^^■jSy^im^'"'^  }      Incompatibilities  in  Prescriptions.  353 
solutions  a  dense  precipitate  occurs ;  but  if  the  following  be  properly 
dispensed  the  precipitate  is  readily  diffused  on  shaking  : — 
K  Acid,  tannici  gr.  5  (or  10) 
Quln.  sulph   gr.  ij 
Acid,  sulph.  dil   3 
Aq.  ad  -   ^j. 
Potassium  bromide  is  considered  incompatible  with  metallic  salts, 
and  certainly  it  was  not  always  safe  to  mix  the  liq.  ferri  perchlor.  of 
the  B.P.,  1887,  with  the  bromide,  but  the  1885  liquor,  being  practi- 
cally neutral,  forms  in  the  following  prescription  a  mixture  in  which 
veryKttle  bromine  is  liberated — generally  none  at  all — for  on  shaking 
the  liquid  with  chloroform  the  latter  is  scarcely  colored,  if  at  all  : — 
B  Liq.  ferri  perchlor   tt^  15 
Pot.  brom   gr.  20 
Aq.  ad   ^j. 
AmBr  and  NaBr  give  similar  results,  still  it  would  be  wise  in  this 
case  to  observe  the  first  rule. 
In  other  instances  "  incompatibility  "  can  be  overcome  by  adding 
something  to  the  prescription.  In  a  case  where  "  ear-drops  were  to 
contain  cocaine  hydrochlorate  with  borax,  the  alkaloid  was  partially 
precipitated,  but  immediately  redissolved  by  a  trace  of  hydrochloric  acid. 
When  alkalies  are  mixed  with  quinine  sulphate  the  alkaloid  is  lib- 
erated, often  in  a  sticky  resinous  form,  but  if  the  powdered  alkaloidal 
salt  be  mixed  with  water  and  a  proper  quantity  of  tragacanth  mucilage, 
and  the  alkali  be  then  added  in  solution,  a  presentable  mixture  results. 
Syr.  ferri  iodidi  gives  with  potass,  iodid.  a  precipitate  of  ferrous 
quickly  changing  to  ferric  hydrate,  because  pot.  iodid.  is  usually  a  lit- 
tle alkaline ;  but  the  addition  of  a  little  citric  acid  to  the  solution  of 
the  iodide  will  keep  the  mixture  clear. 
The  author  concluded  by  saying  that  when  additions  have  to  be 
made,  the  dispenser  ought,  if  possible,  to  first  obtain  the  sanction  of 
the  prescriber,  and  that  in  his  experience  such  sanction  had  always 
been  freely  accorded  ;  in  fact,  one  very  eminent  London  physician  had 
said :  "  If  I  prescribe  anything  incompatible  put  the  matter  right  for 
me,  and  drop  me  a  postcard  afterwards.^'  Such  a  habit  of  dependence 
upon  the  special  knowledge  of  the  pharmacist  was,  he  had  reason  to 
believe,  becoming  more  and  more  general  among  the  members  of  the 
medical  profession ;  it  was  for  pharmacists  to  prove  themselves  worthy 
of  it. 
