352 
Incompatibilities  in  Prescriptions. 
Am.  Jour.  Pharm. 
July,  1888. 
The  dose  of  liq.  strychninse  would  contain  -h  grain  of  alkaloid,  form- 
ing in  the  ounce  mixture  a  solution  of  the  strength  of  1  in  9600, 
while  the  solubility  of  the  alkaloid  in  water  is  about  1  in  5700. 
Potassium  iodide  also  was  sometimes  considered  to  be  incompatible 
with  strychnine.  In  a  case  where  five  grains  of  the  former  were  pre- 
scribed in  an  ounce  of  water  with  doses  of  liquor  strychninse  gradu- 
ally increased  from  5  mimims  to  30  mimims,  no  precipitation  occurred 
until  more  than  20  mimims  of  the  liquor  were  used,  and  even  then, 
by  adding  one  drachm  of  mucil.  tragacanth  to  each  dose,  precipitation 
was  so  retarded  that  by  only  preparing  sufficient  medicine  at  a  time 
to  last  one  day  the  patient  took  it  with  safety.  But  in  another  case, 
where  10  grains  of  the  iodide  were  mixed  with  20  mimims  of  the  liq. 
strychninse  in  an  ounce  of  water,  needle-like  crystals  appeared  in 
twelve  hours.  This  result  was  found  to  be  due  to  the  slight  alkalinity 
(allowed  by  the  British  Pharmacopoeia)  of  the  iodide,  for  when  the 
salt  was  slightly  acidulated  with  acid  hydrochlor.,  before  adding  the 
liq.  strychninse,  no  crystals  appeared  for  four  days,  and  then  in  com- 
paratively small  quantity. 
Another  favorite  combination  is : — 
R  Liq.  hyd.  perchlor  
Ammon.  carb. 
Pot.  iodid  aa  gr.  5 
Aq.  ad     ^j. 
Although  alkaline  carbonates  precipitate  with  mercuric  chloride,, 
still,  if  in  the  above  mixture  the  first  and  third  ingredients  are 
mixed  and  the  carbonate  then  added  in  solution,  no  precipitate 
occurs,  even  after  a  month  has  elapsed.  If  common  water  be  used 
a  slight  precipitate  of  calcium  carbonate  forms,  but  it  is  free  from 
mercury. 
Tannic  acid  is  said  to  be  incompatible  with  mineral  acids.  It  is 
true  that  a  concentrated  solution  gives  a  white  precipitate  with  acid, 
sulph.  dil.,  and  that  as  tannin  is  a  glucoside  it  is  decomposed  by  boil- 
ing with  dilute  acids,  yet,  dispensed  according  to  the  second  and  third 
rules,  the  following  mixture  showed  no  obvious  signs  of  decompo- 
sition : — 
B  Acid,  tannici  !   gr.  10 
Ac.  sulph.  dil   n\,  15 
Aq.  ad   ^j. 
Tannin  is  considered  incompatible  with  alkaloids,  because  in  strong 
