240 
Syrup  of  Hych'iodic  Add, 
f  Am.. Four.  Pharm. 
1      3Iay,  1882. 
this  rapid  decomposition  to  contact  witli  the  air  from  the  agitation 
necessary  to  effect  separation  of  the  bitartrate  precipitate.  It  prob- 
ably, however,  admits  of  another  explanation.  Should  any  one  take 
the  trouble  to  investigate  the  reaction  between  the  two  foregoing  sub- 
stances, they  will  find  that  the  bitartrate  precipitate  is  formed  only  to 
the  extent  of  about  one-half  of  the  theoretical  quantity,  and  further^ 
that  this  is  not  entirely  due  to  the  solvent  power  of  the  hydriodic  acid 
on  the  bitartrate  precipitate,  but  is  due  also  to  the  fact  that  there  is 
not  complete  decomposition  between  the  iodide  of  potassium  and  tar- 
taric acid.  In  short,  the  phenomenon  here  is  very  similar  to  that 
quite  recently  pointed  out  as  taking  place  in  the  preparation  of  Foth- 
ergill's  hydrobromic  acid.  The  resulting  product  is  consequently 
neither  uniform  nor  stable  in  its  nature,  so  that  a  syrup  prepared  from 
it  can  scarcely  be  depended  upon  for  uniformity  of  strength  or  keep- 
ing properties.  Along  with  this  there  was  probably  one  other  circum- 
stance that  militated  against  the  keeping  properties  of  the  earlier  pre- 
parations, viz.,  their  strength.  If  I  remember  rightly,  the  strength 
of  the  solution  as  proposed  by  Dr.  Buchanan  was  as  near  as  possible 
an  equivalent  of  5  grains  iodine  to  each  fluiddrachm,  while  the  syrup 
as  proposed  by  Mr.  Murdoch  contained  2  grains  iodine  in  the  same 
quantity.  Now  it  may  be  pointed  out  that  the  keeping  properties  of 
the  syrup  depend  to  a  great  extent  upon  these  two  things,  namely,  the 
acid  strength  of  the  syrup  and  the  density  of  the  syrup.  Two  ounces^ 
for  example,  of  an  aqueous  solution  of  the  acid,  containing  an  equiva- 
lent of  5  grains  iodine  to  each  drachm,  was  exposed  in  a  capsule,  and 
began  to  decompose  in  one  or  two  hours^  time ;  in  12  hours  the  pres- 
ence of  free  iodine  was  quite  visible,  and  in  three  or  four  days  the 
whole  of  the  iodine  was  set  free.  On  the  other  hand,  the  same  quan- 
tity of  a  syrup  of  similar  strength,  and  of  density  1-320,  was  exposed 
under  the  same  conditions,  and  in  three  or  four  days  it  had  only 
assumed  a  slightly  deeper  straw-colored  shade.  At  the  end  of  this, 
time  it  had  thickened  considerably,  owing  to  evaporation,  and  it  ulti- 
mately got  into  a  kind  of  pasty  mass  in  which  condition,  so  far  as  my 
experiments  have  gone,  it  is  practically  stable.  A  syrup  of  density 
1*180  (about  half  the  sugar  strength  of  the  foregoing)  will  slowly 
decompose  after  a  few  days'  exposure,  but  the  rate  at  which  decompo- 
sition takes  place  will  depend  upon  the  acid  strength,  a  stronger  pre- 
paration decomposing  much  more  quickly  than  a  weaker.  I  have 
prepared  and  exposed  syrups  of  various  strengths  and  densities,  and 
