no  further  reduction  in  rotatory  power  can 
be  observed  after  i?4  hours.  Pending  the  completion  of  this  work 
we  suggest  that  the  following  determinations  on  such  starch  prod- 
ucts as  we  have  been  considering  will  meet  most  commercial  require- 
ments :  (a)  Ash,  (b)  moisture,  (c)  dextrin  gum  by  the  method  de- 
scribed here,  (d)  insoluble  starch  and  (e)  reducing  sugars  by  some 
such  method  as  that  described  by  Lamb  and  Harvey  (loc.  cit.),  (/) 
total  starch  by  difference  [100  —  (a  +  b  +c)  ] ,  (g)  soluble  starch  by 
difference  [/  —  d],  (h)  non-reducing  dextrin  gum,  by  difference 
[c-e]. 
Our  method  may  also  be  applied  to  mixtures  of  starch  and  gum 
arabic,  such  as  are  sometimes  met  with  commercially. 
Analytical  Laboratory, 
Department  of  Customs, 
Ottawa. 
