426  Potassium  Bromide  with  Caffeine.  {AmA^^89a6!m" 
If  it  is  desired  to  estimate  the  chlorides  that  may  have  been 
present  in  a  sample  of  the  granular  salt,  the  filtrate  obtained  by 
treating  the  precipitate  with  ammonium  carbonate  can  be  acidified 
with  nitric  acid,  the  mixture  heated,  and  any  precipitate  obtained 
collected  on  balanced  filters,  dried  like  the  silver  bromide,  and 
weighed. 
To  estimate  the  caffeine,  5  grammes  of  the  salt  are  placed  in  a 
mortar  and  triturated  with  3  c.c.  of  official  solution  of  ferric  chlor- 
ide ;  then  sufficient  sodium  bicarbonate  is  added  to  make  a  magma 
and  impart  an  alkaline  reaction  (about  3-5  grammes).  Twenty  c.c. 
of  chloroform  are  then  thoroughly  rubbed  through  the  magma  with 
the  pestle  and  decanted  into  a  weighed  beaker.  Two  other  portions 
of  chloroform,  of  10  c.c.  each,  are  then  applied  to  the  magma  in  suc- 
cession, and  likewise  transferred  to  the  same  beaker.  The  united 
chloroformic  washings  are  then  carefully  evaporated,  or  distilled  off, 
and  the  beaker  kept  in  a  boiling  water  bath  until  the  weight  is  con- 
stant. 
According  to  the  National  Formulary,  granular  effervescent  potas- 
sium bromide  with  caffeine  should  contain  ii-ii  per  cent,  of  potas- 
sium bromide  and  I- 1 1  percent,  of  caffeine;  but  on  investigating 
three  of  the  prominent  preparations,  which  are  now  placed  on  the 
market  by  as  many  manufacturing  houses,  I  found  them  to  vary 
widely  from  these  amounts.  One  of  the  samples  was  not  at  all  uni- 
form, and  required  to  be  powdered  before  the  results  of  duplicate 
analyses  agreed.  This  suggested  imperfect  mixing  of  the  materials 
before  granulating  the  mass,  a  fault  which  may,  to  some  extent, 
account  for  the  great  variation  of  the  salts  from  standard. 
The  chlorides  present  did  not  exceed  in  any  case  the  amount  of 
potassium  chloride  allowed  by  the  Pharmacopoeia  in  potassium 
bromide. 
The  loss  on  drying  the  salts  at  900  C.  was  but  ri,  12  and  i-o 
per  cent,  of  their  weight. 
The  results  for  the  medicinal  constituents  were  the  following  per- 
centages : 
Sample. 
I  . 
Potassium  Bromide.  Caffeine. 
.    .    .     17-43  "22 
